几种沸石分子筛的催化裂化性能研究:1孔结构和酸性

采用X-射线衍射、X射线荧光光谱、N2吸附、吡啶吸附红外光谱和NH3程序升温热脱附研究了分子筛RE-HY,HZSM-5和Hβ的基本物理化学性质。N2吸附结果表明,三维孔道结构的REHY分子筛和Hβ分子筛具有相近的孔半径和吸附量;与HZSM-5和Hβ分子筛相比,高温条件下,REHY分子筛具有较多的Brφsted酸中心和较少Lewis酸中心。NH3程序升温热脱附表明,三种分子筛中,HZSM-5分子筛的强酸中心最多。     

噻吩、苯和正辛烷在NaY和CeY分子筛上的热脱附

采用智能质量分析仪(IGA),利用程序升温脱附法(TPD)研究了噻吩、苯和正辛烷在NaY和CeY分子筛上的热脱附行为,测定了升温速率为15 K/min时3种吸附质在NaY和CeY上的热重(TG)和微分热重(DTG)曲线。结果表明,3种吸附质在NaY上脱附比较容易,苯和正辛烷在CeY上脱附也很容易,但噻吩在CeY上脱附比较困难,噻吩有一部分不能完全脱附。CeY对噻吩具有较好的吸附选择性,而NaY的吸附选择性不好。     

正己烷在5A分子筛上高温吸附/脱附及扩散性能

采用智能质量分析仪IGA,在较高温度(150—300℃)下,测定5A分子筛对正己烷的吸附/脱附等温线,考察吸附温度对吸附等温线的影响,研究改性5A分子筛的二次孔结构与正己烷吸附/脱附及扩散性能的关系。结果表明:5A分子筛对正己烷的吸附等温线随着吸附温度的升高优惠程度逐渐降低,在300℃下,5A分子筛对正己烷吸附等温线接近线性,压力从14 kPa降至1.4 kPa,被5A分子筛吸附的正己烷可脱附出45.95%;在200℃下,改性5A分子筛(5A-11)对正己烷的脱附质量比是未改性(5A-1)的3.5倍;正己烷在5A-11分子筛上的脱附扩散系数为8×10-13m2/s,约是未改性的20倍;5A-11分子筛拥有较小的二次孔孔径和较为合理的大孔分布,使其对正己烷有着良好的脱附性能。     

Temperature-programmed desorption study of molecular oxygen adsorbed on MFI-type zeolites

The adsorption of molecular oxygen at room temperature on the proton form of MFI zeolites with different Si/Al ratios has been investigated by temperature-programmed desorption (TPD). The internal Si-OH defects (silanol groups) in these zeolites are found to serve as O₂ adsorption sites. The apparent activation energies (17.5–21.8 kcal-mol^-1) of desorption determined from O₂ TPD measurements reveal that the extent of interactions between the Si-OH defects and the adsorbed O₂ molecules becomes weaker with decreasing Al content in the zeolite.     

Heterogeneity of Adsorption Sites and Adsorption Kinetics of n-Hexane on Metal-Organic Framework MIL-101(Cr)

abstract The heterogeneity of adsorption sites and adsorption kinetics of n-hexane on a chromium terephthalate-based metal-organic framework MIL-101(Cr) were studied by gravimetric method and temperatu...     

噻吩在CeY分子筛上的吸附行为

采用智能质量分析(IGA)和程序升温脱附和微分程序升温脱附（TPD/DTPD）法研究了噻吩在CeY上的热脱附行为和吸附热力学,并和NaY进行对比。发现噻吩在CeY分子筛上有很好的选择性吸附,噻吩和CeY分子筛之间的吸附主要是金属离子和硫原子的化学键力作用,而在NaY上的吸附作用属于分子间力作用。吸附热力学也证明了噻吩在CeY上既有物理吸附作用也有强的化学吸附作用。     

Adsorption of Propene in the Presence and Absence of Oxygen or Nitric Oxide on Pt-Loaded ZSM-5, Beta, Y, and Ferrierite Zeolites

Adsorption and desorption of NO and propene on pure and platinum-loaded ZSM-5, Beta, Y and Ferrierite zeolites have been studied by FTIR and temperature programmed desorption (TPD). Platinum-loaded ZSM-5 and Beta are found to have a good adsorption capacity for hydrocarbons and NO at low temperatures. HC-SCR on Pt-zeolites is a promising NO abatement method.     

