Investigation of Small-Pore Zeolites via Vapor-Phase Adsorption of n-Hexane

Cage-based small-pore zeolites are promising catalysts for catalytic applications such as methanol-to-olefins to produce light olefins and selective catalytic reduction to mitigate NO_x emissions. The present paper reports our recent studies on vapor-phase adsorption of n-hexane in a series of small-pore zeolites with cages such as 3A, 4A, 5A, ITQ-29, SSZ-13, SSZ-16, SSZ-17, SSZ-36, SSZ-50, ITQ-12, ZK-5, and Rho. The effects of zeolite compositions and crystal sizes on the adsorption kinetics and capacity are investigated, demonstrating that n-hexane adsorption is a useful tool for characterizing the effective pore sizes and volumes of small pore zeolites.     

Water Vapor Adsorption and Desorption on Materials Hydrothermally Solidified from Clay Minerals

Water vapor isotherms were examined and ¹H-magic-angle spinning nuclear magnetic resonance (¹H-MAS NMR) analysis was conducted to determine the amount of water vapor adsorbed and desorbed on hydrothermally solidified materials derived from clay minerals. The amount of water vapor adsorbed and desorbed decreased with increasing mesopore volume of the materials, which disagreed with the estimation obtained using the Kelvin equation. Water vapor was physisorbed on alumina-like sites in the materials. An increase in the binding energy between water vapor and the materials led to an improvement in the water vapor adsorption–desorption properties of materials.     

Adsorption of Carbon Dioxide on High-Silica Zeolites with Different Framework Topology

Adsorption isotherms of carbon dioxide were measured on six high-silica zeolites TNU-9, IM-5, SSZ-74, ferrierite, ZSM-5 and ZSM-11 comprising three-dimensional 10-ring (8-ring for ferrierite) at 273, 293, 313 and 333 K. Based on the known temperature dependence of CO₂ adsorption, isosteric heats of adsorption were calculated. The obtained adsorption capacities and isosteric adsorption heats related to the amount of CO₂ adsorbed have provided detailed insight into the carbon dioxide interaction with zeolites of different framework topology. The zeolites TNU-9 and ferrierite are characterized by pronounced energetic heterogeneity whereas due to the location of Na⁺ cations in the same positions the isosteric adsorption heats of CO₂ adsorption on IM-5, ZSM-5 and ZSM-11 zeolites are rather constant for molecular ratio CO₂/Na⁺ < 1. As IM-5 zeolite has a maximum adsorption capacity, it appears to have optimum properties for carbon dioxide separation.     

煤系高岭土水热合成干燥用13X型沸石分子筛

研究以内蒙古鄂尔多斯煤系高岭土为原料,水热合成干燥用13X型沸石分子筛。采用单因素条件实验,考察了晶化时间、碱投加量、胶化温度、胶化时间、晶种投加量等制备条件对合成13X型分子筛的影响。通过静态饱和吸水量测定,RD、IR和SEM等表征手段对产品进行表征。发现最佳的反应条件为：合成液中晶种投加量为2%和碱投加量R[n（Na2O）/n（H2O）]控制在5.3,在65℃下胶化3h、然后在100℃下晶化时间24h,此时合成的X型分子筛的静态饱和吸水量为33.47%,合成晶体的外形为八面体晶型,而且形状规则、大小均匀、晶体棱角也比较清晰。     

Characterization of Cuprous Ion in High Silica Zeolites and Reaction Mechanisms of Catalytic NO Decomposition and Specific N2 Adsorption

In this review, we have summarized the recent studies on the characterization of copper ions exchanged into MFI (CuMFI) and suggested the models of active centers for the NO decomposition and the specific N₂ adsorption. The first part deals with the reduction mechanism of copper ions exchanged in MFI during the evacuation process at high temperature. In the second part, it has been claimed that a part of the Cu⁺ species, formed in the evacuation process, take three-coordination structure at the M7 site and are active for the N₂ adsorption. The N₂ adsorption would result in the change in the Cu structure to the distorted tetrahedral coordination. The third part concerns the reaction mechanism of NO decomposition. We have proposed that the Cu⁺—Cu⁺ dimer species are indispensable for the effective NO decomposition and the oxygen-bridged intermediates are produced during the catalytic cycle.     

