Influence of alkali metal doping on surface properties and catalytic activity/selectivity of CaO catalysts in oxidative coupling of methane

Surface properties （viz. surface area, basicity/base strength distribution, and crystal phases） of alkali metal doped CaO （alkali metal/Ca= 0.1 and 0.4） catalysts and their catalytic activity/selectivity in oxidative coupling of methane （OCM） to higher hydrocarbons at different reaction conditions （viz. temperature, 700 and 750 ℃; CH4/O2 ratio, 4.0 and 8.0 and space velocity, 5140-20550 cm^3 ·g^-1·h^-1） have been investigated. The influence of catalyst calcination temperature on the activity/selectivity has also been investigated. The surface properties （viz. surface area, basicity/base strength distribution） and catalytic activity/selectivity of the alkali metal doped CaO catalysts are strongly influenced by the alkali metal promoter and its concentration in the alkali metal doped CaO catalysts. An addition of alkali metal promoter to CaO results in a large decrease in the surface area but a large increase in the surface basicity （strong basic sites） and the C2＋ selectivity and yield of the catalysts in the OCM process. The activity and selectivity are strongly influenced by the catalyst calcination temperature. No direct relationship between surface basicity and catalytic activity/selectivity has been observed. Among the alkali metal doped CaO catalysts, Na-CaO （Na/Ca = 0.1, before calcination） catalyst （calcined at 750 ℃）, showed best performance （C2＋ selectivity of 68.8% with 24.7% methane conversion）, whereas the poorest performance was shown by the Rb-CaO catalyst in the OCM process.     

Styrene epoxidation with hydrogen peroxide over calcium oxide catalysts prepared from various precursors

A series of CaO samples were prepared by calcination of commercially available and synthesis of calcium salt precursors such as calcium acetate,carbonate,hydroxide and oxalate etc.CaO samples were found to be effective for the epoxidation of styrene using hydrogen peroxide as an oxidant in the presence of acetonitrile.To determine the influence of the physicochemical properties and surface basicity on the catalytic activity,the prepared CaO samples were characterized using thermogravimetry(TG),X-ray diffraction(XRD),scanning electron microscopy(SEM),N2-adsorption and temperature-programmed desorption of CO2(CO2-TPD).The results indicate that the amounts of very strong basic sites and high basicity strength on CaO sample are key factors for its excellent catalytic performance.In contrast,the surface area,porosity and the surface structure of CaO sample have a relatively minor effect on the catalytic activity.CaO sample,obtained by the decomposition of Ca(OH)2,prepared by precipitating calcium nitrate with sodium hydroxide in ethylene glycol solution,exhibits the highest amount of very strong basic sites and stronger strength of basic sites,and therefore it catalyses the epoxidation of styrene with the highest rate among the tested CaO samples.Under the selected reaction conditions,the selectivity of 97.5% to styrene oxide at a conversion in excess of 99% could be obtained.     

SELECTIVE SEPARATION OF WATER-ETHANOL MIXTURES THROUGH COPOLYMERIC MEMBRANES: Ⅰ. ACRYLIC ACID AND ACRYLONITRILE COPOLYMER AND ITS IONIZED MEMBRANES

The copolymer of acrylic acid and acrylonitrile has been synthesized and pervaporation properties of the copolymeric membranes have been investigated. In order to elucidate the influence of membrane-permeate interaction on the pervaporation of water-ethanol mixtures and to prepare much improved membranes, the membranes have been treated with alkali metal, alkali earth metal and transition metal salt aqueous solutions. The treated membranes (ionized membranes) exhibited higher separation factors than the untreated membranes. The separation factors of various alkali metal cation membranes decreased in the following order : Li~+>Na~+>K~+, and the permeation rates showed an opposite tendency. The dependence of pervaporation behavior on the copolymer composition ,feed concentration and operating temperature have been studied with both ionized and non-ionized membranes. The apparent activation energies of water and ethanol permeation were calculated.     

