Aerobic Oxidation of Benzyl Alcohol on a Strontium-Based Gold Material: Remarkable Intrinsic Basicity and Reusable Catalyst

Karla Patrícia R Castro,Edmilson M De Moura,Marco Aurélio S Garcia,Carla Verônica R De Moura,Jean Cláudio S Costa,Wiury C De Abreu,Samuel Anderson A De Sousa

doi:10.3390/catal8020083

Abstract

The development of stable and active gold catalysts has arisen as a significant strategy for oxidation of alcohols. Nano-size PVA-stabilized gold nanoparticles immobilized on Sr(OH)2 by colloidal deposition presented high catalytic activity for benzyl alcohol oxidation. In 2.5 h, 2 bar of O2 and without extra-base addition, the calcined support reached 54.6% (100 °C) and 67.4% (140 °C) of conversion, presenting the remarkable and unexplored intrinsic basicity that strontium-based materials retain. With sub-stoichiometric K2CO3 adding, under the same catalytic conditions, the catalyst conducted the reaction with similar activity, but with excellent reusability in the process, without any gold leaching. We investigated the influence that the support synthesis method and the solvent used for the NPs stabilization have on the oxidation activity. The produced materials were fully characterized by XPS, Rietveld refinement, and TEM.

Highlights

Heterogeneous catalysts play an important role globally, with respect to an economic perspective, but they are paramount to ensuring structure for the prosperity of society as a whole.Materials, foodstuffs, and pharmaceuticals, which are essential for the wellbeing worldwide, have intermediates that are heterogeneously catalyzed products
Since differences between oxide and hydroxide have been demonstrated to affect the activity of gold catalysts in magnesium-based supports [12], we decided to explore the influence of strontium-base materials on oxidation of benzyl alcohol, since studies suggested its superior activity when compared to Mg(OH)2 [24], a very common material used for gold catalysts synthesis
PVA-stabilized gold NPs impregnated on strontium-based supports were amply considered on the studies presented

Summary

Introduction

Foodstuffs, and pharmaceuticals, which are essential for the wellbeing worldwide, have intermediates that are heterogeneously catalyzed products. Catalysis by gold-based materials has become one of the most studied topics in chemistry for a wide range of reactions. Studies performed by Prati, Rossi, and partners demonstrated [1,2,3] for the first time that supported gold nanoparticles (NPs) can be used to oxidase alcohols, diols, and polyols in presence of a base, as it was originally considered to be essential for the substrate hydrogen abstraction [4]. The requirement of base addition to achieve satisfactory rates may be in some cases considered a restriction to the use of Au. NPs catalysts, since side reactions or catalyst damage may occur [5]. In order to avoid any drawbacks, the combination of Au NPs with a second metal from the platinum group has received attention as an alternative to monometallic gold-based catalysts, for which base employment is typically required [5,6,7]

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Conclusion