Elsevier

Journal of Rare Earths

Volume 39, Issue 9, September 2021, Pages 1073-1081
Journal of Rare Earths

Effect of calcination process on performance of 3DOM CeMnO3 catalysts

https://doi.org/10.1016/j.jre.2020.09.002Get rights and content

Abstract

A series of 3DOM CeMnO3 perovskite catalysts were prepared by poly(methyl methacrylate) hard-templating-excessive impregnation method at calcination temperature of x °C (x = 600, 700, 800) and the heating rate of y °C/min (y = 1, 2, 5, 10). The samples were characterized by Brunauer-Emmett‐Teller method, scanning electron microscopy, transmission electron microscopy, H2‐temperature programmed reduction, X‐ray photoelectron spectroscopy, X‐ray diffraction, moreover, the effect of the calcination process on the catalytic activity of the samples were discussed by the catalytic combustion of toluene. The results show that the 3DOM CeMnO3 catalysts calcined at 600 °C promote the formation of a perovskite structure, inhibit the reduction of the Mn4+ species in the catalyst with high temperature. The catalyst expresses the complete macroporous structure, large specific surface area (38.8 m2/g), higher adsorption oxygen concentration and Mn4+ substance concentration, with a low T90%=172 °C. By preparing the catalysts at different calcination heating rates, it can be concluded that the catalyst possesses a high concentration of adsorbed oxygen and a low reduction temperature and a large specific surface area (40.42 m2/g) greatly promotes adsorption stage catalytic oxidation reaction and catalytic combustion of toluene at low temperature under the heating rate of 5 °C/min. When the heating rate is 1 °C/min, the catalyst has a complete macroporous structure (>250 nm), which is beneficial to the exchange of macromolecular substances during the catalytic reaction and the catalyst has a high concentration of lattice oxygen suitable for the catalysis of toluene in high temperature flue gas combustion.

Graphical abstract

3DOM CeMnO3 catalyst calcined at 600 °C exhibits a complete macropore structure with a larger specific surface area, a higher concentration of adsorbed oxygen and Mn4+ substance, and shows the best catalytic combustion performance of toluene. The 3DOM CeMnO3 catalyst prepared at a heating rate of 1 °C/min is conducive to the treatment of high-temperature flue gas, while the catalyst prepared at a heating rate of 5 °C/min is more suitable for the treatment of low-temperature flue gas.

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Introduction

Volatile organic compounds (VOCs) mainly from petroleum refining, organic chemical raw material production, printing, pharmaceutical industry, electronic equipment manufacturing industry, etc.1 As the precursor of photochemical smog and ozone,2 VOCs with toxicity and carcinogenicity3 can exert adverse effects on human body, such as stimulating the central nervous system, and also causing great harm to the environment, animals and plants. Catalytic combustion is considered to be available method for VOCs treatment. The catalytic combustion of VOCs treatment does not have secondary pollution and the complete combustion products are CO2 and H2O. Moreover, catalytic combustion expressed the advantages of wide application, low combustion temperature, etc.4, 5, 6, 7

The general structure formula of perovskite oxide is ABO3, and the A site element is generally alkali metal, alkaline earth metal or rare earth metal ion with larger radius, moreover the B is generally transition metal ion with smaller radius. As a potential substitute of noble metal, it has low cost and outstanding catalytic activity, good thermal stability and poison tolerance.

In 1997, three-dimensional ordered macroporous (3DOM) materials were synthesized for the first time by Velev et al.8 Since then, 3DOM materials have been widely studied and gradually applied in various fields, including catalysts and supports,9 photo catalysis,10 photonic crystal,11 electrode materials,12 etc. The pore size of 3DOM structure is single (>50 nm) and adjustable. In addition, the arrangement of pores is uniform and regular. Each pore is connected with the surrounding pores by pore windows, which is closely arranged with high porosity. In the process of catalytic combustion to treat VOCs, 3DOM structure is conducive to the diffusion of substances and can improve the contact efficiency of pollutants and catalysts. Related research13 showed that the catalytic activity of 3DOM catalyst was better than those of the disordered macroporous catalyst and conventional nanoparticle catalyst.

