Gold Supported on Strontium Surface-Enriched CoFe2O4 Nanoparticles: a Strategy for the Selective Oxidation of Benzyl Alcohol

Laise Pereira,Jean Costa,Edmilson De Moura,Aryane Tofanello,Carlos Ribeiro,Marco Garcia,Carla De Moura

doi:10.21577/0103-5053.20190030

Abstract

The synthesis of efficient and reusable gold-based catalysts for the selective oxidation of alcohols is a strategy for the development of green processes. Pre-formed nanoparticles syntheses are an easy way to produce controlled-nanosized gold materials; however, the selection of a support is not trivial. Herein, we proposed a CoFe2O4 support enriched with Sr(OH)2, which holds remarkable properties and is suitable for the synthesis of a stable gold-based catalyst for the oxidation of benzyl alcohol. We suggested that the interaction between the CoFe2O4 and the Sr(OH)2 is highly important for the performance of the catalyst. Under the base-free condition of 2.5 h, 100 oC and 2 bar of O2, the catalyst reached 58% of conversion with 76% of selectivity to benzaldehyde. With K2CO3 addition, the conversion and selectivity to benzaldehyde increased to 87% and 88%, respectively. Any gold leaching was detected in 5 successive runs, attesting the noticeable stability that the catalyst presents. This work provides great potential for the selective oxidation of alcohols with high activity since the magnetic properties of the catalyst provide an easy route and allows the separation of the medium reaction. In addition, we are here proposing an important interaction between the Sr(OH)2 and the magnetic nanoparticles.

Highlights

Prati et al.[9,10] and Porta et al.[11] have shown that gold-based catalysts can be effective for the oxidation of alcohols with increased selectivity when compared to platinum and palladium catalysts;[12] the application of such materials is not observed in large-scale production
We presented the synthesis of a heterogeneous catalyst comprised of Au NPs supported on a Sr(OH)2‐enriched CoFe2O4 support, with a controlled size of metal NPs and well dispersion over the support
The enrichment of the magnetic NPs was essential for the gold impregnation since before such modification no metal loading was possible

Summary

Introduction

Selective oxidation of alcohols is one of the most significant transformations of organic chemistry since it is essential for industrial intermediates production, such as ketones, epoxides, aldehydes and acids.[1,2,3,4] In order to avoid the use of stoichiometric toxic oxidants, metal catalysts have been proposed as green alternatives since they enable the use of molecular oxygen in the gas phase, which generates only water as a byproduct.[5,6,7,8] Prati et al.[9,10] and Porta et al.[11] have shown that gold-based catalysts can be effective for the oxidation of alcohols with increased selectivity when compared to platinum and palladium catalysts;[12] the application of such materials is not observed in large-scale production. We explored the enrichment of CoFe2O4 NPs with strontium hydroxide and its subsequent impregnation with gold as a strategy for the preparation of an oxidation catalyst with high activity and selectivity.

Results

Conclusion