Effect of calcination temperature during the synthesis of Co/Al₂O₃ catalyst used for the hydrogenation of CO₂

Abstract

Alumina supported and unsupported cobalt catalysts were synthesized, characterized and studied for the CO₂ hydrogenation reaction under in situ conditions with simultaneous reactivity measurements to determine the effect of calcination temperature during catalyst preparation. In situ reduction of calcined alumina supported cobalt and unsupported cobalt oxide catalysts revealed that the reduction of the unsupported Co₃O₄ sample occurred more rapidly and proceeded by the intermediate formation of CoO. The reduction of the calcined alumina supported cobalt catalyst was more difficult and depended on the pre-calcination temperature. The formation of CoO was not observed. In situ reduction of the dried alumina supported cobalt catalysts at 823 K revealed the presence of Co²⁺ tetrahedral species by UV–Vis–NIR spectroscopy. In situ DRIFTS with simultaneous reactivity measurements of the CO₂ hydrogenation reaction revealed that the most suitable calcination temperature for alumina supported cobalt catalysts was 473 K, followed by reduction in H₂ at 823 K. Higher calcination temperatures gave rise to stronger cobalt oxide alumina interactions and a loss of activity. Lower calcination temperatures gave rise to a difficult to reduce Co²⁺ tetrahedral species. Thus, the calcination temperature plays an important role in the synthesis of active alumina supported cobalt catalyst.