Selective partial oxidation of light paraffins with hydrogen peroxide on thin-layer supported Nafion-H catalysts

Thin-layer carbon supported Nafion-H catalysts were found to be active and highly selective (S>98%) for the partial oxidation of C₁-C₃ alkanes, in a three phase catalytic membrane reactor (3PCMR), under mild conditions and in the presence of H₂O₂. The influences of the catalyst teflon loading and H₂O₂ concentration on the reaction rate have been evaluated. A reaction pathway, based on the electrophilic hydroxylation of the C-H bond of alkanes with protonated hydrogen peroxide (H₃O ₂ ⁺ ), is discussed.     

Hydrogen transfer and activation of propane and methane on ZSM5-based catalysts

Hydrogen exchange between undeuterated and perdeuterated light alkanes (CD₄-C₃H₈, C₃D₈-C₃H₈) occurs on H-ZSM5 and on Ga- and Zn-exchanged H-ZSM5 at 773 K. Alkane conversion to aromatics occurs much more slowly because it is limited by rate of disposal of H-atoms formed in C-H scission steps and not by C-H bond activation. Kinetic coupling of these C-H activation steps with hydrogen transfer to acceptor sites (Ga ⁿ⁺, Zn ^m+) and ultimately to stoichiometric hydrogen acceptors (H⁺, CO₂,O₂, CO) often increases alkane activation rates and the selectivity to unsaturated products. Reactions of¹³ CH₄/C₃H₈ mixtures at 773 K lead only to unlabelled alkane, alkene, and aromatic products, even though exchange between CD₄ and C₃H₈ occurs at these reaction conditions. This suggests that the non-oxidative conversion of CH₄ to higher hydrocarbons on solid acids is limited by elementary steps that occur after the initial activation of C-H bonds.     

Etude voltamperometrique de la n-acetyl l-tyrosine amide sur electrode a pate de graphite en milleux aqueux I—comportement dans les domaines de balayage superieurs a 0,5 v/enh

Graphite paste electrode allows to determine elementary processes of the electrochemical oxidation in aqueous media of an electrochemical probe such as: N-acetyl L-tyrosine amide. Mathematical analysis of voltammograms gives the following EC mechanism: R?C₆H₅OH?R?C₆H₅O^. + H⁺ + e 2 R?C₆H₅O^. → R?C₆H₅O⁺ + R?C₆H₅O^?, R?C₆H₅O^? + H⁺ → R?C₆H₅OH, R?C₆H₅O⁺ → [R?C₆H₄O]^.. + H⁺, n[R?C₆H₄O]^.. → ?[R?C₆H₄O]^?_n.     

Influence of operating protocol in the temperature-programmed reaction of NO with decane on Cu/mordenite

A Cu/mordenite catalyst was prepared by ion exchange and characterized by N₂ Sorption, XRD, TPR by H₂ and TPD by NO. The catalyst was evaluated in the selective catalytic reduction of NO by decane in O₂-rich atmosphere under temperature-programmed reaction from 293 to 773 K. Two NO reduction profiles at 590 and 650 K occur under these conditions. By testing different operating protocols and different alkanes as reductants, it was concluded that the low temperature peak (590 K) is due to alkane condensed in the porosity of mordenite.     

Selectivity-determining role of C3H8/NO ratio in the reduction of nitric oxide by propane in presence of oxygen over ZSM5 zeolites

