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1.
Ahmed K. Aboul‐Gheit Sohair M. Abdel‐Hamid Sameh M. Aboul‐Fotouh Noha A. K. Aboul‐Gheit 《中国化学会会志》2006,53(4):793-802
The hydroconversion of cyclohexene (CHE) using monometallic catalysts containing 0.35wt% of Pt, Pd, Ir or Re on a γ‐alumina support, as well as bimetallic catalysts containing combinations of 0.35wt% Pt with 0.35wt% of either Pd, Ir or Re on γ‐alumina, were investigated in a plug flow‐type fixed‐bed reactor. The Cyclohexene (CHE) feed was injected continuously with a rate of 8.33 × 10?3mole h?1 on 0.2 g of catalyst using a simultaneous hydrogen gas flow of 20 cm3 min?1 throughout a broad reaction temperature range of 50–400 °C. The dispersion of the metals in the catalysts was determined via H2 or CO chemisorption. The activities of the monometallic catalysts were found to be in the order: Pd > Pt > Ir > Re, whereas those of the bimetallic catalysts were in the order: PtPd > PtIr > PtRe. Cyclohexene hydrogenation and dehydrogenation reactions using the current mono‐ and bimetallic catalysts were kinetically investigated applying the absolute reaction rate theory, whereby reaction rate constant, activation energy, enthalpy and entropy of activation were computed to explain surface variations on these catalysts. 相似文献
2.
Suchaya Pongsai 《Journal of computational chemistry》2010,31(10):1979-1985
In this article, the combination of the Metropolis Monte Carlo and Lattice Statics (MMC‐LS) method is applied to perform the geometry optimization of crystalline aluminosilicate zeolite system in the presence of cationic species (H+), i.e., H‐(Al)‐ZSM‐5. It has been proved that the MMC‐LS method is very useful to allow H+ ions in (Al)‐ZSM‐5 extra‐framework to approach the global minimum energy sites. The crucial advantage of the combination MMC‐LS method is that, in stead of simulating over thousands random configurations via the only LS method, the only one configuration is needed for the MMC‐LS simulation to achieve the lowest energy configuration. Therefore, the calculation time can be substantially reduced via the performance of the MMC‐LS method with respect to the only LS method. The calculated results obtained from the MMC‐LS and the only LS methods have been comparatively represented in terms of the thermodynamic and structural properties. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010 相似文献
3.
In this study, we prepared a modified carbon paste electrode consisting of Nickel entrapped in synthesized ZSM‐5 zeolite (Ni/ZMCPE). Then Ni(II) ions were incorporated to electrode by immersion of modified electrode in 1 M Ni(II) ion solution. Cyclic voltammetry and chronoamperometry experiments were used for electrochemical study of this modified electrode; a good redox behavior of Ni(OH)2/NiOOH couple at the surface of electrode can be observed, the excellent capability of this modified electrode for catalytic oxidation of formaldehyde was demonstrated during the anodic potential sweep in alkaline solution. The amount of transfer coefficient (α), surface coverage (Γ*) of the redox species and catalytic chemical reaction rate constant (k) for formaldehyde were evaluated. Thus, it can be a candidate as an anode for fuel cell application. 相似文献
4.
A New Practical Route to ZSM‐5 Nanoparticles and Optimization of Synthetic Parameters through D‐optimal Design of Experiments
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Saeed Soltanali Rouein Halladj Alimorad Rashidi Mansour Bazmi Saeed Khodabakhshi 《中国化学会会志》2015,62(9):817-825
A D‐optimal experimental design with three levels of SiO2/Al2O3, template/SiO2, H2O/SiO2, Na2O/SiO2 and TPABr/TPAOH ratio parameters has been used to optimize the experimental parameters by an analysis of variances (ANOVA). The effects of these ratios in the initial synthetic mixture on the size of the ZSM‐5 zeolite nanoparticles have been studied. XRD and FE‐SEM analyses were used to characterize synthetic samples. Fischer test results showed that H2O/SiO2 and TPABr/TPAOH ratios are the most and least effective parameters, respectively, in the range studied. The most important two‐way interaction variables were the interaction of template/SiO2 and TPABr/TPAOH molar ratios. The average particle size was in the 34–79 nm range. Furthermore, a mathematical model for the synthesis of ZSM‐5 zeolite nanoparticles was derived using experimental results. The optimized gel composition is as follows: SiO2/Al2O3=91.20, template/SiO2=0.16, H2O/SiO2=40.42, Na2O/SiO2=0.0147 and TPABr/TPAOH=0. 相似文献
5.
