正己烷在Zn/HZSM-5上芳构化反应机理的探讨

比较了正己烷在HZSM-5、Al₂O₃和ZnO/Al₂O₃催化剂上的反应性能，探讨了锌含量和水热处理对Zn/HZSM-5芳构化性能的影响。发现B酸是芳构化反应不可缺少的活性中心，Zn-L因其氢解作用促进烃类的活化和脱氢，Al-L酸只是对正己烷有较弱的活化作用。提出了正己烷在Zn/HZSM-5上的芳构化反应机理。     

Prolonging catalyst lifetime in supercritical isomerization of 1-hexene over a platinum/alumina catalyst

A series of experiments were carried out for the isomerization of 1-hexene in the temperature range and pressure range 10-100 bar, representing operating points both above and below the critical point of 1-hexene. At constant temperature of , increasing the pressure from 10 to 100 bar led to a substantial conversion increase up to a maximum of 78%. At each pressure, loss of conversion of 1-hexene was observed over the course of 8 h reaction time, which was attributed to the formation of oligomers and eventually coke upon the catalyst surface. Loss of conversion occurred initially more rapidly at the intermediate pressures of 40 and 70 bar, compared with at 10 and 100 bar, where a sustained but gradual decrease of conversion occurred. With increasing temperature in the range , conversion was highest at the condition , 40 bar, which is closest to the critical point of 1-hexene. Higher concentrations of oligomers, which act as coke precursors, were detected with increasing temperature and pressure of the reaction. The mass fraction of coke deposited upon the catalysts was dependent upon operating conditions and was within the range 0.63-1.36%, whilst the metal dispersion reduced from 26.8% for the fresh catalyst to 2.82-4.61% for the range of coked samples. A detailed examination of the void space structural changes, occurring after coking under both sub-and super-critical conditions, has been made. In particular, the void space structures were characterised in terms of external accessibility using percolation theory. The catalysts which were operated at reaction conditions where rapid initial deactivation occurred displayed a lower apparent connectivity in comparison with catalysts operated at conditions favouring a gradual sustained deactivation. It has also been found that, under certain conditions, the apparent connectivity of the remaining pore network can, unexpectedly, appear to increase following coking. This has been attributed to the initial loss of the most inaccessible pores within the network.     

锌和磷含量对Zn-P/HZSM-5催化剂芳构化性能的影响

在反应温度430 ℃、压力0.1 MPa、液时空速1 h－1条件下,进行催化裂化汽油中间馏分（75～120 ℃）的芳构化反应,考察了锌和磷含量对催化剂性能的影响。实验结果表明,当锌和磷质量分数分别为2％和4％时,改性催化剂芳构化活性及芳烃选择性最佳,其烯烃转化率、芳烃含量和芳烃收率分别为94.53 ％、68.8 ％ 和51.74 ％。     

Zn对HZSM-5分子筛催化剂物化及甲醇芳构化反应性能的影响

分别以浸渍法和水热合成法向HZSM-5分子筛中引入Zn助剂对其进行改性。采用XRD、SEM、NH₃-TPD和XPS等技术对改性前后的分子筛进行了表征。结果表明,采用两种不同方式引入Zn助剂对分子筛的晶体结构、孔径及形貌影响均很小,但能明显改变分子筛的表面酸性。两种方式引入Zn均使分子筛表面的强酸酸量明显降低,而弱酸酸量有所增大。最后,考察了Zn的引入对HZSM-5催化剂甲醇芳构化催化性能的影响。结果表明,两种方法引入Zn虽然均能提高甲醇芳构化反应的初始活性和芳烃选择性,但容易导致分子筛表面积炭而使催化剂快速失活。     

甲烷芳构化反应催化剂Ｍｏ-Ｍ／ＨＺＳＭ-５表面性质的研究

对甲烷芳构化催化剂Ｍｏ-Ｍ／ＨＺＳＭ-５进行了异丙醇分解、ＮＨ３-ＴＰＤ-ＭＳ、积炭量测定表征,其结果均与芳构化性能有关。芳烃收率高,稳定性好,积炭量较少,而且具有相当量的酸量和一定量强酸量及较强的脱氢中心。     

