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  • Transition Metals Catalyzed Element-Cyano Bonds Activations.
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2015-01-06
    Rui Wang,John R Falck

    Cyano group as a versatile functionalized intermediate has been explored for several decades, as it readily transfers to many useful functionalization groups such as amine, amide, acid, etc., which make it possess high popularization and use value in organic synthesis. Reactions involved with element-cyano bond cleavage can provide not only a new cyano group but also a freshly functionalized skeleton in one-pot, consequently making it of high importance. The highlights reviewed herein include H-CN, Si-CN, C-CN, B-CN, Sn-CN, Ge-CN, S-CN, Halo-CN, N-CN, and O-CN bonds cleavages and will summarize progress in such an important research area. This review article will focus on transition metal catalyzed reactions involving element-cyano bond activation.

  • Chemical composition of diesel particulate matter and its control
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2019-06-11
    Rohini Khobragade, Sunit Kumar Singh, Pravesh Chandra Shukla, Tarun Gupta, Ahmed S. Al-Fatesh, Avinash Kumar Agarwal, Nitin K. Labhasetwar

    In this review, we have systematically discussed diesel particulate composition and its formation, understanding of which is essential to design the effective catalyst compositions. The most commonly used after treatment strategies such as diesel oxidation catalysts, diesel particulate filters, and partial flow filters are described followed by chronological and category-wise discussions on various groups of reported soot oxidation catalysts. A detailed review is also presented on mechanistic and kinetics aspects of non-catalytic direct particulate matter (PM) or soot oxidation in air/O2 and NO2. Recent progress in catalyst development with a focus on the low-cost catalyst for diesel PM oxidation has been given more emphasis considering their renewed importance.

  • An overview of caprolactam synthesis
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2019-08-28
    Rawesh Kumar, Sneha Shah, Prangya Paramita Das, Gami Girish Kumar Bhagavanbhai, Ahmed Al Fatesh, Biswajit Chowdhury

    Caprolactam is the precursor of many industrial chemical productions as in nylon industry, plastic industry, paint industry, lysine synthesis and cross-linking for polyurethanes. The production of caprolactam has been focus much from last three decades among the scientific community to fulfill the industrial need under environment precautions. Herein a sequential and explanatory review broadly covering the transformation of a different substrate as cyclohexanone oxime, cyclohexanone, cyclohexanol, cyclohexane, and biorenewable sources into caprolactam is presented. For every substrate, a wide range of catalyst including homogeneous as well as the heterogeneous system has been deeply considered. This study will be helpful for developing alternative industrial route for production of caprolactam.

  • Review on photocatalytic conversion of carbon dioxide to value-added compounds and renewable fuels by graphitic carbon nitride-based photocatalysts
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2019-08-19
    Anise Akhundi, Aziz Habibi-Yangjeh, Masoud Abitorabi, Shima Rahim Pouran

    Photocatalytic reduction of CO2 is known as one of the most promising methods to produce valuable fuels and value-added compounds. To overcome selectivity and efficiency downsides, various photocatalysts have been designed and developed. This review discusses the state-of-the-art in photo-conversion of CO2 over graphitic carbon nitride (g-C3N4)-based composites. The modification strategies to improve photocatalytic activity of g-C3N4 were classified into different categories and discussed as structural modifications, elemental doping, copolymerization, fabricating heterojunctions between g-C3N4 and other semiconductors, Z-scheme heterojunctions, noble metal/g-C3N4 photocatalysts, and design of ternary nanocomposites based on g-C3N4. Finally, perspectives and future research works in this field were also outlined.

  • Fluid catalytic cracking technology: current status and recent discoveries on catalyst contamination
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 
    Peng Bai, Ubong Jerome Etim, Zifeng Yan, Svetlana Mintova, Zhongdong Zhang, Ziyi Zhong, Xionghou Gao