改性沸石制备及对其铬吸附特性的研究

为了解决天然沸石对废水中重金属吸附能力低的问题,制备出了六种改性沸石并考察了改性沸石对六价铬离子的吸附特性。在这六种改性沸石中,H2 SO4/CuSO4复合改性沸石对铬的吸附性能最佳,其对铬的吸附曲线符合Freundlich方程;其吸附强度是天然沸石的8倍;其吸附动力学曲线符合二级动力学模型,实测值十分接近理论值,这也证明在其对六价铬离子的吸附过程中离子交换起着十分重要的作用。     

Basic Zeolites: Characterization and Uses in Adsorption and Catalysis

The presence of basic centers in some oxides has been recognized for a long time as being important in catalysis [1-4]. Usually both basic and acid sites exist simultaneously. The two centers may work independently or in a concerted way. For instance, in alcohol transformation, dehydration is favored on acidic sites and dehydrogenation on basic centers [3,5]. A large variety of materials are cited as having basic character. They include single-metal oxides (MgO, CaO, ZnO), supported alkali metals (Na/MgO, K/K₂CO₃), mixed-metal oxides (MgO-A1₂O₃, ZnO-SiO₂, MgO-TiO₂), zeolites (X and Y saturated with alkaline cations of low electronegativity), hydrotalcite-type anionic clays, asbestoslike materials, carbon-supported basic catalysts, and basic organic resins.

     

Combined Adsorption/Ultrafiltration of Secondary Effluents Using Powdered Zeolites

The performance of powdered zeolite (PZ) adsorption/ultrafiltration (UF) with real secondary effluents is investigated. With the assistance of PZs, the membrane fouling rate was reduced and the permeate flux recovery as well as the advanced treatment of the secondary effluents were enhanced. 3D excitation emission matrix (3D‐EEM) fluorescence spectra indicate that the removal of fluorescence intensity for aromatic proteins, fulvic acid‐like materials, soluble microbial by‐product‐like materials, and humic acid‐like organics could be improved by PZs. UF membranes with PZs can increase the removal efficiency of organics, especially of those with low molecular weight. The characteristics of the cake layer on the surface of an UF membrane were determined by scanning electron microscopy and electron energy‐dispersive X‐ray spectroscopy for the combined adsorption/UF membrane.     

Basic Zeolites: Characterization and Uses in Adsorption and Catalysis

The presence of basic centers in some oxides has been recognized for a long time as being important in catalysis [1-4]. Usually both basic and acid sites exist simultaneously. The two centers may work independently or in a concerted way. For instance, in alcohol transformation, dehydration is favored on acidic sites and dehydrogenation on basic centers [3,5]. A large variety of materials are cited as having basic character. They include single-metal oxides (MgO, CaO, ZnO), supported alkali metals (Na/MgO, K/K₂CO₃), mixed-metal oxides (MgO-A1₂O₃, ZnO-SiO₂, MgO-TiO₂), zeolites (X and Y saturated with alkaline cations of low electronegativity), hydrotalcite-type anionic clays, asbestoslike materials, carbon-supported basic catalysts, and basic organic resins.     

AgY吸附剂的吸附脱硫性能及竞争吸附研究

以NaY分子筛为载体,通过液相离子交换法制备了Ag改性的AgY分子筛,并对其进行了X射线衍射(XRD).原子吸收光谱(AAS)、N2吸附比表面积(BET)、X射线光电子能谱(XPS)和扫描电镜(SEM)等表征分析.以噻吩/石油醚体系为模型化合物,考察了吸附温度、吸附时间等吸附条件对吸附剂吸附性能的影响,结果表明吸附温度...     

