The Influence of the Gold Particle Size on the Catalytic Oxidation of 5-(Hydroxymethyl)furfural

Oliver Schade,Alexei Nefedov,Jan-Dierk Grunwaldt,Paolo Dolcet,Xiaohui Huang,Christof Wöll,Erisa Saraçi

doi:10.3390/catal10030342

Abstract

For the production of chemicals from biomass, new selective processes are required. The selective oxidation of 5-(Hydroxymethyl)furfural (HMF), a promising platform molecule in fine chemistry, to 2,5-furandicarboxylic acid (FDCA) is considered a promising approach and requires the oxidation of two functional groups. In this study, Au/ZrO2 catalysts with different mean particle sizes were prepared by a chemical reduction method using tetrakis(hydroxymethyl)phosphonium chloride (THPC) and tested in HMF oxidation. The catalyst with the smallest mean particle size (2.1 nm) and the narrowest particle size distribution was highly active in the oxidation of the aldehyde moiety of HMF, but less active in alcohol oxidation. On the other hand, increased activity in FDCA synthesis up to 92% yield was observed over catalysts with a larger mean particle size (2.7 nm), which had a large fraction of small and some larger particles. A decreasing FDCA yield over the catalyst with the largest mean particle size (2.9 nm) indicates that the oxidation of both functional groups require different particle sizes and hint at the presence of an optimal particle size for both oxidation steps. The activity of Au particles seems to be influenced by surface steps and H bonding strength, the latter particularly in aldehyde oxidation. Therefore, the presence of both small and some larger Au particles seem to give catalysts with the highest catalytic activity.

Highlights

The depletion of fossil resources and the ever-growing demand for energy and chemical products drive the need to exploit renewable carbon sources such as biomass [1,2]
AuZ2.1, for which the selectivity switch occurred only at 100 °C, with a decreasing overall carbon occurred only at 100 ◦ C, with a decreasing overall carbon balance. These results show that alcohol balance. These results show that alcohol oxidation is the rate limiting step in this reaction, in line with oxidation is the rate limiting step in this reaction, in line with literature [28] and is more pronounced for literature [28] and is more pronounced for smaller Au particles (
Au particles with different sizes between 2.1 and 2.9 nm supported on ZrO2 showed varying product distributions in HMF oxidation

Summary

Introduction

The depletion of fossil resources and the ever-growing demand for energy and chemical products drive the need to exploit renewable carbon sources such as biomass [1,2]. Inspired by current value chains that are based on a small number of platform chemicals like ethylene or propylene, the production of platform molecules through the partial fragmentation of biomass is one promising approach [3]. 5-(Hydroxymethyl)furfural (HMF) is considered one of the most versatile platform molecules that can be produced from carbohydrate biomass via dehydration [4,5,6]. HMF is obtained from hexoses and can be produced from non-edible polymeric carbohydrates like cellulose [7]. HMF can undergo a variety of reactions like hydrogenation, [8] dehydrogenation [9], or hydrodeoxygenation [10]. Catalysts 2020, 10, 342 oxidation of HMF has gained great interest in recent years. Selective oxidation of HMF can for example

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Discussion

Conclusion