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

Abstract

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.