Research of cellulose pyrolysis mechanism is crucial for thermal utilization of biomass and provides guidance for industrial application. Based on the famous Broido-Shafizadeh model

the pyrolysis of cellulose is divided into two steps. First

cellulose turns into an active molten state named intermediate cellulose

and then subsequently generates levoglucosan

5-hydroxymethylfurfural

glycolaldehyde and other valuable chemical feedstock. In the two steps

the collapse of hydrogen bonds network and the generation of intermediate cellulose at low temperature

the depolymerization reaction and ring cleavage are mainly involved. Focusing on these studies

this work reviews the effects of the degree of crystallinity and different crystallization morphology on cellulose pyrolysis

the depolymerization path of cellulose and the cleavage reaction of pyran rings

especially the generation and characterization of intermediate cellulose. It also introduces the effects of secondary reactions during pyrolysis in detail and proposes some solutions. There are still many unknown and debates on cellulose pyrolysis mechanism

and a deeper understanding of it through experiments and simulations is impending.