Highly shape-selective Zn-P/HZSM-5 zeolite catalyst for methanol conversion to light aromatics

A highly shape-selective and relatively long-lifetime HZSM-5-based catalyst (Zn-2P/HZSM-5) was prepared by chemical modification with both ZnSiF₆·6H₂O and H₃PO₄ solution. The phosphoric acid modification could effectively modulate the Brønsted acid strength of the HZSM-5 catalyst, which promotes the oligomerization, alkylation, cyclization, and hydrogen transfer reactions. The introduction of Zn-Lewis acid sites significantly improved the dehydroaromatization of higher olefins. All of these were very beneficial for the generation of BTX (i.e. benzene, toluene, and xylene) hydrocarbons in aromatization of methanol. The coke amount and the average rate of coke formation decreased over the Zn-2P/HZSM-5 catalysts, which may largely be ascribed to its lower strong acid sites and lower outer surface acidity. The catalytic performance of methanol aromatization showed that the Zn-2P/HZSM-5 catalyst exhibited the highest BTX selectivity of about 46.76% and the longest catalytic lifetime of about 498 h at T = 400 °C, P = 0.1 MPa, and weight hourly space velocity = 0.7 h⁻¹.     

Study on Bifunctionality of Mo／HZSM—5 Catalysts for Methane Dehydro—Aromatization under Non—oxidative Condition

The optimum Mo/[H^ ] ratio per unit cell of the active precursors in Mo/HZSM-5 catalysts for methane dehydro-aromatization,measured by ^1H MAS NMR,was found to be about 1 when adjusting the acid sites by altering either the SiO2/Al2O3 ration or the Mo loading,This implies that a concerted interaction between the Mo species and the Broensted acid sites probably features the bifunctionality of the Mo/HZSM-5 catalyst,On the other hand,it was found that the driving force for Mo species to move into the HSZM-5 zeolite channels and the interaction between the Mo species and the Broensted acid sites are closely and proportionably realtaed with the amount of Broensted acid sites per unit cell.     

Study on Bifunctionality of Mo/HZSM-5 Catalysts for Methane Dehydro-Aromatization under Non-oxidative Condition

The optimum Mo/[H~+] ratio per unit cell of the active precursors in Mo/HZSM-5 catalysts for methane dehydro-aromatization, measured by 1H MAS NMR, was found to be about 1 when adjusting the acid sites by altering either the SiO2/Al2O3 ratios or the Mo loading. This implies that a concerted interaction between the Mo species and the Bronsted acid sites probably features the bifunctionality of the Mo/HZSM-5 catalyst. On the other hand, it was found that the driving force for Mo species to move into the HSZM-5 zeolite channels and the interaction between the Mo species and the Bronsted acid sites are closely and proportionably related with the amount of Bronsted acid sites per unit cell.     

Neutralization of HZSM-5 Br?nsted acid sites by shaping with boehmite

The reduction of the concentration of strongly acidic Brönsted sites of HZSM-5 by neutralization due to added boehmite is reported. Strongly acidic Brönsted sites are neutralized by [AlO·(Al₂O₃)_x]⁺ isopolyoxocations proceeding during the calcination treatment.     

Investigation of catalytic property in the t-butylation of 1,2-dihydroxybenzene using FT-IR and XPS study

Catalytic properties of HZSM-5s with three different Na⁺ ion-exchange levels and SiO₂ /Al₂O₃ ratios used in tert-butylation of DHB (1,2-dihydroxybenzene) are interpreted through pyridine adsorbed FT-IR and XPS study. The DHB conversion decreases as increment of degree of Na⁺ ion-exchange level and of Si content in HZSM-5. Catalytic properties with respect to Na amount in ZSM-5 are more sensitive than those of HZSM-5s with different SiO₂/Al₂O₃ ratios. But selectivity for 4-TBC (4-t-butylcatechol) is not changed significantly. Acidic properties, i.e. acid strength and acid density are characterized by pyridine adsorbed FT-IR and XPS study. Based on FTIR and XPS analyses, DHB conversion and selectivities for DTBC (3,5-di-t-butylcatechol) and 3-TBC (3-t-butylcatechol) depend on type and strength of acid sites, with the result that strong Brønsted acid rather than weak Brønsted or Lewis acid sites are more closely related to the conversion. Furthermore, t-butyl alcohol is selectively adsorbed on the Brønsted acid site of FT-IR band at 3612 cm^-1, which signifies that the Brønsted acid site is the active site. The mechanism for t-butylation of DHB is suggested based on the FT-IR results of adsorption/desorption of reactants.     

