Application of Inelastic Neutron Scattering to the Methanol-to-Gasoline Reaction Over a ZSM-5 Catalyst

Peer reviewed

Identifying the isolated transition metal ions/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy

Isolated transition metal ions/oxides in molecular sieves and on surfaces are a class of active sites for selective oxidation of hydrocarbons. Identifying the active sites and their coordination structure is vital to understanding their essential role played in catalysis and designing and synthesizing more active and selective catalysts. The isolated transition metal ions in the framework of molecular sieves (e.g., TS-1, Fe-ZSM-5, and V-MCM-41) or on the surface of oxides (e.g., MoO3/Al2O3 and TiO2/SiO2) were successfully identified by UV resonance Raman spectroscopy. The charge transfer transitions between the transition metal ions and the oxygen anions are excited by a UV laser and consequently the UV resonance Raman effect greatly enhances the Raman signals of the isolated transition metal ions. The local coordination of these ions in the rigid framework of molecular sieves or in the relatively flexible structure on the surface can also be differentiated by the shifts of the resonance Raman bands. The relative concentration of the isolated transition metal ion/oxides could be estimated by the intensity ratio of Raman bands. This study demonstrates that the UV resonance Raman spectroscopy is a general technique that can be widely applied to the in-situ characterization of catalyst synthesis and catalytic reactions. (C) 2003 Elsevier Science (USA). All rights reserved.

Characterization of iron atoms in the framework of MFI-type zeolites by UV resonance Raman spectroscopy

Silicalite-I, ZSM-5, and Fe-ZSM-5 zeolites prepared from two different silicon sources are characterized by UV resonance Raman (UVRR) spectroscopy, X-ray diffraction (XRD), electron spin resonance (ESR), and UV/visible diffuse reflectance spectroscopy (UV/Vis DRS). A new technique for investigating zeolitic structure, UV resonance Raman spectroscopy selectively enhances the Raman bands associated with framework iron atoms incorporated into MFI-type zeolites, and it is very sensitive in identifying the iron atoms in the framework of zeolites, while other techniques such as XRD, ESR, and UV/Vis DRS have failed in uncovering trace amounts of iron atoms in the framework of zeolites. (C) 2000 Academic Press.

Dry gel conversion of organosilane templated mesoporous silica: from amorphous to crystalline catalysts for benzene oxidation

Mesoporous silica grown using [3-(trimethoxysilyl)propyl]octadecyldimethylammonium chloride as the mesoporogen in the presence of Fe and Al is X-ray amorphous, but contains very small domains with features of MFI zeolite as evidenced by IR and Raman spectroscopy. When applied as a catalyst, this amorphous sample shows good performance in the selective oxidation of benzene using nitrous oxide. Addition of tetrapropylammonium as structure directing agent to the as-synthesized mesoporous silica and subsequent dry gel conversion results in the formation of hierarchical Fe/ZSM-5 zeolite. During dry gel conversion the wormhole mesostructure of the initial material is completely lost. A dominant feature of the texture after crystallization is the high interconnectivity of micropores and mesopores. Substantial redistribution of low-dispersed Fe takes place during dry gel conversion towards highly dispersed isolated Fe species outside the zeolite framework. The catalytic performance in the oxidation of benzene to phenol of these highly mesoporous zeolites is appreciably higher than that of the parent material.

Studies of the Room-Temperature Multiferroic Pb(Fe0.5Ta0.5)0.4(Zr0.53Ti0.47)0.6O3: Resonant Ultrasound Spectroscopy, Dielectric, and Magnetic Phenomena