Modification and sequential treatment of EU-1 zeolite in mild alkali and alkaline-acid conditions

EU-1 zeolites were sequentially treated with low-concentration sodium carbonate(Na_2CO_3) and hydrochloric acid(HCl) solutions.The obtained samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),N_2 adsorption/desorption,temperature programmed desorption of NH_3(NH_3-TPD),solid state~(27)A1 nuclear magnetic resonance(~(27)A1 NMR),and the catalytic performances of the treated samples were tested in the xylene isomerization reaction.The results showed that the external surface area and mesoporous volume of the sample sequentially treated with 0.05 mol·L~(-1) Na_2CO_3 and 0.1 mol·L~(-1) HCl solutions reached73.9 m~2·g~(-1) and 0.162 cm~3·g~(-1),respectively.The catalytic performances of EU-1 zeolites were significantly improved,that the activity of the probe reaction increased from 23.03%to 23.61%and the selectivity increased from85.09%to 87.14%compared with those of parent sample.Furthermore,it was found that only amorphous silica and alumina species was dissolved during the post-treatment process,but the framework structure and the acidic properties of EU-1 zeolite remained intact.     

Tapered element oscillating microbalance (TEOM) studies of isobutane,n‐butane and propane sorption in β‐ and Y‐zeolites

A TEOM is used to elucidate the adsorption/desorption characteristics of alkylation reactants on USY‐ and β‐zeolites. Equilibrium adsorption isotherms were obtained on USY‐ and β‐zeolites using n‐butane, isobutane and propane as proxy reactant molecules (T = 303–398 K, adsorbate partial pressure 0–1.2 bar). Analysis of the transient adsorption/desorption profiles of these molecules from either a bed of the zeolite or pelletized particles of the crystals (with mean size < 1 μm) demonstrate that diffusion in the secondary meso‐/macroporous structure formed in the packing or the pellets controls the overall sorption rates. The experimental adsorption/desorption profiles from the pelletized zeolites were regressed with available mathematical models to obtain effective meso‐/macropore diffusivities for reactant molecules, and nearly perfect fits of the experimental and the modeled profiles. Taking into account the dead volume in the system, a criterion for reliable measurements of either micropore or mesopore diffusivities by the TEOM technique is derived. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Comparative Calorimetric Studies of the Acidity of Zeolites by Static and Temperature-Programmed Methods of Ammonia Adsorption and Desorption

A combined TG-DSC 111 apparatus from Setaram has been used for the characterization of HZSM5, H-Y and H-Ferrierite zeolites. Starting from the NH₄ forms it was possible to determine the weight loss under vacuum at increasing temperature up to 863 K, the subsequent weight gain upon ammonia adsorption at room temperature and finally the weight loss at increasing temperature. The heats of ammonia adsorption and desorption during the same experiments could also be determined. The experimental results indicate clearly a great heterogeneity in acid strengths. These results are compared to those obtained by a static method using a classical gas-handling line linked to a heat-flow microcalorimeter.     

Temperature dependence of the point of zero charge of oxidized and non-oxidized activated carbons

Three activated carbons in the form of grains, fibers and pellets were oxidized with ammonium peroxidisulfate. The oxidized and non-oxidized activated carbons were characterized by: N₂ adsorption at 77 K, temperature programmed desorption up to 1273 K, and potentiometric titrations in the temperature range between 288 and 318 K. The point of zero charge (PZC) of the oxidized activated carbons decreased with increasing temperature and this decrease was in the same direction as the change in 1/2pK_w, the neutral point of water. The non-oxidized activated carbons behaved in a similar manner, but the PZC decreased by more than the corresponding change in 1/2pK_w. Variation of surface charge of the three oxidized activated carbons was fitted to a single second-order function with respect to pH and temperature. However, a single equation could not be found for the three non-oxidized activated carbons. Standard thermodynamic functions at the PZC were obtained from potentiometric curves. Acidity constant distributions were obtained and showed an increase in the number of acidic groups when the temperature increased. The number of carboxylic and phenolic groups obtained from these distributions was compared with that obtained from the deconvolution of temperature programmed desorption spectra.     

Characterization of Acidic OH Groups in Y-Type Zeolites by Means of Different Methods of Temperature-Programmed Desorption (TPD) of Ammonia

The acidic properties of HNaY zeolites with different degrees of exchange have been studied by means of two complementary techniques of temperature-programmed desorption (TPD) of ammonia, namely, FTIR-TPD and conventional TPD. In HNaY zeolites with low exchange levels only a single type of OH group is observed. The analysis of the spectra in the region of NH bending modes during NH₃-FTIR-TPD on zeolites with higher proton content (40% or higher) shows that ammonia is bound in two different adsorption states. This assessment is further confirmed by evaluation of the OH stretching region. Furthermore, desorption energy distribution functions for the different types of OH groups have been calculated using a numerical regularization method.     

Co-adsorption of nitrogen monoxide and nitrogen dioxide in zeolitic de-NOx catalysts

Room temperature adsorption and temperature programmed desorption (TPD) of NO, NO with O₂, and NO after NO₂ saturation were investigated for Na/Y, Na/ZSM5, Cu/ZSM5 and SiO₂ gel. The adsorbates were characterized by TPD, using mass spectrometry to identify the desorbed molecules. In the presence of O₂, the adsorption of NO and NO₂ is non-additive; co-desorption of nearly equal amounts of NO and NO₂ takes place suggesting the formation of a complex with an overall composition N₂O₃ within the zeolite. Since SiO₂ gel does not adsorb NO nor NO₂, the adsorption capacity of the zeolites is a function of their specific structure. The oxidation of NO to NO₂ is catalyzed by Na/Y and Na/ZSM5.     

