Synthesis and catalytic performance of ZSM-5/MCM-41 composite molecular sieve from palygorskite

ZSM-5/MCM-41 composite molecular sieve has been hydrothermally synthesized through a two-step crystallization process using palygorskite (PAL) as silicon and aluminum source. The products were characterized by various means and their catalytic properties for acetalization of cyclohexanone and esterification of acetic acid and n-butanol were also investigated. In the first step ZSM-5 zeolite could be formed from the acid-treated PAL after hydrothermal treatment using tetrapropylammonium bromide as template. XRD patterns, N₂ adsorption and desorption data, and TEM images show that the composite obtained in the secondary step had a well-ordered mesoporous MCM-41 phase and a microporous ZSM-5 zeolite phase. Compared with ZSM-5, ZSM-5/MCM-41 composite possessed more total acid amount, weak acid sites and large pore structure due to the formation of MCM-41 and exhibited higher catalytic activity for the acetalization and esterification reaction.     

以天然矿物为全部硅铝源低成本绿色合成ZSM-5分子筛的研究

ZSM-5分子筛被广泛地应用于催化、吸附分离、离子交换和绿色化工等领域,但目前其合成主要是以无机化学品为硅铝源,从源头来看是非绿色化的过程.我们以热活化的硅藻土和亚熔盐活化的累托土为全部硅铝源,通过调变两种矿物的加入比例调变合成体系的硅铝比,在水热合成体系中制备ZSM-5分子筛.系统地考察模板剂用量、碱度、投料硅铝比、晶化时间等合成条件对产物结构和性质的影响,并对在最优条件下合成的ZSM-5分子筛的物化性质进行了详细地表征,结果表明：以天然矿物为全部硅铝源可以合成出具有较高结晶度、晶粒尺寸约为4 μm的六面体挛晶形貌的ZSM-5分子筛,该分子筛比商业ZSM-5分子筛具有更高的水热稳定性和更优的加氢异构性能.     

ZSM-5／MOR复合分子筛催化剂对混合C4烃转化反应的催化性能

以ZSM-5/丝光沸石(MOR)复合分子筛为催化剂,对混合C4烃的催化转化反应进行了评价,并采用程序升温脱附和原位红外光谱技术对ZSM-5/MOR的酸性进行了表征. 结果表明,与ZSM-5相比, MOR具有很低的催化活性,但ZSM-5/MOR复合分子筛具有较高的催化活性,随着ZSM-5/MOR复合分子筛中ZSM-5含量的增加, C4烃转化率稍有升高;在C4烃转化率大致相同的情况下,乙烯和丙烯的总选择性比较接近,但苯和甲苯的总收率却快速升高. 随着ZSM-5/MOR复合分子筛中ZSM-5含量的增加,弱酸和中强酸的酸量逐渐减少,强酸的酸量有所增加. 由于ZSM-5/MOR复合分子筛中MOR对ZSM-5起到分散作用而产生更多的L酸中心,且此L酸中心处于分子筛的外表面而具有较高的能量,导致苯和甲苯的总收率升高.     

硅烷化处理的纳米ZSM-5的结构表征及催化性能

采用多次浸渍法和化学反应沉积法对纳米HZSM-5分子筛外表面进行了硅烷化处理,考察了改性后纳米ZSM-5对甲苯歧化的催化活性.采用改进的Hammett指示剂法和吡啶吸附红外光谱研究了催化剂的酸性位,采用X射线衍射和29Si MASNMR对催化剂的结构进行了表征.研究结果表明,硅烷化处理降低了纳米ZSM-5酸性位的浓度,从而降低了纳米ZSM-5的催化活性.硅烷化处理还减少了纳米ZSM-5中Si的Q4物种,降低了纳米ZSM-5的相对结晶度,同时硅烷化处理产生了脱铝作用.骨架铝含量的减少导致催化剂的酸性位减少,催化活性降低.     

