HZSM-5型分子筛硅铝比对一步法合成二甲醚的影响

以Cu/Zn/Al(摩尔比为6∶3∶1)甲醇合成催化剂与HZSM-5型分子筛混合,制备了一步法二甲醚合成催化剂。通过改用三种不同Si/Al摩尔比（摩尔比为25、38和50）的HZSM-5型分子筛,考察了催化剂中脱水组分（HZSM-5分子筛）的酸性对二甲醚合成的影响。结果表明,随着催化剂Si/Al摩尔比的降低,分子筛的酸性增强,使得CO单程转化率提高。当催化剂Si/Al＝38时,CO对二甲醚的选择性最高,可达到68.13％,其次是催化剂Si/Al＝50,选择性最差的是Si/Al＝25的催化剂。在553 K、 3 MPa和4 000 h－1的条件下,Si/Al＝25和Si/Al＝38的催化剂CO单程转化率和DME的选择性接近一致。在此条件下,两者的时空产率达到试验的最大值,分别为0.38 gDME/(gcat·h)和0.36 gDME/(gcat·h),在试验范围内,一步法合成二甲醚催化剂最佳的Si/Al摩尔比为25。     

载体酸性对Mo/HZSM-5-Al2O3催化剂上烯烃歧化反应性能的影响

在固定床反应器上考察了Mo/HZSM-5-Al2O3催化剂上乙烯与2-丁烯歧化制丙烯反应的性能.结合X射线衍射、NH3程序升温脱附、吡啶吸附红外光谱、H2程序升温还原和程序升温氧化等表征结果发现,载体酸性的差异导致催化剂酸性和 Mo物种落位方式不同.载体酸性较强时,催化剂积炭严重,反应稳定性差;载体酸性较弱时,Mo物种...     

HZSM-5分子筛用于合成聚甲醛二甲基醚

以磷酸二氢铵为前驱体,使用浸渍法制备了一系列不同磷含量改性的HZSM-5分子筛,并结合X射线衍射、N2吸附和氨程序升温脱附等表征结果探讨了催化剂硅/铝比、粒径尺寸、晶体结构、孔结构及表面酸性对其催化甲醇和三聚甲缩反应生成聚甲醛二甲基醚(PODEn)反应性能的影响,同时与商业催化剂进行了比较.结果表明,硅铝比为50,粒径尺寸为5μm,P2O5含量较低(0～6%)的HZSM-5分子筛表现出较高的催化活性和PODEn选择性.在130℃,原料甲醇和三聚甲醛的质量比为2:1的优化条件下反应时,三聚甲醛转化率可达到95.2%,PODEn(n=2～5)的选择性为62.9%,略好于商业催化剂.     

Methane to Liquid Hydrocarbons over Tungsten-ZSM-5 and Tungsten Loaded Cu/ZSM-5 Catalysts

Metal containing ZSM-5 can produce higher hydrocarbons in methane oxidation. Many researchers have studied the applicability of HZSM-5 and modify ZSM-5 for methane conversion to liquid hydrocarbons, but their research results still lead to low conversion, low selectivity and low heat resistance. The modified HZSM-5, by loading with tungsten (W), could enhance its heat resistant performance, and the high reaction temperature (800℃) did not lead to a loss of the W component by sublimation. The loading of HZSM-5 with tungsten and copper (Cu) resulted in an increment in the methane conversion as well as CO2 and C5 selectivities. In contrast, CO, C2-3 and H2O selectivities were reduced. The process of converting methane to liquid hydrocarbons (C5 ) was dependent on the metal surface area and the acidity of the zeolite. High methane conversion and C5 selectivity, and low H2O selectivity are obtained over W/3.0Cu/HZSM.     

