DFT studies for ligand modification and proton spillover zeolite supported Rh(CO)2 complex

Abstract

In zeolites, the acidic protons are known to migrate across the catalytic framework, and this proton mobility can influence the reactivity of the metal centers anchored within the structure as well. In this study, we employed density functional theory (DFT) calculations to investigate the effects of proton reverse spillover on the ligandexchange mechanisms of atomically dispersed Rh(CO)2 complexes supported on HY zeolite. Particular emphasis was placed on the role of the reverse proton spillover in facilitating the exchange of CO ligands with gas-phase acetylene. The free energy activation barrier (Delta G/=) for proton reverse spillover from the zeolite surface to the Rh center in Rh(CO)2/zeolite is relatively high (19.4 kcal/mol). As acetylene coordinates to the metal, however, the barrier decreases significantly (9.3 kcal/mol), indicating that coordination of C2H2 to Rh promotes proton transfer. Once CO dissociation occurs to give Rh(CO)(C2H2)/zeolite, reverse proton spillover from the surface becomes less favorable, with a barrier of 26.7 kcal/mol. Finally, for the fully substituted Rh(C2H2)2 species, reverse proton migration from the surface to the metal is essentially prohibited due to the very high barrier (44.4 kcal/mol). These results highlight the strong coupling between ligand exchange and proton mobility in zeolitesupported Rh complexes, underscoring how the local coordination environment dynamically tunes the feasibility of proton transfer.