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- Title
Quantitative measurement of Brönsted acidity by TPD of ammonia on H[PMoO] and its Cs1 salt, in bulk and supported on SBA-15.
- Authors
Sasca, Viorel; Popa, Alexandru; Verdes, Orsina
- Abstract
The method for acidity measurement through temperature programmed desorption (TPD) of ammonia was adapted for simultaneous TG/DTG-DTA analysis of the H[PMoO] and its Cs acid salts, in bulk and supported on SBA-15 support. The desorption of NH consists of the NH and HO release in steps as a result of temperature increase. The last step corresponds to expelling of NH by decomposition of species strong bonded like the ammonium cation, simultaneously with constitutive water, within the 300-600 °C range. The MS analysis showed that the oxidation of ammonia to NO and NO during desorption had occurred simultaneously with reduction of Mo. The reoxidation of samples with air in all cases was done finally. In order to separate the water release (water formed by condensation of hydroxyl groups belonging to SBA-15) from the ammonia desorption for supported samples, a TPD of HO was done for every sample. In the case of pure compounds, the mass loss corresponding to the last stage of desorption (after correction with the mass loss as a result of reduction, equal with the mass increase owing to the reoxidation) gives the amounts of NH and constitutive water, which correspond stoichiometrically with the Brönsted acidity. The subtraction of mass loss for TPD of water from the corrected mass loss for TPD of ammonia and water (because of the mass loss as a result of the reduction) gives the amount of NH corresponding stoichiometrically with the Brönsted acidity. The acidic strength was estimated on the basis of the temperatures for the DTG peaks.
- Subjects
AMMONIA; ACIDITY function; TEMPERATURE effect; CHEMICAL decomposition; GAS absorption &; adsorption; HYDROXYL group
- Publication
Journal of Thermal Analysis & Calorimetry, 2016, Vol 123, Issue 1, p557
- ISSN
1388-6150
- Publication type
Article
- DOI
10.1007/s10973-015-4896-2