纳米薄层HZSM-5分子筛催化甲醇制丙烯

在合成系列硅铝比纳米薄层HZSM-5分子筛的基础上,研究了纳米薄层HZSM-5分子筛催化甲醇制丙烯(MTP)的反应性能.在固定床微反装置上详细考察了工艺条件对纳米薄层HZSM-5分子筛催化性能的影响,同时与纳米HZSM-5分子筛对MTP反应的催化性能进行了比较.结果表明,纳米薄层HZSM-5分子筛具有较高的目的产物选择性和较长的催化寿命.在适宜硅铝比(n(SiO2)/n(Al2O3)=213)和反应条件下(温度470°C,甲醇质量空速为3 h-1),丙烯的选择性达到46.7%,三烯(乙烯、丙烯和C4烯烃)选择性达到78.7%.其中,丙烯/乙烯的质量比可达到6.5,是纳米HZSM-5分子筛的2倍,而芳烃的选择性比纳米分子筛明显降低.这是因为纳米薄层HZSM-5分子筛比纳米HZSM-5分子筛具有较宽的(010)晶面、较大的外比表面积和介孔孔容.     

Synthesis of HZSM-5 zeolites with excellent DME aromatization properties by orthogonal test

Abstract

The synthesis conditions of HZSM-5 zeolite, including crystallization temperature, crystallization time and raw material ratio, were investigated by L₃₂ (4⁸) orthogonal test to specifically optimize its performance in dimethyl ether (DME) aromatization for the first time. Based on the total yield of aromatic products, the synthesis conditions of HZSM-5 zeolite with the best DME aromatization properties were obtained by comprehensive analysis and validation experiments. The relationship between the aromatization performance, crystalline structure, pore structure, and acidity of HZSM-5 zeolite were analyzed. The results showed that the HZSM-5 zeolite accompanied by hierarchical structure, an appropriate Brønsted and Lewis acid content and uniform crystal morphology, was successfully synthesized under optimized conditions. Over this unmodified and un-doped catalyst, the conversion of DME approached to 99.3% and the total yield of aromatics reached was 53.5%.     

Acid properties of the HZSM-12 zeolite with different Si/Al ratio by thermo-programmed desorption

In this work was studied the acid properties of a series of HZSM-12 zeolites with different Si/Al molar ratio. The samples of ZSM-12 were synthesized by the hydrothermal method starting from a gel with the following molar composition: 20MTEA:10Na₂O:xAl₂O₃:100SiO₂:200H₂O, where: x=2, 1, 0.67 and 0.50, respectively. After the synthesis, the samples of ZSM-12 were ion-exchanged NH₄Cl solution to obtain zeolite in the acid form (HZSM-12). The acid properties were evaluated by n-butylamine thermodesorption in a TG equipment at three different heating rates. The model-free kinetic model was applied in the TG integral curves to estimate the apparent activation energy (E _a) of the n-butylamine desorption process. The results obtained showed that the HZSM-12 zeolite presents two kinds main of acid sites: one with E _a in the range of 115-125 kJ mol^-1 classified as weak and other kind with E _a varying of 230-250 kJ mol^-1 classified as strong. This revised version was published online in July 2006 with corrections to the Cover Date.     

Distribution of the cobalt-containing component in the pore space of HZSM-5 upon a postsynthetic modification of the zeolite with hydroxo compounds of Co<Superscript>2+</Superscript>

The distribution of the cobalt-containing modifying component in the pore space of zeolite HZSM-5 depending on the total cobalt content of the samples (0.5–5.0 wt %) was quantitatively studied for the first time. At cobalt concentrations to 3.0 wt %, the cobalt-containing modifying component mainly occurred as isolated Co _Oh ²⁺ ions in the micropores (channels) of HZSM-5 at the ion-exchange positions of the zeolite and in one-dimensional CoO and CoAl₂O₄ nanoclusters. A further increase in the cobalt concentration to 5.0 wt % resulted, in addition to the filling of micropores, in the partial filling of the mesopore space of the zeolite with a small amount of three-dimensional CoO and CoAl₂O₄ nanoparticles. Using sorption data and electronic diffuse reflectance spectra, we were the first to find that the effective density of a cobalt-containing modifying component in the pore space of a zeolite matrix was lower than the density of a bulk CoO phase by a factor of 6.     

