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  • Catalytic activity of maghemite supported palladium catalyst in nitrobenzene hydrogenation
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2020-01-09
    Viktória Hajdu, Ádám Prekob, Gábor Muránszky, István Kocserha, Zoltán Kónya, Béla Fiser, Béla Viskolcz, László Vanyorek

    A maghemite supported palladium catalyst was prepared and tested in nitrobenzene hydrogenation. The catalyst support was made by a newly developed combined technique, where sonochemical treatment and combustion have been used. As a first step, maghemite nanoparticles were synthesized. Iron(II) citrate was treated in polyethylene glycol by high-intensity ultrasound cavitation to get a homogeneous dispersion, then the product was combusted. The produced powder contained maghemite nanoparticles with 21.8 nm average particle size. In the second step of catalyst preparation, the magnetic nanoparticles were dispersed in the ethanolic solution of palladium(II) nitrate. The necessary energy for the reduction of Pd2+ ions was achieved in the “hot spots” by acoustic cavitation, thus catalytically active palladium was formed. The prepared maghemite supported Pd catalyst have been tested in nitrobenzene hydrogenation at three different temperatures (283 K, 293 K and 303 K) and constant pressure (20 bar). At 293 K and 303 K, the conversion and selectivity of nitrobenzene was above 99% and 96%, respectively. However, the selectivity was only 73% at 273 K because the intermediate species (azoxybenzene and nitrosobenzene) have not been transformed to aniline. All in all, the prepared catalyst is successfully applied in nitrobenzene hydrogenation and easily separable from the reaction media.

    更新日期:2020-01-09
  • Study of self-oscillations during CO oxidation over Cu foil
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2020-01-06
    V. Yu. Bychkov, Yu. P. Tulenin, A. Ya. Gorenberg, V. N. Korchak

    The oscillatory behavior during CO oxidation over Cu foil has been observed in the temperature range of 350–750 °C. The oscillatory behavior occurred in CO excess similar to the well-known oscillations during CO oxidation over Ni and Co, but in contrast to the oscillations over Pt, Pd, Ir, and Ru. The periodic variation in oxygen imbalance together with variation in color changes during the oscillations and ex situ XRD measurements indicate that the oscillations were closely connected with the reversible oxidation of Cu to Cu2O. The oscillations were accompanied by propagation of oxidation and reduction wavefronts.

    更新日期:2020-01-06
  • Surface modification of alumina with P 2 O 5 and its application in 2-octanol dehydration
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2020-01-06
    Sahar Nazer, Hossein A. Dabbagh, Alireza Najafi Chermahini, Hossein Farrokhpour

    Alumina and phosphorus-alumina with different morphologies were synthesized by the sol–gel method. The morphology, structure, size, phase composition, acidic properties, and thermal behavior were examined by FESEM, TEM, XRD, FT-IR, BET, EDS, NH3-TPD, and TGA-DTA, respectively. It can be found that the morphology of alumina can change from worm-like to spherical by using acetonitrile/2-octanol solvent mixture and by modifying the synthesis steps. Also, the semi-crystalline structure of γ-alumina was changed to amorphous with improved surface area (from 150 to 229 m2 g−1). The addition of phosphorus pentoxide to amorphous alumina with the ratios of 1:9, 2:8 and 1:1 reduced the surface area of the catalyst after calcination from 229 to 129, 16 and 39 m2 g−1, respectively. With the increase of phosphorus/aluminum ratio and an increase in calcination temperature, the structure of phosphorus-alumina transformed from amorphous to crystalline. The reactivity and selectivity of 2-octanol over these composites were monitored using GC and GC-mass analyses.

    更新日期:2020-01-06
  • Optimization of the enzyme catalyzed ultrasound assisted synthesis of cinnamyl butyrate using response surface methodology
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2020-01-02
    Govind V. Waghmare, Chirag Mudaliar, Virendra K. Rathod

    The detailed optimization study for the ultrasound assisted lipase catalyzed synthesis of cinnamyl butyrate under solvent free conditions was described using central composite rotatable design and response surface methodology. The statistical analysis shows that three out of the four variables tested, i.e. molar ratio (A), enzyme loading (B), and ultrasound intensity (D) are found to be statistically significant. The mutual interactions between molar ratio-enzyme loading (AB) and temperature-ultrasound intensity (CD) are also found to be significant along with quadratic interactions of all the parameters (A2, B2, C2, D2). The maximum conversion of 93% was obtained at optimal conditions; molar ratio 2.5 (cinnamyl alcohol:butyric acid); enzyme loading 2.8% of the total mass of reactants; reaction temperature 46 °C and ultrasound intensity 105 W (ultrasound intensity is 7412.68 W/m2). Additionally, hydrodynamic parameters have been determined to estimate the effect of external and intraparticle mass transfer diffusion, which do not show any significant influence on the reaction rate. Reusability study of biocatalyst shows that it can be used up to three cycles with minimal loss of its enzymatic activity.

    更新日期:2020-01-02
  • ZSM-5 zeolites modified with Zn and their effect on the crystal size in the conversion of methanol to light aromatics (MTA)
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2020-01-02
    Misael García Ruiz, Dora A. Solís Casados, Julia Aguilar Pliego, Carlos Márquez Álvarez, Enrique Sastre de Andrés, Diana Sanjurjo Tartalo, Raquel Sainz Vaque, Marisol Grande Casas

    ZSM-5 zeolite catalysts modified with zinc were prepared by two forms of Zn incorporation the synthesis gel, and ion exchange techniques. The physico-chemical properties of zeolites were studied by XRD, N2-adsorption, NH3 temperature-programmed desorption, 27Al and 29Si MAS NMR, SEM, TEM and TGA. ZSM-5 zeolite in its acid form was exchanged using an aqueous zinc salt solution and demonstrated a significantly higher selectivity for the aromatic products in comparison with the purely acidic catalysts. The samples with distribution of ZnOH+ species are more active than the samples with ZnO sites in the zeolites. The synthesis of zeolite ZSM-5 of nanometric size resulted to present high stability and selectivity towards light aromatics. The influence of the form of zinc incorporation, the acidity and the reaction temperature had a great influence on the catalytic activity. The MTA catalyst lifetime is increased by several times due to the enhanced mesoporosity and decreased acidity. In the present work the zeolite HZSM-5 exchanged with Zn with Si/Al 25 ratio presented conversions close to 100% methanol with 32% selectivity to the BTX fraction, however, this catalyst was deactivated after 8 h of reaction with a weight hourly space velocity of 4.74 h−1 at 450 °C. On the other hand, a HZSM-5 zeolite with nanoscale crystals was found to be more stable in the MTA reaction. The nanometric catalyst showed conversions around 100% methanol after 8 h of reaction and 32.5% selectivity to the BTX fraction to 450 °C. These results clearly indicate that crystal size significantly influence the ZSM-5 lifetime and product distribution.

