Synergistic Effect in Au-Cu Bimetallic Catalysts for the Valorization of Lignin-Derived Compounds

Marta Stucchi,Andrea Jouve,György Sáfrán,Simone Cardaci,Laura Prati,Andrea Beck,Sofia Capelli,Alberto Villa,Stefano Cattaneo,Claudio Evangelisti

doi:10.3390/catal10030332

Abstract

The selective oxidation of veratryl alcohol as lignin-derived compound was studied under mild conditions, using Au-Cu catalysts synthesized from pre-formed nanoparticles with different Au:Cu molar ratios. Bimetallic catalysts show higher activity compared to monometallic counterparts, highlighting a clear synergistic effect. By comparing the physico-chemical surface properties of catalysts supported on carbon and Al2O3, we were able to establish a strong support effect, with alumina-based catalysts being more active than carbon-supported ones. Moreover, TEM and X-ray photoelectron spectroscopy (XPS) analyses showed a different composition of nanoparticles (NPs) and metal exposure, and we established that Au is the active phase of the reaction. The co-presence of Au and Cu species, and their different interaction with the support, enabled obtaining more than 70% conversion of veratryl alcohol to veratryl aldehyde as a unique product. Moreover, the Au1Cu1 supported on alumina catalyst was recovered by filtration and reused without significant loss of activity and selectivity up to four times.

Highlights

The transformation of biomass into fuel and chemicals is becoming increasingly essential as a way to mitigate global warming and diversify energy sources
Second-generation biomass is mainly composed of cellulose, hemicellulose and lignin
Particular attention was paid to particle composition that normally constitutes a big challenge in bimetallic catalysts

Summary

Introduction

The transformation of biomass into fuel and chemicals is becoming increasingly essential as a way to mitigate global warming and diversify energy sources. Second-generation biomass is mainly composed of cellulose, hemicellulose and lignin. While designated applications for cellulose already exist, sustainable ways to valorise lignin are yet to be established [1]. Lignin-derived compounds containing significant linkages are commonly used for a better understanding of its catalytic valorisation [2]. Their liquid phase oxidation is a core unit process for producing a variety of fine chemicals [3], with particular interest in the selective oxidation of side

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