High Performance Polyoxometalate-Stabilizing Pt Nanocatalysts for Quinoline Hydrogenation with Water-Mediated Dynamic Hydrogen

In this work, a Keggin-type platinum substituted polyoxometalate (POM) is constructed by the reaction of monolacunary phosphotungstate precursor [PW11O39]7– with chloroplatinic acid. The as-obtained tetrabutylammonium salt (TBA-PWPt) demonstrates that the dimeric Pt2+ ions are incorporated into POM frameworks and linked by two monolacunary POM anions. Notably, once the Pt-substituted Keggin-type POM anion is reduced by H2, the POM anion-stabilizing Pt nanocatalysts are generated, which greatly facilitates forming oxygen vacancies adjacent to Pt0 species. The Pt nanocatalysts show superior catalytic activity and stability for the selective hydrogenation of quinoline into 1,2,3,4-tetrahydroquinoline in water. Detailed investigations elucidate that the stronger adsorption of quinoline on the Pt surface and the H2 is activated by the adsorption at the POMs-Pt interface site. Moreover, density functional theory (DFT) calculations show that H2O is adsorbed at the interfacial oxygen vacancies and then undergoes homolytic dissociation to produce hydroxyl group (OH–) and hydride (H–) species. The H– species are transferred to the N-containing pyridine ring in quinoline hydrogenation, and the OH– species adsorbed on oxygen vacancies help to promote the H2 heterolytic dissociation to produce H+ and H– species. Sequentially, the produced proton and hydroxyl groups generate H2O, and the reaction cycle is completed.