Zn 助剂对WC/HZSM-5催化正己烷芳构化性能影响

以WC/HZSM-5为前驱体制备了一系列不同Zn含量的Zn-WC/HZSM-5催化剂,采用X射线衍射、扫描电子显微镜、N₂物理吸附、傅里叶变换红外光谱和热重分析等手段对Zn-WC/HZSM-5的晶相、形貌、比表面积、酸性质、积炭量等进行了表征,并研究了正己烷芳构化的催化性能,探究了助剂Zn与WC在反应过程中的作用。结果表明,Zn的引入可以提高催化剂的芳烃选择性和芳烃收率。当Zn负载量为1.5%(质量分数)时,所制备的Zn-WC/HZSM-5催化剂芳构化活性最佳,芳烃收率达到36.18%。Zn的引入不仅改变了WC/HZSM-5表面的酸性分布,而且可以减少WC/HZSM-5催化剂的积炭量。     

Cracking of n-dodecane during supercritical state on HZSM-5 membranes

In the new generation of aircraft, jet fuel will serve as both an energy source and a heat sink for cooling through endothermic fuel reactions. Catalytic cracking of hydrocarbon fuel has proved to be potential for endothermic reaction. For this application, we have prepared ZSM-5 membranes as catalyst on the surface of stainless steel by secondary growth method. An optimized activation procedure of ZSM-5 membrane for catalytic cracking reaction is established by combining the results of catalytic reaction with thermal analysis (TGA and DSC). Taking n-dodecane as a model compound, the influence of silica alumina ratio (SAR = nSiO₂/Al₂O₃) of initial gel on the activity of hydrocarbon cracking reaction were studied. The results also demonstrate that the conversion of catalytic cracking reaction is much higher than that of pyrolysis during supercritical state. In addition, hydrogen molar ratio in gas production decreases with increasing the reaction temperature. Besides that, the optimum temperature for coke removal and the reduction of zeolite catalysts is between 550 °C and 600 °C.     

Influence of the different dechlorination time on catalytic performances of PtSnNa/ZSM-5 catalyst for propane dehydrogenation

Catalytic dehydrogenation of propane has recently received considerable attention because of the increasing demand for propene. Among several catalysts, PtSnNa/ZSM-5 catalyst is one of the most suitable ones. In this study, PtSnNa/ZSM-5 catalysts with different content of chlorine were prepared by changing the time of catalyst dechlorination. The obtained catalysts were characterized by X-ray fluorescence (XRF), XRD, nitrogen adsorption, ²⁷Al MAS NMR, NH₃-TPD, H₂ chemisorption and TPR. It was found that with the increase of treatment time, more framework aluminum atoms were removed from tetrahedral positions, leading to the loss of Sn species and the decrease of catalyst acidity. Meantime, the porous properties and the interactions between Pt and Sn of the catalysts changed remarkably, which was disadvantageous to the reaction. Compared with the dechlorinated catalysts, the fresh sample with suitable content of chlorine exhibited the best reaction activity and stability. The average yield of propene was about 30.4% over 45 h for the reaction of propane dehydrogenation at 590 °C. Finally, a model was proposed for the influence of dechlorinated treatment on catalytic properties of PtSnNa/ZSM-5 catalyst for propane dehydrogenation.     

Methane dehydrogenation and aromatization over 4 wt% Mn/HZSM-5 in the absence of an oxidant

Methane dehydrogenation and aromatization over 4 wt% Mn/HZSM-5 in the absence of an oxidant (GHSV = 1600 mL h⁻¹ g⁻¹) was investigated. Mn/HZSM-5 was prepared by impregnation of HZSM-5 with manganese acetate tetrahydrate solution; Mn₃O₄ formed was the precursor of active phase for methane activation. The induction period over Mn/HZSM-5 catalyst before aromatic products appear was long at 700 °C. This period shortened with a rise of the reaction temperature to 800 °C. XPS and TPO results showed that the partly carburized or carburized Mn species formed are probably responsible for methane activation.     

