Side-chain Alkylation Research Articles

Intergrowth MFI Zeolite with Inverse Al Zoning and Predominant Sinusoidal Channels for Highly Selective Production of Styrene.

ZSM-5 zeolites with accessible micropore architecture and tunable acid-base sites are important shape-selective catalysts. However, the presence of exposed straight channels and the external acid-base sites of conventional ZSM-5 has a negative impact on shape selectivity. Herein, we report on the direct synthesis of an intergrowth ZSM-5 zeolite mimicking the mortise-tenon joints. It can be revealed by various methods that the mortise-tenon ZSM-5 shows an inverse Al gradient from the surface to the core of the zeolite. More importantly, the sinusoidal channels predominantly opened to their external surfaces are constructed. The shape-selective capability of the ZSM-5 zeolite has been fully exploited due to the intrinsic inert external surface and unique sinusoidal channel features, thereby resulting in high styrene selectivity (>90%) and good catalytic stability (>100 h) in the toluene side-chain alkylation reaction. In addition, in situ DRIFTS confirms that this intergrowth ZSM-5 contributes to the formation of more active intermediates of HCOO* and H3CO*, which is another reason responsible for the superior performance.

Selective aromatization of 1-hexene to BTX over core-shell structured Silicalite-1@ZSM-5 catalyst

The strong acidity on the external surface of ZSM-5 is a primary factor resulting in the low BTX selectivity and catalyst deactivation during the olefin aromatization. In this study, a membrane-restricted Silicalite-1@ZSM-5 core–shell structured catalytic catalyst was designed and constructed for 1-hexene aromatization using a hydrothermal coating method. TEM and NMR results confirmed the complete coverage of Silicalite-1 on the surface of ZSM-5, with a shell thickness of 50 nm. The further reaction of the TIPB (1,3,5-triisopropylbenzene) molecular probe reactions demonstrated the passivation of the acid sites on ZSM-5 external surface. The inert shell layer passivated the acid sites on the external surface, thereby suppressing the isomerization of PX and the side-chain alkylation reaction of light aromatics. Compared to ZSM-5, the Silicalite-1@ZSM-5 catalyst exhibited a 37.15 % increase in BTX selectivity, a 58.65 % increase in PX selectivity, significantly reduced coke deposition, and demonstrated better stability. This strategy of in-situ epitaxial growth of inert shell layers holds significant promise for enhancing the selectivity of shape-selective catalysts and extending catalyst lifetime.

Preparation of Cs/CuAl-LDO@Al2O3@Fe3O4 magnetic catalysts and reaction mechanism of the side-chain alkylation of toluene to styrene

A series of Cs/CuAl-LDO@Al2O3@Fe3O4 magnetic catalysts with varied CuAl-LDO contents were prepared by growing CuAl-LDH layers on the surface of Al2O3@Fe3O4 magnetic cores, impregnated with Cs and followed by calcination. The as-synthesized catalysts were characterized by XRD, N2 adsorption-desorption, SEM, TEM(EDS), XPS, NH3-TPD, CO2-TPD, and VSM techniques. The catalytic performance and reusability of the catalysts for the side-chain alkylation of toluene with formaldehyde were evaluated in a micro-high-pressure reactor, and the reaction mechanism was further studied. The results showed that the Al2O3@Fe3O4 magnetic core of the catalyst was about 110 nm, and the CuAl-LDO formed a staggered lamellar structure with a shell thickness of around 30–45 nm. The magnetic catalyst demonstrated excellent catalytic performance and reusability for the side-chain alkylation of toluene with formaldehyde in one-step to styrene. As-synthesized magnetic Cs/CuAl-LDO@Al2O3@Fe3O4 catalyst with CuAl-LDO content of 20 wt% delivered toluene conversion of 7.97% under optimized conditions, while the styrene selectivity and the selectivity of side-chain alkylation were 90.17% and 98.36%, respectively. The reaction mechanism showed that the benzene ring of toluene was stably adsorbed on the Al3+ acid sites of the CuAl-LDO layers. The C–H group of the side-chain of toluene formed carboanions and protons under the action of the Cuδ+–Oδ– base sites. Formaldehyde formed a transition state of adsorbed formaldehyde under the action of Cuδ+ acid sites. Finally, these adsorbed states and intermediate species accomplished the side-chain alkylation of toluene with formaldehyde to styrene in one-step under the synergic action of acid-base sites. The synergistic effects of suitable acid-base sites and lamellar spatial structures in the catalyst were the key to styrene formation with high selectivity.

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.

Restructuring Surface Lewis Pairs of FAU Zeolite through N Doping for Boosting the Toluene Side-Chain Alkylation Performance.

Toluene side-chain alkylation with methanol for the styrene monomer formation remains a great challenge. An optimal synergy between acidic and basic sites on zeolites is required for an efficient catalysis process. It is important to modulate the surface Lewis acid-base pairs precisely. Herein, we report a strategy to restructure the surface Lewis acid-base pairs in cesium-modified X zeolite (CsX) by N doping. In the process of toluene side-chain alkylation, the CsX-BN-600 catalyst, where N species is doped into the framework of the X zeolite, exhibits 2.7 times the styrene formation rate and a much better selectivity of 85.7% in comparison to the parent CsX of 70.1% selectivity to styrene at the same reaction conditions. The introduction of N species into zeolites acts as a new Lewis base site and optimizes the Lewis sites due to its ability of electron donation. Meanwhile, the frustrated Lewis pair (FLP) between the deprotonated framework nitrogen in X zeolite and positively polarized C species in the side-chain alkylation reaction is created. Furthermore, the N doping contributes to the generation of the active intermediates of HCOO* and H3CO*. These reasons favor the superiority of the catalyst through N doping.

