Recent research and development efforts are focused on: (1) developing catalytic processes to modify the chemical and physical properties of direct liquefaction bio-oil intermediates to better match petroleum processes for biofuel production; and (2) developing new processes and catalysts to upgrade bio-oils into biofuels. Techno-economic analyses of these pathways highlight the importance of overall product yield for economic viability of biofuels process options. The objective of this chapter is to provide an overview of recent developments in the basic scientific understanding of and technical developments in direct biomass liquefaction processes that use reactive gases, like hydrogen and carbon monoxide, in combination with selective hydrodeoxygenation catalysts to produce low-oxygen-containing bio-crude. A review of hydrodeoxygenation using model compounds with a variety of catalysts at a range of process conditions provides a mechanistic understanding of deoxygenation pathways. Similar studies using real biomass as a feedstock in micropyrolyzers or small laboratory reactors investigate the impact of reactive gases on bio-crude yields and quality.
