Somphonh Peter Phivilay1, Israel E. Wachs1, Wu Zhou2, and Chris Kiely2. (1) Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015, (2) Dept. of Materials Science, Lehigh University, Bethlehem, PA 18015
A series of double-supported Pt/ZrO2/SiO2 catalysts were prepared to determine the influence of ZrO2 nanoparticle (NP) domain size on the reactivity of the catalytic active Pt component. The catalysts were synthesized by first impregnating zirconium tert-butoxide, Zr[OC(CH3)3]4, in toluene, drying and then calcining at 500 °C to form ZrO2. In a second step, aqueous platinum tetra-ammine nitrate, Pt(NH3)4(NO3)2, was impregnated, dried and calcined in air at 500 °C to form the final double-supported Pt/ZrO2/SiO2 catalyst. The ZrO2 loading was varied between 1% and 50% and the Pt loading was maintained constant at 0.1%. In situ Raman and UV-vis spectroscopy and TEM microscopic characterization revealed that the supported ZrO2 phase varied its domain size from isolated surface species to polymeric surface species to NPs (1-3 nm). TEM microscopy revealed that the supported Pt phase was present as 10-70 nm NPs for 1-20% ZrO2/SiO2, where the surface ZrOx species was present (1-12%) and a combination of surface ZrOx species and ZrO2 NPs (15-20%). The Pt NPs, however, were completely absent for higher zirconia loading where ZrO2 NPs are present and reflect the presence of a highly dispersed Pt phase on the ZrO2 NPs. The reactivity of the supported Pt phase was chemically probed with CH3OH oxidation (both steady-state and CH3OH-temperature programmed surface reaction (TPSR) spectroscopy). The reactivity of the methanol oxidation reaction was found to increase with the dimension of the Pt NPs, which also corresponds to lower ZrO2 domain size. Thus, the reactivity of the Pt catalytic active sites could be tuned by the domain size of the ZrO2 nanoligands.