Mechanistic understanding of methanol carbonylation: Interfacing homogeneous and heterogeneous catalysis via carbon supported Ir[sbnd]La

Abstract

The creation of heterogeneous analogs to homogeneous catalysts is of great importance to many industrial processes. Acetic acid synthesis via the carbonylation of methanol is one such process and it relies on a difficult-to-separate homogeneous Ir-based catalyst. Using a combination of density functional theory (DFT) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, we determine the structure and mechanism for methanol carbonylation over a promising single-site IrLa/C heterogeneous catalyst replacement. Here, the Ir center is the active site with the acetyl-Ir complex being a rate controlling intermediate. Furthermore, the La both atomically disperses the Ir and acts as a Lewis acid site. In fact, the La promoter in the IrLa/C catalyst was found to behave similarly to homogeneous promoters by abstracting an iodine from the Ir center and accelerating the CO insertion step. Overall, this work provides key insight into the atomistic nature of the IrLa/C single-site catalyst and allows for the further design and optimization of single-site heterogeneous catalysts.