Pd/La_(0.8)Ce_(0.2)MnO_3/ZSM-5的制备及其甲苯催化燃烧活性

以贵金属改性的钙钛矿为活性组分,通过等体积浸渍法制备了Pd/La0.8Ce0.2MnO3/ZSM-5催化剂,并采用XRD、BET、SEM和H2-TPR等技术对催化剂进行了表征。在固定床反应器上,对Pd/La0.8Ce0.2MnO3/ZSM-5催化剂上的甲苯为目标污染物的催化燃烧进行了研究,考察了焙烧温度、负载量及ZSM-5的性质对其催化活性的影响。结果表明,所得到Pd/La0.8Ce0.2MnO3催化剂仍保持钙钛矿型结构,Pd均匀的分布在催化剂表面,有利于催化剂活性的提高。当ZSM-5硅铝原子比为25、La0.8Ce0.2MnO3负载量为20%、焙烧温度为750℃时,La0.8Ce0.2MnO3/ZSM-5上甲苯的起燃温度和完全转化温度分别为200和279℃;加入0.3%的Pd后,Pd/La0.8Ce0.2MnO3/ZSM-5的催化活性明显提高,甲苯起燃温度下降了90℃,完全转化温度可低至230℃。     

Synthesis, characterization, and adsorption properties of nanocrystalline ZSM-5

Nanocrystalline ZSM-5 with a Si/Al ratio of 20 was synthesized using clear solutions and a hydrothermal synthesis procedure. The resulting ZSM-5 materials were characterized by powder X-ray diffraction, scanning electron microscopy (SEM), nitrogen adsorption isotherms, solid-state nuclear magnetic resonance, and toluene adsorption. A commercial ZSM-5 sample was similarly characterized for comparison with the synthesized materials. The particle sizes of the synthesized ZSM-5 samples were calculated using the measured external surface areas and were determined to be 15 and 60 nm. SEM images indicated that the ZSM-5 samples consist of agglomerated and possibly intergrown particles. Toluene adsorption measurements showed that the ZSM-5 sample with a particle size of 15 nm adsorbed approximately 50% more toluene than the other ZSM-5 samples, most likely due to the adsorption of toluene on the external surface. For the toluene adsorbed on the internal zeolite surface, approximately one toluene molecule was adsorbed per channel intersection for each of the ZSM-5 samples.     

不同硅铝比的ZSM-11沸石分子筛的催化性能

合成了一系列硅铝比为31—176的ZSM-11沸石,以甲苯-甲醇烷基化、间二甲苯异构化和甲苯歧化三个反应作为探针反应,研究了它们的催化性能。将其与酸性质和晶胞参数相关联发现,低硅铝比适于甲苯歧化,中硅铝比适于间二甲苯异构化,高硅铝比适于甲苯-甲醇烷基化反应。各反应所需的酸强度为甲苯歧化>间二甲苯歧化>间二甲苯异构化>甲苯-甲醇烷基化。Na~+的存在以及用4-甲基喹啉或(CH_3)_3SiCl中毒,可抑制强酸位,明显提高甲苯-甲醇烷基化反应生成对二甲苯的选择性,尤以(CH_3)_3SiCl中毒的低Al/u.c.的NaHZSM-11最佳。     

低硅铝比ZSM-5分子筛上C4烃的催化裂解反应

以低硅铝比(n(SiO2)/n(Al2O3)=20-45)的ZSM-5分子筛为催化剂, 研究了混合C4烃的催化裂解反应, 并对不同硅铝比的ZSM-5分子筛进行了酸性表征. 混合C4烃的催化裂解反应结果表明, 低硅铝比的ZSM-5分子筛具有较高的低温催化活性, 高硅铝比ZSM-5分子筛催化剂上乙烯和丙烯的收率高于低硅铝比ZSM-5分子筛催化剂, 低硅铝比ZSM-5分子筛上苯和甲苯的收率高于高硅铝比ZSM-5分子筛催化剂. 在反应温度为625 ℃时, 硅铝比为20的ZSM-5分子筛催化剂上乙烯、丙烯、苯和甲苯的总收率可达79.42%. 酸性表征结果表明, 硅铝比低的ZSM-5分子筛具有更多的Bronsted(B)酸酸量、Lewis(L)酸酸量及总酸酸量, 这是低硅铝比ZSM-5分子筛具有低温高活性及高的苯和甲苯收率的原因.     

