Controlled Hydrodeoxygenation of Biobased Ketones and Aldehydes over an Alloyed Pd–Zr Catalyst under Mild Conditions

Abstract

The substitution of green hydrogen donors for replacing high-pressure H2 to achieve biomass derived ketone and aldehyde hydrodeoxygenation (HDO) under mild conditions has attracted widespread attention. However, it remains a considerable challenge to get rid of acid additives and control product selectivity. Herein, a series of bimetallic Pd–M/HZSM-5 catalysts (M = Zr, Mn, Zn, or La) were fabricated for controlled hydrodeoxygenation of biobased ketones and aldehydes (acetophenone, benzophenone, 4-hydroxyacetophenone, vanillin, furfural) using polymethylhydrosiloxane (PMHS) as the green H-donor, in which >99% conversion and >99% selectivity to ethylbenzene were achieved for hydrodeoxygenation of acetophenone as the probe within 3 h at 35 °C over the as-prepared 0.5%Pd–2.0%Zr/HZSM-5 catalyst with a Pd/Zr mass ratio of 1:4. According to characterizations of TEM-HAADF, XPS, ESR, and H2-TPR, the Pd–Zr alloy structure was formed on the bimetallic Pd–Zr/HZSM-5 catalyst, promoting the transform of Pd–O–Zr solid solution to PdO–ZrO2 and the generation of oxygen vacancy. Moreover, the abundant of oxygen vacancies on the alloyed Pd–Zr/HZSM-5 catalysts enhance the dissociation of silanes to provide the abundance of hydrogen protons, greatly accelerating the hydrogenation of biobased ketones and aldehydes, and then the acid site of the Pd–Zr/HZSM-5 catalyst promotes the dehydration of the intermediates (alcohols) to hydrocarbons. Furthermore, the as-fabricated Pd–Zr/HZSM-5 alloy catalyst can achieve an excellent recycling capability after six uses and exhibits universality toward various biobased ketones and aldehydes at 35 °C. The present findings provide new insights into the design of selective HDO of biomass in a green process.