Using　first-principle　methods,　we　have　shown　that　formaldehyde　can　be　selectively　converted　to　CO2　over　In2O3(110).　The　OH　generated　from　the　splitting　of　water　was　found　to　assist　in　the　dehydrogenation　of　formaldehyde　to　give　the　corresponding　formyl　(CHO)　species.　Rather　than　direct　dehydrogenation,　a　hydrogen　atom　from　the　CHO　was　then　removed　by　a　neighboring　OH　to　produce　CO.　Finally,　in　favoring　of　desorption,　the　CO　seized　a　lattice　O　atom　to　yield　CO2.　Our　calculation　results　indicate　that　In2O3　plays　an　important　role　in　terms　of　selectivity　during　the　methanol　steam　reforming　reaction　without　the　participation　of　the　PdIn　alloy,　confirming　the　experimentally　observed　selectivity　towards　CO2.　©　2013　Dalian　Institute　of　Chemical　Physics,　the　Chinese　Academy　of　Sciences.