XPS and XRD studies of fresh and sulfided Mo2N

Mo surface species of molybdenum nitride and their changes under sulfiding conditions were investigated by XRD and XPS. Mo2N was synthesized by temperature-programmed reaction of MoO3, with NH3. The decomposition of the Mo3d spectra gave a Mo3d doubler which corresponded to Modelta+ (2 less than or equal to delta < 4), Mo4+ and Mo5+ Or Mo6+ species. The BE of the Mo species of passivated Mo2N shifted to higher energy level compared with the freshly prepared Mo2N due to the oxidation of Mo nitride during passivation. When Mo2N was contacted for 4 h with a 15% H2S-H-2 mixture at 400 degrees C, the XRD spectra did not reveal any new phase, which indicates a high stability of Mo2N against sulfidation, but XPS data showed the presence of sulfur, including S-0 and S2- species, and a decrease of the N/Mo atomic ratio revealed some changes in surface composition. More than one monolayer of Mo2N was transformed to sulfide. It is probable that the oxygen incorporated during passivation reacted with sulfur and formed a thin layer of molybdenum sulfide on the Mo2N surface. (C) 1998 Elsevier Science B.V. All rights reserved.

Simultaneous hydrodesulfurization of thiophene and hydrogenation of cyclohexene over dimolybdenum nitride catalysts

A series of unsupported dimolybdenum nitride (gamma-Mo(2)N) catalysts differing in surface area were prepared by temperature programmed reduction of MoO(3) with a mixture of NH(3):N(2) (90:10). Characterization of catalysts by BET, XRD, TPR and XPS techniques was carried out. The samples were used as catalysts in hydrotreating reactions (simultaneous hydrodesulfurization of thiophene and hydrogenation of cyclohexene). Low surface area gamma-Mo(2)N materials show much higher specific conversions than those with higher surface area. These results indicate that HDS and HYD reactions over gamma-Mo(2)N seem to be structure-sensitive. The relative exposure extent of crystalline planes (111) and (200) over the different catalysts can be associated with their hydrogen adsorption capacities and with their catalytic performances. The catalytic activities are significantly affected by the catalyst pretreatment conditions. (C) 1999 Elsevier Science B.V. All rights reserved.

Structure and base properties of calcined hydrotalcites

Five hydrotalcites with Mg/Al molar ratio range of 3-15 were prepared. The structure and basicity of Mg-Al mixed oxides (Mg(Al)O) transformed from hydrotalcites were investigated by TPD, XPS, XRD, FT-IR and NMR techniques. The results of elemental analysis and XPS indicate that Al is enriched in the surface regions of Mg(Al)O, and its amount increases with the Mg/Al molar ratio and, the calcination temperature. Al-27-MAS-NMR results show that Al exists in two chemical environments: tetrahedral aluminium (Al(t)) and octahedral aluminium (Al(o)) in Mg(AI)O. The amount of Al(t) increases with the Mg/Al molar ratio and the calcination temperature. It is assumed that Al(t) may be mainly from the surface Al. Temperature-programmed desorption (TPD) of CO2 shows that the number of basic sites of Mg(Al)O samples increases with the Mg/Al molar ratio, and the maximum number of basic sites is obtained for hydrotalcite calcined at 773 K. Infrared spectra of adsorbed CO2 and B(OCH3)(3) reveal that there are two kinds of basic sites: weak basic OH- sites and strong basic O2- sites on the Mg(AI)O samples, the base strength depends on the Mg/Al molar ratio and calcination temperature.