Gallium oxide promoted zeolite catalysts for oxidehydrogenation of propane

Novel gallium-containing catalysts for oxidehydrogenation of propane, based on zeolite Beta, ZSM-5 and ferrierite, have been prepared and characterised by scanning electron microscopy, IR, MAS NMR and Raman spectroscopies. The catalytic properties of zeolitic matrixes with B, Al, and both ions at tetrahedral sites have been studied. Transformation of propane on pure zeolites and promoted with gallium (III) oxide depended on the structure of the matrix, its morphology and the type of cations occupying zeolite framework sites. Formation of new hydroxyl groups has been evidenced for some MFI zeolites promoted with Ga₂O₃.     

Structural phase evolved Ni2+-doped fluoride nanocrystals in KF−ZnF2−SiO2 glass-ceramics

Incorporation of transition-metal ions (TMIs) in the precipitated nanocrystals (NCs) of glass-ceramics (GCs) greatly improves the photonic properties of these materials. The crystal field and coordination of TMIs show fingerprints for spectroscopic characterization. However, it is difficult to probe the effect of the host NCs’ structural phase on doped TMIs’ d-d orbitals. Herein, ZnF₂:Ni and KZnF₃:Ni based on controllable crystallization in KF-ZnF₂-SiO₂:Ni²⁺ GCs were taken as model systems. Compared to ZnF₂, perovskite-type KZnF₃ has higher binding energy Zn-F bonds in which Ni²⁺ are easier to be segregated, which makes KZnF₃:Ni be better “excited electron trapper” due to hole localization to intra-gap Ni states. These findings contribute to the understanding and design of TMIs-doped GCs in practical applications.     

The influence of the initial acidity of HFER on the status of Co species and catalytic performance of CoFER and InCoFER in CH4-SCR-NO

The role of the initial acidity of ferrierite type zeolite on the status of cobalt and the catalytic activity of CoFER and InCoFER was investigated. Two FER zeolites were used: NH₄FER without any pretreatment (FER-1) and the same zeolite, dehydroxylated at 825 K (FER-2). Dehydroxylation removed most of the Si–OH–Al groups, therefore the resulting zeolite revealed practically no ion exchange capacity. The status of cobalt was followed by IR spectroscopy with probe molecules: CO (a probe for Co²⁺) and NO (a probe for Co³⁺). The introduction of cobalt by solid-state ion exchange produced divalent cobalt in exchange positions and in the form of oxide-like clusters, their respective concentration was determined by quantitative IR experiments of CO sorption. The amount of Co³⁺, present in CoFER-1 and InCoFER-1, was also determined. All these forms of cobalt were practically absent from CoFER-2 and InCoFER-2. The NO conversion and selectivity to N₂ of CoFER-2 in CH₄-SCR-NO was poor, indicating the essential role of the initial acidity of the ferrierite matrix on the formation of catalytically active Co species. The introduction of indium into CoFER only slightly increased the NO conversion and shifted the reaction path from NO₂ towards N₂ formation for FER-1, while greatly improved the catalytic performance of the FER-2 series.     

Catalytic Synthesis of 2-Methyl Pyrazine Over Zn-Modified Zeolites

Cyclization of ethylene diamine and propylene glycol to 2-methyl pyrazine (2-MP) was investigated on Zn-modified zeolites, namely ZSM-5, Beta, and ferrierite catalysts, as a function of temperature, space velocity, and feed ratio. Zn-impregnated ZSM-5 was found to be the promising catalyst with 64% selectivity for 2-MP at 450 °C. ZnO-like species on Zn-impregnated ZSM-5, identified from XPS, enhance the selectivity to 2-MP. The difference in acidity, the nature of the Zn species, and its distribution on Zn-modified ZSM-5 catalysts obtained from FT-IR and XPS are in good agreement and they are correlated with catalytic activity.     

Does Density of Cationic Sites Affect Catalytic Activity of Co Zeolites in Selective Catalytic Reduction of NO with Methane?