    更新日期:2020-01-02
  • Interaction of Pd and Rh with ZrCeYLaO 2 support during thermal aging and its effect on the CO oxidation activity
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2020-01-02
    Aleksey A. Vedyagin, Evgeny A. Alikin, Roman M. Kenzhin, Mikhail Yu. Tashlanov, Vladimir O. Stoyanovskii, Pavel E. Plyusnin, Yury V. Shubin, Ilya V. Mishakov

    Abstract A commercial ceria–zirconia composition modified with yttrium and lanthanum oxides was studied as a support for palladium- and rhodium-containing three-way catalysts. The most attention was paid to an interaction of the supported active metals with the support under high-temperature conditions. It was found that both the metals affect noticeably the porous structure of the support and the loading of metal plays a role in this process. Moreover, oxygen storage capacity of the oxide composition was also influenced by the supported metals. Hydrothermal aging of the metal-loaded samples has decreased the oxygen storage capacity values in more than 2 times. The thermal stability of the monometallic samples was compared with bimetallic Pd–Rh catalysts prepared using a “single-source precursor” approach. The experiments were performed under prompt thermal aging conditions. It was found that monometallic Pd-only samples and bimetallic Pd–Rh samples exhibit excellent stability, while monometallic Rh-only catalysts undergo deactivation being heated up to 800 °C due to diffusion of rhodium into the bulk of the support. All the samples were additionally characterized by a diffuse reflectance UV–vis spectroscopy and a testing reaction of ethane hydrogenolysis. According to the results obtained, the character of the metal-support interaction was found to be strongly affected by the catalyst’s composition. Application of the bimetallic Pd–Rh particles of alloyed type was shown to result in the preferable location of the active components on the support’s surface, thus facilitating high activity and stability of the catalyst.

    更新日期:2020-01-02
  • Microkinetic simulation and fitting of the temperature programmed reaction of methanol on CeO 2 (111): H 2 and H 2 O + V production
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2020-01-01
    Aditya Savara

    Abstract The kinetics and mechanism for temperature programmed reaction following adsorption of an adsorbate can be better understood by simulation and fitting with comparison to experiment. A case study is presented here for the chemistry of adsorption of methanol on a CeO2(111) surface followed by heating. The gas products observed are CH3OH, CH2O, H2, H2O, CO, CO2. At low temperatures (< 500 K), there is formation of H2 and H2O, where the H2O formation is accompanied by lattice oxygen vacancy (V) formation and is thus important in determining the selectivity towards different products. Microkinetic modeling was performed using a recently published method for fitting to gain mechanistic knowledge of the H2 and H2O + V formation at < 500 K. In the kinetic models used here, most of the H2 and H2O + V formation can be explained by a mechanism in which a metastable state of hydrogen on the surface (H*) acts as an intermediate. Two possibilities were investigated for the source of the metastable H* intermediate: H* from CH bond breaking of methoxies, or promotion of H+ to H* via electron transfer from ionic methoxies absorbed in oxygen vacancies (CH3O−/V). From this study, we consider the latter to be more likely at < 500 K. For the H2O formation, it was found to be critical that H2O cannot dissociate directly on oxygen vacancies. Catalytic chemistry was observed in simulations, including catalytic formation of oxygen vacancies. Various features of the experimental results were reproduced, including methoxies being the major carbon containing species on the surface at < 500 K.

    更新日期:2020-01-01
  • Investigation on asphaltene compositions and structures during hydroprocessing of low-temperature coal tar at different reaction temperatures on Ni–Mo–W/γ–Al 2 O 3 catalysts
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2020-01-01
    Zhihui Sun, Yi Wu, Minyan Zheng, Wenhong Li

    Abstract Hydroprocessing of low-temperature coal tar from Shanbei (SLCT) on Ni–Mo–W/γ–Al2O3 catalysts was carried out in an autoclave. The compositions and structures of asphaltenes obtained from hydrotreated products at temperatures of 350–410 °C have been characterized by elemental analysis, FTIR, 1H NMR and fluorescence spectroscopy (FL). Results indicate that temperature has significant influence on the hydrogenation and cracking functions of catalyst. At temperature 370 °C or below, the asphaltene conversions increase obviously while molecular weights are not evidently reduced as temperatures go up. Moreover, compared with asphaltene in SLCT, the asphaltene from hydrotreated products contains higher H/C ratio. It can be speculated that the hydrogenation reaction becomes dominant at lower temperature. In addition, the asphaltenes hydrotreated at higher temperature always contain lower H/C ratio and lower molecular weight. The results may be attributed to some cracking reactions. As for the heteroatoms (S, N and O) in asphaltenes, their removal efficiency is not only affected by temperature, but also the forms located in molecular structure. In addition, as the temperature increased, both the average side chain length and the number of naphthenic rings show a slight decrease. However, the aromatic degree (fA) increases and surprisingly the number of aromatic rings shows a slight increase. It indicates that higher reaction temperature is unfavorable to the hydrogenation of aromatic ring system.

    更新日期:2020-01-01
  • Assessing different alternatives by simulation to optimize a homogeneous transesterification process to improve the produced/consumed energy
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2020-01-01
    Lorena M. Polo, Ignacio Elizalde, Fabián S. Mederos, Fernando Trejo, Edgar Ramírez, J. Felipe Sánchez

    A conceptual biodiesel production homogeneous process was developed, considering the typical reaction conditions, appropriate thermodynamic models as well as the kinetics of a representative reaction for vegetable oils, under assumption to be mass-produced and provide a continuous way the raw material for the production of the biofuel. Reasonable assumptions and the use of a rigorous simulator of processes were employed; the process was simulated for the treatment of 1000 mol/h of oil operating continuously, at 45 and 55 °C, 1.0 wt% catalyst and 6 mol methanol by mol of oil. The processes of catalyst preparation, raw material pumping, heating, isothermal reaction, separation of byproducts by density and distillation were considered, and also auxiliary services of heating and cooling during the process. The convergence of each device was achieved by properly choosing the specifications of the unit operation models. Material and energy balances were obtained at each point in the process and in a global manner. For space-time of 30 min in single and series reactors global efficiencies from ~ 80 to 85% biodiesel was calculated for all explored alternatives. The ratio of energy production of biodiesel to the energy consumed by the process, within the battery limits used in this study, was found to be more than 6 times, thus ensuring the sustainability of the process from energetic point of view. It was found that, for the highest purity and better ratio of energy produced/consumed, the global efficiency process was the lowest.

    更新日期:2020-01-01
  • Impact of D 2 O on peptidization of l -hydroxyproline
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2020-01-01
    Agnieszka Fulczyk, Eliza Łata, Ewa Talik, Teresa Kowalska, Mieczysław Sajewicz

    This is our fourth consecutive study carried out in an order to collect experimental evidence regarding the impact of heavy water (D2O) on the spontaneous oscillatory peptidization of proteinogenic α-amino acids and this time its subject matter is l-hydroxyproline (l-Hyp). Our three earlier studies have been focused on the two sulfur-containing α-amino acids, i.e., l-cysteine (l-Cys) and l-methionine (l-Met), and on one structurally related α-amino acid, i.e., l-proline (l-Pro). It seemed interesting to assess the effect induced by D2O on l-Hyp and to compare it with the effects valid for l-Cys, l-Met, and l-Pro. As analytical techniques, we used high-performance liquid chromatography with the evaporative light-scattering detection (HPLC-ELSD), mass spectrometry (MS), and scanning electron microscopy (SEM). The obtained results make it clear that the impact of heavy water on dynamics of spontaneous peptidization of l-Hyp differs from that exerted on three other α-amino acids discussed (although in all four cases, heavy water significantly hampers spontaneous oscillatory peptidization). With l-Hyp, an increasing proportion of D2O in the reaction mixture results in decreasing yields of both, the soluble lower molecular weight peptides and the insoluble higher molecular weight peptides. With the two sulfur-containing compounds (l-Cys and l-Met), an increasing proportion of D2O in the reaction mixture resulted in growing yields of the soluble lower molecular weight peptides at an expense of decreasing yields of the insoluble higher molecular weight peptides. With l-Pro, still different pattern was observed, namely that the hampering effect of D2O on peptidization was not monotonously dependent on the concentration of D2O in the system, but it was the strongest pronounced for 10% (v/v) D2O in the employed binary methanol–water solvent (with the investigated proportions of D2O in this solvent changing from 0 to 30%). We hope that firm quantitative results presented in this study (and also in the three earlier studies from this cycle) can prove an inspiration for future researchers interested in getting a deeper insight into the role of D2O in life processes, and more specifically in the kinetic and mechanistic aspects thereof. Perhaps it might be noteworthy to add that out of four α-amino acids investigated so far, which can be divided into two groups of the endogenous (l-Cys and l-Pro) and exogenous (l-Met and l-Hyp) species, the endogenous species undergo spontaneous peptidization following the circadian rhythm, whereas the exogenous ones (including l-Hyp) do not.