Dual-Bed Catalytic System for Direct Conversion of Methane to Liquid Hydrocarbons

A dual-bed catalytic system is proposed for the direct conversion of methane to liquid hydrocarbons. In this system, methane is converted in the first stage to oxidative coupling of methane (OCM) products by selective catalytic oxidation with oxygen over La-supported MgO catalyst. The second bed, comprising of the HZSM-5 zeolite catalyst, is used for the oligomerization of OCM light hydrocarbon products to liquid hydrocarbons. The effects of temperature (650-800℃), methane to oxygen ratio (4 10), and SiO2/Al2O3 ratio of the HZSM-5 zeolite catalyst on the process are studied. At higher reaction temperatures, there is considerable dealumination of HZSM-5, and thus its catalytic performance is reduced. The acidity of HZSM-5 in the second bed is responsible for the oligomerization reaction that leads to the formation of liquid hydrocarbons. The activities of the oligomerization sites were unequivocally affected by the SiO2/Al2O3 ratio. The relation between the acidity and the activity of HZSM-5 is studied by means of TPD-NH:j techniques. The rise in oxygen concentration is not beneficial for the C5 selectivity, where the combustion reaction of intermediate hydrocarbon products that leads to the formation of carbon oxide (CO CO2) products is more dominant than the oligomerization reaction. The dual-bed catalytie system is highly potential for directly converting methane to liquid fuels.     

Epoxidation of allyl chloride with H_2O_2 on Ti-ZSM-5 prepared by the isomorphous substitution

The epoxidation of allyl chloride with H2O2 on Ti-ZSM-5 prepared by isomorphous substitution of HZSM-5 with TiCl4 gas was studied. The results show that Ti-ZSM-5 has a high catalytic efficiency for the epoxidation of allyl chloride. The H2O2 utilization reaches 99.50% when the allyl chloride/H2O2 molar ratio is > 1. The effect of solvent species, catalyst concentration, H2O2 and allyl chloride concentration and reaction temperature on the epoxidation was investigated simultaneously. It is found that methanol is the best solvent for the reaction. The reaction rate equation with v = k[Cat. ] [H2O2]1/2-[C3H5Cl] and the apparent activation energy with Ea = 63.462 kJ/mol are obtained according to the kinetics study.     

Effects of ZrO2 on the Performance of CuO-ZnO-Al2O3/HZSM-5 Catalyst for Dimethyl Ether Synthesis from CO2 Hydrogenation

A series of composite catalysts were prepared by the wet mixing method,and the mass ratio of CuO-ZnO-Al_2O_3-ZrO_2 component to HZSM-5 zeolite(molar ratio of SiO_2 to Al_2O_3 being 25)was 2:1. The CuO-ZnO-Al_2O_3-ZrO_2(CuO/ZnO/Al_2O_3=3/6/1 by weight)component was prepared by a modified‘two-step’co-precipitation inethod.The effects of ZrO_2 on the performance of CuO-ZnO-Al_2O_3/HZSM-5 catalyst for dimethyl ether synthesis from CO_2 hydrogenation were investigated.It was found that ZrO_2 improved the properties of CuO-ZnO-Al_2O_3/HZSM-5 as a structural promoter.     

17O magic angle spinning NMR studies of Brønsted acid sites in zeolites HY and HZSM-5

High-resolution 17O/1H double resonance NMR spectra were obtained for two zeolites, one with a low Si/Al ratio (zeolite HY) and one with a high Si/Al ratio (HZSM-5), to investigate their local structure and Br?nsted acidity. Two different oxygen signals, corresponding to Br?nsted acid sites in supercages and sodalite cages of zeolite HY were readily resolved in the two-dimensional (2-D) 1H-17O heteronuclear correlation (HETCOR) NMR spectra allowing the 17O isotropic chemical shift (deltaCS) and quadrupolar coupling parameters (quadrupolar coupling constant, QCC, and asymmetry parameter, eta) for the two oxygen atoms to be extracted. Similar experiments for HZSM-5 showed that the sites in this system are associated with a much larger distribution in NMR parameters than found in HY. 17O-1H rotational echo double resonance (REDOR) NMR was applied to probe the O-H distances in zeolites HY and HZSM-5. Weaker 17O-1H dephasing was observed for zeolite HZSM-5 in comparison to that of HY, consistent with longer O-H bonds and/or increased proton mobility.     

