Production of linear alkylbenzene over Ce containing Beta zeolites

Ce-encapsulated Beta zeolite was synthesized by a one-pot hydrothermal method with citric acid complexing Ce in the absence of Na species.Additional citric acid can effectively prevent the deposition of Ce species during the hydrothermal synthesis of zeolites,leading to uniform distribution of Ce cluster in the framework of Beta zeolites.Moreover,the sodium-free synthesis system resulted that the Brønsted acid sites were mainly located on the straight channels and external surface of Beta zeolites,improving the utilization of Brønsted acid sites.In addition,Ce encapsulated Beta zeolites showed enhanced activity and robust stability in the alkylation of benzene with 1-dodecene based on the synergistic effect between Ce species and Brønsted acid sites,which pave the way for its practical application in the production of alkylbenzene.

Adsorptive desulfurization over hierarchical beta zeolite by alkaline treatment

Hierarchical beta zeolites with SiO2/Al2O3 molar ratios of 16 to 25 were obtained by alkaline treatment in NaOH solution. The effects of treatment temperature on crystallinity, textural properties and chemical composites were studied by XRD, N2 sorption, FT-IR and XRF techniques. The desulfurization performance of parent and alkaline-treated beta zeolites was investigated by static absorption in four model fuels, containing four sulfur compounds of different molecular sizes like thiophene （TP）, 3-methylthiophene （3-MT）, benzothiophene （BT） and dibenzothiophene （DBT）, respectively. The crystallinity was observed to be successfully maintained when the treatment temperature was below 50 ℃. Mesoporosity of beta zeolite was evidently developed with alkaline treatment. The formation of mesopore remarkably improved the desulfurization performance for TP, 3-MT, BT and DBT, especially for DBT with larger molecular diameter. Though the addition of toluene in the model fuels resulted in a significant drop of the desulfurization performance of mesoporous beta zeolite, the introduction of cerium ions to some extent mitigated the effect of toluene, which means that both the adsorbent’s porous structure and the adsorption mode are responsible for the desulfurization performance. The adsorbent of cerium ion-exchanged mesoporous beta showed about 80% recovery of desulfurization after the first regeneration.

All-silica zeolites screening for capture of toxic gases from molecular simulation

The exhaust gases, including SO_2,NH_3, H_2S, NO_2, NO, and CO, are principal air pollutants due to their severe harms to the ecological environment.Zeolites have been considered as good absorbent candidates to capture the six exhaust gases.In this work, we performed grand canonical ensemble Monte Carlo(GCMC) simulations to examine the capability of 95 kinds of all-silica zeolites in the removal of the six toxic gases, and to predict the adsorption isotherms of the six gases on all the zeolites.The simulation results showed that, H_2S, NO, NO_2, CO and NH_3 are well-captured by zeolite structures with accessible surface area of 1600–1800 m^2·g^(-1) and pore diameter of 0.6–0.7 nm, such as AFY and PAU, while SO_2 is well-adsorbed by zeolites containing larger accessible surface area(1700–2700 m^2·g^(-1)) and pore diameter(0.7–1.4 nm) at room temperature and an atmospheric pressure.However, at saturated adsorption, zeolites RWY, IRR, JSR, TSC, and ITT are found to exhibit better abilities to capture these gases.Our study provides useful computational insights in choosing and designing zeolite structures with high performance to remove toxic gases for air purification, thereby facilitating the development and application of exhaust gas-processing technology in green industry.

