J. Engelhardt

Alkylation of toluene with methanol on commercial X zeolite in different alkali cation forms

Abstract Catalytic alkylation of toluene with methanol was studied at atmospheric pressure, 698 K, and toluene/methanol = 5 mol/mol in a fixed bed reactor. Catalysts were prepared from the Na form of a commercial, pelleted X-type zeolite by ion exchange with alkali cations. Selectivity for side-chain alkylation increased when alkali hydroxide solution instead of alkali salts was used for ion exchange. High selectivity for ethylbenzene formation was achieved on zeolites in the K or Cs form containing excess alkali hydroxides. The turnover number in side-chain alkylation increases with the decreasing amount of strongly adsorbed pyridine or acetic acid per cation.

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.

Transformation of ethylene over a molybdena-alumina catalyst reduced with hydrogen

Abstract The transformation of ethylene was investigated at 40 °C over a catalyst containing 9.1 wt% MoO 3 on γ-alumina, reduced with hydrogen at 550 °C. A study was made on catalysts without reversibly adsorbed hydrogen, with hydrogen adsorbed at 550 and at 40 °C, and catalysts oxidized with water vapor and oxygen at 550 °C. Polymerization, dimerization of ethylene and its metathesis with 2-butene were observed. The initial rate of the reactions increased upon the effect of hydrogen adsorbed at 40 °C. The initial rate of dimerization increased and that of metathesis decreased due to hydrogen adsorbed at 550 °C, while the rate of polymerization decreased due to hydrogen adsorbed at 550 °C or to hydrogen present in the ethylene. The rate of dimerization was suppressed and the rate of polymerization was increased due to oxidation with water vapor of the reduced catalyst.

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.

Isomerization and secondary metathesis of 2-butenes over a MoO3/Al2O3 catalyst

Transformation of cis- and trans-2-butene at 40°C was investigated over a MoO3/A2O3 catalyst reduced with hydrogen and subjected to different pretreatments. Isomerization is accelerated by hydrogen preadsorbed either at low or high temperatures. The cometathesis of 2-butenes with the 1-butene intermediate, however, is enhanced only by hydrogen preadsorbed at low and suppressed by hydrogen adsorbed at high temperatures.AbstractПревращения цис- и транс-2-бутенов были исследованы при 40°C на катализаторе MoO3/Al2O3, восстановленном водородом и подвергнутом различной предварительной обработке. Изомеризация была ускорена водородом, преадсорбированном либо при низких, либо при высоких темперптурах. Сообмену 2-бутенов с промежуточным 1-бутеном благоприятствует лишь водород, преадсорбированный при низких температурах; водород, преадсорбировпнный при высоких температурах подавляет сообмен.

The activation of CD4 for H/D exchange over H-zeolites

The H/D exchange was studied between CD4 and H-zeolites using pulsed a microcatalytic reactor and MS analysis. Methane-d3 was the only exchange product, while a large fraction of the reactant was retained by the zeolite. The apparent activation energies (Ea) were determined for CHD3 production assuming first-order reaction kinetics. The Ea was close to 80 kJ mol-1 over the H-ZSM-5 and H-mordenite, and about 50 kJ mol-1 over H-beta. Results suggested that, at the low methane loading applied, the H/D exchange was initiated predominantly by heterolytic dissociation of CD4 to CD3δ- and Dδ+ over Lewis acid-Lewis base pair sites.

Metathesis of propylene and transformation of ethylene and 2-butenes over a reduced molybdena—alumina catalyst treated with hydrogen

The metathesis of propylene, the oligomerization and dimerization of ethylene and the isomerization of cis-2-butene were investigated under identical conditions over a MoO3/Al2O3 catalyst reduced with hydrogen. The hydrogen adsorbed in the course of reduction on the catalyst was: (a) removed by evacuation at 550 °C; (b) left over the catalyst; and (c) removed by evacuation at 550 °C and readsorbed at 40 °C. The rate of ethylene oligomerization is influenced only slightly by the hydrogen adsorbed. Dimerization of ethylene and both cis—trans and double bond shift isomerization of cis-2-butene are accelerated by hydrogen adsorbed both at low and at high temperatures. Propylene metathesis, however, is slightly accelerated by hydrogen adsorbed at low temperature but is greatly suppressed by hydrogen adsorbed at high temperature.

H/D exchange between CD4 and the OH-groups of H-zeolites and γ-Al2O3

The H/D exchange between CD4 and OH-groups was studied over zeolite H-ZSM-5, H-mordenite, H-beta and over γ-Al2O3 using the pulsed microcatalytic method. The apparent activation energy of the exchange was found to be independent of the Brönsted acidity of the solid. Results suggested that methane was activated for the reaction by dissociative adsorption over Lewis acid-Lewis base pair sites.

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.