Preparation, Characterization and Catalytic Testing of GePt Catalysts

Abstract Unsupported and SiO 2 supported GePt bimetallic catalysts were prepared by depositing Ge on to Pt underpotentially. Surface-sensitive cyclic voltammetry of Pt black indicated that Ge covered ca. 40–45% of the Pt surface, whereas XPS showed just ∼96% Pt and ∼4% Ge (normalized to Pt + Ge = 100 % ). High-resolution Ge map of GePt black obtained by Energy Filtered TEM (EFTEM) showed Ge scattered in the near-surface regions. Both catalysts were tested in hexane (nH) transformation reactions between 543 and 603 K and 60 to 480 Torr H 2 pressure (with 10 Torr nH), and compared with the parent Pt catalysts. GePt/SiO 2 catalyst was also tested with methylcyclopentane (MCP). Adding Ge to Pt/SiO 2 lowered the activity; the opposite effect was observed with GePt black. The selectivities of saturated products on bimetallic catalysts decreased, while those of hydrogenolysis products, benzene and hexenes increased in nH transformations over supported catalyst. The reverse effects were observed over the black samples where addition of Ge prevented accumulation of adventitious carbon. Ring opening was the main reaction with MCP, together with some fragments, benzene and unsaturated hydrocarbons. Ring opening of MCP became more selective with decreasing temperature and increasing hydrogen pressure. Ge on GePt black blocked contiguous Pt sites favoring the formation of coke precursors. The different catalytic behavior of GePt/SiO 2 indicated somewhat different Pt–Ge interaction(s).