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In this study, the promoting effects of ruthenium, palladium, and copper on the performance of a 15%Co-1%K/SiO2 catalyst were evaluated during CO2 hydrogenation in a fixed-bed reactor. Reactions were carried out at atmospheric pressure and 270 °C with H2/CO2 ratio of 3. All catalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and temperature-programmed reduction (TPR). Ruthenium, palladium and copper facilitated the reduction of cobalt oxides and increased cobalt dispersion. In terms of catalyst's performance, ruthenium addition led to increased CO2 conversion and methane selectivity with a detrimental effect on C5+ hydrocarbons. Palladium also presented a similar pattern at lower loading but a drop in CO2 conversion and increased reverse water–gas shift activity were observed at 3 wt % Pd loading. Promoting with copper resulted in decreased activity, methane selectivity and C5+ hydrocarbons productivity with a much higher CO selectivity. [ABSTRACT FROM AUTHOR]

In this work, the effect of ethanol co-feeding in the synthesis of higher alcohols from syngas over K-MoS2 catalyst was investigated in a batch reactor, and the yield of higher alcohols was improved. K-MoS2 prepared with thiourea as a sulfur source exhibited better performance for synthesizing higher alcohols from syngas due to its more stacking layers, higher specific surface area and more Mo4+ active species. Ethanol co-feeding could provide more alkyl intermediate species, which was conducive to the insertion of CO, thereby promoting the conversion of CO and the production of higher alcohols. A change in the reaction path from insertion of CO to homocoupling of ethanol was found upon increasing the ethanol to CO ratio. Higher alcohols production was maximized with the side products in an acceptable range for n EtOH/n CO = 0.3. [ABSTRACT FROM AUTHOR]

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]

The catalytic activity of supported Ni and Ru catalysts has been investigated for the CO2 hydrogenation reaction with respect to the nature of the support and operating conditions employed. It has been found that the nature of the metal oxide support affects significantly catalytic performance in a manner which depends strongly on the nature of the dispersed metal. Catalytic activity of Ni increases following the order TiO2 < Al2O3 ~ YSZ < CeO2, contrary to Ru activity, which is significantly improved when supported on TiO2 compared to CeO2, YSZ or Al2O3. Turnover frequency of CO2 conversion and selectivity toward CH4 for Ni/MxOy catalysts are progressively increased with decreasing Ni particle size from 36.1 (for Ni/TiO2) to 8.5 nm (for Ni/CeO2). In contrast, the opposite trend is observed for Ru/MxOy catalysts, where both catalytic activity and selectivity increase with increasing Ru particle size from 2.2 (for Ru/Al2O3) to 4.2 nm (for Ru/TiO2). Results provide evidence that metal dispersion is a key physicochemical parameter determining catalytic activity. Conversion curve of CO2 shifts toward lower temperatures with decreasing gas hourly space velocity or increasing H2:CO2 molar ratio, which is accompanied by an increase of selectivity toward methane. Long-term stability tests conducted over 5%Ni/CeO2 catalyst showed that it is very active, selective and stable for more than 30 h on stream and, therefore, is a promising catalyst for the CO2 methanation reaction. [ABSTRACT FROM AUTHOR]

In the present study, NiO modified ZnAl2O4 and ZnO modified NiAl2O4 spinel along with pure Al2O3, ZnAl2O4 and NiAl2O4 for comparison in the CO2 hydrogenation reaction have been investigated. It was found that NiAl2O4, NiO/ZnAl2O4 and ZnO/NiAl2O4 catalysts exhibited outstanding activity and selectivity towards methane even at high temperature compared to similar spinel structures reported in the literature. NiO/ZnAl2O4 catalyst showed CO2 consumption rate of ~ 19 μmol/g·s at 600 °C and ~ 85% as well as ~ 50% of methane selectivity at 450 °C and 600 °C, respectively. The high activity and selectivity of methane can be attributed to the presence of metallic Ni and Ni/NiO/ZnAl2O4 interface under the reaction conditions as evidenced by the XRD results. High performance Ni–Zn–Al-based oxide/spinel nanostructures is synthesized and NiO/ZnAl2O4 catalyst exhibited higher catalytic activity in the CO2 hydrogenation reaction due to the presence of metal support interaction between Ni and ZnAl2O4 support. [ABSTRACT FROM AUTHOR]

Abstract: CO2 methanation catalysts were prepared by co-sputtering with Ru and metal oxides such as TiO2 and ZrO2 using the polygonal barrel-sputtering method. The co-sputtering technique not only resulted in the decrease in the reaction temperature but also maintained the deposition of smaller Ru particles during the reaction at higher temperature.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Using DFT+U calculations with inclusion of van-der-Waals (vdW) forces, we studied CO activation and the initial steps of CO hydrogenation over Cu and Ru clusters supported on the TiO anatase (101) surface. CO is readily adsorbed and activated on the Ru cluster where direct CO dissociation proceeds with a barrier of 0.8 eV. When H atoms are co-adsorbed on the Ru cluster, H-addition to CO becomes preferred, as the best Ru sites for CO dissociation are blocked. A H atom is added to the CO molecule with formation of a formate [HCOO] species and an activation barrier of 1.2 eV. On Cu/TiO, only weak adsorption modes of the CO molecule are found, whereas H readily adsorbs on the Cu cluster. A reduction of the titania support does not significantly change this picture. Therefore, the only viable pathway for the CO hydrogenation over Cu/TiO is the addition of a pre-adsorbed H atom to CO coming from the gas phase. This corresponds to an Eley-Rideal mechanism for the H-association to CO. The work shows the importance to consider the hydrogen coverage on the metal cluster as an important variable in modeling the CO hydrogenation reaction. Graphical Abstract: [ABSTRACT FROM AUTHOR]