Enhancing effect of Zr on Rh/SiO2 catalysts in propylene hydroformylation: experimental and DFT computational study

Abstract

In this study, Rh supported on SiO₂ was modified with Zr for the first time to investigate its catalytic performance in propylene hydroformylation. The RhZr/SiO₂ catalyst exhibits a butyraldehyde selectivity of over 90% along with a 2.7-fold enhancement in propylene conversion compared to the unmodified catalyst, outperforming previously reported Co- and K-promoted systems. XPS characterization, combined with differential charge density calculations and Bader charge analysis, revealed that the introduction of Zr reduced the electron density around Rh, which facilitates CO adsorption on Rh and thereby promotes the formation of more active HRh(CO)_x species. This conclusion is further supported by CO adsorption energy calculations. Under optimized reaction conditions (20 mL toluene solvent, 0.4 g RhZr/SiO₂ catalyst with ultralow Rh loading of 0.02 wt%, 1.5 g propene, 100 °C, 4 MPa syngas pressure, 4 h), the catalytic system achieved remarkable performance: 75.1% propene conversion, 96.7% butyraldehyde selectivity, and a normal/iso (n/i) ratio of 0.9. Notably, the system exhibited an exceptional intrinsic activity (TOF = 8838 h⁻¹), surpassing all reported ligand-free heterogeneous Rh-based catalysts in recent years. The present work provides an effective strategy for designing modified Rh-based heterogeneous catalysts with ultralow metal loading for hydroformylation applications.