Investigation on the Coordination Mode of IL-Supported Diols Used as Phosphine-Free Ligands for Palladium Catalyzed Heck Reaction

The coordination mode of IL-supported diols used as phosphine-free ligands for palladium catalyzed Heck reaction has been investigated by tuning their compositions. The difference in coordination of these IL-supported diols with metal Pd in Heck reaction was related to the changes of the cation rings, leading to the different activities of Pd catalyst in the reaction. The experimental results indicated that the activities of Pd catalyst were affected mainly by n-electron density of the cation rings. Compared to pyridinium and piperidinium cations, imidazolium cations showed the best coordination to metal Pd. In the meantime, C-2 hydrogen and the length of alkyl side chains had impacts on the coordination as well.     

异丁烯在不同硅铝比的NanZSM-5型分子筛中的吸附：分子模拟研究

Frameworks of NanZSM-5 type zeolites with various Si/A1 ratios have been constructed and optimized with molecular dynamic quench simulation. The results show that the structure parameters of NanZSM-5 type zeolite, including the bond length and atomic charges, are consistent with those predicted by ab initio cluster calculations. It was also observed that atomic charges of Si atoms were shifted to higher field in NanZSM-5 type zeolite with lower Si/Al ratio. Then, the adsorption of isobutene on NanZSM-5 with various Si/Al ratios has been investigated using grand canonical ensemble Monte Carlo simulation and Cvff-300-1.01 forcefield. The simulated adsorption amount was in good agreement with the experimental data. Based on these facts, the effects of Si/Al ratio on the adsorption amount and adsorption isotherms of isobutene on NanZSM-5 were predicted. The results indicated that Si/Al ratio was important for the adsorption of isobutene and the adsorption amount was decreased as the Si/Al ratio was increased, which can be explained that the atomic charge of Na^＋ cation would influence greatly the π electrons of the isobutene double bond due to the Coulomb force. In addition, the adsorption sites of isobutene and interaction energy of isobutene with NanZSM-5 were also discussed.     

Effect of bismuth species on propylene aromatization over BiHZSM-5 catalysts

The catalytic behavior of Bi-impregnated HZSM-5 zeolites in propylene aroma-tization and the surface properties of the zeoh'tes were determined by microreactor, XRD, XPS, NH3-TPD and IR-TPD. The mechanism of the reaction and the effect of surface properties of the zeolites on the reaction were also investigated. Experimental data showed that Bi-impregnation made the strength of B-acid sites decrease, the strength of L-acid sites and the concentration of both strong B-acid sites and strong L-acid sites increase. Bi-impregnation also induced sub-strong acid sites. These were the factors that made the aromatic products of the reaction increase. The strong interaction between the impregnant and zeolite surface reached maximum at Bi2O3 = 3.5 wt%. Above this value, covering effect of impregnant caused a decrease of aromatic products.     

非晶态金属-磷酸铝催化正庚醛和苯甲醛羟醛缩合制茉莉醛(英文)

Amorphous aluminophosphate (AlP) and metal‐aluminophosphates (MAlPs, where M=2.5 mol%Cu, Zn, Cr, Fe, Ce, or Zr) were prepared by coprecipitation method. Their surface properties and catalytic activity for the synthesis of jasminaldehyde through the aldol condensation of n‐heptanal and benzaldehyde were investigated. The nitrogen adsorption‐desorption isotherms showed that the microporosity exhibited by the aluminophosphate was changed to a mesoporous and macroporous structure which depended on the metal incorporated, with a concomitant change in the surface area. Temperature‐programmed desorption of NH3 and CO2 revealed that the materials possessed both acidic and basic sites. The acidic strength of the material was either increased or decreased depending on the nature of the metal. The basicity was increased compared to AlP. All the materials were X‐ray amorphous and powder X‐ray diffraction studies indicated the absence of metal oxide phases. The Fourier transform infrared analysis confirmed the presence of phosphate groups and also the absence of any M‐O moieties in the materials. The selected organic reaction occurred only in the presence of the AlP and MAlPs. The selectivity for the jasminaldehyde product was up to 75%with a yield of 65%. The best conversion of n‐heptanal with a high selectivity to jasminaldehyde was obtained with FeAlP as the catalyst, and this material was characterized to have less weak acid sites and more basic sites.     