The formation of 3DOM structure is affected by many factors, among which the influences of calcination temperature and heating rate cannot be ignored. Zang et al.14 prepared 3DOM La0.8Ce0.2MnO3/cordierite catalyst at 600–800 °C, it was found that the perovskite samples prepared at 600 °C expressed the best low-temperature reducibility, the highest oxygen concentration and the best catalytic oxidation performance of toluene. Li et al.15 calcined different samples of Be/Ce/γ-Al2O3 composite catalyst at 3, 6, 9 and 12 °C/min heating rates, respectively, and concluded that the samples obtained at 6 °C/min heating rate have the smallest particle size of BaCO3 and CeO2, the most uniform distribution on γ-Al2O3 particles, and the reducibility is the best at low temperatures.

According to previous research,16 3DOM CeMnO3 has more regular macroporous structure and high specific surface area compared with 3DOM LaMnO3 and 3DOM NiMnO3, and shows the best catalytic combustion performance. In this work, the effects of calcination temperature and heating rate on the performance and pore structure of 3DOM CeMnO3 catalysts were discussed. All the prepared samples were characterized by BET, XPS, XRD, H2-TPR and the catalytic activity was investigated through the toluene combustion process to obtain the 3DOM CeMnO3 catalyst with the best performance.

Section snippets

Chemical and materials

Methyl methacrylate (MMA) was purchased from Macklin. Potassium persulfate, manganous nitrate, cerium (III) nitrate hexahydrate, polyethylene glycol-400, methanol and P-hydroxybenzoic acid were obtained from Sinopharm Chemical Reagent Co., Ltd.

Catalysts preparation

Synthesis of the PMMA colloidal crystal microspheres was conducted by emulsifier-free emulsion polymerization approach.17, 18, 19 According to literature,16 the PMMA hard-templating with glossy surface and orderly accumulation was obtained by constant

Effect of calcination temperature on catalysts

Four kinds of catalysts (3DOM CeMnO3/500, 3DOM CeMnO3/600, 3DOM CeMnO3/700, 3DOM CeMnO3/800) were prepared in this section. The effect of the calcination temperature on the 3DOM structure and the catalytic performance of the catalysts are mainly discussed. Fig. 1 indicates the SEM images of the four samples at different calcination temperatures. It can be observed that as the calcination temperature increases, the catalyst gradually sinters, and the macroporous structure gradually disappears.

Conclusions

A series of 3DOM CeMnO3 perovskite catalysts with different calcination temperatures and heating rates were prepared by PMMA hard-templating-excessive impregnation method. The change of calcination temperature can affect the morphology, specific surface area, pore size and other physical properties of the catalyst and the catalytic combustion performance. The catalyst has the optimal macroporous structure and the largest specific surface area when the calcination temperature is 600 °C. The

References (24)

Cited by (15)

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    At the same time, the CeO2 diffraction peak intensity of 3DOM La0.7Ce0.3CoO3/MIM was the lowest, which was about 2/3 of 3DOM La0.7Ce0.3CoO3/DCM and 1/2 of 3DOM La0.7Ce0.3CoO3/CDM, indicating that the CeO2 crystal structure of 3DOM La0.7Ce0.3CoO3/MIM was not as complete as 3DOM La0.7Ce0.3CoO3/DCM and 3DOM La0.7Ce0.3CoO3/CDM. Liu et al. [24] reported that the diffraction peak intensity of CeO2 in monolithic catalyst was weak, indicating that there were many lattice defects. More lattice defects in 3DOM La0.7Ce0.3CoO3/MIM made the catalyst produce more oxygen vacancies, which improved the oxygen migration ability.

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    prepared the binary oxide of 3Mn1Ce synthesized by hydrolysis driving redox method, due to the introduction of Ce, besides the excellent catalytic effect (T90 = 210 °C), the catalyst had good structural stability for catalysis and reversible reduction of VOCs. In addition, Liu et al [33]. found that the calcination of 3DOM MnCeO3 at 600 °C had better-adsorbed oxygen concentration, lower reduction temperature and more large specific surface area.

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Foundation item: Project supported by Natural Science Foundation of Shandong Province (ZR2019MEE112).

Co-first authors; they have contributed equally to this work.

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