Recently, lead iron tantalate/lead zirconium titanate (PZTFT) was demonstrated to possess large, but unreliable, magnetoelectric coupling at room temperature. Such large coupling would be desirable for device applications but reproducibility would also be critical. To better understand the coupling, the properties of all 3 ferroic order parameters, elastic, electric, and magnetic, believed to be present in the material across a range of temperatures, are investigated. In high temperature elastic data, an anomaly is observed at the orthorhombic mm2 to tetragonal 4mm transition, Tot = 475 K, and a softening trend is observed as the temperature is increased toward 1300 K, where the material is known to become cubic. Thermal degradation makes it impos- sible to measure elastic behavior up to this temperature, however. In the low temperature region, there are elastic anomalies near ≈40 K and in the range 160–245 K. The former is interpreted as being due to a magnetic ordering transition and the latter is interpreted as a hysteretic regime of mixed rhom- bohedral and orthorhombic structures. Electrical and magnetic data collected below room temperature show anomalies at remarkably similar temperature ranges to the elastic data. These observations are used to suggest that the three order parameters in PZTFT are strongly coupled.

Investigation into the effect of molybdenum-site substitution on the performance of Sr2Fe1.5Mo0.5O6-δ for intermediate temperature solid oxide fuel cells

In this paper, niobium doping is evaluated as a means of enhancing the electrochemical performance of a Sr₂Fe_1.5Mo_0.5O_6-δ (SFM) perovskite structure cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) applications. As the radius of Nb approximates that of Mo and exhibits +4/+5 mixed valences, its substitution is expected to improve material performance. A series of Sr₂Fe_1.5Mo_0.5-xNb_xO_6-δ (x = 0.05, 0.10, 0.15, 0.20) cathode materials are prepared and the phase structure, chemical compatibility, microstructure, electrical conductivity, polarization resistance and power generation are systematically characterized. Among the series of samples, Sr₂Fe_1.5Mo_0.4Nb_0.10O_6-δ (SFMNb_0.10) exhibits the highest conductivity value of 30 S cm^-1 at 550°C, and the lowest area specific resistance of 0.068 Ω cm² at 800°C. Furthermore, an anode-supported single cell incorporating a SFMNb_0.10 cathode presents a maximum power density of 1102 mW cm^-2 at 800°C. Furthermore no obvious performance degradation is observed over 15 h at 750°C with wet H₂(3% H₂O) as fuel and ambient air as the oxidant. These results demonstrate that SFMNb shows great promise as a novel cathode material for IT-SOFCs.

Investigation into the effect of Fe-site substitution on the performance of Sr2Fe1.5Mo0.5O6-δ anodes for SOFCs

Ni-substituted Sr₂Fe_1.5-xNi_xMo_0.5O_6-δ (SFNM) materials have been investigated as anode catalysts for intermediate temperature solid oxide fuel cells. Reduced samples (x = 0.05 and 0.1) maintained the initial perovskite structure after reduction in H₂, while metallic nickel particles were detected on the grain surface for x = 0.2 and 0.3 using transmission electron microscopy. Temperature programmed reduction results indicate that the stable temperature for SFNM samples under reduction conditions decreases with Ni content. In addition, X-ray photoelectron spectroscopy analysis suggests that the incorporation of Ni affects the conductivity of SFNM through changing the ratios of Fe³⁺/Fe²⁺ and Mo⁶⁺/Mo⁵⁺. Sr₂Fe_1.4Ni_0.1Mo_0.5O_6-δ shows the highest electrical conductivity of 20.6 S cm^-1 at 800 °C in H₂. The performance of this anode was further tested with electrolyte-supported cells, giving 380 mW cm^-2 at 750 °C in H₂, hence demonstrating that Ni doping in the B-site is beneficial for Sr₂Fe_1.5Mo_0.5O_6-δ anode performance. 

