CO2 hydrogenation to formate over nano-scale zero-valent nickel catalyst under atmospheric pressure

To reduce the energy consumption in the current CO2 hydrogenation with gaseous H2, a novel method of CO2 hydrogenation with potassium borohydride (KBH4) at moderate temperature and ambient pressure under the catalysis of nano-scale zero-valent nickel (nZVN) was developed. Under the optimal experimental conditions where the nZVN dosage was 0.2 g, KBH4 concentration was 0.28 mol·L−1, solution pH was 9.5, reaction temperature was 65 °C and residence time was 24 s, the average highest CO2 absorption efficiency of 45.88% with formate selectivity of 40.81% was achieved based on the ion chromatograph (IC) analyses of the reaction products. Especially, the physicochemical properties of the fresh and spent catalysts, such as morphological structure, physical structure properties, phase and crystallization and chemical compositions, were characterized systematically by using high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), N2 adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS). In combination with the relevant references, the heterogenetic catalytic transfer hydrogenation reaction mechanism of CO2 with KBH4 over nZVN was proposed.