Exploring heterogeneous bimetallic nanoparticle catalysts for sustainable oxidations

Abstract

Prior work in the group has focused on developing the synthesis and activation of supported monometallic noble metal nanoparticle (Au, Pt and Pd) copper chlorophosphate frameworks (CuClPs), and exploring their potential as oxidation catalysts. Herein, bimetallic variants (AuPt/CuClP, PtPd/CuClP and AuPd/CuClP) have been synthesised, characterised and employed in catalytic reactions. Characterisation by TEM and XPS revealed the presence of small, metallic nanoparticles in the bimetallic CuClP materials, with the AuPt/CuClP sample containing the smallest and most uniform particles. The bimetallic AuPt/CuClP material was found to be highly active in the aerobic oxidation of KA-oil, with the catalyst reduced at 300 °C giving the most promising result (89 mol % conversion, > 99 % selectivity to cyclohexanone). The AuPt/CuClP catalyst reduced at 300 °C showed the most promise, achieving the highest conversion of the monometallic and bimetallic CuClP catalysts, while also showing an increased stability over a range of temperatures compared to the monometallic analogues. Through physical mixture tests, the nature of the bimetallic nanoparticles in the AuPt/CuClP catalyst reduced at 250 °C was probed and predicted to contain discrete sites, however the increased thermal stability of the AuPt/CuClP reduced at 300 °C alluded to a synergistic interaction between the Au and Pt species, suggesting the possibility of alloyed nanoparticle sites.

The catalytic potential of the CuClP materials was further explored in the oxidation of valerolactam, the hydrogenation of furfural, the Beckmann rearrangement of cyclohexanone oxime, and the Baeyer-Villiger oxidation of cyclohexanone. However, the presence of unexpected acid-catalysed products gave rise to the consideration of the inclusion of weak Lewis acid sites in the CuClP framework, although acid characterisation is required in order to confirm this.

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