Side-chain Alkylation Of Toluene Research Articles

Investigating the Role of Cs Species in the Toluene–Methanol Side Chain Alkylation Catalyzed by CsX Catalysts

The side chain alkylation of toluene with methanol was studied on a series of CsX catalysts prepared by varying the Cs species and ion exchange conditions. The effects of various parameters, such as the exchanging temperatures and times on the adsorption/activation properties of different CsX catalysts, were investigated by combining a variety of characterization means for understanding the role of Cs species in the side chain alkylation reaction. On the basis of the various characterization results and their related literature results, it can be proposed that the Cs ions located on the ion-exchanged sites of X zeolites could effectively adsorb and activate toluene molecularly through modifying the basicity of framework oxygen, whereas the cluster of cesium oxide (Cs2O) could ensure the effective conversion of methanol into formaldehyde. Additionally, Cs ions can promote the production of monodentate formate, which enhances the selectivity of styrene. However, too much Cs2O will lead to the excessive decomposition of methanol into CO2, CO, and H2, thus inhibiting the production of styrene. In summary, the presence of suitable amounts of Cs ions and Cs2O clusters plays a significant role in the formation of the side chain products of styrene and ethylbenzene.

Side-chain alkylation of toluene with methanol over cesium-ion-exchanged zeolite LSX and X catalysts

The catalyst CsLSX has a higher basic cation exchange capacity than that of the catalyst CsX. The higher number of aluminum atoms allows the CsLSX catalyst to have more oxygen atoms with a negative charge (Oδ−) in the zeolite framework.

Effects of the Pore Structure and Acid–Base Property of X Zeolites on Side-Chain Alkylation of Toluene with Methanol

Effects of the Pore Structure and Acid–Base Property of X Zeolites on Side-Chain Alkylation of Toluene with Methanol

Enhancing the side-chain alkylation of toluene with methanol to styrene over the Cs-modified X zeolite by the assistance of basic picoline as a co-catalyst

Side-chain alkylation of toluene with methanol is a green pathway to realize the one-step production of styrene under mild conditions, but the low selectivity of styrene is difficult to be improved with by-products of ethylbenzene and xylene. In this study, a new way is introduced to improve the catalytic performance by means of assisting basic compounds as co-catalysts during the toluene side-chain alkylation with methanol to styrene. As a result, high activity of side-chain alkylation appears over the basic Cs-modified zeolite catalysts prepared by ion exchange and impregnation methods. This high performance should be mainly attributed to two co-catalysis actions: (1) the promotion of basic compounds for methanol dehydrogenation to formaldehyde as the intermediate for side-chain alkylation; (2) the suppression of the styrene transfer hydrogenation on basic Cs-modified zeolites to avoid the formation of ethylbenzene. Especially for Cs2O/CsX-ex catalyst, the addition of 2% mol/mol 2-picoline in reaction mixture could achieve both 12.3% toluene conversion and 84.1% styrene selectivity. Whereas the higher concentration of 2-picoline (>6% mol/mol) caused an inhibition to the catalytic activity because the excessive basic compound poisoned the combined acid-base pathway required for the side-chain alkylation process. In addition, two possible side-chain alkylation reaction routes on Cs-modified zeolite under the different 2-picoline absorption were described.

Effect of relative percentage of acid and base sites on the side-chain alkylation of toluene with methanol.

K3PO4/NaX catalysts were prepared by loading potassium phosphate on NaX zeolite, and the catalytic performance was studied for the side-chain alkylation of toluene with methanol to styrene and ethylbenzene. Combined with the characterization of XRD, TPD-NH3, TPD-CO2, and FTIR and the determination of phosphorus content, it is revealed that firstly, the P element loaded on the catalyst surface can prominently promote the percentage of middle base sites, which will accordingly enhance the selectivity of the products (styrene and ethylbenzene) of side-chain alkylation of toluene; secondly, if there are enough middle base sites distributed on the catalysts, the higher percentage of strong base sites benefit the selectivity of styrene, which is confirmed by the performance of the two-stage catalysts.