Catalytic performance of Cu-and Zr-modified beta zeolite catalysts in the methylation of 2-methylnaphthalene

2,6-Dimethylnaphthalene(2,6-DMN) is a commercially important chemical for the production of polyethylenenaphthalate and polybutylene naphthalate. However, its complex synthesis procedure and high production cost significantly reduce the use of 2,6-DMN. In this study, the synthesis of 2,6-DMN was investigated with methylation of 2-methylnaphthalene(2-MN) over metal-loaded beta zeolite catalysts including beta zeolite, Cu-impregnated beta zeolite and Zr-impregnated beta zeolite. The experiments were performed in a fixed-bed reactor at atmospheric pressure under a nitrogen atmosphere. The reactor was operated at a temperature range of 400–500 °C and varying weight hourly space velocity between 1 and 3 h^(-1).The results demonstrated that 2,6-DMN can be synthesized by methylation of 2-MN over beta type zeolite catalysts.Besides 2,6-DMN, the product stream also contained other DMN isomers such as 2,7-DMN, 1,3-DMN, 1,2-DMN and 2,3-DMN. The activity and selectivity of beta zeolite catalyst were remarkably enhanced by Zr impregnation, whereas Cu modification of beta zeolite catalyst had an insignificant effect on its selectivity. The highest conversion of 2-MN reached81%, the highest ratio of 2,6-DMN/2,7-DMN reached 2.6 and the highest selectivity of 2,6-DMN was found to be 20% by using Zr-modified beta zeolite catalyst.

Surface dealuminated Beta zeolites supported WO3 catalyst and its catalytic performance in tetralin hydrocracking

In this study,selective dealumination of Beta zeolites was performed through partially removing the templating agent in Beta zeolites by calcination and then removing the aluminum on the external surface of Beta zeolites with acid treatment.Hydrocracking catalysts were prepared by loading WO_(3)onto these dealuminated Beta zeolites.It was shown that the surface SiO_(2)/Al_(2)O_(3)of selectively dealuminated Beta zeolites was higher than that of conventionally dealuminated samples for the same bulk SiO_(2)/Al_(2)O_(3),and the hydrogenation activity of the catalyst of the selectively dealuminated Beta zeolites was lower than that of conventionally dealuminated Beta zeolites.The experimental results for tetralin hydrocracking to BTX showed that the catalysts based on the selectively dealuminated Beta zeolites had higher BTX selectivity and lower coke formation rate than that the catalysts based on the conventionally dealuminated Beta zeolites.

Preparation and Characterization of Zeolite Beta with Low SiO_2/Al_2O_3 Ratio

Zeolite beta with a low SiO2/Al2O3 ratio was synthesizcd by a novel two-step process. The synthesized sample was characterized with XRD, SEM, FTIR, and N2 adsorption-desorption and solid-state MAS NMR. The results showed that aluminium species were inserted into the framework of zeolite beta. The BET surface area, volume, and particle size of the zeolite beta sample decreased with decreasing SiO2/Al2O3 ratio. Our process was proved an efficient route to synthesize zeolitc beta with a low SiO2/Al2O3 ratio.

Etherification of HMF to biodiesel additives: The role of NH4+ confinement in Beta zeolites

The role of NH4^+ ion confinement in the catalytic etherification of HMF(5-hydroxymethylfurfural) with ethanol to biodiesel additives was evidenced by studying the catalytic behavior of NH4^+-Beta zeolites with SiO2/Al2O3 ratios of 25 and 75.In order to affect the strength and distribution of the acidic sites, as well as the mobility of NH4^+ ions in the zeolites cages, a secondary level of porosity was introduced in the NH4^+-Beta, presenting a different stability versus alkaline treatment, by using a thermal or an ultrasound assisted method.By analyzing the catalytic behavior in these two series of samples with respect to the changes in porosity by nonlocal density functional theory, structure by XRD, amount of acid sites by FT-IR and mobility of NH4^+ cations by measurements of reversible NH4^+ exchange capacity, was evidenced a decrease in catalytic performances both in terms of rate of HMF depletion and productivity to the main products, when confinement of the ammonium ions is lost due to the introduction of mesoporosity.The high capability of ammonium ions release, associated to the mono-dentate configuration,and the minor confinement effect inside the zeolite pore system, due to the more opened pores structure of mesoporous zeolites, hinders both the direct etherification of HMF to EMF [5-(ethoxymethyl)furan-2-carbaldehyde] and the parallel reaction pathway via acetalization, favoring the rapid desorption of the HMFDEA [5-(hydroxymethyl)furfural diethyl acetal] product out of the crystal and the consequent inhibition of the consecutive reactions to EMFDEA [5-(ethoxymethyl)furfural diethyl acetal] and EMF.

