Optimization and understanding of ZnO nanoarray supported Cu-ZnO-Al2O3 catalyst for enhanced CO2-methanol conversion at low temperature and pressure

Cu-ZnO-Al2O3 is the most widely applied catalyst for CO2 hydrogenation to methanol. However, it is still a challenge to produce methanol using this catalyst under low-temperature (<250 degrees C) and low-pressure (<10 bar) conditions with desirable yield and selectivity. In this work, by tuning the experimental processing parameters such as solvent, loading amount, and annealing temperature, highly improved ZnO nanoarray supported Cu-ZnO-Al2O3 catalysts have been successfully demonstrated. By using organic solvent (N,N-dimethylformamide (DMF), acetone, or isopropanol) for dip-coating loading process instead of deionized (DI) water, Cu-ZnO-Al2O3 nano-catalysts was comparatively better dispersed on the nanorod array support with populated and abundant active sites, thus enhancing the methanol yield. With the control of the loading amount and annealing temperature, finely distributed Cu nanoparticles were obtained on the ZnO nanorod surfaces to enhance the interactions between Cu and ZnO nanorod surfaces. Further improvement of the catalyst performance is demonstrated by tuning the reaction space velocity. At 200 degrees C and 10 bar conditions, the optimized catalyst achieved a methanol yield of 6.46 mol h-1 kg-1 with 100 % selectivity. The good stability after prolonged testing of the catalysts demonstrates the potential practical implementation. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements under the 1 bar reveal that the CO2 hydrogenation to methanol on the ZnO nanoarray supported Cu-ZnO-Al2O3 catalyst follows the CO reaction pathway, due to the surface oxygen va-cancies on ZnO nanorods which facilitate CO2 dissociation.

Automated summary

By tuning the experimental processing parameters, highly improved ZnO nanoarray supported Cu-ZnO-Al2O3 catalysts have been successfully demonstrated for methanol production under low-temperature and low-pressure conditions, with desirable yield and selectivity.