Silica-alumina Catalyst Research Articles

Optimization of temperature-time sequences in reaction-regeneration cycles. Application to the isomerization of cis-butene

The isomerization of cis-butene on a silica-alumina catalyst, in successive and uninterrupted reaction-regeneration cycles, in an isothermal integral fixed-bed reactor, has been simulated and experimentally studied. In the program for simulation, the following kinetic equations were used: the main reaction, deactivation, and reactivation. The simultaneous optimization of reaction and regeneration steps, with the aim of maximizing the apparent production rate of 1-butene or trans-butene, has been studied. The reaction was operated following a temperature-time sequence. The regeneration consisted of the combination of a step of stripping treatment with an inert gas and of a step of coke combustion. The results of simulation have been experimentally proven in automated reaction-regeneration equipment, in which the optimum conditions of both steps have been used.

Deactivation of a silica-alumina catalyst by coke deposition

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDeactivation of a silica-alumina catalyst by coke depositionFelix Garcia-Ochoa and Aurora SantosCite this: Ind. Eng. Chem. Res. 1993, 32, 11, 2626–2632Publication Date (Print):November 1, 1993Publication History Published online1 May 2002Published inissue 1 November 1993https://doi.org/10.1021/ie00023a028RIGHTS & PERMISSIONSArticle Views573Altmetric-Citations10LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (744 KB) Get e-Alerts Get e-Alerts

Investigation of zeolite catalysts for the direct partial oxidation of benzene to phenol

The direct oxidation of benzene to phenol using nitrous oxide as an oxidant has been investigated on a range of zeolite catalysts. It has been found that ZSM-5 type zeolites are excellent catalysts for this reaction, giving up to 99% selectivity at high conversions. Zeolites having the EU-1 type structure had low activities and selectivity, and amorphous acidic silica-alumina catalysts were inactive. The acidity of the various catalysts has been assessed using FT-IR of adsorbed pyridine coupled with thermal desorption, and by temperature-programmed desorption of adsorbed ammonia. It has been found that all the types of catalysts have similar acidities even though they have very different catalytic activities. Elimination of Brønsted acid sites has demonstrated that such sites are a necessary but not sufficient requirement for high activity and selectivity in the benzene-to-phenol reaction. The possible role of iron ions has been investigated and it has been concluded that these are not involved in the catalytic reaction on these particular materials. Possible reaction mechanisms have been considered and the importance of the detailed structure of the zeolite has been examined.

Conversion of methanol and isobutanol to MTBE

Over the resin catalyst Amberlyst 15, and under our reaction conditions, the yield of MTBE (methyl tert-butyl ether), from the reaction of methanol and isobutene, is at a maximum in the temperature range of 40–60 °C. Slightly higher temperatures (70–90°C) are needed when using zeolite H-ZSM-5 as catalyst for the etherification reaction. When isobutanol and methanol are passed over these catalysts at temperatures below 100°C, extremely low conversions ( < 1% by mass) are obtained. Over the resin catalyst and at 121 °C, 3.3% of MTBE + MIBE (methyl isobutyl ether) is obtained where MTBE : MIBE = 1:7.4. Since the initial rate of the etherification reaction has been shown to be first order in the alkene, we investigated the dehydration reaction of isobutanol over H-ZSM-5. It was found that this reaction proceeds at temperatures above 150 °C, indicating that the formation of the butenes from isobutanol proceeds at a higher temperature than the etherification reaction. Furthermore, our results with Amberlyst 15 show that the resin catalyst is unable to catalyze the isobutanol dehydration reaction within its recommended usable temperature range. A two-reactor system was therefore employed to implement the overall catalytic conversion of methanol and isobutanol to MTBE. For the dehydration step we employed a silica-alumina catalyst at 225 °C, since this catalyst exhibits a higher dehydration activity for isobutanol than for methanol, as compared with γ-alumina and H-ZSM-5. The product stream from the dehydration step was then fed to reactor 2 which was loaded with the Amberlyst 15 catalyst maintained at 50 °C. The two-reactor system produced a significantly higher yield of MTBE + MIBE ( 27.8% ), with the MTBE : MIBE ratio being reversed to 11.7:1.