Selective catalytic reduction of NO with methane (CH₄-SCR) in an excess of oxygen over Co ions located in ZSM-5 of various Si/Al composition and in ferrierite, mordenite, chabazite and beta zeolite was investigated. From the comparison of the dependence of the TOF values per Co ion for NO conversion to N₂ and Co ions distribution among the cationic sites on total Co ion concentration, the catalytic activity of the individual Co ions was estimated. The -type Co²⁺ ions, located in the main channel of mordenite and ferrierite and coordinated above the rectangle of four framework oxygens of the channel wall exhibit the highest activity in these zeolites. On the other hand, the -type Co²⁺ ions coordinated in the plane of four oxygens of the deformed six-member ring located in the channel intersection of ZSM-5 and in channels of beta zeolite control the activity of these Co zeolites. The sequence of activity of Co²⁺ ions in CH₄-SCR of NO was FER Co>ZSM-5 Co>BEA CoZSM-5 CoFER CoMOR CoCHA CoMOR Co. A correlation between the activity of the individual Co ions in CH₄-SCR of NO and a distance between the cationic sites was observed.     

Experimental and theoretical approaches to the study of TMI-zeolite (TM = Fe, Co, Cu)

Transition metal ions in zeolites TMI-zeolite (TM = Fe, Co, Cu) attract great attention due to their potentialities as catalysts. In the recent years, the high efficiency of TMI-zeolites for the selective catalytic reduction (SCR) of contaminated flue gases has been demonstrated. It has been shown that the structure of the framework, the nature and location of extraframework cation species play a fundamental role in the process. Experimental results based on spectroscopies, as well as on reactivity studies have led to valuable insights about the structure of cationic sites as well as about the active species involved during the catalytic reactions. However, it is not sufficient to obtain all this information. This review reporting density functional theory (DFT) calculations shows that a molecular approach is very useful and has become an indispensable tool for the determination of the geometries, the electronic structures, the spectroscopic properties and the reactivity of TMI-zeolites.     

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.     

Effect of Co content on the catalytic activity of CoSiBEA zeolite in the selective catalytic reduction of NO with ethanol: Nature of the cobalt species

The effect of Co content on the catalytic activity of CoSiBEA zeolites in the selective catalytic reduction (SCR) of NO with ethanol is investigated. The Co_xSiBEA zeolites (x = 0.3, 0.7, 3.6 and 6.75 Co wt.%) are prepared by a two-step postsynthesis method which allows to control the introduction of cobalt into zeolite and thus to obtain catalysts with specific Co sites. The nature of the active sites is characterized by XRD, diffuse reflectance UV–vis, H₂-TPR and XPS.

The catalytic activity of Co_xSiBEA strongly depends on the nature and environment of Co species. Zeolites with isolated lattice tetrahedral Co(II) (Co_0.3SiBEA and Co_0.7SiBEA samples) are active in SCR of NO with ethanol with selectivity toward N₂ exceeding 85% for NO conversion from 20 to 70%. When additional isolated extra-lattice octahedral Co(II) species appear (Co_3.6SiBEA sample), the full oxidation of ethanol by dioxygen becomes a very important reaction pathway. In presence of additional cobalt oxides (Co_6.75SiBEA sample), the activity and selectivity toward N₂ substantially change and full oxidation of ethanol to CO₂ is the main reaction pathway and full NO oxidation also takes place in the temperature range 550–775 K. The lack of correlation between the activity in SCR of NO with ethanol and NO oxidation to NO₂ suggests that the two reactions are more competitive than sequential.     

