Effect of alkali (Cs) doping on the surface chemistry and CO2 hydrogenation performance of CuO/CeO2 catalysts

The reaction of captured carbon dioxide with renewable hydrogen towards the eventual indirect production of liquid hydrocarbons via CO2 reduction to CO (reverse water-gas shift reaction, rWGS) is a promising pathway in the general scheme of worldwide CO2 valorization. Copper-ceria oxides have been largely employed as rWGS catalysts owing to their unique properties linked to copper-ceria interactions. Here, we report on the fine-tuning of CuO/CeO2 composites by means of alkali promotion. In particular, this work aims at exploring the effect of cesium doping (0-4 atoms Cs per nm(2)) on co-precipitated CuO/CeO2 catalysts under CO2 hydrogenation conditions. The as-prepared samples were characterized by N-2 physisorption, X-ray diffraction (XRD), H-2-temperature programmed reduction (H-2-TPR), X-ray photoelectron spectroscopy (XPS), CO2-temperature programmed desorption (CO2-TPD), Fourier-transform infrared spectroscopy (FTIR) of pyridine adsorption and CO-diffuse reflectance Fourier-transform infrared spectroscopy (CO-DRIFTS). The results demonstrated that a low amount of Cs exerted a beneficial effect on CO selectivity, inhibiting, however, CO2 conversion. Specifically, a doping of 2 atoms Cs per nm(2) offers > 96 % CO selectivity and equilibrium CO2 conversion at temperatures as low as 430 degrees C, whereas further increase in cesium loading had no additional impact. The present findings can be mainly interpreted on a basis of the alkali effect on the textural and acid/base properties; Cs doping results in a significant reduction of the surface area and thus to a lower population of active sites for CO2 conversion, whereas it enhances the formation of basic sites and the stabilization of partially reduced Cu+ species, favoring CO selectivity.

Automated summary

The effect of cesium doping on CuO/CeO2 catalysts under CO2 hydrogenation conditions was investigated. Results showed that a low amount of cesium improved CO selectivity but inhibited CO2 conversion. Specifically, doping with 2 cesium atoms per nm(2) at 430 degrees Celsius led to over 96% CO selectivity and equilibrium CO2 conversion.