Improved electrochemical performance of Sr2Fe1.5Mo0.4Nb0.1O6-δ -Sm0.2Ce0.8O2-δ composite cathodes by a one-pot method for intermediate temperature solid oxide fuel cells

In this paper, Sr₂Fe_1.5Mo_0.4Nb_0.1O_6-δ (SFMNb)-xSm_0.2Ce_0.8O_2-δ (SDC) (x = 0, 20, 30, 40, 50 wt%) composite cathode materials were synthesized by a one-pot combustion method to improve the electrochemical performance of SFMNb cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The fabrication of composite cathodes by adding SDC to SFMNb is conducive to providing extended electrochemical reaction zones for oxygen reduction reactions (ORR). X-ray diffraction (XRD) demonstrates that SFMNb is chemically compatible with SDC electrolytes at temperature up to 1100 °C. Scanning electron microscope (SEM) indicates that the SFMNb-SDC composite cathodes have a porous network nanostructure as well as the single phase SFMNb. The conductivity and thermal expansion coefficient of the composite cathodes decrease with the increased content of SDC, while the electrochemical impedance spectra (EIS) exhibits that SFMNb-40SDC composite cathode has optimal electrochemical performance with low polarization resistance (R_p) on the La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ electrolyte. The R_p of the SFMNb-40SDC composite cathode is about 0.047 Ω cm² at 800 °C in air. A single cell with SFMNb-40SDC cathode also displays favorable discharge performance, whose maximum power density is 1.22 W cm^-2 at 800 °C. All results indicate that SFMNb-40SDC composite material is a promising cathode candidate for IT-SOFCs.

Investigations Of Iron Adducts Of C-60 - Novel Fec60 In The Solid-State With Fe Inside The C-60 Cage

By carrying out contact-arc vaporization of graphite in a partial atmosphere of Fe(CO)5, an iron-adduct with C60 has been obtained. The adduct has been characterized by various techniques including mass spectrometry, Fe-57 Mossbauer spectroscopy and Fe K-EXAFS. Properties of this adduct are compared with those of an adduct prepared by solution method where Fe is clearly outside the cage. Results suggest that FeC60 obtained from the gas phase reaction has the Fe atom in the cage.

Transformação de metanol em olefinas leves catalisada por zeólitas HZSM-5

A reação de transformação de MeOH em olefinas leves foi investigada sobre zeólitas HZSM-5 com razões SiO2/Al2O3 (SAR) iguais a 30, 80 e 280. As propriedades ácidas e texturais da amostra com SAR 30 foram modificadas por impregnação com ácido fosfórico. A caracterização físico-química das amostras foi realizada empregando-se as técnicas de FRX, fisissorção de N2, DRX, DTP de NH3 e IV com adsorção de piridina. O desempenho catalítico das mesmas foi comparado tanto em condições reacionais similares (mesma T, pressão parcial de MeOH e WHSV) como em condições de isoconversão. Verificou-se, que quanto maior a SAR da zeólita, menor a densidade total e a força dos sítios ácidos presentes, sendo este efeito mais significativo para os sítios de Brönsted. O efeito do aumento da SAR favoreceu a estabilidade catalítica e a formação de olefinas leves, principalmente propeno. No caso das amostras contendo fósforo, foi observada uma redução linear na área específica BET e no volume de microporos com o aumento do teor de fósforo. Estes resultados, aliados aos obtidos por DRX, sugerem que a redução mais significativa na área específica e no volume de microporos pode ser associada à redução na cristalinidade e à formação de espécies amorfas contendo fósforo, que bloqueariam a estrutura porosa da zeólita. Não se observou alteração significativa na força dos sítios fracos, enquanto a força dos sítios fortes diminuiu significativamente. As amostras apresentando menor SAR e menor teor de fósforo foram mais ativas. Por outro lado, em condições de isoconversão de 916%, a amostra mais seletiva à formação de olefinas foi aquela com maior SAR. Dentre as amostras impregnadas, aquela contendo 4% de fósforo foi a mais seletiva a propeno, enquanto a que continha 6% foi mais seletiva a eteno. A amostra com SAR igual a 280 foi investigada variando-se a temperatura de reação (400, 500 e 540C) e a pressão parcial de metanol (0,038; 0,083 e 0,123 atm), através de um planejamento experimental do tipo Box-Benhnken (32). O rendimento otimizado em olefinas leves foi alcançado a 480C e 0,08 atm. O modelo proposto descreveu bem os dados experimentais e evidenciou a existência de uma faixa ótima de temperatura para maximização do rendimento em propeno e eteno, o qual foi também afetado pela pressão parcial de MeOH na faixa estudada. Palavras-chave: ZSM-5, olefinas, propeno, eteno, processo MTO, fósforo.

