Properties and Characterization of Modified HZSM-5 Zeolites

Physicochemical and catalytic properties of phosphorus and boron modified HZSM-5 zeolites treated with 100% steam at 673 K were investigated. The acidity and distribution of acidic sites were studied by infrared spectroscopy using pyridine as probe molecule and temperature programmed desorption (TPD) of ammonia. The structure of the samples was characterized by XRD, and the textural properties of the catalysts were determined by nitrogen isothermal adsorption-desorption measurements and scanning electron microscopy (SEM). The XRD results show that the modified samples have no novel crystalline phase, indicating a high dispersion of phosphorus and boron species. After treatment, the microporous volume and surface area of the samples markedly decrease, implying the blockage of the channel. The nitrogen adsorption-desorption measurements suggest that the isothermal type of all samples is a combination of isothermal type I and IV, and all hysteresis loops resemble the H4-type in the IUPAC classification. The total acidity of the modified samples, determined by pyridine adsorption IR and TPD of ammonia, decreases in contrast to that of the parent HZSM-5. The conversion of n-heptane over P and B steam-modified HZSM-5 is higher than that of P and B-modified HZSM-5 zeolites but lower than that of the parent HZSM-5.

Effects of Light Rare Earth on Acidity and Catalytic Performance of HZSM-5 Zeolite for Catalytic Cracking of Butane to Light Olefins

The effects of rare earth（RE）on the structure,acidity,and catalytic performance of HZSM-5 zeolite were investigated.A series of RE/HZSM-5 catalysts,containing 7.54% RE（RE=La,Ce,Pr,Nd,Sm,Eu or Gd）,were prepared by the impregnation of the ZSM-5 type zeolites（Si/Al=64：1）with the corresponding RE nitrate aqueous solutions.The catalysts were characterized by means of FT-IR,UV-Vis,NH3-TPD,and IR spectroscopy of adsorbed pyridine.The catalytic performances of the RE/HZSM-5 for the catalytic cracking of mixed butane to light olefins were also measured with a fixed bed microreactor.The results revealed that the addition of light rare earth metal on the HZSM-5 catalyst greatly enhanced the selectivity to olefins,especially to propylene,thus increasing the total yield of olefins in the catalytic cracking of butane.Among the RE-modified HZSM-5 samples,Ce/HZSM-5 gave the highest yield of total olefins,and Nd/HZSM-5 gave the highest yield of propene at a reaction temperature of 600℃.The presence of rare earth metal on the HZSM-5 sample,not only modified the acidic properties of HZSM-5 including the amount of acid sites and acid type,that is,the ratio of L/B（Lewis acid/Brnsted acid）,but also altered the basic properties of it,which in turn promoted the catalytic performance of HZSM-5 for the catalytic cracking of butane.

Effects of Calcination Temperature on the Acidity and Catalytic Performances of HZSM-5 Zeolite Catalysts for the Catalytic Cracking of n-Butane

The acidic modulations of a series of HZSM-5 catalysts were successfully made by calcination at different treatment temperatures, i.e. 500, 600, 650, 700 and 800 ℃, respectively. The results indicated that the total acid amounts, their density and the amount of B-type acid of HZSM-5 catalysts rapidly decreased, while the amounts of L-type acid had almost no change and thus the ratio of L/B was obviously enhanced with the increase of calcination temperature （excluding 800 ℃）. The catalytic performances of modified HZSM-5 catalysts for the cracking of n-butane were also investigated. The main properties of these catalysts were characterized by means of XRD, N2 adsorption at low temperature, NH3-TPD, FTIR of pyridine adsorption and BET surface area measurements. The results showed that HZSM-5 zeolite pretreated at 800 ℃ had very low catalytic activity for n-butane cracking. In the calcination temperature range of 500-700 ℃, the total selectivity to olefins, propylene and butene were increased with the increase of calcination temperature, while, the selectivity for arene decreased with the calcination temperature. The HZSM-5 zeolite calcined at 700 ℃ produced light olefins with high yield, at the reaction temperature of 650 ℃ the yields of total olefins and ethylene were 52.8% and 29.4%, respectively. Besides, the more important role is that high calcination temperature treatment improved the duration stability of HZSM-5 zeolites. The effect of calcination temperature on the physico-chemical properties and catalytic performance of HZSM-5 for cracking of n-butane was explored. It was found that the calcination temperature had large effects on the surface area, crystallinity and acid properties of HZSM-5 catalyst, which further affected the catalytic performance for n-butane cracking.

