CO2 hydrogenation to methanol over Cu/ZnO nanocatalysts prepared via a chitosan-assisted co-precipitation method

Abstract

In this study, CuO–ZnO nanocomposites were prepared by chitosan-assisted co-precipitation method and performed as catalyst for CO2 hydrogenation to methanol. Effects of chitosan concentration on the physicochemical properties of the nanocomposites as well as the catalytic activity have been investigated. The obtained catalysts were characterized by means of scanning electron microscopy, X-ray diffraction, N2 adsorption–desorption, N2O chemisorption and temperature-programmed reduction. Chitosan was found to act not only as a coordination compound to produce a homogeneous combination of CuO–ZnO nanocomposite, but also as a soft template for the formation of hollow nanospheres. The CuO and ZnO crystallite sizes of the hollow nanospheres were found to be 11.5 and 18.8nm, respectively, which were smaller than those of other catalysts. The increase of chitosan concentration caused a change in catalyst morphology and a reduction in BET surface area as well as metallic copper surface area, but still higher than those of the unmodified catalyst. The catalysts prepared by using chitosan as precipitating agent exhibited a higher space time yield of methanol than the unmodified catalyst, which was attributed to a synergetic effect of the CuO nanoparticle incorporated in the CuO–ZnO nanocatalyst. However, when the reaction temperature was increased up to 533K, a decline in the space time yield of methanol was observed for the catalysts prepared at high chitosan concentration.