Synthesis of Single Crystals of Zeolite Betaby Using Two Silica Sources

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Crystallization behavior of zeolite beta from acid-leached metakaolin

Well-crystallized zeolite beta was synthesized by using acid-leached metakaolin as the silica-alumina source and tetraethylammonium hydroxide structure-directing agent.The influence of the composition of the reaction mixture on product crystallinity was investigated,and the crystallization process was studied by examining solid samples obtained at different synthesis times.Results showed that the acid-leached metakaolin was fully converted into soluble aluminum and silicon species,which is crucial for the formation of well-crystallized zeolite beta.At the beginning of the crystallization process,these soluble aluminum and silicon species formed a aluminum-rich intermediate structure with layer morphology.With the crystallization proceeding,more silicon species were incorporated into the zeolite beta framework and the layered structure was changed into spherical particles of zeolite beta with high SiO 2 /Al 2 O 3 ratio and crystallinity.

Deactivation mechanism of beta-zeolite catalyst for synthesis of cumene by benzene alkylation with isopropanol

The alkylation of benzene with isopropanol over beta-zeolite is a more cost-effective solution to cumene production. During the benzene alkylation cycles, the cumene selectivity slowly increased, while the benzene conversion presented the sharp decrease due to catalyst deactivation. The deactivation mechanism of betazeolite catalyst was investigated by characterizing the fresh and used catalysts. The XRD, SEM and TEM results show that the crystalline and particle size of the beta-zeolite catalyst almost remained stable during the alkylation cycles. The drop in catalytic activity and benzene conversion could be explained by the TG, BET,NH_3-TPD and GC–MS results. The organic matters mainly consisted of ethylbenzene, p-xylene and 1-ethyl-3-(1-methyl) benzene produced in the benzene alkylation deposited in the catalyst, which strongly reduced the specific surface area of beta-zeolite catalyst. Moreover, during the reaction cycles, the amount of acidity also significantly decreased. As a result, the catalyst deactivation occurred. To maintain the catalytic performance,the catalyst regeneration was carried out by using ethanol rinse and calcination. The deactivated catalyst could be effectively regenerated by the calcination method and the good catalytic performance was obtained.

响应面模型用于Beta分子筛催化剂蜂窝状整体式成型的研究

Beta分子筛由于具有独特的三维十二元环孔道结构,可提供更多活性组分附着位点,是在实际应用中具有优异性能的工业催化剂。在工业使用中,蜂窝整体式催化剂具有通量高、流场均匀、压降小、不易堵塞的优点,是气固或者液固催化反应的最优解决方案。但由于Beta分子筛吸水率高,收缩率大,导致蜂窝成型困难,严重限制了Beta分子筛的工业应用。基于此,选择拟薄水铝石(SB粉)为黏结剂、硝酸为胶溶剂、田菁粉为助挤剂,在水粉比为0.6的条件下制备一系列蜂窝整体式成型Beta分子筛催化剂,基于响应面法,评价了各原料的配比对蜂窝整体式催化剂机械强度的影响,得到了催化剂的机械强度与3个因素(黏结剂用量、胶溶剂用量、助挤剂用量)之间关系的二阶多项式近似模型函数。将试验结果与预测值进行对比,证明了预测模型的可靠性,并利用该模型找到最优的Beta分子筛蜂窝成型条件为SB粉质量分数36.1%、硝酸质量分数8.4%、田菁粉质量分数4.7%。

Cubic Mesoporous Aluminosilicate with Primary Structure Units of Zeolite Beta in the Pore Wall

Mesoporous aluminosilicate with cubic ordered structure was synthesized by two-step crystallization, which showed stronger acid sites and more effective activity for catalytic alkylation of 2, 4-ditert-butylphenol with tert-butanol than conventional H-AlMCM-48 materials.