Influence of the post-treatment of HZSM-5 zeolite on catalytic performance for alkylation of benzene with methanol

The porous material HZSM-5 zeolite with micro-mesopore hierarchical porosity was prepared by post-treatment （combined alkali treatment and acid leaching） of parent zeolite and its catalytic performance for benzene alkylation with methanol was investigated. The effect of post-treatment on the textural properties was characterized by various techniques （including ICP-AES, XRD, nitrogen sorption isotherms, SEM, NH3-TPD, Py-IR and TG）. The results indicated that the post-treatment could modify the structural and acidic properties of HZSM-5 zeolite. In this procedure, not only additional mesopores were created by selective extraction of silicon but also the acidity was tuned. Consequently, the modified HZSM-5 zeolite showed larger external surface area with less acid sites as compared to the parent zeolite. It was found out that the modified zeolite exhibited a higher benzene conversion and xylene selectivity for alkylation of benzene with methanol as well as excellent life span of the catalyst than conventional ones. This can be explained by the facts that the presence of additional mesopores improved the diffusion property in the reactions. Furthermore, the modified zeolite showed an appropriate Bronsted acidity for effective suppression of the side reaction of methanol to olefins, thus reduced the accumulation of coke on the HZSM-5 zeolite, which was favorable for the catalyst stability. In comparison with the parent HZSM-5 zeolite, the modified zeolite by alkali treatment and acid leaching showed better performance for the benzene alkylation with methanol.

Influence of the Alkali Treatment of HZSM-5 Zeolite on Catalytic Performance of PtSn-Based Catalyst for Propane Dehydrogenation

The porous material ATZ with micro-mesopore hierarchical porosity was prepared by alkali treatment of parent HZSM-5 zeolite and applied for propane dehydrogenation. The zeolite samples were characterized by XRD, N2- physisorption, and NH3-TPD analysis. The results showed that the alkali treatment can modify the physicochemical prop- erties of HZSM-5 zeolite. In this case, the porous material ATZ showed larger extemal surface area with less acid sites as compared to the HZSM-5 zeolite. It was found out that the alkali treatment of HZSM-5 zeolite could promote the catalytic performance of PtSn/ATZ catalyst. The possible reason was ascribed to the low acidity of ATZ. Furthermore, the presence of mesopores could reduce the carbon deposits on the metallic surface, which was also favorable for the dehydrogenation reaction.

Effects of Operating Conditions on the Catalytic Performance of HZSM-5 Zeolites in n-Pentane Cracking

In this work,n-pentane catalytic cracking over HZSM-5 zeolites was studied at 650°C under atmosphere pressure.A particular attention was paid to the measurement of n-pentane conversion,light olefins production,product distribution,coke deposit,etc.Several indexes were defined to evaluate the effects of operating conditions on the catalytic performance of HZSM-5 zeolites.It was found that decreasing the weight hourly space velocity,increasing the reactant partial pressure,and increasing the carrier gas flow rate could inhibit C-H bond breaking and enhance the C-C bond breaking and hydride transfer reactions,leading to reduced alkenes selectivity,which suppressed the formation of external coke and alleviated the deactivation of HZSM-5 zeolites.It was deduced that the catalytic stability of HZSM-5 zeolites was improved at the cost of alkenes selectivity.Compared with decreasing the weight hourly space velocity and increasing the reactant partial pressure,increasing the carrier gas flow rate could enhance the diffusion process and protect alkenes from being consumed in coke formation in order to improve the catalytic stability of HZSM-5 zeolites with less reduction of alkenes selectivity.

