Controlled Synthesis And Catalytic Hydrogenation Performance Of Supported Platinum-based Catalysts

Supported platinum catalysts have high activity, high selectivity and good stability, which make them important applications in fuel cell electrodes, catalytic reforming of oil and the synthesis of fine chemicals, etc. The syntheses of the precursors [Pt(C5H9)2],[Pt(COD)Cl2] and [Fe(H2O)6][PtCl6] regulate the preparations of supported platinum-based catalysts, which are used for hydrogenation of o-chloronitrobenzene and phenanthrene to research the performance of catalysts.The Pt precursor [cis-bis(η2,η1-pent-4-en-1-yl)Pt] was synthesized from potassium tetrachloroplatinate,1,5-cyclooctadiene and5-bromo-l-pentene under inert atmosphere. Pt(C5H9)2is an air-and moisture-stable, low-melting (40-41℃), volatile solid. It can release platinum nanoparticles under mild conditions with hydrogen because of its unique chelate structure. Pt supported on mesoporous silica SB A-15materials with different loadings have been controllably synthesized by metal-organic chemical vapor deposition (MOCVD) of Pt(C5HH9)2under room temperature and reduced pressure. Characterization results of FT-IR, XRD, TEM and HRTEM indicate there are not small molecular substances on the catalysts, and Pt nanoparticles with the average size of4.6±1.1nm were dispersed uniformly on the SBA-15. The performance of Pt/SBA-15for the hydrogenation of o-chloronitrobenzene has been tested and was able to achieve high catalytic activity. With the increase of the platinum loading, the activity of catalysts was enhanced, but the selectivity of o-chloroaniline was reduced.Dichloro(1,5-cyclooctadiene)platinum with stable structure was prepared from potassium tetrachloroplatinate and1,5-cyclooctadiene under mild condition. Hexaaquairon(II) hexachloroplatinate was obtained by mixing the methanol solutions of H2PtCl6-6H2O and FeCl2·4H2O. Pt/SBA-15and PtFe/SBA-15materials with different loadings have been synthesized by impregnation method of [Pt(COD)Cl2] and [Fe(H2O)6][PtCl6] under room temperature. Characterization results of XRD and TEM show the average sizes of Pt and PtFe nanoparticles are about7.5nm and8.5nm respectively. The peak position of PtFe lattice plane relative to the platinum crystal face was shifted to the right, indicating that there are interactions between platinum and iron. The performances of Pt/SBA-15and PtFe/SBA-15for the hydrogenation of phenanthrene have been tested. With the increase of the platinum loading, the activity of catalysts was enhanced, but the selectivity of sym-octahydrophenanthrene was reduced. With the increase of the iron loading, the activity of catalysts was reduced, but the selectivity of dihydrophenanthrene and sym-octahydrophenanthrene was increased. Therefore, the metal loading of catalysts should be moderate, not the higher the better.