Ammonia pools effect in Cs modified X zeolites for side-chain alkylation of toluene with methanol

Ammonia pools effect in Cs modified X zeolites for side-chain alkylation of toluene with methanol

Enhancement of catalytic activity of PAl-NaX catalyst for side-chain alkylation of toluene with methanol: Effects of dehydrogenation component Cu

Activation and desorption of the hydrogen atom in the toluene methyl is a restrictive step for side-chain alkylation of toluene with methanol (SATM). In this work, two dehydrogenation strategies were used to improve the catalytic performance, dehydrogenation component Cu was introduced in PAl-NaX catalyst as well as the acid-base property was adjusted by changing NaOH loading amount. The relationship among the percentage of acid-base sites, low valence Cu species and the catalytic performances was investigated combined with the multiple characterizations, like X-ray photoelectron spectroscopy (XPS), Temperature-programmed desorption (TPD) of NH3 and CO2, etc. together with ternary regression analysis. It is found that the dehydrogenation component Cu, especially low valence Cu species, promotes the selectivity of side-chain alkylation products to a certain degree, but base sites play an even more critical role in enhancing it.

Preparation of Cs/Cu-LDO@X catalysts and reaction mechanism of the side-chain alkylation of toluene to styrene

The Cu-LDH@X composite materials were synthesized using the in-situ self-sacrificial template method, and the acid-base bifunctional Cs/Cu-LDO@X catalysts were prepared by impregnation-calcination. The as-synthesized catalysts were characterized by XRD, N2 adsorption-desorption, SEM, HRTEM (EDS), FTIR, XPS, NH3-TPD, CO2-TPD techniques. The catalytic performance of the catalysts was evaluated in one step by implying a fixed-bed microreactor for the side-chain alkylation of toluene with methanol to styrene. The reaction mechanisms of the side-chain alkylation on the catalysts surface were deeply investigated. The Cs/Cu-LDO@X catalysts with adjustable acid-base sites and nanolayered structures demonstrated good catalytic performance for the side-chain alkylation of toluene. The Cs/Cu-LDO@X-3 catalyst exhibited the best catalytic performance with toluene conversion is up to 6.58%, while the selectivity of side-chain alkylated products and styrene is 91.64% and 54.16% respectively. The reaction mechanism investigation indicates that methanol dehydrogenated firstly to form formaldehyde under the action of the base sites on the catalyst surface, later, the adsorbed toluene on the acid sites underwent side-chain alkylation with formaldehyde. High selectivity of produced styrene owing to the synergistic interactions of acid-base sites and layered space-confined effects of the catalytic system.

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.

Synthesis of tert-amylbenzene for side-chain alkylation of cumene catalyzed by a solid superbase

Abstract The side-chain alkylation of cumene and ethylene over a solid superbase catalyst K/KOH/γ-Al2O3 is investigated. The effects of the reaction temperature, pressure, and time on the conversion of cumene and selectivity of tert-amylbenzene (TAB) are discussed. The experimental results show that the conversion of cumene to tert-pentylbenzene increases with the increase in reaction temperature and ethylene pressure. The catalytic reaction has certain operational flexibility in terms of the reaction temperature, pressure, and time. In addition, the catalytic reaction can achieve directional conversion. The optimum operating conditions are obtained using a single factor test. The conversion of cumene is 99.8% and the selectivity toward TAB is 97.9% under catalyst concentration of 4 wt%, reaction temperature of 55°C, reaction pressure of 0.45 MPa, and reaction time of 30 min. The deactivation of catalyst is mainly caused by oxygen and water in the raw material.

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.

Cesium-modified hollow ZSM-5: Efficient acid-base catalyst for side-chain alkylation of 2-picoline with formaldehyde

Hollow ZSM-5 was successfully fabricated using a tetrapropylammonium hydroxide (TPAOH) hydrothermal treatment with an “dissolution-recrystallization” process. The side-chain alkylation of 2-picoline with formaldehyde was studied on a series of cesium modified ZSM-5 catalysts. Among these catalysts, Cs2O/Cs-hollow ZSM-5 (Cs2O/Cs-hZSM-5) was found to be the most effective catalyst, which exhibited not only the highest 2-picoline conversion (50.1 %), but also the highest TOF value (2.557 h−1) and the lowest Ea (39.7 kJ mol−1). Meanwhile, the Cs2O/Cs-hZSM-5 catalyst exhibited excellent reaction durability, which was related to the hollow structure of ZSM-5. In addition, the possible 2-picoline side-chain alkylation reaction pathways over cesium modified hollow ZSM-5 catalysts were proposed. The results of this study suggested that cesium modified hollow ZSM-5 is a promising candidate as a catalyst for the reaction of 2-picoline side-chain alkylation with formaldehyde in industrial applications.

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.

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.

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.

Promoting effect of copper oxide on CsX zeolite catalyst for side-chain alkylation of toluene with methanol

Cesium exchanged X zeolites (CsX) have been widely used as the catalyst for toluene side-chain alkylation with methanol to produce styrene. In this work, copper oxide was recognized as an efficient promoter to improve the performance of CsX catalyst in both the reactivity and styrene selectivity. Based on systematic characterization of CuO modified CsX samples and further analysis of their catalytic performance, the promoting effect of CuO additive was explored. On one hand, the introduced Cu species promoted the dehydrogenation of methanol to formaldehyde, which acted as real alkylating agent and enhanced toluene conversion. On the other hand, the catalyst acid-base property was sensitively modulated, and thereby the undesired transfer hydrogenation of styrene to ethylbenzene was suppressed. Furthermore, the universality of CuO promoter was proved by loading on some well-known catalysts (Cs2O/CsX, B2O3/CsX and ZnO/CsX), and the effect of reaction condition was also studied with the most efficient CuO–B2O3/CsX catalyst.

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.