A comparative study on liquid phase alkylation of 2-methylnaphthalene with long chain olefins using different solid acid catalysts

A comparative study has been made over a variety of solid acid catalysts, which include isopoly and heteropoly ions supported on various supports such as zirconia, titania, a large variety of zeolites and a couple of mesoporous materials for liquid phase alkylation of 2-methylnaphthalene with 1-octene. All the catalyst systems were characterized by nitrogen sorption analysis, X-ray diffraction and NH₃-TPD. Inspite of their high acid amounts zeolites gave poor catalytic performance due to their diffusional constraints; on the other hand mesoporous materials lacked diffusional constraints but due to their low acid amounts resulted in poor conversions. Isopoly and heteropoly ions supported on zirconia and titania were found to be catalytically active for the reaction due to total surface acidity. Among them, isopolytungstate supported on zirconia exhibited the best catalytic activity and was used for further optimization of reaction conditions. Excellent conversions of all olefins (>92%) with high selectivity of monoalkylmethylnaphthalene (>95%) was obtained under optimized reaction conditions. The catalyst could be recycled for several times without any obvious loss of its activity.     

NANOCAVITY EFFECTS ON N2O DECOMPOSITION ON DIFFERENT TYPES OF FE-ZEOLITES (Fe-FER,Fe-BEA,Fe-ZSM-5 AND Fe-FAU): A COMBINED THEORETICAL AND EXPERIMENTAL STUDY

Nitrous oxide decomposition on iron-exchanged zeolites (Fe-FER, Fe-ZSM-5, Fe-BEA, and Fe-FAU) has been studied both theoretically, by using the ONIOM (B3LYP/6-31G(d,p):UFF) method, and experimentally, by temperature programmed reaction, to determine the effect of different zeolitic nanostructured pore networks on the catalytic activity. The ONIOM quantum mechanical calculations show that the nitrous oxide molecule adsorbs with slightly stronger interactions energies on Fe-FER and Fe-ZSM-5 than on the larger pore Fe-BEA and Fe-FAU zeolites. In the transition state leading to the decomposition of nitrous oxide, the smallest pore ferrierite zeolite exerts the strongest van der Waals interactions on the reacting species and, thus, results in the lowest activation energy. Therefore, the predicted intrinsic activity trend is Fe-FER > Fe-BEA ～ Fe-ZSM-5 ～ Fe-FAU. On the other hand, the temperature programmed reaction on zeolites containing trace amounts of iron impurities shows an observed activity trend of Fe-FER > Fe-BEA > Fe-ZSM-5 > > Fe-FAU. The experimentally observed activity trend can be explained by the intrinsic activity of each zeolite except for Fe-FAU. Nitrous oxide decomposition in Fe-FAU could be limited by the mass transfer process and not governed by the intrinsic activity. It is known that cations are preferentially located on the six-membered ring in the sodalite cage of the faujasite, to which the reactants have a very limited access.     

微波辐射加热金属离子改性Hβ分子筛催化合成蒽醌

在微波辐射加热下用不同金属离子(Al3+、Ti4+、Fe3+)对Hβ分子筛进行改性,并将其用于催化苯与苯酐合成蒽醌。采用XRD、NH3-TPD和吡啶-IR对分子筛进行了表征。结果表明,微波辐射加热能提高分子筛的改性效率,改善其催化性能,且对分子筛晶体结构没有破坏作用。不同金属离子改性分子筛的催化效果差别很大,其中,0.5 mol/L的Al2(SO4)3溶液改性的Hβ分子筛催化效果最好,蒽醌产率38.87%,选择性92.78%。分子筛的表面酸性质对其催化性能有较大影响,催化剂表面的中强度酸是催化活性中心,L酸量与B酸量的比值对分子筛的催化性能有重要影响。     

