Preparation and Catalytic Properties of Transition Metal Doped ZSM-5 Zeolites

Metal silicates of ZSM-5 type structure were prepared by doping silicate gels with chromium, manganese, cobalt, nickel, and copper ions, respectively, followed by reacting hydrothermally. The resultant materials were characterized by the metal content, x-ray powder diffraction, ion exchange capacity, surface area, thermal stability, and temperature programmed desorption of ammonia for acidity measurement. In addition, the catalytic properties of these metal silicates were examined using ethanol conversion as a probe reaction. The effect of transition metal content on the catalysis for dehydration, dehydrogenation, oligomerization, cracking, and cyclization to the aromatics was established and compared with that of HZSM-5 catalyst.     

Pd/Co双金属纳米颗粒的制备及催化制氢性能

采用聚乙烯吡咯烷酮(PVP)保护的化学共还原法制备了Pd/Co双金属纳米颗粒, 研究了PVP及还原剂(NaBH₄)的用量、金属盐浓度、金属比例等对Pd/Co双金属纳米颗粒催化NaBH₄制氢性能的影响. 透射电子显微镜(TEM)的结果表明, 所制备的Pd/Co双金属纳米颗粒的平均粒径在1.5-2.8 nm之间. Pd/Co双金属纳米颗粒(BNPs)的催化活性远高于Pd与Co单金属纳米颗粒的活性; 当Pd/Co的理论原子比为1/9时, 双金属纳米颗粒的催化活性最高可达15570 mol·mol^-1·h^-1 (文中纳米颗粒的催化活性均为每摩尔Pd的活性). 密度泛函理论(DFT)的计算结果表明, Pd原子与Co原子之间发生电荷转移, 使得Pd原子带负电而Co原子带正电, 荷电的Pd和Co原子进而成为催化反应的活性中心. 所制备的Pd/Co双金属纳米颗粒具有很好的催化耐久性, 即使重复使用5次后, 该催化剂仍具有较高的催化活性, 且使用后的纳米颗粒催化剂也没有出现团聚现象. 双金属纳米颗粒催化NaBH₄水解反应的活化能约为54 kJ·mol^-1.     

Influence of the ZSM-5 Support Acidity on the Catalytic Performance of Pd/ZSM-5 in Lean Methane Oxidation

Although zeolites are characterized by their special acidic properties, there is still no clear consensus on the effect of zeolite support acidity on the catalytic activity of supported Pd catalyst in methane oxidation. Herein, a series of Pd/H-ZSM-5 and Pd/Silicalite-1 catalysts was prepared by the deposition-precipitation method and used in lean methane oxidation. The effect of ZSM-5 support acidity on the catalytic performance of Pd/ZSM-5 was investigated. The results indicate that with the decrease of Si/Al ratio(x), viz., the increase of acid sites in H-ZSM-5(x), the catalytic activity of Pd/H-ZSM-5(x) increases substantially; the activity of various catalysts in the lean methane oxidation decreases in the order of Pd/H-ZSM-5(28)>Pd/H-ZSM-5(48)>Pd/H-ZSM-5(88)>Pd/H-ZSM-5(204)>Pd/Silicalite-1. Furthermore, various characterization measures reveal that the catalytic activity of Pd/H-ZSM-5(x) in lean methane oxidation is mainly related to the Lewis acid sites in the H-ZSM-5 support, whereas less relevant to the Brønsted acid sites. The abundant Lewis acid sites in H-ZSM-5 are capable to enhance the interaction between the Pd species and H-ZSM-5 support, which can inhibit the agglomeration of Pd particles and improve the dispersion of Pd species, and thus boost the catalytic activity of Pd/H-ZSM-5 in methane oxidation.     