    The fluid catalytic cracking (FCC) technology is one of the pillars of the modern petroleum industry which converts the crude oil fractions into many commodity fuels and platform chemicals, such as gasoline. Although the FCC field is quite mature, the research scope is still enormous due to changing FCC feedstock, gradual shifts in market demands and evolved unit operations. In this review, we have described the current status of FCC technology, such as variation in the present day feedstocks and catalysts, and particularly, great attention is paid to the effects of various contaminants of the FCC catalysts of which the latter part has not been sufficiently documented and analyzed in the literature yet. Deposition of various contaminants on cracking catalyst during FCC process, including metals, sulfur, nitrogen and coke originated from feedstocks or generated during FCC reaction constitutes a source of concern to the petroleum refiners from both economic and technological perspectives. It causes not only undesirable effects on the catalysts themselves, but also reduction in catalytic activity and changes in product distribution of the FCC reactions, translating into economic losses. The metal contaminants (vanadium (V), nickel (Ni), iron (Fe) and sodium (Na)) have the most adverse effects that can seriously influence the catalyst structure and performance. Although nitrogen and sulfur are considered less harmful compared to the metal contaminants, it is shown that pore blockage by the coking effect of sulfur and acid sites neutralization by nitrogen are serious problems too. Most recent studies on the deactivation of FCC catalysts at single particle level have provided an in-depth understanding of the deactivation mechanisms. This work will provide the readers with a comprehensive understanding of the current status, related problems and most recent progress made in the FCC technology, and also will deepen insights into the catalyst deactivation mechanisms caused by contaminants and the possible technical approaches to controlling catalyst deactivation problems.

  • Dexterity of gold catalysis in controlling the regioselectivity of cycloaddition reactions
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 
    Chandrasekar Praveen

    Gold catalysis in the last two decade has witnessed remarkable improvements in terms of efficiency and scope of application in numerous organic reactions. In particular, the unique ability of gold catalysts to activate π-bonds to effect various cycloaddition reactions has received significant attention. However, the catalytic application of gold in creating new opportunities for the regioselective cycloaddition reactions went largely unnoticed. Steric/electronic environment of substrates, ancillary ligand and reaction time seems to be some of the associated regio-directing factors in the gold-catalyzed cycloaddition reactions. Hence, in this review on gold catalyzed regioselective cycloaddition reactions, a complete update about the different types of gold-catalyzed cycloaddition of substrates like alkynes, alkenes, allenes, and ynamides along with the factors governing the selectivity is discussed. Applications towards natural product synthesis and tandem reactions to showcase the synthetic utility of such processes are also highlighted.

  • Heterogeneous photocatalysis: guidelines on experimental setup, catalyst characterization, interpretation, and assessment of reactivity
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-11-28
    Francesco Parrino, Vittorio Loddo, Vincenzo Augugliaro, Giovanni Camera-Roda, Giovanni Palmisano, Leonardo Palmisano, Sedat Yurdakal

    Soon after the publication of the first pioneering works on heterogeneous photocatalysis, the number of papers on this topic continuously increased. This intriguing field of research is very complex as it endows with an interdisciplinary overview that involves different aspects of chemistry, physics, material and environmental sciences. Even if photocatalytic applications in real processes are often difficult to be implemented and scaled-up, investigations at laboratory scale are easy to be performed, and in some cases they may give rise to misconceptions. For this reason, the present work aims to sum up most of the common experimental techniques and procedures generally used in heterogeneous photocatalysis and to highlight the guidelines and the rules that a rigorous analysis and study of a photocatalytic system must follow. The paper focuses on the importance of standardization of photocatalytic experiments with special attention on the possibility to compare results obtained under different experimental conditions.

  • Hydrogen bond activation strategy for cyclic carbonates synthesis from epoxides and CO2: current state-of-the art of catalyst development and reaction analysis
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-12-02
    Mengshuai Liu, Xin Wang, Yichen Jiang, Jianmin Sun, Masahiko Arai

    Chemical fixation of CO2 into useful organic compounds has been attracting much attention from the viewpoint of CO2 emission reduction and energy structure reformation. A useful and widely investigated chemical utilization of CO2 is the cycloaddition of CO2 to epoxides for the synthesis of cyclic carbonates. Efforts have been paid to the design and preparation of various catalyst systems that are active and selective to the production of the desired products under mild conditions and in green processes. This article is to review the current state of the catalyst development and the experimental and theoretical analysis of reaction mechanism for the cyclic carbonate synthesis from epoxides, one of currently important reactions involving CO2 as a reactant with 100% atom economy. Particular attention is given to the catalysis of multifunctional catalyst systems such as metal- and hydrogen-bond donor (HBD)-based catalysts.

  • Removal of VOCs from gas streams via plasma and catalysis
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-11-13
    Wei-Chieh Chung, Dan-Hua Mei, Xin Tu, Moo-Been Chang

    Emission of volatile organic compounds (VOCs) has resulted in various environmental issues. Therefore, development of effective VOC removal technology is essential for reducing the adverse effects associated. This work provides a systematic review on VOC removal from gas stream via catalytic oxidation, plasma degradation, and plasma catalysis. For catalytic oxidation of VOCs, possible reaction mechanisms and how physicochemical properties of catalyst influences catalytic performance are presented and discussed, followed by plasma removal of VOCs, VOC degradation, and byproduct formation mechanisms. Next, interactions between plasma and catalyst are interpreted for comprehensive understanding. Last, perspectives are provided for further development of VOC removal technology.

