Conversion of hydrogen/carbon dioxide into formic acid and methanol over Cu/CuCr2O4 catalyst

Cu/CuCr2O4 catalysts were prepared by impregnation method at various calcination temperatures (300, 400, and 500 degrees C) and then reduced in H-2 stream. The aggregated particles and decreasing surface area/pore volumes of the deactivated catalysts during HCOOH and CH3OH formations were also observed. Particularly, the EXAFS data showed that first shells of Cu atoms transforms from Cu-O to Cu-Cu after catalytic reactions, their bond distances and coordination numbers are quite different, respectively. It revealed that metallic Cu atoms are one of the important active species over catalyst surface at different reaction temperatures having many unoccupied binding sites for HCOOH and CH3OH formations. Additionally, the optimal calcination temperature for Cu/CuCr2O4 catalysts was demonstrated at 400 degrees C that attributed to its strongest acidity and basicity. The catalytic reactions in the duration of HCOOH and CH3OH preparation were proposed that were composed of HCOOH formation, CH3OH formation, and CH3OH decomposition happening at CuCr2O4, Cu, and CuO active sites, respectively. The highest CO2 conversion (14.6%), HCOOH selectivity/yield (87.8/12.8%), and TON/TOF values (4.19/0.84) were obtained at 140 degrees C and 30 bar in 5 h, respectively. Optimal rate constant (2.57 x 10(-2) min(-1)) and activation energy (16.24 kJ mol(-1) of HCOOH formation were evaluated by pseudo first-order model and Arrhenius equation, respectively. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.