Highly active heterogeneous rhodium catalysts for the liquid‐phase hydrogenation of aromatic and other unsaturated compounds under mild conditions

Abstract

AbstractHighly active heterogeneous rhodium hydrogenation catalysts ‐ rhodium on support ‐ have been prepared by pyrolysis of commercially available Rh4(CO)12, highly dispersed on a suitable support, e.g. SrTiO3, TiO2‐anatase, TiO2‐rutile, BaTiO3 or SrZrO3. The inactive materials initially obtained were activated by exposure to air at room temperature. The activities of these catalysts were determined in the liquid‐phase hydrogenation of aromatic compounds at atmospheric pressure and at low temperatures (max. 70 °C). They appear to be at least twice as active as catalysts prepared from impregnated RhCl3 or [RhCl(CO)2]2 on SrTiO3 or a commercially available catalyst (5% Rh on Al2O3).The gas‐phase hydrogenation of benzene at room temperature takes place exothermally. Very high activities were also found in the liquid‐phase hydrogenation of alkenes and alkynes, whereas low activities were shown in the hydrogenation of nitriles. Almost no activity was observed in the liquid‐phase hydrogenation of nitro compounds and ketones.Catalysts, prepared from Rh6(CO)16, showed lower activities as compared with those prepared from Rh4(CO)12. Hardly any activity was found using Ir4(CO)12 as starting carbonyl cluster and no activity was observed when Ru3(CO)12, Co4(CO)12, Os3(CO),2 or Fe3(CO)12 was used.