Effect of Si/Al Ratio and Rh Precursor Used on the Synthesis of HY Zeolite-Supported Rhodium Carbonyl Hydride Complexes

Abstract

Rh(CO)2 complexes anchored on various dealuminated HY zeolites were used as precursors for the surface-mediated synthesis of Rh(CO)(H)x species. The carbonyl ligands of the initial Rh(CO)2 complexes react with gas-phase C2H4 to form Rh(CO)(C2H4) species and subsequently well-defined Rh(CO)(H)x complexes when the former are exposed to H2 at room temperature. Zeolite-supported Rh(C2H4)2 and Rh(NO)2 can also be used as precursors, but both complexes must be converted into Rh(CO)2 first to allow the formation of Rh(CO)(H)x species. The Rh(CO)(H)x species thus formed are characterized by a set of well-defined νCO and νRhH bands in their Fourier transfrom infrared spectra. Density fuctional theory calculations provide strong evidence for the formation of a family of Rh(CO)(H2), Rh(CO)(H)2, and Rh(CO)(H) complexes, all of which are attached differently to the zeolite framework. The fraction of each individual complex formed varies significantly with the Si/Al ratio of the zeolite and the nature of the precursor ...