Mechanism of Formic Acid Disproportionation Catalyzed by an Iridium Complex Immobilized on Bipyridine-Periodic Mesoporous Organosilica: A Case Study based on Kinetics Analysis

This work investigated the kinetics of formic acid (FA) disproportionation using an Ir complex immobilized on bipyridine-periodic mesoporous organosilica (BPy-PMO). The selectivity for methanol (MeOH) is increased using this catalyst compared to conventional homogeneous Ir complexes. This enhanced selectivity is attributed to the retention of H-2 and CO2 generated by the competing FA dehydrogenation in PMO mesochannels having a high aspect ratio. However, no direct evidence for this process was previously obtained. The present work clarified the unique catalysis mechanism associated with a PMO catalyst exhibiting higher MeOH selectivity based on a hypothesis that the generation of MeOH via FA hydrogenation is promoted by the confinement of H-2 in the PMO pores. The results obtained from the present kinetics study and data regarding H-2 diffusion in the PMO pores strongly support this hypothesis.