Jie Meng,Fan Fang,Nengjie Feng,Hui Wan,Guofeng Guan
To improve the catalytic activity when utilizing metal oxides for the combustion of VOCs, Mn/Al-SBA-15 catalysts have been successfully synthesized through an emerging wetness impregnation technique involving Mn(NO3)2 on Al-SBA-15, which has been directly prepared from attapulgite by a hydrothermal method. Compared to Mn/SBA-15, which is prepared with TEOS as its silicon source, all the as-prepared Mn/Al-SBA-15 catalysts demonstrated enhanced catalytic performance in the oxidation of toluene. From this research, the 8% Mn/Al-SBA-15 catalyst presented the best catalytic performance, due to the high efficiency resulting from the high chemical valence of Mn4+. When the concentration of toluene was 2000 ppm, and the space velocity was 60 000 mL (g h)−1, 8% Mn/Al-SBA-15 could effectively reduce the T50 and T90 values of toluene to 201 and 278 °C, respectively; while the 8% Mn/SBA-15 catalyst could reduce the T50 and T90 values of toluene to 223 and 298 °C, respectively. A systematic investigation has been conducted to reveal the synergistic effects of Al doping and manganese loading on the enhanced catalytic performance. The experiments showed impressive results, demonstrating that Al doping can not only increase the surface acidity of SBA-15, but it can also be beneficial for achieving a uniform dispersion of MnOx on the surface and in the pores of Al-SBA-15, resulting in the enhancement of the catalytic performance.
Abstract In this work, NiCo 2 O 4 with a hierarchical porous flower-like structure was fabricated and used as catalyst support for Pd nanoparticles. The NiCo 2 O 4 was composed of porous nanoplates without overlapping, and the Pd nanoparticles were uniformly distributed on these nanoplates. Pd–NiCo 2 O 4 with the Pd loading of 2.0 wt% showed extremely high activity and stability, methane (1.0% CH 4 /Air) can be totally oxidized at 330 °C and the T 90 is 309 °C, which is much lower than that of pure NiCo 2 O 4 (T 90 = 405 °C). At wet condition with the presence of 10 vol% water vapor, the catalytic activity was still acceptable with the T 90 of 366 °C, and no activity decrease or permanent damage for the catalyst was observed after 35 h reaction, showing high stability. A series of techniques including TEM, SEM, XRD, H 2 -TPR, BET and especially quasi in situ XPS combined with in situ MS were used to characterize the catalysts and investigate the catalysis mechanism. Two pathways of CHO evolution were proved by the quasi in situ XPS and in situ MS results: OCHO intermediate dehydrogenation pathway at lower temperature and CO oxidation pathway of CHO at higher temperature. Graphical Abstract
Xiaoyu Zhang,Xin Xu,Xinyu Wang,Huibin Liu,Mingli Fu
The improvement of catalytic efficiency is of great significance to the removal of volatile organic compounds (VOCs), a class of key air pollutants leading to ground-level ozone pollution. Herein, a series of micro-spherical Ca-Mn mixed oxides (Ca x Mn y O z ), namely CaMn 3 O 6 , Ca 2 Mn 3 O 8 and CaMnO 3 , were prepared by a two-step precipitation method, and defects were constructed on which by selective dissolution to enhance the low-temperature catalytic performance in the oxidation of propane (C 3 H 8 ) as a representative short-chain alkane VOCs. The synthesized Ca x Mn y O z oxides demonstrated drastically different response to the dissolution modification initiated by acid treatment. Specifically, after acid dissolution, while CaMn 3 O 6 and Ca 2 Mn 3 O 8 maintained largely their original structures, the perovskite-type CaMnO 3 underwent lattice rearrangement and was transformed into γ-MnO 2 -like product with only a tiny amount of Ca. In C 3 H 8 oxidation, the catalytic performance of CaMnO 3 was significantly improved after selective dissolution, as indicated by a significant decrease of T 90 , i.e. the temperature to achieve 90% C 3 H 8 conversion, from 455 °C to 240 °C. Mechanistic investigation by in-depth X-ray photoelectron spectroscopy studies revealed that selective dissolution led to higher Mn 4+ concentrations and more oxygen vacancies on the oxide surfaces, thus facilitated electron transfer and O 2 activation in C 3 H 8 oxidation reactions. This study paves a new path for the design of cost-effective oxide catalysts toward the abatement of short-chain alkane VOCs.
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