ESR and TPD Study of the Interaction of Nitromethane and Ammonia with HZSM-5 and CuZSM-5 Zeolites

The properties of complexes formed on HZSM-5 and CuZSM-5 zeolites in the course of ammonia and nitromethane adsorption are studied. Ammonia adsorbs on CuZSM-5 and forms two species, which decompose at different temperatures T _dec. One is due to the formation of the Cu²⁺(NH₃)₄ complex (T _dec = 450 K), and the other is assigned to ammonia adsorbed on copper(II) compounds, Cu²⁺O^– and Cu²⁺–O^2––Cu²⁺, or CuO clusters (T _dec = 650–750 K). Ammonia adsorption on Cu⁺ and Cu⁰ is negligible compared with that on the Brönsted acid sites and copper(II). Nitromethane adsorbed on HZSM-5 and CuZSM-5 at 400–500 K transforms into a series of products including ammonia. Ammonia also forms complexes with the Brönsted acid sites and copper(II) similar to those formed in the course of adsorption from the gas phase, but the Cu²⁺(NH₃)₄ complexes on CuZSM-5 are not observed. Possible structures of ammonia and nitromethane complexes on Brönsted acid sites and the Cu²⁺ cations in zeolite channels are discussed. The role of these complexes in selective NO _x reduction by hydrocarbons over the zeolites is considered in connection with their thermal stability.     

Mo/HZSM-5丙烷芳构化催化性能及其吸附量热的研究

采用等量浸渍法制得一系列不同担载量的Ｍｏ／ＨＺＳＭ－５催化剂,运用ＸＲＤ和ＦＴＩＲ方法考察了Ｍｏ物种在催化剂表面的分散状态,首次采用微分吸一热技术对Ｍｏ／ＨｚＳＭ－５催化剂的表面酸性进行表征。同时研究了催化剂对丙烷芳构化的反应活性。结果表明：对于担载Ｍｏ的ＨＺＳＭ－５分子筛催化剂,Ｍｏ物种在ＨＺＳＭ－５分子筛表面上顺序为ＨＺＳＭ－５〉１％Ｍｏ／ＨＺＳＭ－５〉２％Ｍｏ／ＨＺＳＭ－５分子筛本身表面的酸     

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.     

硼和氟掺杂ZSM-5分子筛的制备及其甲醇制丙烯反应性能

采用两步水热晶化法,通过在合成体系中加入硼酸、氟化铵、氟硼酸铵,合成出了硼和氟改性的ZSM-5分子筛。利用X射线衍射、氮气吸附-脱附、29Si固体核磁共振波谱、傅里叶变换红外光谱、扫描电子显微镜以及NH₃程序升温脱附等测试手段对样品进行了表征。结果表明：硼和氟掺杂条件下可以合成具有较高结晶度的ZSM-5分子筛,杂原子掺杂提高了分子筛的硅铝比;硼和氟掺杂可以显著降低ZSM-5分子筛的Lewis酸量,但提高了Brønsted酸量;硼和氟共同作用可以降低ZSM-5分子筛的颗粒尺寸。甲醇制丙烯评价结果显示：较低的Lewis酸量和适宜的Brønsted酸性有利于提高丙烯选择性和催化剂寿命;NH₄BF₄改性的ZSM-5分子筛（Z5-BF2）表现出较高的丙烯选择性和较长的催化剂寿命。     

