Synthesis, characterization and in situ DRIFTS during the CO2 hydrogenation reaction over supported cobalt catalysts

Several supported cobalt catalysts were synthesized, characterized, and studied by in situ diffuse reflectance Fourier-transformed infrared (DRIFT) spectroscopy during the CO2 hydrogenation reaction. The calcined supported cobalt catalysts possessed Co3O4 on the different supports. The alumina supported cobalt catalysts formed increasing amounts of cobalt aluminate at calcination temperatures greater than 973 K. For magnesia supported cobalt catalyst a solid solution was observed at 1173 K. The most active alumina supported cobalt catalyst is formed upon reduction of the freshly calcined samples at 823 K in hydrogen. During hydrogen-reduction the supported Co3O4 phase is converted to CoO and cobalt metal at intermediate temperatures and to cobalt metal at 823 K. Reduced alumina supported cobalt is able to adsorb CO2 as carbonate species; however, silica supported cobalt does not show carbonate species. For magnesia supported cobalt the presence of adsorbed CO2 is not conclusive. The supported cobalt catalysts are active for the CO2 hydrogenation reaction and the conversion depends on the reduction temperature, loading, and support. During reaction absorbed CO is present on the supported cobalt metal irrespective of the support, whereas, surface formate species is only observed on alumina and magnesia supported cobalt catalysts. The carbonate and formate species does not correlate with the CO2 conversion and appears to be formed on the metal–support interface. Thus, the reduction temperature, loading, and support are important factors while designing the supported cobalt catalysts.