氟硅酸铵改性纳米HZSM-5分子筛催化甲醇制丙烯

在静态条件下, 采用不同浓度的氟硅酸铵溶液对纳米ZSM-5分子筛进行了改性处理. 利用粉末X射线衍射(XRD)、²⁷Al 魔角旋转固体核磁共振(²⁷Al MAS NMR)、X射线荧光光谱(XRF)、X射线光电子能谱(XPS)、N₂ 吸附、透射电镜(TEM)、NH₃程序升温脱附(NH₃-TPD)、吡啶吸附红外光谱(Py-IR)等技术对改性前后纳米ZSM-5分子筛的骨架结构、织构性质、酸性质进行了表征. 并在常压、反应温度为450℃、甲醇质量空速(WHSV)为1 h^-1的条件下, 研究了改性前后纳米HZSM- 的甲醇制丙烯(MTP)催化性能. 结果表明, 合适浓度的氟硅酸铵处 理能够选择性地脱除纳米ZSM-5 分子筛的外表面铝, 从而使得HZSM-5 的酸密度降低, 比表面积和孔容增大, MTP催化性能显著提高. 氟硅酸铵改性后纳米HZSM-5 的丙烯选择性和丙烯/乙烯(P/E)质量比分别由原来的 28.8%和2.6提高到45.1%和8.0, 催化剂寿命增加了近2倍.     

Synthesis and characterization of polycrystalline ZnO/HZSM-5 nanocomposites

Polycrystalline ZnO/HZSM-5 nanocomposites were synthesized by the impregnation method using a home prepared HZSM-5 zeolite as porous support and Zn(C₅H₇O₂)₂ or Zn(NO₃)₂ as zinc precursors. As-prepared samples were characterized by ICP, XRD, SEM (EDS), TEM (SAED), BET and DRS techniques. A small amount of sub-nanometeric ZnO clusters were introduced into the channels of HZSM-5 zeolite. These ZnO clusters exhibited absorption band onset at about 280 nm, different from ZnO particles at about 370 nm. The significant blue shift possesses high quantum size effect in sub-nanometeric ZnO clusters. SAED and TEM images revealed that the ZnO nanoparticles, supported on the surface of HZSM-5 zeolite, were identified as polycrystalline structure with the particle size of about 20-25 nm. XRD results provided evidence of the strong host-guest interactions between HZSM-5 framework and ZnO structure. The samples prepared by Zn(C₅H₇O₂)₂ were more porous and smaller than those prepared from the Zn(NO₃)₂. This was confirmed by SEM and XRD results.     

Effect of Fe-Mo promoters on HZSM-5 zeolite catalyst for 1-hexene aromatization

The promotional effect of Fe-Mo species introduced into HZSM-5 (Zeolyst Int., SiO₂/Al₂O₃ ≈ 30) zeolite catalyst by the wetness impregnation method for the 1-hexene aromatization was investigated. The structure and catalytic performance for the aromatization of 1-hexene over xFeyMo-ZSM-5 catalysts in comparison with unmodified HZSM-5 catalysts were studied. The xFeyMo-ZSM-5 catalysts contain fixed loading (5 wt%) and variable Fe/Mo ratio. The catalysts were characterized by BET, ICP-AES, HRSEM-EDS, HRTEM, XRD, FTIR, H₂-TPR, NH₃-TPD, and pyridine DRIFT spectroscopy. The characterization data confirmed the existence of Fe and Mo species in the zeolite matrix. With Fe and Mo species implementation to HZSM-5 zeolite, the amount of the acid sites decreased, but the selectivities to C₉₊ aromatics increased. The catalyst evaluation was performed at 350 °C for 6 h on-stream at atmospheric pressure using a fixed-bed quartz tube reactor. The selectivity to products of different carbon number was affected by the Fe/Mo ratio within the zeolite. It was found the product distribution of grouped fractions of C₁–C₁₇₊ from the liquid product. The results indicate that the optimum ratio of Fe/Mo is 1–1.5. The highest selectivity for gasoline and distillate ranges was obtained for the 2.5wt%Fe2.5wt%Mo- and 3wt%Fe2wt%Mo-ZSM-5 samples, which was higher than that for parent HZSM-5 catalyst.     