ZSM-5的水热改性及其在合成气经二甲醚制汽油中的应用

对合成气经二甲醚制汽油两段等压反应系统中的ZSM-5分子筛催化剂进行原位水热处理,研究了不同温度下水蒸气处理ZSM-5分子筛的结构、表面酸性及催化反应性能。XRD、XRF、BET、NH₃-TPD 和 TPO等表征手段表明,水热处理温度为400℃时会使ZSM-5分子筛大部分非骨架铝脱除,酸中心数量减少,比表面积增加,提高了催化剂的活性及产物选择性。     

气相转移法与水热合成法合成ZSM-5/SAPO-5核壳结构复合分子筛的比较

以磷酸、拟薄水铝石和硅溶胶为原料,三乙胺为模板剂,在不同晶化温度和晶化时间的实验条件下,分别采用水热合成法和气相转移法合成了一系列ZSM-5/SAPO-5核壳结构复合分子筛,并用X射线衍射、扫描电镜、X射线能量散射谱、红外光谱和N2吸附等手段对其进行了表征.结果表明,所合成的分子筛是以ZSM-5为核,以SAPO-5为壳的双结构复合分子筛.晶化温度的提高和晶化时间的延长有利于分子筛结晶度的提高.与水热合成法相比,采用气相转移法可以减小壳层SAPO-5的颗粒尺寸,减少脱离ZSM-5表面独立生长的SAPO-5的量,改善SAPO-5在ZSM-5表面的分布.重油裂化结果表明,核壳结构复合分子筛对生成低碳烯烃的催化性能优于机械混合的样品.     

ZSM-5分子筛的脱硅改性及加氢改质性能

考察了水热与碱联合处理过程中两者的先后顺序对ZSM-5分子筛酸性和孔结构的影响,并与单独的水热和碱处理进行了比较。结果表明,水热后的碱处理对ZSM-5分子筛具有骨架脱硅、骨架补铝和清除非骨架铝物种三重作用,而碱处理后的水热处理具有骨架脱铝和部分骨架稳定化双重作用。与先水热处理再碱处理相比,先碱处理后的水热处理在优化分子筛酸性和产生介孔方面更加有效。基于水热-碱联合处理的HZSM-5分子筛所制备的催化剂对催化裂化汽油的加氢改质表现出适中的异构化活性、较高的烯烃芳构化活性以及最高的稳定性。     

几种分子筛的转晶和混晶的控制及单一晶体的优化合成

 以六亚甲基亚胺作模板剂，在配料比一定的情况下，详细考察了反应温度和反应时间对MCM－22，ZSM－5，ZSM－35和丝光沸石分子筛成晶的影响．结果表明，MCM－22的最佳合成温度在低温区，ZSM－35易在提高反应温度或延长反应时间时形成，而作为中间相的ZSM－5和丝光沸石则在反应温度与反应时间合理匹配时才能以单一相生成．同时，探讨了晶种的加入对产物晶相的影响．在特定的温度和时间区间，能够合成出比例可控的ZSM－35＋MCM－22混晶，ZSM－5＋ZSM－35混晶和ZSM－35＋丝光沸石混晶，并从分子筛孔道和结构单元的特点出发，就转晶发生对温度和时间的依赖性作了解释．     

Dealuminated ZSM-5 Zeolite Catalyst for Ethylene Oligomerization to Liquid Fuels

Ethylene oligomerization using ZSM-5 zeolite was investigated to study the role of Bronsted acid sites in the formation of higher hydrocarbons. The oligomerization of olefins, dependent on the acidity of ZSM-5 zeolite, is an important step in the conversion of natural gas to liquid fuels. The framework Si/Al ratio reflects the number of potential acid sites and the acid strength of the ZSM-5 catalyst. ZSM-5 with the mole ratio SiO2/Al2O3 equal to 30 was dealuminated for different periods of time according to the acidic ion-exchange method to produce ZSM-5 with various Si/Al ratios. The FT-IR analysis revealed that the integrated framework aluminum band, non-framework aluminum band, and silanol groups areas of the ZSM-5 zeolites decreased after being dealuminated. The performance of the dealuminated zeolite was tested for ethylene oligomerization. The results demonstrated that the dealumination of ZSM-5 led to higher ethylene conversion, but the gasoline selectivity was reduced compared to the performance     

Characterization and Activity of Cr, Cu and Ga Modified ZSM—5 for Direct Conversion of Methane to Liquid Hydrocarbons

Direct conversion of methane using a metal-loaded ZSM-5 zeolite prepared via acidic ion exchange was investigated to elucidate the roles of metal and acidity in the formation of liquid hydrocarbons. ZSM-5 (SiO2/A12O3=30) was loaded with different metals (Cr, Cu and Ga) according to the acidic ion-exchange method to produce metal-loaded ZSM-5 zeolite catalysts. XRD, NMR, FT-IR and N2 adsorption analyses indicated that Cr and Ga species managed to occupy the alllmlnum positions in the ZSM-5 framework. In addition, Cr species were deposited in the pores of the structure. However, Cu oxides were deposited on the surface and in the mesopores of the ZSM-5 zeolite. An acidity study using TPD-NH3, FT-IR, and IR-pyridine analyses revealed that the total number of acid sites and the strengths of the BrSusted and Lewis acid sites were significantly different after the acidic ion exchange treatment.Cu loaded HZSM-5 is a potential catalyst for direct conversion of methane to liquid hydrocarbons. The successful production of gasoline via the direct conversion of methane depends on the amount of aluminum in the zeolite framework and the strength of the BrSnsted acid sites.     

