Propelling the hydrogen economy: from chemical storage and delivery to utilization in biomass conversion

Since H2 is a non-polluting, inexhaustible, efficient, and sustainable energy carrier, it has been forecast to become one of the major carriers of energy in the future and is also essential in the production of feedstock chemicals derived from renewable carbon sources. Initially, a Ru(II) catalyst with meta-trisulfonated triphenylphosphine ligands was shown to be a versatile homogeneous catalyst for the reversible dehydrogenation/hydrogenation of N-heterocycles. N-heterocyclic liquid organic hydrogen carrier compounds are attractive H2 storage and delivery compounds. Hydrogen is also essential in reductive fragmentation of lignin, an abundant biomass source that can be cleaved under reductive conditions to produce value-added renewable aromatic platform chemicals. In native lignin most of the units are linked by C-O bonds. Therefore, selective catalytic cleavage of the C-O bonds plays a pivotal role in maximizing the efficiency of the process while maintaining desirable functionality. A pseudo-homogeneous catalytic system consisting of in situ generated platinum nanoparticles dispersed in ionic liquids was used for upgrading high oxygen content bio-oil through hydrodeoxygenation. To improve further the stability of the catalyst, well-defined rhodium nanoparticles dispersed in sub-micrometer size carbon hollow spheres were prepared, which were able to hydrogenate lignin derived products under mild conditions. Confinement of active rhodium nanoparticles within a carbon shell, prevents the intact lignin polymer from entering and interacting with the catalyst. Thus, this catalysts was used to demonstrate that solvolysis leads to fractionation and fragmentation of lignin, with the internal catalysts hydrogenating any reactive fragments generated. An atomically dispersed catalyst, comprising single Pt atoms on Ni nanoparticles supported on carbon, were used in depolymerization of lignin and showed enhanced activity on selective C-O bonds cleavage.