Cresol Izomerization in the Presence of Acid Catalysts

It is shown for toluene oxidation with nitrous oxide that modifying HZSM-5 zeolite with zinc oxide nanoparticles considerably improves the selectivity and yield of cresols. It is found that a 2% ZnO/HZSM-5 composite catalyst also exhibits enhanced and stable activity at high temperatures. For the o-cresol isomerization reaction, this modification of HZSM-5 zeolite greatly reduces the contribution from disproportionation and cracking reactions proceeding with formation of phenol, C₆–C₉ aromatic hydrocarbons, and xylenols. The regularities of their formation in the presence of the studied catalysts are determined using the results from thermodynamic calculations for the equilibrium concentrations of cresol isomers.     

浆态床合成二甲醚复合催化剂失活原因探索

在反应温度260℃、压力5.0MPa的条件下,对浆态床反应器中二甲醚合成复合催化剂的失活规律进行了研究。结果表明, Cu基催化剂失活较快是导致浆态床二甲醚合成催化剂不稳定的主要原因。通过分析Cu基催化剂在浆态床反应器和固定床反应器中的活性变化规律,发现在浆态床反应器中不能及时导出反应体系的H2O对催化剂的毒副作用导致了浆态床Cu基催化剂快速失活。对失活催化剂进行的TPR、XRD和SEM EDS表征结果可以看出,Cu粒子的长大和积炭是Cu基催化剂失活的重要原因,与已有文献报道不同的是并未发现明显的Cu元素流失。     

Ga/HZSM-5分子筛上乙烯二聚反应的理论研究

应用理论计算方法研究了Ga/HZSM-5及Al/HZSM-5 分子筛上乙烯二聚生成1-丁烯的反应历程, 比较了分子筛酸性对反应能量的影响. 计算采用分为两层的76T簇模型, 应用量子力学和分子力学联合的 ONIOM2 (B3LYP/6-31G(d, p):UFF) 方法. 乙烯二聚过程可按照分步机理和协同机理进行, 均得到表面丁基烷氧中间产物. 计算结果表明, 与在Al/HZSM-5分子筛上的反应过程相比, 乙烯在 Ga/HZSM-5分子筛上的吸附能低 20.62 kJ·mol^-1, 但质子化反应的活化能只高出1.26 kJ·mol^-1; 而乙基烷氧中间体与乙烯分子结合过程的活化能高出 62.55 kJ·mol^-1, 原因是Ga 原子半径大, 降低了六元环过渡态的稳定性. 若按协同机理, 质子转移和C―C键聚合同时进行, 在 Ga/HZSM-5分子筛上的活化能较Al/HZSM-5的高16.44 kJ·mol^-1. 因此乙烯二聚按照协同机理有利. 研究还表明, 表面丁基烷氧中间体脱质子, 生成1-丁烯并吸附在复原的分子筛酸性位上. 该反应在两种酸中心上的活化能几乎相同, 但明显高于其他各步的活化能, 因此成为整个反应的速度控制步骤.     

FT-IR evidence for the participation of protonic sites in the heterolytic cleavage of C?H bonds of methane over HZSM-5 zeolite

It has been observed by FT-IR spectroscopy that both kinds of Brönsted acid protons present in HZSM-5 zeolite may be involved in the adsorption of methane at low temperature (173 K) and exchange with CH₄ or CD₄ at high temperature (>500°C). The sites which can adsorb methane at low temperature are the active sites for methane conversion at high temperature. Over HZSM-5 zeolite, the activation of methane is suggested to occur via a heterolytic cleavage of C–H bond with the assistance of protons.     