Growth of ZSM-5 crystals within hollow β-zeolite

A zeolite composite composed of ZSM-5 andβ-zeolites has been synthesized by a procedure of the nucleation and crystallization of ZSM-5 zeolite in the hollowβ-zeolite.The property ofβ-zeolite crystals with aluminum-poor interior and aluminum-rich outer rim results in silicon extraction favorably in the aluminum-poor bulk rather than the aluminum-rich external surface.Subsequently,alkaline treatment ofβ-zeolite crystals during the second-step synthesis leads to a preferential dissolution of the aluminum-poor center and the formation of hollowβ-zeolite crystals.ZSM-5 zeolite crystals are therefore embedded and grown within the hollowβ-zeolite.The catalytic activities of Co-Hβ,Co-HZSM-5 and Co-HZSM-5/BEA are investigated during the reaction of methane catalytic reduction NO in the presence of O₂.     

Effect of ZSM-11 crystallinity on its catalytic performance in benzene to phenol oxidation with nitrous oxide

Evolution of ZSM-11 zeolite crystal and pore structure has been studied at 150°C depending on the synthesis time. The amorphous gel was shown to be catalytically inert over the whole induction period, which precedes the crystallization process. The concentration of active sites and the catalytic activity in the oxidation of benzene to phenol is related to the zeolite structure formation and the increasing degree of crystallinity.     

H(Fe)ZSM-5分子筛的合成、表征及其催化性能的研究

用水热法合成出含铁ZSM-5沸石,并对其物相、外貌、结构组成、吸附、表面酸性和催化活性等性能作了测试。ESR和XPS测定结果表明Fe~(3+)进入沸石骨架。实验结果表明,表面总酸性较弱,L酸位浓度较大的H(Fe)ZSM-5在甲醇转化反应中有利于低碳烃的齐聚和异构化,而酸性较强的HZSM-5易使低碳烯烃氢转移而生成大量的气态烃。     

Zeolite synthesis using degradable structure-directing agents and pore-filling agents

Zeolites and molecular sieves are synthesized using organic structure-directing agents (SDAs) that have the potential to be degraded into fragments within the pore space so that they can be readily extracted at mild conditions. The zeolites and molecular sieves, VPI-8, ZSM-12, and ZSM-5, are synthesized using the ketal-containing SDA, 8,8-dimethyl-1,4-dioxa-8-azoniaspiro[4,5]decane (SDA-1). As expected, solids with unidimensional pore systems (VPI-8, ZSM-12) are much more difficult to process by this methodology than solids containing multidimensional pore systems (ZSM-5). Pore-filling agents (PFAs) such as isobutylamine and cyclopentylamine are used together with the ketal-containing SDA-1 to prepare ZSM-5. Extraction of the PFA is shown to be feasible, and its removal provides space for components to enter the zeolite micropores where they react with and cleave SDA-1. Removal of the cleavage fragments from SDA-1 gives ZSM-5 that has the appropriate pore volume, framework aluminum (measured by 27Al NMR), and catalytic behavior. Reasons for desiring this new type of zeolite synthesis method are enumerated.     

Dealuminated ZSM—5 Zeolite Catalyst for Ethylene Oligomerization to Liquid Fuels

Ethylene oligomerization using ZSM-5 zeolite was investigated to study the role of Broensted acid sites in the formation of higher hydrocarbons,The oligomeriztion of olefins,dependent on the acidity of ZSM-5 zeolite ,is an important step in the conversion of natural gas to liquied fuels,The framework Si/Al ratio reflects the number of potential acid sites and the acid strength of the ZSM-5 catalyst,ZSM-5 with the mole ratio SiO2/Al2O3 equal to 30 was dealuminated for different periods of time according to the acidic ion-exchange method to produce ZSM-5 with various Si/Al ratios,The FT-IR analysis revealed that the integrated framework aluminum band,non-framework aluminum band,and silanol groups areas of the ZSM-5 zeolites decreased after being dealuminated,The performanc of the dealuminated zeolite was tested for ethylene oligomerization.The results demonstrated that the dealumination of ZSM-5 led to higher ethylene conversion,but the gasoline selectivity was reduced compared to the performance of a ZSM-5 zeolite ,The characterization results revealed the amount of aluminum in the zeolitic framework,the crystallinity of the ZSM-5 zeolite,and the Si/Al ration affected the formation of Broensted acid sites,The number of the Broensted acid sites on the catalyst active sites is important in the olefin conversion to liquied hydrocarbons.     

