Dealkylation Of Toluene Research Articles

Effect of Microwave Radiation on the Development of a Porous Aluminum Carrier of the Active Mass of Catalysts in Heterogeneous Catalytic Reactions

In this study, we prepared a fine-grained, aluminum-reinforced alumina support matrix of the active mass of catalysts, which showed activity in heterogeneous catalytic reactions stimulated by electromagnetic radiation in the microwave range. The support absorbed microwave radiation of 2.45 GHz. We compared the textural characteristics of samples of Аl/Аl<sub>2</sub>О<sub>3 </sub>supports obtained by conventional heat treatment to those synthesized by heat treatment in a microwave field. We found several advantages of heat treating potential supports of the active mass by using microwave radiation. Using the examples of joint deep oxidation of n-butane and carbon monoxide, dealkylation of toluene with water vapor into benzene, and acidylation of diethyl amine with m-toluic acid, we found that after exposure to microwave radiation, the fine-grained aluminum powder-reinforced Аl/Аl<sub>2</sub>О<sub>3</sub> support can be used for preparing catalysts that can be used in reactions stimulated by a microwave electromagnetic field.

Steam Reforming of Toluene Over Pt/Ce x Zr1−x O2/Al2O3 Catalysts

Steam reforming of toluene was investigated over Pt/Ce x Zr1−x O2/Al2O3 catalysts with different ceria and zirconia content (x = 0.25, 0.50, 0.75, and 1.00). Toluene was used as model molecule representative of tar produced in biomass gasification. The main reactions over Pt/Ce x Zr1−x O2/Al2O3 catalysts are the steam reforming of toluene and the water–gas shift. The dealkylation of toluene to benzene and methane takes place only at the beginning of the reaction. Toluene conversion significantly decreases during the reaction for all catalysts excepted for Pt/CeO2/Al2O3 catalyst. Catalyst deactivation was attributed to carbon deposition as revealed by Raman spectroscopy. A clear relationship is observed between the acidity of the catalyst and the amount of carbon formed over Pt/Ce x Zr1−x O2/Al2O3 catalysts. Decreasing the Ce/Zr ratio increased the density of acid sites as well as the amount of carbon formed. This result suggests that the main route for carbon deposition proceeds by the oligomerization of toluene molecule on the acid sites of the support. Pt/CeO2/Al2O3 catalyst was quite stable during steam reforming of toluene without carbon deposition. For this catalyst, ceria covered the acid sites of alumina and did not introduce significant Lewis acid sites.

Reforming of Syngas from Biomass Gasification: Deactivation by Tar and Potassium Species

A synthesis gas (syngas) with a composition corresponding to that of a biomass gasifier has been reformed over Rh-containing monolith catalysts in the absence and presence of typical undesired species in the syngas. When toluene, a typical light tar component, was added, there was some loss of conversion, probably due to competitive adsorption and reaction with toluene, although dealkylation of toluene can not be ruled out. Significant deactivation due to the tar was not detected. Potassium components impregnated onto the catalyst (KNO3 and KCl) in low concentrations gave slight enhancement of the reforming rates, but at higher concentrations there was severe deactivation.

Catalytic Transformation of Toluene over a High-Acidity Y-Zeolite Based Catalyst

The catalytic transformation of toluene has been investigated over Y-zeolite-based catalysts in a novel riser simulator under different operating conditions. Several experiments were performed in the temperature range of 400−500 °C to understand the transformation of toluene over a high-acidity Y-based zeolite catalyst (H-Y). It has been observed that toluene can transform either through disproportionation, producing benzene and xylene isomers, or through dealkylation, producing gases and benzene. The rates of both reactions are essentially dependent on the reaction temperature. The dealkylation reaction was determined to be favored by high temperature. The benzene/xylene ratio was determined to increase with temperature, because of the high xylene dealkylation rate. Toluene transformation was determined to be controlled by both Y-zeolite acidity and reaction temperature. While high acidity and high reaction temperature favor toluene dealkylation, medium acidity and low reaction temperature favor toluene ...

