Designing a Rh-based bimetallic catalyst for heterogeneous ethylene hydroformylation: combining theoretical predictions and experimental screening

Abstract

An approach to the design of a Rh-based bimetallic catalyst for ethylene hydroformylation was introduced. Among late 3d transition metals (Fe, Co, Ni, Cu and Zn), the thermodynamic feasibility of alloying with Rh was evaluated using phase diagrams, with Cu excluded from consideration. The reducibility of the oxide precursor to form an alloy with Rh was examined by H₂ temperature-programmed reduction (H₂-TPR), further excluding Fe and Zn from the potential alloying elements. Density functional theory (DFT) calculations were employed to select descriptors for catalytic performance, suggesting that a lower CO adsorption energy would enhance hydroformylation activity, and a larger difference between CO and H adsorption energies would promote selectivity to aldehydes and alcohols (oxy selectivity), suggesting that Co would be a better alloying element than Ni. As predicted, a RhCo bimetallic catalyst was successfully synthesized, which showed the highest oxy yield in ethylene hydroformylation among all the bimetallic catalysts, with a superior selectivity compared to that of a monometallic Rh catalyst.