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

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.

Ionic liquid-stabilized metal oxoclusters: from design to catalytic application

“…Catalytic hydrogenation and hydrogenolysis are chemical processes used to modify or transform organic compounds by introducing hydrogen atoms into the molecular structure. POMs doped with Pd, 143 Pt 144–147 and Ru 148,149 nanoparticles (NPs) are reported to be efficient hydrogenation/hydrogenolysis catalysts. Han et al designed a multifunctional catalyst denoted as Pd NP/POM–IL composite supported on SiO 2 (Pd/H 2 [POM–IL]@SiO 2 ) for the reductive hydrolysis of C–O bonds in diaryl ethers in water, yielding selective ketone products in high yields (>80%) (Fig.…”

“…In quinoline hydrogenation, our recent investigation demonstrates that the POM anion-stabilizing Pt nanocatalysts can greatly facilitate to forming oxygen vacancies adjacent to Pt 0 species on POM catalysts. 147 The oxygen vacancy concentration of the POM catalyst exhibited a decisive role in the catalytic hydrogenation of quinoline in the aqueous media. Further studies indicated H 2 O actually participated in the hydrogenation and acted as an indirect hydrogen source.…”