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The adsorbed CO 2 molecules can be easily activated to CO 2 * species by accepting electrons, which subsequently react with the activated H* species to generate the formate or CO intermediate species. Then, the generated intermediate species can be deeply hydrogenated to produce CH 4. The Co0 species and oxygen vacancies on the xCo/MnO catalysts surface both act as the active centers to catalyze the CO 2 hydrogenation reaction. The Co loading can deeply affect the CO 2 hydrogenation reaction by affecting the concentration of oxygen vacancies, metal-support interaction and the basic site numbers on the prepared xCo/MnO catalysts, which are critical to the formation of active centers and the CO 2 adsorption ability of the xCo/MnO catalysts. [Display omitted] • xCo/MnO catalysts with high CO 2 hydrogenation performances can be prepared. • The Mn 1-y Co y O solid solution can be formed in the prepared xCo/MnO catalysts. • Co0 species are the main active centers for CO 2 hydrogenation. • The basic and hydrogenation active sites can be regulated by Co loading. CO 2 hydrogenation technology has great potential for mitigating the greenhouse effect and creating a green economy. The development of catalysts plays a key role in the progress of CO 2 hydrogenation technology. In this study, the xCo/MnO catalysts for CO 2 hydrogenation reaction were prepared by the impregnation method using MnO x as the catalyst support. And the effects of the Co loading on the CO 2 hydrogenation performances of the prepared xCo/MnO catalysts were investigated. The active Co0 species on the xCo/MnO catalysts surface are the main active centers for the CO 2 hydrogenation reaction, and the medium basic sites on the xCo/MnO catalysts are the main CO 2 adsorption sites. The MnO x support possesses a large number of medium basic sites, which can enhance the CO 2 molecules adsorption ability of the xCo/MnO catalysts. An effective regulation of the basic and hydrogenation active site numbers on the xCo/MnO catalysts surface can be achieved by changing the Co loading amount, which in turn can affect the CO 2 molecules adsorption, activation and hydrogenation abilities of the xCo/MnO catalysts. Moreover, the Mn 1-y Co y O solid solution was found to be formed in the prepared xCo/MnO catalysts, which is conducive to the dispersion of metal Co nanoparticles on the MnO surface and the generation of oxygen-deficient sites. The CO 2 desorption amount on the 12Co/MnO catalyst reached 1.76 mmol/g, which provided the catalyst with strong CO 2 adsorption and activation abilities, enabling it to exhibit great CO 2 hydrogenation performance. Under the conditions of atmosphere and 420 °C, the CO 2 conversion and CH 4 selectivity on the prepared 12Co/MnO catalyst reached 57.5 % and 78.8 %, separately. Furthermore, the CO 2 conversion was able to consistently remain at the initial 57.5 %, and the CH 4 selectivity was maintained above 70.0 % in the 10 times CO 2 hydrogenation cycle tests on the 12Co/MnO catalyst. Our study highlights the potential of using MnO x as catalyst support in the CO 2 hydrogenation reaction, and the findings will provide convenient for the future studies. [ABSTRACT FROM AUTHOR]

The greenhouse gases CH 4 and CO 2 can be use as feedstock to prepare syngas (CO + H 2) by CH 4 /CO 2 reforming reaction, and the syngas can be used to produce high value-added chemicals through Fischer-Tropsch reaction. That is, the CH 4 /CO 2 reforming reaction can provide an effective way to rationally use CO 2 and CH 4. The CoCe catalysts were prepared by impregnation method and grinding method, respectively, and the physicochemical properties were characterized by H 2 -TPR, XRD, BET, Quasi in-situ XPS and CO 2 -TPD. The synergistic effects between Co and Ce species can promote the CH 4 and CO 2 molecules to be continuously and rapidly activated, so that the CoCe catalysts exhibited good catalytic activity for the CH 4 /CO 2 reforming reaction. The preparation methods can affect the dispersion of the Co species and the thermal stability of the oxygen vacancies on the CoCe catalysts to affect catalytic activity. The impregnation method is conducive to the Co species dissolving into the CeO 2 lattice to form oxygen vacancies with high thermal stability, and the Co species on the CeO 2 surface were in a highly dispersed state, which can provide more stable catalytic activity centers. Thus, the catalysts prepared by impregnation method displayed superior catalytic performances for CH 4 /CO 2 reforming reaction. And the CH 4 and CO 2 conversions can reach 43.4% and 29.0% at the reaction temperature of 600 °C, respectively. For the CoCe composite catalyst prepared by impregnation method, a large number of Co species can dissolved into the CeO 2 lattice to form Co-O-Ce solid solutions and oxygen vacancies with high thermal stability, and the Co species on the CeO 2 surface were in a highly dispersed state, so the CoCe catalyst prepared by impregnation method exhibits good CH 4 /CO 2 reforming reaction catalytic performance. [Display omitted] • Synergistic effects between Co and Ce species can be effectively regulated by the preparation method. • The synergistic effects between Co and Ce species can promote the CH 4 /CO 2 reforming performances. • External defects can promote the formation of oxygen vacancies to enhance CH 4 /CO 2 reforming activity. [ABSTRACT FROM AUTHOR]

