Abstract
Supported single-metal-site catalysts are well known for their 100% atom utilization efficiency, uniformly isolated active sites and well-defined coordination environment. Methanol carbonylation is a classic homogeneous reaction for acetic acid production. Here, we present the crucial role of H2 on the stability of single-metal-site Ir1/AC catalyst for heterogeneous methanol carbonylation. Metal leaching and carbon deposition are verified to be the main reasons of catalyst deactivation. Metal leaching is probably due to the formation of volatile [Ir(CO)3I] species, and carbon deposition is supposed to arise from the high energy barrier rate-determining step of CH3COI reductive elimination. However, hydrogenation of the surface intermediate species alleviates the carbon forming problem greatly and competitive adsorption of H2 with CO on active species inhibits the formation of [Ir(CO)3I]. Consequently, H2 is essential to avoid the activity decay of the Ir1/AC catalyst.
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