CO2 hydrogenation to methanol over Zr- and Ce-doped indium oxide

In recent decades, climate change has become a major issue that needs to be addressed. Many efforts have been made on the reduction of CO2 emissions and its conversion in energy carriers and high value-added products such as methane, methanol, dimethyl-ether, and hydrocarbons. The present study focuses on the development of catalysts for hydrogenating CO2 to methanol, which is a useful chemical and an alternative liquid fuel. According to the literature, In2O3-based catalysts are particularly selective in the hydrogenation of CO2 to methanol, reducing the production of CO even at high space velocities compared to the more common ternary catalysts such as Cu/ZnO/Al2O3 or Cu/ZnO/ZrO2. Therefore, the effects of CeO2 and ZrO2 on In2O3-based catalysts were investigated in the present study. The InxCe100− x and the InxZr100− x mixed oxides catalysts were synthesized via gel-oxalate coprecipitation by varying the atomic ratios between the elements. Subsequently, they were analysed with several characterisation techniques to rationalise the catalytic performances that were obtained by testing the samples in a fixed bed reactor under different reaction conditions. The addition of different amounts Ce or Zr modified the structure and morphology of the samples and promoted the adsorption of CO2 from 1.8 mmolCO2⋅gcat − 1 up to 10.6 mmolCO2⋅gcat − 1. ZrO2 stabilises the structure and the results suggests that the greater specific activity (168 mgCH3OH⋅gIn2O3 − 1 ⋅h− 1 at 300 ◦C and 2.5 MPa of In40Zr60) could be ascribed to the electronic promotion of Zr. On the contrary, the addition of CeO2 did not reveal a beneficial effect on the activity. Concerning the stability, In2O3-ZrO2 binary oxides seemed to be affected mainly by sintering; whereas In2O3-CeO2 were affected by at least three deactivating phenomena: sintering, reduction of In2O3 to metallic indium and coking. Consequently, the deactivation rate of these binary oxides increased from 1.04 ⋅ 10− 2 h− 1 of the In100 to 4.13 ⋅ 10− 2 h− 1 of the In40Ce60.