Effect of F and Mg on the Dispersion of Mo/Al2O3 and W/Al2O3

Mulcahy, Francis M.; Houalla, Marwan; Hercules, David M.

doi:10.1006/jcat.1993.1008

Cited by 19 publications

(5 citation statements)

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“…Addition of an acidic component (e.g., chromia) should, in principle, lead to a decrease in the PZC of the support. 44 The magnitude of change in the PZC is a function of the acid strength of the Cr phase. A large decrease in the PZC is expected if the Cr phase is highly dispersed or present as a monolayer, because most of the hydroxyl sites will be closely associated with the Cr phase.…”

Section: Discussionmentioning

confidence: 99%

Dispersion and Coverage of Cr/Al2O3 Catalysts

Scierka¹,

Houalla²,

Proctor³

et al. 1995

J. Phys. Chem.

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A series of chromia-alumina catalysts was prepared by equilibrium adsorption from ammonium chromate solutions at various pH's. The uptake of Cr increased from 0.4 to 2.5 wt % Cr with decreasing pH from ca. 10 to 2.7. The results were interpreted on the basis of an electrostatic model of adsorption from solution and a reaction between the Cr anions and OH of the alumina support. X-ray photoelectron spectroscopy (XPS) Cr 2p3,2/A12p intensity ratios for dried and calcined catalysis indicated that the Cr phase is highly dispersed or present as a surface compound. The surface coverage of the calcined Cr/A1203 catalysts was monitored by C02 chemisorption and ion scattering spectroscopy (ISS). C02 chemisorption was found to overestimate surface coverage of the Cr species. This was attributed to selective adsorption of Cr on alumina sites which also bind C02. The ISS results indicated that the Cr phase covers only a small fraction of the alumina surface (up to 26%). The surface coverages measured by ISS were generally consistent with those predicted from theoretical considerations.

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Section: Discussionmentioning

confidence: 99%

Dispersion and Coverage of Cr/Al2O3 Catalysts

Scierka¹,

Houalla²,

Proctor³

et al. 1995

J. Phys. Chem.

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“…In order to take advantage of the relatively high surface area of Al203, a number of studies have been carried out in which the A203 support was modified by such oxides, e.g., MgO [8] In this study, we systematically examlne the influence of B on the state of Mo/AI203-B203 catalysts. The Surface and bulk structure of Mo/A203-B203 catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR).…”

Section: Introductionmentioning

confidence: 99%

Effect of Boron Addition on the State and Dispersion of Mo Supported on Alumina

Morishige¹,

Akai²

1995

Bulletin des Soc Chimique

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The influence of B on the state and dispersion of Mo phases on A1203 have been investigated by bulk and surface characterization techniques, e.g., XRD, XPS and TPR, respectively. In the absence of B, the dispersion of Mo phases Is in good agreement with the theoretical value calculated from Kerkhof-Moulijn model, suggesting that Mo atoms disperse easily on A1203 surface. XPS results indicate that B addition to A1203 leads the Mo dispersion to decrease in comparison with the theoretical mondayer value. This result is also confirmed by XRD analysis, which shows the formation of crystalline Moo3 particles with B addition. TPR profiles for Mo/A1203 consists of two reduction peaks, a low temperature peak (400°C-4500C) and a high temperature one (77OoC-810"C), respectively. The peak intensity of the higher temperature decreases rapidly with B addition, whereas that of lower temperature increases wi.h increasing B contents. Consequently, these results suggest that B addition weakens the interaction between Mo species and the A1203 surface. INTRODUCTIONCatalysts based on molybdenum or tungsten sulfide and promoted by nickel and/or cobalt have been used extensively for hydrotreating in petroleum refining such as hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodemezallization (HDM) for many years. Many studies have been focused on both elucidation of the structure of active phases and enhancement of HDS, HDN and HDM activities.The chemistry and structure of CoMolAlnOs catalysts have been well studied. Several models have been proposed to describe the interactlon between Mo and Co species. These models include the mondayer model [ l , 21, Co-Mo-S complex model [3-51, intercalation model [6] and contact synergy (remote control) model [7]. Recently, the Co-Mo-S model is generally believed as the active structure for the CoMolAlnOs catalysts.In order to take advantage of the relatively high surface area of Al203, a number of studies have been carried out in which the A203 support was modified by such oxides, e.g., MgO [8]

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“…Thus, they are widely used in several industrially important reactions such as hydrotreatments, hydrocracking of heavy fractions from oil, dehydration of alcohols, metathesis, oxidations, and isomerization of olefins [17]. The supports used with these catalysts are A1 2 O 3 and TiO 2 [18,19], SiO 2 [20], MgO [21], activated carbon [22], polymers [8,23], and MgF 2 [24].…”

Section: Introductionmentioning

confidence: 99%

Highly efficient epoxidation of alkenes with hydrogen peroxide catalyzed by tungsten hexacarbonyl supported on multi-wall carbon nanotubes

Nooraeipour

Tangestaninejad

Mirkhani

et al. 2011

Transition Met Chem

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The preparation, characterization, and catalytic activity of W(CO) 6 supported on multi-wall carbon nanotubes modified with 4-aminopyridine is reported. The catalyst, [W(CO) 5 @Apy-MWCNT], was characterized by physico-chemical and spectroscopic methods and found to be an efficient heterogeneous catalyst for green epoxidation of alkenes with hydrogen peroxide in MeCN solvent. The catalyst showed good stability and reusability properties in the epoxidation reactions.

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Effect of F and Mg on the Dispersion of Mo/Al2O3 and W/Al2O3

Cited by 19 publications

References 0 publications

Dispersion and Coverage of Cr/Al2O3 Catalysts

Dispersion and Coverage of Cr/Al2O3 Catalysts

Effect of Boron Addition on the State and Dispersion of Mo Supported on Alumina

Highly efficient epoxidation of alkenes with hydrogen peroxide catalyzed by tungsten hexacarbonyl supported on multi-wall carbon nanotubes

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