硅烷化和有机弱碱改性Mo/HZSM-5对甲烷无氧芳构化催化性能的影响

催化剂的形态及晶粒的组装对其催化性能有重要影响,采用硅烷化处理对Mo基催化剂表面酸性进行毒化制备了核壳型（Mo基催化剂@Silicalite-1）复合材料;采用四丙基氢氧化铵或正丁胺有机弱碱对Mo/HZSM-5进行刻蚀,然后经过脱硅再结晶分别制备了表面富硅型中空结构Mo/HZSM-5微球和表面富硅、核内含有多级孔道的Mo/HZSM-5微球。采用XRD、TEM、N₂等温吸脱附和NH₃-TPD对催化剂结构进行表征,并考察了三种不同后处理方法对Mo基催化剂在甲烷无氧芳构化反应中催化性能的影响。硅烷化和有机碱处理均能够调变Mo/HZSM-5催化剂的表面酸性,而经有机碱处理以后,催化剂结晶度、介孔比表面积和孔容均具有不同程度的增加,三种不同后处理方法均能改善Mo/HZSM-5催化剂的反应稳定性,对产物的分布也产生了显著影响。     

Thermal and spectroscopic properties of zinc perchlorate/poly(vinylpyrrolidone) blends and a comparison with related hydrogen bonding systems

We have investigated the thermal and spectroscopic properties of blends of poly(vinylpyrrolidone) (PVP) with zinc perchlorate. Analyses by differential scanning calorimetry indicates that blending with zinc perchlorate increases the values of T_g of PVP. We calculated the interaction strength of the zinc salt/PVP blends based on an extended configuration entropy model. The presence of ion-dipole interactions between PVP and the zinc salt was confirmed based on Fourier transform infrared (FTIR) and solid-state NMR spectroscopies, which suggest that the zinc cations coordinate with the carbonyl groups of PVP. The single value of measured by solid-state NMR spectroscopy observed for all the zinc salt/PVP blends is smaller than that of pure PVP, which is a finding that indicates that the domain size of this blend system decreases upon increasing the zinc salt content. Based on FTIR and solid-state NMR spectroscopic analyses, we conclude that the ion-dipole interactions in the zinc salt/PVP blend are stronger than the hydrogen bonds in systems such as the poly(vinylphenol) (PVPh)/PVP blend and the PVPh-co-PVP copolymer.     

Effect of addition of Zn on the catalytic activity of a Co/HZSM-5 catalyst for the SCR of NOx with CH4

The selective catalytic reduction (SCR) of NO_x by methane in the presence of excess oxygen was studied on a Zn-Co/HZSM-5 catalyst. It was found that the addition of Zn could improve effectively the selectivity of methane towards NO_x reduction. When prepared by a coimpregnation method, the Zn-Co/HZSM-5 catalyst showed much higher catalytic activity than the two catalysts of a Zn/Co/HZSM-5 and Co/Zn/HZSM-5 prepared by the successive impregnation method. It is considered that there exists a cooperative effect among the Zn, Co and zeolite, which enhances the reduction of NO to NO₂ reaction and the activation of methane.     

Study on attrition of spherical-shaped Mo/HZSM-5 catalyst for methane dehydro-aromatization in a gas-solid fluidized bed

As a potential methane efficient conversion process,non-oxidative aromatization of methane in fluidized bed requires a catalyst with good attrition resistance,especially in the states of high temperature,long-time rapid movement and chemical reaction.Existing evaluation methods for attrition resistance,such as ASTM D5757 and Jet Cup test,are targeted for fresh catalysts at ambient temperature,which cannot well reflect the real process.In this study,spherical-shaped Mo/HZSM-5 catalyst prepared by dipping and spray drying was placed in a self-made apparatus for attrition testing,in which the catalyst attrition under differ-ent system temperatures,running time and process factors was investigated with percent mass loss (PML),particle size-mass distribution (PSMD) and scanning electron microscope (SEM).Carbon deposition on the catalyst before and after activation,aromatization and regeneration was analyzed by thermogravimetry(TG),and the attrited catalysts were evaluated for methane dehydro-aromatization (MDA).The results show that the surface abrasion and body breakage of catalyst particles occur continuously,with the increase of system temperature and running time,and make the PML rise gradually.The process factors of activation,aromatization and regeneration can cause the catalyst attrition and carbon deposits,which broaden the PSMD in varying degrees,and the carbon-substances on catalysts greatly improve their attrition resistance at high temperature.Catalyst attrition has a certain influence on its catalytic performance,and the main reasons point to particle breakage and fine powder escape.     

