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不同粒径ZSM-5分子筛在苯与甲醇烷基化反应中催化性能及反应条件优化
Catalytic Properties of Different Crystal Sizes for ZSM-5 Zeolites on the Alkylation of Benzene with Methanol and Optimization of the Reaction Conditions
 [PDF]

袁苹,王浩,(),薛彦峰,李艳春,王凯,董梅,樊卫斌,秦张峰,王建国
- , 2016, DOI: 10.3866/PKU.WHXB201604141
Abstract: 采用水热合成法合成了不同粒径的ZSM-5分子筛催化剂,系统考察了分子筛粒径变化对苯与甲醇烷基化反应的影响。研究结果表明,随着ZSM-5分子筛粒径增大,不但苯的转化率和二甲苯选择性降低,而且催化剂稳定性明显下降。其中,粒径为0.25 μm的ZSM-5分子筛在苯烷基化反应中的催化性能最佳,且催化剂稳定性最好。另外,采用拉曼光谱和热重等方法对催化剂积碳物种和失活机理进行了深入研究,发现催化剂失活主要是由于反应过程中生成的大分子稠环芳烃堵塞了分子筛孔道并覆盖活性位点造成的。最后,考察了反应温度、原料组成及空速对苯烷基化反应的影响并优化出最佳的苯烷基化反应条件。
The hydrothermal synthesis method is used to prepare various crystal sizes of ZSM-5, and the effect of the crystal size on the alkylation of benzene with methanol is systematically investigated. The research results show that the conversion of benzene, selectivity of xylene, and the stability of the catalyst all decrease significantly with increasing crystal size. The ZSM-5 zeolite with a crystal size of 0.25 μm possesses the best catalytic performance and stability compared with other larger-sized zeolites. In addition, the deposition species and deactivation mechanism were also studied by Raman spectroscopy and thermogravimetric analysis. The results indicate that the catalyst deactivation may be attributed to the formation of polycyclic aromatic molecules, which can block the channel of the zeolite and cover the active sites. Finally, the effects of the reaction temperature, ratio of benzene to methanol, and space velocity on the alkylation of benzene with methanol are also investigated, and the optimum reaction conditions are determined
The Effect of Alkaline Treatment to the Structure of ZSM5 Zeolites
Savitri Octaviani
Makara Seri Sains , 2012,
Abstract: Hierarchical zeolites combining micro- and mesoporosity were prepared using desilication method in alkaline solution of NaOH 0.2 M on two types of ZSM5: ”template free” commercial ZSM5 (Si/Al 8.62) and ‘templated’ as-synthesized ZSM5 (Si/Al 25). The powder X-ray diffraction patterns revealed that crystallinity and short-range order in the alkaline treated zeolites were virtually unchanged compared to both of the parent zeolites. The surface measurement on the ”template free” ZSM5 zeolites showed that the surface area was reduced by 2.33%, but the adsorption isotherm can be categorized into Type IV which is typical of for mesoporous material, supported by the change in mesopore volume, and the BJH pore size distribution (from 10 to 18 nm). On the other hand, the surface area of the alkaline treated as-synthesized ZSM5 was increased by 8.25%, but its isotherm adsorption curve falls into Type I for microporous structure. The mesopore volume was increased by 26%, from 0.037 cm3/g to 0.046 cm3/g, with the intrinsic zeolite properties were mainly preserved. Based on these results, it can be concluded that the existence of organic template plays an important role in preserving the zeolitic structure during the alkaline treatment.
CORRELATION WITH DIFFERENT MODELS FOR ADSORPTION ISOTHERMS OF M-XYLENE AND TOLUENE ON ZEOLITES
ZOUBIR BENMAAMAR,ABDELKHADER BENGUEDDACH
Journal of Applied Sciences in Environmental Sanitation , 2007,
Abstract: The ability of NaY, KY, BaY, BaX and NaX zeolites to adsorb m-xylene and toluene was studied experimentally. Thus, the adsorption isotherms of two volatile organic compounds, toluene and m-xylene, on NaY, KY, BaY, BaX and NaX were measured at 298, 308, 318, and 333 K using a vacuum microbalance system. The toluene and the m-xylene were chosen because they belong to the same chemical family. The experimental data obtained were correlated with different existing adsorption isotherm models such as the Langmuir model, the Freundlich model, the Fowler-Guggenheim model, the Hill-De Boer model and the Sips model. The Langmuir model is well adapted to the description of m-xylene and toluene adsorption on NaY, KY, BaY, BaX and NaX zeolites at all four temperature. The Sips model is also found to be well adapted to describe the adsorption of toluene on to NaY, KY, BaY, BaX and NaX zeolites at all four temperature. The Freundlich model, the Fowler-Guggenheim model, and the Hill-De Boer model were not satisfactory. The adsorption affinity of m-xylene on NaY, KY, BaY, BaX and NaX zeolites is sufficiently greater than the affinity of toluene. The adsorption affinity of m-xylene and toluene decreased in the following order NaY>NaX>BaX>KY>BaY. These results demonstrate the high capacity of NaY, KY, BaY, BaX and NaX zeolites to remove vapors of m-xylene and toluene at very low concentrations. However, in the volumetric method, the accuracy of the data depends on the precision with which the equilibrium pressure is measured. Besides, the existence of dead volume, the value of which is never known with high precision, is a source of error. That is why, the gravimetric method remains the most accurate method for measuring gas-solid equilibrium data for pure gases.