Catalytic cracking of 1-butene to propylene by Ag modified HZSM-5

Silver modified HZSM-5 （AgHZ） zeolite catalysts were prepared by ion exchange method and their catalytic properties in the l-butene cracking reaction were measured. The catalysts were characterized by infrared spec- troscopy with pyridine adsorption （Py-IR）, N2 adsorption and X-ray diffraction （XRD）. The effects of Ag loading and steaming treatment on catalytic performances were studied. It is found that the activity ofHT_SM-5 （HZ） catalyst significantly decreases with the steaming time, whereas AgHZ catalysts show stable activity in the steaming time of 24-48 h and their activities increase with the Ag loading. When the steaming time is 24-48 h, the yield of propylene over HZ catalyst significantly decreases, whereas it is stable over AgHZ catalysts. The AgHZ catalysts with Ag loadings of 0.28%-0.43% （by mass） show similar propylene yields （-30%）, which are higher than that over the AgHZ catalyst with a Ag loading of 0.55% （by mass）. These results indicate that the steam-treated AgHZ catalysts with optimum Ag loadings have higher yield of propylene and are more stable than the steam- treated HZ catalyst. The regeneration stability measurement in butene cracking also shows that the AgHZ catalyst steam-treated under a suitable condition has better stability than the HZ catalyst.

Catalytic activity of phosphorus and steam modified HZSM-5 and the theoretical selection of phosphorus grafting model

The modification of HZSM-5 zeolite with phosphorus and steam has been studied. Results show that 1% phosphorus and steam modified HZSM-5 has the highest catalytic activity for n-heptane. Physicochemical and catalytic properties of 1% phosphorus and steam modified HZSM-5 zeolites have been investigated. The X-ray diffraction （XRD） results exhibit that there is considerable variation in the relative intensity of the individual diffraction peaks. The acidity of the samples decreases with an increase in the steaming temperature, which is determined by the IR of adsorbed pyridine and temperature programmed desorption （TPD） of ammonia. The oxidation state of phosphorus shown by XPS is ＋5, and a model for surface structure modification is proposed. The nitrogen adsorption isotherm for all samples is a combination of type I and type IV, all hysteresis loops resemble the H4-type. The density functional and cluster model methods have been invoked to select the phosphorus grafting model, and it was found that the phosphorus grafting model were more probable in the form of the terminal oxygen coordinating with aluminum.

Investigation of the Surface State of Zeolite HZSM-5 Pretreated with Toluene by Using Fast Atom Bombardment Mass Spectrometry (FABMS)

Toluene pretreatment caused many activated toluene species existing on the surface of zeolite HZSM-5, by which the activity of sample was increased. Moreover, variation in the surface Si+/Al+ ratio of HZSM-5 was sensitively detected by FABMS.

Ce改性HZSM-5分子筛催化甲醇与丁烯耦合转化制丙烯性能研究

为了进一步提高HZSM-5分子筛在甲醇与丁烯耦合转化制丙烯反应中的催化性能,采用浸渍法对HZSM-5分子筛进行Ce改性,得到了一系列具有不同Ce负载量的x Ce/HZSM-5催化剂。考察了Ce负载量和反应条件(甲醇与丁烯物质的量之比、反应温度和空时)对催化性能的影响,并结合催化剂表征结果,分析了Ce改性对催化性能和物化性质的影响,探讨了x Ce/HZSM-5催化剂的构效关系。结果表明,在温度550℃、压力0.1 MPa、甲醇与丁烯物质的量之比0.8、空时2.3(g cat·h)mol CH_(2)的最佳反应条件下,Ce负载量(w)为2.5%的2.5Ce HZSM-5催化剂具有最高的丙烯收率,为41.9%。Ce与HZSM-5分子筛上羟基官能团(OH)发生相互作用,降低了B酸酸量,同时生成新的L酸中心Ce(OH)^(2+),调变了催化剂表面酸中心密度和酸类型分布,提高了丙烯选择性和收率。

HZSM-5催化生物质与废塑料协同热解制取苯系物研究进展

苯系物是一类重要的化工原料和燃料添加剂,具有广泛的工业应用和经济价值,主要来源于化石燃料。生物质与废塑料协同热解可以有效制取苯系物且具有废物利用和环境保护等优点。本文综述了氢交换索康美孚沸石-5(HZSM-5)催化生物质与废塑料协同热解制取苯系物研究进展,首先讨论了生物质与废塑料在无催化剂条件下直接制取苯系物的特点;然后重点论述了基于HZSM-5催化剂、金属改性HZSM-5、碱/碱土金属耦合HZSM-5以及不同催化方式制取苯系物的途径;通过金属改性、碱/碱土金属耦合以及催化方式可提高苯系物选择性和产率。本文为生物质和废塑料的高效催化转化提供一定的参考。

