The extrusion of noble metal nanoparticle catalysts for sustainable oxidation reactions

Abstract

Through employing a combination of complimentary structural, spectroscopic and high-resolution microscopy techniques, the superior properties of a [PtCl4]2- precursor to yield well-defined, isolated nanoparticles (predominantly 2-3 nm) upon microporous framework architectures, have been established. These are prepared via a one-step, in situ methodology, within three-dimensional porous molecular architectures, to afford robust heterogeneous catalysts. The catalytic activity of these materials can be intrinsically linked to the degree of nanoparticle formation. The [PtCl4]2- precursor bestows a greater propensity for nanoparticle formation across a range of activation conditions by comparison to [PdCl4]2- and [AuCl4]- precursors. This, in concert with the surrounding microporous architecture, donates superior catalytic performance for the aerobic oxidation of KA oil to cyclohexanone (precursor for adipic acid and ε-caprolactam), under continuous flow conditions. It is able to approach unrivalled yields of >90% by adapting a ‘closed-loop’ system.
Detailed spectroscopic investigations into the nature of the active sites at the molecular level, coupled with high-resolution electron microscopy, reveal that the intricacies of the synthetic methodology and associated activation procedures play a vital role in regulating the locality, morphology and size of the metal nanoparticles produced. Theseinvestigations also offer insights into the potential consequences of prolonged catalytic exposure.
All three (Au, Pt & Pd) nanoparticle systems demonstrate a profound influence on the activation of molecular oxygen and alkyl peroxides for a plethora of selective catalytic oxidations. Furthermore, this design strategy offers adequate scope for the creation of multi-metallic (e.g. Pd-Cu, Au-Cu & Au-Pt), multifunctional heterogeneous catalysts, in the continued quest for the activation of molecular oxygen in sustainable catalytic processes.

More information

Identifiers

ORCID for Robert Raja: orcid.org/0000-0002-4161-7053

Catalogue record

Export record