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The desorption kinetic parameters (the desorption activation energy (Ed) and the desorption pre-exponential factor (A)) and the surface acidity (the strength and number of acid sites) of spherical and octahedral nano-SnO2 with different particle sizes for NH3 were measured by a temperature-programmed desorption method. Afterwards, the shape and size dependence of the desorption kinetic parameters and surface acidity of nano-SnO2 were discussed. The results show that shape and size have significant influences on the desorption kinetics and surface acidity of nano-SnO2. For the desorption on spherical or octahedral nano-SnO2, Ed, ln A, and the strength and number of acid sites increase with decreasing particle size. When the diameter is larger than 20 nm, Ed, ln A, and the number of surface acid sites are linearly related to the reciprocal of the particle size, respectively. For different shapes of nano-SnO2 with the same equivalent diameter, the desorption kinetic parameters of octahedral nanoparticles are larger than those of spherical ones, that is, Ed octahedron > Ed sphere and ln A octahedron > ln A sphere. The influence mechanism of shape and size on the desorption kinetic parameters of nano-SnO2 can be attributed to the influence of shape and particle size on the surface acidity of nano-SnO2. [ABSTRACT FROM AUTHOR]