Insight into the mechanism of catalytic combustion of acrylonitrile over Cu-doped perovskites by an experimental and theoretical study

• This work focused on the purification of one kind of very toxic nitrogen-containing volatile organic compounds (NVOCs), namely acrylonitrile.
• Selective catalytic combustion for achieving high C2H3CN conversion and ideal N2 selectivity was conducted over the perovskite-typed oxides.
• The reaction mechanism was proposed based on both the experimental (in-situ DRIFT investigation) and theoretical (DFT calculation) studies.
• Cu incorporation into LaFeO3 perovskite was verified to greatly reduce the energy barrier for the rate-determining step of N2 formation.

A series of LaFeO3, La2Cu2O4, and Cu-doped perovskite-typed LaB0.8Cu0.2O3 (B = Fe, Co, and Mn) catalysts were studied for the selective catalytic combustion of acrylonitrile (C2H3CN). The physicochemical properties of these materials were characterized by XRD, N2 sorption, H2-TPR, and XPS, thereafter correlating to their diverse evolutions of N2 yield. The best performance was achieved over the LaFe0.8Cu0.2O3 sample owing to an easy transformation from Cu2+ to Cu0 at low temperatures. Moreover, the mechanism on selective catalytic combustion of acrylonitrile over LaFeO3 and LaFe0.8Cu0.2O3 was investigated by in-situ DRIFTs and density functional theory (DFT) calculations. It has been noted that malonic acid species were generated on the surface of LaFe0.8Cu0.2O3 sample and the acrylic species steadily existed over LaFeO3, indicating that the strongly oxidative copper ion promotes an oxidation of C-terminal to carboxylic acid species at low temperatures. In addition, the copper substitution into LaFeO3 can greatly reduce energy barrier for the transformation from NHO to NOH, which is thought as the rate-determining step for N2 formation. In summary, the catalytic combustion of acrylonitrile commonly follows an oxidation-dominate mechanism over LaFe0.8Cu0.2O3, whereas fulfills with a hydrolysis-dominate mechanism over LaFeO3. 5% H2O addition into the feed caused a slightly and reversible decrease in N2 yield as well as an improved NO production, while a poisoning by 100 ppm SO2 was found due to serious coverage of active centers by sulfurous species.

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