Side-chain Alkylation of Toluene with Methanol, Modification and Deactivation of Zeolite Catalysts of the Reaction

The review deals with main aspects of the toluene methylation reaction on basic catalysts. The side reactions of decomposition of methanol to CO and H2 on strong basic sites and ring alkylation of toluene on Lewis acid sites (cations of high polarizing ability) hinder obtaining high yields of the target products – styrene and ethylbenzene. Both types of sites are necessary for the course of the target reaction. So optimizing their strength and quantity is an important prerequisite for the selectivity of the side-chain alkylation catalysts. The advantage of fojasite-based systems for this reaction was confirmed by the works of many researchers. However, the possibilities of use of zeolites of other structural types and representatives of a new generation of molecular sieves are being studied, as well as ways of modifying such materials to increase their catalytic efficiency. The main direction of modification is to regulate the balance of acidity and basicity. Effective charge of framework oxygen atoms, which determines basicity of zeolite framework, increases due to the introduction of guest compounds into the catalyst, and this effect is more significant than influence on basicity of ion exchange for cations of elements of low electronegativity. However, the role of this method of modifying in increasing the selectivity remains crucial due to potentiality to decrease the Lewis acidity of cations. Compounds of other elements and transition metals also are used for modification, as well as promotion with metallic copper and silver. Techniques are applied, but not widely, to deprive the external surface of crystallites of active sites. This method of modification is effective for slowing down their deactivation by coke. Acid sites, in particular BAS, are most often distinguished among the sites responsible for coke formation. The mechanism of coke formation in the absence of such centers is also proposed. On the whole, this issue not fully disclosed and requires a deeper study.

Highly dispersed Pt nanoparticles in the Cs-modified X zeolite with enhancement for toluene side-chain alkylation with methanol

Modification of Cs/X with highly dispersed Pt NPs improved the activity and durability in the side-chain alkylation of toluene.

Efficient synthesis of styrene from toluene with MeOH: Via a ternary composite catalyst

To achieve high selectivity of styrene from toluene and methanol, a new strategy, the coupling of methanol dehydrogenation and side-chain alkylation of toluene by ternary composite catalyst combining methanol dehydrogenation, B/SiO2 and CsX components, is proposed. The methanol dehydrogenation component could promote the in-situ formation of formaldehyde (HCHO) intermediate, transferring to B/SiO2 and CsX components. The formation of HCHO over dehydrogenation component is driven by the side-chain alkylation reaction over CsX-B/SiO2 during the coupling reaction. In addition, B/SiO2 is beneficial to stabilize HCHO. When CuO/SiO2 is applied as the dehydrogenation component, the styrene and ethylbenzene yield reaches 31.0 % at a methanol conversion of 60.1 % with the styrene/ethylbenzene molar ratio in products of 3.1 over CsX-CuO/SiO2-B/SiO2. The effective method to prepare a ternary composite catalyst provide helpful guideline for developing a more efficient CsX-based catalyst for conversion of toluene with methanol into styrene in the further.

Synthesis of HTLcs modified by K3PO4 for side chain alkylation of toluene with methanol

A series of calcined HTLcs catalysts were prepared and modified with potassium phosphate by impregnation method to clarify the influence of catalyst alkalinity on the side chain alkylation of toluene with methanol for synthesis of ethylbenzene and styrene. The catalysts were characterized by X-ray diffraction (XRD), N2 physical adsorption–desorption, Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), NH3 temperature-programmed desorption (NH3-TPD) and CO2 temperature-programmed desorption （CO2-TPD）. It was found that the selectivity of styrene was highest (39.25%) when the K3PO4 loading was 7.5 wt%. And the total yield of styrene and ethylbenzene could reach 65.08% with 10 wt% K3PO4 loading. This might due to the fact that the addition of K3PO4 could adjust the acid and basic sites of catalysts. In addition, appropriate strength and amount of basic sites were favorable to producing more styrene.

Role of ball milling during Cs/X catalyst preparation and effects on catalytic performance in side-chain alkylation of toluene with methanol

Ball milling modification was performed on Cs/X catalysts before or after cesium ion exchange. Multiple characterization results (such as pyridine-FTIR, XPS, and solid-state NMR) demonstrated that ball milling played a distinct role in these two different preparation procedures of the catalyst. Ball milling performed after the cesium modification has a strong influence on the Cs/X structure and acid–base properties, which results in the enhancement of the catalytic performance for side-chain methylation of toluene with methanol. Detailed studies revealed that ball milling intensified the interactions between oxides and molecular sieves, which not only increased the dispersion of the Cs species but also generated some weaker basic centers. It is proposed that the new basic centers could be Si–O–Cs and Al–O–Cs, which are produced by breaking of the Si–O–Al bonds of the zeolite framework under the synergetic effect of ball milling and alkali treatment. These new active sites may help to promote the side-chain methylation reaction. However, excessive ball milling will lead to the vanishing of zeolite micropores, thus deactivating side-chain methylation activity, which indicates that microporosity plays a key role in side-chain methylation and individual basic centers cannot catalyze this reaction.