  • Emerging role of nanobiocatalysts in hydrolysis of lignocellulosic biomass leading to sustainable bioethanol production
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-06-11
    Mahendra Rai, Avinash P. Ingle, Raksha Pandit, Priti Paralikar, Jayanta Kumar Biswas, Silvio Silverio da Silva

    Catalytic conversion (hydrolysis) of carbohydrate polymers present in the lignocellulosic biomass into fermentable sugars is a key step in the production of bioethanol. Although, acid and enzymatic catalysts are conventionally used for the catalysis of various lignocellulosic biomass, recently application of immobilized enzymes (biocatalysts) have been considered as the most promising approach. Immobilization of different biocatalysts such as cellulase, β-glucosidase, cellobiose, xylanase, laccase, etc. on support materials including nanomaterials to form nanobiocatalyst increases catalytic efficacy and stability of enzymes. Moreover, immobilization of biocatalysts on magnetic nanoparticles (magnetic nanobiocatalysts) facilitates easy recovery and reuse of biocatalysts. Therefore, utilization of nanobiocatalysts for catalysis of lignocellulosic biomass is helpful for the development of cost-effective and ecofriendly approach. In this review, we have discussed various conventional methods of hydrolysis and their limitations. Special emphasis has been made on nanobiocatalysts used for hydrolysis of lignocellulosic biomass. Moreover, the other most important aspects, like nanofiltration of biomass, conversion of lignocellulose to nanocellulose, and toxicological issues associated with application of nanomaterials are also discussed.

  • Olefin epoxidation with metal-based nanocatalysts
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-07-03
    Angelique Blanckenberg, Rehana Malgas-Enus

    Alkene epoxidations are an important class of reactions carried out in industry; however, current methods are plagued by problems, including high cost, difficulty in recovering catalysts, and generation of large quantities of acidic and chlorinated waste. In recent years, nanocatalysts have been considered as robust, heterogeneous alternatives to homogeneous catalysts. This work evaluates silver- and base metal-containing nanocatalysts as olefin epoxidation catalysts, highlighting the industrial applicability and green aspects of these catalytic systems. The nanocatalysts discussed are mostly supported or composite materials that showed (generally) good activity and selectivity for various/multiple olefin epoxidation reactions.

  • Paal–Knorr synthesis of pyrroles: from conventional to green synthesis
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-10-19
    Avula Balakrishna, António Aguiar, Pedro J. M. Sobral, Mohmmad Younus Wani, Joana Almeida e Silva, Abilio J. F. N. Sobral

    The pyrrole molecular framework is found in a large number of natural and synthetic compounds of great importance. Since functionalized pyrroles are essential for the progress of many branches of science, its synthesis by simple, efficient and eco-friendly routes are particularly attractive in modern organic and bio-organic chemistry. To this end, a number of synthetic methods have been developed, in which the Paal–Knorr pyrrole synthesis stands out to be the easiest route to synthesize pyrroles. In spite of the efficiency, Paal–Knorr synthesis of pyrroles is considered limited by harsh reaction conditions, such as prolonged heating in acid, which may degrade sensitive functionalities in many potential precursors. Through this route almost all dicarbonyls can be converted to their corresponding heterocycles and therefore it is a synthetically valued process. To address the adverse issues this reaction route has undergone numerous modifications recently and today it can be said that this reaction route is a prominent green route for the synthesis of pyrroles. This review is a tour from the evolution and application of this harsh synthetic route to the eco-friendly greener route developed for the synthesis of pyrroles.

  • Aqueous biphasic hydroformylation of olefins: From classical phosphine-containing systems to emerging strategies based on water-soluble nonphosphine ligands
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-11-05
    Leah C. Matsinha, Shepherd Siangwata, Gregory S. Smith, Banothile C. E. Makhubela

    This review provides an overview of recent developments in the area of aqueous biphasic hydroformylation of higher olefins using metal catalysts and surfactants, cosolvents, thermoregulated ligands, cyclodextrins, and most importantly emerging water-soluble nonphosphine ligands. Water-soluble phosphine ligands have been widely explored for aqueous biphasic hydroformylation; however, phosphines are generally expensive and are prone to oxidation hence the recent interest in exploring other ligands. Various approaches have been used to introduce hydrophilicity to the ligands. The catalytic activity of monometallic and heterobimetallic systems containing nonphosphine ligands in aqueous biphasic media is emphasized in this review.

