CO₂ hydrogenation to methanol at high reaction temperatures over In₂O₃/ZrO₂ catalysts: Influence of calcination temperatures of ZrO₂ support

This work investigated the role of calcination temperatures (600, 700, 800, 900 and 1000 °C) of ZrO₂ support on the physicochemical properties of In₂O₃/ZrO₂ catalysts (denoted as 20In/Zr-X with X, calcination temperature of ZrO₂ support) as well as their catalytic activity in CO₂ hydrogenation to methanol at high reaction temperatures (320–400 °C). The calcination temperature played a crucial role on crystal structure of In₂O₃ and ZrO₂, reducibility of In₂O₃ and adsorption-desorption of CO₂ and H₂. XRD analysis revealed that cubic In₂O₃ and amorphous ZrO₂ were presented in 20In/Zr-600. With increasing calcination temperature of ZrO₂ support from 600 to 1000 °C, the tetragonal ZrO₂ was formed and the In₂O₃ and ZrO₂ crystallite sizes were enlarged. The degree of In₂O₃ reduction was found to gradually decrease with increasing the calcination temperature of ZrO₂ support due to the increase of In₂O₃ crystallite size. The adsorption strength of CO₂ and H₂ with the catalysts surface was found to be as follows: ZrO₂ > 20In/Zr-1000 > 20In/Zr-900 > 20In/Zr-800 > 20In/Zr-700 > 20In/Zr600 > In₂O₃. The different calcination temperatures of ZrO₂ support did not significantly affect the formation of CO but strongly dominated the yield of CH₃OH and CH₄. At reaction temperatures of 320–340 °C, the 20In/Zr-800 provided the maximum yield of CH₃OH. However, as the reaction temperature was further increased, the maximum yield of CH₃OH was obtained over the 20In/Zr-900, indicating that higher adsorption strength of CO₂ and H₂ enhanced the formation of CH₃OH at higher reaction temperatures. Moreover, the strong interaction of H₂ and CO₂ with the catalysts surface suppressed the formation of CH₄.