N-Butylamine Decomposition over Hierarchical Porous Copper–Manganese Composite Oxides: Overcoming the Limitation Between Activity and N<sub>2</sub> Selectivity
Qiyuan Liu, Mudi Ma, Lianghui Xia, Junwei Xu, Jingjing Wang, Yaruo Zhao, Qianwenhao Fan, Reem Albilali, Chi He
Abstract
Nitrogen-containing volatile organic compounds (NVOCs) can cause great damage to human health and the atmospheric environment. However, the efficient oxidation of n -butylamine at low temperature and effective inhibition of the production of hazardous NH 3 and NO x byproducts remain a great challenge. Herein, hierarchical Cu–Mn composite oxide catalysts with diverse Cu–Mn ratios were rationally prepared, and the intrinsic role of Cu and Mn sites in n -butylamine oxidation was elucidated. As a powerful catalyst, n -butylamine (1000 ppm; GHSV = 60 000 h –1 ) can be completely mineralized over Cu 0.25 Mn 0.75 at 280 °C with greatly enhanced N 2 selectivity (95%) and low yield of nitrogen-containing byproducts (NH 3, NO, NO 2, and N 2 O). The superior n -butylamine conversion and mineralization rate of Cu 0.25 Mn 0.75 is owing to its high content of Mn 4+ species and the formation of preferred crystal face for n -butylamine absorption. The proper Cu–Mn ratio of catalyst can inhibit the production of NH 3 in low temperature, and its high pore volume promote the diffusion of NH x species which further suppress NH x oxidation to NO x . Hence, the proper Cu/Mn ratio is conducive to enhancing N 2 selectivity. In situ DRIFTS results show that amides, alcohols, and acids are the main intermediates during n -butylamine combustion. The C–N breakage is the rate-controlling step, and the mineralization rate of intermediates can be remarkably boosted over Cu 0.25 Mn 0.75 due to its high content of Mn 4+ species. This study enriches our understanding of designing efficacious catalysts combining high activity and N 2 selectivity for industrial NVOC purification.