Selective catalytic reduction of NO to N2 with copper and cobalt exchanged ZSM-5 zeolites: the effect of calcium addition
Martins, Leandro;Peguin, Robson Pablo S.;Wallau, Martin;Urquieta-González, Ernesto Antonio;
Journal of the Brazilian Chemical Society , 2005, DOI: 10.1590/S0103-50532005000400016
Abstract: zsm-5 catalysts containing either cu or co cations individually or cu/ca or co/ca cation combinations were prepared by ion exchange. these materials were tested as catalysts for the reduction of no to n2 in the presence of propane or methane. cu2+ and [cu-o-cu]2+ species were identified in ion exchangeable sites in the copper-containing catalysts. the amount of the latter cation increased with increasing copper content and in the presence of ca2+ and was the most active in the reduction of no. however, at temperatures higher than 400 oc its activity decreased markedly. for cobalt-exchanged zeolites, co2+ in charge-compensation sites or co3+ in extra-framework precipitates were present in the catalysts. it was verified that the amount of co3+ diminished with the presence of ca2+. for the catalysts prepared in this study no significant differences in specific activity for the reduction of no or for methane oxidation were observed in the presence of calcium.
单一模板线性多胺一步合成多级孔ZSM-5沸石微球
One-Step Synthesis of Hierarchical ZSM-5 Zeolite Microspheres Using Alkyl-Polyamines as Single Templates
 [PDF]

陈丽,薛腾,朱树燕,王一萌
- , 2015, DOI: 10.3866/PKU.WHXB201411174
Abstract: 线性多胺模板剂(二乙烯三胺(DETA)、三乙烯四胺(TETA)、四乙烯五胺(TEPA))作为单一模板合成了均匀的10-15 μm的多级孔沸石ZSM-5微球. 实验发现, 在水热过程中, 50 nm纳米的沸石晶体粒子自发地堆积成微球, 并且这些微球具有较大的介孔体积, 在傅-克烷基化反应中具有高的催化活性. 同时,我们发现线性多胺起到了模板剂和空隙填充剂的多重功能,这点明显不同于以前我们报道的线性二胺作为模板剂在合成ZSM-5沸石时,主要是起模板剂的作用.
Diethylenetriamine (DETA), triethylenetetramine (TETA), and tetraethylenepentamine (TEPA) were used as single templates to synthesize mesoporous zeolite ZSM-5 microspheres. The obtained 10-15 μm hierarchical aggregates had a uniformspherical morphology, which was spontaneously assembled by primary zeolite nanocrystals of 50 nmin size during the hydrothermal synthesis. The ZSM-5 aggregates had a tunable textual porosity, large mesopore volume, and high catalytic activity in the Friedel-Crafts alkylation. Diamine templates only acted as structure directing agents in our previous work. The current alkyl-polyamine templates acted as structure directing agents and space fillers in the synthesis of the hierarchical zeolites
Species active in the selective catalytic reduction of no with iso-butane on iron-exchanged ZSM-5 zeolites
Batista, M. S.;Wallau, M.;Urquieta-González, E. A.;
Brazilian Journal of Chemical Engineering , 2005, DOI: 10.1590/S0104-66322005000300003
Abstract: fe-zsm-5 catalysts were prepared by ion exchange in aqueous medium or in the solid state and tested in the catalytic reduction of no with iso-butane. x-ray powder diffraction (xrd), atomic absorption spectroscopy (aas), electron paramagnetic resonance spectroscopy (epr), x-ray absorption spectroscopy (xanes, exafs), temperature-programmed reduction by h2 (h2-tpr) and m?ssbauer spectroscopy (m?s-s) were used for sample characterisation. irrespective of the method used in catalyst preparation, epr, xanes and m?s-s showed fe atoms in the oxidation state of 3+. m?s-s and h2-tpr data on fe-zsm-5 prepared by ion exchange in the solid state allowed quantification of a lower hematite (fe2o3) concentration and a higher proportion of fe cations than samples prepared in an aqueous medium. in all the catalysts studied these fe cations were the active sites in the reduction of no to n2 and in the oxidation of iso-butane. it is further suggested that coordination of fe species is another important aspect to be considered in their behaviour.