An FT-IR study of the reactivity of hydrocarbons on the acid sites of HZSM5 zeolite

The interaction of HZSM5 zeolite with n-butane, iso-butane, n-heptane, 1-butene, cis-2-butene, trans-2-butene, iso-butene, benzene and toluene in the temperature range 100–773 K has been investigated using FT-IR spectroscopy. Low temperature experiments allowed to characterise hydrogen-bonded species of all adsorbates both with the internal bridging OHs of HZSM5 and with the external terminal OHs. H-bonds apparently involve C–C σ-type orbitals of alkanes and CC π-type orbitals of alkenes and aromatics. Evidence is provided for a partial steric hindrance in the interaction of benzene and toluene with the internal OHs. Hydrogen bondings with alkanes are precursors for dehydrogenation with the formation of carbenium ions that go fast towards the tert-butyl– sec-butyl equilibrium, giving rise to skeletal isomerization and cracking. Poly-isobutene like species are formed at the surface by high-temperature interaction with both alkanes and alkenes. Isobutene is a likely precursor for such species, that are intermediates of coking and can contribute also to cracking to light olefins. H-bonded species are also thought to be intermediates for the formation of the so-called ‘σ-bonded’ intermediate of electrophilic aromatic substitution, giving rise to toluene dealkylation and/or dismutation, obtained in the IR cell.

Formula omitted] sol-gel catalysts: catalystic properties

Platinum-tin supported catalysts at various tin and platinum contents were prepared by the sol-gel method by adding tetrabutyltin to a homogeneous solution containing aluminum tri-sec-butoxide (TBA). After gelation, the solids were dried, calcined and then impregnated with an aqueous solution of hexachloroplatinic acid. Catalysts prepared by this method show specific BET areas around 270 m 2/g and platinum dispersion up to 90%. Ammonia adsorption shows that there are less acidic sites in tin-alumina sol-gel preparations than in sol-gel alumina. Activity measurements for n-heptane dehydrocyclization show that PtSn sol-gel catalysts are more active than catalysts prepared by successive impregnation of a commercial alumina. Moreover, selectivity to benzene formation was found 54% lower with sol-gel catalysts than with commercial based catalysts. A high tolerance to thiophene poisoning during n-heptane dehydrocyclization was also found. Additional catalytic tests for cyclohexane dehydrogenation, isopropanol dehydration and toluene dealkylation were performed. High selectivity to acetone in the dehydration reaction and very low activity for toluene dealkylation were found for sol-gel preparations. The high activity in n-heptane dehydrocyclization and the high selectivity to acetone in PtSn-alumina sol-gel catalysts was interpreted as a result of the modification by tin of the support acidity. Nevertheless, the tolerance to thiophene poisoning and the low dealkylation rate observed for sol-gel preparations can only be explained by an important tin-alumina support effect on platinum activity.

X-ray photoelectron spectroscopy characterization of the reduction and oxidation behaviour of Ni-containing HZSM-5 zeolites

The surface characteristics of NiHZSM-5 zeolites prepared by ion-exchange, impregnation and mechanical mixing methods have been studied by XPS. The results show that because of the interaction between NiII species and the zeolite, nickel can exist in many forms on the surface of the zeolite, e.g. NiO, Ni(OH)2 and NiAI2O4. The degree of reduction of NiII species depends mainly on its form, and decreases in the order NiO > Ni(OH)2 > NiAI2O4. The metallic nickel particles formed by reduction of NiII species by hydrogen were unstable, and the redox cycle was not completely reversible either. The analysis of surface composition indicates that HZSM-5 zeolite does not have a uniform composition. Surface enrichment of aluminium and nickel was observed and can be explained by several factors, including the sample preparation method, the stage of the redox cycle and the treatment conditions. Toluene conversion on this kind of catalyst has also been investigated. The surface NiO species provide weak catalytic sites for the dealkylation of toluene whilst the surface Ni(OH)2 species act as relatively weak catalytic sites for the disproportionation of toluene. However, the Nio species exhibit strong catalytic activity towards the cracking and deakylation of toluene.

Kinetics of toluene disproportionation over unmodified and modified ZSM-5 zeolites

The kinetics of toluene disproportionation has been studied over both unmodified and Si-Mg modified ZSM-5 catalysts using an integral reactor and taking into account the reversibility of the reaction. It has been found that xylene dealkylation is the major secondary reaction, whereas toluene dealkylation can be considered negligible. For the unmodified ZSM-5, heterogeneous models based as the alkyl-transfer mechanism allowed the experimental results to be fit better than first and second pseudohomogeneous models, the best concordance being obtained when toluene adsorption is assumed as the rate-limiting step. The corresponding kinetic equations has been further applied to the modified zeolite (SiMg/ZSM-5), leading to the development of a kinetic model which includes the effect of the toluene and p-xylene intracrystalline diffusion rate and the presence of nonselective acid sites on the external zeolite surface. This model describes adequately the selective formation of p-xylene over modified ZSM-5, reproducing the experimental product distribution with an average relative error of 2.8%

Properties of supported rhodium catalysts for steam dealkylation of toluene

The effect of modification of γ-aluminia support by Cr2O3 on physical and catalytical properties of supported rhodium catalysts was investigated. Various techniques were used for characterization of catalysts: porosimetry, diffusion and permeation measurements, determination of surface OH groups, temperature-programmed reduction and catalytic behaviour in steam dealkylation of toluene. Using the transport parameters determined for pelleted catalysts the effect of internal diffusion on the reaction was predicted and compared with experiments.

