The Combination of Calcium Oxide and Cu/ZrO₂ Catalyst and their Selective Products for CO₂ Hydrogenation

Abstract

The catalytic activities of Cu/ZrO₂_CaO catalysts were investigated on CO₂ hydrogenation. The CO₂ hydrogenations were carried out over combination of calcium oxide and Cu/ZrO₂ catalyst. Two calcination temperatures were chosen at 300 and 650^oC according to thermal decomposition results. The catalysts were characterized by means of N₂ adsorption-desorption, H₂ temperature programmed reduction and X-ray diffraction. The CO₂ hydrogenation under atmospheric pressure and at 250^oC was carried out over copper-based catalysts combined with calcium oxide namely i.e. Cu/ZrO₂_CaO300, Cu/ZrO₂_CaO650, Cu/ZrO₂_Cu/CaO and Cu/ZrO₂+CaO. The catalytic activities over all catalysts were consistent for 4 hours. The catalytic reaction rates over copper-based catalysts were in the range of 21.8 – 47.4 μmol L^-1 s^-1 g cat^-1. The modification of calcium oxide can improve the catalytic activity of copper-based catalysts to 47.4 μmol L^-1 s^-1 g cat^-1. The calcination temperature can cause a difference in active species that impact on product selectivity. The CaO consisting in copper-based catalysts, i.e. Cu/ZrO₂_CaO650, facilitate the growth of long chain hydrocarbon, whereas Cu/ZrO₂_CaO300 favors the formation of carbon monoxide plausibly arising from reverse water gas shift reaction. Directly combined calcium oxide with Cu/ZrO₂ via physically mixing, i.e. Cu/ZrO₂+CaO, can improve the rate of methanol production.