Theoretical Study on a 42 T Model of Beta Zeolite by Density Functional Theory Simulation

Density functional theory was applied to study the structure of Beta zeolite. A model cluster containing 41Si atoms, 1 Al atom, 70 O atoms and 29 H atoms was constructed. The model structures were optimized using the Becke＇s three-parameter hybrid method with the Lee-Yang-Parr correlation functional （B3LYP） and the 6-31G basis set applying the Gaussian03 program package. The NMR parameters were calculated to validate the rationality of the model. It was found that in the optimization models, all O-H bond lengths were in range of 0.984-0.985A^°, among which the model with O-H bond length of 0.98478A^° was more stable than the others. The ^1H and ^27Al chemical shifts of the most stable model were 4.03434 and 55.74 ppm, which were pretty consistent with Larry＇ s experimental data of 4.1 and 54 ppm. The relationship between other structure parameters and total relative electric energy has also been found. All the results exhibit that the 42 T （the total number of Si and Al atoms is 42） model has common properties of the standard of zeolite Beta.

Pt/Beta催化剂上Pt金属中心/酸中心浓度比对加氢异构化性能的影响

以工业Beta沸石为载体,负载不同含量的Pt,得到了不同金属中心/酸中心浓度比(c_(M)/c_(A))的催化剂,对其进行物化表征,并以正庚烷为模型化合物对不同c_(M)/c_(A)催化剂进行异构化反应性能评价。结果表明:Pt粒子均匀地负载在沸石的外表面上,对沸石结构没有影响,酸性略有下降。对于催化剂的正庚烷异构化反应活性,当催化剂c_(M)/c_(A)小于0.037时,反应过程由金属中心数量控制,产生大量多支链异构体产物和裂化产物;当c_(M)/c_(A)大于0.285时,反应过程由酸中心数量控制,有氢解反应发生。在反应压力为0.4 MPa、反应温度为207℃、质量空速为1.0 h^(-1)、氢/烃摩尔比为5、催化剂质量为1.0 g的条件下,当催化剂c_(M)/c_(A)为0.266、正庚烷转化率为70.75%时,异构体总选择性为95.14%,总收率为67.31%,其中多支链异构体收率为15.63%,裂化产物收率低于5%。

A New Route to Syntheses of Zeolite Beta

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An IR Study on Adsorption of CO and NO on Copper Ion-exchanged Zeolite Beta

Thee adsorption of CO and NO on copper ion-exchanged zeolite Beta was investigated using IR method.It was found that the thermalvacuum pretreatment procedure could result in the reduction of Cu2+ions in zeolite Beta.The adsorption of CO on Cu+sites in zeolite Beta closely follows Langmuir isotherm.Another Cu+species may form during the reaction between water and CO.The catalytic decomposition of NO on the zeolite was observed at room temperature,indicating that the decomposition reaction may occur between two coordinated NO ligands of the same dinitrosyhc complex.Furthermore,the appearance of two series of NO adsorption bands reveals that copper ions existing at different cation sites may have different effect on the adsorption and decomposition of NO molecules.

THE EFFECT OF ACID TREATMENT ON THE STABILITY OF POLYMORPHS IN BETA ZEOLITE

The stability of beta zeollie in acid solution and the effect of acid treatment on the polymorphs in beta zeolite were studied. This zeolite is easily dealuminated by HCI treatment but its framework highly resistent to acidity.In β zeolite, polymorph A is less stable than polymorph B.The chirality of β zeolite can be modified by the method of acid treatment.

ZnO-beta zeolite:As an effective and eco-friendly heterogeneous catalyst for the synthesis of benzothiazole derivatives

A cheap and recyclable ZnO-beta zeolite was used as catalyst for the synthesis of benzothiazole derivatives.This method provides several advantages such as environmental friendliness,short reaction times,high yields,simple work-up procedure and catalyst was successfully reused for four cycles without significant loss of activity.