    更新日期:2020-01-01
  • The effect of different Ca precursors on the activity of manganese and cerium oxides supported on TiO 2 for NO abatement
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-24
    Xiaobo Wang, Jie Zhou, Jia Wang, Aifang Ding, Keting Gui, Hywel R. Thomas

    Abstract The different forms of Ca (CaCl2 and Ca(OH)2) poisoned manganese and cerium oxides supported on TiO2 catalysts were prepared by impregnation method and used for selective catalytic reduction (SCR) of NO with NH3. The Ca poisoning effects were investigated by many characterization methods including N2 adsorption/desorption, X-ray diffraction, X-ray photoelectron spectroscopy, H2-temperature programmed reduction and NH3-temperature programmed desorption techniques. The results showed that the addition of Ca led to greatly decrease of catalytic activity of catalysts and the catalytic activity was ranked in the order: CaCl2 poisoned catalyst < Ca(OH)2 poisoned catalyst < fresh catalyst, which indicated that the poisoning effect of different forms of Ca was different and the deactivation caused by CaCl2 was more serious. The characterization results demonstrated the addition of Ca greatly decreased the specific surface area of catalysts, the contents of surface active species (Mn4+ and Ce3+), the amounts of weak Brønsted acid sites and the low-temperature redox ability, especially for the CaCl2 poisoned catalyst, all of which led to the weaken of the catalytic activity of catalysts.

    更新日期:2019-12-25
  • Synthesis 5-hydroxymethylfurfural (5-HMF) from fructose over cetyl trimethylammonium bromide-directed mesoporous alumina catalyst: effect of cetyl trimethylammonium bromide amount and calcination temperature
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-18
    Halit L. Hoşgün, Ayşe Gül Türe, E. Zafer Hoşgün, Berrin Bozan

    In this study, mesoporous alumina was synthesized using aluminium isopropoxide as Al precursor and cationic surfactant cetyl trimethylammonium bromide (CTAB) as structure directing agent and it was tested in the dehydration reaction of fructose into 5-HMF. The experiments were carried out in a microwave reactor at 200 °C for 5 min. The various ratio of CTAB/Al2O3 and calcination temperature between 400 and 700 °C were selected as synthesis parameters. The synthesized samples were analyzed by BET and XRD. The highest surface area was obtained as 602.22 m2/g with the weight ratio of CTAB to Al2O3 of 1.00 at the calcination temperature of 400 °C. When calcination temperature increased from 400 to 700 °C, surface area decreased into 286.14 m2/g. N2 adsorption/desorption isotherms of samples showed characteristic mesoporous type IV according to IUPAC classification. According to XRD patterns, all catalysts were in the amorphous structure. The maximum 5-HMF yield of 51% was achieved with the alumina catalyst calcined at 400 °C and CTAB/Al2O3 ratio of 1.0. Although the surface area decreased by rising the calcination temperature from 400 to 550 °C, the fructose conversion reached the highest value (97.54%).

    更新日期:2019-12-19
  • Adsorption kinetics and isotherms of berberine by ZSM-5 molecular sieves from Cortex Phellodendron
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-18
    Yunlong Liu, Jie Guo, Zhuobing Xiao, Dazhao Peng, Ke Song

    In this paper, a porous material (ZSM-5 molecular sieves) with remarkable structure is select to apply for berberine adsorption from the extracts of the Cortex Phellodendron. The batch experiments show that the optimum adsorbent dosage was 2.0 g and pH 8 is favorable for the berberine adsorption. The adsorption of berberine by ZSM-5 molecular sieve is more in consistence with the pseudo-second-order kinetic model and chemical adsorption plays a major role. There exist three diffusion stages during the adsorption of berberine, indicating that intraparticle diffusion is not the only rate-controlling step. Isothermal adsorption data is more in consistence with the Langmuir model, indicating that adsorption occurs at the monolayer interface. Thermodynamic results show that the adsorption is a spontaneous and exothermic process with entropy decrease. Under the conditions of pH 2 and concentration of eluents of 80%, the elution rate is 98.73%. The purity of berberine increased from 31.4 to 73.1%. After repeating adsorption for 15 times, the adsorption capacity of ZSM-5 molecular sieve for berberine remains well, which indicates that ZSM-5 has great purification capacity and reusability. These results confirm that ZSM-5 has potential superior properties for the purification and isolation of active ingredients from medicinal herbs.

    更新日期:2019-12-19
  • Synthesis of alumina support and effect of its properties on thiophene hydrodesulfurization
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-18
    Sakeena H. AlSairafi, N. AlNajdi, H. AlSheeha, Mohan S. Rana

    A number of alumina supports were synthesized by using a homogeneous sol–gel precipitation technique. The role of organic additive and its effect on surface active sites as well as textural properties have been analyzed. The support was characterized by N2 adsorption–desorption, X-ray diffraction (XRD). fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermal gravimetric and differential scanning calorimetry analysis (TGA/DSC). The surface functional group characterization was carried out by using isopropanol (IPA) as a probe molecule for the acid–base site identification. The solid was used as support for a catalyst and to compare active metal site genesis as a supported catalyst where thiophene reaction was carried out, and activity was compared with the commercial alumina support. The characterization results indicated that the pore enlarging agent (poly (ethylene) glycol, PEG) improve not only textural properties but also significantly modified surface properties, which was evident during the hydrodesulfurization (HDS) of thiophene.

    更新日期:2019-12-19
  • Attapulgite-anchored Pd complex catalyst: a highly active and reusable catalyst for C–C coupling reactions
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-17
    Quanlu Yang, Hongli Wu, Huiying Zhan, Juanjuan Hou, Meiei Gao, Qiong Su, Shang Wu

    Natural clay, attapulgite was successfully employed to prepare reusable heterogeneous catalyst of ATP–APTES–Pd through simple and green steps. The catalyst was characterized by ICP, IR, XRD, XPS, SEM, and TG. The novel complex exhibited excellent activity for a wide scope of Suzuki and Heck cross-coupling reactions without phosphine ligand, respectively. Remarkably, the catalyst is easy to separate, stable and can be reused several times in good activity without any additional activation treatment.