固体酸催化剂上的甲苯硝化反应

研究了ＨＭ，ＨＺＳＭ－５和其它几种固体酸催化剂上的甲苯硝化反应，发现高硅铝比ＨＺＳＭ－５沸石的活性及对位选择性最高，甲苯转化率达６５％，ｐ／ｏ比达０．７８．通过考察沸石晶粒大小、酸性强弱、脱铝程度和阳离子交换等因素对反应活性和选择性的影响，发现该反应主要在沸百孔内进行，对位选择性与沸石的孔径存在一定对应关系．沸石催化剂除能促进ＨＮＯ３解离成ＮＯ外，对甲苯也有活化和富集作用，因而反应活性与催化剂的酸性有关，适当增加沸石的亲油性也有利于提高硝化反应活性．     

ZnCrO_x/HZSM-5催化合成气直接转化制异构烷烃

分别采用共沉淀法和水热法制备了ZnCrO_x复合金属氧化物和HZSM-5沸石,通过物理混合得到双功能催化剂,实现了合成气一步高选择性制备异构烷烃。采用XRD、TEM、氮吸附和NH3-TPD等技术对催化剂进行了表征,考察了双功能催化剂中HZSM-5沸石组分硅铝比以及ZnCrO_x/HZSM-5质量比(OX/ZEO mass ratio)对合成气催化转化反应性能的影响。结果表明,随着HZSM-5硅铝比的增加,催化剂酸密度下降,CO转化率略有下降,产物中C5+选择性显著提高,异构烷烃比例不断增加。此外,在保证CO转化率的前提下提高双功能催化剂中ZnCrO_x组分的比例,产物中C5+的选择性也显著上升。在400℃、2.0 M Pa、进料空速(GHSV)为3600 mL/(h·gcat)的条件下,合成气(H2/CO(volume ratio)=2)转化率达到35%,C5+选择性超过44%,且C5+中异戊烷比例高达65%。     

Co-ZSM-5催化剂上乙烯选择性催化还原Nox表面中间物种的组成

 采用预处理-瞬态反应产物分析方法定量研究了Co-ZSM-5催化剂上乙烯选择性催化还原氮氧化物反应过程中表面中间物种的组成. 催化剂在275 ℃经0.1%NO-0.05%C2H4-10%O2/Ar混合气处理后生成了表面中间物种NCaObHc, 该物种与NO/O2/Ar混合气反应比与单独的NO或O2反应生成更多的N2. 通过质谱、红外吸收四组分 (CO2, CO, CH4和N2O)分析仪及气相色谱-质谱联用等技术分析了表面中间物种与NO/O2/Ar混合气反应的产物,确定了表面中间物种中三种元素N, C和H的平均原子数之比为1.0∶1.8∶5.0 (氧物种由于实验原因很难确定).     

不同方法制备的Cu/HZSM-5催化剂上NO的催化分解反应

采用离子交换法、固相分散法和微波固相法等不同方法制备了Cu/HZSM-5催化剂,以BET、XRD和XPS等手段对催化剂样品进行了表征。结果表明,不同方法制备的Cu/HZSM-5催化剂上Cu物种的落位分布状态不同,离子交换法制备的催化剂Cu物种更多地落位于分子筛孔道内,微波固相法和固相分散法制备的催化剂Cu物种较多地落位分布在分子筛外表面。固相分散法制备的样品未能使铜物种完全分散于分子筛表面,在13.1°、16.8°、35.5°和38.0°等处仍存在CuO的晶相衍射峰。催化分解NO反应的活性考察结果表明,用微波固相法制备的催化剂催化分解NO的活性及稳定性明显超过另两种方法所制备的催化剂,在无氧条件下NO最初转化率高达89.2%,经反应25h后,转化率仍维持在70%以上;在富氧气氛下催化分解NO活性降低速率低于由离子交换法制备的催化剂。结合表征结果可以得出,落位于分子筛外表面以离子交换态形式存在的Cu物种对催化分解NO反应更为有利,而且催化稳定性更好。     

