Vasile Hulea

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.

Modified SBA-15 mesoporous silica for heavy metal ions remediation

N-Propylsalicylaldimino-functionalized SBA-15 mesoporous silica was prepared, characterized and used as an adsorbent for heavy metal ions. The organic-inorganic hybrid material was obtained using successive grafting procedures of SBA-15 silica with 3-aminopropyl-triethoxysilane and salicylaldehyde, respectively. For comparison an amorphous silica gel was functionalized using the same procedure. The structure and physicochemical properties of the materials were characterized by means of elemental analysis, X-ray diffraction (XRD), nitrogen adsorption-desorption, thermogravimetric analysis and FTIR spectroscopy. The organic functional groups were successfully grafted on the SBA-15 surfaces and the ordering of the support was not affected by the chemical modification. The behavior of the grafted solids for the adsorption of heavy metals ions from aqueous solutions was investigated. The hybrid materials showed high adsorption capacity and high selectivity for copper ions. Other ions, such as nickel, zinc, and cobalt were adsorbed by the modified SBA-15 material. The adsorbent can be regenerated by acid treatment without altering its properties.

Mesoporous silica functionalized with 1-furoyl thiourea urea for Hg(II) adsorption from aqueous media.

New organic-inorganic hybrid materials were prepared by covalently anchoring 1-furoyl thiourea on mesoporous silica (SBA-15). By means of various characterization techniques (X-ray diffraction, nitrogen adsorption-desorption, thermogravimetric analysis, and FTIR spectroscopy) it has been established that the organic groups were successfully anchored on the SBA-15 surfaces and the ordering of the inorganic support was preserved during the chemical modifications. The hybrid sorbents exhibited good ability to remove Hg(II) from aqueous solution. Thus, at pH 6, the adsorption capacity of mercury ions reached 0.61 mmol g(-1).

Effects of channel structures and acid properties of large-pore zeolites in the liquid-phase tert-butylation of phenol

The liquid-phase alkylation of phenol with tert-butanol in the presence of the H+ form of the zeolites with FAU, BEA, and MOR topologies was investigated. Over dried catalysts, tert-butyl phenyl ether is the main product of alkylation. The accumulation of water molecules on the catalyst surface suppresses this reaction. The irreversible C-alkylation of phenol becomes the main reaction only after an induction period. The catalytic activity and selectivity are controlled by the porous structure and acid properties of the zeolite. The three-dimensional interconnecting pore system of Beta and USY zeolites showed a higher catalytic activity than the monodimensional system of pores of the MOR zeolites. As concerns the catalytic selectivity, the USY zeolites were selective for the ortho-butylation, whereas BEA zeolites were the most efficient catalysts for the para isomer forming.

The aldol condensation of lower aldehydes over MFI zeolites with different acidic properties

Various MFI type zeolites were synthesized taking into account two factors affecting zeolitic acidity “by synthesis”, namely the nature of the substituted heteroelement and the Si/Me3+ ratio. The surface properties with respect to chemical composition and acidity were investigated by temperature-programmed reduction, X-ray photoelectron spectroscopy, temperature-programmed desorption of ammonia, Fourier transform infrared spectroscopy and microcalorimetry. Vapor phase aldol condensation of acetaldehyde and formaldehyde over these catalysts has been carried out, and it has been observed that the structural features of the catalysts do play an important role in controlling conversion and selectivity. A reasonable acidity and activity relationship is established. A mechanism for cross-aldol condensation involving both Bronsted and Lewis acid sites is proposed.

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.

Influence of the acid-base properties of solid catalysts derived from hydrotalcite-like compounds on the condensation of formaldehyde and acetaldehyde

Abstract The vapor-phase aldol condensation of formaldehyde with acetaldehyde was studied using various oxide mixtures obtained in situ from hydrotalcite-like materials as catalysts. All samples exhibited catalytic activity, but the selectivity to both the aldol condensation and the acrolein formation is governed by the balance of acidic and basic properties. The oxides containing Mg and Al or Co and Al showed a high selectivity to aldol condensation (90% at 300°C) as well as to cross-condensation (80% at 300°C). The effects of both the reaction variables (temperature, mole ratio of reagents) and the catalyst variables (nature of cations, nature of anions) were studied.

Synthesis, characterization, and catalytic activity of SAPO-34 obtained with piperidine as templating agent

The synthesis of SAPO-34 in the presence of a new templating agent, namely piperidine, was investigated. The effects of the gel composition, the template concentration, the time and temperature of crystallization on the degree of crystallinity and the purity of the crystalline phase were examined. It was found that SAPO-34 and SAPO-20 are competing phases at high piperidine concentrations, whereas SAPO-34, SAPO-17 and SAPO-35 are the phases present at low template concentrations. Pure SAPO-34 with high crystallinity was obtained at a piperidine/Al2O3 ratio of 1.1:1.0. An optimal synthesis procedure giving an homogeneous SAPO-34 framework without Si islands, consists of heating a gel of composition 1.0Al2O3/0.6P2O5/1.1Pip./0.8SiO2/100H2O at 200 °C for 4–8 days. Such a reproducible procedure gives rise to an acidic catalyst active in the aldol condensation of acetaldehyde with formaldehyde.

Transalkylation of the alkylaromatic hydrocarbons in the presence of ultrastable Y zeolites Transalkylation of toluene with trimethylbenzenes

Abstract The catalytic properties of Y zeolites, dealuminated by steam stabilization, for the transalkylation of toluene with trimethylbenzene were investigated in a pulse microreactor. Some factors influencing this reaction were taken into account: the reaction temperature, the degree of dealumination, the nature of acid sites and the deposited coke. The transalkylation reaction proceeds with good yields on USY. At bulk silica to alumina ratios around 5, a higher activity is observed for the transalkylation of toluene than for the disproportionation of trimethylbenzenes. Both HNaY and USY samples were characterized using FTIR and XPS of chemisorbed pyridine. These techniques allowed to detect the presence of the three kinds of acidic sites: the Bronsted acid sites, the Na+ cations and the extra framework AlO+ species. The effect of these three sites on catalytic results are discussed as well as the reactivity of alkylaromatic hydrocarbons in the reaction network and the reaction mechanism.

Transalkylation of toluene with trimethylbenzenes catalyzed by various AFI catalysts

Substitution of transition metals in the AlPO4-5 framework was found to afford novel heterogeneous catalysts for the transalkylation of toluene (T) with trimethylbenzenes (TMBs). The activity of MeAPO-5 catalysts follows the order of SiAPO>MgAPO>MnAPO>ZnAPO>CoAPO which can be correlated with the acid properties of catalysts. The same correlation was found for MeAPSO-5 catalysts. The strength of acid sites of the catalyst influences the competition among various reactions that occur during the transalkylation process. Generally, the transalkylation and/or disproportionation reactions occur on stronger acid sites, while the isomerization of xylenes (Xs) and TMBs predominate on weaker acid sites.