  Lignocellulosic biomass is an abundant renewable resource that can be
upgraded to chemical and fuel products through a range of thermal conversion
processes. Fast pyrolysis is a promising technology that uses high temperatures
and fast heating rates to convert lignocellulose into bio-oils in high yields
in the absence of oxygen. Hemicellulose is one of three major components of
lignocellulosic biomass and is a highly branched heteropolymer structure made
of pentose, hexose sugars, and sugar acids. In this study,
$\beta$-D-xylopyranose is proposed as a model structural motif for the
essential chemical structure of hemicellulose. The gas-phase pyrolytic
reactivity of $\beta$-D-xylopyranose is thoroughly investigated using
computational strategies rooted in quantum chemistry. In particular, its
thermal degradation potential energy surfaces are computed employing Minnesota
global hybrid functional M06-2X in conjunction with 6-311++G(d,p) Pople basis
set. Electronic energies are further refined by performing DLPNO-CCSD(T)-F12
single point calculations on top of M06-2X geometries using cc-pVTZ-F12 basis
set. Key thermodynamic quantities (free energies, barrier heights, enthalpies
of formation, and heat capacities) are computed. Rate coefficients for the
initial steps of thermal decomposition are computed by means of reaction rate
theory. For the first time, a detailed elementary reaction kinetic model for
$\beta$-D-xylopyranose is developed by utilizing the thermodynamic and kinetic
information acquired from the aforementioned calculations. This model
specifically targets the initial stages of $\beta$-D-xylopyranose pyrolysis,
aiming to gain a deeper understanding of its reaction kinetics. This approach
establishes a systematic strategy for exploring reactive pathways, evaluating
competing parallel reactions, and selectively accepting or discarding pathways
based on the analysis.