《应用有机金属化学》2017,31(6)
The effect of weak base modification on the catalytic performance of ZSM‐5 catalyst for conversion of methanol to aromatics was investigated. The catalysts were characterized using X‐ray diffraction, X‐ray fluorescence, N2 adsorption–desorption, NH3 temperature‐programmed desorption, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetry. The results showed that catalysts treated with weak base (NaHCO3, Na2CO3 and NH3⋅H2O) exhibited a pore structure with interconnected micropores and mesopores. The existence of mesopores was beneficial for improving the diffusion of reactants and products, and the coke deposition resistance capacity of treated catalysts was enhanced greatly. Meanwhile, compared to traditional ZSM‐5 zeolite, the ratio of Brønsted to Lewis (B/L) acid sites of ZSM‐5/NH3⋅H2O (B/L = 7.35) zeolite slightly increased but the amount of acid sites reduced, while those of ZSM‐5/NaHCO3 (B/L = 0.127) and ZSM‐5/Na2CO3 (B/L = 0.107) significantly reduced. Further, the catalyst treated with NH3⋅H2O solution was evaluated in the methanol to aromatics reaction and led to an enhanced aromatization reaction rate. The liquid hydrocarbons product distribution exhibited higher aromatic hydrocarbons yield (56.12%) and selectivity (40.28%) of benzene, toluene and xylene (BTX) with isoparaffin content reducing to 26.17%, which could be explained by appropriate B/L acid sites ratio, higher pore volumes and higher surface area. 相似文献
6.
A novel conversion of 2, 4‐diaryl‐2, 3‐dihydro‐1 H‐1, 5‐benzodiazepins into 2, 4‐diaryl‐3 H‐1, 5‐benzodiazepines by the reaction with m‐chloroperbenzoic acid (MCPBA) was reported. 相似文献
7.
Extended use of supported Pt catalysts causes thermal migration of Pt particles to form large agglomerates,thus decreasing the catalytic activity.The combination of Pt with Re protects Pt against migra... 相似文献
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9.
NIAEI Aligholi SALARI Dariush HOSSEINI Seyed Ali KHATAMIAN Masumeh JODAEL Azadeh 《中国化学》2009,27(3):483-488
Gas phase catalytic combustion of ethyl acetate, as one of volatile organic compounds (VOC), was studied on nanostructure ZSM-5, HZSM-5 and Co-ZSM-5 with different cobalt loadings. Nanostructure of ZSM-5 was determined by XRD, SEM and TEM. Catalytic studies were carried out under atmospheric pressure in a fixed bed reactor. Results showed that the Co-ZSM-5 catalysts had better activity than others and at temperatures below 350 ℃, amount of Co loading was more effective on catalytic activity. The order of conversion of ethyl acetate over different Co loading is as follows: Co-ZSM-5 (0.75 wt%)<Co-ZSM-5 (1.5 wt%)<Co-ZSM-5 (15 wt%)<Co-ZSM-5 (2.8 wt%). Besides the higher the inlet concentration of ethyl acetate, the lower the conversion yield, and oxygen concentration in catalytic oxidation conditions has not so large influence on conversion. Furthermore, the presence of water vapor in inlet gaseous feed has an inhibitive effect on ethyl acetate conversion and at the temperatures above 400˚C, the effect decreases. 相似文献
10.
ZSM‐5 coatings, have been synthesized onto a monolithic cordierite substrate by an environmental friendly and high coating selectivity method—Vapor Phase Transport (VPT). With this method, an aluminosilicate gel coated onto the monolithic cordierite substrate has been transformed into a ZSM‐5 layer under vapors of n‐butylamine and water, n‐Butylamine played a key role in the forming of ZSM‐5 layer on the cordierite substrate. The ZSM‐5/cordierite monolith composites prepared by this method were ion‐exchanged with Cu2+ and tested for the selective catalytic reduction of NO by propane. The deNOx activities of Cu/ZSM‐5 monolith catalysts were not only dependent on the ion‐exchange methods, but also on the ZSM‐5 loading of the monolith catalysts. The best result was obtained over the Cu (B3)/ZSM‐5 monolith catalyst, which had a ZSM‐5 loading of about 13% and was prepared by a pressure exchange procedure. At a temperature of 723 K and a space velocity of 10,000 h?1 (based on the monolith volume), 85% of NO conversion and 93% of C3H3 conversion were achieved over the Cu(B3)/ZSM‐5 monolith catalyst. 相似文献
11.
