Abstract
Highly active heterogeneous rhodium hydrogenation catalysts ‐ rhodium on support ‐ have been prepared by pyrolysis of commercially available Rh~4~(CO)~12~, highly dispersed on a suitable support, e.g. SrTiO~3~, TiO~2~‐anatase, TiO~2~‐rutile, BaTiO~3~ or SrZrO~3~. 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 RhCl~3~ or [RhCl(CO)~2~]~2~ on SrTiO~3~ or a commercially available catalyst (5% Rh on Al~2~O~3~).
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 Rh~6~(CO)~16~, showed lower activities as compared with those prepared from Rh~4~(CO)~12~. Hardly any activity was found using Ir~4~(CO)~12~ as starting carbonyl cluster and no activity was observed when Ru~3~(CO)~12~, Co~4~(CO)~12~, Os~3~(CO),~2~ or Fe~3~(CO)~12~ was used.