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%。     

Studies on the synthesis of diacetyl over oxidation zeolite catalysts

Diacetyl (2,3-butanedione) synthesis from methyl ethyl ketone over oxidation zeolites using O₂ as oxidant was studied. Various zeolites with Fe, V and Ti as active sites were employed. VS-1, Ti-NCL, Ti-MCM-41 and FeBEA type materials were synthesized and characterized by BET, FTIR, XRD, pyridine adsorption and template desorption. The detailed study of the effect of reaction temperature, the effect of concentration of oxygen and the addition of water was realized. The most active catalyst was zeolites with V as oxidation center.     

Selective Oxidation of Methanol to Dimethoxymethane over Mesoporous Al‐P‐V‐O Catalysts

The synthesis and application of bifunctional mesoporous Al‐P‐V—O catalysts with both acidic and redox sites for selective oxidation of methanol to dimethoxymethane (DMM) is described. The catalysts were characterized by N₂ adsorption/desorption, X‐ray diffraction, temperature‐programmed desorption, X‐ray photoelectron spectroscopy, and infrared spectroscopy. It is shown that porosity; redox property and surface acidity of the catalysts were greatly influenced by the Al/V/P ratio. The synergistic effect of phosphorus and vanadium was investigated. Al‐P‐V—O catalysts exhibited good catalytic activity because of the controlled reducibility and the acidic sites. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2587–2593, 2013     

轻石脑油中C_6烷烃在5A分子筛上的吸附/脱附等温线研究

测定了轻石脑油中正、异构C6烷烃在5A-1分子筛上的低温(25～80℃)及高温(150～300℃)吸附/脱附等温线,分析了吸附温度、吸附压力、脱附压力对5A-1分子筛吸附/脱附性能的影响。结果表明:正己烷在5A-1分子筛上低温(25～80℃)及高温(150～300℃)下的吸附等温线均为I型吸附等温线,且随着吸附温度的升高,等温线优惠程度逐渐降低。吸附温度25℃、平衡压力7.5kPa时,异构C6烷烃在5A-1分子筛上的吸附量较小,对正己烷平衡吸附量影响不大。对于轻石脑油中的C_6烷烃来说,较适宜的吸附温度优选200～250℃,在该温度范围内,正己烷平衡吸附量为5.68～9.03g/(100g);脱附压力为1.4 kPa时,正己烷脱附量为0.69～2.35g/(100g),能够满足变压吸附的操作要求。     

Esterification of levulinic acid to ethyl levulinate over bimodal micro–mesoporous H/BEA zeolite derivatives

A series of bimodal micro–mesoporous H/BEA zeolite derivatives were prepared by the post-synthesis modification of H/BEA zeolite by NaOH (0.05 M–1.2 M) treatment. Samples were characterized by powder XRD, low temperature nitrogen adsorption/desorption, temperature programmed desorption of ammonia and ICP. The mesopore formation was found to play a crucial role in liquid phase esterification of levulinic acid with ethanol. The enhanced catalytic activity of a bimodal micro–mesoporous H/BEA zeolite derivative (H/BEA_0.10) prepared by treatment with 0.1 M NaOH can be mainly attributed to the high mesoporosity coupled with better preserved crystallinity and acidic properties.     

HZSM-5分子筛上吸附苯和甲醇的TPSR-MS研究

对不同硅铝比HZSM-5分子筛进行程序升温表面反应-质谱(TPSR-MS)实验和原位程序升温氧化(TPO)。结果表明,苯在HZSM-5分子筛上于60℃下吸附后程序升温脱附的过程中检测到乙烯,硅铝比越低,检测到的乙烯越多,HZSM-5分子筛上的残碳量越大。甲醇在HZSM-5分子筛上于60℃下吸附后程序升温脱附的过程中检测到甲苯,但未检测到苯,硅铝比越低,检测到的甲苯量越大;同时检测到氢气,硅铝比越低,氢气量越小,TPO检测到的残炭量越小。吸附温度越高,甲醇越易转化成甲苯。     

Sorption of methanol on zeolite HBeta investigated by in situ MAS NMR spectroscopy

Methanol adsorption and desorption experiments were performed on acidic zeolites applying a new in situ MAS NMR technique. ¹H MAS NMR spectra of dehydrated zeolites were recorded during injection of nitrogen gas loaded with methanol into the MAS rotor. The spectra indicated that in zeolite HBeta also silanol groups are involved in the adsorption of methanol which is in contrast to the behaviour of SiOH groups in zeolites HZSM-5 and HY. The desorption experiments show that about 70% of the methanol molecules contributing to adsorbate complexes in zeolite HBeta are weakly hydrogen-bonded at silanol groups. This revised version was published online in July 2006 with corrections to the Cover Date.