Sistemas SCR y NSR-SCR para DeNOx en corrientes de escape diésel: Formulaciones, cinética y modelización

314 p.

用~(29)Si固体核磁共振方法研究M—ZSM-5分子筛

杂原子ZSM-5分子筛对某些特定的催化反应具有很高的活性和选择性,因而杂原子在分子筛中的存在状态成为人们十分关注的问题,作者曾用许多结构研究方法对杂原子ZSM-5分子筛进行了表征。本文用~(29)Si MAS NMR方法研究了M-ZSM-5 (M=Ga、B、Zn、Ni)分子筛杂原子的存在状态。

贵州红枫湖沉积物-水界面Fe、Mn地球化学研究

在地球环境的界面及其附近，发生着重要的物理、化学和生物反应，进行着频繁的物质交换和输送。研究和认识环境界面的地球化学过程对揭示环境演化、评价环境净化、认识成矿机理均具重要的科学意义。Fe、Mn是地表水环境中两个丰度最大的微量营养元素，也是典型的氧化还原敏感性元素，因其氧化物的吸附特性而对其它微量元素的地球化学行为有着显著的控制作用。因此，Fe、Mn地球化学的研究历来是水环境领域中令人瞩目的一个焦点。地表水环境中Fe、Mn的研究始于海底锰结核的发现及其成因问题的探讨，而Fe、Mn在湖泊研究中受到重视则始于湖泊富营养化问题的出现。二次大战使湖泊Fe、Mn的研究一度中断，直到七十年代因水资源短缺和水环境污染问题的出现才使这一研究重新受到重视，并于近十年得到迅速发展在采样技术、分析方法、Fe、Mn的形态、氧化还原作用、早期成岩作用以及地球化学循环机理的研究上取得了一系列重要的进展。其中以英国Davison的工作最引人注目。一般认为，Fe、Mn在湖泊中的行为受氧化还原边界层的控制。但是，由于研究方法的局限，缺乏将湖水和沉积物作为一个整体的系统研究。尤其是未能对沉积物-水界面及其附近Fe、Mn的行为开展细致的工作，因此在Fe、Mn循环机理的认识上尚存许多疑点。有鉴于此，本项研究着重探讨沉积物-水界面及其附近Fe、Mn的地球化学行为和特征。利用自制的湖泊沉积物和孔隙水取样装置，分别于春秋两季在红枫湖按垂直剖面采集湖水、界面水、孔隙水和沉积物样。采用滤膜技术作湖水、界面水和孔隙水Fe、Mn的形态分析，并作沉积物Fe、Fe~(3+)、Fe~(2+)、Mn、S和孔隙水P、HCO_(3~-)、SO_4~(2-)、NO_(3~-)等项目的分析，完成湖水、界面水的水化学全分析和沉积物的X-射线衍射分析。从而获得以下结果和认识：1.形态。湖水中Fe、Mn均呈微粒态；界面水中Fe呈微粒态，Mn则以微粒态为主，尚有部分离子态；孔隙水中Fe以离子态为主，存在部分胶体态，Mn则以离子态存在。2.特征剖面。春秋季湖水中距沉积物-水界面5m以上，Fe、Mn分布均一，5m以下，Fe、Mn均向界面递增10倍左右；界面水中，Fe、Mn继续向界面递增，但Fe在距界面10cm左右向界面略有递减，同时，在距界面20cm高度Fe的溶解态出现峰值分布，而Mn的溶解态则向界面递增；孔隙水中Fe、Mn均呈峰值分布，并均于12cm深度以下趋于稳定，其中Mn峰位于3cm深度，Fe峰则位下去8cm深度，Fe在10cm深度还存在一谷值分布；沉积物中Fe于7cm深度含量略呈下降趋势，Mn则在界面出现高值，并于0.5cm深度含理突降。3.界面通量。Fe在界面的沉降通量为10.9mg.cm~(-2)a~(-1)，扩散通量为-0.24mg.cm~(-2)a~(-1)，净重通量则为10.7mg.cm~(-2)a~(-1)，扩散量只有沉降通量的2%；Mn在界面的沉降通量为0.203mg.cm~(-2)a~(-1)，扩散通量为-0.062mg.cm~(-2)a~(-1)，净通量则为0.141mg.cm~(-2)a~(-1)，扩散通量占沉降通量的30%。Fe、Mn在界面的平流通量均可忽略不计。4.氧化还原作用。Fe、Mn在沉积物中按氧化电位的高低先后充当有机质分解的主要氧化剂，发生还原溶解，然后经扩散作用重新进入湖水中，并在氧化过程的作用下于界面附近形成微粒态Fe、Mn的富集。5.平衡矿物。沉积物孔隙水中Fe(II）的平衡矿物在8-12cm深度范围内为单硫铁矿（FeS)和黄铁矿（FeS_2)，12cm深度以下为菱铁矿（FeCO_3)；Mn（II）的平衡矿物则为菱锰矿（MnCO_3)。6.界面循环机理。在湖泊中Fe、Mn循环均受沉积物-水界面的控制围绕界面进行，循环过程由还原、扩散、氧化和沉降四个环节组成，其中Mn循环就在界面附近，而Fe循环则深入沉积物内部。Mn的界面循环相当激烈，Fe则较为缓和。Fe、Mn界面循环的结果使界面附近的湖水和沉积物中出现Fe、Mn的富集，其中Fe的富集程度 相对较小，Mn则非常显著。7.环境效应。Mn的界面循环可能导致~（210）Po的沉积后再迁移，而~（210）Pb的沉积后再迁移则可能与Fe的界面循环有关；Fe、Mn界面循环所形成的富集层对湖泊水库的水质构成严重的潜在威胁；根据Fe、Mn的还原优势作用带可以确定湖泊沉积物的氧化还原环境。

