Catalytic hydrodeoxygenation (HDO) is a fundamental process for bio-resources upgrading to produce transportation fuels or added value chemicals. The bottleneck of this technology to be implemented at commercial scale is its dependence on high pressure hydrogen, an expensive resource which utilization also poses safety concerns. In this scenario, the development of hydrogen-free alternatives to facilitate oxygen removal in biomass derived compounds is a major challenge for catalysis science but at the same time it could revolutionize biomass processing technologies. In this review we have analysed several novel approaches, including catalytic transfer hydrogenation (CTH), combined reforming and hydrodeoxygenation, metal hydrolysis and subsequent hydrodeoxygenation along with non-thermal plasma (NTP) to avoid the supply of external H 2 . The knowledge accumulated from traditional HDO sets the grounds for catalysts and processes development among the hydrogen alternatives. In this sense, mechanistic aspects for HDO and the proposed alternatives are carefully analysed in this work. Biomass model compounds are selected aiming to provide an in-depth description of the different processes and stablish solid correlations catalysts composition-catalytic performance which can be further extrapolated to more complex biomass feedstocks. Moreover, the current challenges and research trends of novel hydrodeoxygenation strategies are also presented aiming to spark inspiration among the broad community of scientists working towards a low carbon society where bio-resources will play a major role. Figure 1. Three basic phenylpropane monomers: (1) p-coumaryl alcohol; (2) coniferyl alcohol; (3) sinapyl alcohol.

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In the context of Carbon Capture and Utilisation (CCU), the catalytic reduction of CO 2 to CO via reverse watergas shift (RWGS) reaction is a desirable route for CO 2 valorisation. Herein, we have developed highly effective Ni-based catalysts for this reaction. Our study reveals that CeO 2 -Al 2 O 3 is an excellent support for this process helping to achieve high degrees of CO 2 conversions. Interestingly, FeO x and CrO x , 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 CO 2 utilisation units.

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The RWGS reaction represents a direct approach for gas-phase CO 2 upgrading. This work showcases the efficiency of Fe/CeO 2 -Al 2 O 3 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/CO 2 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 runsan 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 *Revised manuscript Click here to view linked References

Advanced catalytic technologies are crucial to enable the transition toward a low-carbon industry with minimized CO 2 emissions. This paper showcases the application of highly effective Ru-promoted Ni-based catalysts for gas-phase CO 2 upgrading: CO 2 methanation and reverse water−gas shift. The addition of small amounts of Ru results in a remarkable enhancement of CO 2 conversion and selectivity. The bimetallic Ru-Ni catalyst displays greater metallic dispersion, tuned electronic properties and outstanding stability for long-term runs, a mandatory requisite for its implementation in actual CO 2 conversion units. The singularity of our advanced catalyst lays on its capacity to work effectively for both the CO 2 methanation and the reverse water−gas shift, allowing end-product flexibility by adjusting the reactor temperature. Such versatility opens a big range of possibilities to adapt this technology in heavy carbon industries whose net CO 2 emissions represent a big share in the global greenhouse gases emissions.

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