Two different kinds of γ-Al2O3 precursors: stick-like ammonium aluminum carbonate hydroxide and willow leaf-like boehmite could be selectively synthesized via a facile hydrothermal method by just adjusting reaction temperature. After heat treatment, γ-Al2O3 with two different morphologies (stick-like and willow leaf-like) were synthesized and used as supports for CoMo hydrodesulfurization catalysts. Fourier transform infrared spectroscopy of pyridine adsorption and NH3-temperature-programmed desorption showed that stick-like γ-Al2O3 (ACH) and willow leaf-like γ-Al2O3 (AOH) exhibited a lower Lewis acidity than commercial γ-Al2O3. X-ray diffraction indicated that CoMo oxidic catalysts supported on ACH and AOH contained more β-CoMoO4 phase. X-ray photoelectron spectroscopy and high resolution transmission electron microscopy revealed that after presulfurization, more CoMoS active sites and multilayered (Co)MoS2 slabs formed on ACH and AOH supports, thereby creating catalysts with a higher hydrodesulfurization activity in the hydrodesulfurization of thiophene and 4,6-dimethyldibenzothiophene.
Feng Cui,Guangci Li,Xuebing Li,Mohong Lu,Mingshi Li
The carbon-covered aluminas were prepared by using different monocarboxylic acids as carbon sources to modify active alumina, and then were used as supports to prepare supported CoMo catalysts for hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). These monocarboxylic acid molecules can be readily converted to carbon species by thermal decomposition in a nitrogen atmosphere and deposited on an alumina surface. The carbon species can then effectively weaken the interaction between active metals and alumina, which improves the migration and growth of surface Mo species. This result further affected the morphology and orientation of surface sulfur species, that is, the slab length and stacking number of the MoS2 slabs, which closely relates to HDS activity. Since the surface Mo species supported on the alumina modified with acetic acid consisted of the MoS2 slabs with the shortest lengths, leading to the presence of more easily reducible sulfur species during the reaction, the corresponding catalyst exhibited the highest HDS activity for 4,6-DMDBT. In addition, the stacking numbers for all of the catalysts were relatively low, which hindered the adsorption of 4,6-DMDBT on the brim sites of the MoS2 stacks, and thus the HDS reaction mainly occurred through the direct desulfurization route.
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