Initial reaction mechanisms of cellulose pyrolysis revealed by ReaxFF molecular dynamics

•Cellulose pyrolysis is simulated with large-scale models by GPU-based ReaxFF MD.•Chemical mechanisms studied with the unique VARxMD for reaction analysis.•Overall spectrum of product tendency and underlying detailed reactions revealed.•Simulated product evolution (500–1400K) agrees well with Py-GC/MS (673–1073K).•A reaction scheme for major pyrolyzates is obtained.