  • Carbonaceous materials modified catalysts for simultaneous SO2/NOx removal from flue gas: A review
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-06-19
    Kiman Silas, Wan Azlina Wan Ab Karim Ghani, Thomas S.Y. Choong, Umer Rashid

    Globally, considerable effort and resources are being channeled toward controlling the rising threat from pollution and other related impacts from man-made activities, which have detrimental effects on human health and the environment. The presence of some associated gases such as nitrogen oxides and sulfur oxides in the flue gas interfering with the carbon capture processes are responsible for acid rain and ground-layer ozone formation. The wet flue gas desulfurization and the selective catalytic reduction technologies are associated with high investment, production of secondary pollution, poor catalyst durability, and high temperature requirements. In response to these limitations, the development of a hybrid environmental catalyst, especially using activated carbon, carbon-coated monolith, and metal oxides, is desirable. For a catalyst to be competitive, it must be cost-effective with enhanced sorption capacity, regenerability, and be safe for disposal. Some of the recent methods for dispersing the metal oxides on the supports and the simultaneous removal of sulfur oxides and nitrogen oxides were enumerated in this review and the possible ways for improvement have been presented.

  • Remote C-H bond activation/transformations: A continuous growing synthetic tool; Part II
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-06-01
    Ritika Sharma, Upendra Sharma

    The selective functionalization of inert C-H bonds is always challenging due to their abundance and large bond dissociation energies. Despite recent advancements, the engagement of inert building blocks for distant functionalization is the most appealing approach for the past decade for the construction of complex molecules. Along with the upsurge of proximal C-H bond activation methods, the presence of directing group or participation of ligand surmounts the challenge of regioselective remote C-H bond transformation. Remote C-H functionalization has emerged as an important tool for the direct synthesis of a variety of natural as well as pharmaceutical products. In this area, chemists are continuously designing and exploring new catalysts, ligands and directing group for the functionalization of C-H bonds which are beyond proximity. Earlier success in this area was limited to meta-position, but recently scientists have come out with new templates which can reach even para-position. The developed catalytic transformations provide access for production of a wide range of value-added products without using classical methods such as Friedel-Craft reactions, Heck coupling, etc., providing atom economical alternate and avoiding the toxic waste generation. On this topic, we have recently published a review article entitled “Distant C-H Activation/Functionalization: A New Horizon of Selectivity beyond Proximity” in the same journal, i.e., Catalysis Reviews: Science and Engineering, 2015, 57(3), 345. In continuation of this article, the present review article will cover the catalytic processes on the mentioned topic mainly developed from 2014 to 2017. The main focus will be on mechanistic pathways and the critical role of template as well as ligands. The purpose of this review is to highlight the recent advancements in remote C-H catalysis and a path ahead.

  • Heterogeneous catalysts for hydrogenation of CO2 and bicarbonates to formic acid and formates
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-06-01
    Dmitri A. Bulushev, Julian R.H. Ross

    Formic acid and formates are often produced by hydrogenation of CO2 with hydrogen over homogeneous catalysts. The present review reports recent achievements in utilization of heterogeneous catalysts. It shows that highly dispersed supported metal catalysts are able to carry out this reaction by providing activation of hydrogen on the metal sites and activation of CO2 or bicarbonate on the support sites. Important advances have recently been achieved through utilization of catalysts using CxNy materials as supports. The high activity of these catalysts could be assigned to their ability to stabilize the active metal in a state of single-metal atoms or heterogenized metal complexes, which may demonstrate a higher activity than metal atoms on the surface of metal nanoparticles.

  • An overview of solid base heterogeneous catalysts for biodiesel production
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-07-11
    Akshey Marwaha, Amit Dhir, Sunil Kumar Mahla, Saroj Kumar Mohapatra

    The alcoholysis process requires high activity catalysts for biodiesel production. Heterogeneous catalysts have been proven to possess highly active nature and are environment-friendly. The present article emphasizes on various types of solid base catalysts that have been used in the recent past for the production of biodiesel by transesterification of oils. The parameters and conditions affecting the transesterification reaction and biodiesel yield have also been mentioned in the article. Heterogeneous catalysts have the capability to be recycled for many runs in the process without greatly abating the biodiesel yield. Also, such catalysts possess noncorrosive nature, thus making the biodiesel safe to be used in engine without any damage. The exploitation of waste materials as catalysts would reduce the overall production cost of biodiesel. Calcium-based catalysts in the reviewed literature have shown promising outcomes for the future use and would make the process economical for large-scale industrial applications.