    更新日期:2019-12-18
  • Modeling and optimization of thermally coupled reactors of naphtha reforming and propane ammoxidation with different feed distributions
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-16
    Samira Ebrahimian, Davood Iranshahi

    In this paper, the thermal coupling of naphtha reforming with propane ammoxidation was simulated using a one-dimensional homogenous model for two processes. By this technique, the required heat for the endothermic naphtha reforming process is provided by the exothermic propane ammoxidation which caused the related furnaces to be removed. The propane ammoxidation takes place in the tube side while the naphtha reforming occurs in the shell side of thermally coupled reactors. Depending on the feed distribution, four configurations including (1) series naphtha-series ammoxidation, (2) series naphtha-parallel ammoxidation, (3) parallel naphtha-parallel ammoxidation, and (4) parallel naphtha-series ammoxidation were investigated to select the best configuration which yields the highest efficiency. The modeling results showed that the first configuration is the best configuration in which produces the aromatics 4 kmol h−1 greater than the conventional naphtha reforming (CNR). Hence the optimization of the first configuration with the genetic algorithm method was done to obtain the optimal value of its key variables. The molar flow rate of aromatics was achieved to 141.9 kmol h−1 at optimized input temperature of naphtha reforming (776.94 K), input temperature of propane ammoxidation (779.9 K) and the number of tubes (395).

    更新日期:2019-12-17
  • Ni,Co/SiO 2 and Ni/SiO 2 ,Co bimetallic microsphere catalysts indicating high activity and stability in the dry reforming of methane
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-14
    Gamze Gunduz-Meric, Suleyman Kaytakoglu, Levent Degirmenci

    Two separate synthesis procedures were applied to alter the location of Cobalt (Co) in bimetallic silica (SiO2) microsphere catalyst with Nickel (Ni) as the second active metal. Co was either encapsulated with simultaneous Ni addition inside core structure (Ni,Co/SiO2) or impregnated on the shell following initial encapsulation of Ni inside the microsphere (Ni/SiO2&Co). Catalysts were tested in dry reforming of methane (DRM) reaction at 750 °C with a feed mixture of CH4:CO2:N2 = 1:1:1. Reactions were performed in a stainless steel temperature-controlled tube reactor. Results indicated the highest activity values with 4Ni-1Co ratio in catalyst structure and Co impregnated on catalyst structure revealed higher activity for all loadings compared to Ni,Co/SiO2 catalysts. CH4 and CO2 conversions for 3 h of reaction were obtained as 87 and 94%, and H2/CO ratio was determined as 0.84 in the presence of Ni/SiO2&Co catalyst with 4Ni-1Co loading. Coke formation was not detected for the catalyst with 4Ni-1Co loading and the highest coke amount was 2% among all catalysts. Time on stream test in the presence of Ni/SiO2&Co catalyst with 4Ni-1Co loading was conducted for 12 h in identical conditions, and results revealed a stable activity with conversions equal to 3 h of reaction. Coke suppression during DRM reaction was attributed to microsphere structure, Co presence and SiC formation. SiC formation was introduced as a unique situation emanated as a result of the reaction between SiO2 and C.

    更新日期:2019-12-17
  • Comparative study on the adsorption, kinetics, and thermodynamics of the photocatalytic degradation of six different synthetic dyes on TiO 2 nanoparticles
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-14
    Siti Lailatul N. Zulmajdi, Nur Izzah Iwanina Zamri, Hartini M. Yasin, Eny Kusrini, Jonathan Hobley, Anwar Usman

    Organic effluents have become a serious global environmental concern. Therefore, the removal of pollutive compounds from water systems is essential, and one of potential methods is photocatalysis, employing metal oxides as catalyst. The present study, for the first time, compared the photocatalytic degradation of six different synthetic dyes, including methylene blue (MB), rhodamine B (RhB), crystal violet (CV), methyl violet (MV), malachite green (MG), and brilliant green (BG) as models of organic effluents in aqueous solutions, on anatase titanium dioxide (TiO2) nanoparticles under UV light illumination. The results show the complete degradation of the dyes within 30 min of irradiation. The effects of initial concentration, catalyst dosage, and medium temperature on the photocatalytic degradation of the dyes suggested that the six different dyes in this study were adsorbed in the same way and undergo an oxidation reaction with photo-generated OH· radical on the surface of TiO2 catalyst. The photo-induced degradation of all the dyes follows pseudo first-order kinetics, which can be explained using the Langmuir–Hinshelwood model. The photocatalytic degradation of the dyes was found to be a diffusion-controlled reaction, and its degradation rate was enhanced at higher temperature. Interesting finding is that, under the same experimental conditions, the photodegradation rate was estimated to be 0.77, 0.71, 0.44, 0.30, 0.23, and 0.15 min−1 for CV, BG, MB, MV, MG, and RhB, respectively, suggesting the different potential barriers of demethylation or deethylation reaction of the dyes, which is related to their molecular structure, size, and reactivity. From thermodynamic viewpoint, the activation energy attributed to the potential barrier of the photocatalytic degradation is related to diffusion-controlled reaction between the dyes and generated hydroxyl radical on the TiO2 catalyst surface.

    更新日期:2019-12-17
  • Chemoselective synthesis of drug-like pyrrolo[2,3,4-kl]acridin-1-one using polyoxometalate@lanthanoid catalyst
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-14
    Mansoureh Daraie, Nahid Lotfian, Majid M. Heravi, Masoud Mirzaei

    The incorporation of polyoxometalates (POMs) or metal oxides into the metal–organic frameworks opens new research avenues for the synthesis of heterogeneous catalysts. In this project, a catalytic system based on neodymium clusters and Keggin-type of heteropoly acid (HPA) (Na[Nd(pydc-OH)(H2O)4]3}[SiW12O40]) was used as heterogeneous catalyst for one pot synthesis of pyrroloacridines, via multi component reactions involving dimedone, isatin and aniline in green condition. The novelty of this work originates from using inorganic–organic hybrids based upon POMs in catalyzing organic transformation. Compared with parent HPA (89.0% yield in 15 min for [SiW12O40]4−), this hybrid catalyst showed higher catalytic activity (94% yield in 8 min) in pyrroloacridines synthesis. The hybrid compound could be reused at least five times without obvious loss of the catalytic activity.

    更新日期:2019-12-17
  • NiMoW/P-Al 2 O 3 four-component catalysts with different Mo:W molar ratios and P 2 O 5 contents: the effect of the composition and active phase morphology on the catalytic activity
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-14
    P. S. Solmanov, N. M. Maximov, N. N. Tomina, I. I. Zanozina, A. A. Pimerzin, S. P. Verevkin

    NiMoW/P-Al2O3 catalysts were synthesized with a different ratio of Mo:W (W-free sample, Mo:W = 2:1, Mo:W = 1:1, Mo:W = 1:2 and Mo-free sample) and various P2O5 contents in the carrier (up to 5 wt%). The surface of the sulfide phase of the samples was investigated by means of high-resolution transmission electron microscopy (HR TEM) and X-ray photoelectron spectroscopy (XPS). The catalytic activity of patterns was estimated in the reactions of hydrodesulfurization of dibenzothiophene (DBT) and hydrogenation of naphthalene. The results are presented in the form of three-dimensional diagrams “P2O5 content—ratio Mo/W—catalytic activity” or “P2O5 content—ratio Mo/W—property”. The influence of the phosphorus content on the maximum peak position of the binding energy S2p/1 of the S2− atomic group for the investigated systems is shown. Comparison of the shape of the curve of changes in the binding energy with the previously presented results on the catalytic activity of the samples in the HDS of a vacuum gas oil allows us to conclude that phosphorus is able to change the electronic state of the active phase of the catalysts, which leads to a change in their catalytic activity in the reactions of HDS.