Cu and Co exchanged ZSM-5 zeolites: activity towards no reduction and hydrocarbon oxidation
Martins, Leandro;Peguin, Robson Pablo Sobradiel;Urquiet-González, Ernesto Antonio;
Química Nova , 2006, DOI: 10.1590/S0100-40422006000200009
Abstract: |cux|[siyal]-mfi and |cox|[siyal]-mfi catalysts were prepared by ion exchange from |na|[siyal]-mfi zeolites (y = 12, 25 and 45). the activity of the catalysts was evaluated in the reduction of no to n2 in an oxidative atmosphere using propane or methane as reducing agents. the cu catalysts were only active with propane and they presented higher activity than the co-based catalysts, the latter being active with both hydrocarbons. h2-tpr and drs-uv/vis data allowed correlation between the activity towards no reduction and the presence of cationic charge-compensating species in the zeolite. it was also verified that the hydrocarbons are preferentially oxidised by o2, a reaction that occurs simultaneously with their oxidation with no.
Cu and Co exchanged ZSM-5 zeolites: activity towards no reduction and hydrocarbon oxidation  [cached]
Martins Leandro,Peguin Robson Pablo Sobradiel,Urquiet-González Ernesto Antonio
Química Nova , 2006,
Abstract: |Cu x|[Si yAl]-MFI and |Co x|[Si yAl]-MFI catalysts were prepared by ion exchange from |Na|[Si yAl]-MFI zeolites (y = 12, 25 and 45). The activity of the catalysts was evaluated in the reduction of NO to N2 in an oxidative atmosphere using propane or methane as reducing agents. The Cu catalysts were only active with propane and they presented higher activity than the Co-based catalysts, the latter being active with both hydrocarbons. H2-TPR and DRS-UV/Vis data allowed correlation between the activity towards NO reduction and the presence of cationic charge-compensating species in the zeolite. It was also verified that the hydrocarbons are preferentially oxidised by O2, a reaction that occurs simultaneously with their oxidation with NO.
Experimental proof for resonant diffusion of normal alkanes in LTL and ZSM-12 zeolites  [PDF]
K. Yoo,R. Tsekov,P. G. Smirniotis
Physics , 2015, DOI: 10.1021/jp0307708
Abstract: The intra-crystalline diffusion of normal alkanes in LTL and ZSM-12 zeolite was experimentally studied via gravimetric measurements performed at different temperatures. A periodic dependence of the diffusion coefficient on the number of carbon atoms in alkane was detected, which is an experimental proof for resonant diffusion. The present observations were described on the base of the existing theory of the resonant diffusion and several important parameters of the alkane-zeolite interaction and zeolite vibrations were obtained. In the considered temperature region the diffusion coefficient follows the Arrhenius law with periodic dependences of the pre-exponential factor and activation energy on the number of carbon atoms in alkanes. A compensation effect of simultaneous increases of the pre-exponential factor and the activation energy was also established.
The Variety of Carbon-Metal Bonds inside Cu-ZSM-5 Zeolites: A Density Functional Theory Study  [PDF]
Takashi Yumura,Saki Hasegawa,Atsushi Itadani,Hisayoshi Kobayashi,Yasushige Kuroda
Materials , 2010, DOI: 10.3390/ma3042516
Abstract: Large-scale density functional theory calculations (DFT) found various types of binding of an unsaturated hydrocarbon (C 2H 2 and C 2H 4) to a ZSM-5 zeolite extraframework copper cation. We employed the DFT calculations based on the B3LYP functional to obtain local minima of an unsaturated hydrocarbon adsorbed on one or two copper cations embedded inside ZSM-5, and then compared their stabilization energies. The DFT results show that the stabilization energies are strongly dependent on the copper coordination environment as well as configurations of two copper cations. Consequently, the inner copper-carbon bonds are influenced substantially by a nanometer-scale cavity of ZSM-5.
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