Adsorption of cyclohexadiene, cyclohexene and cyclohexane on Pt(1 1 1) |
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Authors: | Mark Saeys M-F Reyniers M Neurock |
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Institution: | a Laboratorium voor Petrochemische Techniek, Ghent University, Krijgslaan 281(S5), B-9000 Gent, Belgium b Department of Chemical Engineering, University of Virginia, 102 Engineers’ Way, Charlottesville, VA 22904-4741, United States c Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576, Singapore |
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Abstract: | The adsorption of 1,3-cyclohexadiene, 1,4-cyclohexadiene, cyclohexene and cyclohexane on Pt(1 1 1) was studied using ab initio density functional theory. For 1,3-cyclohexadiene three adsorption modes were distinguished: bridge 1,2-di-σ/3,4-π, hollow 1,4-di-σ/2,3-π and bridge 1,4-di-σ/2,3-π with adsorption energies of −155, −147 and −75 kJ/mol, respectively. Three stable adsorption modes were also identified for 1,4-cyclohexadiene: bridge quadra-σ, hollow di-σ/π and bridge di-π with adsorption energies of −146 kJ/mol, −142 kJ/mol and −88 kJ/mol, respectively. Cyclohexene was found to adsorb in six modes: 4 di-σ and 2 π-adsorption modes. The preferred configuration was found to be boat di-σ with an adsorption energy of −81 kJ/mol. The three other di-σ adsorption modes have comparable adsorption energies, ranging from −64 to −69 kJ/mol. Molecular strain and C Pt bonding energies are used to elucidate stability trends. Cyclohexane is found to adsorb only at the hollow site whereby the axial hydrogen atoms are positioned over surface Pt-atoms with an adsorption energy of −37 kJ/mol. The calculations correctly predict the weakening of the axial C H bonds and provide a possible explanation for the large shift in the vibrational frequencies. |
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Keywords: | Density functional calculations Chemisorption Catalysis Hydrocarbons |
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