    更新日期:2019-12-17
  • Comparison of carbon deposition features between Ni/ZrO 2 and Ni/SBA-15 for the dry reforming of methane
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-14
    Xiaoping Zhang, Feng Wang, Zhengwei Song, Shengjian Zhang

    Ni-based catalysts supported on ZrO2 and SBA-15 were employed in dry reforming of methane. The relation between carbon deposition and the deactivation of supported Ni catalysts was studied. Ni/ZrO2 exhibited superior stability, despite of its high coking rate. Therefore, there was no direct relationship between the coking rate and the deactivation rate. In order to investigate the nature of the coke species during dry reforming of methane, TG-DTA/CO2-TPO/TPSR/TEM experiments were conducted on the spent catalysts. Characterization results showed that the formation of CNTS on Ni/ZrO2 could be responsible for the superior stability. For comparison, the dominant carbon species was encapsulating carbon on Ni/SBA-15, leading to serious deactivation. The main difference between Ni/ZrO2 and Ni/SBA-15 was the reactivity of carbon species towards carbon dioxide. Coke deposited on Ni/ZrO2 was oxidized by CO2 at lower temperature, although carbon species on the two catalysts was similar. Additionally, the results of TPSR illustrated that the surface oxygen species over the zirconia support was involved in the oxidation of coke by CO2. The activity of Ni/ZrO2 was completely restored after the in-situ regeneration with CO2, indicating that carbon deposition was greatly removed by CO2.

    更新日期:2019-12-17
  • Hydrogen generation from ammonia borane by chemically dealloyed platinum nanoparticles
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-14
    Levent Semiz

    In this study, platinum catalysts were prepared from cosputtered platinum-aluminum alloys by dealloying method and utilized in hydrogen generation from ammonia borane. Aluminum was selectively removed from the alloy by sodium hydroxide. The resultant platinum particles obtained after dealloying was found to have nanoporous structure. The effect of Al sputtering power on hydrogen generation performance of particles was evaluated. The catalysts were characterized by SEM, TEM, and Zeta-Sizer. The maximum hydrogen generation rate of the catalysts was measured as 82.8 (± 2.2) L H2 min−1 g−1catalyst. The effect of catalyst amount was also evaluated. The activation energy of the reaction was calculated as 20.4 (± 0.8) kJ mol−1. Furthermore, the catalysts could preserve their catalytic activity upon consecutive runs with effective washing steps.

    更新日期:2019-12-17
  • Fine-tuning the catalytic activity by applying nitrogen-doped carbon nanotubes as catalyst supports for the hydrogenation of olefins
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-12-14
    Emőke Sikora, Adrienn Kiss, Zsuzsa H. Göndör, Péter Pekker, Ferenc Kristály, Milán Szőri, Anita Rágyanszki, Béla Viskolcz, Béla Fiser, László Vanyorek

    Nitrogen-free multi-wall carbon nanotubes (MWCNTs) and N-doped bamboo-like carbon nanotubes (BCNTs) were synthesized by using catalytic vapor deposition (CVD) and used as catalyst support materials. Pd, Rh, Ru, and Ir have been deposited onto the nanotubes to achieve metal/nanotube catalysts. The catalytic activity of the samples was fine-tuned by changing the type of support. BCNT supported Pd and Rh (Pd/BCNT, Rh/MWCNT) catalysts were found to be the most active for liquid phase hydrogenation of octadecene amongst these samples. The initial olefin hydrogenation rate of the Pd/BCNT sample was slightly higher than the corresponding MWCNT-supported catalyst. Based on the hydrogenation reaction, the performance of these catalyst had been ranked as follows: Pd/BCNT ≈ Rh/MWCNT > Pd/MWCNT > Rh/BCNT > > Ir/MWCNT > Ru/BCNT > Ir/BCNT > Ru/MWCNT. The structural properties of chemisorbed Pd on MWCNT and N- BCNT were also characterized by means of computational chemical methods in order to shed some light on the nature of metal binding properties of N-doped and undoped surfaces. The calculations shown preference towards the edges of the surfaces which is in good agreement with the experimental findings.

    更新日期:2019-12-17
  • Promotion of the Ni/γ-Al 2 O 3 catalyst for the hydrogenation of naphthalene by silica coating
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-08-06
    Jianguo Wu, Shibiao Ren, Rong Zhao, Zhicai Wang, Zhiping Lei, Shigang Kang, Chunxiu Pan, Zhanku Li, Jingchong Yan, Hengfu Shui

    The γ-Al2O3 was coated with silica through the chemical liquid deposition method with tetraethyl orthosilicate as a deposition agent. The effects of the silica coating on the reduction behaviors of nickel species, acidity and hydrogenation activities of the Ni/γ-Al2O3 catalysts were studied. The results show that the silica coating has a great promotion on the reduction behaviors of nickel species as the catalyst was activated under air atmosphere but little influence under H2. The acidity of the catalyst was improved by the silica coating. Therefore, the activities of Ni/γ-Al2O3 catalysts for the hydrogenation of naphthalene are promoted by the silica coating, but the promotion effects on the catalysts activated under air and H2 atmosphere are difference. The promotion on the catalyst activated under air is due to the enhancement of its reduction degree and acidity, but only acidity for the catalyst activated under H2. As a result, the activity is improved about 230% for the catalyst activated under air but only about 110% for the catalyst activated under H2.

    更新日期:2019-12-11
  • Silver and copper–magnetite nanocomposites as green and magnetic recoverable catalysts for the preparation of cyclopentadiene derivatives from a tri-component condensation
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-09-03
    Sayyed Hamed Adyani, Esmaiel Soleimani, Zinatossadat Hossaini

    Utilizing Citrus sinensis peels extract, acting as the stabilizing and reducing agents, an eco-friendly and green method is described for the preparation of copper/magnetite and silver/magnetite nanocomposites (NCs) via biological reduction of Ag+ and Cu2+ ions. The total phenolic compounds of the C. sinensis peels extract and extract’s ability to inhibition the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) radical were determined. The obtained results verified which the C. sinensis peels extract has the capability to reduce the silver(I) and copper(II) ions to its metallic nanoparticles (NPs). The deposition of silver and copper NPs on magnetite (Fe3O4) ones was confirmed by absorption bands at λmax values of 422 and 732 nm in their UV–Vis spectra, being related to the plasmon bands of silver and copper NPs. The catalytic performance of silver/Fe3O4 and copper/Fe3O4 NCs was investigated in the three-component condensation reaction of synthesis of 1,3-cyclopentadiene derivatives. The present synthetic method is the simple, economic, green route and effective with high efficiency.

    更新日期:2019-12-11
  • A modification of the Langmuir rate equation for diffusion-controlled adsorption kinetics
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-10-19
    Stefano Salvestrini

    It is widely agreed that the classical Langmuir rate equation cannot be applied for describing the kinetics of adsorption processes whose rate is controlled by diffusive transport phenomena. To overcome this limit, we propose a modification of the Langmuir rate equation, referred to as Diffusion-Controlled Langmuir Kinetics (DCLK), assuming that the macroscopic forward rate of adsorption is inversely related to the square root of time. We tested the DCLK model on experimental adsorption kinetic data. The results indicate that the DCLK model describes the kinetic data better than the traditional pseudo-second order model. Consistently with the intraparticle adsorption/diffusion theory, the adsorption amount predicted by the DCLK model proportionally increases with the square root of time at the beginning of the process. The effect of temperature on the adsorption rate and the relative role played by kinetics and thermodynamics are discussed.