Effect of variations in acid properties of HZSM-5 on the coking behavior and reaction stability in butene aromatization

In order to investigate the effect of acid properties on the coke behavior and stability of butene aromatization, we prepared the AHZSM-5 samples with various acid properties by the methods of hydrothernial treatment and K addition. The reaction of butene aromatization was carried out at 350 degrees C and 0.5 MPa in a continuous flow fixed bed. The characterization of the fresh/coked catalysts with NH3-TPD, N-2 adsorption-desorption measurement, and TG techniques has shown that a large amount of acid sites (high acid density) of the AHZMS-5 catalyst can cause a large quantity of coke deposit and serious channel blockage, and so result in a rapid loss of aromatization activity. On the contrary, after a great reduction in strong acid sites of AHZSM-5 catalyst resulting from some K-modification, the presence of only many weak acid sites also could not lessen the formation of coke nor improve the reaction stability of butene aromatization. Interestingly, the simultaneous reduction in the strong and weak acid sites to a desirable level by hydrothermal treating the AHZSM-5 catalyst at a proper temperature can effectively suppress the coke formation and channel blockage, and thus improve its olefin aromatization stability. (c) 2005 Elsevier B.V. All rights reserved.

Production of light olefins and aromatic hydrocarbons through catalytic cracking of naphtha at lowered temperature

Naphtha catalytic cracking were carried out at 650 degrees C over modified ZSM-5. Light olefins and BTX could be obtained over the catalysts. The products showed variable distribution with different catalyst modification. Some modification, such as Fe, Cu and La favored the BTX generation and P and Mg modification favored the light olefins production. In N-2 stream cracking catalyzed by LaZSM-5, more than 50% naphtha feed were converted to BTX, while in steam cracking, with an improved modified catalyst, P, La/ZSM-5, naphtha can be converted to light olefins with high activity and long-term stability.