Combined experimental and computational study to unravel the factors of the Cu/TiO2 catalyst for CO2 hydrogenation to methanol

The hydrogenation of CO2 to methanol over Cu-nanoparticles supported on TiO2 nanocrystals was studied at 30 bar pressure and 200-300 degrees C. 5 wt% Cu-TiO2 catalyst was synthesized by a modified hydrothermal method (CuTiO2HT) and by incipient wetness impregnation method (Cu-TiO2IMP). TEM analysis of the Cu-TiO2HT catalyst revealed the formation of Cu-nanoparticles (3-5 nm), while larger Cu particle sizes were observed on the CuTiO2IMP catalyst. The Cu-TiO2HT catalyst showed superior catalytic activity (CO2 conversion - 9.4 %) and methanol selectivity (-96 %) at 200 degrees C and 30 bar pressure. Low CO2 conversions (-6%) and high CO selectivity (-40 %) was obtained on the Cu-TiO2IMP catalyst. Density functional theory (DFT) calculations indicated the CO2 activation to methanol to proceed via a reverse water gas shift pathway with a significantly lower (93 kJ/mol) CO2 activation barrier on the Cu-nanoparticles, relative to the larger Cu particles (127 kJ/mol). In addition, the higher selectivity towards methanol over the Cu-TiO2HT catalyst was attributed to the higher CO and HCO stability on the Cu nanoparticles. Time of stream (TOS) study of the Cu-TiO2 catalysts showed no significant deactivation even after 150 h with molar feed ratio 1:3:1 (CO2:H-2:N-2) at 200 degrees C.

Automated summary

The study investigated the hydrogenation of CO2 to methanol over Cu nanoparticles supported on TiO2 nanocrystals at high pressure and temperature. It was found that the Cu-TiO2HT catalyst exhibited superior catalytic activity and methanol selectivity compared to Cu-TiO2IMP catalyst due to the formation of smaller Cu nanoparticles. Density functional theory calculations indicated a lower CO2 activation barrier on Cu nanoparticles, contributing to the higher selectivity towards methanol. Time of stream studies showed no significant deactivation of Cu-TiO2 catalysts even after 150 hours of operation.