High resolution electron microscopy characterization of small Pt-Pd2SiO particles in oxide-reducing cycles

In this work we characterized a commercial PtPd alloy (Pt80%Pd20%) supported on amorphous silica using conventional electron microscopy, high resolution electron microscopy and gas chromatography. The samples were maintained on an oxide-reducing cycles, in order to observe the changes in morphology, crystalline structure and chemical phases formed during these treatments. A PtPd alloy wire was evaporated on a SiO2 planar film and reduced in H2 to form the bimetallic particles, which we call a ‘model’ catalyst. The same particles were observed after each chemical treatment. We did not observe segregation of any metal using high resolution electron microscopy (HREM) when the sample was reduced in H2 at 673 K at least at this atomic concentration. We correlated the changes in morphology, and crystalline structure of the sample maintained at different chemical treatments with the catalytic activity. The monometallic ‘real’ catalysts (Pt2SiO and Pd2SiO) prepared by the impregnation method on a comercial silica (Aerosil) were tested in benzene hydrogenation at 373 K and were compared with the bimetallic ‘real’ catalysts also prepared by this method and maintained on an oxide-reducing cycles. We observed differences in catalytic activity for each catalyst maintained at different oxide reducing cycles which we attributed to variations in particles sizes and morphologies and also to the different chemical phases formed in each treatment.