The structures of the main products resulting from photocyclodimerization of the title compound 2 and of other 3‐methyl‐substituted ‘oxacyclohex‐2‐en‐1‐ones’ (=dihydropyranones) were determined by X‐ray crystallography. In connection, the 13C‐NMR chemical shifts of the cyclobutane C‐atoms of these dimers allow a clear differentiation between head‐to‐head and head‐to‐tail regioisomers, all structurally related to those of isophorone ( 1 ). 相似文献
12.
Toluene was methylated with methanol and disproportionated using catalysts containing different Pt contents (0.2, 0.4 and 0.6%) supported on H‐ZSM‐5 or H‐mordenite (H‐M) zeolites in a fixed‐bed flow‐reactor operated atmospherically at temperatures of 300–500 °C in a flow of hydrogen. Platinum dispersion in the zeolite supports and acid sites strength distribution were evaluated using hydrogen chemisorption (1:1 stoichiometry) and ammonia temperature programmed desorption (TPD) in a differential scanning calorimeter (DSC). Toluene methylation was much faster on all catalysts than toluene disproportionation (DISP). Both reactions were more accelerated using H‐ZSM‐5 containing catalysts than H‐M containing catalysts. The yield of xylenes, and in particular para‐xylene, was significantly influenced by the yield of trimethylbenzenes (TMBs) in product. The selectivities for para‐, ortho‐ and meta‐xylenes production were found largely dependent on the Pt content in the catalysts, particularly when supported on H‐ZSM5‐zeolite. However, using Pt/H‐M catalysts, these selectivities were not strictly controlled by Pt content in the catalysts. 相似文献
13.
The ethene diffusion characteristics in the framework of H[Al]ZSM‐5 at 300 K and 400 K have been studied by molecular dynamics (MD) simulation. The data have been obtained for the molecular kinetic, potential and total energies, mean square displacement and self‐diffusion coefficient, interaction and beat of adsorption. The dependence of molecular diffusion on temperature has been explored. 相似文献
14.
Hierarchical ZSM‐5 zeolites with micro‐, meso‐ and macroporosity were prepared from diatomite zeolitization through a vapor‐phase transport process on solid surfaces. The aromatization performance of the catalysts was investigated on a fixed bed reactor by using FCC gasoline as feedstock. The crystal phase, morphology, pore structures, acidity and coke depositions of the hierarchical ZSM‐5 zeolites were characterized by means of X‐ray diffraction (XRD), scanning electron microscope (SEM), N2 adsorption/desorption, Fourier transform infrared (FT‐IR) and thermogravimetry‐mass spectrogram (TG‐MS), respectively. The results show that the prepared hierarchical ZSM‐5 zeolite possesses excellent porosity and high crystallinity, displaying an improved aromatization performance and carbon deposition resistance due to its meso‐ and macroporous structures. 相似文献
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16.
Hendrik E. van der Bij Dr. Luis R. Aramburo Dr. Bjørnar Arstad Dr. James J. Dynes Dr. Jian Wang Prof. Dr. Bert M. Weckhuysen 《Chemphyschem》2014,15(2):283-292
A variety of phosphated zeolite H‐ZSM‐5 samples are investigated by using a combination of Fourier transfer infrared (FTIR) spectroscopy, single pulse 27Al, 29Si, 31P, 1H‐31P cross polarization (CP), 27Al‐31P CP, and 27Al 3Q magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, scanning transmission X‐ray microscopy (STXM) and N2 physisorption. This approach leads to insights into the physicochemical processes that take place during phosphatation. Direct phosphatation of H‐ZSM‐5 promotes zeolite aggregation, as phosphorus does not penetrate deep into the zeolite material and is mostly found on and close to the outer surface of the zeolite, acting as a glue. Phosphatation of pre‐steamed H‐ZSM‐5 gives rise to the formation of a crystalline tridymite AlPO4 phase, which is found in the mesopores of dealuminated H‐ZSM‐5. Framework aluminum species interacting with phosphorus are not affected by hydrothermal treatment. Dealuminated H‐ZSM‐5, containing AlPO4, retains relatively more framework Al atoms and acid sites during hydrothermal treatment than directly phosphated H‐ZSM‐5. 相似文献
17.
