Effect of Natural Zeolite on Pore Structure of Cemented Uranium Tailings Backfill

The use of some environmental functional minerals as backfill-modified materials may improve the leaching resistance of cemented uranium tailings backfill created from alkali-activated slag(CUTB),but these materials may participate in the hydration reaction of the cementitious materials,which could have a certain impact on the pore structure of the CUTB,thus affecting its mechanical properties and leaching resistance.In this paper,natural zeolite is selected as the backfill-modified material,and it is added to alkali-activated slag paste(AASP)and CUTB in cementitious material proportions of 4%,8%,12%,and 16%to prepare AASP mixtures and CUTB mixtures containing environmental functional minerals.After the addition of natural zeolite,the porosity of the CUTB generally increases,but when the content is 4%,the porosity decreases to 22.30%.The uniaxial compressive strength(UCS)of the CUTB generally decreases,but the decrease is the smallest when the content is 4%,and the UCS is 12.37 MPa.The addition of natural zeolite mainly reduces the number of fine pores in the CUTB,but the pores with relaxation times T_(2)of greater than 10 ms account for about 10%of the total pores,and there are a certain number of large pores in the CUTB.The main product of alkali-activated slag is calcium(alumino)silicate hydrate(C-(A)-S-H gel).When natural zeolite is added,the hydration products develop towards denser products with a high degree of polymerization and the formation of low polymerization products is reduced.This affects the internal fracture pores of the hydration products and the interface pores of the CUTB,has an irregular effect on the pore characteristics of the CUTB,and influences the UCS.

Effect of secondary pore distribution on adsorption diffusion performance of n-hexane on 5A zeolite pellets

Adsorption rates of n-hexane on the 5A zeolite at 100 to 300 ℃ and 0.01 to 10 kPa are determined by an intelligent gravimetric analyzer （IGA-100）, and the adsorption diffusion performance of n-hexane on 5A zeolite pellets with different secondary pore distributions is analyzed. The results indicate that 5A-1 and 5A-6 zeolites have similar micropore and mesopore size distribution, while the 5A-6 zeolite has a larger secondary pore volume when the pore diameter is between 0.1 and 1 μm and more secondary pores when the pore diameter is less than 0.01 μm. The effective diffusion coefficient of nhexane on the 5A-6 zeolite pellet is 10 ^-6 to 10 4 cm^2/s, about 2 to 5 times higher than that on the 5A-1 zeolite. The effective diffusion coefficient of n-hexane on the 5A-1 zeolite pellet improves from 5 × 10^-7 to 2 × 10 6cm^2/s when the temperature increases from 100 to 300 ~C. However, the effective diffusion coefficient of n-hexane on the 5A-6 zeolite remains almost unchanged at different temperatures. The molecular average free path of n-hexane decreases from 627.15-963.28 to 0.63-0, 96 Ixm with the adsorption pressure increasing from 0.01 to 10 kPa. Such a flee path is close to the secondary pore diameter, resulting in significant Knudsen diffusion in the secondary pores. Thus, the effective diffusion coefficient of n-hexane on the 5A zeolite pellets increases before 1 kPa and decreases after 1 kPa.

Ultrafine tuning of the pore size in zeolite A for efficient propyne removal from propylene

The removal of trace propyne(C_(3)H_(4))from propyne/propylene(C_(3)H_(4)/C_(3)H_(6))mixtures is a technical and challenging task during the production of polymer-grade propylene in view of their very similar size and physical properties.While some progress has been made,it is still very challenging to use some highly stable and commercially available porous materials via an energy-efficient adsorptive separation process.Herein,we report the ultrafine tuning of the pore apertures in type-A zeolites for the highly efficient removal of trace amounts of C_(3)H_(4)from C_(3)H_(4)/C_(3)H_(6)mixtures.The resulting ion-exchanged zeolite 5 A exhibits a large C_(3)H_(4)adsorption capacity(2.3 mmol g^(-1)under 10^(-4)MPa)and high C_(3)H_(4)/C_(3)H_(6)selectivity at room temperature,which were mainly attributed to the ultrafine-tuned pore size that selectively blocks C_(3)H_(6)molecules,while maintaining the stro ng adsorption of C_(3)H_(4)at low pressure region.High purity of C_(3)H_(6)(>99.9999%)can be directly obtained on this material under ambient conditions,as demonstrated by the experimental breakthrough curves obtained for both 1/99 and 0.1/99.9(V V)C_(3)H_(4)/C_(3)H_(6) mixtures.