Study of the Conversion of Postconsumer Polystyrene on CeO2/HZSM-5 Type Materials

The catalytic conversion of polystyrene (PS) was studied in the presence of the materials type HZSM-5, CeO2, 10% CeO2/HZSM-5 and 20% CeO2/HZSM-5, which were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and nitrogen adsorption at 77K. The catalytic tests were performed via thermogravimetric analysis (TG) at heating rates of 5, 10 and 20˚C min−1 in a temperature range from 30˚C to 900˚C. For the tests, a ratio of 30% by mass of each catalytic material mixed with PS was used and the activation energy of the degradation process was determined by the Vyazovkin method. The obtained results showed that the addition of the catalyst to the PS in general reduced its degradation temperature. The 10% CeO2/HZSM-5 catalyst showed greater efficiency, as it resulted in lower activation energy for PS degradation. Thus, the combination of CeO2 with HZSM-5 resulted in materials with potential for application in the catalytic degradation of polystyrene and the results indicate that the production of a composite material can be a good strategy to generate an increase in catalytic activity and a decrease in energy process activation.

改性HZSM-5催化剂用于MTP反应的研究

考察了不同硅铝比的HZSM-5催化剂和磷、镁或铈改性的HZSM-5催化剂在甲醇制丙烯(MTP)反应中的催化性能。研究了在Mg-HZSM-5和Ce-HZSM-5的催化作用下,反应温度、液时空速、进料组成对MTP反应的影响。确定较佳的反应条件为:温度为380℃～400℃,WHSV在5 h-1左右,纯甲醇进料。在此条件下,Ce-HZSM-5的丙烯产率达55%。

改性HZSM-5分子筛催化醛氨缩合反应

采用离子交换方法制备了不同金属离子改性HZSM-5分子筛的M/HZSM-5(M分别为Co,Pb,Cd和Zn),利用原位红外和氨气-程序升温脱附法(NH_3-TPD)研究了催化剂的酸性,并考察了改性前后催化剂在醛氨缩合反应中的催化活性。结果表明,改性后得到的Co/HZSM-5,Pb/HZSM-5和Cd/HZSM-5的催化活性提高,zn/HZSM-5催化活性下降。HZSM-5分子筛通过金属离子改性后,HZSM-5的骨架结构没有被破坏,金属离子均匀地分布在分子筛表面。分子筛的酸性强弱、酸量和酸中心类型的分布均发生了一定的变化,在金属离子含量基本相同的情况下,不同的金属离子对分子筛表面酸性的调变能力不同。

钾-钙双金属改性对HZSM-5分子筛催化甲醇制丙烯的影响

针对甲醇制丙烯反应体系,研究了不同金属、双金属改性的HZSM-5的催化性能。结果表明,钾改性提高了催化剂的稳定性和催化性能,当钾改性液的质量分数为2%时,改性效果最好,在此基础上,以2%K-HZSM-5作为不同钙负载的改性对象。结果表明,钾钙共同改性,具有较好的协同改性效果,大大提高了丙烯的选择性,有效的降低了乙烯和副产物的产率。

咪唑改性HZSM-5分子筛的制备及催化CO_2加氢合成二甲醚

以咪唑为添加剂,四丙基氢氧化铵为模板剂,采用水热法制备了咪唑改性HZSM-5型分子筛,用XRD、SEM、EDS、BET、TG和NH3-TPD对合成的分子筛进行了表征。结果表明,当在制备分子筛的前驱液中加入少量咪唑时,制备的HZSM-5型分子筛粒径明显减小且分布更加均匀,酸性增强,并具有更好的抗高温性能。采用浸渍法制备了CuO-ZnO-Al2O3/咪唑改性HZSM-5双功能催化剂,探讨了其催化二氧化碳加氢制备二甲醚的活性,在反应温度270℃、反应压力3.0 MPa、V(CO2)∶V(H2)=1∶3、n(CuO)∶n(ZnO)=2∶1和m(CuO-ZnO2-Al2O3)∶m(咪唑改性HZSM-5)=2∶1的条件下,CO2的单程转化率和二甲醚的选择性分别达到了42.3%和33.1%。

