The　hydrogenation　of　acetylene　by　Ga-doped　ceria　is　investigated　using　density　functional　theory　(DFT).　Different　from　a　previously　proposed　mechanism　that　contains　an　unattainable　barrier,　our　models　are　based　on　two　Ga-doped　ceria　surfaces　with　oxygen　vacancies,　representing　respectively　low　and　high　Ga　dopant　concentrations.　The　doping　of　Ga　is　shown　to　promote　the　formation　of　surface　oxygen　vacancies,　which　create　a　template　containing　frustrated　Lewis　pairs　to　facilitate　heterolytic　H-2　dissociative　chemisorption.　This　mechanism　is　similar　in　spirit　to　our　recently　proposed　mechanism　for　bare　and　Ni-doped　CeO2　catalysts　(J.　Am.　Chem.　Soc.,　2018,　140,　12964-12973)　and　calls　for　the　formation　of　Ga-H　hydride　species　along　with　O-H　ones　on　the　ceria　surface.　The　former　has　recently　been　experimentally　observed,　thus　providing　strong　support　for　this　mechanism.　The　rate-limiting　step　in　doped　CeO2　(1　1　1)　with　low　Ga　concentrations　has　a　barrier　that　is　0.18　eV　for　the　Ga/O　FLP　and　0.05　eV　for　the　Ce/O　FLP　higher　than　that　of　undoped　CeO2　(1　1　1),　while　that　for　high　Ga　concentrations　is　0.21　eV　lower,　consistent　with　the　experimental　observed　concentration　dependence　of　catalytic　activity.　However,　different　from　the　Ni　dopant,　which　was　found　to　be　a　promoter,　the　Ga　dopant　is　not　only　a　promoter　but　also　an　active　participant　in　the　catalysis.　(C)　2019　Elsevier　Inc.　All　rights　reserved.