Disproportionation of Toluene by Modified ZSM-5 Zeolite Catalysts with High Shape-selectivity Prepared Using Chemical Liquid Deposition with Tetraethyl Orthosilicate

Shape-selective catalysts for the disproportionation of toluene were prepared by the modification of the cylinder-shaped ZSM-5 zeolite extrudates with chemical liquid deposition with TEOS （tetraethyl orthosilicate）.Various parameters for preparing catalysts were changed to investigate the suitable conditions.The resulting cata-lysts were tested in a pressured fixed bed reactor and characterized by SEM （scanning electron microscopy）.The conversion of toluene and para-xylene selectivity were influenced remarkably by the n（SiO2）/n（Al2O3） ratio of ZSM-5 zeolite,the type and amount of deposition agent,acid and solvent used,and the time and cycle of deposition treatment.TEOS was proved to be a more efficient agent than the conventional polysiloxanes when the deposition amount was low.The catalyst prepared at the suitable conditions exhibited a high para-xylene selectivity of 91.1% with considerable high conversion of 25.6%.SEM analyses confirmed the formation of a layer of amorphous silica on the external surface of ZSM-5 zeolie crystals,which was responsible for the highly enhanced shape-selectivity.

Anti-carbon deposition performance of twinned HZSM-5 encapsulated Ru in the toluene alkylation with methanol

Toluene methylation with methanol to produce para-xylene has been extensively and intensively studied.However,the methanol-to-hydrocarbons(MTH)side reaction in this reaction is difficult to be inhibited,which will cause a mass of carbon deposition and cover the catalyst surface,resulting in catalyst deactivation.Here,a dual-functional Ru@HZSM-5 catalyst with high para-selectivity and low carbon deposition was prepared by encapsulating Ru metal with HZSM-5.According to catalytic performance studies,the Ru@HZSM-5 catalyst produced xylene selectivity of 98%and para-xylene selectivity of 96%.Meanwhile,we find that carbon precursors(e.g.ethylene)were very little when Ru catalyst was used,but the results of HZSM-5 catalyst were completely opposite.Ru@HZSM-5 catalyst achieves a lower carbon deposition rate of only 6%of HZSM-5.The main possible reason for this is that the initial C-C bond between methanol and the olefin is difficult to form.

Performance of HZSM-5 as Catalyst for Alkylation of Methyl-naphthalene with Methanol in Supercritical Phase

The alkylation of methylnaphthalene（MN） with methanol in the presence of HZSM-5 is a promising route for producing 2,6-dimetylnaphthalene（2,6-DMN） with a high selectivity. However, the conversion of MN is very low and the catalyst will be deactivated rapidly with increasing time on stream. In this study, the effects of the reaction pressure on the reactivity, selectivity and life of the catalyst of alkylation of MN over HZSM-5 modified by BaO were investigated. It was observed that with the enhancement of pressure, the conversion of MN increased, but the selectivity of 2,6-DMN kept unchanged, which was about 40% -42%. When the alkylation was carried out under a supercritical condition, the conversion of MN was 3-6 times higher and the life of catalyst was 25-30 times longer than those at an ambient pressure. The thermogravimetric analyses of the deactivated catalysts at different reaction pressures indicate that the amount of coke deposited on the catalysts was about 10% to 12 %, and the coke-burning reactions mainly took place in a temperature range from 720 to 860 K, and the apparent activation energies of the coke-burning catalysts at 0. 1 MPa（ 10 h） and 7. 6 MPa（ 108 h） were, respectively, 65.90 and 84. 72 kJ/mol. It is concluded from tile results that the supercritical condition is advantageous to enhancing the conversion of alkylation and extraction in situ, and to transporting those high molecular-weight poly-aromatic compounds so as to extend the catalyst life successively.

Improved Stability and Shape Selectivity of 2,6-Dimethylnaphthalene by Methylation of Naphthalene with Methanol on Modified Zeolites

2,6-Dimethylnaphthalene (2,6-DMN) is a key intermediate for polyethylene naphthalate synthesis. The selective synthesis of 2,6-DMN from naphthalene and methanol was carried out over different zeolites (HZSM-5, Hβ, HUSY and SAPO-11) modified by 0.1wt% PdO under atmospheric pressure. Among the adopted zeolites, SAPO-11 exhibits exceptional shape-selectivity and stability to synthesize 2,6-dimethylnaphthalene from methylation of naphthalene, due to the special pore structure of SAPO-11 which inosculated better with 2,6-dimethylnaphthalene than with 2,7-dimethylnaphthalene.

