Shape- and size-dependent desorption kinetics and surface acidity of nano-SnO2

The desorption kinetic parameters (the desorption activation energy (E-d) 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, E-d, ln A, and the strength and number of acid sites increase with decreasing particle size. When the diameter is larger than 20 nm, E-d, 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, E-d octahedron > E-d 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.