    更新日期:2019-12-11
  • Kinetics of the isomerization of α-pinene epoxide over Fe supported MCM-41 and SBA-15 materials
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-08-13
    Julián E. Sánchez-Velandia, Andrea Agudelo-Cifuentes, Aida L. Villa

    A kinetic study for the isomerization of α-pinene epoxide over Fe/SBA-15 and Fe/MCM-41 catalysts was developed using a pseudo-homogeneous (polynomial law) and heterogeneous (LHHW formalism with one and two actives sites) models. TEM analysis of Fe/SBA-15 and Fe/MCM-41 showed that the materials have the typical hexagonal organization; FTIR adsorption–desorption of pyridine revealed the presence of Lewis acidity in both Fe/SBA-15 and Fe/MCM-41 catalysts. The presence of Fe3+ and Fe2+ species was concluded from XPS analysis; however, active site for α-pinene epoxide isomerization was attributed to Fe3+. With toluene as solvent, it was found that in both catalysts, the more adequate kinetic model was the unimolecular LHHW model with two active sites of the same type. Apparently, α-pinene epoxide isomerization is much faster over Fe/MCM-41 (5.78 L h−1 gFe−1) than over Fe/SBA-15 (1.14 L h−1 gFe−1). The activation energy for both Fe catalysts was evaluated using solvents of different polarity. In the case of Fe/MCM-41, the less energetic barrier was observed with toluene (30.99 kJ mol−1), while tert-butanol (13.76 kJ mol−1) was more favorable in the case of Fe/SBA-15 catalyst. Fe/MCM-41 is a very robust catalyst because it can be used up to four times without a significant loss of catalytic activity in comparison with Fe/SBA-15 that only can be used two times. Finally, a reaction mechanism was proposed for the isomerization of α-pinene epoxide over both Fe/SBA-15 and Fe/MCM-41 catalysts.

    更新日期:2019-12-11
  • Mechanistic details for the reaction of methyl acrylate radical anion: a DFT study
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-08-20
    Hossein Tavakol, Mohammad A. Ranjbari, Mohammad Taqi Jafari-Chermahini

    In the present work, based on the reported experimental observations, theoretical methods were employed to study the electron-induced reaction of methyl acrylate. Our calculations revealed that two routes are possible among ten proposed pathways for this reaction. In both of these routes, the reaction proceeds via four distinct steps including dimerization, cyclization, methanol elimination, and trimerization. The results showed that the most favorable mechanism proceeds via a stepwise pathway involving dimethyl acrylate radical anion. Finally, structural, kinetics and thermodynamics of both possible paths have been calculated and compare to obtain the most possible route for this reaction.

    更新日期:2019-12-11
  • Selective benzene reduction from gasoline using catalytic hydrogenation reactions over zeolite Pd/13X
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-09-25
    Nemat Alimohammadi, Sohrab Fathi

    In this study, the selective hydrogenation of benzene in a mixture of benzene and normal heptane was investigated by 13X zeolite modified with Pd as catalyst (Pd/13X). The modification of 13X zeolite was carried out using a specified amount of Pd (NO3)2 in the solution and the experimental tests were conducted in the catalyst evaluation set-up (Cata-test). The characterizations of 13X and Pd/13X were studied by XRD, FTIR, SEM, TEM and BET. Several variables affecting the catalyst performance such as temperature, pressure, WHSV and H2/HC mole ratio were investigated and optimized. It was found that the conversion of benzene was equal to 95% at the operating conditions of T = 200 °C, p = 1 MPa, WHSV = 20 h−1 and H2/HC molar ratio of 1.3.

    更新日期:2019-12-11
  • Monodisperse mesoporous La 2 O 3 flakes for the synthesis of glycerol carbonate by efficiently catalyzing the transesterification of dimethyl carbonate with glycerol
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-08-26
    Chengguang Yue, Mingming Fan, Pingbo Zhang, Lihua Liu, Pingping Jiang

    Monodisperse mesoporous La2O3 flakes were prepared by hydrothermal methods using polyethylene glycol as pore-expanding agent, the catalyst exhibited better catalytic activity than normal La2O3 in the reaction of glycerol and dimethyl carbonate to produce glycerol carbonate. The influence of the molecular weight of polyethylene glycol and the mass ratio of La(NO3)3·6H2O/polyethylene glycol on the catalyst was investigated. The results showed that the morphology of La2O3 was remolded to porous flakes interestingly by the suitable type and dosage of pore-expanding agent, this change made the La2O3 catalyst particles have higher alkalinity, better crystallinity, larger specific surface area and good dispersion, which greatly improved the catalytic performance of the catalyst. In addition, the optimal reaction conditions were studied. As a result, the as-prepared porous La2O3 modified by polyethylene glycol-20000 showed excellent catalytic performance with high glycerol carbonate yield of 99.4% under the optimal reaction conditions as follows: the glycerol/dimethyl carbonate molar ratio was 1:5, the catalyst dosage was 5.0 wt% to glycerol, the reaction temperature was 85 °C and the reaction time was 0.5 h. The catalyst had outstanding stability after six cycle reactions with almost no loss of catalytic activity. Thereby, the catalyst was considered to possess the promising potential in industrial production for catalyzing glycerol to the high value-added chemical glycerol carbonate.

    更新日期:2019-12-11
  • Kinetics and mechanism of the oxidation of vanillic acid using smectite clay
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-09-04
    Nourzed Frikha, Soumaya Bouguerra, Sonda Ammar, Francisco Medina, Ridha Abdelhedi, Mohamed Bouaziz

    In this study, the oxidation of vanillic acid (VA) into protocatechuic acid (PCA) was investigated using montmorillonite KSF as inexpensive and environmentally benign solid acid, with peroxide hydrogen to afford excellent yields (more than 75%) endowed with high selectivity. To our knowledge, the aforementioned method was used for the first time in green, clean synthesis. The influence of the several operating parameters were performed using an experimental design Box–Behnken methodology. The progress of the concentrations of VA and its oxidation product PCA was accomplished using ultra-high-performance liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (RP-UHPLC-DAD-QTOF-MS) and mass spectrometry. Accordingly, PCA would be advantageous when used in food as well as cosmetic and pharmaceutical industries. Finally, a mechanistic pathway for the VA oxidation was proposed.

    更新日期:2019-12-11
  • Torrefaction of Leucaena Leucocephala under isothermal conditions using the Coats–Redfern method: kinetics and surface morphological analysis
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-09-03
    Aznie Nadiera Awang, Alina Rahayu Mohamed, Noor Hasyierah Mohd Salleh, Peng Yong Hoo, Nur Nasulhah Kasim

    The effects of temperature and holding times on the torrefaction of Leucaena Leucocephala (Leucaena) were elucidated via a novel isothermal decomposition approach. The torrefaction was performed in a fixed-bed reactor at temperature ranged from 200 to 300 °C for 20, 40 and 60 min. The effects of both torrefaction temperature and holding time were studied quantitatively and qualitatively by evaluating the distribution product yields and surface morphological changes. Quantitatively, the mass yield decreased with increasing temperature for all tested holding times, while the liquid and gas yields increased steadily due to the release of volatiles from the biomass decomposition. Qualitatively, significant morphological changes on Leucaena due to torrefaction were evidently captured via SEM imaging analysis. For torrefaction temperatures from 200 to 260 °C, the raw and torrefied Leucaena showed that pore evolution process had become evident. However, for torrefaction temperatures from 280 to 300 °C, the torrefied Leucaena revealed that the internal structure of torrefied Leucaena underwent pore development process. The pore development was noticeably observed for all temperatures. The values of activation energy (Ea) and pre-exponential factor (ln A) for the torrefaction were calculated based on the Coats–Redfern method for first order reaction. The values of Ea and ln A for 20, 40 and 60 min were found to be 39.75, 40.10 and 42.31 kJ/mol, and 3.92, 4.14 and 4.67. As a conclusion, the torrefaction of Leucaena from 200 to 300 °C for 20 min holding time is more reactive as compared to that at higher holding time.

