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

Cu-ZrO 2 catalysts supported on nitrogen-doped CNTs were tested for CO 2 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 H 2 adsorption capability; the activated CO 2 adsorption predominantly controls CO 2 conversion. In addition, pyridinic nitrogen contributes to the strong adsorption of CO 2 , stimulating methanol formation, while pyrrolic nitrogen contributes to the medium adsorption of CO 2 , 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 (102.21   mg   g −1 cat   h −1 ); pyrrolic nitrogen dominant CNTs supported catalyst (CZ/CNT-NH 2 ) obtains more highly active structure, giving the highest intrinsic activity (TOF values).