ChemInform Abstract: Selective Toluene Disproportionation over ZSM‐5 Zeolites.

Selective toluene disproportionation to benzene and xylenes is investigated over HZSM-5 and modified HZSM-5 zeolites. The zeolites are modified with nickel, magnesium, phosphorus and boron, characterised by sorption, acidity measurement and X-ray photoelectron spectroscopy, and their activity towards toluene disproportionation is discussed in the light of their physico-chemical properties. The two types of active sites have been identified; one promoting disproportionation and the other cracking and dealkylation of toluene. It is found that the latter sites are suppressed due to incorporation of the modifiers. The modified zeolites are found to be para-selective which appears to be consistent with the commonly accepted view that modifiers like magnesium, phosphorus and boron reside in the channels and react with Bronsted acid sites, leading to partial blockages and thus favouring the formation of p-xylene. The effect of poisoning the zeolite with 1-methylisoquinoline is also investigated. In the case of poisoned catalyst, p-xylene is produced at levels up to 99%. The total elimination of other isomers from the products is suggested due to the selective poisoning of the non-selective sites (on the external crystal surface) and to partial blocking of the pore openings.

Selective toluene disproportionation over ZSM‐5 zeolites

AbstractSelective toluene disproportionation to benzene and xylenes is investigated over HZSM‐5 and modified HZSM‐5 zeolites. The zeolites are modified with nickel, magnesium, phosphorus and boron, characterised by sorption, acidity measurement and X‐ray photoelectron spectroscopy, and their activity towards toluene disproportionation is discussed in the light of their physico‐chemical properties. The two types of active sites have been identified; one promoting disproportionation and the other cracking and dealkylation of toluene. It is found that the latter sites are suppressed due to incorporation of the modifiers. The modified zeolites are found to be para‐selective which appears to be consistent with the commonly accepted view that modifiers like magnesium, phosphorus and boron reside in the channels and react with Brønsted acid sites, leading to partial blockages and thus favouring the formation of p‐xylene. The effect of poisoning the zeolite with 1‐methylisoquinoline is also investigated. In the case of poisoned catalyst, p‐xylene is produced at levels up to 99%. The total elimination of other isomers from the products is suggested due to the selective poisoning of the non‐selective sites (on the external crystal surface) and to partial blocking of the pore openings.

Dealkylation of coal liquid under CO-steam atmosphere, II. Model reactions using alkylbenzenes on supported nickel catalysts

Dealkylation of alkyl aromatics is a fundamental reaction in the upgrading of coal liquid produced by the usual hydrogenative liquefaction of coal. To develop a catalyst for the studied reaction, we performed the catalytic dealkylation of toluene and of ethylbenzene as model compounds by using a CO/steam mixture under atmospheric pressure at 380–620°C in a conventional flow system with a fixed bed of catalyst. Some runs with H 2 and H 2/steam in place of CO/steam were also perfomed. Both toluene and ethylbenzene are practically inert under CO/steam even at 500°C. Among the various catalysts examined, MgO-supported nickel catalyst was found to be effective for demethylation of toluene. On this catalyst a benzene yield of greater than 30% is obtained from the reaction of toluene at 500°C. The striking feature of the MgO-supported nickel catalyst is the depression of coke formation even at 500°C. The size of the Ni particles in the MgO-supported catalyst is estimated by XRD to be smaller than 10 A. Serious coke formation occurs on silica-supported and alumina-supported nickel catalysts of which activities are usually higher than that of MgO-supported catalyst. The addition of K 2CO 3 to these two catalysts partly depresses coke formation and enhances their catalytic activities. This K 2CO 3 addition effect is primarily due to the fact that potassium increases the dispersion of Ni on the catalyst carrier. The extent of the coke formation is considered to be strongly dependent upon the size of Ni particles. CO/steam mixture is found to be superior to H 2 as a reducing agent, and is especially effective on the MgO-supported nickel catalyst. The supported nickel catalysts facilitate dealkylation of ethylbenzene to give benzene yield of 21.2% and toluene yield of 11.6% at 380°C without serious coke formation.