Catalytic skeletal isomerization of linear butenes to isobutene

The increased demand for isobutene, used for the production of the octane-enhancer methyl tert-butyl ether, has generated tremendous interest in the catalytic conversion of the linear butenes to isobutene. In this review we survey the progress made since the late 1970s in implementing the catalytic skeletal isomerization reaction of these linear alkenes. Halogenated catalysts, especially those based on alumina, and prepared using a variety of compounds of fluorine, chlorine or bromine, have been shown to exhibit both high conversions and selectivities for the reaction, resulting in high yields of isobutene, when water is added to the feed stream. Elution of the halogen from the catalyst leads to the loss of catalytic activity and necessitates the continuous or discontinuous addition of the halogen compound. As a consequence, environmental and other considerations are most likely to weigh against the industrial usage of these catalysts. Another class of catalysts exhibiting high activities and selectivities, again in the presence of water, are the silicated aluminas. No information is, however, available on their long-term stability. Even alumina on its own displays high activity and selectivity, provided water is co-fed with the hydrocarbon stream. More recent results obtained over other types of catalysts such as zeolites and molecular sieves are also presented. Most promising are the results obtained with the zeolite ferrierite which gives high yields of the branched isomer in the absence of any other additive or diluent. The catalyst also appears to be fairly stable showing no decrease in the yield of isobutene after 14 days on-stream. The high yields of isobutene can be ascribed to the small channel diameters which prevent the extensive dimerization or oligomerization of the linear butenes or of the product isobutene. Plans for the first large-scale demonstration plant to produce isobutene from n-butenes using ferrierite as catalyst have already been announced in the United States.     

Catalytic activity of faujasite-type zeolites towards the claus reaction

Commercial NaY and NaX zeolites showed significant catalytic activity towards the Claus reaction. Bronsted acidity retarded the catalytic activity to a much greater extent than Lewis acidity. Electron Spin Resonance (ESR) spectroscopic studies indicated the formation of SO₂^? anion radicals on the catalyst surface upon SO₂ adsorption. The reactivity of SO₂^? towards H₂S depended upon many factors. When the electron donating property of NaX was increased by impregnation with a small amount of NaOH, the Claus activity was enhanced and the activity of NaX containing 2.0 wt% NaOH was similar to that of a commercial Claus alumina catalyst. Infrared (IR) spectroscopic studies indicated physical and dissociative adsorption of H₂S; SO₂ was found to chemisorb on the zeolites.     

Selective preparation of light aromatic hydrocarbons from catalytic fast pyrolysis vapors of coal tar asphaltene over transition metal ion modified zeolites

The catalytic cracking of coal tar asphaltene (CTA) pyrolysis vapors was carried out over transition met-alion modified zeolites to promote the generation of light aromatic hydrocarbons (L-ArHs) in a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) micro-reactor system.The effects of ultra stable Y(USY),Co/USY and Mo/USY on the selectivity and yield of L-ArHs products and the extent of deoxygena-tion (Edeoxygenation),lightweight (Elightweight) from CTA pyrolysis volatiles were investigated.Results showed that the yields of L-ArHs are mainly controlled by the acid sites and specific surface area of the catalysts,while the deoxygenation effect is determined by theirs pore size.The Elightweight of CTA pyrolysis volatiles over USY is 9.65％,while the Edeoxygenation of CTA pyrolysis volatiles over Mo/USY reaches 20.85％.Additionally,the modified zeolites (Mo/USY and Co/USY) exhibit better performance than USY on L-ArHs production,owing to the synergistic effect of metal ions (Mo,Co) and acid sites of USY.Compared with the non-catalytic fast pyrolysis of CTA,the total yield of L-ArHs obtained over USY (4032 mg·kg-1),Co/USY (4363 mg·kg-1) and Mo/USY (4953 mg·kg-1) were increased by 27.03％,38.19％ and 54.78％,respectively.Furthermore,the possible catalytic conversion mechanism of transition metal ion (Co and Mo) modified zeolites was proposed based on the distribution of products and the characterizations of catalysts.     

Effect of noble metals in the decomposition of nitrous oxide over Fe-ferrierites

The decomposition of nitrous oxide was studied over Fe-ferrierite, Me-ferrierites and Fe/Me-ferrierites (Me: Pt, Rh and Ru). Flow as well as batch experiments were carried out and showed a synergy between Fe and Me ions. Ions of noble metals in Fe-ferrierite increased the catalytic activity in the sequence Pt < Rh ≅ Ru. Addition of NO substantially decreased the decomposition of N₂O over Rh/ferrierite and Ru/ferrierite, but not over bimetallic ferrierites. NO _x species created during the decomposition of nitrous oxide alone as well as with addition of NO, and employment of nitrous oxide labeled with ¹⁸O allowed us to assume a changing decomposition mechanism in the presence of Me ions in Fe-ferrierites.     

