Effects of surface acidities of MCM-41 modified with MoO_3 on adsorptive desulfurization of gasoline

摘要

A series of MCM-41 samples containing molybdenum oxide as active species in the mesoporous channels loaded by spontaneous monolayer dispersion (SMD) and impregnation (IM) have been prepared and characterized using XRD, N_2 adsorption-desorption analysis, Fourier transform infrared spectroscopy (FTIR) and intelligent gravimetric analyzer (IGA). The relative number of hydroxy on the adsorbents was investigated by in situ FTIR. Surface acidities of the adsorbents were studied by infrared spectroscopy of adsorbed pyridine and correlated with reactivity for adsorptive desulfurization. The IGA technique was employed to investigate adsorption behavior of thiophene and benzene on the adsorbents at 303 K. It is shown that MoO_3 can be highly dispersed up to 0.2 g g~(-1) in the MCM-41 channels by the SMD strategy with the ordered mesoporous structure of the MoMM samples remaining intact. The ordered mesostructure of MCM-41 is, however, destroyed at higher MoO_3 contents of 0.26 and 0.32 g g~(-1) with particle sizes of 1.2 nm and 3.6 nm, respectively, observed. For the MoMI(0.2) sample prepared by the IM method, the aggregation of the MoO_3 particles takes place with a particle size of 6.5 nm obtained. The results are also revealed that the dispersion extent of the MoO_3 species is related to the abundant surface hydroxy of MCM-41. The host species and guest species undergo solid-state reaction to form Si-O-Mo bonds in the mixtures which enhance both the Lewis acid and Broensted acid of the samples. It has been concluded that the surface acidities of the sorbents contributes to the desulfurization performance which has also been investigated in this study. The octahedral coordinated species (Mo_7O_(24)~(6-)) are the adsorptive active species for desulfurization compared with the tetrahedral coordinated ones (MoO_4~(2-)).