Jacques Joffre

Selective dialkylation of naphthalene with hindered alkylating agents over HM and HY zeolites under liquid phase conditions

Abstract Liquid-phase alkylation of naphthalene with cyclohexyl derivatives as alkylating agents has been studied over HM and HY zeolites. The reaction can be carried out efficiently over HY zeolites, for which high conversions and good selectivities in 2,6- and 2,7-dicyclohexyl naphthalenes (DCN) are obtained after very short reaction times. The ratio 2,6-DCN/2,7-DCN is near to 1, as in the case of the isopropylation reaction over the same catalysts. Such a result is in agreement with the values of critical diameters of 2,6- and 2,7-dicyclohexyl and diisopropyl naphthalenes, calculated by molecular mechanics. The 2,6-dicyclohexyl-naphthalene is a crystalline compound which is easily separated from the reaction mixture by crystallization, which constitutes an interesting advantage of cyclohexylation in comparison with isopropylation.

Tert-butylation of toluene over zeolite catalysts

Three large-pore zeolites (H-MOR, H-Y and H-BEA) were studied as catalysts in the liquid-phase tert-butylation of toluene by tert-butanol. The catalytic activity and para-selectivity of zeolite catalysts and the main secondary reactions (isomerization of 4-tert-butyltoluene and its dealkylation) are discussed. The most active zeolite catalysts for the studied reaction were H-MOR (17.5) and H-BEA (12.5) zeolites. The most para-selective were mordenite zeolites with maximum selectivity to desired 4-tert-butyltoluene near 90%, which was supported by molecular modelling. Tert-butylation of toluene over zeolite catalysts can be an ecofriendly process for obtaining 4-tert-butyltoluene which is intermediate product for fine chemicals.

A quantum-chemical study of site modeling for the adsorption and desulfurization of thiophene

Abstract The active site of MoS 2 is modeled to obtain information on the initial steps of thiophene hydrodesulfurization. The model consists of a MoS 3 H + 3 cluster with three anionic vacancies. Quantum-chemical extended Huckel theory studies were carried out on the adsorption and desulfurization steps for different geometries of the complex between the site and thiophene. The calculations show that the vertical adsorption of the S atom of thiophene on the Mo atom of the model catalyst is favored over any horizontal adsorption. In every case adsorption weakens the CS thiophene bonds. Desulfurization by straight rupture of these bonds to form a C 4 H 4 radical leads to a moderate activation barrier. This theoretical approach to the problem, initially based on available data, leads to conclusions which are in good agreement with experimental results.

Diels-Alder cycloaddition reaction between dihydropyran and acrolein over various H-form zeolites

Abstract The Diels-Alder cycloaddition reaction of dihydropyran with acrolein was performed in the presence of various H-form zeolites such as H-Faujasites, H-β, H-Mordenites which differ both in their shape selective as well as their acidic properties. The activity of the different catalysts was determined and the reaction products were identified. High yields in cycloadduct were obtained over dealuminated HY (Si/Al=15) and Hβ (Si/Al=25) compared to HM (Si/Al=10). These results were accounted for in terms of acidity, shape selectivity and microporosity vs mesoporosity properties. The activity and the regioselectivity were then discussed in terms of frontier orbital interactions on the basis of MNDO calculations for thermal and catalyzed reactions by complexing the diene and the dienophile with Bronsted and Lewis acidic sites. From these calculations, Bronsted acidic sites appeared to be more efficient than Lewis acidic sites to achieve Diels-Alder reactions.

Catalytic properties of nickel molybdenum sulphides supported on nickel and magnesium aluminates

Abstract The hydrodesulphurization (HDS) of thiophene at atmospheric pressure, hydrodenitrogenation (HDN) of 2,6 diethylaniline (DEA) and of 1,2,3,4 tetrahydroquinoline (THQ) at 70 atm in a dynamic flow microreactor - these molecules being present alone or mixed in the feed - and finally HDN of mixtures of quinoline (Q) at 70 atm or of phenanthridine (Ph) at 140 atm with DEA in a batch reactor were the test reactions used to compare the performances of (Ni)MoS catalysts supported on MgAl 2 O 4 and NiAl 2 O 4 with a classical NiMoS/γ Al 2 O 3 commercial catalyst. Some of the catalysts supported on NiAl 2 O 4 appeared to be superior to the commercial one, whereas those supported on MgAl 2 O 4 were found to be less active. HDS of thiophene, as well as the amount of carbon monoxide adsorbed at 0°C by sulphided catalysts permitted the prediction of the order of HDN activity of the catalysts for the conversion of some nitrogen-containing molecules. A strong inhibiting effect of molecules like Q, THQ or Ph (or some of their products formed during the process) on the HDN of DEA has been found and attributed to the competitive adsorption of these molecules on the supported active phase.

16-P-08 - Computational analysis of the shape-selective isopropylation of biphenyl over large pore zeolites

Publisher Summary This chapter presents the computational analysis of molecular dimensions and diffusion energies of the various mono- and di-isopropylbiphenyl isomers, using molecular mechanics and quantum mechanics methods. The 4,4′-diisopropylbiphenyl has the lowest kinetic diameter and diffusion energy, which is in agreement with the experimental results regarding the high para-selectivity observed in the isopropylation reaction of biphenyl over H-mordenites. The calculations in the biphenyl series show that modeling analysis appears to be useful for understanding the experimental results and confirms other computational results in the field of the shape-selective alkylation of naphthalene.

25-P-07-Shape-selective tert-butylation of biphenyl over HM, HY and Hβ zeolites in the liquid phase

Publisher Summary This chapter discusses the alkylation of biphenyl with tert-butanol that has been carried out over different zeolites under liquid phase conditions. HM (17.5) and HY (15) zeolites have been found to be the most active, with a maximum biphenyl conversion near 60%. Dealuminated mordenite HM (17.5) leads to very high selectivities to 4-( tert -butyl)biphenyl (TBB) (99%) and 4,4’-di( tert -butyl)biphenyl (DTBB) (96%). Selectivity to linear 4-TBB and 4,4’-DTBB depends on the diffusional possibilities of relatively voluminous mono tert -butyl- and di-( tert -butyl)biphenyl isomers from the zeolite pores. The most suitable temperature has been found to be 160°C. An increase in temperature leads to a significant decrease of selectivities to the desired products as a result of secondary reactions.