Chemistry of Thiophene, Pyridine, and Cyclohexylamine on Ni/MoS_xand Ni/S/Mo(110) Surfaces:  Role of Nickel in Hydrodesulfurization and Hydrodenitrogenation Processes

Abstract

Synchrotron-based high-resolution photoemission has been used to study the interaction of thiophene, pyridine, and cyclohexylamine (CHA) with pure and Ni-promoted MoS x films and S/Mo(110) surfaces. The MoS x films exhibit Mo 3d and valence spectra that are very similar to those of MoS 2 . On the MoS x systems, the behavior of thiophene closely resembles that seen on MoS 2 (0002). The molecules are weakly chemisorbed, and most of them desorb at temperatures around 200 K. A small fraction of the adsorbed thiophene is bonded to Mo sites that have S vacancies and desorbs between 250 and 300 K. A similar behavior is observed for adsorbed pyridine. In contrast, CHA displays a rich chemistry on these surfaces. Mo centers that have a limited number of S vacancies and do not do chemistry with thiophene, pyridine, or H 2 are able to cleave the C-N bond in a nonaromatic H-rich molecule like CHA. The addition of Ni enhances the chemical activity of MoS x . On the NiMoS x systems, the adsorption energies of thiophene and pyridine are 5-10 kcal/mol larger than those on pure MoS x . But no dissociation of these molecules is observed on the NiMoS x surfaces. The Ni T S interactions reduce the reactivity of nickel, and the presence of this metal alone is not enough to promote or facilitate the cleavage of aromatic C-S or C-N bonds. Hydrogen seems to play an important role in this aspect. Extensive decomposition of thiophene is observed after creating S vacancies in MoS x and Ni/S/Mo(110) surfaces by reaction with atomic hydrogen (2H gas + S surface f H 2 S gas + vacancy surface ). The role of Ni in NiMoS x catalysts for hydrodesulfurization and hydrodenitrogenation processes is discussed in light of these results.

Hydrodenitrogenation of Petroleum

“…This was also confirmed for W/Al 2 O 3 and NiW/ Al 2 O 3 catalysts prepared from either the oxy-salts or thio-salts (127,239). For the latter catalysts (ATT/Al 2 O 3 ), neither activation energy nor heat of adsorption were changed by the addition of fluoride (125,237). The similar activation energy found for both pathways in Fig.…”

“…Topsøe et al (6,236) showed that Ni promoter facilitates formation of a catalytically active Ni -Mo(W) -S phase. The enhancement in HDN activity of the NiMoS 2 system compared with that for unpromoted MoS 2 observed by Rodriguez et al (237), was attributed to the ability of Ni to supply active hydrogen. As a consequence, the reducibility of the sulfide phase is improved.…”

“…This was attributed to the enhanced sulfidibility of WO 3 /Al 2 O 3 , as well as to the greater fraction of edges and corners of WS 2 that were decorated with Ni than were those in ATT/Al 2 O 3 . Rodriguez et al (237) observed an increase in the adsorption energy of PY on NiMoS 2 compared with that on pure MoS 2 . The CNH of MCHamine was hardly affected by Ni.…”

Chemistry of SO2, H2S, and CH3SH on Carbide-Modified Mo(110) and Mo2C Powders: Photoemission and XANES Studies

“…The sample was flashed to temperatures in the range of 1800−2500 K using an e-beam heater. Standard procedures were followed to remove carbon (heating in O 2 at 700−1000 K, and subsequent ion sputtering or fast heating to 2000 K) and sulfur (ion sputtering and/or fast heating to 2500 K) from the Mo crystal. Surfaces of carbide-modified molybdenum were prepared by exposing the Mo(110) sample to large doses of ethylene at 600 K, followed by annealing to 1200 K. , After 4−6 cycles of C 2 H 4 dosing/annealing, a good (4 × 4) pattern was seen with low-energy electron diffraction (LEED) for the carbide overlayers.…”

Interaction of sulphur with bimetallic surfaces: Effects of structural, electronic and chemical properties

“…The films exhibit Mo 3d and S 2p XpS spectra that are very similar to those of MoS2. They show no reactivity toward CO, 02 or H2 at 1(90-400 K. But they can be activated after the creation of S vacancies by reaction with atomic H [62], providing convenient surfaces for examining the chemistry of desulfi.uizationreactions on molybdenum sulfide [63].…”