Preparation, characterisation and selective hydrocarbon transformation applications of flatmodel and zeolite-supported platinum catalysts

[摘要] English: Allyl, amino and silanol (Si-OH) functionalised silicon wafers with epitaxial layer of SiO2(SiO2/Si-wafers) were used as two-dimentional supports to prepare flat model Pt/SiO2/Si-wafer catalysts byspin coating and grafting of suitable platinum precursors followed by calcination and reduction. X-rayphotoelectron spectroscopy (XPS) revealed that H2PtCl6 reacted with surface allyl groups to form π-olefin Pt2+supported complexes. Residual Si-OH groups also reacted with H2PtCl6 to form Pt4+ species. Together, thedifferent surface Pt species formed a heterogeneous coating on the surface of Si-wafer. The platinisation ofaminated silicon surfaces with K2PtCl4 dissolved in aqueous ethanol resulted in the reduction of the Pt(II)precursor and immobilisation of the resultant metallic Pt particles on the model Si-wafer. Calcination andreduction of the surface Pt species resulted in the formation of relatively small Pt particles, 1-5 nm averageparticle diameter, which interacted with the silicon surface via boundary Pt2+-O-Si bonds or Pt2+-N-Si bonds.The prepared flat model Pt/SiO2/Si-wafer catalysts had catalytic activity in solvent-free aerobic oxidation of1-octadecanol to carbonyl compounds. A selection of the prepared flat model Pt/SiO2/Si-wafer catalysts werealso shown to have activity in hydrogenation of alkene and carbonyl functional groups.The preparation and characterisation of Pt catalysts supported on alkaline KL-zeolite and acidicHY-zeolites are also described. Two types of Pt/KL-zeolite catalysts were investigated. Those Pt/KL-zeolitecatalysts prepared by vapour phase impregnation had a high particle dispersion (91.5 % vs. 75.8 %) andsmaller particles sizes (average diameter = 1.2 nm vs.1.5 nm) compared to the equivalent Pt/KL-zeolitecatalysts that were obtained by incipient wetness impregnation. In aromatisation of n-alkanes, the Pt/KLzeolitecatalysts obtained by vapour phase impregnation were more active and more tolerant to oxygenatespresent in the feed than the Pt/KL-zeolite catalysts obtained by incipient wetness impregnation. A correlationbetween the concentrations of acetic acid in the feed, the amount of coke deposit on spent catalysts andcatalyst deactivation was established. Pt/KL-zeolite and Pt/HY-zeolite catalysts were also applied in liquidphase oxidation of primary alcohols under mild conditions (ca.100 °C and ambient pressure). Moderatesubstrate conversion (10-40 %) was achieved.

[发布机构] University of the Free State