Pore Structure and Catalytic Performance of Steam-Dealuminated ZSM-5/Y Composite Zeolites

For investigating the effect of dealumination on the pore structure and catalytic performance, ZSM-5/Y composite zeolites synthesized in situ from NaY gel were dealuminated by steaming at different temperatures. XRD (X-ray diffraction) characterization indicates that the relative crystallinity of the composite zeolites decreases with the increase in Si/Al ratio after steaming. N2 adsorption-desorption suggests that more mesopores are formed while the BET (Brunauer, Emmett and Teller) specific surface area and the micropore specific surface area decrease as the temperature of steaming rises. Daqing heavy oil was used as feedstock to test the catalytic cracking activity of ZSM-5/Y composite zeolites. The experimental results of the catalytic cracking performance reveal that the distribution of products differs due to the different conditions of hydrothermal treatment. Further hydrothermal treatment leads to an increase in the yield of light oil, and a decrease in the yield of gas products and coke.

Adsorptive desulfurization over hierarchical beta zeolite by alkaline treatment

Hierarchical beta zeolites with SiO2/Al2O3 molar ratios of 16 to 25 were obtained by alkaline treatment in NaOH solution. The effects of treatment temperature on crystallinity, textural properties and chemical composites were studied by XRD, N2 sorption, FT-IR and XRF techniques. The desulfurization performance of parent and alkaline-treated beta zeolites was investigated by static absorption in four model fuels, containing four sulfur compounds of different molecular sizes like thiophene （TP）, 3-methylthiophene （3-MT）, benzothiophene （BT） and dibenzothiophene （DBT）, respectively. The crystallinity was observed to be successfully maintained when the treatment temperature was below 50 ℃. Mesoporosity of beta zeolite was evidently developed with alkaline treatment. The formation of mesopore remarkably improved the desulfurization performance for TP, 3-MT, BT and DBT, especially for DBT with larger molecular diameter. Though the addition of toluene in the model fuels resulted in a significant drop of the desulfurization performance of mesoporous beta zeolite, the introduction of cerium ions to some extent mitigated the effect of toluene, which means that both the adsorbent’s porous structure and the adsorption mode are responsible for the desulfurization performance. The adsorbent of cerium ion-exchanged mesoporous beta showed about 80% recovery of desulfurization after the first regeneration.

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.

Synthesis, characteristics of hierarchical EU-1 zeolite for xylene isomerization probe reaction

Introduced a method of synthesizing hierarchical EU-1 zeolite with organosilanes as additive, and studied the influences of following different kinds of organosilanes on the synthesis of hierarchical EU-1 zeolite: γ-glycidoxy propyl trimethoxy silane(GPTMS), N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxyl silane(APAEDMS),and N-(β-aminoethyl)-γ-aminopropyl dimethoxyl(ethyoxyl) silane(TMPED). The hierarchical EU-1 samples were characterized by XRD, SEM, N_2 adsorption, FT-IR and NH_3-TPD to analyze the crystallinity, morphology, surface area, pore size distribution and acidity. The results showed that hierarchical EU-1 zeolites were successfully synthesized; organosilanes have great influence on crystal morphology of EU-1 zeolites; the exterior surface area of hierarchical EU-1 zeolite, which synthesized with organosilanes(APAEDMS) adding into synthesis system, increased by 62.1% and mesopore volume increased by 129.1% compared with conventional EU-1 zeolites, thus can reduce the diffusional restriction markedly in catalytic reaction. The catalytic performance of hierarchical EU-1zeolites were evaluated in m-xylene isomerization on fixed bed reactor. The catalytic data showed that the isomerization activity PX/X of the hierarchical EU-1 zeolites reached around 24.09% in theoretical thermodynamic equilibrium from 23.83%, and the selectivity of C_8 aromatic hydrocarbon increased from 75.16% to 84.87%. The conversion of p-xylene increased from 16.30% to 18.41%.