The reaction of (NO + C₃H₈ + O₂) can result in selective formation of NO₂ over H-ZSM5, Cu,H-ZSM5, Ag,H-ZSM5, and Li,H-ZSM5 catalysts when the concentrations of NO and O₂ are 0.1 and 9%, SV > 60,000 h⁻¹ (typical for automotive exhausts), and C₃H₈/NO > 1. Despite stoichiometric excess of reductant hydrocarbon below this limit, the in situ formed NO₂ does not react with C₃H₈, thus conversion of NO to N₂ is negligible. NO can be reduced by C₃H₈ selectively to N₂ only when C₃H₈/NO ≧ 1. Contrary to many suggestions the reaction temperature, concentration of oxygen, space velocity, and type of exchange ions have minor influence on the selectivity for N₂. These parameters affect the rates of reactions (NO + ₂), (C₃H₈ + NO_x) and (C₃H₈ + O₂), therefore they also affect the production of N₂ in the HC-SCR process, but only when the ratio of C₃H₈/NO permits. The metal-exchanged zeolites were prepared in situ by solid-state ion exchange from H-ZSM5. Despite the low degree of copper exchange (63%), Cu,H-ZSM5 produces substantially more N₂ than H-ZSM5, Ag,H-ZSM5, or Li,H-ZSM5. However, the selectivity for N₂ is lowest over Cu,H-ZSM5, which also produces considerable NO₂ in the reaction of (NO + C₃H₈ + O₂) even at C₃H₈/NO ≧ 1. Contrary to prior findings, the catalytic activity of Cu,H-ZSM5 for the oxidation of NO by O₂ to NO₂ in absence of hydrocarbon was comparable to that of H-ZSM5 at high space velocities (2.3 l g⁻¹ min⁻¹). By replacing 30 and 40% of the protons of H-ZSM5 by Ag⁺ and Li⁺ ions in Ag,H-ZSM5 and Li,H-ZSM5, respectively, the catalytic activity for this reaction becomes negligible at temperatures ≧100°C. Some mechanistic consequences of these experimental observations are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

NO2 formation and its effect on the selective catalytic reduction of NO over Co/ZSM-5

Catalytic performance of Co/ZSM-5 with different metal loadings and of HZSM-5 was compared in the NO + O₂, C₃H₈ + O₂, and NO + C₃H₈ + O₂ reactions. It was found that Co/ZSM-5 catalysts containing only isolated cobalt ions in cationic positions are inactive in NO₂ formation. To achieve appreciable NO conversion in the SCR process over these catalysts higher reaction temperatures are required. These results make it possible to suggest that NO₂ formation is not a prerequisite for the SCR of NO with hydrocarbons over Co/ZSM-5. With increasing Co loading, however, Co/ZSM-5 begins to exhibit activity in NO₂ formation. This is explained by the formation of cobalt oxide particles on the zeolite carrier, which are active in the NO₂ formation. Increase in NO₂ formation strongly enhances catalytic activity in SCR of NO at lower reaction temperatures. Comparison of the C₃H₈ conversion in the C₃H₈ + O₂ and C₃H₈ + O₂ + NO reactions provides evidence that NO₂ activates hydrocarbon molecules resulting in the formation of the reaction intermediates of the SCR process.On leave from N.D. Zelinskii Institute of Organic Chemistry, Leninskii Pr. 47, Moscow, Russia.     

Dimerization of Terminal Arylalkynes in Aqueous Medium by Ruthenium and Acid Promoted (RAP) Catalysis: Acetate‐ Assisted (sp)C?(sp2)C Bond Formation

The hexamethylbenzene ruthenium(II) dimer [{RuCl(μ‐Cl)(η⁶‐C₆Me₆)}]₂ (5 mol%), tested among a series of ruthenium(II) and ruthenium(IV) complexes, represents an efficient precatalyst source for the dimerization of terminal arylalkynes ArCCH [Ar=C₆H₅, 3,4,5‐(OMe)₃C₆H₂, 4‐MeOC₆H₄, 2‐MeOC₆H₄, 4‐MeC₆H₄, 2,4,5‐Me₃C₆H₂, 4‐BrC₆H₄, 4‐ClC₆H₄, 4‐FC₆H₄, 4‐HC(O)C₆H₄, 4‐CH₂CHC₆H₄, 3‐NCC₆H₄, 4‐O₂NC₆H₄, 4‐EtO₂C‐(CH₂)₃OC₆H₄, 4‐HO(CH₂CH₂O)₃C₆H₄, 3‐HO(CH₂CH₂O)₃‐C₆H₄] in acetic acid/water mixture (1:1, v/v). The reactions proceed for 24 h at room temperature under heterogeneous conditions and afford the dimeric enyne derivatives (E)‐Ar CHCH CC Ar in high yields and stereoselectivity. The preformed acetato complex [RuCl(η⁶‐C₆Me₆)(κ²‐OAc)] catalyzes the dimerization of phenylacetylene under analogous conditions, with rapid substrate conversion. The presence of cosolvents of acetic acid different from water reduces dramatically the efficiency and selectivity of the reaction. The aqueous medium facilitates the activation stage of the precatalyst by assisting the splitting of the ruthenium dimer. The addition or generation in situ of acetate salts results in shorter reactions times (0.5–3 h) and excellent yields, due to the rapid formation of active acetato complexes. Circumstantial evidence indicates that the π‐bound alkyne molecule is activated by intramolecular proton abstraction. This is currently the most efficient, E‐selective and wide‐scope catalytic system for the alkyne dimerization reaction in protic aqueous media.     

