(786d) Synthesis and Characterization of Metal Carbide and Nitride Nanoparticle Catalysts for Bio-Oil Deoxygenation

Pyrolysis bio-oil is a promising intermediate for biomass-to-fuels processes because this liquid oil holds the potential to supply diesel and jet fuels, in addition to many valuable chemical intermediates. Elemental analysis of bio-oil reveals that despite its dark brown viscous appearance, it is compositionally different from petroleum. Bio-oils contain relatively little S and N, but have a high O content, typically near 40 wt% and as high as 50 wt%. This oxygen is present in the 400 compounds across a variety of functionalities, including acids, aldehydes, esters, alcohols, ethers, ketones, phenolics, sugars, and furans. Due to these stark chemical differences from petroleum, pyrolysis oil cannot be directly used as a transportation fuel nor can it be “dropped-in” to existing petroleum refinery processes. The oil must first be upgraded, however, efficient deoxygenation has proven to be especially challenging. Therefore, deoxygenation remains a critical obstacle to enabling transportation fuel production from pyrolysis oil at the industrial scale, and there is a continuing need for new catalytic processes and chemistries. This presentation will focus on our recent advancements in the syntheses of transition metal carbides and nitrides for use as deoxygenation catalysts. Both high-temperature tube-furnace synthetic methods (>600 ^oC) and lower temperature solution-phase methods (<400 ^oC) have been employed to prepare nanoparticle carbide and nitride materials with diameters ranging from 5 – 100 nm. Notably, size control was achieved in the high-temperature synthesis of Mo₂N by varying the gas flow rate, and average particle sizes of 5 or 50 nm can be selected. The structural characterization of Mo, W, and V (and mixed-metal) carbide/nitride will be presented, including in-situ experiments to observe compositional changes under flowing reactive gases (e.g., nitride-to-carbide). The carbide/nitride active phases were dispersed on silica for characterization relevant to deoxygenation conditions. The acidity of the catalysts was probed using FTIR spectroscopy with pyridine adsorption to differentiate and quantify Lewis acid sites and Bronsted acid sites on the catalysts. Finally, hydrogen activation is an essential parameter for deoxygenation catalysis, and the hydrogen activation chemistry of these catalysts will be presented and compared.