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Title: Fundamentals of methanol synthesis on metal carbide based catalysts: activation of CO2 and H2
Author: Posada Pérez, Sergio
Viñes Solana, Francesc
Rodriguez, J. A.
Illas i Riera, Francesc
Keywords: Teoria del funcional de densitat
Density functionals
Issue Date: 18-Dec-2014
Publisher: Springer Verlag
Abstract: CO2 hydrogenation to methanol and other alcohols constitutes an appealing route to recycle the large amount accumulated in the atmosphere through fossil-derived fuels burning. However, CO2 high chemical stability makes the overall process difficult and appropriate catalysts are needed. Transition metal carbides, either as active phase or as a support for noble metal clusters, have been shown to be able to activate CO2. Here, the mechanism involved in the decomposition of H2 and CO2 on many early transition metal carbides (TMC) surfaces is analyzed with the help of density functional theory (DFT) based calculations complemented by key experiments. Results show that H2 dissociation on VC and δ-MoC is unlikely, that TiC and ZrC are more reactive leading to an exothermic but activated process and that the C:Mo ratio is determinant factor since H2 dissociation on β-Mo2C(001) surface is even more exothermic. The DFT based calculations also show that CO2 adsorption on TMC results in an activated species with TMC→CO2 charge transfer, C-O bond elongations and OCO bending. Supporting Cu4 and Au4 clusters on TMC(001) surfaces leads to more active catalysts due to the induced charge polarization. For H2 dissociation, TiC appears to be the best support, enhancing H2 both thermodynamics and kinetics. CO2 is strongly adsorbed on supported Cu4 and Au4 clusters, and the adsorption energy strength correlates with the methanol formation rate: Cu4/TiC(001) > Au4/TiC(001) > Cu/ZnO(001) >> Cu(111), thus providing potential alternative catalysts for methanol synthesis, in principle dozens of times better than commercial Cu/ZnO based catalysts.
Note: Versió postprint del document publicat a:
It is part of: Topics in Catalysis, 2014, vol. 58, num. 2-3, p. 159-173
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ISSN: 1022-5528
Appears in Collections:Articles publicats en revistes (Ciència dels Materials i Química Física)

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