水热脱铝ZSM-5/Y复合分子筛的表征和催化裂化性能

ZSM-5/Y是一种通过原位合成方法制备的新型复合分子筛材料,用XRD、IR光谱、N2吸附／脱附等手段,研究了水热处理对ZSM-5/Y物化性质的影响,并以正己烷为原料考察了样品的催化裂化性能.结果表明,与机械混合样品相比,在550 ℃和700 ℃水热处理条件下,复合分子筛中的Y型沸石相具有更好的结晶保留度.复合分子筛的中孔孔径分布范围大于机械混合分子筛,但复合分子筛样品所表现出的中、大孔体积小于相应的机械混合分子筛.吡啶吸附定量IR研究表明,550 ℃水热处理使复合分子筛的B酸量和L酸量减少;而机械混合样品则是B酸量和L酸量变化很小.进一步700 ℃水热处理则使B和L酸量都大量减少.与氢型样品相比,550 ℃脱铝样品的正己烷裂化活性显著增加,700 ℃脱铝后活性明显降低.产物分布的分析表明活性的提高与反应机理的改变有关.     

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.     

制备条件对Au/LaCoO_3催化氧化CO性能的影响

采用溶胶-凝胶法制备了钙钛矿型复合氧化物LaCoO_3, 并用沉积-沉淀法(DP法)制备了Au/LaCoO_3催化剂. 考察了制备条件对催化剂催化氧化CO活性的影响. 结果表明, 制备过程中, 溶液pH、 pH调节顺序及催化剂焙烧温度对催化剂活性均有一定影响. Au/LaCoO_3催化剂的最佳制备条件为: 沉积过程中在HAuCl4溶液中先加入载体后, 再调节溶液pH=8, 得到的催化剂经250 ℃焙烧后可提高催化剂稳定性.     

Peculiarities of Catalytic Oxidation of Ethane by Nitrous Oxide on ZSM-5 Type Zeolites Containing Iron Ions in Different Localization Sites

The temperature dependence of the Fe-HZSM-5 activity and selectivity in the process of catalytic oxidation of ethane by the excess of N₂O at 250–350°C exhibits a pronounced hysteresis. The oxidized catalysts free from condensation products are active only in the complete oxidation of ethane. At low temperatures of the reaction of the C₂H₆ + N₂O mixture with the catalyst, coke formation takes place and the coordination state of iron ions differs from the initial sample. Under these conditions, the process of complete oxidation of ethane is essentially suppressed and the process of oxidative dehydrogenation dominates. The catalytic properties of iron-containing zeolites prepared either by direct synthesis or by introduction of iron ions into the cationic positions of H[Al]ZSM-5 are quite similar, because irreversible formation of new iron species considerably different from the initial species takes place during the catalytic reaction on both series of samples. The activity of HZSM-5 containing trace amounts of iron is much lower than that of iron-containing samples.     

多金属ZSM-5催化剂的制备及其催化氨化合成2,6-二甲基吡啶

通过掺杂制备了一系列多金属改性的ZSM-5催化剂,并用于丙酮和甲醇氨化合成2,6-二甲基吡啶的反应中.在固定床反应器上筛选出催化性能良好的催化剂6%Pb-0.5%Fe-0.5%Co/ZSM-5(200),探讨了过渡金属掺杂的促进作用,并考察了反应温度、氨醇比、酮醇比、水含量和停留时间对反应性能的影响.结果表明,该催化剂...     

（K,Na）ZSM—5的酸碱性质及催化性能

采用红外光谱、程序升温脱附、原子吸收光谱、等离子光谱、Hammett指示剂非水滴定和催化活性测试等方法研究了经不同浓度的KOH溶液交换得到的(K,Na)ZSM-5的酸碱性质。结果表明,(K,Na)ZSM-5具有中等强度的L酸位(K~+,Na~+)及弱碱位(AlO_4~-或骨架O~(2-))和强碱位(OH~-).KOH浓度增大.酸性减弱,碱性增强.所得(K,Na)ZSM-5具有较高的异丙醇脱氢、脱水活性.催化性能与酸碱性密切相关.     

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.     

Kinetic Analysis of the Mechanism of Oxidation of CO on Co/ZSM-5

We have studied the kinetic behavior of oxidation of carbon monoxide on Co-containing zeolite ZSM-5. We have shown that the kinetic curves obtained for the dependence of the reaction rate on the reagent concentration can be described by an Eley–Rideal mechanism, which assumes that oxygen can be adsorbed on the surface of the catalyst in both atomic and molecular form, followed by reaction of CO from the gas phase with the adsorbed oxygen.     

