110th Anniversary: Near-Total Epoxidation Selectivity and Hydrogen Peroxide Utilization with Nb-EISA Catalysts for Propylene Epoxidation

Abstract

The Nb-EISA catalyst with relatively low Nb loadings (∼2 wt %) shows exceptional propylene epoxidation performance with H2O2 as oxidant at 30–40 °C, 5–9 bar propylene pressure with nearly total propylene oxide (PO) selectivity (>99%), H2O2 utilization (>99%) toward PO formation, high productivity (∼3200 mg/h/g), and mild Nb leaching (3–6%). The predominantly Lewis acidic nature of the Nb-EISA catalysts favors epoxidation while their relatively low Brønsted acidity inhibits H2O2 decomposition and Nb leaching. At higher Nb loadings (8–17 wt %), the catalytic performance deteriorates. However, significant performance improvements were achieved when the Nb-EISA materials are calcined in N2 (instead of air) during synthesis, depositing a carbon layer in the pores. The resulting pore hydrophobicity not only inhibits epoxide ring opening but also increases propylene concentration inside the pores resulting in higher EO productivity and lower H2O2 decomposition. The carbonized Nb-EISA materials also show improved stability to leaching.