Positron Annihilation Study of Mo Dispersion in MoO3/Al2O3 Catalysts

摘要

MoO3/Al2O3 catalysts were prepared by the impregnation method. The pore structure and dispersion of Mo inside the pores in Al2O3 were studied using positron annihilation lifetime spectra (PALS) and coincidence Doppler broadening (CDB) spectra. The PALS measurement revealed two long lifetime components related with positronium annihilation. This suggests that there are two types of pores with different size in the Al2O3 support. It is found that Mo species are mainly dispersed inside the large pores of the support after MoO3 was loaded, which leads to the decrease of the pore volume. As the MoO3 loading exceeds 18%, the size of the large pores is decreased to the similar size of the small pores.