    更新日期:2019-12-11
  • Kinetic modeling of cottonseed oil transesterification with ethanol
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-09-11
    Thibério P. C. Souza, Ronaldy J. M. C. L. Silva, James C. Melo, Isabelle C. P. Tschoeke, Josivan P. Silva, Jose G. A. Pacheco, José M. F. Silva

    This study aimed to evaluate the kinetic behavior of cottonseed oil transesterification with ethanol based on a pseudo first order kinetic model. A 23 factorial planning with three central points was performed by considering temperature, catalyst concentration and alcohol/oil molar ratio as dependent variables and biodiesel concentration as response signal. It was observed that the highest conversion was obtained for the following conditions: temperature between 50 and 70 °C, high alcohol/oil molar ratio and low percentage of catalyst. All samples were collected during time intervals of 5–10–15–30–60 and 90 min. A set of kinetic constant values were obtained for each operating condition ranging from 72 to 23l min−1. Indeed, it was possible to obtain the kinetic parameters frequency factor k0 = 5807.05 dm3*mol−1*min−1 and Ea = 16.84 kJ*mol−1 for biodiesel production with ethanol.

    更新日期:2019-12-11
  • Electron paramagnetic resonance study of electronic changes of vanadium in poisoned hydrodesulfurization catalysts submitted to oxidation, carbiding and nitriding processes
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-09-12
    Susana Pinto-Castilla, Delfín Moronta, Daniel Figueroa, Josmir Rodríguez, Raquel S. Del Toro, Paulino J. Betancourt-Figueroa, Joaquín L. Brito

    Changes in the oxidation state and chemical environment of vanadium in poisoned and regenerated hydrotreatment (HDT) catalyst were followed by electron paramagnetic resonance (EPR). Oxovanadyltetraphenil porphyrin was used as model poison molecule on synthesized CoMo/Al2O3 HDT-UCV-1 catalyst. Unconventional methodologies of carbiding and nitriding were applied to the deactivated catalyst aiming at recovering its catalytic properties. The results showed that the vanadium incorporation method affected the metallic species on the catalyst surface, particularly the V-support interaction. This work represents an important contribution about the understanding of new phases formed in the spent catalysts after reactivation by means of nitriding and carbiding processes, which are expected to improve the catalytic HDT response.

    更新日期:2019-12-11
  • Self-oscillations and surface waves during CO oxidation over Co
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-09-12
    V. Yu. Bychkov, Yu. P. Tulenin, M. M. Slinko, A. Ya. Gorenberg, D. P. Shashkin, V. N. Korchak

    The paper looks into the temporal and spatial dynamics of a new oscillating system comprised of CO oxidation over Co. Reaction rate oscillations occurring in CO excess were similar to the ones observed over Ni. The periodic variation of oxygen imbalance together with the variation in colour changes during the oscillations indicated that the oscillations were closely connected with the reversible oxidation of Co to various Co oxides. The periodic oxidation/reduction of cobalt proceeded as surface waves. Unexpectedly, widely varying spatial structures and wavefront velocities were detected during the heating and cooling branches under identical reaction conditions: regular self-oscillations transforming into a “surface turbulence” state.

    更新日期:2019-12-11
  • Base-free glycerol oxidation over N-TiO 2 supported Au–Pt catalysts
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-10-01
    Dhia Cherni, Noomen Moussa, Mohamed Faouzi Nsib, Claudio Evangelisti, Laura Prati, Alberto Villa

    N-Doped TiO2 materials were used as support for the bimetallic gold-platinum nanoparticles catalysts. Via the sol immobilization technique, the metal particle dimension varied during the immobilization on the different supports. The prepared TiO2 samples were characterized by X-ray diffraction (XRD), N2 physisorption (BET) and X-ray photoelectron spectroscopy (XPS), while the AuPt-TiO2 catalysts were characterized by transmission electron microscopy (TEM). The oxidation of glycerol by molecular oxygen in the aqueous phase over AuPt/N-TiO2 was investigated in a continuous upflow batch reactor under base-free conditions. The difference in the catalyst activities could be ascribed to the different support. The results revealed that N-doped TiO2 based catalyst support showed a higher activity in the oxidation of glycerol compared to the unfunctionalized one. The highest conversion (92% after 6 h) and the highest selectivity to glyceric acid (79.9%) were achieved using AuPt on TiO2 prepared with chitosan.

    更新日期:2019-12-11
  • A new facile synthesis, kinetic mechanism and some thermodynamic studies of thermal transformation of α-LiZnPO 4 ·H 2 O
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-08-08
    Nantawat Phonchan, Chanaiporn Danvirutai, Pittayagorn Noisong, Sujittra Youngme, Sira Sansuk

    α-LiZnPO4·H2O was successfully synthesized via a new simple route in an aqueous media at ambient temperature. The as-prepared and the calcined powders were confirmed by standard characterization methods. The SEM micrographs of the title compound and its dehydration product were studied. The experimental enthalpy of dehydration was evaluated from DSC data, which was found to be close to the standard enthalpy of water vaporization. α-LiZnPO4·H2O dehydrates in a single step. Therefore, this compound is an additional ideal case for studying the decomposition kinetics. Non-isothermal dehydration kinetics was studied from TG data using Ozawa–Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS) methods including their iterative procedures, as well as some reliable solid-state kinetic equations of Coats–Redfern, Madhysudanan–Krishnan–Ninan (MKN), Tang and Wanjun. The most probable mechanism function was determined using the master plots method. The dehydration mechanism was found to be the chemical reaction with the one-third order reaction or the type F1/3 reaction model with the differential form of f(α) = 3/2 (1 − α)1/3 and the integral form of g(α) = 1 − (1 − α)2/3. The calculated activation energy value is exact and reliable. The discussions about the results of XRD, SEM, DSC, FTIR and the most probable mechanism function of dehydration are consistent.

    更新日期:2019-12-11
  • Synthesis of fatty acid methyl ester via transesterification of waste frying oil by a zinc-modified pumice catalyst: Taguchi approach to parametric optimization
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-10-24
    Adeyinka S. Yusuff, Kazeem A. Bello

    Methanolysis of waste frying oil (WFO) was conducted to synthesize fatty acid methyl esters (FAME) using zinc-modified pumice (ZMP) as a heterogeneous catalyst. The ZMP catalyst was prepared via incipient wetness impregnation method and characterized by various spectroscopic techniques such as Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). Taguchi design approach was employed to optimize the transesterification process variables, which include reaction temperature (50–70 °C), reaction time (1–3 h), methanol/WFO molar ratio (6:1–12:1) and catalyst loading (1–3 wt%). The transesterification reaction kinetic and impact of reaction temperature on the reaction rate were investigated. The kinetic data obtained at different temperatures were evaluated using zero-order and pseudo-first-order models. Among the process variables studied, FAME yield was mostly affected by the reaction temperature, methanol/WFO molar ratio, and catalyst loading. The maximum FAME yield of 91.05 wt% was attained at the optimum reaction temperature of 60 °C, 3 wt% catalyst loading, and 12:1 methanol/WFO molar ratio. The better activity exhibited by the ZMP catalyst in the transesterification reaction was attributed to the interaction among several metal oxides present in the catalyst as confirmed by the EDX, XRF and XRD analyses. The catalyst stability study showed that the ZMP could be reused up to four times. The pseudo-first-order model gave the best fit with the catalytic reaction data, and the activation energy was 50.61 kJ mol−1.