Intermetallic compounds as heterogeneous catalysts

Some intermetallic compounds such as RE xNi y, where RE represents lanthanum or rare-earth mischmetal alloy exhibit an appreciable activity in catalytic reactions, particularly in carbon monoxide hydrogenation, toluene dealkylation and ethane hydrogenolysis. However, we found that, during the reaction, the intermetallic compound decomposed into a metal-support system, the support being an oxide or hydride according to the performed reaction.

Fouling of a platinum-rhenium reforming catalyst using model reforming reactions

It is well known that rhenium stabilizes a commercial platinum reforming catalyst; however, the exact role of Re is still in doubt. The function of Re was investigated by determining and then comparing the fouling characteristics of two model reforming reactions catalyzed by bifunctional Pt and PtRe catalysts. The methylcyclohexane (MCH) dehydrogenation reaction was used to probe for changes in the metallic function and the methylcyclopentane (MCP) dehydroisomerization reaction was used to determine variations in the acidic function. Both sulfided and unsulfided catalysts were investigated. Presulfiding either a Pt or PtRe catalyst altered significantly the observed reaction rates and deactivation characteristics of the metallic function. The addition of Re to a Pt reforming catalyst greatly reduced the rate of those structure-sensitive secondary reactions catalyzed by the metallic function: toluene dealkylation, MCP ring opening, and long-term MCH fouling. The addition of Re, however, did not affect the structure-insensitive MCH reaction or the initial MCP fouling rate; also, little or no affect was noted in the MCP fouling characteristics. The results presented suggest that there is a metal-metal interaction between Pt and Re.

Some aspects of the bifunctional action of nickel-zeolite catalysts in the conversion of toluene

The bifunctional action of nickel-zeolite catalysts toward toluene conversion is studied. The additive behavior of both components of the catalysts is confirmed on the basis of the interpretation of their activity from three points of view: bifunctional catalysis, catalysis on the metal, and catalysis on the acidic component. New two-component catalysts of the type NiO CaNaY 3.2–5.0 (nickel content from 2.5 to 7.5 wt%) are developed. After reduction they are active for the dealkylation of toluene and under certain conditions for the disproportionation of toluene. The catalysts may be used for production of benzene and xylenes from toluene.

The chemistry and catalysis of the water/toluene reaction: 2. The role of support and kinetic analysis

The influence of support on the activity of rhodium for the water/toluene reaction and the H 2/toluene reaction is investigated. It is shown that an effective catalyst for water/hydrocarbon reactions is bifunctional in the sense that both metal and support provide activation sites for reactants. In the selective steam dealkylation of toluene, as in total steam reforming reactions, the support significantly influences the catalyst's specific activity when based on the metal surface area. For example, in the steam dealkylation reaction the rate of benzene formation over a Rh S iO 2 catalyst is only 1 37 th the rate over a Rh Al 2O 3 catalyst. The absence of support leads to an even further drop in the specific activity of rhodium, as a rhodium black catalyst is only 1/200th the activity of the Rh Al 2O 3 catalyst. In contrast the support has no influence on the specific activity of rhodium for the H 2/toluene (hydrodealkylation) reaction. A Langmuir-Hinshelwood approach is used to describe the kinetics of the water/toluene reaction in terms of a surface reaction between activated water species (from support sites) and activated toluene (on metal sites for Rh and the other Group VIII metals investigated). This approach leads to a simple power-law rate expression of the form: r = kP Tol n P H 2O (1 − n) 2 . The observed kinetic parameters reported in Part I of this series of papers agree well with those predicted from this rate expression.

Role of urania as a promoter of supported rhodium in the catalyzed steam dealkylation of toluene

The steam dealkylation of toluene was studied using platinum group catalysts with and without urania, and the results were tabulated. The Rh-Al/sub 2/O/sub 3/ catalyst promoted by urania proved to be the most effective catalyst. The effect of CO on the steam dealkylation for Rh catalyst and for Rh-UO/sub 3/ catalyst was reported. The three step role of urania was described. (DDA)

Steam Dealkylation of Toluene over Rh Catalysts Promoted by Various Metal Oxides

Steam Dealkylation of Toluene over Rh Catalysts Promoted by Various Metal Oxides

Dealkylation of toluene on metals of the platinum group in the presence of steam

Dealkylation of toluene on metals of the platinum group in the presence of steam

A new process for toluene dealkylation

A new process for toluene dealkylation