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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Ni-foam-supported Co(OH)F and Co–P nanoarrays were developed for energy-efficient hydrogen production with the assistance of urea electrolysis.

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Minimizing the particle size of transition metals and constructing heteroatom-co-doped carbon with a high surface area are deemed imperative in maximizing the atomic utilization of carbon-based materials. Herein, the atomically dispersed Co sites anchored on interconnected B, N-doped carbon nanotubes (B, N, Co/C nanotubes) are prepared through facile molten-salt-assisted pyrolysis of B/N/Co precursors following chemical etching. The Co single atom is demonstrated to form a Co–N4 planar configuration by XAFS analysis. The developed B, N, Co/C nanotubes exhibit excellent oxygen reduction reaction (ORR) performance in alkaline medium. They not only display a positive half-wave potential (E 1/2, 0.87 V), surpassing that of commercial Pt/C (0.84 V), but also show an outstanding stability (only 1 mV degrade can be observed after 10,000 cycles) and a high fuel selectivity. These excellent ORR performances derive from the efficient synergy of atomically dispersed Co active sites, unique 3D tubelike assembly structure, large specific surface area, and high graphitization degree. Moreover, the B, N, Co/C nanotubes assisted by RuO2 as an air cathode can enable rechargeable Zn–air batteries with larger power density (125.0 mW cm–2), higher specific capacity (746.8 mA h gZn –1), and better cycling stability than those of conventional Pt/C + RuO2-based Zn–air batteries.

This work showcases an innovative route for biocompound upgrading via hydrodeoxygenation (HDO) reactions, eliminating the need for external high-pressure hydrogen supply. We propose the use of water as reaction media and the utilization of multifunctional catalysts that are able to conduct multiple steps such as water activation and HDO. In this study, we validate our hypothesis in a high-pressure batch reactor process using guaiacol as a model compound and multicomponent Ni-based catalysts. In particular, a comparison between ceria-supported and carbon/ceria-supported samples is established, the carbon-based materials being the suitable choice for this reaction. The physicochemical study by X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, and temperature-programmed reduction reveals the greater dispersion of Ni clusters and the strong metal-support interaction in the carbon/ceria-based samples accounting for the enhanced performance. In addition, the characterization of the spent samples points out the resistance of our catalysts toward sintering and coking. Overall, the novel catalytic approach proposed in this paper opens new research possibilities to achieve low-cost bio-oil upgrading processes.