Two kinds of novel styryl chemosensory 2‐FMNC and 3‐FMNC, were designed and synthesized by an apporiate introduction of 9‐benzylidene‐9H‐fluorene group as fluorophore with the aim at avoiding photoisomerisation. These 9‐benzylidene‐9H‐fluorene derivatives showed the similar selectivity and sensitivity upon addition of metal ions. The sensitivity of FMNC to alkaline earth metal ions was Ba2+>Sr2+>Ca2+≈Mg2+. 相似文献
18.
Hexane Cracking over Steamed Phosphated Zeolite H‐ZSM‐5: Promotional Effect on Catalyst Performance and Stability
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Hendrik E. van der Bij Dr. Florian Meirer Sam Kalirai Dr. Jian Wang Prof. Dr. Bert M. Weckhuysen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(51):16922-16932
The nature behind the promotional effect of phosphorus on the catalytic performance and hydrothermal stability of zeolite H‐ZSM‐5 has been studied using a combination of 27Al and 31P MAS NMR spectroscopy, soft X‐ray absorption tomography and n‐hexane catalytic cracking, complemented with NH3 temperature‐programmed desorption and N2 physisorption. Phosphated H‐ZSM‐5 retains more acid sites and catalytic cracking activity after steam treatment than its non‐phosphated counterpart, while the selectivity towards propylene is improved. It was established that the stabilization effect is twofold. First, the local framework silico‐aluminophosphate (SAPO) interfaces, which form after phosphatation, are not affected by steam and hold aluminum atoms fixed in the zeolite lattice, preserving the pore structure of zeolite H‐ZSM‐5. Second, the four‐coordinate framework aluminum can be forced into a reversible sixfold coordination by phosphate. These species remain stationary in the framework under hydrothermal conditions as well. Removal of physically coordinated phosphate after steam‐treatment leads to an increase in the number of strong acid sites and increased catalytic activity. We propose that the improved selectivity towards propylene during catalytic cracking can be attributed to local SAPO interfaces located at channel intersections, where they act as impediments in the formation of bulky carbenium ions and therefore suppress the bimolecular cracking mechanism. 相似文献
19.
The grafting reaction of tetramethyltin on the surface of ZSM‐5 zeolite (Si:Al = 55.0) was studied under vacuum conditions, and the chemical compositions, structure and properties of the resulting solid were characterized by in situ FTIR, ICP, XRD, XPS, UV–vis DRS, temperature programmed decomposition (TPD) and N2 adsorption. The results show that the reaction occurs on the surface of ZSM‐5 zeolite at 223 K without destroying the zeolite framework. The BET surface area and the pore volume of the zeolite decrease and the surface properties change; however, the microporous structure is retained during the reaction and post treatment. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
20.
The reaction of 1H‐imidazole‐4‐carbohydrazides 1 , which are conveniently accessible by treatment of the corresponding esters with NH2NH2?H2O, with isothiocyanates in refluxing EtOH led to thiosemicarbazides (=hydrazinecarbothioamides) 4 in high yields (Scheme 2). Whereas 4 in boiling aqueous NaOH yielded 2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thiones 5 , the reaction in concentrated H2SO4 at room temperature gave 1,3,4‐thiadiazol‐2‐amines 6 . Similarly, the reaction of 1 with butyl isocyanate led to semicarbazides 7 , which, under basic conditions, undergo cyclization to give 2,4‐dihydro‐3H‐1,2,4‐triazol‐3‐ones 8 (Scheme 3). Treatment of 1 with Ac2O yielded the diacylhydrazine derivatives 9 exclusively, and the alternative isomerization of 1 to imidazol‐2‐ones was not observed (Scheme 4). It is important to note that, in all these transformations, the imidazole N‐oxide residue is retained. Furthermore, it was shown that imidazole N‐oxides bearing a 1,2,4‐triazole‐3‐thione or 1,3,4‐thiadiazol‐2‐amine moiety undergo the S‐transfer reaction to give bis‐heterocyclic 1H‐imidazole‐2‐thiones 11 by treatment with 2,2,4,4‐tetramethylcyclobutane‐1,3‐dithione (Scheme 5). 相似文献