Density Functional Theory Calculations Complement Mass Spectrometry Experiments in the Investigation of Biomass Fast Pyrolysis and Ion-Molecule Reaction Mechanisms

Biomass fast-pyrolysis, or the rapid heating in the absence of oxygen, is a promising method for biomass conversion necessary for a renewable energy economy. Although kinetic models of cellulose pyrolysis have existed since the 1970s, current models and hypothesized reaction networks fail to explain the product distribution even for a simple model compound, the cellulose dimer, cellobiose. A novel approach of using mass spectrometry to instantly characterize fast pyrolysis vapors allows for identification of initial products to help delineate the reaction pathways that dictate the final product distribution of fast pyrolysis of biomass and model compounds. The use of this set-up to study fast pyrolysis of glucosaccharide-based compounds, such as cellobiose, 13C-labeled cellobiose, cellohexaose, cellotriosan, and cellulose has revealed that the reaction pathway of unraveling the reducing end of the polysaccharide by multiple losses of glycolaldehyde (or isomer) is competitive with the well-established mechanism of levoglucosan production via nucleophilic attack of the hydroxymethylene group at the anomeric carbon concerted with glycosidic bond cleavage. Computational investigation on the reaction barriers of this reducing end unraveling mechanism in tandem wit