High Performance Polyoxometalate-Stabilizing Pt Nanocatalysts for Quinoline Hydrogenation with Water-Mediated Dynamic Hydrogen
Xinjia Wei, Yongjun Jiang, Yuan Ma, Huiying Liao, Sheng Dai, Pengfei An, Zhi-Qiang Wang, Xue‐Qing Gong, Zhenshan Hou
Abstract
In this work, a Keggin-type platinum substituted polyoxometalate (POM) is constructed by the reaction of monolacunary phosphotungstate precursor [PW 11 O 39 ] 7– with chloroplatinic acid. The as-obtained tetrabutylammonium salt (TBA-PWPt) demonstrates that the dimeric Pt 2+ 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 H 2, the POM anion-stabilizing Pt nanocatalysts are generated, which greatly facilitates forming oxygen vacancies adjacent to Pt 0 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 H 2 is activated by the adsorption at the POMs-Pt interface site. Moreover, density functional theory (DFT) calculations show that H 2 O 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 H 2 heterolytic dissociation to produce H + and H – species. Sequentially, the produced proton and hydroxyl groups generate H 2 O, and the reaction cycle is completed.