XPS and TPR Studies of Nitrided Molybdena−Alumina

Abstract

The relationship between the surface molybdenum species and adsorbed nitrogen species on nitrided 1.0−18.7% MoO3/Al2O3 was elucidated by XPS and temperature-programmed reduction (TPR). The MoO3/Al2O3 samples were nitrided by temperature-programmed reaction with NH3. From the XPS analysis, Mo3+ and Mo4+ ions were predominant on the surface of the nitrided Mo/Al2O3 samples. From the TPR measurement, the ammonia desorption was due to nitrogen species adsorbed on alumina. The nitrogen desorption was due to two kinds of nitrogen desorption from the structures of γ-Mo2N and β-Mo2N0.78 and four kinds of nitrogen desorption from NH X species adsorbed on MoO2, Mo3+ ion (γ-Mo2N), Mo2+ ion (molybdenum nitride on alumina such as highly dispersed molybdenum nitride), and alumina.

Preparation of Cobalt Nitride from Co–Al Hydrotalcite and its Application in Hydrazine Decomposition

“…The former peak can be ascribed to the reduction of a small amount of NH x (x = 1-3) adsorbed on the surface of the catalyst. The weakly adsorbed NH x species are easily reduced by H 2 and desorbed as NH 3 at low temperature [23,24]. The latter peak can be assigned to the reduction of the lattice N atoms in the Co 4 N phase.…”

XPS evidence for molybdenum nitride formation in ZSM-5

“…With a few notable exceptions, almost all of the published work on these materials has referred to the unsupported bulk compounds, and increasing the surface area (and hence the catalytic reactivity) has been a major objective. Some studies have used alumina [4], carbon [5] or mesoporous silica [6] supports to enhance the dispersion of the carbide or nitride phase.…”

Surface Properties and Active Sites of Nitrided Mo/Al2O3 Catalysts for the Hydrodenitrogenation of Carbazole

“…On the other hand, in Fig. 7B, the loss of nitrogen was observed in several peaks below 700 K and broad peaks above 900 K. , and h 100 wt% [58] molybdenum nitride catalysts [58,65,71], several peaks due to the ammonia and nitrogen gases were observed. The ammonia loss was due to the ammonia-adsorbed on the Al 2 O 3 and the adsorbed NH x species on molybdenum.…”

“…8 [58], the XPS analysis of the 1.0-18.7 wt% Mo/Al 2 O 3 catalysts revealed that the nitrogen release peak around 660 K was related to the Mo 2? ion of molybdenum nitride (c-Mo 2 N or b-Mo 2 N 0.78 ), which facilitated the C-N hydrogenolysis.…”

“…Additionally, phosphorus-doped tungsten oxynitride has been prepared from heteropolyanion precursors [48]. Attention has been directed to a number of different areas, including (1) the preparation of bimetallic nitride catalysts, such as Co, Ce, Ti, and Zr-doped Mo nitrides with higher HDN activities than the pure c-Mo 2 N catalyst [42,[49][50][51][52]; (2) the specific reactivity of nitrogen compounds, such as indole [26,31], pyridine [30,[32][33][34], quinoline [24] and carbazole [25,28,29], on Mo 2 N and promoted Mo 2 N/Al 2 O 3 catalysts for C-N hydrogenolysis; (3) the activities of bulk molybdenum nitride and nitrided Mo/Al 2 O 3 in comparison to sulfided catalysts for HDN [28,53] (in the latter case, nitrides are more active), although molybdenum sulfide and sulfided NiMo/c-Al 2 O 3 catalysts were more active than the corresponding nitride for the HDN and HDS of coal-derived naphtha [17] and the light gas and heavy gas oils [54], respectively, at higher temperatures ([598 K)); (4) the kinetics of the Mo 2 N/Al 2 O 3 catalyst for HDN [22,55,56] including the competitive reaction with HDS and the effects of additives and catalyst deactivation [22,54,57]; and (5) the active surface sites on Mo 2 N/Al 2 O 3 catalysts which have been studied using XPS [55,[58][59][60], NMR [61,62], the temperature-programmed desorption(TPD)/temperature-programmed surface reaction with hydrogen (TPSR) [58,[63][64][65]…”