Reaction—regeneration cycles in the isomerization of cis-butene and calculation of the reactivation kinetics of a silica—alumina catalyst

The reactivation kinetics has been determined (activity vs time of stripping and of combustion) as a function of temperature and time of the reaction step, for a silica—alumina catalyst used in the isomerization of cis-butene to 1-butene and trans-butene. A pronounced hysteresis has been found in the relationship of activity—coke-content in the reaction—regeneration cycles, which shows that the elimination of “volatile” coke in the stripping with an inert (previous to combustion of “non-volatile” coke) means an important recuperation of activity. The experimentation involved the analysis of coke in a thermoanalyser and carrying out reaction-regeneration cycles. The evolution of acidity in the reactivation has been analysed. This analysis shows that the very strong acidic sites are the ones that are initially reactivated. The calculated kinetics of reactivation has been used together with the kinetic equations of the main reaction and of deactivation in the simulation of subsequent cycles of reaction—regeneration. The simultaneous optimization of reaction and regeneration steps, with the aim of maximizing the apparent production rate of 1-butene or trans-butene, has been studied. The results of simulation have been experimentally proven in the automated reaction—regeneration equipment, in which the optimum conditions of both the steps have been used.

The strength of one-electron acceptor sites of some X and Y zeolites: An ESR study

In the present study the one-electron acceptor sites of some X and Y zeolites and of a silica—alumina catalyst have been investigated by adsorption of a series of electron donor compounds (anthracene (An), dibenzo- p-dioxin (Dx), phenoxathiin (Phx) and phenothiazine (Pht)) which have different ionization potentials but similar molecular “diameters”. The donor compounds yielded on the studied surfaces adsorbed cation radicals of which the electron spin resonance (ESR) spectra have been measured. For the zeolite samples, using the above donors, the one-electron acceptor sites could be distinguished according to their oxidizing strength. The ratio between the concentrations of the sites measured with Pht and An as donors is proposed as a parameter for evaluating the strength distribution of oxidizing sites on the studied samples. Some differences between the results obtained on zeolites and on silica—alumina are underlined. The ratio between the concentrations of “inner” and “outer” surface acceptor sites could be evaluated by using Pht and perylene, the ionization potential values of which are close but the molecular “diameters” are different.

Calculation of the kinetics of deactivation by coke of a silica-alumina catalyst in the dehydration of 2-ethylhexanol

The kinetics of deactivation by coke deposition of a silica-alumina catalyst in the dehydration of 2-ethylhexanol has been studied, from experiments following temperature-time sequences in an isothermal integral reactor, in automated reaction equipment. The data analysis method has consisted of simultaneously solving the mass conservation equation for the reactant and the kinetic equation of deactivation. The validity of the kinetic model calculated, which is a separable one of the Langmuir-Hinshelwood-Hougen-Watson type, and the experimental method of data analysis has been proven by comparing the results of reactor simulation with experiments carried out under different reaction conditions. The application of this rigorous method has been compared with the application, for the same reaction system, of simplified methods conventionally used in the literature for differential or integral reactor data analysis. The results show the interest of the experimental procedure proposed and of the data analysis method, which reduce the experimentation, lead to reproducible results, and do not have the limitations determined for the simplified methods of data treatment.

Catalysis by the Rh/B system: Part 2. Highly regioselective vapour phase hydroformylation of propene at atmospheric pressure on Rh/B on silica and silica-alumina

A Rh/B catalyst prepared by reducing rhodium trichloride supported on silica and silica-alumina with NaBH 4 at low temperature is used after thermal treatments in the vapour phase, propene hydroformylation in a flow reactor at atmospheric pressure. A good regioselectivity toward normal isomers, that remains constant at increasing temperatures, is detected ( S L=0.88). The surface composition of silica-alumina catalysts is apparently not affected by thermal treatments whether in argon or in CO/H 2 or in hydroformylation mixture flow. The geometrical arrangements of the active sites appear to play an important role in controlling the regioselectivity of the catalytic system.

