Effect of ultrasonic waves on the activity of chromia‐alumina catalyst

Mathur, Indresh; Bakhshi, Narendra N.; Mathews, J. F.

doi:10.1002/cjce.5450500306

Cited by 9 publications

(5 citation statements)

References 12 publications

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“…16 These result suggests that chlorinated hydrocarbons may be susceptible to degradation under similar conditions. Based upon these and other findings [45][46][47][48] there appears to be a significant potential for chemical alteration when high intensity ultrasonic radiation is used to enhance extraction of adsorbed organic contaminants. The study discussed in this paper begins to address some of the basic questions associated with the use of ultrasonic radiation as a method of treating hazardous wastes by examining its effects in regenerating activated carbon contaminated with phenanthrene.…”

Section: Tiieory Of Tiie Use Of Ultrasonicsmentioning

confidence: 83%

Effect of Ultrasonic Radiation on Contaminants Adsorbed on Activated Carbon

Tumeo¹,

Wheat²

1991

Proceedings of International Arctic Technology Conference

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Section: Tiieory Of Tiie Use Of Ultrasonicsmentioning

confidence: 83%

Effect of Ultrasonic Radiation on Contaminants Adsorbed on Activated Carbon

Tumeo¹,

Wheat²

1991

Proceedings of International Arctic Technology Conference

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“…The EPMA data showed considerable scatter in spite of the polishing, and the smoothed concentration profiles contained oscillations. Such scatter was even more evident in the results of Mathur et al (1972).…”

Section: Introductionmentioning

confidence: 87%

Thermal behavior of shell molybdena‐alumina catalysts

Duncombe

Weller

1985

AIChE Journal

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Heat treatment of "shell" molybdena-alumina catalyst pellets results in macroscopic redistribution of the molybdena. Redistribution is minimal at 625°C but extensive at 750°C. After 6 hours at 750", a sharp maximum is observed in the radial distribution. This is a result of opposing factors: radial diffusion inward from the initial shell, and preferential sintering of the alumina support in the shell region.Loss of molybdena by vaporization is not appreciable at 750°C but is serious at 875°C. A computer program has been developed to convert SEM-EDAX (scanning electron microscopy energydispersive analysis of x-ray) data for unpolished pellet sections to a quantitative, smooth profile of Mo concentration as a function of reduced radial position. Conventional preparation of these catalysts by impregnation of pelleted alumina with ammonium heptamolybdate is known to lead to a peripheral distribution of molybdena ("shell" catalysts). In contrast to supported metal catalysts, which sinter by growth of metal crystallites but without macroscopic redistribution of the metal, molybdena-alumina suffers gross change of the Mo distribution within the pellet and, ultimately, loss of molybdena by vaporization. Superimposed on these effects is a molybdena-catalyzed sintering of the alumina support.The changes in radial distribution of Mo in the pellet can be followed crudely by optical microscopy and more exactly by energydispersive analysis of x-rays (EDAX) with a scanning electron microscope (SEM). Previous work of this kind on other systems (especially chromia-alumina), with use of an electron probe microanalyzer (EPMA), has employed metallurgically polished sections of catalyst pellets; the radial concentration profiles deduced from the EPMA data have shown marked undulations, even after data smoothing procedures. Of interest in the present SEM-EDAX work are the questions: (1) Is it possible to achieve semiquantitative concentration profiles from SEM-EDAX data on rough (unpolished) surfaces of sectioned catalyst pellets? and (2) Do the correction procedures lead to plausible profiles without undulations? If so, it becomes possible to follow the time-temperature history of the Mo redistribution in molybdena-alumina catalysts with some degree of convenience and assurance. CONCLUSIONS AND SIGNIFICANCEThe changes in Mo distribution within a molybdena-alumina pelleted catalyst on heat treatment in air have been followed both by optical microscopy and, in much greater detail, by a scanning electron microscope equipped with an energydispersive x-ray analyzer (SEM-EDAX). Rough, unpolished surfaces of catalyst sections can be satisfactorily analyzed if the SEM-EDAX data are subjected to proper corrections; these include corrections for peak/background (to accommodate rough surfaces), and for x-ray backscattering and electron stopping by the matrix (a, x-ray absorption (A), and fluorescence by nonanalyte elements (F). A computer program has been developed which incorporates these corrections and includes a systematic procedure for ter...

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“…The catalysts studied in this work were prepared by the impregnation of Davison 3.175 X 3.175 mm (x/8 X l/s in.) 77-alumina pellets with chromic acid (Mathur et al, 1972;1975). Five different concentrations of chromic acid in water were used (0.05, 0.50, 2.0, 0196-4321 /80/1219-0216$01.00/0 5.0 and 16.5 M) to produce catalysts with varying chromium contents.…”

Section: Methodsmentioning

confidence: 99%

Chromia-Alumina Catalysts: Chromia Area by Excess Oxygen Measurements

Mathur¹,

Mathews²,

Bakhshi³

1980

Ind. Eng. Chem. Prod. Res. Dev.

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Chromia-alumina catalysts with chromium concentrations varying from 0.90 to 17.5 wt % were prepared by the impregnation of 77-alumina with chromic acid. Chromia areas were measured by oxygen chemisorption and by excess oxygen determination. The areas by both methods were equal for the 0.90 wt % chromium catalyst. For higher chromium contents the area determined by excess oxygen measurement is higher than that determined by oxygen chemisorption because of subsurface chromium oxidation. At 17.5 wt % chromium the difference between the two measurements is 15% of the area. It is concluded that excess oxygen can be a good measure of chromia area if subsurface oxidation is not too great.

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Effect of ultrasonic waves on the activity of chromia‐alumina catalyst

Cited by 9 publications

References 12 publications

Effect of Ultrasonic Radiation on Contaminants Adsorbed on Activated Carbon

Effect of Ultrasonic Radiation on Contaminants Adsorbed on Activated Carbon

Thermal behavior of shell molybdena‐alumina catalysts

Chromia-Alumina Catalysts: Chromia Area by Excess Oxygen Measurements

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