Preparation and characterization of early transition metal carbides and nitrides

Oyama, S. Ted; Schlatter, James C.; Metcalfe, Joseph E.; Lambert, Joseph M.

doi:10.1021/ie00081a013

Cited by 214 publications

(82 citation statements)

References 7 publications

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“…A reasonable explanation for the faster and more complete carburization of Cu-containing Fe oxides is the presence of smaller crystallites, because the rate of carburization of metal oxides is typically controlled by oxygen diffusion from the oxide core to its surface. 16 The presence of Cu metal at particle surfaces cannot possibly influence rates of oxygen diffusion through an oxide core or a carbide shell. For a given crystallite size, Fe 2 O 3 and Fe 2 O 3 -Cu should show similar rates and extents of carburization.…”

Section: Resultsmentioning

confidence: 99%

Spectroscopic and Transient Kinetic Studies of Site Requirements in Iron-Catalyzed Fischer−Tropsch Synthesis

et al. 2001

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The structure, reduction/carburization, and catalytic performance of K-and Cu-promoted Fe 2 O 3 during initial contact with synthesis gas were examined by combining kinetic analysis of the initial stages of FischerTropsch synthesis (FTS) with X-ray absorption spectroscopy. Oxygen removal initially occurs without FTS reactions as Fe 2 O 3 is reduced to inactive oxygen-deficient Fe 2 O 3 species. Hydrocarbon synthesis reactions become detectable only as Fe 3 O 4 forms and rapidly converts to FeC x . FTS reactions require only the incipient conversion of the surface layers to a dynamic and active surface phase, which consists of FeC x with steadystate surface coverages of vacancies, formed via oxygen and carbon removal during the formation of monomers, CO 2 , and H 2 O. Such surfaces tend to respond to changes in the contacting gas phase within turnover times by changing the relative surface concentration of carbon, oxygen, CO, and hydrogen. The catalytic behavior of these dynamic surfaces is largely independent of the carbide or oxide nature of the particle cores. These findings, combined with the rapid formation and interconversion of Fe 3 O 4 and FeC x within characteristic FTS turnover times, make the definite assignment of FTS activity to either phase neither appropriate nor kinetically rigorous. The presence of K and Cu increases FTS rates, and the steady-state extent of carburization by providing nucleation sites for the formation of smaller FeC x crystallites. These smaller active domains lead, in turn, to shorter diffusion paths and to a larger number of sites for CO adsorption/dissociation and for FTS reactions. These structural promotion effects of K and Cu were consistent with reaction rates, X-ray absorption spectra, and site density measured on promoted and unpromoted catalysts as a function of time in contact with synthesis gas.

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Section: Resultsmentioning

confidence: 99%

Spectroscopic and Transient Kinetic Studies of Site Requirements in Iron-Catalyzed Fischer−Tropsch Synthesis

et al. 2001

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“…The production of dimolybdenum nitrides (gMo 2 N) with high surface area by temperature programmed reaction of MoO 3 with NH 3 was reported some years ago [1,2]. The dimolybdenum nitrides synthesized by this method have been extensively studied due to its competitive catalytic activities for many reactions, for instance, ammonia synthesis [3], ethane hydrogenolysis and CO hydrogenation [4,5].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, a renewed interest has been developed in exploring preparation methods of Mo nitride with high surface area. Following NH 3 -based synthesis [1,2,19], high surface area g-Mo 2 N prepared by temperature programmed reaction of MoO 3 with a mixture of N 2 /H 2 was reported [20]. Another method, in which the ultra®ne particles of transition metal nitrides were produced by evaporating transition metals in low pressure N 2 or NH 3 gas by electron beam heating [21,22] has been employed for the preparation of Mo nitrides with high surface area.…”

Section: Introductionmentioning

confidence: 99%

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

Zhang

Xin

Rodrı́guez-Ramos

et al. 1999

Applied Catalysis A: General

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“…The mathematical calculations were also performed to transpire what is happening in the reduction of molybdenum and tungsten oxide with CO 2 /CH 4 to produce molybdenum and tungsten carbide respectively. Oyama et al, 28 have previously studied the diffusivities of oxygen and nitrogen the solution turned dark gray and an opaque charcoal layer formed above the aqueous solution, a result similar to that of Mo 2 C. As with the Mo 2 C solid-liquid mixture, only rigorous agitation using a touch mixer dispelled the charcoal-like layer into the solution. Additionally the "jet waves" described during Mo 2 C sonication were also observed during the WC dispersion.…”

Section: Kinetic Synthesis Models For Mo2c and Wcmentioning

confidence: 95%

Synthesis and characterization of nanostructured molybdenum & tungsten carbide materials, and study of diffusion model

Covington

Munirathinam

Islam

et al. 2012

Polish Journal of Chemical Technology

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Powders of two molybdenum carbides (Mo 2 C and MoC 1-x ) and tungsten carbide (WC) were prepared by means of temperature programmed reaction (TPR) method. Mo 2 C and MoC 1-x were synthesized by reacting MoO 3 with a preselected molar ratio of methane/hydrogen and carbon monoxide/hydrogen gas mixtures respectively. WC was prepared using tungsten oxide (WO 3 ) and a methane/hydrogen gas mixture. These carbides were ultrasonically dispersed in de-ionized water. Samples were characterized using room temperature x-ray diffraction and scanning microscopy. A kinetic diffusion model is also studied to determine diffusivities in solids where the diffusing species desorbs or reacts at the external surfaces, and where the diffusivity does not vary appreciably with concentrations. The method involves measuring the fl ux of the diffusive species into the solid under the infl uence of a temperature program.

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Preparation and characterization of early transition metal carbides and nitrides

Abstract: required for selective heteroatom removal is only about 600 scf/bbl (Robinson, 1978).

Cited by 214 publications

References 7 publications

Spectroscopic and Transient Kinetic Studies of Site Requirements in Iron-Catalyzed Fischer−Tropsch Synthesis

Spectroscopic and Transient Kinetic Studies of Site Requirements in Iron-Catalyzed Fischer−Tropsch Synthesis

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

Synthesis and characterization of nanostructured molybdenum & tungsten carbide materials, and study of diffusion model

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