高浓度体系小晶粒B改性ZSM-5分子筛的制备及甲醇制丙烯催化性能

在高浓度体系(n(H2O)∶n(Si O2)4)下,以粗孔硅胶和偏铝酸钠为原料,TPABr为模板剂,水热晶化法制备了小晶粒B改性ZSM-5分子筛,单釜产率达50%以上.采用XRD、FT-IR、SEM、NH3-TPD、XRF、N2物理吸附等方法对其结构进行了表征,评价了其在甲醇制丙烯(MTP)反应中的催化性能.结果表明,制备的小晶粒B改性ZSM-5分子筛粒度分布均匀,粒径约500 nm.在MTP反应中,B改性的样品比未改性样品含有更多的弱酸位,表现出更好的的活性、选择性和稳定性,其中n(Al2O3)∶n(B2O3)=1∶1的样品效果最好,甲醇转化率在95%以上运行476h,丙烯平均选择性46.32%.     

Effect of Production Conditions of Hierarchical SnAl-BEA Zeolites on Their Acidity and Catalytic Activity in Tandem Process for the Production of 4-Methoxybenzyl-sec-Butyl Ether

Theoretical and Experimental Chemistry - Hierarchical SnAl-silicate zeolites of the BEA structural type with Lewis (up to 130 μmol/g) and Brønsted (up to 330 μmol/g) acid sites, the...     

杂原子ZSM－5、ZSM－11和ZSM－48型分子筛的合成

在Na₂O-SiO₂-M_xO_y-H₂O体系中,以HMDA为模板剂用动态法和静态法合成了Ti-ZSM-48型分子筛,首次以85%(wt)HMDA+15%(wt)TPA⁺为模板剂用低温陈化的静态法合成了第四周期过渡金属杂原子M-ZSM-5型分子筛,并与以HMDA、TPA⁺为模板剂合成M-ZSM-5和以TBA⁺为模板剂合成M-ZSM-11进行了对比研究。利用XRD技术跟踪晶体生长过程,考查了模板剂、合成方法、pH值、Na⁺含量等因素对晶化动力学的影响,得出了合成各种杂原子分子筛的最佳条件。各种测试均表明杂原子进入了分子筛骨架。     

形貌、晶粒大小不同的ZSM-5分子筛的表征及催化性能的研究

对3种不同形貌、晶粒大小的ZSM—5分子筛催化剂进行了表征和催化性能的研究．用XRD、SEM和NH3—TPD等方法对ZSM—5分子筛进行表征，结果表明小品粒分子筛的结晶度优于大晶粒分子筛，其酸性随着晶粒的减小而增强．对于MTG反应，ZSM—5分子筛酸性、晶粒大小和晶体形貌等因素对其催化活性产生显著影响．小晶粒的ZSM—5分子筛更有利于C5 和C9 的生成，而大晶粒的ZSM—5分子筛对对二甲苯的选择性高．TG结果表明ZSM—5分子筛上积炭覆盖酸性中心是导致催化失活的主要因素．     

两种ZSM-5沸石的晶体结构及其与吸附、扩散和反应性能的关系

用x-射线粉末衍射法研究了两种ZSM-5沸石的晶体结构。两者同属Pnma空间群,晶胞参数分别为:5001—a=20.118(?),b=19.923(?),c=13.410(?);5020—a=20.048(?),b=19.884(?),c=13.352(?)。两者基本结构形貌相近,但与5001相比,5020的骨架结构内存在更大的“应力”,因而较易遭到破坏,两种样品的孔道开口直径分别为:5001-正弦形通道5.080—5.650(?),平均5.367(?),直通道5.207—5.390(?),平均5.307(?);5020—正弦形通道5.111—5.655(?),平均5.368(?),直通道4.993—5.404(?),平均5.226(?)。两者正弦形通道开口尺寸和形状十分接近,而直通道开口尺寸和形状有一定差异,这种孔道结构上的差异是二者性能差别的一个不可忽视的原因。     

杂原子ZSM－5分子筛催化剂上C_3H_6催化还原NO反应的研究

杂原子ＺＳＭ－５分子筛催化剂上Ｃ_３Ｈ_６催化还原ＮＯ反应的研究张文祥，贾明君，张春雷，吴通好，敖雪桔（吉林大学化学系，长春，１３００２３）（齐齐哈尔环境监测中心站）关键词杂原子分子筛，一氧化氮，催化还原ＮＯｘ对环境的危害已引起了人们的广泛重视。自Ｉｗ...     

