Mixed‐Metal Promotion in a Manganese‐Molybdenum Oxynitride as Catalyst to Integrate C─C and C─N Coupling Reactions for the Direct Synthesis of Acetonitrile from Syngas and Ammonia

Abstract

AbstractTransition metal nitrides and their oxy‐ and carbo‐nitride analogues attract interest as catalysts in various sustainability areas. They offer potential in the development of conversion routes for the synthesis of nitrogenated organic compounds, via the integration of C─C and C─N coupling reactions from sustainable C1 and N1 feedstocks, linking carbon and nitrogen renewable cycles. Herein, a series of structurally uniform (NH4)nHmMxMoyOz·2H2O ammonium metal molybdate materials (C 2/m) serve as catalyst precursors, providing atomic‐level metal mixing. Among various 3d transition metals, Mn proves the most effective promoter. A [MnMo] mixed‐metal catalyst exhibits superior selectivity to acetonitrile (56 % among all organic products) and stability, significantly outperforming monometallic [Mo] and [Mn] counterparts. Multimodal physicochemical characterization, including temperature‐resolved X‐ray diffraction, Xray absorption near‐edge structure and extended X‐ray absorption fine structure, and depth‐profiling X‐ray photoelectron spectroscopy, shows partial nitridation to a cubic (Fm‐3m) mixed‐metal oxynitride as the working catalyst under operation conditions. Consistent with first‐principles thermochemistry, manganese is found to disrupt extended molybdenum nitride domains, preserving manganese‐enriched oxynitride domains under the markedly nitriding reaction conditions. Density functional theory predicts these partially oxidic domains to facilitate C─C coupling reactions compared to fully nitrided surfaces, enhancing conversion of the stable reaction intermediate HCN to acetonitrile.