  • Characterization of acid-base catalysts through model reactions
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-03-16
    Michel Guisnet, Ludovic Pinard

    Physicochemical methods are frequently used for characterizing the acid-base catalysts which are involved in many industrial processes, with the problem of large differences between their operating conditions and those of catalytic reactions. This drawback does not exist with model reactions, their use demanding essentially a thorough knowledge of their mechanism: intermediates, characteristics of the active sites: nature (acid, base, acid base), strength, density, environment and their effect on the reaction rate. The contribution of model reactions of hydrocarbons (alkanes, alkenes, methylbenzenes) and functional compounds (alcohols, 2-methylbut-3-yn-2-ol, acetone) in the characterization of various acid-base catalysts: oxides (SiO2-Al2O3, Al2O3, MgO, etc.) and zeolites, is critically evaluated.

  • Simultaneous abatement of diesel soot and NOX emissions by effective catalysts at low temperature: An overview
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-04-12
    Ganesh Chandra Dhal, Subhashish Dey, Devendra Mohan, Ram Prasad

    The diesel engine generally achieves the highest fuel, energy, and thermal efficiency due to its very high compression/expansion ratio (14:1 to 25:1). Diesel engines can have a thermal efficiency that exceeds 50%. The main problem is that they emit more pollution like fine black soot particulates (C8H to C10H) and nitrogen oxides (NOX). These pollutants have been causing serious problems for human health and the global environment and also impacts on the engine. There are many types of catalysts investigated for simultaneous control of these two pollutants, i.e., platinum group metals (PGM; Pt, Pd, Rh, and Ir) based, spinel-type oxides, hydrotalcite, rare earth metal oxides, mixed transient metal oxides, etc. The high raw material cost of PGM catalysts has become a significant issue, so developing non-PGM catalysts are one of the promising challenges. There are no extra reductants required because soot catalytically oxidizes itself in the presence of NOX at a faster rate than molecular oxygen and simultaneously NOX is reduced to nitrogen. The order of oxidation potential of NOX to oxidized soot in comparison to molecular oxygen is as follows: NO2 > NO > O2. To meet the very strict EPA US 2010 and Euro VI regulations of particulate matter (PM) and NOX for heavy-duty and light-duty vehicular stringent emission, it is very important to apply the integrated catalytic systems to significantly remove PM and NOX simultaneously. Many papers related to simultaneous control of soot and NOX over different catalysts have been published but till now some of effective catalysts showing high conversion at low temperatures (possibly within the range typical of diesel exhaust: 150–450°C) have not been reviewed. Thus, this article provides a summary of published information regarding the effective catalysts, their preparation methods, properties, and application for simultaneous control of diesel soot and NOX.

  • Ceria–zirconia mixed oxides: Synthetic methods and applications
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-01-10
    Damma Devaiah, Lankela H. Reddy, Sang-Eon Park, Benjaram M. Reddy

    The primary objective of this review was to illustrate the significance of ceria–zirconia (CZ) mixed oxides as catalysts and catalyst supports as employed for a wide variety of catalytic applications both in the liquid and gaseous phases. In particular, we were interested in bringing together the recent literature pertaining to these mixed oxides with catalysis perspective. The most prominent application of CZ mixed oxides is in three-way catalysis (TWC) as oxygen storage and release material for several years by replacing cerium dioxide as it shows better efficiency and a high thermal stability. Doping with zirconium oxide, as it is alone a non-reducible oxide, makes the CZ mixed oxide a highly reactive, thermally stable, and more reducible with elevated oxygen storage capacity (OSC) that are important for TWC applications. Apart from the TWC use, the CZ mixed oxides have a huge number of applications, as a direct component or a support, ranging from water–gas shift reaction, reforming of hydrocarbons, dehydration of alcohols, CO2 utilization, catalytic combustion of pollutants, fine chemicals production, photocatalysis, and so on. All these applications are mainly dependent on three parameters of the mixed oxides, namely, OSC or redox nature, acid–base properties, and crystalline phases. Besides, most of the applications are influenced by the physical properties such as specific surface area, pore volume, pore diameter, crystallite size, and so on. In this review, many details pertaining to the synthesis of these mixed oxides by various conventional and non-conventional methods, their characterization by several techniques, and their application for various reactions of energy and environmental significance, as reported in the literature, are assessed.