Selective kinetic deactivation model for a triangular reaction scheme

A kinetic model of selective deactivation has been proposed, with kinetic equations of the Langmuir—Hinshelwood—Hougen—Watson type, for the isomerization of cis-butene, with a triangular reaction scheme. The silica—alumina catalyst has a considerable heterogeneity in the acidity strength of its active sites; so, an activity has been associated with the strongly acidic sites, which take part in the isomerization of cis-butene to trans-butene and which are deactivated rapidly. Another activity different from the previous one (equal for both individual reactions) has been associated with all the active sites (including sites of moderate acidity) which take part in the isomerization of cis-butene to 1-butene and of trans-butene to 1-butene and whose deactivation rate is smaller than that of strongly acidic sites. The kinetic study has been carried out by experiments following temperature—time sequences. The methodology proposed in previous papers for the calculation of kinetic parameters has been extended to the kinetic model of selective deactivation. Comparing the kinetic models of deactivation for two catalysts with different acidity strength distributions, the need for a kinetic model of selective deactivation is attributed to the heterogeneous nature of the acidic structure of the catalyst.

アルキルフェノール類の合成および分析

C3-C6 alkylphenols of 47 kinds were synthesized. Polymethylphe-nols were synthesized by transferring methyl groups from tetramethylbenzene to coexisting dimethylor trimethylphenols on asilicaalumina or a zeolite catalyst. Diethylphenols were synthesized transferring ethyl groups from diethylbenzene to coexisting ethylphenols on a silicaalumina catalyst. Other phenols were synthesized by allowing the phenols to react with alkyl bromide on aluminium chloride. The position of the alkyl group was determined by superposition of the reaction pathways. The 47 synthesized phenols and 26 commercial phenols were analyzed by GC-FID and GC-MS and their retention indices were calculated.

Isopropylamine adsorption for the characterization of acid sites in silica-alumina catalysts

The adsorption and reaction of isopropylamine has been studied using temperature-programmed desorption (TPD) and thermogravimetric analysis (TGA) on a series of silica-alumina catalysts as a function of alumina content, and the results have been correlated with cracking activities for n-hexane. The TPD-TGA curves on the amorphous silica-aluminas exhibit similar features to that observed on high-silica zeolites in that a well-defined feature is observed which desorbs as propene and ammonia between 575 and 650 K. This desorption feature appears to be due to strong Bønsted sites which are not present on either pure silica or alumina. The concentration of these sites increases in a regular manner with Al content and correlates well with the n-hexane cracking activity. This suggests that the TPD-TGA measurement of isopropylamine is a useful probe of the catalytically active sites on amorphous silica-aluminas.

Derivation of the Expanded Form of the BJH Equation and its Application to the Pore Structure Analysis of Mesoporous Adsorbents

The BJH equation, [Formula: see text], used for pore structure analyses via its application to the N2desorption isotherms at 78 K of porous materials, has been modified by substituting the value of ciand expanding the last term. The quantity vnis the volume of the pores involved in the nth desorption step and is given in terms of the volume of N2, (ΔV)n, exuded from the porous material, the constants Rnand ciwhich depend on the average pore size and average thickness of the physically adsorbed multilayer, Δtnbeing the decrease in thickness of the multilayer as a result of the nth desorption step and Aithe surface area of the set of pores involved in the ith desorption step. A derivation of the modified equation is presented. It has been applied to the N2desorption data of bone char used by Barrett, Joyner and Halenda (BJH). The effect of the multilayer thickness (t) values given by Pierce and de Boer on the pore size distribution of bone char has been studied. The pore size distribution data are compared with those obtained by the original BJH and Pierce methods. The pore system conforms very well with the idealised open-ended cylindrical pore model.The expanded BJH equation has also been applied to the desorption isotherms of fresh and sintered silica-alumina cracking catalysts over the entire range of silica/alumina ratios. The multilayer thickness (t) values given by de Boer have been used in the calculations. The pore systems of the catalysts, vacuum-dried at 400°C, are observed to conform to the cylindrical pore model as revealed by the excellent agreement between the cumulative surface areas obtained in P.S.D. calculations and the BET surface areas. The pore systems of the catalysts, sintered at different temperatures in a dry oxygen stream, deviate considerably from the cylindrical pore model. Enlargement of the pores and their nonconformity with the ideal pore model are attributed to modifications of the pore structures brought about by the phenomenon known as ‘self-steaming’ with the water vapour released from the catalysts.

