Roles of nitrogen species on nitrogen-doped CNTs supported Cu-ZrO2 system for carbon dioxide hydrogenation to methanol

Abstract

Cu-ZrO2 catalysts supported on nitrogen-doped CNTs were tested for CO2 hydrogenation to methanol in a fixed-bed plug flow reactor. The characterization results indicate that the presence of pyridinic nitrogen increases the copper oxide dispersion, promotes their reduction, decreases the Cu particle size and enhances H2 adsorption capability; the activated CO2 adsorption predominantly controls CO2 conversion. In addition, pyridinic nitrogen contributes to the strong adsorption of CO2, stimulating methanol formation, while pyrrolic nitrogen contributes to the medium adsorption of CO2, mainly boosting CO formation. Thus, pyridinic nitrogen dominant CNTs supported catalyst (CZ/CNT-N) possesses more active sites compared with the other three catalysts, leading to maximum methanol yield (8.64%) and space time yield (102.21mgg−1cath−1); pyrrolic nitrogen dominant CNTs supported catalyst (CZ/CNT-NH2) obtains more highly active structure, giving the highest intrinsic activity (TOF values).