氟改性对纳米HZSM-5分子筛催化甲醇制丙烯的影响

 在比较了纳米和微米 HZSM-5 分子筛催化甲醇制丙烯反应性能的基础上, 对纳米 HZSM-5 分子筛进行了氟改性. 利用透射电镜、N2 吸附、X 射线衍射、氨程序升温脱附和吡啶吸附-红外光谱技术对改性前后的样品进行了表征, 并在常压、500 oC 和甲醇空速 (WHSV) 为 1.0 h–1 的反应条件下, 在连续流动固定床微型反应器上考察了其催化甲醇制丙烯的性能. 结果表明, 当氟含量<10% 时, 随氟含量的增加, 改性纳米 HZSM-5 分子筛的酸量减少, 酸强度降低, 从而使丙烯选择性和催化剂稳定性不断提高. 但过量 (15%) 氟的改性使纳米 HZSM-5 分子筛的酸量、比表面积和孔容均明显减小, 致使其稳定性反而降低. 在适量 (10%) 氟改性的纳米 HZSM-5 分子筛上, 丙烯选择性和维持甲醇完全转化的反应时间分别由原来的 30.1% 和 75 h 增加到 46.7% 和 145 h.     

Bimetallic Lanthanum-Cerium-Loaded HZSM-5 Composite for Catalytic Deoxygenation of Microalgae-Hydrolyzed Oil into Green Hydrocarbon Fuels

Due to their high lipid content, microalgae are one of the most significant sources of green hydrocarbons, which might help lessen the world’s need for fossil fuels. Many zeolite-based catalysts are quickly deactivated by coke production and have a short lifetime. In this study, a bimetallic Lanthanum-Cerium (La-Ce)-modified HZSM-5 zeolite catalyst was synthesized through an impregnation method and was tested for the conversion of hydrolyzed oil into oxygen-free hydrocarbon fuels of high energy content. Initially, hydrolyzed oil (HO), the byproduct of the transesterification process, was obtained by the reaction of crude oil derived from Chlorella vulgaris microalgae and a methanol. Various catalysts were produced, screened, and evaluated for their ability to convert algal HO into hydrocarbons and other valuable compounds in a batch reactor. The performance of HZSM-5 was systematically tested in view of La-Ce loaded on conversion, yield, and selectivity. NH₃-TPD analysis showed that the total acidity of the La-Ce-modified zeolites was lower than that of the pure HZSM-5 catalyst. TGA testing revealed that including the rare earth elements La and Ce in the HZSM-5 catalyst lowered the catalyst propensity for producing coke deposits. The acid sites necessary for algal HO conversion were improved by putting La and Ce into HZSM-5 zeolite at various loading percentages. The maximum hydrocarbon yield (42.963%), the highest HHV (34.362 MJ/Kg), and the highest DOD% (62.191%) were all achieved by the (7.5%La-2.5%Ce)/HZSM-5 catalyst, which was synthesized in this work. For comparison, the hydrocarbon yield for the parent HZSM-5 was 21.838%, the HHV was (33.230 MJ/Kg), and the DOD% was 44.235%. In conclusion, La and Ce-loading on the parent HZSM-5 may be responsible for the observed alterations in textural properties; nevertheless, there is no clear correlation between the physical features and the hydrocarbon yield (%). The principal effect of La and Ce modifying the parent HZSM-5 zeolite was to modify the acidic sites needed to enhance the conversion (%) of the algal HO during the catalytic deoxygenation process, which in turn raised the hydrocarbon yield (%) and increased the HHV and DOD%.     

Catalytic Oxidation of Methane by Nitrous Oxide on H[Al]ZSM-5 Zeolite, Silicalite, and Amorphous SiO2 Modified by Iron, Silver, and Gadolinium Ions

Methane oxidation by an excess of N₂O on the catalytic sites formed in HZSM-5 zeolite, silicalite, and SiO₂ after modification with iron, silver, and gadolinium cations in different combinations is studied. Introduction of iron and silver ions into H[Al]ZSM-5 zeolite is shown to result in the formation of the sites that are active in methane oxidation, while the systems obtained on the basis of crystalline silicalite or amorphous SiO₂ demonstrate poor or no catalytic activity, respectively. Complete oxidation of methane with 100% conversion is observed on the Fe/HZSM-5 and Ag/HZSM-5 catalysts at temperatures higher than 350 and 450°C, respectively. A decrease in the reaction temperature and in the methane conversion is accompanied by coking of the catalysts and, in the case of Fe/HZSM-5, by the appearance of trace amounts of methanol and formic acid in the gas phase. The temperature dependence of the activity and selectivity for the Ag/HZSM-5 and (Ag + Gd)/HZSM-5 catalysts exhibits a pronounced hysteresis at 330–480°C, and the formation of coke proceeds much faster than in the case of iron-containing samples. Catalytic properties of (Fe + Ag)/HZSM-5 are similar to those of Fe/HZSM-5. The introduction of Gd does not influence significantly the activity and selectivity of the catalysts. ESR and TG–DTA were used to determine the state and distribution of Fe, Ag, and Gd in the samples and to examine the processes of coke formation.     

