In the context of Carbon Capture and Utilisation (CCU), the catalytic reduction of CO2 to CO via reverse water-gas shift (RWGS) reaction is a desirable route for CO2 valorisation. Herein, we have developed highly effective Ni-based catalysts for this reaction. Our study reveals that CeO2-Al2O3 is an excellent support for this process helping to achieve high degrees of CO2 conversions. Interestingly, FeOx and CrOx, which are well-known active components for the forward shift reaction, have opposite effects when used as promoters in the RWGS reaction. The use of iron remarkably boosts the activity, selectivity and stability of the Ni-based catalysts, while adding chromium results detrimental to the overall catalytic performance. In fact, the iron-doped material was tested under extreme conditions (in terms of space velocity) displaying fairly good activity/stability results. This indicates that this sort of catalysts could be potentially used to design compact RWGS reactors for flexible CO2 utilisation units.
The RWGS reaction represents a direct approach for gas-phase CO2 upgrading. This work showcases the efficiency of Fe/CeO2-Al2O3 catalysts for this process, and the effect of selected transition metal promoters such as Cu, Ni and Mo. Our results demonstrated that both Ni and Cu remarkably improved the performance of the monometallic Fe-catalyst. The competition Reverse Water-Gas Shift (RWGS) reaction/CO2 methanation reaction was evident particularly for the Ni-catalyst, which displayed high selectivity to methane in the low-temperature range. Among the studied catalysts the Cu promoted sample represented the best choice, exhibiting the best activity/selectivity balance. In addition, the Cu-doped catalyst was very stable for long-term runs – an essential requisite for its implementation in flue gas upgrading units. This material can effectively catalyse the RWGS reaction at medium-low temperatures, providing the possibility to couple the RWGS reactor with a syngas conversion reaction. Such an integrated unit opens the horizons for a direct CO2 to fuels/chemicals approach.