低硅铝比ZSM-48分子筛合成及其正构十二烷临氢异构催化性能研究

通过静态水热合成法,溴化六甲二铵作为结构导向剂合成出系列低硅铝比的ZSM48沸石分子筛(Si/Al100),所合成样品中最低硅铝比为38.6(ICP-AES),这将拓宽ZSM-48高硅沸石分子筛的应用范围。制备Pt负载双功能催化剂,用于正构十二烷临氢异构催化反应。结果表明,硅铝比的改变可以影响催化剂的活性,投料硅铝比为70的双功能催化剂具有最优的催化性能,但硅铝比改变对异构产物的分布没有明显的影响,其异构产物以支链在中间位的异构体为主。     

酸碱处理对ZSM-5分子筛物化性质和反应性能的影响

考察了碱处理、先碱后两步酸处理对HZSM-5分子筛物化性质以及苯与甲醇烷基化反应性能的影响。结果表明,碱处理在脱除分子筛中非骨架硅的同时,提高了晶孔的利用率,也中和了分子筛的强酸中心,使催化剂活化甲醇的能力减弱,苯与甲醇反应活性降低;先碱后两步酸处理既脱除了分子筛中的非骨架铝,也恢复了一部分强酸中心,提高了苯与甲醇的反应活性。进一步考察了先碱后两步酸处理中不同碱浓度的影响,结果表明,适宜浓度的碱处理后再两步酸处理,一方面,能脱除分子筛的非骨架硅铝物种,使分子筛的颗粒粒径更加均匀;另一方面,分子筛的强酸中心有所减少,降低了催化剂的积炭失活速率,苯转化率提高15%以上。     

Oxidative conversion of methane over MgO/ZSM-5 catalysts with different Si/Al ratios

It is found that the lower the Si/Al ratio of ZSM-5 in the catalytic system MgO/ZSM-5, the higher is the activity and selectivity in the reaction of oxidative conversion of methane. The catalytic properties reflect quite closely the basic properties of the samples, studied by means of temperature-programmed desorption of CO₂.     

HZSM-5/SAPO-11复合分子筛的制备、 表征及在异丁烷芳构化反应中的催化性能

将经聚二烯丙基二甲基氯化铵(PDDA)预处理的HZSM-5分子筛置于SAPO-11分子筛的合成母液中, 在水热体系中原位制备了一系列HZSM-5/SAPO-11复合分子筛, 并对分子筛的结构、 形貌及酸性进行了表征, 考察了其在异丁烷芳构化反应中的催化性能. 结果表明, 所得复合分子筛由HZSM-5表面包覆约20 nm的SAPO-11微晶组成, 且通过调变SAPO-11的Si含量可以有效调变复合分子筛的酸性, 提高芳构化强弱酸协同催化作用, 有效抑制裂解副反应. 结合异丁烷芳构化转化率及液体收率结果可知, 当SAPO-11合成溶胶中硅铝摩尔比为0.6时, HZSM-5/SAPO-11复合分子筛的芳构化活性及稳定性最佳.     

微孔/微介孔H-ZSM-5分子筛上甲苯甲醇的烷基化性能

以不同硅铝比的H-ZSM-5分子筛为研究对象,考察了Na OH碱处理、酒石酸处理及Na OH碱处理-酒石酸处理相结合的方法对其物化性能和催化性能的影响.处理前后分子筛的表征结果表明,酸处理和碱处理可通过调变催化剂的酸性和孔道结构影响其催化性能.酸处理对低硅铝比H-ZSM-5的酸性和催化性能影响较大,而碱处理则主要影响高硅铝比分子筛的酸性和催化性能.酸处理和碱处理相结合则能同时调变分子筛的酸性和孔道结构,进而提高其在甲苯甲醇制二甲苯反应中的催化活性.其中,碱处理的高硅铝比H-ZSM-5分子筛表现出最优异的催化活性.     

Oxidative dehydrogenation of isobutane to isobutylene over supported transition metal oxide catalysts

Para-selectivity of ZSM-5 zeolites with similar bulk Si/Al ratio, but different particle size and surface Al concentration has been investigated in toluene disproportionation. Results showed that enhancedpara-selectivity is a consequence not only of the particle size but also of the external surface aluminium concentration in the particles.     

