Unveiling the initial pyrolytic mechanisms of cellulose by DFT study

Using density function theory (DFT) simulations, ten chemical reaction pathways of cellobiose model compound are proposed to explore the initial mechanism of cellulose pyrolysis. All chemical reaction pathways lead to the depolymerization of cellulose chains with several primary products, such as levoglucosan, hydroxyacetaldehyde and 5-hydroxymethylfurfural. It is found that the H+ cation plays a significant role in breaking the glucosidic bonds in pathway 3 at the early stage of cellulose pyrolysis due to its low energy barrier. The concerted reaction mechanism in pathway 1 is also critical to reduce the degree of polymerization of cellulose and to form the valuable outcome LG. Based on thermodynamic and kinetic analyses, pathways 1 and 8 are parallel competing reactions consuming cellulose chains. A rational mechanism of forming formaldehyde is proposed in pathway 10. Pathways 2, 4, 5, 7 and 9 are different routes to break cellulose chains at high temperature. The study has the potential to highlight the initial reactions of cellulose pyrolysis. (C) 2015 Elsevier B.V. All rights reserved.