Effect of Fe Additives on the Catalytic Performance of Ion-Exchanged CsX Zeolites for Side-Chain Alkylation of Toluene with Methanol

The side-chain alkylation of toluene with methanol was investigated over some Fe-modified Cs ion-exchanged X zeolite (CsX) catalysts prepared via the impregnation method using different iron sources. The absorption/activation behaviors of the reactants on the surface of the catalysts were studied by in situ Fourier-transform infrared (FT-IR) spectroscopy and temperature programmed desorption (TPD) mass measurements. Modification of CsX with a small amount of FeCl3 could result in a considerable decrease in catalytic activity, due mainly to the remarkable decrease in the density of acidic and basic sites of the catalysts. Interestingly, the Fe(NO3)3-modified CsX with an optimum Fe loading of 0.15 wt.% shows improved catalytic activity and high yield compared to the side-chain alkylation products. Modification of CsX with Fe(NO3)3 could also result in a decrease in basic sites of the catalyst. However, such a change does not bring an obvious negative effect on the adsorption/activation of toluene, while it could effectively inhibit the generation of the undesired bidentate formate. Furthermore, the introduced FeOx species (derived from the decomposition of Fe(NO3)3) may also act as new Lewis acidic sites to participate in the activation of methanol and to stabilize the formed active intermediates (i.e., unidentate formate). Therefore, modification of CsX with a suitable amount of Fe(NO3)3 may adjust its adsorption/activation ability for reagents by changing the acid–base properties of the catalyst, which can finally enhance the catalytic performance for the side-chain alkylation of toluene with methanol.

Side-chain alkylation of toluene with methanol to produce styrene: an overview

Styrene is a key building-block chemical for the production of polymers with significant application value.

Elucidating the Distribution and Speciation of Boron and Cesium in BCsX Zeolite Catalysts for Styrene Production.

An improved understanding of the nature and distribution of boron and cesium species in BCsX zeolites is a prerequisite to guide future developments in the environmentally attractive, yet challenging, production of styrene through the side-chain alkylation of toluene with methanol. Herein, standard characterization and catalytic tests are complemented by integrated visualization through time-of-flight secondary-ion mass spectrometry and energy-dispersive X-ray spectroscopy and detailed assessment by 133 Cs and 11 B NMR spectroscopy, to correlate the properties and performance during successive ion-exchange and impregnation steps in the preparation of both powders and millimeter-sized granules. The results highlight a significant impact of catalyst scaleup on the effective introduction of boron species, which originates chemical heterogeneity that is linked to selectivity losses. They also illustrate the complexity of elucidating the role of this promotor, which interacts with cesium cations and exhibits different coordination states and chemical environments, depending on the pretreatment.

Zinc oxide as efficient additive to cesium ion-exchanged zeolite X catalyst for side-chain alkylation of toluene with methanol

Side-chain alkylation of toluene with methanol to form styrene and ethylbenzene was studied over cesium ion-exchanged zeolite X (Cs-X) with various catalyst additives to find out effective catalyst systems for styrene formation as well as to elucidate the roles of the additives. Out of 13 types of additives examined, only ZnO exerted substantial positive effects on both toluene conversion and styrene selectivity. The role of ZnO was estimated to promote conversion of methanol to formaldehyde on the basis of IR study of adsorbed methanol. The formation of formaldehyde accelerated the formation of styrene as well as suppressed the transfer hydrogenation of styrene with methanol to form ethylbenzene. The positive effect of ZnO was also observed for Cs-X containing Cs+ in excess of ion-exchange capacity (Cs2O-Cs-X). The negative effect of additives such as Al2O3 was suggested to be caused by the formation of CO2 by water gas shift reaction and Bourdouard reaction.

The promoting effects of alkali metal oxide in side-chain alkylation of toluene with methanol over basic zeolite X

The side-chain alkylation of toluene with methanol was investigated on a series of catalysts which were prepared by ion-exchange or subsequent impregnation of zeolie X with potassium hydroxide or cesium hydroxide aqueous solution. The catalysts were characterized by X-ray diffraction, scanning electron microscopy, X-ray fluorescence, Ar physical adsorption-desorption, NH3 temperature-programmed desorption (TPD), CO2-TPD, pyridine adsorption Fourier-transform infrared (FT-IR) spectroscopy, FT-IR spectroscopy in OH stretch region, thermogravimetric/differential thermal analysis, ultraviolet-Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that alkali metal oxide played extremely important roles in the modification of catalysts and in the catalytic reaction pathway. Strong basic sites were formed by modification of basic zeolite X with alkali metal oxide. These basic sites promoted the dehydrogenation of methanol to formaldehyde which was recognized as the true alkylating agent in side-chain alkylation. Consequently, side-chain alkylation of toluene with formaldehyde was enhanced. As toluene was mainly adsorbed and activated on alkali metal cations bonded on the zeolite framework, the synergistic effects between alkali metal oxide and alkali metal cations were proposed. One of the possible reaction path ways for side-chain alkylation of toluene with methanol over basic zeolite was described. Alkali metal ion-exchanged zeolite X modified with alkali metal oxide demonstrated relatively high side-chain alkylation activity. However, the improvement of styrene selectivity faced with great challenges.

