Heterogeneous Catalysis: Not Always Supported Metallic Nanoparticles

Heterogeneous catalysts are utilised in the majority of large scale industrial processes, in fact the use of metallic nanoparticles supported on high surface area oxides as catalysts is a technology that modern society depends on for clean air, water, food production and many commodity chemicals. This seminar will demonstrate that supported metal nanoparticles are not always the most active form of a heterogeneous catalyst and that in some cases isolated cationic species or colloidal nanoparticles can significantly outperform the nanoparticle analogues.

This will be demonstrated using three examples: firstly the selective oxidation of methane to methanol will be used as an example of a system where the support material can have a detrimental effect on the catalysis. Using colloidal AuPd particles we can selectively oxidise methane to methanol with incorporation of molecular oxygen at room temperature with over 95% selectivity. Secondly in the case of acetylene hydrochlorination where we have performed the first operando X-Ray absorption study of the catalyst under reaction conditions and demonstrated that the active site is in fact isolated cationic Au-Cl species rather than the often-reported Au nanoparticles, which are in fact an artefact of other characterisation techniques. Finally the effect of isolated Pd sites compared to Pd nanoparticles in the oxygen reduction reaction to generate hydrogen peroxide with high selectivity in the oxygen reduction reaction.

These examples provide new opportunities to build new links between heterogeneous-homogeneous-electro catalysis through the rational design of catalytic sites and environments without being limited to supported metallic nanoparticles.