Effect of iridium loading on HZSM-5 for isomerization of n-heptane

The effect of iridium loading on the properties and catalytic isomerization of n-heptane over Ir-HZSM-5 is studied. Ir-HZSM-5 was prepared by impregnation method and subjected to isomerization process in the presence of flowing hydrogen gas. XRD and BET studies show that the presence of iridium stabilizes the crystalline structure of HZSM-5, leading to more ordered framework structure and larger surface area. TGA and FTIR results substantiate that iridium species interacts with OH group on the surface of HZSM-5. Pyridine FT-IR study verifies the interaction between iridium and surface OH group slightly increased the Bro¨nsted and Lewis acid sites without changing the lattice structure of HZSM-5. The presence of iridium and the increase of strong Lewis acid sites on HZSM-5 were found to bring an increase about 4.1%, 33.2% and 11.8% in conversion, selectivity and yield of n-heptane isomerization, respectively.     

镁改性对HZSM-5分子筛催化乙烯制丙烯的影响

采用等体积浸渍法制备了一系列不同Mg含量(0–1.0%)的HZSM-5分子筛。利用X射线衍射(XRD)、N_2吸附/脱附、铝魔角旋转固体核磁共振(~(27)AlMASNMR)、~(29)SiMASNMR、氨-程序升温脱附(NH_3-TPD)和吡啶吸附傅里叶变换红外(Pyridine-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,在常压连续流动固定床反应器上考察其对乙烯转化制丙烯(ETP)反应的催化性能,评价了反应条件和Mg改性的影响。结果表明,在温度为550°C、乙烯体积空速GHSV=3000 h~(-1)的适宜反应条件下,0.5%适量镁改性HZSM-5导致乙烯转化率有所下降,但丙烯选择性增加到45%以上,而副产物芳烃的选择性降到8%以下。反应前样品的酸性表征和反应后积碳样品的TPO及~(13)CCP/MASNMR谱图分析表明适量镁改性使HZSM-5分子筛的总酸量和强B酸量减少而中强酸量增加,从而提高了丙烯的选择性,但是过量的镁改性使分子筛的总酸量明显减少,导致催化剂的活性显著下降。     

硅烷化处理对Mo/HZSM-5催化剂上甲烷脱氢芳构化活性的影响

 结合催化剂的活性评价及固体高分辨核磁共振谱、X射线光电子能谱和X射线荧光光谱和热重等技术,考察了硅烷化处理对Mo/HZSM-5催化剂上甲烷脱氢芳构化活性的影响. 结果表明,采用大分子有机硅烷对HZSM-5分子筛进行硅烷化处理,除去了分子筛外表面的酸性位,并使分子筛本身发生了脱铝. 硅烷化处理使Mo/HZSM-5催化剂在进行甲烷脱氢芳构化反应时催化剂上总的积碳量明显减少,从而提高了催化剂的活性.     

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.     

Activation of Mo/HZSM-5 for methane aromatization

The effect of Mo/HZSM-5 pretreatment at 973 K in inert (He), oxidizing (artificial air), and carbu-rizing (CH4/He mixture) atmospheres on its performance in non-oxidative methane dehydroaroma-tization (MDA) was investigated. The effect of post-synthesis silylation on deactivation of external acid sites was also studied. Precarburization resulted in increased aromatic selectivity and im-proved catalyst stability. The benzene selectivity was the highest for the silylated Mo/HZSM-5 cata-lyst (benzene+naphthalene selectivity after 1 h on stream was close to 100%). The deactivation of precarburized zeolites was less pronounced than that of zeolites heated in air or He. During heating in air or He, larger fractions of the molybdenum oxide species diffused into the micropores than during heating in methane. Carburization of the molybdenum oxide species in the micropores dur-ing MDA resulted in the formation of molybdenum carbide particles, and these contributed to pore blocking, making the Br?nsted acid sites inaccessible. The formation of molybdenum carbides dur-ing heating in methane resulted in a less mobile Mo phase. It is argued that the presence of molyb-denum carbide particles in the micropores contributes to rapid catalyst deactivation, in addition to the formation of hard coke on the external surface.     