无黏结剂Zn/ZSM-11催化剂的异丁烷和二甲醚芳构化催化性能

采用常规浸渍法制备系列Zn/ZSM-11催化剂,对其进行N2吸附-脱附和Py-IR表征,并用于催化异丁烷和二甲醚芳构化反应。结果表明,氧化铝成型Zn/ZSM-11催化剂(Cat-A)的BET比表面积和孔体积最大,无黏结剂Zn/ZSM-11分子筛催化剂(Cat-C)的最小;氧化硅成型Zn/ZSM-11催化剂(Cat-B)的微孔体积与Cat-C的差别不明显。催化剂的B酸量及B酸/L酸顺序为:Cat-ACat-BCat-C。与Cat-A和Cat-B相比,Cat-C上异丁烷转化率和产物中芳烃收率最高。     

Influence of operating conditions,Si/Al ratio and doping of zinc on Pt-Sn/ZSM-5 catalyst for propane dehydrogenation to propene

The direct catalytic dehydrogenation of propane to propene is an important route to enhance propene production. In the present experimentation the focus was to investigate the influence of incipient operating conditions, Si/Al ratio of zeolite support and effect of zinc doping on Pt-Sn/ZSM-5 catalyst performance. The catalysts were extensively investigated by reaction tests in a continuous plug-flow quartz micro-reactor. The experimental data shows that the manipulation of operating parameters significantly improves the reaction performance, while huge dynamicity is observed in product distribution. Reaction temperature, 600 °C is found to be most suitable, while increasing the weight hourly space velocity (WHSV), propene selectivity improves at the expense of lower conversion. The OPE was drawn to observe overall reaction network. It was found that the acidity of zeolitic support plays a more important role in achieving desired product selectivity than additional metallic content. Accordingly, the Si/Al ratio of the ZSM-5 zeolite the pro- pene selectivity was enhanced, leading to remarkable improvement in the total olefins selectivity which was remarkably improved owing to a suppression of secondary reactions. At Si/Al ratio 300, the selectivity of propene and total olefins becomes stable at 73% and 90% respectively. The doping of Zn on Pt-Sn/ZSM-5 improves only propene selectivity, but is severely affected by quick deactivation.     

Hybrid catalysts containing zeolite ZSM-5 and supported gallium oxide in the aromatization of n-butane

It is shown that in the aromatization of n-butane, hybrid catalysts containing irreducible oxides (silica and alumina) as co-catalysts provide aromatic yields which are almost twice that obtained with “pure” zeolite ZSM-5 zeolite. The interpretation of these results is based on the hydrogen back spillover concept. The addition of Ga₂O₃ to these co-catalysts enhances further the aromatizing performance of the hybrid catalysts. It is believed that such an additional improvement is due to the gallium species located in the interface between the two types of particles, and the Ga containing regions of the zeolite crystallites near the pore openings. This contamination results from the transfer of some partially reduced gallium oxide from the co-catalyst surface to the zeolite pores. In such a case, it is probable that the reaction is governed by the conventional bifunctional catalysis mechanism. These gallium oxide sites appear more active than the normal ones because of their location near the zeolite pore openings which enables them to react with both inward-and outward-diffusing molecules.     

Mg/HZSM-5分子筛催化甲醇与1-丁烯偶合制丙烯

采用水热法合成纳米和微米尺寸的HZSM-5分子筛,并用浸渍法负载Mg对纳米HZSM-5分子筛进行改性,通过XRD、SEM、N_2等温吸附-脱附、NH_3-TPD和TGA对分子筛进行表征,并将其用于甲醇与1-丁烯偶合制丙烯反应,考察分子筛晶粒尺寸、Mg负载量、反应温度、空时和甲醇与1-丁烯物质的量比对催化剂反应性能的影响。结果表明,纳米HZSM-5分子筛具有比表面积大、孔道短和孔口多等特点,表现出较好的活性和稳定性及较强的容碳能力。利用Mg对纳米HZSM-5进行改性,提高了HZSM-5分子筛上原料的转化率和丙烯收率,在反应温度550℃、反应压力0.1 MPa、空时1.6 gcat·(h·mol_(CH_2))~(-1)和甲醇与1-丁烯物质的量比为3的条件下,1%Mg/HZSM-5分子筛催化剂上的丙烯收率最高,达41.8%,比未改性的纳米HZSM-5分子筛催化剂提高9.7个百分点。     

