Preparation of M/γ-Al2O3 sorbents and their desulfurization performance in hydrocarbons

M/gamma-Al2O3 sorbents with different metals (Ag, Cu, Ni, Zn) as the active component loaded on a gamma-Al2O3 support were prepared by the incipient wetness impregnation method, and their adsorption behavior for thiophene was investigated. The results show that all these metals can obviously promote the desulfurization activity of the prepared sorbents, and Ag is the best one. Then silver was selected to modify gamma-Al2O3 with a different loading amount, and the desulfurization behavior of Ag/gamma-Al2O3 series sorbents in a thiophene-benzene solution was evaluated. It was found that the silver content has a significant impact on desulfurization efficiency, and the A15 sorbent with 13.7 wt% silver has the best adsorption desulfurization performance. XRD results show that the simple Ag-0 is the main active component in Ag/gamma-Al2O3 sorbent. SEM/EDS and BET characterization show that the specific surface area and pore volume decrease obviously when the silver loading amount is more than 13.7 wt%, because of the agglomeration of silver. The desulfurization mechanism of the Ag/gamma-Al2O3 sorbent was explored by using thiophene which has both a conjugated pi bond and sulfur, tetrahydrothiophene which has sulfur but no conjugated pi bond, benzene which has a conjugated pi bond but no sulfur, cyclohexane which has no conjugated pi bonds or sulfur as the model compounds. The desulfurization efficiencies of A15 sorbent in thiophene-benzene, thiophene-cyclohexane, thiophene-tetrahydrothiophene- benzene and thiophene-tetrahydrothiophene-cyclohexane solutions were compared. The results indicate that the thiophene adsorption on Ag/gamma-Al2O3 sorbent is mainly dominated by two kinds of connection between thiophene and silver. One is the connection between the conjugated pi bond and silver (pi-complexation), and the other one is the connection between sulfur and silver (S-metal bond). This is also the main reason that benzene has the competitive adsorption behavior on thiophene.