铁改性的Mo/ZSM-5催化剂上NO的选择性催化还原反应

采用浸渍法制备了Mo/ZSM-5, Fe/ZSM-5和不同Fe和Mo摩尔比的Fe-Mo/ZSM-5样品, 并以氨为还原剂对其NO选择性催化还原活性以及反应条件对催化性能的影响进行了研究. 结果表明, Fe-Mo/ZSM-5样品的NOx转化率明显比单独的Mo/ZSM-5和Fe/ZSM-5的高. 当n(Fe):n(Mo)为1.5时, Fe-Mo/ZSM-5样品具有最佳催化性能, 其NOx转化率在430 ℃时达到了96%, 并且能在高空速和不同O2气浓度的条件下保持高的催化活性. 同时采用XRD和XPS技术分别对催化剂的体相结构和表面性质进行了研究, 结果表明, 当n(Fe):n(Mo)=1.5时, Fe和Mo元素之间以及与载体HZSM-5之间存在较强的相互作用, 并且其表面的Mo3d的含量最高. 这可能与其高的催化活性有关. 另外还发现, 在反应过程中Fe-Mo/ZSM-5催化剂表面的氮氧物种主要是吸附态NO, 因此可以推测NO的催化还原反应机理是, 在催化剂表面上, 吸附态NO与吸附NH3物种直接反应生成氮气, 而非经过氧化为NO2的途径.     

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.     

HZSM-5分子筛上C_(6～8)混合链烃和邻二甲苯的加氢裂化

在连续流动固定床装置上,探讨了不同酸性HZSM-5上C6~8混合链烃(以下简称混合烃)和邻二甲苯加氢裂化的变化规律,并在稳定条件下考察了反应温度、质量空速以及氢烃体积比等反应参数的影响。混合烃的加氢裂化伴随着芳构化反应,酸性较弱的HZSM-5主要发生加氢裂化反应,裂化产物以正构烷烃为主,甲烷和异构烷烃较少。酸性强的HZSM-5上,起初以芳构化反应为主,稳定之后产物分布与弱酸催化剂接近。混合烃的加氢裂化反应表现出明显的温度效应,而质量空速和氢烃体积比的影响较小。在380℃、3.0 MPa、质量空速1.02 h-1、氢烃体积比1 000的条件下,100 h内混合烃的转化率均在99%以上,稳定的裂化反应选择性在95%以上。邻二甲苯发生加氢裂化及异构、歧化反应,酸性强的HZSM-5裂化产物收率高,裂化产物分布与混合烃的基本相同。稳定的邻二甲苯裂化反应选择性小于10%。     

不同硅铝比两亲性HZSM-5沸石的制备和表征

 采用三甲基氯硅烷并通过控制水的添加量对硅铝比分别为25, 42和101的HZSM-5沸石进行外表面修饰,制得三种两亲性沸石样品. 水的添加量对沸石催化剂的两亲性有显著影响. 红外光谱和低温氮吸附等测试结果表明,两亲性沸石样品具有与各自母体沸石相似的酸性及略小的比表面积. 在环己烯水合及乙酸异戊酯水解的相界面反应中,两亲性沸石分布于水-油两相界面,并表现出明显高于各自母体沸石的催化活性. 硅铝比为42的两亲性HZSM-5样品表现出最佳的相界面催化性能. 相对于环己烯水合反应,两亲性HZSM-5沸石更适用于乙酸异戊酯水解的相界面催化反应.     

