Ferenc Lónyi

On the interpretation of the NH3-TPD patterns of H-ZSM-5 and H-mordenite

Abstract The species obtained from adsorption of ammonia over zeolite H-ZSM-5 and H-mordenite were characterized by temperature-programmed desorption (NH 3 -TPD) and infrared spectroscopy (IR). At ammonia loadings of NH 3 /Al>1, the IR spectra indicated the formation of NH 4 + · n NH 3 associations, where n ⩾1. At loadings of NH 3 /Al 4 + ions and Lewis-bound NH 3 were recorded. The decomposition of the NH 4 + ions and desorption of NH 3 from strong Lewis acid sites gave rise to TPD peaks above about 673 K. The peaks at temperatures lower than about 673 K were assigned to ammonia released from protonated NH 3 associations.

A study of the acidic and catalytic properties of pure and sulfated zirconia–titania and zirconia–silica mixed oxides

Protonated pyridine (PyH+) was not found on ZrO2 (Z) or ZrO2–TiO2 (ZT), but was detected on sulfated oxides (Z‐S, ZT‐S) by IR spectroscopy. In contrast, ZrO2–SiO2 samples containing about 30–80 mol% ZrO2 showed Brønsted acidity both in non‐sulfated (ZS) and sulfated (ZS‐S) forms. The total acidity was determined by NH3‐TPD. Introduction of sulfate ions increased the site‐specific catalytic activity (TOF) in the conversion of cyclopropane or n‐hexane. The effect of sulfate ions was more significant on samples rich in zirconia. Results suggest that Zr is homogeneously distributed in ZS samples rich in silica. Zirconia‐bound dimeric sulfate, generating strong acidity, could not be formed in these preparations due to the absence of fairly large ZrO2 domains.

Para-selectivity of toluene ethylation over ZSM-5 catalysts

The title reaction was studied around 400 °C in an excess of toluene at atmospheric pressure when hydrogen was present in order to avoid coke formation. Space time, reaction temperature, catalyst pretreatment temperature, catalyst aging and poisoning with organic bases, and introduction of inorganic additives containing phosphorus and/or magnesium into the catalyst were varied. The change of yields and selectivities points to the primary formation of p-ethyltoluene in the course of ethylene addition. Secondary reactions are the isomerization to m-ethyltoluene and hydrodeethylation of ethyltoluenes. Disproportionation of toluene is a simultaneous transformation. The para-selectivity increased when the side reactions were suppressed by the reduction of Bronsted acidity. The effects of diffusion control can be disregarded.

New approaches to prepare supported Sn-Pt bimetallic catalysts

General principles of modification of supported Pt catalysts with tin tetraalkyls are summarized and a new approach to prepare supported Sn−Pt catalysts is described. The new approach leads to the formation of Multilayered Organometallic Complexes (MLOC) anchored onto supported platinum. The formed MLOC can be decomposed either in reductive or oxidative atmosphere with the formation of new type of supported Sn−Pt catalysts with high Sn/Pts ratios. The decomposition in a reductive atmosphere leads to the formation of alloy-type bimetallic phases, while the decomposition in the presence of oxygen provides Lewis-acid type surface species anchored to supported platinum.

The effect of adamantane addition on the conversion of n-heptane over H- and Pt/H-zeolites

H- and Pt/H-forms of zeolites Y and mordenite were studied in atmospheric n-heptane (n-C7) hydroconversion at 423–443 K. Adamantane (Ad) additive was found to increase the isomerization and suppress the cracking activity of the H-zeolites. It had minor or no influence on the hydroconversion activity of the Pt/H-forms. Species obtained from Ad adsorbed on zeolites were examined by IR spectroscopy. The Ad-saturated samples (Ad/H-zeolites) were boiled with n-C7 and the liquid phase was analyzed by GC–MS. Results suggested that Ad was activated over the H-zeolites for further reactions via protolysis of its C–H bonds. The Ad and the formed adamantyl carbenium ions (Ad + ) participated in hydride transfer processes. In these processes, the Ad remained unconverted and acted as co-catalyst increasing n-C7 isomerization selectivity. Results suggested that under conditions of n-C7 hydroconversion no or minor amount of Ad + was generated on the Pt/H-zeolite catalysts. Over strong acid mordenite bulky carbocations and Ad compounds were rapidly formed contributing to the decay of the activity in n-C7 conversion.

