Elucidating structure-property relationships in the design of metal nanoparticle catalysts for the activation of molecular oxygen

A novel synthetic strategy for the design of metal nanoparticles by extrusion of anionic chloride precursors from a porous copper chlorophosphate framework has been devised for the sustainable aerobic oxidation of vanillyl alcohol (4-hydroxy-3-methoxybenzyl alcohol) to vanillin (4-hydroxy-3-methoxybenzaldehyde) using a one-step, base-free method. The precise nature of the Au, Pt, and Pd species has been elucidated for the as-synthesized and thermally activated analogues, which exhibit fascinating catalytic properties when subjected to diverse activation environments. By employing a combination of structural and spectroscopic characterization tools, it has been shown that analogous heat treatments have differing effects on extrusion of a particular metal species. The most active catalysts in this series of materials were the extruded Pt nanoparticles that were generated by reduction in H2, which exhibit enhanced catalytic behavior, when compared to its Au or Pd counterparts, for industrially significant, aerobic oxidation reactions

Exploring heterogeneous bimetallic nanoparticle catalysts for sustainable oxidations

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, &gt; 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.</p

Elucidating structure-property relationships in the design of metal nanoparticle catalysts for the activation of molecular oxygen

© 2015 American Chemical Society. A novel synthetic strategy for the design of metal nanoparticles by extrusion of anionic chloride precursors from a porous copper chlorophosphate framework has been devised for the sustainable aerobic oxidation of vanillyl alcohol (4-hydroxy-3-methoxybenzyl alcohol) to vanillin (4-hydroxy-3-methoxybenzaldehyde) using a one-step, base-free method. The precise nature of the Au, Pt, and Pd species has been elucidated for the as-synthesized and thermally activated analogues, which exhibit fascinating catalytic properties when subjected to diverse activation environments. By employing a combination of structural and spectroscopic characterization tools, it has been shown that analogous heat treatments have differing effects on extrusion of a particular metal species. The most active catalysts in this series of materials were the extruded Pt nanoparticles that were generated by reduction in H2, which exhibit enhanced catalytic behavior, when compared to its Au or Pd counterparts, for industrially significant, aerobic oxidation reactions.Link_to_subscribed_fulltex

Probing the origin of in situ generated nanoparticles as sustainable oxidation catalysts

A novel method for the in situ generation of catalytically active small metal nanoparticles, by anion extrusion on a parent porous copper chloropyrophosphate framework, has been developed to generate gold, platinum and palladium nanoparticles for sustainable catalytic oxidations using molecular oxygen as the oxidant. Transmission electron microscopy coupled with detailed structural and physico-chemical characterisation, in combination with in-depth kinetic analysis have afforded profound insights into the nature of the active site for facilitating structure–property correlations