Cracking of long chain n-paraffins on silica—alumina and rare earth exchanged Y zeolite

Abstract The present work reports for the first time a study of cracking of model paraffinic compounds in the boiling range of vacuum gas oil. The cracking reactions are investigated on commercial silica—alumina catalysts and rare earth exchanged Y zeolite (RE-Y) using the ASTM procedure for microactivity test. Effect of alumina content, temperature and hydrothermal treatment on activity and product selectivity is studied. Increase in alumina content results in higher activity without significant difference in product selectivity. Hydrothermal treatment results in decrease in the quantity of C 1 -C 4 products. RE-Y exhibited higher activity as compared to silica—alumina. The yield of gasoline and middle distillate range products was found to be higher on RE-Y. The product patterns are analysed on the basis of a detailed mechanism in the following paper.

Positronium-Brönsted site interaction in silica-alumina catalysis

The lineshapes of Doppler-broadened positron annihilation radiation were determined at different acidity content of a silica-alumina catalyst. Analysis of the results together with those obtained from temperature programmed desorption and infrared spectra demonstrated that positronium atoms are selectively oxidized by surface protons and do not react with Lewis acid sites. A mechanism for the oxidation reaction is proposed.

Additional Formation of Brønsted Acid Sites on Silica–Alumina Catalyst Surfaces by Depositing Silica Component

Abstract The chemical vapor deposition (CVD) of silica onto an amorphous silica–alumina was investigated using tetraethoxysilane in order to create Brønsted acid sites on the surface of original silica-alumina. Silica loading could be readily controlled by the CVD time at 160 °C; the silica covered an internal wall of mesopore of the support of silica–alumina. The resulting CVD silica–alumina was catalytically more active than the original silica–alumina support for such test reactions as the cracking of cumene and the isomerization of 1-butene. The characteristic changes in the amount of Brønsted acid sites were clarified by means of the temperature-programmed desorption of adsorbed 2,6-dimethylpyridine. Strong Lewis acid sites of the original silica–alumina were converted into strong Brønsted acid sites upon depositing the silica component.

Effect of pressure on the transformation of methanol into hydrocarbons on an amorphous silica—alumina

The effect of pressure on the transformation of methanol into hydrocarbons on an amorphous silica—alumina catalyst was studied. The increase in pressure (above atmospheric) produced a sharp increase in the production of hydrocarbons with five or more C atoms (C 5+), an increase in the total aromatics selectivity in the C 5+ fraction, and a better catalyst stability. Small changes were observed in the selectivity for solid aromatics in the C 5+ fraction when pressure increased.

Solid-state NMR of silica—alumina prepared by chemical vapor deposition

A supported type of silica—alumina catalyst prepared by depositing silica on an alumina (CVD SiO 2/Al 2O 3) was characterized by solid-state magic-angle spinning (MAS) NMR measurement. The 31P MAS NMR of trimethylphosphine chemisorbed on the catalyst elucidated a change in acid properties (Brönsted or Lewis type) with silica loading. Lewis acid sites on the alumina surface were converted into Brönsted acid sites by the deposition of silica. At lower silica loadings, both Brönsted and Lewis acid sites existed. Above 12 wt.% silica loading, Lewis acid sites disappeared and only Brönsted acid sites were observed. The catalytic activities of CVD SiO 2/Al 2O 3 for cumene cracking and 1-butene isomerization varied with silica loading, and the catalytic behaviors were correlated with the amount of Brönsted acid sites generated by silica deposition. The 29Si MAS NMR of silica deposited on the alumina surface revealed the microstructures of silica. The silica which was highly dispersed, forming a silica bilayer, exhibited high catalytic activities and strong Brönsted acidity. Further silica layering decreased both the catalytic activities and the acidity.

