Cu-ZnO@Al2O3 hybrid nanoparticle with enhanced activity for catalytic CO2 conversion to methanol

Abstract

A facile approach is demonstrated for the fabrication of Cu-ZnO-based hybrid nanostructures for the catalytic CO2 conversion to methanol. The method combines colloid stabilization of Al2O3 nanoparticles (as support material) and controlled co-precipitation of Cu (active metal) and ZnO (promoter) onto the Al2O3 nanoparticles. Complementary approaches, including X-ray diffractometry, Brunauer-Emmett-Teller surface area analysis, N2O pulse chemisorption, CO2-based temperature-programmed desorption, transmission electron microscopy coupled with energy dispersive spectroscopy, inductively coupled plasma optical emission spectrometry and thermal gravimetric analysis are employed for the characterization of catalyst materials. The results show a successful synthesis of ultrafine Cu-ZnO nanocrystallites deposited on the Al2O3 nanoparticle clusters (Cu-ZnO@Al2O3). Hybridization with Al2O3 nanoparticles enhanced metal dispersion and number of basic sites of the Cu-ZnO-based nanocatalyst. Aminosilane-based surface functionalization on the Al2O3 nanoparticle increased metal surface area in the hybrid nanostructure. The CO2 conversion catalyzed by the synthesized Cu-ZnO@Al2O3 was shown to be proportional to active surface area of the hybrid nanostructure. An optimum selectivity of the synthesized catalyst was identified (≈47–49%) when the mass fraction of Al2O3 was (35–36) %, in correspondence to the highest moderate basicity of the synthesized hybrid nanostructures. The highest yield of methanol achieved 12989 ± 2007 µmolg−1 h−1 by the developed Cu-ZnO@Al2O3. Our work demonstrates a prototype study of fabricating high-performance hybrid nanocatalyst with the support of mechanistic understanding in material synthesis for the synergistic catalysis of CO2 hydrogenation to methanol.