NO Oxidation Kinetics on Iron Zeolites: Influence of Framework Type and Iron Speciation

Zeolites having MFI, FER and *BEA topology were loaded with iron using solid state cation exchange method. The Fe:Al atomic ratio was 1:4. The zeolites were characterized using nitrogen adsorption, FTIR and DR UV–Vis–NIR spectroscopy. The catalytic activity in NO oxidation and the occurrence of NO _x adsorption was determined in a fixed-bed mini reactor using gas mixtures containing oxygen and water in addition to NO and NO₂ and temperatures of 200–350 °C. Under these reaction conditions, the NO _x adsorption capacity of these iron zeolites was negligible. The kinetic data could be fitted with a LHHW rate expression assuming a surface reaction between adsorbed NO and adsorbed O₂. The kinetic analysis revealed the occurrence of strong reaction inhibition by adsorbed NO₂. FER and MFI zeolites were more active than *BEA type zeolite. MFI zeolite is most active but suffers most from NO₂ inhibition of the reaction rate. FTIR and UV–Vis spectra suggest that isolated Fe³⁺ cations and binuclear Fe³⁺ complexes are active NO oxidation sites. Compared to the isolated Fe³⁺ species, the binuclear complexes abundantly present in the MFI zeolite seem to be most sensitive to poisoning by NO₂.     

丙烷在不同硅铝比的NanZSM-5型分子筛上的吸附性质的分子模拟

用巨正则系综蒙特卡罗（GCMC）和构型偏倚蒙特卡罗（CBMC）相结合的分子模拟方法,研究了丙烷在不同硅铝比的NanZSM-5型分子筛中的吸附性质,并建立了丙烷在不同硅铝比的NanZSM-5型分子筛上的双点Langmuir等温线模型。计算结果显示,模拟结果与文献报导的实验结果相吻合,分子筛骨架上的硅铝比对丙烷的吸附量和吸附等温线无明显影响,并证实双点Langmuir等温线模型能较好地描述丙烷在不同硅铝比的NanZSM-5型分子筛上的吸附性质。     

Parameters Influencing Photoassisted Adsorption of NO on TiO2 Powder

The use of semiconductor materials as photocatalysts for cleaning gas processes has received increasing interest in the last decade. In order to make more active catalysts, it is worthwhile to investigate the main processes influencing photocatalytic reactions in more detail. One of these is the process of coadsorption of the reaction components on the catalyst surface under irradiation. It is shown that photoassisted NO adsorption can serve as a model system in order to investigate the influence of irradiation intensity and temperature on the adsorption isotherm, respectively. This advantage stems from the fact that NO is a radical, offering the possibility to stabilize electrons as well as holes on the TiO₂ surface. This results in the formation of NO/NO pairs. The proposed adsorption model, however, does not only consider this pair formation but, in addition, the adsorption of NO molecules on charged sites while the complementary charged sites are stabilized by traps present on the surface. The proposed adsorption isotherm is supported by experimental results.     

Adsorption and decomposition of NO on carbon and carbon-supported catalysts

The interactions of NO with carbon and carbon-supported catalysts have been investigated by means Fourier transform infrared spectroscopy. Nitric oxide direct decomposition over carbon-supported catalysts (Cu, Pt) was studied in a temperature ranging from 473 to 623 K. NO conversion increased with increasing reaction temperature in the whole temperature range. The carbon-supported Pt catalyst has a very high activity for the decomposition of NO in the absence of oxygen. As a result of NO chemisorption isocyanate (-NCO) species on the surface of carbon containing Cu were observed. When the reaction temperature was increased, the -NCO band at 2229 cm⁻¹ became more intense.     