添加Mo对Cu/HZSM-5催化剂性能影响

负载催化剂;二氧化碳加氢;二氧化碳;添加Mo对Cu/HZSM-5催化剂性能影响     

Nature of the Ftir Band in Acidic Zeolites

The nature of a FTIR band (1490 cm ^-1 ) in the spectrum of zeolite HZSM-5 after pyridine adsorption was investigated. It is shown that the source of this band is not a combined contribution from Brönsted and Lewis acidic sites as widely believed.     

不同锌盐改性的HZSM-5催化剂上甲醇芳构化反应

分别用ZnSO4,Zn(AcO)2,Zn(NO3)2和ZnCl2溶液对HZSM-5分子筛浸渍改性得到不同Zn盐改性的HZSM-5催化剂.采用X射线衍射、N2物理吸附、热重-质谱分析、氨程序升温脱附和吡啶吸附红外光谱等方法对改性后的催化剂进行了表征,并在固定床反应装置上考察了其甲醇芳构化反应性能.结果表明,不同Zn盐改性的HZSM-5催化剂上Zn物种的存在形式不同会导致其表面酸中心强度与分布具有较大差异,经ZnSO4改性的HZSM-5催化剂表面上强B酸中心和Zn物种的存在使其表现出最佳的甲醇芳构化反应性能.     

Effect of Phosphoric Acid on HZSM-5 Catalysts for Prins Condensation to Isoprene from Isobutylene and Formaldehyde

A series of HZSM-5 zeolites modified with different amounts of phosphoric acid(P/HZSM-5) was prepared. The physicochemical features of the P/HZSM-5 catalysts were characterized via X-ray diffraction(XRD), N₂ adsorption-desorption, NH₃-temperature programmed desorption(NH₃-TPD) and Fourier tranform infrared(FTIR) spectra of the adsorbed pyridine, and the performances of the catalysts for Prins condensation to isoprene from isobutylene and formaldehyde were investigated. The maximum isobutene conversion and isoprene selectivity were 10.3% and 94.6% on the HZSM-5 catalyst with a Si/Al molar ratio of 600 using 5%(mass fraction) phosphoric acid. The phosphoric acid modification not only modulated the amount of acidic sites but also regulated the acid type. An appropriate amount of weak Lewis and Brönsted acid sites served as the active sites for the condensation of isobutene with formaldehyde, and the strong acid sites could cause side reactions and coke deposition.     

Enhanced Stability of Mo-Promoted Zn/HZSM-5 Catalyst for Methanol to Aromatics

A Mo-promoted Zn/HZSM-5 catalyst was prepared by isometric impregnation method (IM). The physicochemical properties of catalysts were characterized by X-ray diffraction, registration of N₂ adsorption-desorption isotherms, transmission electron microscopy, NH₃ temperature-programmed desorption and IR spectroscopic study of pyridine adsorption. The results show that by doping zeolite with Mo species it is possible to tune the microstructures, acidity and crystallinity of the catalyst. Additionally, it was found that the 1%Mo(IM)–5%Zn(IE)/HZSM-5 catalyst had a high catalytic activity and stability for methanol to aromatics (MTA) reaction. The yield of aromatics reached 77.3% at 450°C and TOS = 3 h. When the TOS = 98 h, the yield of total aromatics remains at a 60.4% level. The lifetime of catalysts was influenced by the synergetic effect of Brønsted and Lewis acid sites, so the modification with Mo may bring an opportunity to prolong the lifetime of Zn/HZSM-5 catalyst in the MTA reaction. The metal components are sintered and lost in continuous reaction-regeneration cycles. Accordingly, the activity of deactivated catalyst cannot be completely restored to the initial level.     

Influence of Pretreatment Conditions on Methane Aromatization Performance of Mo／HZSM—5 and Mo—Cu／HZSM—5 Catalysts

Mo/HZSM-5 is a good catalyst for methane aromatization, and the reaction performance of Mo/HZSM-5 and Cu modified Mo/HZSM-5 catalysts under various pretreatment conditions has been studied. The results indicate that the catalyst presented a distinguished catalytic activity, benzene selectivity and a high stability when the bed temperature was raised in N2 atmosphere.