Observations of Ethylene-for-CO Ligand Exchanges on a Zeolite-Supported Single-Site Rh Catalyst by X-ray Absorption Spectroscopy

Quick-scanning X-ray absorption fine structure (QXAFS)measurementswere used to characterize the exchanges of ethylene and CO ligandsin a zeolite HY-supported single-site Rh complex at a sampling rateof 1.0 Hz. The two ligands were reversibly exchanged on the rhodium,with quantitative results determined for the C2H4-for-CO exchange that are consistent with a first-order process.The apparent rate constant for the exchange decreased with increasingtemperature. Fourier-transform infrared spectra characterizing theC(2)H(4) sorbed in the zeolite showed that the amountdecreased with increasing temperature, consistent with the decreasein the exchange rate with increasing temperature. The results, illustratingthe dynamics of ligand exchanges on a single-site supported metalcatalyst, demonstrate the broad emerging applicability of the QXAFStechnique for characterizing the dynamics of reactive intermediateson catalysts.

Automated summary

Quick-scanning X-ray absorption fine structure (QXAFS) measurements were used to investigate the exchanges of ethylene and CO ligands on a zeolite HY-supported single-site Rh complex. The results showed reversible exchange of the two ligands on the rhodium, with C2H4-for-CO exchange following first-order kinetics and decreasing rate with increasing temperature. Fourier-transform infrared spectra revealed a decrease in the amount of C2H4 sorbed in the zeolite with increasing temperature, consistent with the decrease in exchange rate. These findings illustrate the broad applicability of QXAFS technique in characterizing the dynamics of reactive intermediates on catalysts.