The　local　structure　of　the　metal　single-atom　site　is　closely　related　to　the　catalytic　activity　of　metal　single-atom　catalysts　(SACs).　However,　constructing　SACs　with　homogeneous　metal　active　sites　is　a　challenge　due　to　the　surface　heterogeneity　of　the　conventional　support.　Herein,　we　prepared　two　Rh1/CeO2　SACs　(0.5Rh1/r-CeO2　and　0.5Rh1/c-CeO2,　respectively)　using　two　shaped　CeO2　(rod　and　cube)　exposing　different　facets,　i.e.,　CeO2　(111)　and　CeO2　(100).　In　CO　oxidation　reaction,　the　T　100　of　0.5Rh1/r-CeO2　SACs　is　120　°C,　while　the　T　100　of　0.5Rh1/c-CeO2　SACs　is　as　high　as　200　°C.　Via　in-situ　CO　diffuse　reflectance　infrared　Fourier　transform　spectroscopy　(CO-DRIFTS),　we　found　that　the　proximity　between　OH　group　and　Rh　single　atom　on　the　plane　surface　plays　an　important　role　in　the　catalytic　activity　of　Rh1/CeO2　SAC　system　in　CO　oxidation.　The　Rh　single　atom　trapped　at　the　CeO2　(111)　crystal　surface　forms　the　Rh1(OH)adjacent　species,　which　is　not　found　on　the　CeO2　(100)　crystal　surface　at　room　temperature.　Furthermore,　during　CO　oxidation,　the　OH　group　far　from　Rh　single　atom　on　the　0.5Rh1/c-CeO2　disappears　and　forms　Rh1(OH)adjacent　species　when　the　temperature　is　above　150　°C.　The　formation　of　Rh1(OH)adjacentCO　intermediate　in　the　reaction　is　pivotal　for　the　excellent　catalytic　activity,　which　explains　the　difference　in　the　catalytic　activity　of　Rh　single　atoms　on　two　different　CeO2　planes.　The　formed　Rh1(OH)adjacent-O-Ce　structure　exhibits　good　stability　in　the　reducing　atmosphere,　maintaining　the　Rh　atomic　dispersion　after　CO　oxidation　even　when　pre-reduced　at　high　temperature　of　500　°C.　Density　functional　theory　(DFT)　calculations　validate　the　unique　activity　and　reaction　path　of　the　intermediate　Rh1(OH)adjacentCO　species　formed.　This　work　demonstrates　that　the　proximity　between　metal　single　atom　and　hydroxyl　can　determine　the　formation　of　active　intermediates　to　affect　the　catalytic　performances　in　catalysis.[Figure　not　available:　see　fulltext.]　©　2023,　Tsinghua　University　Press.