    更新日期:2019-12-11
  • Synthesis of hierarchical ZSM-5 aggregates by an alkali-treated seeds method with cetyltrimethylammonium bromide for the methanol to gasoline reaction
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-09-03
    Jingjing Zhao, Yaquan Wang, Chao Sun, Aijuan Zhao, Cui Wang, Xu Zhang, Ziyang Wang, Taotao Zhao, Wenrong Liu, Jiaxin Lu, Shuhui Wu

    A series of hierarchical ZSM-5 aggregates with a relatively low SiO2/Al2O3 ratio (~ 50) were successfully synthesized using alkali-treated commercial ZSM-5 as seeds and cetyltrimethylammonium bromide (CTAB) as mesogenous template. The effect of the amounts of CTAB on the physicochemical and catalytic properties of the synthesized catalysts was characterized by XRD, FE-SEM, FE-TEM, N2 physical adsorption, ICP-OES, NH3-TPD, Py-IR and TGA. Moreover, the possible formation mechanism of the hierarchical ZSM-5 aggregates was studied. The results indicated that the mesoporosity of the hierarchical ZSM-5 aggregates was greatly enhanced with the addition of CTAB. The primary crystal size of the ZSM-5 aggregates significantly decreased owing to the protective effect of CTAB, which inhibits the further crystal growth. The hierarchical ZSM-5 aggregates prepared with addition of a suitable amount of CTAB showed large specific surface areas and large external surface areas, abundant intercrystalline mesopores and appropriate concentration of acid sites, which resulted in excellent catalytic performance in the methanol to gasoline reaction. The stability of the catalyst was remarkably improved and the gasoline yield was given a rise of 10% compared with the catalyst prepared in the absence of CTAB.

    更新日期:2019-12-11
  • Improved catalytic performance of mesoporous ZSM-5 nanocrystalline zeolite prepared by the cationic surfactant-ammonium salt mixed agent method in the methanol to gasoline reaction
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-10-31
    Mina Sadrara, Mohammadreza Khanmohammadi Khorrami, Amir Bagheri Garmarudi

    A mixed organic agent system was employed to achieve mesoporous highly crystalline ZSM-5 zeolite. Decyltrimethylammonium bromide (DeTAB) and tetramethyl ammonium hydroxide (TMAOH) were used as the mesogenous and molecular templates respectively in the synthesis gel with a composition of 60SiO2: 1Al2O3:12Na2O:3150H2O:xDeTAB:8TMAOH. The sole presence of DeTAB as the mesogenous template in the synthesis gel led to the high degrees of mesoporosity in the ZSM-5/xD samples but negatively affected the intrinsic properties of zeolites. At the high concentration of DeTAB (x = 0.7), the mesopore volume dramatically increased while the relative crystallinity and the total acid sites critically decreased. By adding the TMA+ ions as a microporous template to the ZSM-5/0.7D synthesis gel, not only a zeolite with well-developed mesoporosity was obtained but also its crystal structure and the intrinsic acidity were preserved. The catalyst samples were characterized by FESEM, TEM, XRD, FT-IR, nitrogen adsorption–desorption isotherms, NH3-TPD and TGA techniques. The ZSM-5/0.7D/T exhibited higher surface area, higher mesopore volume, higher crystallinity and more acid sites than the ZSM-5/0.7D. The catalytic conversion of methanol to gasoline was conducted in a fixed bed reactor at T = 390 °C and WHSV = 4.74 h−1. In ZSM-5/0.7D/T catalyst the mesoporosity formation without severely damaging the crystal structure and the acidity of the zeolite led to the best catalytic performance including the highest liquid hydrocarbon yield, most stable catalytic performance and longest catalytic lifetime.

    更新日期:2019-12-11
  • An experimental and computational study of biosurfactant production from soy molasses
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-08-22
    Ana Carolina Borges Silva, Marília Silva Rodrigues, Ruy de Sousa Júnior, Miriam Maria de Resende

    Mathematical modeling was performed of rhamnose production in a batch process, with model validation and optimization of a continuous fixed bed process. The batch experiments were performed for 72 h in a rotary incubator at 27 ± 1.0 °C and 120 rpm, with an initial inoculum concentration of 3 g/L in 150 mL of soy molasses at 100 g/L. Parameter determination was performed using multiple response nonlinear regression, with integration of a set of differential equations, employing the Runge–Kutta algorithm and application of the Contois model. The model was fitted to the experimental data and the sum of squared residuals was 47.61. The fitted parameters were validated in an experiment employing a column operated continuously at a flow velocity of 0.288 cm/h (flow rate of 0.02 mL/min), applying the plug flow reactor (PFR) and axial dispersion models. The optimal conditions were determined by the graphical assessment of the response variable behavior. The best validation results were obtained for the axial dispersion model. The optimum velocity was 0.3 cm/h, with less significant improvements in productivity at higher flow rates, for the substrate concentration range studied.

    更新日期:2019-12-11
  • Selective synthesis of monolaurin catalyzed by layered zinc laurate
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-09-11
    William Franco da Silva, Debora Merediane Kochepka, Laís Pastre Dill, Fernando Wypych, Claudiney Soares Cordeiro

    In the present study, zinc laurate (ZL) was synthesized by precipitation and characterized by X-ray diffraction, Fourier transform infrared spectroscopy and thermal analysis. ZL was applied for monolaurin synthesis by esterification of lauric acid with glycerol using a 23 factorial design to determine the best conditions for monolaurin production. Conversion of nearly to 70% was achieved by using a lauric acid:glycerol molar ratio of 1:1, 2 wt % of catalyst and 140 °C, reaching to 33% of monolaurin selectivity. Statistical analyses at a confidence level of 95% indicated that the decrease in lauric acid:glycerol molar ratio was significant to enhance the monolaurin production. Moreover, the solid was able to be reused, preserving its original structure and the catalytic activity, which indicated the potential use in continuous processes.

    更新日期:2019-12-11
  • Seed-assisted grinding synthesis of SAPO-34 catalyst and its prolonged catalytic lifetime in the conversion of methanol to olefins
    React. Kinet. Mech. Catal. (IF 1.428) Pub Date : 2019-08-12
    Huihui Lu, Weiting Duan, Xinhong Zhao

    A cost-effective route has been developed for the synthesis of nano-sized triclinic SAPO-34 zeolite via seed-assisted grinding method using lower dosage of morpholine as the sole template. The synthesis conditions including silica source, silica concentration, crystallization temperature and time were refined to obtain SAPO-34 zeolite with high phase purity and crystallinity. Particularly, seed crystals preactivated by different methods were utilized to induce the synthesis of nano-sized SAPO-34 zeolites in the subsequent study. The resultant SAPO-34 samples were characterized by XRD, SEM, N2 physisorption and NH3-TPD techniques. It was found that the introduction of seed crystals activated by mechanical milling for 20 min and chemical etching with 0.0001 M and 0.01 M H3PO4 can not only effectively reduce the crystal size of SAPO-34 zeolites from 3–4 μm to 500–800 nm level, but also can modify their texture and acid properties. This nano-sized SAPO-34 catalyst exhibits a remarkably prolonged catalytic lifetime in methanol to olefins (MTO) reaction in comparison to the conventional micron-sized counterpart. Analogous to solvent-free synthesis of zeolites, this seed-assisted grinding synthesis method is simpler, more efficient than conventional hydrothermal synthesis. More importantly, this method provides a new avenue for preparing superior MTO catalyst.

    更新日期:2019-12-11
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