Syntheses and Characterization of 1D, 2D and 3D Organotin Polymers with Benzimidazole-5,6-dicarboxylic Acid and Trimethyltin Chloride

Three types of di- and trimethyltin(IV) polymers [Me₂Sn(C₉H₄N₂O₄)]_n · 4H₂O 1, [(Me₃Sn)₂(C₉H₄N₂O₄)]_n · H₂O 2 and [(Me₃Sn)₂(C₉H₄N₂O₄)]_n · CH₃OH 3 have been synthesized by the reaction of trimethyltin chloride with benzimidazole-5,6-dicarboxylic acid under three different experimental conditions. All the complexes were characterized by elemental analysis, IR, NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopy and X-ray crystallography diffraction analysis. The structure analyses reveal that complex 1 has a 1D helical chain in which benzimidazole-5,6-dicarboxylic acid act as a tetradentate (O,O-chelation) ligand coordinating to dimethyltin (IV) ions, two water molecules take part in the coordination giving seven-coordinated tin centers in the component. Complex 2 and 3 are 2D and 3D corrugated polymers in which the deprotoned acid as tetradentate ligand affords by three oxygen atoms and a nitrogen atom.     

Syntheses and Crystal Structures of Di- and Trimethyltin Carboxylates: Ladders and 1D Zig–Zag Chains Polymers

A series of organotin(IV) carboxylates complexes; namely, [(Me₂Sn)₄O₂(RCOO)₄] (R = C₁₂H₁₅ 1, C₉H₁₁ 2, C₈H₈ClO 3, C₇H₉ 4) and [Me₃(RCOO)]_n (R = C₁₂H₁₅ 5, C₉H₁₁ 6, C₈H₈ClO 7, C₇H₉ 8) have been synthesized. All complexes were characterized by elemental analysis, FT-IR, and NMR (¹H, ¹³C and ¹¹⁹Sn) spectroscopy. Among them, the structures of complexes 1–3 and 5–8 were also determined by X-ray crystallography. The structural analysis showed that complexes 1–3 are the same tetranuclear monomer, and complexes 5–8 are the same 1D zigzag chain coordination polymer. Furthermore, each complex 1, 2 and 3, can form a supramolecular chain through weak intermolecular interactions.     

Decomposition of Carboxylic Acids in Water by O3, O3/H2O2, and O3/Catalyst

This paper studies the decomposition of formic, oxalic and maleic acids by O₃, O₃/catalyst, and O₃/H₂O₂. The catalytic effect of Co²⁺, Ni²⁺, Cu²⁺, Mn²⁺, Zn²⁺, Cr³⁺, and Fe²⁺ ions is investigated. The results showed that—Co²⁺ and Mn²⁺ have the highest catalytic activity for the decomposition of oxalic acid while the catalytic effect of the studied ions is insignificant on the rate of decomposition of formic acid. Maleic acid decomposes by ozone into formic acid and glyoxylic acid, which subsequently oxidizes to oxalic acid. Though the studied ions have no effect on the decomposition of maleic acid, they have a significant effect on the produced oxalic and glyoxylic acids. In the presence of Cu²⁺ ions glyoxylic acid is mainly transformed into formic acid and traces of oxalic acid. In such case, a complete decomposition of maleic acid and its degradation products is achieved within 45 min. The results also show that combining H₂O₂ with O₃ results in an increase in the rate of decomposition of oxalic acid. However, O₃/H₂O₂ system is less active than O₃/Co²⁺ or O₃/Mn²⁺.     

