Thermo-catalytic conversion of cellulosic feedstock, such as lignocellulose, to platform chemicals offers a renewable alternative to fossil-based chemicals. Mechanistic insights behind thermochemical conversion of lignocellulose would facilitate thermo-catalytic process development for bio-based chemicals. This study employed synchrotron-based Fourier transform infrared (FTIR) microspectroscopy to investigate chemical changes in acid-catalyzed cellulose and lignocellulose and glucose during pyrolysis. Major changes in glucose occurred at 200 °C, where it underwent reactions including ring opening and tautomerization. Acid treatment did not change the molecular structure of cellulose but disrupted the lignocellulose network. The observed synchrotron FTIR spectral features provided evidence for acceleration of catalytic dehydration of cellulose and lignocellulose to levoglucosenone and furans. Catalytic passivation of alkali and alkaline earth metals in lignocellulose was also observed at low acid concentration.