改性HZSM-5分子筛的表征及用其催化合成环十五内酯

采用浸渍法制备出了不同金属离子(Fe、Mo、Mo-Fe)改性的HZSM-5分子筛,用XRD,FTIR,NH3-TPD等检测方法考察了改性HZSM-5分子筛上Fe、Mo和Mo-Fe的体相状态和酸性;并将改性HZSM-5分子筛用于催化15-羟基十五烷酸甲酯合成环十五内酯。结果表明,Mo-Fe/HZSM-5分子筛的Mo-Fe引入到HZSM-5分子筛骨架中,分子筛的酸量和酸强度增加,15-羟基十五烷酸甲酯的最大转化率为58.85%,环十五内酯选择性为16.48%。

Au、Pt改性HZSM-5纳米沸石催化剂上的甲醇羰基化反应性能研究

采用固定床-微反装置,在临氢和非临氢状态下,评价了金、铂改性的纳米HZSM-5催化剂上甲醇的反应活性和羰基化选择性.结果表明:在300℃时,载体HZSM-5、0.3%Pt/HZSM-5、2.0%Pt/HZSM-5、3.0%Pt/HZSM-5催化剂甲醇临氢转化率分别为43.89%、95.05%、87.24%、62.49%;甲酸甲酯选择性分别为39.29%、80.07%、84.49%、64.37%;乙酸甲酯选择性分别为32.35%、22.79%、13.46%、11.29%.相比之下,在纳米HZSM-5载体上负载0.3%Au、2.0%Au和3.0%Au时,甲醇的临氢转化率分别为71.72%、82.90%和55.13%.甲酸甲酯选择性分别为60.97、81.85%和42.19%.乙酸甲酯选择性分别为20.48%、20.70%和19.16%.不难看出,随着金负载量的增加,甲醇转化率、乙酸甲酯选择性和甲酸甲酯选择性均有所增加.另外,在临氢和不临氢情况下,催化剂的性能有明显的区别.不临氢时,随着Au和Pt负载量的增加,甲醇转化率降低明显,产物甲酸甲酯选择性也是降低的,而乙酸甲酯的选择性有所增加.当引入氢时,甲酸甲酯的选择性随氢增加,并且乙酸甲酯的选择性显著降低.以上结果可能与催化剂的表面酸性、结构特征、晶体尺寸等密切相关.

Al改性HZSM-5分子筛催化甲醇制烯烃反应研究

研究了Al负载HZSM-5催化剂上甲醇制烯烃反应过程。考察了Al负载量、反应温度、空速、反应时间等因素对催化效果的影响。随着Al含量的增加,Al-HZSM-5催化剂的比表面积、孔体积逐渐减小,但骨架结构没有变化,乙烯和丙烯选择性明显优于改性前的HZSM-5。Al的最佳负载质量分数为6.0%,此时低碳烯烃的选择性有最大值为69.3%;380℃为最佳反应温度,空速最佳范围在786mL/（g.h）~996mL/（g.h）。随着反应时间增长,催化剂会逐渐积碳失活。

改性HZSM-5分子筛在乙醇脱水制生物乙烯工业小试中的应用研究

主要研究了改性HZSM-5分子筛在固定床反应器上催化乙醇脱水制生物乙烯的应用情况,考察了反应温度、质量空速、乙醇质量浓度以及催化剂粒度等工艺条件对改性HZSM-5分子筛催化性能的影响,同时考察了催化剂的单程寿命。结果显示,反应温度在200~300℃,乙醇质量空速为1.2 h^(-1)的条件下,采用470 g/L的乙醇溶液,催化剂粒度在10~20目之间,乙醇转化率为99%以上,乙烯选择性为98%以上,单程可连续运转1 104 h,表明改性HZSM-5在乙醇脱水工业小试中的催化性能优异。