  • Converting olefins to propene: Ethene to propene and olefin cracking
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2018-02-14
    Vincent Blay, Eva Epelde, Rubén Miravalles, Leo Alvarado Perea

    Demand for propene as a petrochemical building block keeps growing, while its availability has been decreased by the adoption of shale gas resources, among others. Efforts to optimize its production by conventional means (including modified fluid catalytic cracking) and new on-purpose production technologies (including ethene to propene (ETP) and olefin cracking) are being pursued. This work reviews the progress made on olefin conversion processes, including the ETP reaction, which is still under development, and the cracking of butenes and higher olefins (C5–C8). The factors analyzed include the catalytic performance of different zeolite materials and their modifications to increase catalyst stability, yield, and selectivity to propene, as well as the effect of operating conditions, reaction thermodynamics, and mechanisms involved. The work is complemented by a survey of commercial technologies and developments on olefin conversion processes.

  • Progress in the design of zeolite catalysts for biomass conversion into biofuels and bio-based chemicals
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2017-10-31
    David P. Serrano, Juan A. Melero, Gabriel Morales, Jose Iglesias, Patricia Pizarro

    This article reviews the recent advances in the development of zeolite catalysts for biomass valorization processes to produce both biofuels and/or bio-based chemicals, which is an emerging and fast expanding field. The work deals with different types of feedstocks, including vegetable oils, lignocellulose and sugars, as well as with a number of relevant intermediates and platform molecules. Transformation of biomass into valuable products is hindered by a number of factors, mainly related to its complex composition, as biomass typically consists of bulky molecules with high oxygen content. Accordingly, biomass processing usually requires the combination of multiple steps and severe conditions, hence concepts like atom efficiency, product selectivity, and catalyst deactivation become of special relevance. A great progress has been achieved in the past years engineering the properties of zeolites for being adapted to the challenges associated to biomass valorization. The possibility of tailoring the main physicochemical properties of zeolites has become now a reality, being the major reason that explains the success achieved by this class of materials in a growing variety of biomass conversion pathways, as those described in this work: catalytic cracking and pyrolysis, hydrotreatments, with special relevance for hydrodeoxygenation processes, as well as in a high number of condensation, isomerization, and dehydration reactions. Thus, the development of hierarchical zeolites, exhibiting enhanced accessibility, and the possibility of introducing and combining in a controlled way different types of active sites (Brønsted and Lewis acid centers, basic sites, and metal phases) are the main basis of the excellent performance of zeolites in numerous biomass conversion routes.

  • Catalytic performance of advanced titanosilicate selective oxidation catalysts – a review
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2017-11-03
    Jan Přech

    This review article aims to cover the state-of-the-art of titanosilicate catalysts for selective oxidations developed within past seven years. Many elaborated materials (e.g., layered and pillared titanosilicates, hierarchical composite materials, and others) have been prepared and thoroughly characterized; however, their catalytic properties have been usually investigated only using a single or few model substrates and compared with a benchmarking material. The main goal of this article is to summarize the novel catalysts and compare their catalytic performance with each other. The comparison is focused on epoxidation. In addition, phenol hydroxylation and sulphide oxidation are briefly covered.

  • Recent trends in the synthesis of high-silica zeolites
    Catal. Rev. Sci. Eng. (IF 9.000) Pub Date : 2017-10-26
    Allen Burton

    Novel zeolites continue to be synthesized using organic structure directing agents in combination with unconventional choices of inorganic conditions. The latter include synthesis in concentrated fluoride media, synthesis in concentrated hydroxide media, synthesis in the presence of germanium, and synthesis with high concentrations of boron. Post-synthetic treatments of germanosilicates with the ADOR method have resulted in fully intact zeolites that cannot be obtained through direct synthesis. Unusual compositions of known frameworks have been obtained through topotactic condensation of layered precursors. Coupled with the appropriate choice of inorganic conditions, the use of new SDA molecules has also produced materials with known frameworks but with amazingly small crystal dimensions that are less than 10 nm. The preparations of once “exotic” materials are now being performed with commercially available or easily prepared organic structure directing agents. In some instances methods have been found to prepare high-silica zeolites from seeded preparations in the absence of an organocation. Methods to target zeolite catalysts for a particular reaction have been realized by identifying structure directing agent molecules that are a mimic of the transition state of the reaction.

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上海纽约大学William Glover