Co-hydrolysis and Seed-Induced Synthesis of Basic Mesoporous ZSM-5 Zeolites with Enhanced Catalytic Performance

For zeolite catalysts, the regulation of active site and pore structure plays an important role in the enhancement of their catalytic performance. In this work, a one-pot and organic template-free co-regulation route is proposed to straightforwardly synthesize basic mesoporous ZSM-5 zeolites with adjustable alkaline-earth metal species. The synthesis pathway combines two decisive strategies: 1) the seed-induced interface assembly growth method and 2) the acidic co-hydrolysis/condensation of aluminosilicate species and alkaline-earth metal (e.g., Mg, Ca, Sr, or Ba) sources. It is interesting that the mesoporous structure was self-evolved through particle-attached seed-interfacial crystallization without the assistance of any template. Meanwhile, the incorporation of alkaline-earth metals species is homogeneous and highly dispersed in the solid products during the whole crystallization process, and finally generate the superior basicity. Catalysis tests of the as-synthesized samples displayed their novel performance in the typical base reaction of Knoevenagel condensation, even for bulky substrates owing to the enhanced diffusion arising from the meso/microporous network. This finding opens new possibilities for facile, cost-effective, and environmentally friendly synthesis of mesoporous high-silica zeolites with tunable acid/base properties, and deepens our understanding of the particle-attached crystallization.     

ZSM-5型分子筛的表面酸性与催化活性

合成了一批不同硅铝比的HZSM－5沸石分子筛，并用CO62 ,Fe^3 离子对其进行改性，测定了它们在醛氨缩合反应合成吡啶中的活性和选择性。对照它们的NH3－TPD，吡啶吸附红外光谱，研究了催化剂的表面酸性与醛氨缩合催化活性的关系。研究表明，硅铝比较小时，HZSM－5的酸中心较多，但过多的酸中心会引发其它的裂解反应和缩合反应，从而降低催化剂的活性和选择性；当硅铝比为120左右时，催化活性达到最大，吡啶碱产率达60％；若继续增大硅铝比，则无足够的酸中心进行反应，用Co^2 ,Fe^3 离子对HZSM进行改性，其B酸中心变化不明显，L酸中心减少，对氨气的吸附能力有所下降，从而保证了适当的酸中心暴露，有利于反应，采用CoZSM-5催化剂，吡啶碱产率可达78％。     

等级孔微孔-介孔Fe2O3/ZSM-5中空分子筛催化材料的制备及催化苄基化性能

ZSM-5分子筛具有极其均匀的孔道结构、 良好的形状选择性和催化活性及耐水热稳定性, 是一种高效、 绿色的固体催化剂, 被广泛应用于石油催化裂化、 精细化工和环境保护等领域. 但其单一的微孔结构大大降低了客体分子的流通扩散性, 导致由大分子参与的芳烃烷基化反应受到极大限制. 本文采用NaOH/四丙基氢氧化铵(TPAOH)混合碱处理微孔ZSM-5, 制备了具备高结晶度、 高比表面积的等级孔微孔-介孔ZSM-5中空分子筛材料, 该材料在保持微孔孔道良好水热稳定性和大量活性中心的同时, 还通过介孔的引入进一步促进反应物及产物的扩散, 使间三甲苯苄基化反应的转化率提高了3.8倍. 通过在等级孔微孔-介孔ZSM-5中空材料上负载Fe, 开发出了具有双功能的等级孔微孔-介孔Fe₂O₃/ZSM-5中空催化剂, 该催化剂在苯的苄基化反应中表现出优异的催化性能, 当Fe负载量(质量分数)为6.67%, 反应温度为75 ℃, 反应时间为15 min时, 转化率高达98.3%, 选择性为81.6%, 最终收率达到80.2%.