Relevant advances in the catalytic conversion of bioglycerol to carbon-neutral hydrogen, propanediols or propylene

The enormous production of bioglycerol is yet largely considered as a waste to treat than a real economic opportunity in the biodiesel industry, which generate different management and environmental issues. To this respect, our research efforts focuses on the valorisation of bioglycerol excess into value-added products (e. g. hydrogen, propanediols or propylene), while considering crucial aspects like the minimization of costs, energy consumption and greenhouse gases emission. The adopted strategies (Scheme 1) consist in designing efficient catalytic systems (catalysts and reactors) to selectively direct the conversion of bioglycerol to the target chemical, depending to the involved reaction (steam reforming, aqueous-phase reforming, hydrogenolysis or hydrodeoxygenation). In this review, we highlight: i) the importance of producing such carbon-neutral chemicals, and ii) the economic and environmental potentialities raising from using bioglycerol as raw materials. Subsequently, we emphasize the main progresses made in the design of efficient transition metals-based alumina or silicas catalysts, and importantly how to re-modulate their physiochemistry for establishing the true catalyst structure-reactivity-selectivity relationship in each reaction, and unveil the factors affecting the catalyst stability under H2O-rich reaction medium. Special emphasis is placed on the identification of the reaction pathways through which glycerol is converted, while underling the individual or synergic contribution of versatile metallic, acid or redox sites to form the final product. Then, the bioglycerol conversion and products distribution are evaluated under different operating conditions and reactors type (closed or semi-continuous batch, and continuous-flow fixed-bed). Moreover, our results and the arising research insights are contrasted with the current state-of-the-art on glycerol transformation to fill existing gaps and postulate future trends. The objective is to share with the related-research community an integral analysis of the most relevant mechanistic, kinetic and engineering breakthroughs in the field of bioglycerol valorization, thereby, opening new opportunities for a zero-waste biorefinery