Effect of CsxH3?xPW12O40 addition on the catalytic performance of ZnFe2O4 in the oxidative dehydrogenation of n-butene to 1,3-butadiene

Oxidative dehydrogenation of n-butene to 1,3-butadiene over ZnFe₂O₄ catalyst mixed with Cs _x H_3−x PW₁₂O₄₀ heteropolyacid (HPA) was performed in a continuous flow fixed-bed reactor. The effect of Cs _x H_3−x PW₁₂O₄₀ addition on the catalytic performance of ZnFe₂O₄ was investigated. Cs _x H_3−x PW₁₂O₄₀ itself showed very low catalytic performance in the oxidative dehydrogenation of n-butene. However, addition of small amount of Cs _x H_3−x PW₁₂O₄₀ into ZnFe₂O₄ enhanced the catalytic performance of ZnFe₂O₄ catalyst. The catalytic performance of ZnFe₂O₄-Cs _x H_3−x PW₁₂O₄₀ mixed catalysts was closely related to the surface acidity of Cs _x H_3−x PW₁₂O₄₀. Among the catalysts tested, ZnFe₂O₄-Cs_2.5H_0.5 PW₁₂O₄₀ mixed catalyst showed the best catalytic performance. Strong acid strength and large surface acidity of Cs_2.5H_0.5PW₁₂O₄₀ was responsible for high catalytic performance of ZnFe₂O₄-Cs_2.5H_0.5PW₁₂O₄₀ mixed catalyst. Thus, Cs_2.5H_0.5PW₁₂O₄₀ could be utilized as an efficient promoter and diluent in formulating ZnFe₂O₄ catalyst for the oxidative dehydrogenation of n-butene.     

Modulating acid site spatial location of Zn/ZSM-5 catalyst to boost the stable aromatization of hexane

Engineering acid site spatial location of zeolite catalyst harbors tremendous potential to boost catalytic performance but still remains a grand challenge for aromatization reaction. Herein, we successfully manipulate acid site spatial location inside the ZSM-5 channels to promote the hexane aromatization via the simple SiO₂ coating treatment. Multi-techniques demonstrated that the medium strong L acid in the channel originated from the Si(Al) O Zn structure is mainly retained in the Zn/ZSM-5-Si catalyst by covering the acid sites outside the channel. Surprisingly, there is a good linear relationship between BTEX yield and this medium strong L acid content. Based on the reaction kinetics, in situ FT-IR and theoretical calculations, it is found that the L acid with confinement effect served as the main active site could prominently enhance the cyclization of propene intermediate and the dehydrogenation of cycloalkane due to the strong affinity between the C/H and ZnOx, and control the desorption of BTEX (mainly benzene, toluene, ethylbenzene, and p-xylene) by weakening the binding of hydrogen proton to π electrons. Compared with the ordinary Zn/ZSM-5 catalyst, the yield of BTEX is increased by nearly 10%, and the Zn/ZSM-5-Si catalyst exhibits excellent anti coking deactivation ability. This strategy together with mechanistic results may pave the rational design of efficient Zn/ZSM-5 catalysts for aromatization reaction.     

Study of the Effects of External and Internal Diffusion on the Propane Dehydrogenation Reaction over Pt‐Sn/Al2O3 Catalyst

In the study of a reaction on a heterogeneous catalyst, external and internal mass diffusion play an important role since they can have an inherent affect on the kinetics of the reaction. Therefore, in the study of intrinsic rates of reaction, the effects of external and internal mass diffusion must be eliminated or considered prior to proper kinetic studies. In this study, the effects of external and internal mass diffusion on the propane dehydrogenation reaction over a Pt/Sn catalyst were investigated. Some experiments were performed in a laboratory scale setup and the required data was gathered. The rate of reaction was considered to be first order based on propane. External diffusion was studied using Mears' criterion and internal diffusion was investigated by the Thiele Module and the Internal Effectiveness Factor, based on experimental data.