New insights into the structure and catalytic performance of alizarin-zirconium hybrids for Meerwein-Ponndorf-Verley reductions: first-principles approach

A novel bifunctional mesoporous zirconium-alizarin (Zr-AZN) hybrid was successfully synthesized by using a template-free self-assembly method. Systematic characterizations demonstrated that the catalyst possessed abundant acid-base couple sites (density: 0.47 vs. 0.79 mmol g(-1), acid/base molar ratio: 0.59) and high porosity. Zr-AZN exhibits superior catalytic activity toward the Meerwein-Ponndorf-Verley (MPV) reduction of different biomass-derived carbonyl compounds compared to other catalysts, especially of ethyl levulinate (EL) to gamma-valerolactone (GVL), in quantitative yields (96%) with a high GVL formation rate of 1205 mu mol g(-1) h(-1) and TOF of 0.47 h(-1). Theoretical calculations show that the structure of Zr-AZN with the highest catalytic activity originates from the complexation that occurs at the 1,2-dihydroxyl (catechol) group, instead of the 1-hydroxy-9-keto group. Furthermore, it also presents a higher activity and selectivity and a lower computed apparent activation free energy (19.4 vs. 29.3 kcal mol(-1)) for the hydrogenation of EL compared to Sn-AZN.

Automated summary

Zr-AZN is a novel bifunctional mesoporous catalyst with abundant acid-base couple sites and high porosity, showing superior catalytic activity towards the reduction of biomass-derived carbonyl compounds. Its structure with the highest catalytic activity originates from the complexation at the 1,2-dihydroxyl group, instead of the 1-hydroxy-9-keto group.