Adsorption of N-Butane/I-Butane in Zeolites: Simulation and Theory Study

Zeolite adsorption is one of the best available technologies for gas separation. We use molecular simulation to produce the data of adsorption of n-butane and i-butane and their mixture at different temperatures and pressures in different zeolites. In BEA, MOR, CFI, ISV, and BOG the amount of adsorption of i-butane is higher than n-butane, but the case is just the contrary in MFI, MEL, TER, and TON. The heats of adsorption decrease with temperature increasing for all investigated cases except for i-butane in MFI and MEL. The IAST (ideal adsorbed solution theory) is used to predict the n-butane/i-butane mixture adsorption. For the systems of BEA, MOR, CFI, and ISV, IAST theory provides predictions that are in good agreement with simulation. We propose SACIAST (surface area corrected IAST) by introducing a correcting parameter C_r into IAST to predict the adsorption of mixture in MFI, MEL, TER, TON, and BOG since the original IAST failed to predict the mixture data in these zeolites because of the pore structure of these zeolites. The SACIAST we proposed is a new modified theory based on IAST which has never been reported in the literature before, and it predicts the mixture adsorption very well.     

锂渣合成NaX分子筛结构表征和吸附特性研究

采用水洗分离和碱熔消化方法对硫酸法生产碳酸锂过程中排放的废弃锂矿渣(锂渣)进行预处理,然后用水热合成制备NaX分子筛(NaX-1、NaX-2)。分析了原料锂渣中石英含量以及预处理前后锂渣物相变化;用XRD、SEM和TG-DTA等手段对锂渣合成NaX-1、NaX-2分子筛的物相、晶体形貌和热稳定性进行了表征,用真空重量法测定其对水的吸附性能,并与NaX分子筛标样进行了对比。结果表明,原料锂渣中石英含量为14.1%(wt);采用水洗分离石英和碱熔消化后的锂渣均可作为合成NaX分子筛的原料,所合成的NaX-1、NaX-2分子筛均在6.1°、10.0°、15.4°、20.0°、23.3°、26.7°、30.9°等出现NaX分子筛特征衍射峰,其晶体规整,呈八面沸石型;用碱熔消化处理后的锂渣合成的NaX-2分子筛,晶体粒径为1~2μm,比用水洗分离石英后的锂渣合成的NaX-1分子筛晶粒(3~5μm)小;NaX-1、NaX-2分子筛具有良好的热稳定性,在800℃下未发生晶格结构破坏;NaX-1、NaX-2对水的平衡吸附量分别0.3234、0.3208 kg·kg-1,与NaX分子筛标样(0.3303 kg·kg-1)接近。     

Microcalorimetric and FTIR Study of the Adsorption of Carbon Dioxide on Alkali-Metal Exchanged FER Zeolites

Adsorption of CO₂ on alkali-metal exchanged (Li⁺, Na⁺, K⁺) FER zeolites was investigated by means of microcalorimetry and FTIR spectroscopy. The adsorption enthalpies strongly depend on coverage for all investigated materials and they are also influenced by concentration of Al in the framework. Especially, samples of Na- and K-FER with lower Si/Al ratio (8.6) exhibited substantially larger initial interaction energy than samples with Si/Al 27.5. Differences in zero-coverage adsorption energy of zeolites with different cation concentration (Si/Al ratio) are 9 and 7.2 kJ/mol for Na- and K-FER zeolites respectively. This phenomenon is attributed to formation of bridged CO₂ adsorption complexes formed between two cations, which are characterized by IR absorption band of ν₃ stretching vibration mode at 2370 and 2357 cm^?1 for Na- and K-FER respectively.     

The Adsorption Sites of CO and NO Molecules on Metal Surfaces

This article briefly reviews recent structural results obtained for the adsorption of CO and NO on the closest-packed single-crystal metal surfaces. We discuss mainly the question of adsorption sites (top, bridge, hollow), in connection with site assignments based on C–O and N–O vibrational stretch frequencies. It is by now well established that, especially for high-coverage molecular structures (i.e., high-density monolayers), one cannot rely on simple site assignments based on these frequencies: molecular interactions change the frequencies, such that the frequency ranges deduced for carbonyl and nitrosyl cluster compounds are in some cases violated.