Pore-mouth catalysis boosting the formation of iso-paraffins from syngas over bifunctional catalysts

Recent studies confirm that the emerging bifunctional catalysts consisting of metal oxide and zeolites can directly convert syngas into high-quality gasoline,however,the formation mechanism of iso-paraffins and the difference with the conventional FT/zeolite catalyst have not been investigated.Herein,three one-dimensional SAPO zeolites with diverse micropore sizes were synthesized and assembled with ZnAlO_(x)with spinel structure.It was found that ZnAlO_(x)/SAPO-41 and ZnAlO_(x)/SAPO-11 with medium micropore sizes favored the formation of C_(5)–C_(11)hydrocarbons with a high content of iso-paraffins.The characterizations pointed out that the formation of iso-paraffins over SAPO-11 followed a pore-mouth catalysis mechanism,which means the isomerization of linear hydrocarbons can only take place near the pore mouth region of zeolites.This mechanism only allows the formation of mono-branched iso-paraffins in the C_(5)–C_(11)range,which are less prone to be cracked than their di-branched isomers.A careful comparative analysis between ZnAlO_(x)/SAPO-11 and Co/H-meso-ZSM-5 was also made in terms of product distribution,activity,and stability.

Dual-template synthesis of HZSM-5 zeolites with tailored activity in toluene methylation with CH3Br

Shape-selective zeolites(UZ-x/y) were synthesized by a one-pot method using TPAOH(y) and/or MeEt3 N^+I^-(x) as templates.The use of MeEt3 N^+I^- affects the crystal growth and the distribution of acid sites on the external surface of the zeolites.The catalysts show excellent catalytic activity towards toluene alkylation with CH3 Br.With toluene conversion of 36.3% and p-xylene selectivity of 66.2%,HZ-40/0 is the most effective among the prepared catalysts,showing a p-xylene yield of 21.2%.The improved para-selectivity is mainly due to the decrease of acid sites on the external surface of the catalysts.

铂和HF掺杂的H-ZSM-5分子筛催化甲苯与甲醇烷基化反应(英文)

Toluene was alkylated with methanol in a flow type reactor at temperatures between 300 and 500 °C using H-ZSM-5 zeolite, 0.2%Pt/H-ZSM-5 and hydrofluorinated 0.2%Pt/H-ZSM-5 with HF concentrations of 1.0%, 2.0%, 3.0%, or 4.0%. Pt primarily enhances toluene conversion, total xylenes production, and p-xylene relative to its thermodynamic equilibrium. As the concentration of HF increases from 1.0% to 3.0%, the catalyst activity increases because of the increase in the number of acid sites and their strength. Additionally, the surface area and Pt dispersion also increases. An advantage of increased HF doping is that the formation of voluminous trimethylbenzene (TMB) byproducts is inhibited. However, at a HF concentration of 4.0%, Al and Si are partially leached and then deposited mostly in the wider catalytic pores. This was determined by evaluating the pore volume distribution and we determined that reactivity inhibition was ob-viously present and was due to diffusion restriction.

Photogenerated singlet oxygen over zeolite-confined carbon dots for shape selective catalysis

Singlet oxygen as an activated oxygen species played an important role in organic synthesis. Suitable catalyst for converting ubiquitous oxygen molecule to singlet oxygen under mild conditions has attracted a wide range of attention. Herein, carbon dots have been confined into mesopores of silicalite-1 nanocrystals framework and acted as active sites for generation of singlet oxygen. The high oxygen-adsorption capacity of zeolite nanocrystals facilitated the photocatalytic generation rate of singlet oxygen, outpacing the free-standing carbon dots for 14-fold. The integrated carbon dot-zeolite nanocrystal hybrid also exhibited a special size-dependent selectivity for organic synthesis by using the in situ formed and confined singlet oxygen as active oxygen species.

Overcoming the limitations of anthracene alkylation using SZ-DeAl-DFNS acid catalyst

In situ formation of composite micro-mesoporous dendritic fibrous nano-silica(DFNS) and Al-DFNS was prepared using a cetylpyridinium bromide(CPB) template synthetic system. Dealumination is induced by impregnation of zirconium with flux followed by a sulfuric acid treatment. This procedure results in a series of highly uniform nano-spheres, which exhibit stronger acid property than that of Al-MCM-41. In the selective alkylation of anthracene with tert–amyl alcohol, SO_(4)^(2-)modified Zr-contained dealuminated Al-DFNS(SZ-De Al-DFNS) shows great catalytic activity and higher conversion(60.8%). The DFNS samples were characterized with XRD, SEM, TEM, NH_(3)-TPD and other techniques. The results reveal that DFNSs consist of center-radial micro-mesopores and that the acid contribution of SZ-De Al-DFNS is much broader,as compared with amorphous aluminosilicate.

Highly selective hydration reaction of a-pinene over H-mordenites pretreated with quaternary ammonium salts

The application of shape-selectivity of zeolite in petrochemistry has been an ac-tive research area since it was first proposed by Weisz and Frilette, and the tendencyto utilize the potential for specific, highly selective syntheses in the field of inter-mediates and fine chemicals has continued steadily in recent years. Nevertheless,