3 years ago

Mn based catalysts for driving high performance of HCN catalytic oxidation to N2 under micro-oxygen and low temperature conditions

Mn based catalysts for driving high performance of HCN catalytic oxidation to N2 under micro-oxygen and low temperature conditions
In this work, a series of MnOx/TiO2-Al2O3 oxides synthesized via sol–gel method were evaluated for catalytic oxidation of HCN under micro-oxygen and low temperature conditions. The reaction temperature, oxygen concentration, Mn content, relative humidity and calcination temperature of catalysts were the five crucial factors that were determined during the study. 15wt% of MnOx/TiO2-Al2O3 performed excellently on HCN catalytic oxidation, and nearly 100% HCN conversion and 70% N2 yield were obtained at 200°C. The comparison of H2-TPR, BET, FTIR and XPS results from fresh and used catalysts revealed that both oxygen types, namely chemisorbed and lattice oxygen, as well as adsorbed water molecules and several chemical states of Mn, including Mn4+, Mn3+ and Mn2+, were the main active species on the catalyst’s surface. It was found that the occurrence of hydrolysis of HCN was accompanied by the HCN catalytic oxidation process. In HCN catalytic oxidation process, the catalytic hydrolysis of HCN that occurred could be ascribed to two sources of adsorbed water molecules: (i) the catalyst itself, which contained adsorbed water molecules; (ii) the re-adsorption of water molecules that produced by HCN oxidation reaction. The water vapor introduced had obvious inhibition to HCN conversion and N2 yield may be due to the competitive adsorption between water molecules and HCN. Based on XPS, FTIR results and early studies, HCN pre-reacted with water molecules from the catalyst’s surface to produce NH3 and CO. Both of these products were readily further oxidized to produce N2, H2O and CO2 under low temperatures, but they were oxidized to NO instead at high temperatures. Meanwhile, only a small amount of N2O as an undesirable by-product produced in this reaction process.

Publisher URL: www.sciencedirect.com/science

DOI: S1385894717316273

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