Alcohol-Assisted Synthesis of Sheet-Like ZSM-5 Zeolites with Controllable Aspect Ratios

Sheet-like ZSM-5 has been regarded as a promising material for catalytic applications due to its diffusion superiority. However, it still remains a challenge to obtain a desirable sheet-like morphology because of the complex synthesis process of zeolites. Here, a facile strategy for synthesizing sheet-like ZSM-5 is developed by only adding ethanol as zeolite growth modifier in the synthesis gel. It is thought that ethanol might be preferentially absorbed on the {010} surface of zeolite crystals, interact with the exposed silicon hydroxyl groups on the crystal {010} facet, and suppress the growth of b axis, resulting in the sheet-like shape. Through finely tunning synthesis parameters, sheet-like ZSM-5 crystals with thin b-axis thickness of 90 nm and different aspect ratios could be obtained. Owing to its shorter diffusion path and optimized acidity, sheet-like ZSM-5 exhibits better catalytic performance than conventional ZSM-5 in the alkylation of benzene with ethanol.     

PtSnNa/SUZ-4:丙烷脱氢反应的高效催化剂

丙烷脱氢制丙烯是优化利用炼厂气和油田伴生气资源的一条重要途径.随着丙烯需求量的逐步增加,丙烷脱氢制丙烯日益受到重视.负载型PtSn/γ-Al2O3催化剂具有优良的丙烷脱氢活性和选择性,但在高温、低氢压的反应条件下,催化剂易积炭而失活.近年来,选用了微孔分子筛如ZSM-5和介孔分子筛如SBA-15和MCM-41作为PtSn催化剂的载体,结果表明,具有规整孔道结构的负载型PtSn/分子筛催化剂的丙烷脱氢反应稳定性明显优于PtSn/γ-Al2O3催化剂.SUZ-4分子筛与ZSM-5分子筛结构相似且孔径相当,所不同的是ZSM-5由十元环交叉孔道组成,而SUZ-4由十元环和八元环孔道垂直相交组成.我们用微型催化反应装置结合XRD、BET比表面积和孔体积测试、NH3吸附-程序升温脱附(NH3-TPD)、氢化学吸附、热重分析(TG)、H2程序升温还原(H2-TPR)和程序升温氧化(TPO)等多种物理化学手段研究了负载型PtSnNa/SUZ-4和PtSnNa/ZSM-5催化剂的结构和丙烷脱氢反应性能,以及这两种催化剂在丙烷脱氢反应中催化性能差异的原因.实验结果显示,在丙烷脱氢反应中,负载型PtSnNa/SUZ-4催化剂上丙烯选择性和反应稳定性明显优于PtSnNa/ZSM-5催化剂,说明载体一定程度上会影响催化剂上丙烷脱氢反应性能.XRD,BET比表面积和孔体积测试等表征手段结果表明,SUZ-4和ZSM-5的孔体积和比表面积比较接近,载体的结构又类似,且两者的积碳量也相近,故载体的基本性质和积碳量的差异不是引起催化剂性能差异的原因.NH3-TPD结果表明,H-SUZ-4的酸强度明显强于H-ZSM-5.由于浸渍法制备负载型PtSn催化剂所用前体为具有强酸性的混合溶液(H2PtCl6+SnCl4),存在于SUZ-4分子筛孔道内表面的强酸中心不利于上述前体与SUZ-4分子筛孔道内表面结合.ZSM-5分子筛孔道内表面比较弱的强酸中心,促进了催化剂前体在ZSM-5分子筛孔道内表面的分散与结合.和ZSM-5为载体的催化剂相比,PtSnNa/SUZ-4上Pt粒子大部分分散在载体的外表面,从而金属上的积碳不易引起催化剂的失活.故多孔材料上Pt的分布是影响催化活性差异的主要原因.为进一步证明多孔材料上Pt的分布是影响催化活性差异的主要原因,我们通过二苯并噻吩预处理催化剂的手段证明Pt粒子在分子筛孔内外的分布情况.由于二苯并噻吩的尺寸比较大(0.8 nm)不能进入到分子筛的孔道内(SUZ-4:0.56 nm,ZSM-5:0.56 nm),所以载体孔道外的部分Pt会被二苯并噻吩预处理而失去活性,而孔道内的Pt不会因为预处理仍具有催化活性.实验结果表明,PtSnNa/SUZ-4经过二苯并噻吩预处理后,催化活性大大降低;而PtSnNa/ZSM-5经过二苯并噻吩预处理后,催化活性几乎没有变化.说明PtSnNa/SUZ-4上Pt粒子大部分分散在载体的外表面,从而金属上的积碳不易引起催化剂的失活.     

