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Zn- and Mn-doped Cerium-oxide based catalyst textured as a solid solutional as well as interfacial form was compared in CO2 hydrogenation reaction to understand the role of texture as well as dopant type. Ce0.9M0.1O2 (M = Zn, Mn) solid solution was prepared by hydrothermal method and CeO2 supported 10 mol% metal oxide (Metal = Zn, Mn) were prepared by wet impregnation method, where the catalysts were characterized by XRD, N2 adsorption/desorption isotherm, TEM, Raman spectra, HAADF-STEM and H2-TPR. During the CO2 activation reaction, CO was the major product with minor amounts of methane, ethane, methanol and ethanol. In the case of the Zn-doped CeO2 catalyst, the presence of Zn improved catalytic activity in both solid solutional and interfacial form due to the synergetic effect of Zn-Ce-based oxide. However, for MnOx/CeO2 catalysts, the CO2 consumption rate significantly decreased for 10 mol% MnOx/CeO2, Ce0.9Mn0.1O2 and Mn3O4, where the MnOx addition inhibits the reduction of CeO2. In the case of the pure CeO2, DRIFTS spectra show that formate intermediate formed by reaction between activated CO2 and OH transformed into methoxy species through formaldehyde intermediates, which leads to the formation of small amount of methanol and ethanol. [ABSTRACT FROM AUTHOR]

• Series of free-standing as well as controlled size Pt nanoparticles-loaded mesoporous metal oxides. • Pt-free NiO exhibited the highest catalytic activity and showing 100% CH 4 selectivity. • Striking catalytic properties can be ascribed to the presence of metallic Ni and the optimal dynamics of Ni/NiO x structure. In this study, a series of free-standing as well as controlled size Pt nanoparticles-loaded mesoporous metal oxides (NiO, Co 3 O 4, CeO 2 and MnO 2) with high surface area and designed pore structure were prepared by hard template method and used as catalysts for CO 2 hydrogenation together with dry reforming of CO 2 with methane. The physicochemical properties of catalysts were analysed by N 2 adsorption-desorption isotherm, XRD, TEM, and H 2 -TPR. Pt-free and Pt-loaded mesoporous NiO and Co 3 O 4 performed with high catalytic activity and selectivity for both CO 2 activation reactions. Pt-free NiO exhibited the highest catalytic activity and also showing 100% CH 4 selectivity between 473–673 K and ˜1:1 H 2 /CO 2 ratio between 673–973 K in CO 2 hydrogenation and dry reforming with methane, respectively. The enhanced catalytic properties can be due to the existence of metallic Ni as well as the optimal dynamics of Ni/NiO x structure under reaction conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • PtNPs enhance CO 2 methanation activity in mesoporous and commercial Co 3 O 4 differently. • Partial coverage of Co-Pt alloy particles by the Co x O y layer has been postulated. • New basic centres are responsible for the higher enhancement effect of the Pt/c-Co 3 O 4. Based on our previous investigations, it turned out that the Co 3 O 4 material is a promising catalyst in the ambient pressure CO 2 methanation. This work aims at understanding the Pt-Cobalt-Oxide surface interaction and its effect on the catalytic performance. The incorporation of Pt nanoparticles into the mesoporous Co 3 O 4 (Pt/m-Co 3 O 4) and commercial Co 3 O 4 (Pt/c-Co 3 O 4) improves the catalytic activity of both catalysts by a factor of ∼ 1.4 and ∼ 1.9 respectively at 673 K. The same tendency towards the increased basicity was also observed. Morphology-induced surface basicity was previously shown to play a key role in determining the catalytic activity of free-standing supports. From HR-TEM (-EDX), EXAFS, CO 2 -TPD, and CO chemisorption measurements it was established that during the pre-treatment, Co-Pt alloy particles partially covered by the Co x O y layer are formed. It has been postulated that this structure transformation generates new basic centres, the amount of which per unit surface area is significantly larger for Pt/c-Co 3 O 4 and this in turn is responsible for the higher enhancement effect of the Pt/c-Co 3 O 4 catalyst in the CO 2 methanation. This study emphasizes the importance of the surface structure exploration for the dynamic catalytic systems in order to reach maximum activity and selectivity in the CO 2 methanation. [ABSTRACT FROM AUTHOR]

• MnCo 2 O 4 has high activity & superior methane selectivity compared to published data. • MnCo 2 O 4 structure is stable and can be reactived. • Co/MnO interphase are responsible for methane production even at high temperatures. We report on a cobalt/manganese-oxide interface catalyst with outstanding activity and selectivity towards methane even at high temperatures and ambient pressure in CO 2 hydrogenation. The catalyst was formed from a MnCo 2 O 4 -based spinel structure during the oxidative-reductive pretreatment process just before the catalytic tests. Several Mn-, Fe- and Ni-containing cobaltite spinel and reverse spinel structures were tested to find the best overall performer. The reusable MnCo 2 O 4 -based structure featured a CO 2 consumption rate of ~8500 nmol*g−1*s−1. Even though methane is not the thermodynamically favoured product, it was produced with ~80% and ~50% selectivity at ambient pressure at 673 K and 823 K, respectively. This unexpected finding is linked to the presence of a unique nanostructured Co/Mn(II)O catalyst with a surface composition of Mn 3.3 Co 2.0 O 4.7 formed after the pretreatment activation step. Over this phase, the reduction of CO 2 progresses through bridge bonded formate located at the Co/Mn2+ interface and this is mostly responsible for high temperature methane formation. This hypothesis is proven here by the reported combination of ex-situ XRD, TPR, HRTEM-ED, HAADF-EDX and in-situ NAP-XPS and DRIFTS techniques. [ABSTRACT FROM AUTHOR]