The surface active centers, which include metal Co, surface oxygen vacancies, and Co0–CeO 2-δ interface structures, can be constructed on the mesoporous Co/CeO 2-δ catalysts by wet impregnation method. And the surface active centers can be regulated by the Co species dosage. The interaction between the metal Co and CeO 2-δ can promote surface oxygen vacancies and Co0–CeO 2-δ interface structures to be formed and be conducive to inhibit the aggregation and sintering of Co species in high temperature environment. The prepared Co/CeO 2-δ catalysts have better catalytic performances for CO 2 hydrogenation than the single component Co and CeO 2-δ catalysts, which can be attributed to the synergistic effect between Co0 active centers, surface oxygen vacancies, and Co0–CeO 2-δ interface structures. Therefore, the Co/CeO 2-δ catalysts have strong adsorption and activation ability for reactant CO 2 and H 2 molecules to improve the CO 2 hydrogenation activity. At atmospheric pressure and 400 °C, the CO 2 conversion and CH 4 selectivity on the Co/CeO 2-δ catalyst with Co loading of 12% could reach 59.7% and 95.7%, respectively, and maintained good stability in 9 cycles for CO 2 hydrogenation reaction. • Co0–CeO 2-δ interface structure can be constructed by impregnation method. • Interaction between Co and Ce species promote oxygen vacancy and Co0 to form. • Co0 and oxygen vacancy are mainly active centers in CO 2 hydrogenation. • There is synergy effect among Co0–CeO 2-δ , pore structure, oxygen vacancy, and Co0. [ABSTRACT FROM AUTHOR]

[Display omitted] • Porous CoCex catalyst can be prepared by hydrothermal assisted soft template method. • Co0 species are the active centers for CH 4 /CO 2 dry reforming. • Ce species can produce strong electronic effects with Co species. • Oxygen vacancies can promote the oxidative elimination of carbon deposition. The CoCex composite catalysts prepared by hydrothermal assisted template agent CTAB, have superior catalytic performances for CH 4 /CO 2 dry reforming (DRM). The physicochemical properties of the catalysts were investigated in depth with the help of XRD, H 2 -TPR, CO 2 -TPD, ICP, Quasi in-situ XPS and N 2 adsorption–desorption measurements. The transition metal Co is the main active center in the DRM reaction, which can easily release the outer electrons in the reaction to activate the reactant molecules. The introduction of Ce species can promote the highly dispersed metal Co species and catalytic active centers to be formed, as well as the adsorption and activation of CO 2 molecules by the catalyst. Ce species can produce strong electronic effects with Co species, which can promote the electron-deficient CeO 2-δ and electron-rich Coδ- species to be formed. The formation of CeO 2-δ species facilitates the adsorption and activation of CO 2 molecules, and the active oxygen species on the CeO 2-δ surface facilitates the oxidative activation for CH 4 molecules. The CH 4 and CO 2 reactant molecules can be adsorbed and activated by the formed Coδ- species to form CH 4-x (x = 0–4) and CO 2 δ- reactive species, which can promote the DRM reaction. The Co/Ce molar ratio has an important effect on the physicochemical properties and CO 2 adsorption performance of CoCex catalysts. And the CoCe2 catalyst prepared at a 2.0 Co/Ce molar ratio exhibited superior catalytic performance and high stability for the DRM reaction. The CH 4 and CO 2 conversion of the CoCe2 catalyst reached 88.6%, and 52.1% at 700 °C, respectively. In addition, the CoCe2 catalyst can maintain high cycle stability for CH 4 /CO 2 dry reforming. [ABSTRACT FROM AUTHOR]