Surface organometallic chemistry on metals II. Characterization of new bimetallic catalysts generated by reaction of Sn(n-C4H9)4 with silica-supported rhodium

摘要: Reaction of Sn(n-C4H9)4 with Rh supported on silica results in a new bimetallic RhSn catalyst which is extremely active and selective the reduction ethyl acetate to ethanol. Whereas Rh/SiO2 gives rise selectivity for ethanol 57%, obtained by organo-metallic route higher activity as high 98%. Above Sn/Rh value 0.3, varies linearly tin content suggests that enhanced catalytic due intermetallic phase. The catalysts have been characterized at various steps preparation. starting reduced A CO exhibits typical infrared absorption bands linear bridged CO. oxidized refluxing heptane occurs mostly between Rh2O3 organotin compound give an unreduced RhIII7z.sbnd;SnRx surface complex B, existence has suggested from mass balance, STEM, IR spectroscopy. Reduction B 773 K under H2 leads particles average size 2.2 nm do not contain any organic fragment (catalyst C). C chemisorbs only 0.1 H/Rht 0.4 CO/Rht sharp contrast values (1.1 1.1 CO/Rht). chemisorption single band 2000 cm−1 corresponding coordination presence apparently three effects: (i) it decreases significantly amount adsorbed; (ii) isolates rhodium atoms their neighbors; (iii) increases slightly electron density rhodium. Redox behavior RhSn/SiO2 toward O2 silanol groups also observed. With fully C, Rh(0) Sn(0) are SnO2. Thermal treatment flowing He oxidation (or adsorbed water) partially Sn species. evolved during this process. origin (without hydrogenolysis property) these ascribed phase isolated neighbors without “ensemble” able cleave CC CO bonds acetate.