Isopropylation of p-Terphenyl over Solid Acid Catalysts.

Product selectivities both at early stage and thermodynamic equilibrium for the titled reaction were studied over silica-alumina and H-mordenite catalysts.For isopropylation with propylene over silica-alumina catalyst, 2-, 2'-, and 4-positions were more readily alkylated than 3-position at early stage of the reaction. After attaining thermodynamic equilibrium, the fraction of 3-isopropyl-p-terphenyl in the isomer mixture increased to 58%. On the other hand, the fraction of 4-isopropyl-p-terphenyl was 78% over the H-mordenite catalyst, due to the shape selectivity of H-mordenite, whereas it was 35-50% over the silica-alumina catalyst. The fraction of 4, 4-diisopropyl-p-terphenyl in the diisopropyl isomers was also as high as 75% over the H-mordenite catalyst, compared with 10-20% over the silica-alumina catalyst.

Effect of medium acidity on the spectral behaviour of some pyrazinyl diolefinic laser dyes

The spectral behaviour of the diolefinic dyes, 2,5-distyrylpyrazine (DSP) and 1,4-bis(β-pyrazinyl-2-vinyl) benzene (BPVB) have been studied in different media. The electronic absorption and emission spectra of the two dyes are bathochromically shifted with increase in medium acidity. A solution of each dye in 98% sulphuric acid acquired a deep blue colouration which changes through orange to a pale yellow upon dilution with water. The deep blue colour observed is responsible for the appearance of a new absorption peak at 550 nm, indicating the presence of a charge-transfer species being formed by the protonation of nitrogen heteroatoms of the pyrazinyl rings. The excimeric emission and excitation spectra of DSP and BPVB adsorbed from toluene onto the surface of silica-alumina ( ∼ 13% Al 2O 3) catalyst (activated at 650°C in air) are broad, structurless and substantially bathochromically shifted by ∼ 110 nm compared with the corresponding peaks obtained for dilute solutions containing no catalyst. Poly-DSP undergoes monomerization upon adsorption on the surface of the activated silica-alumina catalyst. The depolymerization process is believed to be via cyclobutane ring rupture.

Model silica-alumina acid catalysts for surface science and catalysis studies prepared by argon ion beam sputter deposition using HY-zeolite targets

Thin films of silica-alumina were prepared by argon ion beam sputter deposition on gold foil using different HY-zeolites as targets. X-ray photoelectron spectroscopy (XPS) results on thin films (< 10 nm) revealed that the Si/Al ratio in the films initially decreases with deposition time, but later becomes very similar to that of the target zeolite. Similarly, the position of O 1s, Al 2p, Si 2p peaks converged to the binding energies for zeolite target used. Based on the line shape of the O KVV Auger transition, we find that there is no segregation of silica and alumina in the films. By scanning electron microscopy (SEM) and scanning Auger electron spectroscopy (SAE) the thin films appear homogeneous. X-ray diffraction (XRD) results on thicker films (∼ 1 μm) indicate that the silica-alumina layers are amorphous. To test the catalytic activity cumene cracking was performed in a glass reactor. The sputter deposited thin silica-alumina films were active in cumene cracking at 573 K but at least a total of 20 cm2 macroscopic surface area was needed to easily distinguish the activity of the film from the background activity. Similar thin films prepared from alumina or silica or the a mixture of the two were inactive. Thus, the sputtered thin film retains some chemical memory of the target.