CO2 Activation and Hydrogenation on Cu-ZnO/Al2O3 Nanorod Catalysts: An In Situ FTIR Study

Abstract

CuZnO/Al2O3 is the industrial catalyst used for methanol synthesis from syngas (CO + H2) and is also promising for the hydrogenation of CO2 to methanol. In this work, we synthesized Al2O3 nanorods (n-Al2O3) and impregnated them with the CuZnO component. The catalysts were evaluated for the hydrogenation of CO2 to methanol in a fixed-bed reactor. The support and the catalysts were characterized, including via in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The study of the CO2 adsorption, activation, and hydrogenation using in situ DRIFT spectroscopy revealed the different roles of the catalyst components. CO2 mainly adsorbed on the n-Al2O3 support, forming carbonate species. Cu was found to facilitate H2 dissociation and further reacted with the adsorbed carbonates on the n-Al2O3 support, transforming them to formate or additional intermediates. Like the n-Al2O3 support, the ZnO component contributed to improving the CO2 adsorption, facilitating the formation of more carbonate species on the catalyst surface and enhancing the efficiency of the CO2 activation and hydrogenation into methanol. The synergistic interaction between Cu and ZnO was found to be essential to increase the space–time yield (STY) of methanol but not to improve the selectivity. The 3% CuZnO/n-Al2O3 displayed improved catalytic performance compared to 3% Cu/n-Al2O3, reaching a CO2 conversion rate of 19.8% and methanol STY rate of 1.31 mmolgcat−1h−1 at 300 °C. This study provides fundamental and new insights into the distinctive roles of the different components of commercial methanol synthesis catalysts.

Structural Disorder of AlMg‐Oxide Phase Supporting Cu/ZnO Catalyst Improves Efficiency and Selectivity for CO2 Hydrogenation to Methanol

“…It appeared that basic sites were more easily accessible in the disordered catalyst, resulting in better CO 2 conversion and higher STY of methanol for the catalyst prepared at 450 °C. While basic sites are mostly characteristic of ZnO, [25] the reduction of the number of weak basic sites with an increase in crystallinity was also shown for the MgAl‐oxide support (Figure S7d, Table S2) due to the consumption of MgO to form AlMg‐oxide with increasing the temperature of thermal treatment. The basic sites at higher desorption temperatures were not evaluated as they resulted from strongly chemisorbed CO 2 that is not desorbed during the reaction conditions.…”

Immobilization of a Molecular Copper Complex and a Carboxylate-Terminated Cocatalyst on a Metal Oxide Electrode for Enhanced Electrocatalytic Oxygen Reduction

“…Metal oxides (MO x ) have been reported to serve as an ideal electroactive platform for surface functionalization and catalyst immobilization. This is because these MO x materials feature tuneable electronic properties, transparency, and affinity toward various functional groups (e.g., −PO 3 H and −COOH) that could be readily utilized for surface anchoring. − Zhao et al have demonstrated that simply adding pendant acid/base relays on a TiO 2 surface can steer the ORR pathways, thereby switching the mechanism from a sequential single-electron transfer process to a concerted 4e – /4H + reduction process …”

Immobilization of Molecular Copper complex and Carboxylate-terminated Co-catalyst on Metal Oxide Electrode for Enhanced Electrocatalytic Oxygen Reduction

“…This is because these MOX materials feature tuneable electronic properties, transparency, and affinity toward various functional groups (e.g., -PO3H, -COOH) that could be readily utilized for surface anchoring. [37][38][39][40][41][42][43] Zhao et al have demonstrated that simply adding pendant acid/base relays on a TiO2 surface can steer the ORR pathways, thereby switching the mechanism from a sequential single-electron transfer process to a concerted 4e -/4H + reduction process. [44] Taking advantages of MOx surfaces as a support for assembling multiple components, we herein describe the immobilization of a novel copper (II) dipicolylamine (denotes as CuL) complex on mesoporous nickel oxide (meso-NiO) surfaces to form surface-bound electrocatalyst for oxygen reduction in water.…”