Effects of Cesium Ions and Cesium Oxide in Side-Chain Alkylation of Toluene with Methanol over Cesium-Modified Zeolite X

The side-chain alkylation of toluene with methanol was studied on cesium-modified zeolite X prepared by ion-exchange and impregnation with different cesium precursors. The catalyst was characterized by X-ray diffraction, scanning electron microscopy, X-ray fluorescence spectroscopy, Ar physical adsorption–desorption, NH3 temperature-programmed desorption (TPD), CO2-TPD, thermogravimetric/differential thermal analysis, ultraviolet-Raman spectroscopy, energy-dispersive spectrometry, and X-ray photoelectron spectroscopy. Cesium hydroxide was found to be the most effective precursor for modifying zeolite X. Cesium ions bonded on the framework and cesium oxide formed in the pore were found to take different roles in this reaction. Cesium ions could adsorb and activate toluene or modify the basicity of framework oxygen, whereas cesium oxide could ensure the effective conversion of methanol to formaldehyde and inhibit the process of coke deposition. A possible reaction pathway for this reaction over cesium-modif...

ChemInform Abstract: Solid Base Catalysts: Fundamentals and Their Applications in Organic Reactions

AbstractReview: 33 refs.

Side-chain alkylation of toluene with methanol over boron phosphate modified cesium ion-exchanged zeolite X catalysts

A series of boron phosphate (BPO4) modified ion-exchanged CsX zeolites, prepared by impregnation method, were characterized by a variety of means and utilized as catalysts for the side-chain alkylation of toluene with methanol. Both BPO4 and Cs species are highly dispersed on the surface/channel of the BPO4/CsX zeolites. The addition of a small amount of BPO4 has no obvious effect on the basic strength of catalysts, but decreases the number of basic sites slightly. Meanwhile, more weak Lewis acidic sites appear with the increasing BPO4 loading. Compared with CsX, the BPO4 modified CsX catalysts exhibit lower ability for the adsorption/activation of methanol to produce surface intermediates like formaldehyde, unidentate formate and bidentate formate. Catalytic reaction results showed that modification of CsX with boron phosphate can improve both the conversion of toluene and the selectivity of styrene. The inhibition role in producing the unfavorable bidentate formate might be a key factor for finally resulting in the improvement of the catalytic properties of BPO4/CsX catalysts for the side-chain alkylation of toluene with methanol.

Synthesis and application of novel solid acid-base catalysts for side chain alkylation of toluene with methanol

Novel solid acid-base catalysts with aluminum and nitrogen were prepared from phenolic compounds and formaldehyde by using triblock copolymer Pluronic F127 as a template via evaporation induced organic-organic assembly method. The catalysts were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS). The acid-base properties of the catalyst were determined by temperature programmed desorption (TPD) using CO2 and NH3 as probe molecules. The side chain alkylation of toluene with methanol over the catalyst was studied, the results demonstrated that the catalyst Cat-TDMMP was of the higher activity [(ethylbenzene + styrene) yield was 41.0%] than the conventional alkali exchanged zeolites [(ethylbenzene + styrene) yield was about 20%]. This fact may due to the strength and distance of the specific surface acid-base pairs of the catalyst, which are favored to bimolecular side-chain alkylation reaction.

Solid base catalysts: fundamentals and their applications in organic reactions

Solid base catalysis studied over the last a half of century is reviewed briefly including mainly those performed in our laboratories. The review begins with advantages of solid base catalysts over homogeneous base catalyst in industrial use followed by definition of Brϕnsted base and Lewis base. The materials known as solid base catalysts are listed, and four reasons for which these materials are recognized as solid base catalyst are explained. For all solid base catalysts, variations in activity as a function of pretreatment temperature show a volcano shape; an incline with the temperature results from an appearance of basic sites by removal of water and carbon dioxide from the surface and a decline results from an elimination of basic sites by rearrangement of surface atoms. The reactions catalyzed by solid base catalysts can be classified into three types: double bond isomerization, addition of anion and proton to various double bonds, and alcohol decomposition. These are represented by 1-butene isomerization, hydrogenation of conjugated 1,3-butadiene and dehydration of 2-butanol. Their mechanisms are explained. In addition, bifunctional base-catalyzed reactions in which basic sites participate in one step of successive steps are exemplified for methyl isobutyl ketome synthesis, metathesis, Tishchenko reaction and side-chain alkylation of toluene. Some industrial processes and future perspectives are briefly described.