Catalytic performance of imidazole modified HZSM-5 for methanol to aromatics reaction

A facile approach was developed for the preparation of nano-sized HZSM-5 with a hierarchical mesoporous structure by adding imidazole into conventional zeolite synthesis precursor solution. The physicochemical properties of modified HZSM-5 were characterized by X-ray diffraction(XRD), N_2 adsorption–desorption isotherms, scanning electron microscopy(SEM), NH_3-temperature-programmed desorption(NH_3-TPD) and pyridine adsorption infrared spectroscopy(Py-IR). The coke in spent catalysts was characterized by thermogravimetry(TG). The results showed that hierarchical HZSM-5 zeolites with excellent textural properties, such as abundant porous structure, uniform particle size and suitable acidity, could be synthesized by the recipe of one-pot synthesis routes. Moreover, the obtained HZSM-5 exhibited higher selectivity of total aromatics as well as longer lifetime in the catalytic conversion of methanol to aromatics, comparing with conventional HZSM-5. It is expected that the synthesis approach demonstrated here will be applicable to other zeolites with particular textural properties and controllable particle sizes, facilitating the emergence of new-type porous materials and their related applications in catalysis and separation.     

甲醇催化转化制丙烯中HZSM-5分子筛的尺寸效应

甲醇催化制丙烯(MTP)是一个具有重要工业应用的研究课题, 目前普遍采用的催化剂是HZSM-5 分子筛. 通过调节分子筛合成原料的配比、晶化温度和晶化时间等参数, 对所制备的不同晶粒尺寸的HZSM-5 分子筛, 综合利用X射线衍射(XRD)、扫描电镜(SEM)、N₂吸附和氨气程序升温脱附(NH₃-TPD)等手段表征了其晶格结构、表观形貌、孔结构以及酸性质. 利用固定床反应装置对HZSM-5 分子筛甲醇催化制丙烯的活性和稳定性进行了评价, 并采用热重(TG)分析技术对催化剂的积炭性能进行了考察. 实验结果表明, HZSM-5 分子筛粒度的减小可以增加分子筛比表面积、孔体积, 同时有更多开放的孔口及短的孔道长度, 有利于反应物分子的吸附和传质,并降低了产物分子在孔道中的扩散距离及发生二次反应的几率, 提高了催化剂的抗积炭能力和容炭能力以及稳定性; 而且所合成的小尺寸分子筛单位质量的总酸量及强酸量均有不同程度的下降, 有利于提高目标产物丙烯的选择性.     

氧化镁改性对纳米HZSM-5分子筛催化甲醇制丙烯的影响

采用浸渍法制备了一系列不同Mg含量(0-8%,w)的改性纳米HZSM-5分子筛.利用X射线衍射(XRD)、铝固体魔角旋转核磁共振(27AlMASNMR)、N2吸附/脱附、氨-程序升温脱附(NH3-TPD)和吡啶吸附傅里叶变换红外(FT-IR)光谱等技术对改性前后样品的结构和酸性进行了详细表征;并在常压、500℃和甲醇空速(WHSV)为1.0h-1的反应条件下,在连续流动固定床反应器上考察了其对甲醇制丙烯反应的催化性能.结果表明,随着Mg含量的增加,丙烯和丁烯的选择性逐渐增大,而甲烷、乙烯和芳烃的选择性逐渐降低.催化剂的稳定性先随Mg含量的增加而增加,当Mg含量为2%时达到最大,之后又随Mg含量的增加而降低.MgO改性对纳米HZSM-5分子筛催化性能的影响主要是由其酸性和织构性能的改变而引起的.     

