N-Butylamine Decomposition over Hierarchical Porous Copper-Manganese Composite Oxides: Overcoming the Limitation Between Activity and N₂ Selectivity

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 NH3 and NOx 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 Cu0.25Mn0.75 at 280 degrees C with greatly enhanced N-2 selectivity (95%) and low yield of nitrogen-containing byproducts (NH3, NO, NO2, and N2O). The superior n-butylamine conversion and mineralization rate of Cu0.25Mn0.75 is owing to its high content of Mn4+ species and the formation of preferred crystal face for n-butylamine absorption. The proper Cu-Mn ratio of catalyst can inhibit the production of NH3 in low temperature, and its high pore volume promote the diffusion of NHx species which further suppress NHx oxidation to NOx. 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 Cu0.25Mn0.75 due to its high content of Mn4+ species. This study enriches our understanding of designing efficacious catalysts combining high activity and N-2 selectivity for industrial NVOC purification.