ChemInform Abstract: The Adsorption of Metal Oxyanions on Alumina

Mulcahy, Francis M.; Fay, Martin J.; Proctor, Andrew; Houalla, Marwan; Hercules, David M.

doi:10.1002/chin.199040014

Cited by 8 publications

(16 citation statements)

References 1 publication

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“…0.70 mg Mo/m2 (26, 29.38, 46), while on catalysts prepared by the equilibrium absorption method, maximum Mo adsorption levels between 0.30 and 0.60 mg Mo/m2 are observed (20,23,27). This apparent discrepancy can result from differences in contact times and mostly from much higher AHM concentrations (by a factor of 30 to 200) in the former method.…”

Section: Figmentioning

confidence: 69%

“…It is seen that at a pH close to the IEP there are still sites available for molybdate adsorption. Recent results obtained by several groups showed that while electrostatic interactions between molybdate and the alumina surface may occur, other factors such as acid-base or condensation reactions influence molybdate adsorption (22,23). The true AHM adsorption isotherm under near-neutral conditions, consists of two branches (Figure 4) (22).…”

Section: Physlcocherntcal Properties Of Alumhamentioning

confidence: 98%

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A Review of Support Effects on the Activity and Selectivity of Hydrotreating Catalysts

Luck¹

1991

Bulletin des Soc Chimique

119

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INTRODUCTIONThe hydroprocessing technology was first developed in Germany by BASF in the 1920s, for hydrogenation of brown coal tar in one step into gasoline without coke formation. It was found that cobalt, molybdenum and tungsten sulfides were especially active catalysts (1). Later a low-temperature " T H " process was developed for the same reaction, using activated alumina supported catalysts containing either 10% Mo03-3% NiO or 27% WS23% NiS. The very same compositions are still used today in many commercial hydrotreating (HDT) catalysts! During the development of these catalysts, the effect of various oxide supports on the cracking of gas oil was studied. The following order of cracking activity was found :

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Section: Figmentioning

confidence: 69%

Section: Physlcocherntcal Properties Of Alumhamentioning

confidence: 98%

A Review of Support Effects on the Activity and Selectivity of Hydrotreating Catalysts

Luck¹

1991

Bulletin des Soc Chimique

119

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“…An electrostatic model has often been used to explain the adsorption of ions on metal oxide supports. 43,44,[50][51][52][53][54][55] This model considers the charge of the ion, the pH of impregnating solution, and the PZC of support to be the primary factors affecting adsorption. Figure 6 shows the chromate species present at various pH regions (A) and the proposed adsorption scheme (B).43 Cr in solution is primarily present as Cr2072-at pH < 5 and as C1-04~-at pH > 8.45 At a pH below the PZC of the support (7.2), the support acquires a net positive charge, which in turn attracts anions from bulk solution to the support-solution interface where anions become electrostatically bound.…”

Section: Adsorption Of Cr Onmentioning

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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“…A strong interaction between Mo ions and surface hydroxyl groups on alumina led to the formation of the complex of Al-O-Mo oxyanions [30,31]. On carbon-based support, the adsorption process becomes more complex as various oxygen groups may get involved.…”

Section: Mo Oxyanion Species Adsorption On Different Mwcnts During Immentioning

confidence: 98%

“…The behaviors of Mo ion adsorption on alumina, titania and carbon supports had been extensively investigated [30][31][32][33]. A strong interaction between Mo ions and surface hydroxyl groups on alumina led to the formation of the complex of Al-O-Mo oxyanions [30,31].…”

Section: Mo Oxyanion Species Adsorption On Different Mwcnts During Immentioning

confidence: 99%

Fabrication of molybdenum carbide catalysts over multi-walled carbon nanotubes by carbothermal hydrogen reduction

Chen

et al. 2007

Catal Lett

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Molybdenum carbide catalysts were successfully prepared using original multi-walled carbon nanotubes (MWCNTs) and nitric acid treated ones as support and carbon source by carbothermal hydrogen reduction from 580°C to 700°C. Ammonium heptamolybdate was used as Mo precursor and the effects of oxygen functional groups on MWCNT surface were investigated. TEM and XRD results show that oxygen functional groups act as anchor sites to interact with the Mo oxyanion species during impregnation, which promote the dispersion of Mo precursors. Due to the relatively strong interaction between Mo precursors and MWCNTs, the agglomeration of Mo carbide particles is prevented even when the treatment temperature is as high as 700°C. Moreover, as the support, modified MWCNTs exhibit better thermal resistances. The temperature (580°C) for Mo 2 C formation over MWCNTs is much lower than that over conventional carbon supports using carbothermal hydrogen reduction. The methylcyclohexane dehydrogenation was used as a probe reaction to test the catalytic performances of the Mo 2 C catalysts obtained.

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ChemInform Abstract: The Adsorption of Metal Oxyanions on Alumina

Abstract: (perrhenate, permanganate, molybdate, tungstate, chromate) is studied at pH 4.5.

Cited by 8 publications

References 1 publication

A Review of Support Effects on the Activity and Selectivity of Hydrotreating Catalysts

A Review of Support Effects on the Activity and Selectivity of Hydrotreating Catalysts

Dispersion and Coverage of Cr/Al2O3 Catalysts

Fabrication of molybdenum carbide catalysts over multi-walled carbon nanotubes by carbothermal hydrogen reduction

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