Design of New Functional Materials Based on Complex Oxides with a Tunnel Structure of the Ramsdellite, Hollandite, and Ba2Ti9O20 Types

The phase relationships in binary, ternary, and more complex Me ₂ ⁺O–Me ²⁺O–Me ₂ ³⁺O₃–Me ⁴⁺O₂–TiO₂ systems (Me ⁺ = Li⁺, K⁺, Rb⁺, Cs⁺; Me ²⁺ = Mg²⁺, Sr²⁺, Ba²⁺, Zn²⁺; Me ³⁺ = Al³⁺, Fe³⁺, Ga³⁺; Me ⁴⁺ = Sn⁴⁺, Zr⁴⁺) are investigated in the concentration regions corresponding to the compositions of titanates with a tunnel structure: Li₂(Me ²⁺,Me ³⁺) _y (Me ⁴⁺,Ti)₄O₈ ramsdellites, (Me ⁺,Me ²⁺) _x (Me ²⁺,Me ³⁺) _y (Me ⁴⁺,Ti)₈O₁₆ hollandites, and (Ba,Me ²⁺)₂(Me ⁴⁺,Ti)₉O₂₀ phases. The homogeneity regions of the solid solutions with the above structures are determined, and their crystal chemical characteristics, phase transformations, and thermal and electrical properties are studied. The results obtained and the data available in the literature are analyzed and generalized. The general approaches to the prediction of changes in the structure and properties of the studied titanates with a variation in the chemical composition due to isomorphous substitutions in different structural positions of the crystal lattice are discussed.     

Oxidation of cyclopentene catalyzed by phosphotungstic quaternary ammonium salt catalysts

A series of phosphotungstic quaternary ammonium salts, Q₃ (PW₁₂O₄₀) and Q₃(PW₄O₁₆) [Q = (C₅H₅)N⁺(C₁₆H₃₃), (C₁₆H₃₃)N⁺(CH₃)₃, (C₄H₉)₄N⁺, and (CH₃)₄N⁺], were used as the catalysts in oxidation of cyclopentene. The catalysts [(C₅H₅)N(C₁₆H₃₃)]₃(PW₄O₁₆) and [(C₁₆H₃₃)N(CH₃)₃]₃(PW₄O₁₆) showed high catalytic activity in the selective oxidation of cyclopentene while using H₂O₂ (50%) as an oxidant and 2-propanol as a solvent. The oxidation products mainly consisted of glutaraldehyde, cis-1,2-cyclopentanediol and trans-1,2-cyclopentanediol. The above-mentioned two catalysts were dissolved completely in the reaction medium during the catalysis process and precipitated themselves from the reaction system after reaction, showing the characteristics of reaction-controlled phase-transfer catalysis. The types of quaternary ammonium cations and the phosphotungstic anions in phosphotungstic quaternary ammonium salts affected catalytic activity.     

Decamethylosmocene-catalyzed efficient oxidation of saturated and aromatic hydrocarbons and alcohols with hydrogen peroxide in the presence of pyridine

Decamethylosmocene, (Me₅C₅)₂Os (1), is a pre-catalyst in a very efficient oxidation of alkanes with hydrogen peroxide in acetonitrile at 20–60 °C. The reaction proceeds with a substantial lag period that can be reduced by the addition of pyridine in a small concentration. The lag period can be removed if 1 is incubated with pyridine and/or H₂O₂ in MeCN prior to the alkane oxidation. Alkanes, RH, are oxidized primarily to the corresponding alkyl hydroperoxides, ROOH. Turnover numbers attain 51,000 in the case of cyclohexane (maximum turnover frequency was 6000 h^?1) and 3600 in the case of ethane. The oxidation of benzene and styrene also occurs with a lag period to afford phenol and benzaldehyde, respectively. A kinetic study of cyclohexane oxidation and selectivity parameters (measured in the oxidation of n-heptane, methylcyclohexane, isooctane, cis- and trans-dimethylcyclohexanes) indicates that the oxidation of saturated, olefinic, and aromatic hydrocarbons proceeds with the participation of hydroxyl radicals. The 1/H₂O₂/py/MeCN system also oxidizes 1-phenylethanol to acetophenone.     

