Density Functional Theory (DFT) study on the pyrolysis of cellulose: The pyran ring breaking mechanism

Abstract

Pyran ring breaking is a key step for cellulose pyrolysis to produce small molecular products. Cellotriose was employed as the model compound of cellulose to explore the mechanism of pyran ring breaking based on Density Functional Theory (DFT). Four kinds of reaction mechanisms were studied: (1) directly breaking mechanism, (2) Retro–Diels–Alder mechanism, (3) C6OH assisted pinacol ring cleavage mechanism and (4) Retro–Aldol mechanism. The calculated results showed that pyran ring break via Retro–Aldol mechanism (with C3O formed) was kinetically favored over Retro–Diels–Alder mechanism (with C3C4 bond formed), followed by C6OH assisted pinacol ring cleavage mechanism, 2′+2′+2′ and 2+2+2 mechanism. Activation energies for both of the two-step mechanisms, Retro–Diels–Alder and Retro–Aldol, varied on the positions of CC bond and CO group formed. The results provided a better understanding on pyran ring breaking mechanism during cellulose pyrolysis.