Annie Finiels

Zeolite Y Crystals with Trimodal Porosity as Ideal Hydrocracking Catalysts

Effektive Poren: Zeolith-Y-Kristalle mit Mikroporen (ca. 1 nm), kleinen (ca. 3 nm) und grosen Mesoporen (ca. 30 nm) wurden aus zuvor mit Dampf und Saure behandeltem Material durch Auslaugen mit Base erhalten. Die Zeolith-Y-Kristalle mit trimodaler Porositat (siehe elektronentomographische Aufnahme) zeigen beim Hydrocracking eine nahezu ideale Selektivitat fur und erhohte Ausbeuten an Kerosin und Diesel.

Nickel-based solid catalysts for ethylene oligomerization – a review

Ni-based inorganic porous materials are the most important heterogeneous catalysts for ethylene oligomerization. In spite of extensive research carried out in previous decades on these catalysts, only a few aspects have been reviewed in the literature. We illustrate here the main properties of these materials and their catalytic performances in oligomerization reactions performed under mild conditions. The major groups of oligomerization catalysts, including NiO on various carriers and Ni-exchanged zeolites, sulfated-alumina or silica–alumina, are described in the first part of this review. The nature of the active sites and their role in the ethylene oligomerization process are pointed out. In the second part, the literature dealing with the catalyst performances under various reaction parameters is reviewed. The influence of catalyst properties (in particular the catalyst pore size) and reaction conditions (i.e. temperature and pressure) on the productivity and the product distribution in oligomerization is methodically discussed. The excellent performances of Ni-exchanged ordered mesoporous silica–alumina, which are the best oligomerization catalysts known today, are carefully emphasized.

The effect of structure on reactivity in zeolite catalyzed acylation of aromatic compounds: A ϱ - σ+ relationship

Abstract A ϱ - σ+ relationship for zeolite catalyzed acylation of aromatic compounds by car☐ylic acids was studied. The large negative value of ϱ indicates that the mechanism is an electrophilic substitution in which the transition state resembles the Wheland intermediate. Obedience to the Brown selectivity relationship is also reported.

Acetylation of dimethoxybenzenes with acetic anhydride in the presence of acidic zeolites

Abstract The acetylation of 1,2-, 1,3- and 1,4-dimethoxybenzenes with acetic anhydride has been investigated in the liquid phase (chlorobenzene as solvent) over the H-forms of various zeolites. H-Y and H-Beta have been shown to be efficient catalysts in such a reaction, and led to the selective formation of the corresponding dimethoxyacetophenones. 1,2-Dimethoxybenzene (veratrole) has been chosen as a model substrate for the kinetic study of the reaction over H-Y (Si/Al=15) as catalyst. The reaction proceeds through a modified Eley–Rideal type mechanism, wherein the chemisorbed acetic anhydride generates the electrophilic acylium ion, which then reacts with veratrole in the liquid phase. The competitive adsorption of both reactants and products has been evidenced. It has been especially shown that the deactivation of the catalyst was due to a partial adsorption on the active sites of the catalyst of either the reaction product (3′,4′-dimethoxyacetophenone in the case of 1,2-dimethoxybenzene as the substrate) or/and of acetic acid formed in the reaction.

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.

Benzoylation of 1,2-dimethoxybenzene with benzoic anhydride and substituted benzoyl chlorides over large pore zeolites

Abstract The benzoylation of 1,2-dimethoxybenzene (veratrole) with benzoic anhydride and substituted benzoyl chlorides has been investigated in the liquid phase (chlorobenzene as solvent) over the H-forms of various zeolites. H-Y and H-BEA have been shown to be efficient catalysts in such a reaction, and led to the selective formation of the corresponding dimethoxybenzophenones. The effect of various experimental parameters on the initial rate of the reaction of veratrole with benzoic anhydride over H-Y zeolite has been studied, leading to propose a suitable mechanism based on the difference of adsorptions of the aromatic substrate and the acylating agent. Moreover, the study of the reaction of veratrole with a series of substituted benzoyl chlorides (4-CH3, 4-OCH3, 4-tert-butyl, 4-Cl, 2-Cl and 2-Br benzoyl chlorides, respectively) over the same H-Y zeolite led to conclude that, due to the high reactivity of the aromatic substrate, the electrophilicity of the acylating agent does not play a relevant role under the given heterogeneous conditions.

Distillate-range products from non-oil-based sources by catalytic cascade reactions.

An original two-step process efficiently catalyzed by functionalized mesoporous materials is proposed as a potential route for converting light olefins into long-chain hydrocarbons in the distillate range. In the first step, ethylene can be selectively transformed into C₄ -C₁₀ olefins with an even number of carbon atoms, over nickel-exchanged AlMCM-41, at 150 °C. When the nickel-catalyzed oligomerization was assisted by a second acid-catalyzed step over H-MCM-41, olefins with chains longer than 10 carbon atoms were mainly produced with a productivity of 180 g g⁻¹  h⁻¹.

Role of hydrophobic effects in organic reactions catalysed by zeolites

The role of hydrophobic effects of dealuminated mordenites (Si/Al ratios varying from 7 to 100) has been investigated in two reactions carried out in aqueous/alcoholic media: hydroxymethylation of furfuryl alcohol with aqueous formaldehyde and hydration of phenyl-acetylene in alcohol medium. For both reactions, initial rates and turn over frequencies (TOF) increase in a significant extent with increasing Si/Al ratios. It is shown that the differences thus observed in the TOF values are characteristic of variations in the hydrophobicity of the various dealuminated mordenites, which is confirmed by the corresponding increase of the hydrophobicity parameter h, determined by thermogravimetric analysis of such samples. The hydrophobic character of the zeolites is also discussed in terms of the softness and activity of the corresponding Bronsted acid sites.

Ethylene oligomerization over Ni-containing mesostructured catalysts with MCM-41, MCM-48 and SBA-15 topologies

Nickel ion exchanged MCM-41, MCM-48 and SBA-15 mesostructured materials with a controlled concentration of nickel and acidic sites were prepared, characterized, and successfully used as catalysts in the ethylene oligomerization performed in slurry batch mode (T = 150°C, p = 3.5 MPa). Larger pores or a 3D pore system, as well as an equilibrated balance between acid and nickel ion sites were very favorable for the oligomerization process.

A new selective route to 5-hydroxymethylfurfural from furfural and furfural derivatives over microporous solid acidic catalysts

Abstract Hydroxymethylation of furfural and its 1,3 dithiolane derivative with aqueous formaldehyde was performed in a batch mode in the presence of dealuminated mordenites as catalysts, at 363 K. Starting from furfural, the selectivity to 5-hydroxymethylfurfural is about 30% whatever the catalysts. However, the selectivity can rise up to 50% if an organic co-solvent is used for simultaneous extraction of 5-hydroxymethylfurfural from the aqueous phase. The low selectivity to 5-hydroxymethylfurfural was attributed to the weak reactivity of furfural resulting from the deactivation of the position 5 on the furan ring due to the electron-withdrawing character of the aldehyde group. The direct consequence of this deactivation is that the main reaction is the fast addition of formaldehyde to the aldehyde group of furfural, leading to resins. However, the unfavorable electronic effect can be bypassed by protection of the aldehyde via a thioacetal function with now an electron-donating character. In this way, hydroxymethylation of the 1,3-dithiolane derivative of furfural is easily achieved to yield the corresponding 1,3-dithiolane derivative of 5-hydroxymethylfurfural. The latter aldehyde can then be easily recovered by deprotection of the thioacetal function.