Notable Effects of Aluminum Alkyls and Solvents for Highly Efficient Ethylene (Co)polymerizations Catalyzed by (Arylimido)‐ (aryloxo)vanadium Complexes

The effects of both Al cocatalyst and solvent on catalytic activity in the ethylene polymerization by the (arylmido)(aryloxo)vanadium(V) complex, VCl₂(N‐2,6‐Me₂C₆H₃)(O‐2,6‐Me₂C₆H₃) ( 1 ), have been explored in detail. The activity of 5.84×10⁵ kg PE/mol V⋅h (TOF 2.08×10⁷ h⁻¹) has been achieved by 1 /EtAlCl₂ catalyst in CH₂Cl₂ at 0 °C, and the activity in toluene increased in the order: i‐Bu₂AlCl>EtAlCl₂>Me₂AlCl>Et₂AlCl> Et₂Al(OEt), AlEt₃, AlMe₃ (negligible activities). Both aluminum alkyl cocatalyst and solvent also affected the catalytic activity and the norbornene (NBE) incorporation in the ethylene/NBE copolymerization using complex 1 , whereas the NBE contents were not strongly affected by the kind of aryl oxide ligand in VCl₂(N‐2,6‐Me₂C₆H₃)(OAr) [OAr=O‐2,6‐Me₂C₆H₃ ( 1 ), O‐2,6‐i‐Pr₂C₆H₃ ( 2 ), O‐2,6‐Ph₂C₆H₃ ( 3 )].     

Catalytic reactions of dioxygen with ethane and methane on platinum clusters: Mechanistic connections,site requirements,and consequences of chemisorbed oxygen

C₂H₆ reactions with O₂ only form CO₂ and H₂O on dispersed Pt clusters at 0.2–28 O₂/C₂H₆ reactant ratios and 723–913 K without detectable formation of partial oxidation products. Kinetic and isotopic data, measured under conditions of strict kinetic control, show that CH₄ and C₂H₆ reactions involve similar elementary steps and kinetic regimes. These kinetic regimes exhibit different rate equations, kinetic isotope effects and structure sensitivity, and transitions among regimes are dictated by the prevalent coverages of chemisorbed oxygen (O^*). At O₂/C₂H₆ ratios that lead to O^*-saturated surfaces, kinetically-relevant CH bond activation steps involve O^*O^* pairs and transition states with radical-like alkyls. As oxygen vacancies (¹) emerge with decreasing O₂/alkane ratios, alkyl groups at transition states are effectively stabilized by vacancy sites and CH bond activation occurs preferentially at O^** site pairs. Measured kinetic isotope effects and the catalytic consequences of Pt cluster size are consistent with a monotonic transition in the kinetically-relevant step from CH bond activation on O^*O^* site pairs, to CH bond activation on O^** site pairs, to O₂ dissociation on ^** site pairs as O^* coverage decrease for both C₂H₆ and CH₄ reactants. When CH bond activation limits rates, turnover rates increase with increasing Pt cluster size for both alkanes because coordinatively unsaturated corner and edge atoms prevalent in small clusters lead to more strongly-bound and less-reactive O^* species and lower densities of vacancy sites at nearly saturated cluster surfaces. In contrast, the highly exothermic and barrierless nature of O₂ activation steps on uncovered clusters leads to similar turnover rates on Pt clusters with 1.8–8.5 nm diameter when this step becomes kinetically-relevant at low O₂/alkane ratios. Turnover rates and the O₂/alkane ratios required for transitions among kinetic regimes differ significantly between CH₄ and C₂H₆ reactants, because of the different CH bond energies, strength of alkylO^* interactions, and O₂ consumption stoichiometries for these two molecules. Vacancies emerge at higher O₂/alkane ratios for C₂H₆ than for CH₄ reactants, because their weaker CH bonds lead to faster scavenging of O^* and to lower O^* coverages, which are set by the kinetic coupling between CH and OO activation steps. The elementary steps, kinetic regimes, and mechanistic analogies reported here for C₂H₆ and CH₄ reactions with O₂ are consistent with all rate and isotopic data, with their differences in CH bond energies and in alkyl binding, and with the catalytic consequences of surface coordination and cluster size. The rigorous mechanistic interpretation of these seemingly complex kinetic data and cluster size effects provides useful kinetic guidance for larger alkanes and other catalytic surfaces based on the thermodynamic properties of these molecules and on the effects of metal identity and surface coordination on oxygen binding and reactivity.     

