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Elucidation by computer simulations of the CUS regeneration mechanism during HDS over MoS[sub 2] in combination with [sup 35]S experiments.
- Source :
-
Research on Chemical Intermediates . 2003, Vol. 29 Issue 6, p589-607. 19p. - Publication Year :
- 2003
-
Abstract
- The first part of this paper is a short review of the [sup 35]S radioactive tracer methods developed in recent years. Then, the experimental results obtained so far on Mo/Al[sub 2]O[sub 3] catalysts are compared with computer simulation results recently claimed in order to elucidate the coordinatively unsaturated site (CUS) creation/replenishment/ regeneration mechanism over MoS[sub 2] crystallites. The computer simulations allowed us to pre-select thermodynamically acceptable mechanisms among a set of suggested ones. Then, by comparison of the calculated activation energies with the [sup 35]S experiments results we could further validate the most probable mechanism. This mechanism involved the dissociative adsorption of an H[sub 2] molecule on the metallic edge of a MoS[sub 2] crystallite surface with further creation of a CUS by release of one H[sub 2]S molecule in the gas phase. Both laboratory and computer simulated experiments permitted to calculate the activation energy for the H2S liberation reaction. In both cases, this energy was about 10- 12 kcal/mol, confirming the accuracy of the proposed mechanism. Moreover, the calculated activation energy of the rate-limiting step for the creation of one CUS by the proposed mechanism was about 23 kcal/mol, which was also in good agreement with the experimental activation energy of the dibenzothiophene (DBT) hydrodesulphurisation (HDS) reaction (typically about 20- 22 kcal/mol). This correlation indicated that the DBT HDS reaction rate might be intrinsically governed by the CUS formation/replenishment process, i.e. that the vacancy formation process is a crucial parameter in the global HDS reaction mechanism. Nevertheless, in the case of the 4,6-dimethyl DBT (4,6-DMDBT) HDS reaction, the experimental activation energy is higher (approx. 30 kcal/mol), confirming that external parameters induced by the 4,6-DMDBT-specific properties themselves are likely to play an important role in the reaction process, in addition to the ones intrinsic to the catalytic phase. [ABSTRACT FROM AUTHOR]
- Subjects :
- *CHEMICAL reactions
*HYDROGEN
*MOLECULES
*MOLYBDENUM
*OXIDES
*COMPUTER simulation
Subjects
Details
- Language :
- English
- ISSN :
- 09226168
- Volume :
- 29
- Issue :
- 6
- Database :
- Academic Search Index
- Journal :
- Research on Chemical Intermediates
- Publication Type :
- Academic Journal
- Accession number :
- 11343225
- Full Text :
- https://doi.org/10.1163/156856703322539636