A DFT study of the cracking reaction of thiophene activated by zeotype catalysts: role of the basic Lewis site

A DFT study of the cracking reaction of thiophene catalyzed by zeolite is reported. The use of different zeotype catalysts (viz. acidic, metal-exchanged and methoxy) has been shown to successfully induce this reaction. It appears that the thiophene cracking reaction is catalyzed by a basic Lewis site and that acid Bronsted site has only a limited influence on the reaction

A DFT study of the cracking reaction of thiophene activated by zeotype catalysts: role of the basic Lewis site

A DFT study of the cracking reaction of thiophene catalyzed by zeolite is reported. The use of different zeotype catalysts (viz. acidic, metal-exchanged and methoxy) has been shown to successfully induce this reaction. It appears that the thiophene cracking reaction is catalyzed by a basic Lewis site and that acid Bronsted site has only a limited influence on the reaction

A DFT study of the cracking reaction of thiophene activated by small zeolitic clusters

A theoretical study of the cracking reaction of thiophene by small zeolitic cluster catalysts is reported. Cluster density functional theory calculations have been performed. It is shown that cracking of thiophene is catalyzed by Lewis basic oxygen atoms. Several active sites are proposed and tested. Moreover, it appears that the use of a partner molecule, strongly adsorbed to the acidic proton, allows for an important decrease of the cracking activation energy barrier. The effect of hydrogenation of thiophene prior to the cracking reaction has been checked. Interestingly, hydrogenation does not affect dramatically the activation energy barrier (-10 kJ/mol). However a large stabilization of the product of the reaction has been found (-40 kJ/mol)

A DFT study of isomerization and transalkylation reactions of aromatic species catalyzed by acidic zeolites

A theoretical study of the isomerization and transalkylation reactions of aromatic species catalyzed by acidic zeolite is reported. Cluster DFT calculations have been performed. All different reported mechanisms of isomerization and transalkylation have been investigated and analyzed. The aromatic species considered in this study are benzene, toluene, and alkylated thiophene and derivatives

A periodic density functional theory study of intermolecular isomerization of toluene and benzene catalyzed by acidic mordenite zeolite: Effect of the zeolite steric constraints

A periodic density functional theory study of the isomerization reactions of toluene and benzene catalyzed by acidic mordenite is reported. Reaction energy diagrams including transition-state energies of disproportionation and direct transalkylation reactions are presented and analyzed. Alternative reaction pathways have been considered. The use of periodic structure calculations allows analysis of steric constraints that occur within zeolite micropores. General rules concerning the influence of steric constraints in relation with reaction mechanism are describe

A periodic density functional theory study of thiophenic derivative cracking catalyzed by mordenite

A periodic density functional theory study of thiophenic derivative cracking catalyzed by proton- or lithium-exchanged mordenite has been performed. The same qualitative trends in activation energies as those described employing the cluster approach method have been obtained. However, the zeolite framework appears not to stabilize the transition state complexes. This is explained by the zwitterionic nature of the thiophenic derivatives cracking transition state complexes. The zeolite framework has more subtle effect on reactivity, as shown by the alteration of the ionic nature of the transition state complex in the case of better fit with the zeolite cavity. Notwithstanding, thiophenic derivative cracking catalyzed by zeolites remains difficult. General comments concerning the use of zeolite catalysts in hydrodesulfurization are made. Predictions on zeolite-based catalysts more suitable to achieve hydrodesulfurization are described

A theoretical study of the solid acid catalyzed desulfurization of thiophene

Desulfurization of thiophene upon contact with acidic zeolite has been studied theoretically using a DFT-based method. Two different mechanisms have been compared: one occurring in the absence of hydrogen and one occurring with the participation of hydrogen. Interestingly, the presence of hydrogen does not affect significantly activation barriers but dramatically changes the overall enthalpy of reaction. A detailed description of the two different mechanisms is given

A periodic density functional theory study of thiophenic derivative cracking catalyzed by mordenite

A periodic density functional theory study of thiophenic derivative cracking catalyzed by proton- or lithium-exchanged mordenite has been performed. The same qualitative trends in activation energies as those described employing the cluster approach method have been obtained. However, the zeolite framework appears not to stabilize the transition state complexes. This is explained by the zwitterionic nature of the thiophenic derivatives cracking transition state complexes. The zeolite framework has more subtle effect on reactivity, as shown by the alteration of the ionic nature of the transition state complex in the case of better fit with the zeolite cavity. Notwithstanding, thiophenic derivative cracking catalyzed by zeolites remains difficult. General comments concerning the use of zeolite catalysts in hydrodesulfurization are made. Predictions on zeolite-based catalysts more suitable to achieve hydrodesulfurization are described