Benzyl alcohol oxidation with Pd-Zn/TiO2: computational and experimental studies

Ewa Nowicka,Sultan Althahban,Tom D Leah,Greg Shaw,David Morgan,Christopher J Kiely,Alberto Roldan,Graham J Hutchings

doi:10.1080/14686996.2019.1598237

Abstract

ABSTRACT Pd–Zn/TiO2 catalysts containing 1 wt% total metal loading, but with different Pd to Zn ratios, were prepared using a modified impregnation method and tested in the solvent-free aerobic oxidation of benzyl alcohol. The catalyst with the higher Pd content exhibited an enhanced activity for benzyl alcohol oxidation. However, the selectivity to benzaldehyde was significantly improved with increasing presence of Zn. The effect of reduction temperature on catalyst activity was investigated for the catalyst having a Pd to Zn metal molar ratio of 9:1. It was found that lower reduction temperature leads to the formation of PdZn nanoparticles with a wide particle size distribution. In contrast, smaller PdZn particles were formed upon catalyst reduction at higher temperatures. Computational studies were performed to compare the adsorption energies of benzyl alcohol and the reaction products (benzaldehyde and toluene) on PdZn surfaces to understand the oxidation mechanism and further explain the correlation between the catalyst composition and its activity.

Highlights

Oxidation is a key reaction in organic synthesis and industrial processes
Amongst the many catalytic systems tested to date, supported metal nanoparticle catalysts combined with molecular oxygen offers great potential in terms of general environmental friendliness
Periodic plane-wave DFT calculations were performed using the Vienna Ab initio Simulation Package (VASP) [15,16], the Perdew–Burke–Ernzerhof functional revised for solids [17] and a kinetic energy of 450 eV to expand the plane-waves of the Kohn-Sham valence states

Summary

Introduction

Oxidation is a key reaction in organic synthesis and industrial processes. The products of the oxidation of alcohols, such as aldehydes, are valuable both as intermediates and final components to the pharmaceutical and perfume industries [1]. Numerous methods have been developed for promoting a wide variety of oxidation transformations including the use of stoichiometric and powerful oxidants [2]. Many of these reactions are unselective, meaning that a number of undesirable side products are formed, which increase the cost of the process because of the subsequent need for purification steps. Molecular oxygen in combination with a suitable heterogeneous catalyst offers a possible route to perform such reactions in a more efficient and environment-friendly way [3]. Amongst the many catalytic systems tested to date, supported metal nanoparticle catalysts combined with molecular oxygen offers great potential in terms of general environmental friendliness

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Conclusion