Effect of sulfidation pressure on the structure and activity of Ni(CyDTA)W/γ-Al2O3 hydrodesulfurization catalysts

Abstract

In this paper NiW/γ-Al2O3catalysts were prepared by consecutive impregnation of a W/γ-Al2O3 catalyst with an aqueous solution of nickel salt. The structural control of the nickel ion precursor in the impregnation solution was achieved by the addition of 1, 2cyclohexanediamine-N, N, N', N'-tetraacetic acid (CyDTA) as a chelating agent at different pH. The influence of the sulfidation pressure (1 bar vs 40 bar) on the activity and structure of the NiW catalysts was investigated. The catalysts performances were tested in hydrodesulfurization (HDS) of thiophene after sulfidation at atmospheric or high pressure. The catalysts were characterized by X-Ray photoelectron spectroscopy (XPS), temperatureprogrammed reduction (TPR) and infrared spectroscopy of adsorbed CO (IR/CO) to explain the modification in surface species composition due to the chelating agent CyDTA and sulfiding conditions. NiW catalysts prepared in presence of CydTA and sulfided under high pressure displayed the highest HDS activity. These two factors enhanced the sulfidation degree of W-based species as characterized by XPS. A linear correlation was found between the HDS activity and the sulfidation degree. In addition, chelating agent addition induced a decrease on metal-support interaction, as pointed out by TPR, and strongly favored the creation of CUS sites on the NiWS phase as seen by IR/CO. All these features favored a high catalytic activity. In addition, high pressure sulfidation not only leads to more active NiW catalysts but improved the butene-over-butane ratio.

The influence of activation atmosphere on the active phase and hydrotreating activity of LDH-based NiW pre-sulfurized catalysts

“…The intensive band at 2170 cm −1 is assigned to CO involved in hydrogen bonding with the support hydroxyl Reaction Chemistry & Engineering Paper groups. 44 The band at 2123 cm −1 is characteristic of CO adsorbed on Ni at promoted W sites whereas the band at 2058 cm −1 is attributed to CO adsorbed on W close to Ni. 45 They can respectively characterize WS 2 edges completely promoted by Ni and partially promoted by Ni, 44 both corresponding to the NiWS phase.…”

“…44 The band at 2123 cm −1 is characteristic of CO adsorbed on Ni at promoted W sites whereas the band at 2058 cm −1 is attributed to CO adsorbed on W close to Ni. 45 They can respectively characterize WS 2 edges completely promoted by Ni and partially promoted by Ni, 44 both corresponding to the NiWS phase. 12,45 The intensities of the two bands for LDH-300H are higher than those for LDH-300N, suggesting more NiWS phase in the former, which is consistent with the XPS results.…”

Constructing a superior Co–Mo HDS catalyst from a crystalline precursor separated from the impregnating solution

“…Moreover, organic chelators can react with alkali and neutral OH groups, weakening the interaction between the γ-Al 2 O 3 support and CoMoS active phase, and making MoS 2 slabs more stable, which is good for the formation of more type II CoMoS active phase. Citric acid, 16,17 ethylenediaminetetraacetic acid, 18 ethylene glycol, 19 1,2-cyclohexanediamine- N , N , N ′, N ′-tetraacetic acid, 20 ethylenediamine 21 and nitrilotriacetic acid 19 are the mostly-used organic chelators to prepare new precursors. However, Mo and Co elements are dispersed in different cations and anions of the new precursor, respectively, which means that they are not linked directly, neither by bridging O (–O–) nor any other bonds.…”