The effects of alkali metal(Na+,K+) on the exchange degree of Hβ zeolite and the catalytic properties of the alkalized zeolites

The effects of alkali metals (Na+,K+) on the exchange degree of Hβ zeolite under different conditions and the conversion of α(or β)-methylnaphthalene over the alkalized zeolites were studied. The results showed that the H+ of Hβ zeolite is totally replaced by the Na+ of NaCl solution, while partially exchanged by the K+ of KC1 solution, there is an exchange equilibrium between the H+ and K+ for Hβ zeolite (Si/Al=17.23) and the value of equilibrium is 88.39. The exchange degree also increases with increasing the Si/Al of the samples. It was suggested that these resluts are attributed to the electrostatic field in the pore of Hβ zeolite and the nature of zeolite and the properties of alkali metal. The isomerization of α(or β)-methylnaphthalene is the main reaction over the samples and it is more favour on the proper acid-base sites of KHβ zeolite.     

The effect of FER zeolite acid sites in methanol-to-dimethyl-ether catalytic dehydration

In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim of this work was to investigate how the acid sites concentration, strength, distribution and typology(Br?nsted and Lewis) affect methanol conversion, DME selectivity and coke formation. It was found that the aluminium content affects slightly acid sites strength whilst a relevant effect on acid sites concentration and distribution(Br?nsted/Lewis) was observed as 24% of Lewis sites were found on Alrichest samples, whilst less than 10% of Lewis acid sites were observed on FER at higher Si/Al ratio. All the investigated catalyst samples showed a selectivity toward DME always greater than 0.9 and samples with the lowest Si/Al ratio exhibit the best performances in terms of methanol conversion, approaching the theoretical equilibrium value(around 0.85) at temperatures below 200 °C. Turnover-frequency analysis suggests that this result seems to be related not only to the higher amount of acid sites but also that the presence of Lewis acid sites may play a significant role in converting methanol. On the other hand, the presence of Lewis acid sites, combined with a high acidity, promote the formation of by-products(mainly methane) and coke deposition during the reaction. As final evidence, all the investigated catalysts exhibit very high resistance to deactivation by coke deposition, over 60 h continuous test, and a GC–MS analysis of the coke deposited on the catalyst surface reveals tetra-methyl benzene as main component.     

Effect of Alkali Treatment on the Structure and Catalytic Properties of ZSM-5 Zeolite

Catalytic properties of ZSM-5 zeolite samples pretreated with NaOH solution have been investigated. The samples are characterized by XRD, SEM, chemical analysis, and N2 adsorption.The results indicate that mesopores are created in ZSM-5 crystals under alkali treatment without change the microporous structure and acidic strength of the zeolite, but the crystallinity is greatly decreased under severe treatment. IR indicates that the concentration of silanol is greatly enriched by alkali treatment. The etherification activities of ZSM-5 zeolites are greatly increased byalkali-treatment. The noticeably improved catalytic activity of treated samples is ascribed to the formation of mesopores and greatly enriched silanol group.     

碱金属盐对ZSM-5分子筛晶化的影响

Effect of different alkali metal salts on the crystal size and the crystallization rate of ZSM-5 zeolite was de-tailedly investigated in this paper. The samples prepared by adding the different alkali metal salts were character-ized by using XRD， TEM， TG-DSC， BET and IR techniques. The XRD results showed that， for the nanosized ZSM-5 zeolite， the characteristic peaks broadened on the XRD patterns in comparison with the microsized ZSM-5 zeolite. The SEM results verified that the crystal size of zeolites prepared by adding different alkali metal salts had different results， and adding NaCl， NaC₂H₃O₂ and KCl showed the better effect of reducing crystal size， which are about of 40～60nm size. The crystallization curve of adding the different alkali metal salts suggested that the crystallization rate was significantly affected by the anions in the alkali metal salt besides the cations. Moreover， the crystal size likewise depended on the anion in the alkali metal salt. In addition， the BET results suggested that the nanosized ZSM-5 zeolite possessed a larger outer surface area in comparison with the microsized ZSM-5 zeolite. The thermostability of the samples was determined by TG-DSC technique， indicating that the nanosized ZSM-5 zeolite had a poor thermostability as compared with the microsized ZSM-5 zeolite. The possible difference of the samples with different crystal sizes on IR spectra was also given.     

