Unveiling the promotion effect of Zr species on SBA-15 supported nickel catalysts for CO2 methanation

Abstract

Introducing promoters on Ni-based catalysts for CO2 methanation have been proved to be positive for enhancing their performance. And the correlation of the promotion mechanism and the reaction pathway is significant for designing efficient catalysts. In this contribution, series of Zr species promoted SBA-15 supported Ni catalysts were prepared by citric acid complexation method under a range of Zr/Ni atomic ratios from 0 to 2.5. In situ and ex situ characterizations were carried out. It was found that the addition of citric acid was conductive to improve CH4 selectivity due to the higher concentrations of Ni0 confined in SBA-15, harvesting sufficient H atoms for CH4 formation following formate pathway via a formyl intermediate. Furthermore, a coverage layer of Zr species was found on the support at Zr/Ni = 1.7, which interacted with the Ni particles, providing higher concentrations of medium basic sites for CO2 activation. Accordingly, the optimum catalytic performance was obtained on ZrNi-1.7(CI), achieving CO2 conversion as high as 78.1% and nearly 100% CH4 selectivity at 400 °C, following the formate hydrogenation pathway. In addition, the ZrNi-1.7(CI) showed good stability owing to the confinement effect of SBA-15 and the Ni–Zr interaction, no carbon deposits were detected after 50 h test.