Synthesis and Characterization of ZSM-5/β Co-Crystalline Zeolite

ZSM-5/β co-crystalline zeolites with different content of ZSM-5 have been synthesized by adding different amount of ZSM-5 to the synthetic system of β zeolite with NaAlO2, silica sol as the source of aluminum and silica, respectively, and TEA as the template under controlled condition of the synthesis. The ZSM-5/β co-crystalline zeolite was studied by XRD, SEM, BET and NH3-TPD. The reaction activity of toluene alkylation was investigated with a mixture of toluene-methanol as the feedstock in a pulse micro-reactor over the ZSM-5/β co-crystalline zeolite. It is found that ZSM-5/β co-crystalline zeolite has two kinds of zeolite structure including ZSM-5 and β zeolite, not in the form of a physical mixture. The pore structure of ZSM-5/β co-crystalline zeolites is different from that for β zeolite, ZSM-5 and their physical mixture. In addition, the peaks of both high and low temperature desorption of ammonia over the ZSM-5/β co-crystalline zeolite shift 23 ℃ to lower temperatures and the acid amount of its strong acid is 3% more than the physical mixture. So the ZSM-5/β co-crystalline zeolite produces the highest content of xylene, which is 10.4% higher than the physical mixture. And the ZSM-5/β co-crystalline zeolite has better selectivity for toluene alkylation and weaker de-methylation than β zeolite, ZSM-5 and their physical mixture.     

ZSM-5分子筛酸性质对甲醛合成三聚甲醛催化性能的影响

ZSM-5分子筛是合成三聚甲醛的有效催化剂。本工作通过XRF、XRD、SEM、NH₃-TPD、Py-FTIR和²⁷Al MAS NMR等手段对一系列不同SiO₂/Al₂O₃物质的量比的ZSM-5分子筛催化剂进行了表征,研究了ZSM-5分子筛中Brønsted酸中心和Lewis酸中心对其甲醛合成三聚甲醛催化性能的影响。结果表明,SiO₂/Al₂O₃物质的量比为250的ZSM-5分子筛具有合适的Brønsted酸中心用于催化甲醛缩聚为三聚甲醛的反应,同时其Lewis酸中心量极少,可有效抑制Cannizzaro或Tishchenko等副反应,提高三聚甲醛的选择性,因而具有最佳的合成三聚甲醛催化性能。寿命实验评价结果显示,SiO₂/Al₂O₃物质的量比为250的ZSM-5分子筛具有良好的催化稳定性,单程寿命长达114 h,并且可通过550℃焙烧再生恢复其催化活性。     

Hierarchical mesoporous zeolites: direct self-assembly synthesis in a conventional surfactant solution by kinetic control over the zeolite seed formation

By kinetic control over the zeolite seed formation, we report the direct fabrication of hierarchical mesoporous zeolites using hexadecyl trimethyl ammonium bromide (CTAB) as the soft template in a conventional solution route. Nanometer-sized, subnanocrystal-type zeolite seeds with a high degree of polymerization are essential to prevent the formation of a separate amorphous mesoporous phase and the phase separation between the mesophase and zeolite crystals in the presence of CTAB and a certain amount of ethanol. The mechanisms for the formation of hierarchically porous zeolites in the solution process, including the effect of mother liquid aging, formation of subnanocrystal zeolite seeds and their self-assembly effect with CTAB, and the role of ethanol are proposed and discussed in detail. The prepared mesoporous ZSM-5 zeolite showed much higher catalytic activity than conventional counterparts for aldol condensations involving large molecules, especially in the synthesis of vesidryl.