The search for suitable support materials and optimal promoters is an attractive approach to control the product selectivity in Fe-catalyzed CO₂ hydrogenation to C₂₊-hydrocarbons (CO₂-modified Fischer–Tropsch synthesis (CO₂-FTS)). This study systematically investigates the effects of metal oxide dopants for ZrO₂ as well as a K promoter with or without a transition metal co-promoter for supported FeO_x species in Fe/ZrO₂-based catalysts on their performance in CO₂-FTS. By combining K with a Mn promoter (Mn/K ratio = 0.4) on a Fe/YZrO_x catalyst, CH₄ selectivity was hindered without decreasing C₂-C₄ olefin selectivity at 300 °C and 15 bar. The low CH₄ selectivity is worth mentioning in comparison with state-of-the-art Fe-based catalysts. The reaction-induced catalyst restructuring was analyzed, revealing a positive influence of the transition metal promoters on the in-situ formation of catalytically active Fe carbides. Temperature-programmed experiments provided insight into the catalyst ability to interact with CO₂ and H₂, and thus into the nature of surface iron carbides formed in-situ. Furthermore, the influence of K and Mn on the formation of surface intermediates under realistic conditions was studied using operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), complementing our understanding of the role of the promoters in improving the formation of the desired products.

Oxidative coupling of methane (OCM) is one of the most promising approaches to produce ethylene and ethane (C₂-hydrocarbons) in the post-oil era. The MnO_x-Na₂WO₄/SiO₂ system shows promising OCM performance, which can be further enhanced by cofed steam. However, the positive effect of steam on C₂-hydrocarbons selectivity practically disappears above 800 °C. In the present study, we demonstrate that the use of SiC as a support for MnO_x-Na₂WO₄ is beneficial for achieving high selectivity up to 850 °C. Our sophisticated kinetic tests using feeds without and with steam revealed that the steam-mediated improvement in selectivity to C₂-hydrocarbons is due to the inhibition of the direct CH₄ oxidation to carbon oxides because of the different enhancing effects of steam on the rates of CH₄ conversion to C₂H₆ and CO/CO₂. Other descriptors of the selectivity improvement are MnO_x dispersion and the catalyst specific surface area. The knowledge gained herein may be useful for optimizing OCM performance through catalyst design and reactor operation.

The oxidative dehydrogenation of propane with CO₂ (CO₂-ODP) is a promising technology for the efficient production of propene in tandem with CO₂ reduction to CO. However, the rational design of high-performance catalysts for this green process is still challenged by limited understanding of the nature of active sites and the reaction mechanism. In this work, the effects of SnO₂ promoter on Pt/CeO₂ activity and propene selectivity in CO₂-ODP are elucidated through varying the Sn/Pt molar ratio. When the ratio increases, propane conversion gradually decreases, while the propene selectivity increases. These dependences are explained by increasing the electron density of Pt through the promoter. The strength of this effect is determined by the Sn/Pt ratio. Owing to the electronic changes of Pt, CO₂-ODP becomes more favorable than the undesired CO₂ reforming of propane. Sn-modified Pt–O–Ce bonds are reasonably revealed as the active sites for CO₂-ODP occurring through a redox mechanism involving the activation of CO₂ over oxygen vacancies at Sn-modified Pt and CeO₂ boundaries. These atomic-scale understandings are important guidelines for purposeful development of high-performance Pt-based catalysts for CO₂-ODP.