Dehydrocyclization of Alkanes Over Zeolite-Supported Metal Catalysts: Monofunctional or Bifunctional Route

The direct catalytic conversion of alkanes into aromatics has found potentially important industrial applications. Initially only alkanes with 6 and more carbon atoms in the chain were concerned. Supported platinum catalysts were found active for the aromatization of alkanes; the drawbacks of these catalysts were their deactivation with time on stream and the existence of simultaneous parallel reactions. Much discussion has been published on the aromatization of C₆₊ alkanes. A bifunctional mechanism which involves both the metal and the acid sites of the support and a monofunctional mechanism involving only the metallic sites operate over, respectively, Pt supported on acidic support and Pt supported on nonacidic support. In the present review the mechanisms proposed for the aromatization of alkanes are described. Over monofunctional Pt catalysts two possible mechanisms prevail: 1,6 ring closure on the Pt surface involving primary and secondary C-H bond rupture, followed by dehydrogenation of the cycloalkanes into aromatics (1,5 ring closure to a lesser extent also contributes to aromatic production); or dehydrogenation of the alkanes into olefins, dienes, and trienes followed by thermal ring closure. Zeolites were found most suitable as support for preparing catalysts more active and more selective in the alkane aromatization. In addition catalysts based on noble metals supported on zeolite appeared more resistant against deactivation by coke. In this review the aromatization of hexane, heptane, and octane over Pt-zeolite catalysts is discussed in detail. Comparisons between different zeolite structures and different dehydrogenation sites are given. In particular a critical analysis of the results and interpretation concerning Pt-KL catalysts strongly suggests that the exceptional high selectivity towards aromatization of n-hexane exhibited by Pt-KL could not be explained by only the nest or constraint effect exerted by the channel dimension and morphology, not by only the terminal cracking properties, not by only the partial electron transfer from the zeolite support to the Pt particles, and not by only the Pt particle size. Zeolite structure also affects the aromatic product distribution, in particular when the alkane contains more than 7 carbon atoms. It is shown how Pt on medium-pore zeolites such as In-ZSM-5, silicalites will favor the aromatization of C₈ alkane isomers into ethylbenzene-styrene with respect to other C₈ aromatics. Aromatization of light alkanes, C₂-C₅, requires the increase of the hydrocarbon chain length up to 6 carbon atoms and higher, followed by cyclization reaction. Recently new processes to convert C₂-C₅ alkanes into aromatics have been disclosed, M2-forming from Mobil, Cyclar from BP-UOP, and Aroforming from IFP-Saluted. In general these processes use bifunctional catalysts possessing a dehydrogenating and an acid function. The catalysts consist of a metal ion or metal oxide supported on a microporous acid solid. In this review we analyze the results concerning mainly platinum supported on pentasil-type zeolite. It is shown that althoug Pt has better dehydrogenating properties as compared with gallium and zinc, the efficiency of catalysts based on Pt-ZSM-5 for light alkane aromatization is less because undersirable reactions such as hydrogenolysis and ethene (olefins) hydrogenation occur on the platinum surface, resulting in the production of unreactive alkanes, CH₂, C₂H₆. These drawbacks could be partially suppressed by alloying Pt and by increasing the reaction temperature.     

On the influence of the acid-base character of catalysts on the oxidative dehydrogenation of alkanes

