Improving Fe/Al2O3 Catalysts for the Reverse Water-Gas Shift Reaction: On the Effect of Cs as Activity/Selectivity Promoter

Abstract

The conversion of CO2 into CO via the Reverse Water–Gas Shift (RWGS) reaction is a suitable route for CO2 valorisation. Fe-based catalysts are highly active for this reaction, but their activity and selectivity can be substantially boosted by adding Cs as a promoter. In this work we demonstrate that Cs modifies the redox behaviour and the surface chemistry of the iron-based materials. The metallic dispersion and the amount of metallic Fe centres available for the reaction depends on Cs loading. 5 wt. % of Cs is an optimum amount of dopant to achieve a fair activity/selective balance. Nevertheless, depending on the RWGS reactor operational temperature, lower concentrations of Cs also lead to acceptable catalytic performance. Along with the excellent activity of the prepared materials this work showcases their robustness for long-term runs and the strong impact of H2/CO ratio in the overall catalytic performance.

Recent Developments in the Modelling of Heterogeneous Catalysts for CO2 Conversion to Chemicals

“…Noble metal catalysts, mainly Pt and Rh based supported catalysts, have high activity towards hydrogen dissociation, relatively moderate strength with the adsorption of reaction intermediates and the incompletely filled D‐orbital electrons make them easier for the adsorption of reactants with moderate strength, which is further benefiting to form the intermediate “active compound” in RWGS reaction . Besides mentioned catalysts other metal catalysts as active components or as supports are Pd, Ni, Co, Fe, Fe supported on CNTs and carbide (Mo 2 C) catalyst …”

Tailoring of Hydrotalcite-Derived Cu-Based Catalysts for CO2 Hydrogenation to Methanol

“…Indeed, it is generally known that the stabilization of Cu δ+ sites, as specific active centers for CO 2 adsorption/activation, can be attributed either to the incorporation of the copper phase into the metal-oxide lattice or to the formation of a definite metal-support interaction, suitable to promote and ensure the progressive hydrogenation rate of CO 2 via several intermediates and transition states until methanol. On the contrary, an evidently weak CO x adsorption on the catalytic surface sites prevents the sequential hydrogenation via C-O bond dissociation, while enhancing the parallel path of RWGS [29,30]. Since the molar fraction of Zn also affects the metallic properties of the catalyst (see Figure 4), a further elaboration was carried out, considering the rate of methanol formation as a function of the N 2 O/CO 2 ratio, taken as a parameter capable of justifying the relative redox contribution of metallic sites with respect to sites of oxide nature (see Figure 9).…”

Stabilization of Metal Single Atoms on Carbon and TiO2 Supports for CO2 Hydrogenation: The Importance of Regulating Charge Transfer

“…Literature reports can provide a first explanation to this phenomenon, since it has been shown that alkali promoters contribute to weaken the CO adsorption on catalyst's surface, hindering its further hydrogenation into CH 4 . [ 94 ] We will see later on that this result can be rationalized if we consider the charge transfer between the support and the ruthenium (see Section 2.2.3, Figure 9). Second, the CO selectivity increases with ToS at the three temperatures investigated, and this effect is more accentuated in the case of the catalyst not promoted by sodium.…”