Influence of the Tortuosity and the Acidity of H-ZSM-5 on the Selectivities in Ethylation of Toluene

The primary product of title reaction is p-ethyltoluene, which isomerizes to m- and very slowly to o-ethyltoluene. The yields of ethyltoluenes are decreased by hydrodeethylation. Disproportionate accompanies the above transformations. The change of yields and selectivities of p-ethyltoluene with the spacetime, the reaction temperature (350-500 * C), catalyst pretreatment temperature (400-700 * C), time on flow and with the amount of adsorbed pyridine or 2,6-lutidine are discussed on the basis of kinetical considerations. Inclusions of oxides of phosphorus and/or magnesium suppress the side reactions by decreasing the concentration of the Bronsted acid sites.

Alkylation of toluene with ethylene on HZSM-5

Alkylation of toluene with ethylene on unmodified large-crystal HZSM-5 has been studied in a flow system at 673 K, atmospheric pressure. The yield of ethyltoluenes increased and that of benzene and xylenes decreased with time on stream. This change in yields was accelerated by increasing the ethylene content of feed and by pretreating the catalyst with ethylene. Selectivity for toluene ethylation increase with increasing space velocity.AbstractАлкилирование толуола этиленом на немоифицированном цеолите HZSM-5 с крупньми кристаллами исследовали в проточной системе при 673 К и атмосферном давлении. Вы-ход этилтолуолов увеличивэется, выход бензола и ксилола уменьшается со временем на струе. Это изменение в выхо-дах было усилено увеличением содержания этилена на пи-тании и предварительной обработкой катализатора этиле-ном. Селективность этилирования толуола увеличивается с увеличением объемной скорости.

Preparation of new type of supported Sn-Pt bimetallic catalysts containing Lewis acid sites anchored to the platinum

Abstract Methods of Surface Organometallic Chemistry (SOC) were used to prepare new type of supported Sn-Pt catalysts. In the new approach the focus was laid on the stabilization of tin in the form of SnOxanchored directly to the platinum. The new surface species have been characterized by different methods. The results indicate the platinum nano-clusters are decorated by SnOx surface entities with Lewis-acid character. The new Sn-Pt/A12O3 catalysts were tested in hydrocarbon reactions above 500 °C. Due to the presence of new acid sites in the atomic closeness to the platinum the new Sn-Pt catalysts showed decreased aromatization and increased isomerization selectivities.

The influence of adamantane on the reaction ofn-heptane over H-Y, H-β and H-mordenite zeolites

The effect of adamantane (Ad) on the activity and selectivity of acidic zeolites Y, β and mordenite (M) in the isomerization and cracking ofn-heptane (C7) in He at 443 K was studied.Ad was found to promote the isomerization of C7. TheAd uptake of the zeolites, and the IR spectra obtained from the zeolite-boundAd were determined. It was found thatAd did not remain completely unconverted under the conditions of the C7 reaction. The activity of the catalysts in the conversion ofAd increased in the sequence of H-Y<H-β<H-M. Existing data suggest that a fraction of theAd, responsible for the cocatalytic effect, can participate in hydride transfer processes and remain unconverted, while another fraction, depending on catalyst acidity, is converted to dimer and oligomers.

The hydroconversion of n-heptane over reduced and oxidized Pt/H-zeolite catalysts

The low-temperature (<443 K) hydroconversion of n-heptane was studied over Pt-containing HY, H-mordenite and Hβ zeolites under atmospheric pressure. Activities and selectivities were found to be different for samples pre-oxidized in O 2 or pre-reduced in H 2 at 773 K. H 2 -TPR results suggest that the high-silica content Pt,H-zeolites contain (Pt 2 O) 2+ species which are reduced to Pt 0 in two consecutive steps. When sample was evacuated, the OH-groups of the zeolite oxidized most of the Pt 0 atoms close to Pt 2+ . The oxidation state of the Pt atoms was characterized also by IR spectroscopy using CO as a probe. It was shown that in contact with C 7 /H 2 mixture, most Pt species did not maintain its original oxidized (Pt 2+ ) or reduced (Pt 0 ) state. Data suggest that pre-oxidized and pre-reduced catalysts contain Pt (1+δ)+ and Pt δ+ species, respectively, under reaction conditions. It is suggested that the reaction chain of n-C 7 conversion is initiated and terminated in a redox type process over Pt (1+δ)+ while in the presence of Pt δ+ the conventional bifunctional mechanism may prevail.