An Energetics Study of Formation of Some Organic Compounds in Fischer-Tropsch Synthesis by the Method of Unity Bond Index-Quadratic Exponential Potential (UBI-QEP)
Javadi, Nabi | 2012
- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 43533 (03)
- University: Sharif University of Technolog
- Department: Chemistry Science
- Advisor(s): Gobal, Fereydoon
- The purpose of this project is the prediction of the activation barriers and enthalpy for elementary steps in the process of Fischer-Tropsch over the surfaces of Fe, Cu and Fe/Cu alloys catalyst by using of UBI-QEP method aiming at finding prediction of the activity and selectivity on the basis of energy criteria.
UBI-QEP methods is based on conservation of bond index of adsorbed molecules and follow the quadratic exponential potential for energy, calculate the enthalpy and activation barriers of reaction pathways in a heterogeneous catalytic process and select the most desirable path to take.
The elementary steps such as dissociation of CO, hydrogenation of carbidic carbon, C-C chain growth by insertion of versus CO into the metal-alkyl bonds, and chain termination leading to hydrocarbons (alkanes versus -olefins) or oxygenates are discussed in detail. The results show that metallic Fe is necessary to produce the carbidic carbon from CO dissociation but the synthesis of hydrocarbons and oxygenates can effectively proceed on Cu surface. For optimum performance of Fischer-Tropsch synthesis catalyst this conflicting properties must be optimized. In this regard we studied Fe/Cu alloy catalyst. On all the catalyst surfaces, the energetically preferred path for intiation of alkyl chain growth is via insertion of a group into the carbon-metal bond of a group. On all the catalyst surfaces the activation barrier for termination of alkyl chain growth by -elimination of hydrogen is found to be lower than that for -addition of hydrogen and as a consequence olefins are expected to form more readily than paraffins. In the production of ethane the surface in comparison with other catalysts surfaces is more selective. Among the catalysts that we studied, catalyst is more active in the production of ethane. The results for ethanaldehyd synthesis show that surface possesses the highest activity and selectivity.
- Alloy ; Heterogeneous Catalysis ; Fischer-Tropsch Synthesis ; Unity Bond Index-Quadratic Exponential Potential (UBI-QEP)Theory