亚微米ZSM-5负载Cr催化剂上乙烷CO2气氛下脱氢制乙烯

石油资源的日趋短缺使天然气和页岩气的开发利用受到重视,因而低碳烷烃脱氢制取低碳烯烃也随之引起了人们越来越多的关注.由于乙烷纯脱氢反应的平衡收率低,能耗高,而氧气氧化脱氢又易将乙烷深度氧化为CO2或CO,因此开发具有反应条件温和、装置投资和操作费用低等优势的CO2气氛下乙烷脱氢的技术路线日益得到重视. CrOx是该反应理想的催化剂之一, CO2的加入可使CrOx对乙烷脱氢的催化活性提升3倍,然而受困于CrOx过小的比表面积,通常将CrOx制备成负载型催化剂使用. CrOx的常见载体有Al2O3, ZrO2和SiO2等氧化物及MCM-41, SBA-15, SBA-1和MSU-x等介孔硅材料, ZSM-5作为载体负载CrOx用于低碳烷烃脱氢的研究则较少,所得结果也不甚理想.我们采用亚微米尺寸的ZSM-5作为载体制备了负载型CrOx催化剂,研究了其在CO2气氛下催化乙烷脱氢反应,发现该催化剂具有非常优异的脱氢活性,高硅铝比和Na型的ZSM-5作载体对反应更加有利,而且在反应进行50 h后,催化剂依然保持很好的活性和很高的乙烯收率,这是在一般负载型CrOx催化剂上所不能实现的.
　　X射线光电子能谱(XPS)表征发现, Na型ZSM-5载体制得的催化剂具有更高的Cr6+/Cr3+比.一般认为, Cr6+是Cr系催化剂进行低碳烷烃脱氢反应时的活性位(或活性位前驱体),因此可以初步判定, Na型载体具有很好催化效果的原因可能是由它制得的催化剂具有更多的反应活性位.程序升温还原(H2-TPR)表征结果证实了这一点, Na型载体明显具有更高的H2消耗量;也就是说, Na型载体制得的催化剂具有更多的可还原Cr物种,即脱氢活性位.进一步表征发现,反应活性还与Cr物种存在形式有关.文献报道,低聚态的Cr物种和孤立态的Cr物种比Cr2O3有更好的催化活性.通过漫反射紫外-可见光谱(UV-Vis)对Cr物种的存在形态进行表征后发现, Na型载体上Cr主要以四配位形式存在,而在H型载体上出现了对应于六配位的Cr物种;激光Raman表征结果表明, Na型载体上出现的都是低聚态Cr物种和孤立态Cr物种,而H型载体上出现了明显的对应于α-Cr2O3的峰,说明相较于H型载体, Na型载体更有利于Cr组分分散,这也是Na型ZSM-5载体催化剂具有更高活性的原因之一.
　　CO2引入后对乙烷脱氢反应具有明显的促进作用,特别是在CO2/C2H6=5时,催化剂上C2H6转化率是非CO2气氛下的3.2倍;同时, CO2的引入也提高了脱氢反应的稳定性.在非CO2气氛下,反应进行6 h后, C2H6转化率降低到初活性的60%左右,而在CO2/C2H6=5时,相同时间内催化剂活性下降仅有5%左右.实验分析了CO2对脱氢反应具有促进作用的原因.在脱氢反应温度650 oC下, CO2/H2=1时进行了逆水煤气反应测试,发现CO2的转化率达到22.5%,说明引入CO2后可以通过逆水煤气反应有效地消耗掉乙烷脱氢反应生成的H2,从而促进反应向脱氢方向进行; CO2的引入也可以促进Cr物种的CrOx/CrOx-1循环,从而提高催化剂效率,减缓催化剂失活; CO2还可与反应中生成的积碳类物质发生Boudouard反应,将反应活性位暴露出来,从而提高催化剂的稳定性. CO2气氛下反应6 h后催化剂的积碳量为3.0%,低于非CO2气氛下的3.4%,同时在脱氢反应中生成的CO量与消耗掉的CO2量的比值约为1.4,也有力地说明Boudouard反应的存在.     

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     

Comparative study of the deactivation of Cr-BEA, Cr-MOR and Cr-ZSM-5 in catalytic decomposition of VOC

The catalytic activity and stability studies of chromium exchanged beta, mordenite and ZSM-5 zeolites for VOCs decomposition are reported. Difference in deactivation behavior by the zeolites was observed. Cr-ZSM-5 (Si/Al=240) was the most stable catalyst due to its high Si/Al ratio. It also has less coking tendency due to its uniform sized intersecting channel system. This revised version was published online in June 2006 with corrections to the Cover Date.     

载体组成对负载型PtSn/ZSM-5催化剂上丙烷脱氢反应性能的影响

用微型催化反应装置结合吡啶吸附的红外光谱、NH3-程序升温脱附、热重、H2化学吸附和程序升温还原等物理化学手段研究了载体组成对负载型PtSn/ZSM-5催化剂上丙烷脱氢反应性能的影响.结果表明,负载型PtSn/ZSM-5催化剂对丙烷脱氢的催化性能与载体组成密切相关.随着ZSM-5载体中SiO2/Al2O3比的增加,催化剂表面的酸中心总量和强酸中心量逐渐减少.当SiO2/Al2O3摩尔比从45增至108时,催化剂对丙烷脱氢反应的催化活性提高,并且催化剂的积炭量下降.当SiO2/Al2O3摩尔比增至304时,Sn组分与载体ZSM-5之间的相互作用减弱,经H2还原后催化剂中Sn0物种所占的比例增加,导致催化剂H2化学吸附量和丙烷脱氢反应活性下降.     

