Isolated Ni sites anchored on zeolites for direct synthesis of acetic acid from methane oxidative carbonylation

Abstract

Direct conversion of methane to acetic acid with high activity and selectivity over non-noble metal-based catalysts under mild reaction conditions remains a grand challenge. Specifically, 1.2Ni-ZSM-5 with 88.9 % isolated Ni sites achieved a high acetic acid yield of 2920 μmol/gcat. and a remarkable selectivity up to 82.3 % from methane oxidative carbonylation. Combined with high angle annular dark field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy analyses, it was revealed that the isolated Ni species with Ni-O6 moieties anchored in the micropores of ZSM-5 were suggested to be the active sites. The isotopic labeling experiments and monitoring of reaction intermediates demonstrated that CH3COOH was formed via the direct coupling of methyl radicals and carbon monoxide molecules. This work suggests that the well-designed Ni sites can promote the transformation of CH4 to C2+ oxygenates instead of traditional C1 oxygenates as main products.