Effusion studies of the catalyzed decomposition of magnesium sulfate

Knittel, D. R.; Lau, K. H.; Hildenbrand, D. L.

doi:10.1021/j100452a005

Cited by 22 publications

(4 citation statements)

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“…The composition of the effusate from MgS04 (s) was dependent not only on orifice size, but also on the fractional degree of decomposition (I), making the interpretation of the results somewhat complex. In accord with the results of Pechkovsky (5) on the kinetics of sulfate decompositions, it was also found that some transition metal oxides catalyzed the decomposition process and dramatically increased the observed effusion pressure (2); certain noble metals were later found to show similar catalytic properties. Because of this complex and unexpected behavior, we extended our effusion studies to other metal sulfate systems and redirected our interest to clarification of the decomposition process itself, including the underlying chemical and kinetic factors.…”

supporting

confidence: 85%

“…Both pressures and vapor molecular weights are estimated to be accurate within 5%, as corroborated by frequent checks on laboratory vapor pressure standards. For an effusing vapor containing more than one gaseous species, the molecular weight M is a weight average value defined by the relation (2) where m i and Mi are the mass fraction and molecular weight of the i gaseous species. The magnetic mass spectrometer (6) was used to examine the effusate from the solid sulfates.…”

Section: Methodsmentioning

confidence: 99%

“…Small additions of certain noble metals and p-type semiconducting oxides catalyze reaction (12) adjacent to the decomposition site, promoting full equilibration of reaction (6). The common feature responsible for the catalytic activity of the metals and p-type oxides is apparently their affinity for oxygen chemisorption (2).…”

Section: Disc(jssionmentioning

confidence: 99%

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Mechanistic Aspects of Metal Sulfate Decomposition Processes

Hildenbrand

Lau

Brittain

1990

Materials Chemistry at High Temperatures

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The decomposition reactions of the crystalline sulfate phases Ca50 4 , Mg50 4 , Zn50 4 , ZnO . 2Zn50 4 , Cu50 4 , and CuO . Cu50 4 were studied by the torsion-effusion method with simultaneous mass-loss measurement, and by mass spectrometry. Decomposition pressures and vapor compositions were derived from the results. In all instances, these phases decompose to the corresponding oxides or oxysulfates, plus a gas phase that would be predominantly 50 2 and O 2 at equilibrium. However, most of the processes are severely limited kinetically because of failure to attain 50r 50 2 equilibrium in the gas phase, and direct desorption of 50 3 is frequently observed. Certain noble metals and p-type semiconducting oxides are observed to catalyze the 50r 502 conversion and in some instances lead to dramatic increases in the observed effusion pressure. In a few cases, the catalytic additives convert the gas phase to the equilibrium 50 2 + O2 composition, but have no detectable effect on decomposition pressure, suggesting that the 503 to 502 conversion mayor may not be closely coupled to the initial sulfate ion decomposition step. An attempt is made to correlate this wide range of observed behavior. In addition, decomposition pressures derived by extrapolation to zero orifice size are compared with values calculated from thermochemical data to test the suitability of the effusion method for thermodynamic studies of these materials.

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confidence: 85%

Section: Methodsmentioning

confidence: 99%

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Mechanistic Aspects of Metal Sulfate Decomposition Processes

Hildenbrand

Lau

Brittain

1990

Materials Chemistry at High Temperatures

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“…Another alternative to successfully do that is the use of catalysts that can act through product selectivity. Knittel et al 38 As kinetic data may have an important role in understanding the chemical process, several authors have performed experimental studies on the thermal decomposition of metal sulfates [39][40][41][42] . The thermal decomposition of anhydrous magnesium sulfate was carried out by Brownell 43 at temperatures between 890 and 972 °C applying thermogravimetric analysis with an air atmosphere, reporting apparent activation energy of 343.1 kJ.mol -1 .…”

Section: Introductionmentioning

confidence: 99%

Effect of an Alumina Supported Palladium Catalyst on the Magnesium Sulfate Decomposition Kinetics

et al. 2020

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The sulfur related thermochemical water-splitting cycles are an important class of chemical processes considered for hydrogen production. Recently, the magnesium sulfate thermal decomposition has been reported as a potential unit operation in one of these cycles. Therefore, some interest has been observed in the use of catalysts to lower the activation energy of such reactions. In this context, the present manuscript reports the thermodynamics and kinetics modeling results associated with this reaction system in the presence of a Pd catalyst supported over γ-Al 2 O 3 . The presence of such species is responsible for shifting the decomposition temperature to lower values in at least 100 °C. It was observed that the magnesium content is still oriented towards MgO formation. The obtained results indicate that the Pd/Al 2 O 3 catalyst could be a good alternative in reducing the thermal decomposition temperature as its presence was responsible for diminishing the process activation energy from 368.2 to 258.8 kJ.mol −1 .

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