直接法合成ZSM—5型分子筛的物理化学表征

用高分辨~(29)Si、~(27)Al和~(23)Na NMR对直接法合成的不同硅铝比ZSM-5型分子筛局域结构作了表征,用~(29)Si和~(27)Al魔角旋转核磁共振研究了经不同温度水蒸气处理ZSM-5型分子筛的骨架脱铝,对不同条件下ZSM-5型分子筛中发生的正交-单斜晶型变化进行了系统的X射线衍射实验研究。     

甘油脱水合成丙烯醛ZSM-5催化剂的孔结构和酸性调控

研究了ZSM-5 孔结构和表面酸性对甘油脱水合成丙烯醛反应性能的影响. 在碱浓度为0.2 mol·L^-1的NaOH溶液中, 分别在65和85 ℃条件下对ZSM-5进行化学刻蚀, 成功地制备了含微介孔的ZSM-5催化剂, 提高了催化剂的表面强酸密度. 碱处理后的ZSM-5催化剂在甘油脱水反应中的稳定性得到显著提高, 在ZSM-5-at85 (经85 ℃碱处理的ZSM-5)催化剂上甘油转化率在反应10 h 后仍可保持95%以上, 丙烯醛选择性达到78%. 采用N₂吸附-脱附等温线、X射线粉末衍射(XRD)、²⁷Al 固体核磁共振(²⁷Al MAS-NMR)和透射电子显微镜(TEM)等手段对ZSM-5 结构和表面性质进行了表征, 实验结果表明在碱处理过程中骨架中的硅发生了溶脱现象, 在分子筛表面上形成了大量介孔, 但是ZSM-5 的MFI 拓扑结构没有发生变化, 骨架中的大部分铝得到保持. X射线光电子能谱(XPS)、X射线荧光光谱(XRF)和氨气程序升温脱附(NH₃-TPD)证实了在碱处理后ZSM-5分子筛外表面的Si/Al 摩尔比低于其骨架中的比例, 由此表明脱硅现象主要发生在ZSM-5 的外表面, 在新产生的介孔区域由于Si/Al 摩尔比的降低使得强酸密度得到提高. 具有微介孔结构和较高酸密度的ZSM-5催化剂增强了反应物扩散性能和容碳能力, 这对于提高甘油脱水合成丙烯醛催化剂的活性和稳定性起到了关键作用.     

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.     

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.     

Ozone-Assisted Catalysis of Toluene with Layered ZSM-5 and Ag/ZSM-5 Zeolites

This paper presents a new type of ozone-assisted catalysis for toluene decomposition. The different catalytic activities of ZSM-5 and Ag/ZSM-5 were incorporated into a layered catalyst with a tandem configuration. Instead of increasing the amount of metal catalyst, the layered catalyst was formed, which had an equal amount of bare ZSM-5 and Ag/ZSM-5 and could achieve both high toluene conversion and CO₂ selectivity concurrently. The properties of each catalyst were evaluated with respect to toluene conversion, formation of intermediates, CO₂ selectivity and ozone demand factor. The bare ZSM-5 exhibited higher toluene conversion than the Ag/ZSM-5, while its activity toward deep oxidation was limited. However, the Ag/ZSM-5 was found to be effective for the deep oxidation of reaction intermediates (HCOOH and CO). Separate oxidation tests with HCOOH and CO revealed that the ZSM-5-supported Ag nanoparticles could oxidize the HCOOH and CO in the absence of ozone, which was not possible with the bare ZSM-5. Plausible pathways for the oxidation of toluene with O₃ over ZSM-5 and Ag/ZSM-5 were proposed based on the experimental evidence.     

CuCoMn-zeolite双功能催化剂转化生物质基合成气制取液态烃

选用四种不同的分子筛（SAPO-34, ZSM-5, Y, MCM-41）与CuCoMn（高醇合成组元）构成双功能催化剂,利用N2吸脱附、H2-TPR、XRD、NH3-TPD等表征了催化剂的结构性质. 研究了催化剂在生物质基合成气一段法制取液态烃燃料的应用. 相比于CuCoMn催化剂,加入分子筛的双功能催化剂均不同程度地提高了液体烃燃料的选择性及收率,且收率按顺序递减呈CCM-ZSM-5〉CCM-SAPO-34〉CCM-Y〉CCM-MCM-41. 同时,共沉淀法制备的CuCoMn-ZSM-5 （20wt%, Si/Al=100） 具有最佳的CO转化率（76%）及液体产物收率（30%）. 相比于CuCoMn氧化物,双功能催化剂的比表面及孔容均得到提高. CCM-ZSM-5具有适中的微孔尺寸和中等强度的酸性,增加CCM-ZSM-5中ZSM-5含量或降低ZSM-5中的Si/Al比,均有利于提高酸性位的数量,主要是较弱的酸性位. 而共沉淀法制备的CCM-ZSM-5具有更好的金属分散性及还原性能.