Catalytic activity of phosphorus and steam modified HZSM-5 and the theoretical selection of phosphorus grafting model

The modification of HZSM-5 zeolite with phosphorus and steam has been studied. Results show that 1% phosphorus and steam modified HZSM-5 has the highest catalytic activity for n-heptane. Physicochemical and catalytic properties of 1% phosphorus and steam modified HZSM-5 zeolites have been investigated. The X-ray diffraction （XRD） results exhibit that there is considerable variation in the relative intensity of the individual diffraction peaks. The acidity of the samples decreases with an increase in the steaming temperature, which is determined by the IR of adsorbed pyridine and temperature programmed desorption （TPD） of ammonia. The oxidation state of phosphorus shown by XPS is ＋5, and a model for surface structure modification is proposed. The nitrogen adsorption isotherm for all samples is a combination of type I and type IV, all hysteresis loops resemble the H4-type. The density functional and cluster model methods have been invoked to select the phosphorus grafting model, and it was found that the phosphorus grafting model were more probable in the form of the terminal oxygen coordinating with aluminum.     

Acidity of (CH_3)_3SiCl-Modified ZSM-5 Zeolite and Its Catalysis in Toluene Disproportionation Reaction

HZSM-5 zeolites modified by Si(CH3)3 Cl were studied by TPD, IKand 27Al NMR to characterize their surface properties and bycatalytic reaction of toluene disproportionation.It was found that the concentration of the stronger Bronsted acid sites were decreased and the stronger Lewis acid sites were increased after modifieation with Si(CH3),Cl. The TPD peaks of NH3, presumally attributed to stronger acid sites (peak Ⅱ ) were decreased by the deposition of Si(CH3)3 Cl on the surface of the zeolites.The selectivity to the para xylene can be attained not only by controlling the pore opening and channels of the zeolite, hut also by changing the concentration of the stronger acid sites and the acidic type on the surface of the zeolite.     

Synthesis of Poly(isosorbide carbonate) via Melt Polycondensation Catalyzed by Ca/SBA-15 Solid Base

Ca/SBA-15 solid bases with different Ca/Si atomic ratios were prepared by a one-pot route and employed as catalysts for the production of poly(isosorbide carbonate)(PIC)from diphenyl carbonate and isosorbide via a transesterification polymerization process.The relationship between physicochemical properties and catalytic performance for Ca/SBA-15 in this melt process was investigated by means of various characterization techniques.It was found that basic site amount and strength were responsible for this transesterification process;the weak and medium basic sites inclined to promote polycondensation reaction.It was worth noting that strong basic sites could favor the decomposition of the resultant PIC,resulting in the decrease of weight-average molecular weight(Mw)and yield,and the sample with Ca/Si atomic ratio of 0.4 exhibited the best catalytic performance,giving PIC with Mw of 4.88×104 g/mol and Tg of 169°C at the optimal conditions.This excellent activity can be ascribed to the presence of rich basic sites and specific basic strength on the surface of0.4Ca/SBA-15.     

Preparation of Co- or Mn-substituted LTL zeolites and their catalytic properties in cyclohexane oxidation

Co-or Mn-substituted LTL zeolites were hydrothermally synthesized by a novel organic-ligand-assisted method.XRD,UVVis DRS,XPS,and EPR techniques verified that the Co and Mn ions were incorporated into the zeolite framework.No organic species were retained in as-synthesized Co or Mn-LTL zeolites,which resulted in porous materials without calcination.In the oxidation of cyclohexane with tert-butyl hydroperoxide(TBHP),the Co-LTL and Mn-LTL gave a 40%–48%KA oil(cyclohexanone and cyclohexanol)yield as well as nearly 100%TBHP conversion under mild reaction conditions.The reactions were confirmed to be heterogeneous and to have proceeded catalytically.No loss of catalytic activity or leaching of metal active sites ions were observed during 4 reuses.     

Separation and determination of pyrrolidinium ionic liquid cations by ion chromatography with direct conductivity detection

A method for rapid and simultaneous determination of multiple pyrrolidinium ionic liquid cations by ion chromatography with direct conductivity detection was developed.Chromatographic separations were performed on a cation exchange column using ethylenediamine-acetonitrile as the mobile phase.The effects of chromatographic column and the mobile phase,as well as the column temperature on the retention of the cations were investigated.The retention rules of the cations under different chromatographic conditions were formulated.The retention of the cations followed the carbon number rule.The method has been successfully applied to the determination of three ionic liquids synthesized by a chemical laboratory.     