Electrochemical study of the thionine dye incorporated into ZSM-5 and HZSM-5 zeolites

The electrochemical properties of thionine dye adsorbed into ZSM-5 and HZSM-5 zeolites (TH/ZSM-5, TH/HZSM-5) are studied in 0.5 M KCl solution. The dye is strongly retained and not easily leached from the zeolites matrix. The samples are incorporated into the carbon paste electrode (TH/ZSM-5/P, TH/HZSM-5/P) for cyclic voltammetric measurements. The redox reactions of thionine incorporated into ZSM-5 zeolite contain a quasi-reversible, two-electron one proton in the pH range 1 to 10, but thionine-loaded HZSM-5 zeolite undergoes a quasi-reversible two-electron two-protons redox reaction under acidic conditions and a one proton two-electron redox reaction takes place under basic conditions. The separation of the anodic and cathodic potentials (E _p) is high in thionine-loaded zeolites (>100) with respect to the solution of thionine (E _p = 34 for ZSM-5/P and 36 mV for HZSM-5/P), indicating that there are strong interaction between thionine molecules and the zeolites. The midpoint potentials (E _m) for TH/ZSM-5/P and TH/HZSM-5/P are −0.203 and −0.381 V, respectively. However, the midpoint potentials for the solution of thionine for the electrode system of ZSM-5/P and HZSM-5/P are −0.335 and −0.407 V, respectively. Thus, thionine dye molecules incorporated into the zeolites can be reduced more easily with respect to solution of thionine. In various electrolyte solutions, the midpoint potentials remains constant, but the midpoint potential of the thionine-zeolite electrodes depends on the solution pH. Influence of the pH of the solution on the midpoint potential of an immobilized dye reveals that thionine molecules are accessible to protons. This property is ascribed to the formation of mesopores in the structure of our zeolites suffering from a calcination step. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 7, pp. 794–800. The text was submitted by the authors in English     

Aniline alkylation over MFI zeolites and its relation to stepwise desorption of ammonia

A clear correlation between aniline alkylation over HZSM-5 zeolite and the acidity as measured by stepwise temperature programmed desorption (STPD) of NH₃ and cumene dealkylation has been established.     

Catalytic Deoxygenation of Hydrolyzed Oil of Chlorella Vulgaris Microalgae over Lanthanum-Embedded HZSM-5 Zeolite Catalyst to Produce Bio-Fuels

Microalgae is one of the most important sources of green hydrocarbons because it contains a high percentage of lipids and is likely to reduce reliance on fossil fuels. Several zeolite-based catalysts have a short lifetime due to coke-formation deactivation. In this study, a lanthanum-modified HZSM-5 zeolite catalyst for the conversion of crude oil into non-oxygenated compounds (hydrocarbons) and oxygenated compounds has been investigated. The crude oil of Chlorella Vulgaris microalgae was extracted using Soxhlet and converted into hydrolyzed oil (HO) through a transesterification reaction. The experiments were conducted in a batch reactor (300 °C, 1000 rpm, 7 bar of N₂, the catalyst to the algal HO ratio of 15% (wt.%) and 6 h). The results were organized into three groups: product yield, chemical composition, and carbon number distribution. The liquid products were investigated, including their elemental composition, higher heating value (HHV), atomic ratios of O/C and H/C, and degree of deoxygenation (DOD%). The loading of lanthanum into HZSM-5 zeolite with different loading percentages enhanced the acid sites needed for the algal HO conversion. Among all the synthesized catalysts, 10%La/HZSM-5 produced the highest conversion of the algal HO, the highest yield of hydrocarbons, the highest HHV, and the highest DOD%; those were 100%, 36.88%, 34.16 MJ/kg, and 56.11%, respectively. The enhanced catalytic conversion was due to the presence of lanthanum, which alters the active sites for the desired reactions of catalytic deoxygenation. The main effect of the modification of the parent HZSM-5 zeolite with lanthanum led to adjusting the acidic sites needed to increase the conversion (%) of the algal HO in the catalytic deoxygenation process and thus increase the hydrocarbon yield (%), which in turn led to an increase in the HHV and DOD%. The proposed La-based zeolite composite is promising for different energy applications due to its unique benefits compared to other expensive and less-stable catalysts.