Vanadium oxides supported on metal oxide, i.e. Al₂O₃, MgO and Mg-Al mixed oxide, and V-containing microporous materials (VAPO-5 and MgVAPO-5) have been tested in the oxidative dehydrogenation of C₂-C₄ alkanes. In all cases, tetrahedral vanadium species (isolated and/or associated) were mainly observed from⁵¹V-NMR and diffuse reflectance spectroscopies. The reducibility of V⁵⁺-species, determined from the onset-reduction temperature, decreases as follows: VO_x/AL > VAPO-5 > MgVAPO-5 =VO_x/MG > VO_x/MG + AL. The acid character of catalysts, determined from the FTIR spectra of pyridine adsorbed, decreases as: MgVAPO-5 > VO_x/AL > VAPO-5 > VO_x/MG + AL > VO_x/MG. A similar trend between V-reducibility of the catalyst and its catalytic activity for the alkane conversion was observed. However, the selectivity to olefins depends on the acid-base character of catalyst and the alkane fed. In the ODH ofn-butane, the higher the acid character of the catalyst the lower the selectivity to C₄-olefins, while in the ODH of ethane an opposite trend between the catalyst acidity and the selectivity to ethene was observed.On leave from the Department of Industrial Chemistry and Materials, V. le Risorgimento 4, 40136 Bologna, Italy.     

Copper active sites for the selective reduction of nitrogen monoxide by propane on Cu-MFI catalysts and non-zeolitic supported-copper solids

The selective reduction of NO by C₃H₈ is performed on copper-based catalysts: Cu/Al₂O₃, Cu/SiO₂, Cu/SiO₂–Al₂O₃ solids, fresh and hydrothermally-treated Cu-MFI with various Si/Al ratios. For all the Cu-MFI solids and for the non-zeolitic supported-copper solids with low copper loadings, O₂ promotes the reduction of NO. The C₃H₈–NO reaction rate correlates with the number of accessible and isolated Cuⁿ⁺ ions deduced from the infrared spectroscopy of adsorbed CO. When only one type of sites is detected, the FTIR spectroscopy of adsorbed CO allows an estimation of the copper dispersion. This revised version was published online in July 2006 with corrections to the Cover Date.     

Facile,Efficient Copolymerization of Ethylene with Bicyclic,Non‐Conjugated Dienes by Titanium Complexes Bearing Bis(β‐Enaminoketonato) Ligands

Copolymerizations of ethylene with 5‐vinyl‐2‐norbornene or 5‐ethylidene‐2‐norbornene under the action of various titanium complexes bearing bis(β‐enaminoketonato) chelate ligands of the type, [R¹NC(R²)CHC(R³)O]₂TiCl₂ ( 1 , R¹=Ph, R²=CF₃, R³=Ph; 2 , R¹=C₆H₄F‐p, R²=CF₃, R³=Ph; 3 , R¹=Ph, R²=CF₃, R³=t‐Bu; 4 , R¹=C₆H₄F‐p, R²=CF₃, R³=t‐Bu; 5 , R¹=Ph, R²=CH₃, R³=CF₃; 6 , R¹=C₆H₄F‐p, R²=CH₃, R³=CF₃), have been shown to occur with the regioselective insertion of the endocyclic double bond of the monomer into the copolymer chain, leaving the exocyclic vinyl double bond as a pendant unsaturation. The ligand modification strongly affects the copolymerization behaviour. High catalytic activities and efficient co‐monomer incorporation can be easily obtained by optimizing the catalyst structures and polymerization conditions.     

Redox and photo‐redox properties of isolated Mo5+ ions in MoH‐ZSM‐5 and MoH‐beta zeolites: in situ ESR study

Redox and photo‐redox properties of isolated Mo⁵⁺ ions stabilized in H‐ZSM‐5 and H‐beta zeolites are studied by in situ ESR in flowing O₂, NO, H₂, and C₃H₆. Upon oxidation of pre‐reduced samples at 20 °C, NO demonstrates a higher oxidative ability, as compared with O₂. Interaction of Mo⁵⁺ ions with propene at 20 °C results in formation of a chemisorption complex with enhanced reactivity of Mo(V) toward NO. Illumination of the Mo⁵⁺/HZSM‐5 sample with UV‐visible light causes measurable acceleration of Mo(V) oxidation by NO at 20 °C. Therefore, photochemical activation of the oxidation step could be realized, in principle, for Mo/zeolite catalysts. At 500 °C in the reaction mixture NO + H₂, the step of the catalytic site reduction is fast, and the dynamic equilibrium of the redox reaction Mo(VI) ↔ Mo(V) for MoH‐ZSM‐5 and MoH‐beta seems to be strongly shifted to Mo⁵⁺. This revised version was published online in July 2006 with corrections to the Cover Date.