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Improved CO2 Hydrogenation on Ni–ZnO/MCM-41 Catalysts with Cooperative Ni and ZnO Sites

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journal contribution
posted on 2020-11-19, 13:33 authored by Pradeep S. Murthy, Ziqing Wang, Lizhuo Wang, Jinhui Zhao, Zichun Wang, Weibin Liang, Jun Huang
A set of Ni–ZnO/MCM-41 catalysts with different proportional Ni and ZnO loadings (up to 10 wt % in total) were synthesized for the carbon dioxide (CO2) hydrogenation reaction. Ni nanoparticles and ZnO promoter were both loaded onto a MCM-41 support via the impregnation method. The catalysts were comprehensively characterized by Brunauer–Emmett–Teller, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and hydrogen temperature-programmed reduction measurements. Catalyst properties, including the porosity, Ni metal particle size, and Ni particle location, were all found to be influenced by the presence of the ZnO promoter. ZnO was suspected to improve Ni nanoparticle insertion into the MCM-41 mesoporous channels to form Ni–ZnO interfaces. Both CO and CH4 were produced during the CO2 hydrogenation reaction under the molar ratio of CO2/H2 at 1:3 at 350 °C. The CO2 conversion rate and CO selectivity were found to increase as the reaction temperature increased from 350 to 700 °C. Among all studied materials, the catalyst containing 9 wt % Ni and 1 wt % Zn (denoted as sample E throughout the report) revealed the highest CO2 conversion and selectivity toward CO (∼60% CO2 conversion and 98.5% CO selectivity at 600 °C), while the catalyst containing 1 wt % Ni and 9 wt % Zn (denoted as sample A throughout the report) revealed the lowest activity (∼2.5% CO2 conversion and 95% CO selectivity at 600 °C). This study illustrated that cooperative catalysis can be applied to tune the CO2 hydrogenation reaction toward the reverse water–gas shift reaction for value-added CO production. When both Ni and ZnO are coupled in MCM-41, a hybrid system was designed and synthesized, in which Ni functions for H2 dissociation and ZnO functions for CO2 adsorption and accumulation.