CO2 hydrogenation by aqueous NaBH4 solution catalyzed by zero-valent nickel supported on carbon nanofibers

Abstract

In the reaction system with NaBH4 as a hydrogen donor, inhibiting the formation of hydrogen is the key to promote the efficient catalytic hydrogenation of CO2. In this study, nanoscale zero-valent nickel supported on carbon nanofibers (Ni0/CNFs) was fabricated as a catalyst for CO2 hydrogenation in aqueous NaBH4 solution. The characteristics of Ni0/CNFs were examined. By SEM, it was observed that spherical nickel nanoparticles were distributed homogeneously on the surface of strip-shaped carbon nanofibers. EDS mappings indicated that elements were evenly distributed on the catalyst, which might contribute to the uniform exposure of active sites. Via XRD, it was determined that all the diffraction peaks corresponded to the crystal face of nickel metal and that the absence of diffraction peaks of carbon nanofibers indicated that the crystallinity of the carrier was low. XPS study showed that nickel existed on the catalyst surface in two forms: zero valence metal and oxidation state. The effects of catalyst addition amount, NaBH4 concentration, NaOH dosage, stirring rate on the yield of formate and hydrogen generation rate (HGR) were investigated. By optimizing the above parameters, the concentration of formate reached 150 mmol/L and the hydrogen production rate was 10.55 mL/min. Compared with the non-catalytic conditions, the concentration of formate increased by 57 % and the HGR decreased by 78 %. Moreover, the relationship between CO2 hydrogenation and NaBH4 hydrolysis was clarified. This research could enhance comprehension of CO2 hydrogenation in aqueous NaBH4 solution and contribute to the development of CO2 capture and utilization storage technology. The significance of this study lies in clarifying the connection between CO2 hydrogenation and borohydride hydrolysis in CO2 catalytic hydrogenation technology.