Catalytic combustion of methane over palladium exchanged zeolites

Palladium cation exchanged zeolites (ZSM-5, mordenite and ferrierite) were studied as catalysts for methane combustion. Pd-zeolites showed much higher activities than PdO/Al₂O₃. For comparable palladium loadings, PdO/Al₂O₃ requires a reaction temperature of ca. 70–80°C higher than Pd-ZSM-5 for conversions between 50–100%. The catalytic activity of Pd-ZSM-5 seems to be related to its reducibility. Temperature-programmed reduction experiments with carbon monoxide showed a lower reduction temperature (ca. 157°C) for Pd-ZSM-5 than for PdO/Al₂O₃ (225°C). Further, the positioning of the palladium by ion exchange offers a highly dispersed form of Pd^II supported on the high surface area zeolite.     

New strategy of creation of local catalytic sites in definite electronic and coordination states

Atomic-scale engineering of catalytic functions of isolated redox sites in confined environments of zeolitic channels is proposed as a new approach to the investigation of structure-properties relationship in heterogeneous ‘biomimetic’ catalysis. It is shown that the design of such catalysts, on the base of high-silica zeolites, containing isolated transition-metal cations as active redox sites, may present promising opportunities for creation of new types of contacts from a practical point of view. A detailed analysis of transition-metal cation incorporation into high-silica zeolites by either conventional or solid-state exchange is given. Stabilization of one or several transition-metal ions by matrices of high-silica zeolites (mainly H-ZSM-5) is discussed. The influence of different factors on the processes of cationic-species stabilization is analyzed. These data are correlated with the results of catalytic testing in reactions of total oxidation of hydrocarbons (HC), direct decomposition of NO_x and SCR of NO_x by HC. The relationship between catalytic activity and selectivity of cationic sites and their coordination and electronic state, regulated by either thermal treatment or introduction of different anionic ligands, is analyzed.     

On the estimation of average crystallite size of zeolites from the Scherrer equation: A critical evaluation of its application to zeolites with one-dimensional pore systems

This article presents an overview of the application of the Scherrer equation and Williamson–Hall analysis for the approximation of crystallite sizes of zeolites. Special emphasis is placed on the proper selection of hkl reflections for estimating a particular dimension of a specimen with anisotropic crystals. Crystal sizes of zeolites with one-dimensional pores (such as ZSM-12, ZSM-48, ferrierite, or Theta-1) are especially prone to misreporting or error from a direct application of the Scherrer equation. We have collected synchrotron powder diffraction data on a group of MTT-type zeolites of varying morphologies. For typical values of strain we have determined for these zeolites, we find that large crystal lengths can be underestimated by orders of magnitude when the effects of stress are not (or cannot be) included in the analysis.     

Methane Combustion over Pd Catalysts Loaded on Medium and Large Pore Zeolites

Methane combustion was conducted over Pd catalysts supported on medium (ZSM-5, ferrierite, TNU-9, TNU-10) and large (USY, mordenite, beta) pore zeolites. Among the catalysts studied here, Pd/H-TNU-10 exhibited the highest combustion activity, together with excellent durability in the presence of water vapor. A combination of TEM and Pd K-edge XAFS measurements reveals the formation of highly dispersed PdO particles within the TNU-10 pores. This is also the case of Pd/H-ferrierite, while frequently there are large particles (60–100 Å) on its outer surface. In contrast, most of PdO on zeolites other than these two medium pore materials were found to exist as aggregated particles (>50 Å) on their outer crystallite surface. It appears that zeolite structures with intersecting 10- and 8-ring pores may be better supports for stabilizing nanometric PdO particles than those with the uniform 10-ring size or with the 12-ring pore system.