Synthesis of Poly(isosorbide carbonate) via Melt Polycondensation Catalyzed by a KF/MgO Catalyst

MgO loaded with KF was prepared by using tlie impregnation method and was employed as the catalyst for tlie direct traiisesterification of diphenyl carbonate(DPC) witli isosorbide to synthesize high-molecular-weight poly(isosorbide carbonate)(PIC). The relationship between physical-chemical properties and catalytic performance for KF/MgO in this melt process was investigated by various characterization techniques. The basic site amount and strength were found to be responsible for this transesterification process, and the medium and strong basic sites tended to promote the polycondensation reaction. 20-KF/Mg0-500 exhibited the best catalytic performance, giving PIC with Mw of 84200 and glass transition temperature(rg) of 173℃ under optimal conditions. Additionally, 20-KF/MgO-500 was found to catalyze the transerification of DPC with isosorbide and other diols to syntliesize the corresponding poly(aliphatic diol-co-isosorbide carbonate)s(PAICs). This excellent activity can be ascribed to the presence of an abundance of basic sites and their specific basic strength on the surface of KF/MgO.     

SELECTIVE SEPARATION OF WATER-ETHANOL MIXTURE THROUGH COPOLYMERIC MEMBRANES. I . ACRYLONITRILE AND MALEIC ANHYDRIDE COPOLYMERIC MEMBRANES

Acrylonitrile (AN) and maleic anhydride (MA) copolymer has been synthesized by radical polymerization using ammonium persulfate and sodium bisulfite as initiator. The pervaporation properties of the copolymeric membranes prepared have been investigated for the first time. The dependences of pervaporation characteristics on copolymer composition , feed concentration and operating temperature have been studied. In order to improve the separation properties of the copolymeric membranes, the membranes were hydrolyzed with 10 wt% sodium hydroxide or potassium hydroxide aqueous solution. The hydrolyzed membranes containing more than 0. 069 MA mol fraction showed higher tensile strength and separation properties than the original membranes.     

Structures and oxygen storage/release capacities of Ce_xZr_(1-x)O_2: Effects of Zr content and preparation method

Ceria-zirconia solid solution has been prepared by the urea grind combustion and citric acid sol-gel methods for catalytic applications as oxygen storage/release materials in this study. The properties and oxygen storage/release capacities of samples with different Zr contents were characterized and evaluated by X-ray diffraction(XRD), N_2 adsorption, scanning electron microscopy(SEM), Raman spectroscopy, and insitu CO–CO_2 looping test. The results demonstrate that the samples prepared by two methods are all of excellent lattice [O] release/storage properties and maintain good long-term cycle stability. But the preparation method significantly impacts the homogeneity of samples related to their redox properties and the content of Zr over 20%, which greatly changed the properties of ceria-zirconia solid solutions and caused their changing of crystalline symmetry from cubic to tetragonal. The samples prepared by citric acid solgel method are of more homogeneous particle sizes and higher specific surface areas than that by urea grind combustion method, which is benefit to the oxygen release rather than oxygen storage. The bulk oxygen amount migrated to surface increases with the increasing Zr content, however, the amount of lattice oxygen migration decreases when Zr content is over 20%. When Zr content is 20%, the differences of storage/release capacities from two different preparation methods are reduced at high temperature in the long-term loop reaction.     

A STUDY ON THE MORPHOLOGY AND PROPERTIES OF IPP/IIR BLENDS

The effect of isobutylene-isoprene rubber (IIR) on the crystallizing behavior of isotactic polypropylene (IPP) as well as the morphology of the blends in relation with its properties have been studied by DSC, WAXD, polarized light microscope, SEM and mechanical properties test. The experimental results show that IIR has slight influence on melting point, crystallinity, crystallization rate of IPP. It seems certain that IIR has not entered into IPP phase in melt state. IIR has retarding action on the growth of IPP crystal and is an effective nucleating agent of IPP spherulites. The impact strength of the blend increases rapidly with IIR content more than 30 parts; the tensile strength of the blend, however, decreases as IIR content increases. The temperature and time of alter heat-treatment also have great influence on the impact strength of the blend. The impact strength of IPP/IIR (100/20) heat-treated at about 130℃for 2h is 5 times as high as that of the untreated blend.