Low-temperature activation of methane over rare earth metals promoted Zn/HZSM-5 zeolite catalysts in the presence of ethylene

At low temperature of 723 K, methane can be easily activated in the presence of ethylene in the feed, and converted to higher hydrocarbons (C2–C4) and aromatics (C6–C10), through its reaction over rare metals modified Zn/HZSM-5 zeolite catalysts without undesirable carbon oxides formation. Methane can get 37.3% conversion over the above catalysts under low temperature, and the catalysts show a longer lifetime than usual metal supported HZSM-5 zeolite catalysts without adding any rare earth metals. The effects of methane activation over various rare earth metal promoted Zn/HZSM-5 catalysts on the products and influences of several reaction conditions such as temperature, catalyst lifetime and molar ratio of CH4/C2H4 have been discussed.     

尿素燃烧法制备CuO-ZnO/HZSM-5及其催化CO_2加氢合成二甲醚的性能

以尿素为燃烧剂,先采用燃烧法制备CuO-ZnO催化剂,接着采用研磨法将其与HZSM-5分子筛均匀混合形成CuO-ZnO/HZSM-5双功能催化剂.采用固定床反应器,在反应温度260℃、压力3.0 MPa、空速1 500 h-1条件下,考察了不同Cu/Zn(摩尔比)催化剂在CO_2加氢合成二甲醚反应中的催化性能.通过XRD、N_2等温吸附脱附、H2-TPR、NH3-TPD对催化剂进行表征,研究了不同Cu/Zn对催化剂结构及表面酸性的影响.结果表明:当Cu∶Z n=6∶4时,催化剂对CO_2催化加氢直接合成二甲醚反应的催化活性和选择性最佳,CO_2的转化率、DME的选择性分别为11.95%和28.74%,且在催化剂上具有更多的低温还原Cu和较强的酸中心,从而提高了CO_2加氢活性和二甲醚的选择性.     

一步法合成二甲醚整体式催化剂的制备及反应性能研究

以蜂窝陶瓷为载体、γ-Al₂O₃为惰性涂层、C301/HZSM-5为活性组分制备出一种整体式合成二甲醚催化剂。BET、XRD和SEM分析结果表明,活性组分均匀负载在载体表面上,催化剂具有良好的结构和织构特点。在固定床反应器中考察了整体式催化剂上CO加氢一步法合成二甲醚的反应性能,并与C301/HZSM-5颗粒（粉末）催化剂进行了比较。在温度260℃、压力4.0MPa、合成气空速1500mL/(g·h)的条件下,整体式催化剂上CO转化率达到79.62%,二甲醚选择性为70.58%,分别比C301/HZSM-5颗粒催化剂高出7.78%和9.44%。100h的稳定性实验结果表明,整体式催化剂可以保持较高的活性和选择性,而颗粒状催化剂的活性有明显的下降。
     

柴油机尾气碳颗粒燃烧中La-Mn-Fe-Cu/HZSM-5的催化性能

采用柠檬酸络合浸渍法制备分子筛负载钙钛矿型金属复合氧化物催化剂。采用XRD、SEM、XPS和H₂-TPR等手段对催化剂性能进行表征,并在微型固定床反应器中对催化剂进行活性评价。结果表明,B位离子由多种金属离子组成的催化剂,可使碳颗粒燃烧温度降低,生成CO₂的选择性高。B位离子种类及配比直接影响催化剂性能,Cu离子加入可提高生成CO₂的选择性,Co离子加入可降低碳颗粒燃烧温度,调节Fe/Mn离子摩尔比可以改善碳颗粒燃烧温度和生成CO₂的选择性。其中,LaMn_0.2Fe_0.7Cu_0.1O₃/HZSM-5催化剂性能较好,碳颗粒燃烧温度较低,T_ig、T_m和T_f分别为236.6、419.0和458.7 ℃,生成CO₂选择性较高,为88.3%。