Effects of Added HY Zeolite on the Catalytic Behavior of Pt/OMC-HY in the Hydrogenation of Naphthalene

In this work,HY zeolites were embedded in the ordered mesoporous carbon(OMC)to prepare a support for a noble metal catalyst Pt/OMC-HY,and the hydrogenation of naphthalene to decalin was carried out over the catalyst.The results showed that Pt/OMC-HY-0.14(in which the mass ratio of HY to phenolic resin oligomer is 0.14)possessed much better catalyst performance than Pt/OMC,which was related to its proper surface acidity,hierarchical pore structure,metal dispersion,and the interaction between metal and support.Furthermore,Pt/OMC-HY-0.14 had better sulfur tolerance than Pt/OMC.In addition,the sulfur tolerance mechanism of Pt/OMC-HY-0.14 was studied,which revealed that the competitive adsorption of DBT on the metal sites with aromatics was the main reason for catalyst deactivation,and the improvement of sulfur tolerance could be achieved by the aid of the acidity of HY zeolite.Based on the acidity,the hydrogenation of DBT can be promoted obviously,and consequently the competitive adsorption of DBT on the metal sites can be reduced.

类沸石型咪唑酯骨架材料制备及其CO_(2)吸附性能

由有机配体和金属离子链接的类沸石型咪唑酯骨架(ZIFs)是金属有机框架材料中独特的一个子类,其孔结构可控,且气体储存性能优异。本研究采用溶剂热法制备了ZIF-8、ZIF-9、ZIF-68三种ZIFs材料,并对其进行X射线衍射、N_(2)吸附脱附、热重、红外等测试表征。X射线衍射分析结果显示三种ZIFs材料的衍射峰与其标准卡一致,表明材料的成功制备。N_(2)吸附脱附测试结果表明ZIF-8的比表面积和孔体积最大,分别高达2 284.83 m^(2)/g和3.13 cm^(3)/g;ZIF-8、ZIF-9和ZIF-68最可几孔径分别约为1.00、6.44和0.6 nm。热重测试结果表明,ZIF-8的热稳定性最好。ZIFs材料的CO_(2)吸附性能研究结果表明ZIF-68吸附性能最高,273 K/1 bar及298 K/1 bar条件下,可达74.37和42.62 cc/g,这可能是因为ZIF-68晶体中约0.6 nm孔径更易于CO_(2)气体吸附。研究结果表明,0.6 nm孔径尺寸较易于吸附CO_(2)温室气体,且ZIFs材料是一种较理想的CO_(2)吸附材料。

高硅ZSM-5沸石孔道和酸性的协同调控及其催化甲醇制丙烯反应性能

通过碱处理结合铬改性策略实现了对高硅ZSM-5沸石孔道和酸性的协同调控,制备出了一种具有适宜酸性的高硅多级孔沸石催化剂。在碱处理的过程中,通过精细调节合成凝胶组成,在沸石晶体中引入的丰富共生界面,诱导了介孔的形成,从而打破了沸石硅铝比对常规碱处理法的限制。在铬改性的过程中,独特的多级孔结构促进了铬在催化剂中的分散,从而实现了对酸性的深度改性。在甲醇制丙烯催化反应中,制备的催化剂表现出了极佳的催化稳定性以及很高的丙烯和总低碳烯烃选择性。

碱处理改性ZSM-5分子筛孔结构对VOCs吸附性能的影响

采用氢氧化钠和四丙基氢氧化铵混合碱溶液处理制备一系列改性ZSM-5分子筛,通过X射线衍射(XRD)、扫描电子显微镜(SEM)、N_(2)吸附、水接触角测定等手段对改性样品进行了分析表征,采用固定床吸附器对比评价5A、NaY和不同碱改性ZSM-5分子筛吸附剂对正己烷和乙酸乙酯的动态吸附性能。结果表明:氢氧化钠和四丙基氢氧化铵摩尔浓度均为0.2 mol/L的碱改性ZSM-5-G-3样品的比表面积及总孔体积分别为425 m^(2)/g和0.585 cm^(3)/g,比改性前高硅ZSM-5-G-1样品分别提高了17.7%和174.6%,介孔比表面积增加8.6倍,达到317 m^(2)/g,介孔体积增加12.3倍,达到0.531 cm^(3)/g;随着碱溶液浓度的增加,改性分子筛材料水接触角减小;25℃时,正己烷和乙酸乙酯在ZSM-5-G-3吸附剂床层上的穿透吸附量分别为76.99和101.08 mg/g,比改性前ZSM-5-G-1吸附剂床层分别提高了40.3%和17.4%。改性ZSM-5-G-3样品对挥发性有机化合物(VOCs)吸附性能的显著提高主要归因于碱改性提供了更多的吸附位和介孔结构。

