We propose the complicated catalytic mechanisms for the acetic acid molecule catalyzed by transition metal oxide MoO2based on density functional theory calculations.The geometries and energetic values of all stationaries and transition states involved in the three different reaction pathways (Channels Ⅰ,Ⅱ and Ⅲ) are reported and analyzed.All reaction mechanisms are fully different from that of MoxOycatalyzing volatile organic compounds (VOCs) in previous studies.The completely new mechanisms catalyzed by MoO2 for acetic acid have been discovered for the first time.Channels Ⅰ (ⅠA and ⅠB) and Ⅱ are both addition reactions and channel Ⅲ is hydrogen abstraction reaction by producing a leaving group.The barrier energies of reaction are also compared with other catalytic reactions,showing that MoO2 catalyst expresses a lower barrier energy (8.22 kcal/mol) by addition reaction,which represents MoO2 tends to absorb acetic acid pollution gas via addition reaction rather than release toxic substances.This also means that MoO2 is a more effective and representative catalyst and is suitable for further study of catalytic carboxylic acids,so the reaction mechanisms may provide a useful theoretical guidance and solution for the catalysis of carboxylic acids.