On the development of kinetic models for solvent-free benzyl alcohol oxidation over a gold-palladium catalyst

Federico Galvanin,Meenakshisundaram Sankar,Stefano Cattaneo,Donald Bethell,Vivek Dua,Graham J Hutchings,Asterios Gavriilidis

doi:10.1016/j.cej.2017.11.165

Abstract

Bimetallic Au-Pd nanoparticles supported on TiO2 show excellent catalytic activity and selectivity to benzaldehyde in the solvent-free transformation of benzyl alcohol to benzaldehyde, where toluene is the main observed by-product, together with smaller amounts of benzoic acid, benzyl benzoate and dibenzyl ether. However, despite the industrial relevance of this reaction and importance of tuning the selectivity to the desired benzaldehyde, only a few attempts have been made in the literature on modeling the reaction kinetics for a quantitative description of this reaction system. A kinetic model for the oxidation of benzyl alcohol over Au-Pd is proposed in this paper. The model assumes that hydrogenolysis, disproportionation and dehydrogenation reactions may occur in parallel, and it has been found satisfactory after a model discrimination procedure was applied to a number of simplified candidate models developed from microkinetic studies. Despite its relative simplicity, the proposed model is capable of representing the reactant conversion and distribution of products observed in experiments carried out at different temperature, pressure and catalyst mass in a stirred batch reactor. Major findings include the quantitative evaluation of the impact of hydrogenolysis and disproportionation pathways on benzaldehyde production. At low temperature the disproportionation reaction is the dominant route to toluene formation, while hydrogenolysis dominates at high temperature.

Highlights

Benzyl alcohol oxidation is an important alcohol oxidation reaction in industry due to the demand for benzaldehyde as an intermediate in the production of fine chemicals, fragrances and flavouring additives [1]
The goal of this paper is to develop a structurally simple kinetic model of benzyl alcohol oxidation over a Au-Pd/TiO2 catalyst capable of representing in a quantitative way the experimental observations obtained from a stirred reactor operated in batch mode
Kinetic models were developed from microkinetic studies based on individual reaction steps starting from the assumption that a number of elementary reactions may take place simultaneously on the catalytic surface

Summary

Introduction

Benzyl alcohol oxidation is an important alcohol oxidation reaction in industry due to the demand for benzaldehyde as an intermediate in the production of fine chemicals, fragrances and flavouring additives [1]. Stoichiometric oxidants are often used for this transformation, it is highly desirable to use catalytic systems along with environmentally benign oxidants like O2, H2O2 or air. Many heterogeneous catalysts have been reported to be active for this transformation, including copper-containing catalysts [2], supported Au [3] and Pd [4,5] monometallic catalysts and Au–Pd bimetallic catalysts [6,7]. After the discovery that an alloy of Au and Pd leads to a significant enhancement in activity and selectivity by comparison to the Au or Pd mono-metallic catalysts [10], supported Au–Pd catalysts have been extensively used for the oxidation of various alcohols, including benzyl alcohol [11,12]. AuPd nanoparticles supported on TiO2 have been recently shown to be highly effective in the oxidation of benzyl alcohol [7] exhibiting excellent catalytic activity

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