Synthesis of Extra-large Pore of Zeolite Mineral

In the late 1970s, the discovery of the alumindnophosphate molecular sieveminerals which have been called a new generation led to framework composition oxideoutside of the aluminium-silicon system. The largest secondary building unit (SBU)of 18 T-atom rings has been maintained more than 180 years[2]. Only just in 1988,the molecular sieve with eighteen membered-ringr was reported by Davis and calledVIP-5 after the Virginia Polytechnic Institute. But a dissent has been expressed byDuncan for this. It was considered that VPI-5 does not represent a

ZSM-5分子筛结构对苯烷基化反应性能影响的数值模拟研究

以ZSM-5分子筛催化苯和乙烯烷基化为体系,建立并验证了一种三维各向异性扩散-反应数学模型,该模型考虑了分子筛形貌、孔结构和扩散各向异性的影响。模拟发现当分子筛颗粒体积和abc轴尺寸保持不变时,改变分子筛形貌并不会显著影响其表观活性,因而该情况下无须调控分子筛形貌;而当分子筛颗粒体积不变时,仅缩短b轴尺寸才能显著降低扩散阻力,提高催化剂表观活性,因而合成ZSM-5分子筛时缩短b轴尺寸最有利于扩散和反应。在分子筛颗粒中引入大孔可显著提高分子筛催化剂利用率和表观活性,保持大孔孔隙率不变时,减小大孔孔径更有利。存在最优大孔孔隙率以平衡扩散阻力和活性材料含量,当分子筛粒径4μm、大孔孔径300 nm时,最优大孔孔隙率0.16,对应最高表观反应速率80.5 mol/(m^(3)·s)。另外,由于分子筛内扩散各向异性的影响,当大孔取向平行于c轴时最有利。结果可为苯和乙烯烷基化ZSM-5分子筛催化剂乃至其他分子筛催化剂的设计优化提供一定的理论指导。

基于不同孔径和酸性分子筛的催化剂异构反应差异性研究

分别以2种不同孔径和酸性的一维十元环结构分子筛ZIP-1(小孔)和BCM-168(大孔)为酸性组分制备了2种贵金属临氢异构化催化剂A200和B350,采用微型反应装置考察其对正十六烷的异构化反应性能,并对其产物进行倾点与收率的计算以模拟实际油品的切割效果。结果表明,孔径较大且Bronsted酸强度较弱的BCM-168分子筛制备的B350催化剂对正十六烷的异构化选择性更好,且在高转化率下A200与B350的选择性差距增大。通过对正十六烷异构产物进行模拟切割,发现2种催化剂反应产物的组成结构不同,B350催化剂异构化产物支化度更高。在实际油品评价中,通过分析产物烃组成与碳数分布,发现B350催化剂使烷烃断键生成碳数较接近的产物;而由孔径较小且Br?nsted酸强度较高的ZIP-1分子筛制备的A200催化剂,易促进烷烃多次裂解生成碳数较少的短链烷烃。同时发现,催化剂的过度异构化会使产物裂解为沸点较低的组分,使得目的产物大分子异构烃类收率降低。

沸石负载贵金属加氢异构催化剂研究进展

直链烷烃加氢异构制异构烷烃是石油化工中生产高辛烷值组分、改善柴油和润滑油性能的重要反应。加氢异构反应需采用金属中心和酸中心组成的双功能催化剂,通过耦合金属活化有机烃加氢/脱氢和酸催化烯烃骨架异构实现协同作用。归纳了近年来用于加氢异构反应的沸石基双功能催化剂的作用机理,总结了双功能催化剂中沸石分子筛孔结构与酸性质的调变、活性金属性能调控和催化剂制备三方面的研究,重点围绕一维孔沸石基分子筛负载金属的双功能催化剂,探讨了催化剂双中心亲密性对双中心协同作用机理和加氢异构反应性能的影响,并对催化剂的工业应用情况进行了总结分析和展望。

纳米ZSM-5分子筛的磷改性

采用浸渍法制备了不同磷含量的工业微米ZSM-5分子筛(Z-0)和纳米ZSM-5分子筛(NZ-0),并利用XRD、低温N_(2)吸附-脱附、Py-IR、SEM、NH3-TPD等方法进行了表征,对结构性能进行了分析。实验结果表明,随着磷含量的增加,两种改性分子筛的结晶度、比表面积、孔体积、酸量均逐渐下降,改性磷含量建议不高于6%(w);与Z-0改性试样相比,NZ-0改性试样具有更高的结晶度保留率、介孔孔体积和比表面积,同时NZ-0改性试样的B酸酸量降幅更小,具有更高的B/L比值,且中强酸酸量降幅更小。与Z-6相比,采用NZ-6制备的丙烯助剂具有更高的丙烯产率。

