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PhD position - DFT modeling of biomass upgrading ... (No replies)
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A PhD position is open at University of Lorraine (Nancy, France). Candidates must have a solid background in theoretical chemistry, if possible on periodic systems. Please send CV, recommandation letter of the Master 2 training advisor and master marks to [email protected] (average of master must be higher than 13/20 or 65/100).
Deadline for application : 28 April
The recovery of biomass is one of the pillars of a future economy based on sustainable development. Mastering this recovery is a major societal issue. Fast pyrolysis allows us the generation of bio-oils with a very good yield [1]. The compounds resulting from pyrolysis are diverse, complex and depend on the origin of the biomass. They include furan compounds, organic acids, aldehydes, alcohols, ketones. The high oxygen content of bio-oils makes them viscous, chemically and thermally unstable. Moreover these oils have a lower energy density compared to petroleum fuels.
Conversion of oxygenated compounds is thus mandatory. Various processes are used namely the catalytic condensation C-C to obtain molecules of increasing lengths from compounds of one to six carbon atoms, and deoxygenation. Zeolites are particularly suitable heterogeneous catalysts in such reactions [2]. In particular, HZSM-5 zeolite is known for its high catalytic activity in the conversion of methanol to hydrocarbons [3]. In addition, these materials, thermally stable, have adjustable characteristics (structure, pore size compensating cation charges, acidity) that make them attractive for this application. Mesoporous silicas are also interesting because their use allows us to limit the formation of coke.
In the framework of the thesis, we are going to use density functional theory to elucidate reaction mechanisms and the role of transition metals (Co, Pt, Pd, In, Fe, Ni, Cu, Ag) within the silica and zeolite structures (such as FAU, MOR, or ZSM-5). In principle, these metals may be present in different oxidation states. The adsorption energies of the various compounds involved (furan and other oxygenates, water, CO) will be calculated to evaluate their potential inhibitory effects. The nature of the bonds (covalent or hydrogen bonding) may also be known, as well as the preferential adsorption sites. Regarding the hydrodeoxygenation reactions, our efforts will focus on the study of the reaction mechanism (breaking C-O bond) and the role of the transition metals.
The simulations will be conducted with the periodic code VASP, taking into account the van der Waals interactions by methods implemented in this code [4,5]. Various approaches will be employed to explore the potential energy surface, including geometry optimization without and with constraints [6]. From the ab initio adsorption energies obtained at 0 K, the adsorption enthalpies will be determined by taking into account the chemical potential of gas phase molecules under typical temperatures and pressures of the bio-oil process conditions [7,8]. The exploration of reaction pathways by the static method Nudged Elastic Band (NEB) may be optionally followed by transition path sampling (TPS) simulations taking into account the effects of temperature [9].
Furthermore, the influence of the pore size or nature of the oxide (Fe, Co) on the adsorption energies of molecules and deoxygenation mechanisms will be considered. The different results of these theoretical calculations will face experimental data from the literature or those that will be produced as part of collaborations around this thesis, especially with the LRGP and SRSMC. The comparison of theoretical results with material characterization and catalytic tests of biomass upgrading is expected to propose new formulations optimized for these processes.
References
[1] R. Olcese, M. Bettahar, B. Malaman, J. Ghanbaja, L. Tibavizco, D. Petitjean, A. Dufour, App. Catal. B: Environmental 2013, 129, 528.
[2] C. Liu, T.J. Evans, Lei Cheng, M.R. Nimlos, C. Mukarakate, D.J. Robichaud, R. S. Assary, L. A. Curtiss, J. Phys. Chem. C 119, 24025 (2015).
[3] M. Boronat, C. Martınez-Sanchez, D. Law, A. Corma, J. Am. Chem. Soc. 130, 16316 (2008).
[4] T. Bucko, J. Hafner, S. Lebègue, and J. G. Ángyán, J. Phys. Chem. A 114, 11814 (2010).
[5] T. Bucko, S. Lebègue, J. Hafner, and J. G. Ángyán, Phys. Rev. B 87, 064110 (2013).
[6] T. Bucko, J. Hafner, and J. G. Ángyán, J. Chem. Phys. 122, 124508 (2005).
[7] M. Badawi et al. J. Catal. 282, 155 (2011).
[8] M. Badawi, J.-F. Paul, S. Cristol, and E. Payen, Catal. Comm. 12, 901 (2011).
[9] T. Bucko, L. Benco, J. Hafner, and J. G. Ángyán, J. Catal. 279, 220 (2011).