Low-temperature VOCs oxidation performance of Pt/zeolites catalysts with hierarchical pore structure

Different zeolites supported Pt catalystswithmicro-mesoporous structurewere prepared by organic base tetrapropylammonium hydroxide(TPAOH)treatment and their catalytic oxidation activity for various volatile organic compounds(VOCs)were evaluated.The results reveal that the synergistic effect between Pt nanoparticles and surface acid sites plays an important role in VOCs low-temperature removal.The small size and high dispersion of Pt nanoparticles on the surface of the zeolites would promote the catalytic oxidation of aromatics and alkanes over the Pt/zeolite catalysts,while strong acidity and abundant acid sites of catalysts are in favour of the oxidation of the VOCs containingNandOheteroatoms.In addition,it was found that Pt/ZSM-5 catalyst exhibits the highest oxidation activity for various VOCs low-temperature removal amongst all the catalysts due to the balance of both Pt dispersion and abundant acid sites in the catalyst.This comprehensive consideration should be very helpful when designing and preparing novel catalysts for the low-temperature removal of VOCs.

半合成催化裂化催化剂主要组分对其孔结构的影响

采用N_(2)吸附-脱附法、压汞法、SEM和TEM等手段分析了以稀土改性Y型分子筛为主要活性组元的催化裂化催化剂(FCC-1)及其主要组分的孔结构特点,重点考察了铝溶胶、酸化拟薄水铝石和硅溶胶3种常用黏结剂对催化剂孔结构的影响。结果表明:FCC-1催化剂的微孔主要来自分子筛,黏结剂对分子筛微孔结构的影响包括物理堵孔和化学作用,当铝溶胶、酸化拟薄水铝石和硅溶胶分别与分子筛按照质量比1/2混合后,分子筛微孔比表面积损失率分别为23.0%、14.2%和7.7%,即铝溶胶影响分子筛微孔的程度最大。FCC-1催化剂的介孔主要来自黏结剂粒子堆积孔,与黏结剂粒子大小、形貌和堆积方式有关,粒径分别为1~2 nm、4~5 nm和10~50 nm的铝溶胶、酸化拟薄水铝石和硅溶胶经过500℃焙烧后分别以无定型氧化铝致密堆积、γ-Al_(2)O_(3)颗粒状紧密堆积和SiO_(2)球状紧密堆积,所得粒子堆积孔的最可几孔径分别为4.8、5.7和7.3 nm。FCC-1催化剂的大孔主要来自分子筛颗粒和/或高岭土颗粒之间的堆积孔。

HMCM-22分子筛催化丙烯齐聚反应性能的研究

研究了HMCM-22分子筛催化丙烯齐聚反应性能,并与HZSM-5、HY、HMOR、Hβ分子筛进行比较。通过一系列物性表征手段及丙烯齐聚反应性能评价,考察了5种分子筛孔结构、酸性质与丙烯齐聚反应性能的关系。结果表明,分子筛的拓扑结构和酸性对丙烯齐聚反应活性、选择性和稳定性有显著的影响,HMCM-22分子筛具有多维孔道结构与适中酸性,产物扩散性能好,抗积炭性能优异,在丙烯齐聚反应中的活性与稳定性最优。进一步对HMCM-22分子筛进行孔道和酸性调变以考察其催化丙烯齐聚反应性能,发现B酸酸量与总酸量大的HMCM-22分子筛初始活性高且更易生成高碳数产物,但C_(3n)选择性偏低,介孔比例适中的分子筛稳定性更好。HMCM-22分子筛稳定性评价结果表明,在300 h内丙烯转化率均保持在85%以上,C_(3n)选择性达77.6%,具有优异的丙烯齐聚活性、选择性和稳定性。

气体物理吸附在石油炼制与化工催化剂研究中的应用

90%以上石油化工生产过程涉及催化材料,催化材料的传质能力直接关系其催化性能,因此,作为体现催化材料传质能力的重要指标之一,比表面积和孔结构是石油化工催化材料研发、生产和质量控制中重点监测的物性参数。气体物理吸附法是当前表征石油化工催化材料比表面积和孔结构的主要技术手段。主要介绍了气体物理吸附法测定技术及主要技术进展,结合近年来石油化工催化材料在孔道调变、梯级孔构建、载体性能研究与催化剂积炭失活解析的部分实例阐述气体物理吸附法在石油化工催化材料表征中的应用。在此基础上,对物理吸附法的未来发展方向进行了展望。