Catalytic removal of NO

The aim of this paper is to review the catalytic reactions for the removal of NO and, more particularly, to discuss the reduction of NO in the presence of NH₃, CO, H₂ or hydrocarbons as well as the decomposition of NO. The nature of the different active species, their formation due to dispersion and their interaction with different supports as well as the corresponding correlations with catalytic performance are also discussed. Another goal of this review is to explain the mechanism and kinetics of these reactions on different surfaces as well as the catalyst stability.     

Alkylation of Hydroquinone with tert-butanol over Silica-immobilized Triflate Derivatives

Friedel-Crafts alkylations of α-methylnaphthalene with various alkylating agents were first carried out in the presence of methanesulfonic acid (MeSA). The Brønsted acid catalyst MeSA exhibited outstanding catalytic performance, and was found to be excellent catalyst and solvent for alkylation reaction of aromatic hydrocarbon. It’s found that alkenes can be used as excellent alkylating agent for alkylation of α-methylnaphthalene. The effects of various reaction parameters like type of alkylating agent, dosages of catalysts, reaction temperature and reaction time were investigated in detail. Moreover, the performance of reuse for catalysts was also studied. It’s found that, under the optimal reaction conditions, more than 90% of conversion for olefins and 100% of selectivity for the desired products were obtained. Compared with traditional catalysis technology, the reaction, catalyzed by MeSA catalyst, no volatile solvents needed, good selectivity for desired products could be obtained. The catalyst can be isolated easily from the reaction mixtures by decantation, and was successfully reused. The methanesulfonic acid could be considered as environmentally friendly novel catalyst and solvent for long-chain alkylation of α-methylnaphthalene with alkenes. The catalytic reaction mechanism for alkylation in the presence of MeSA was proposed as well.     

Effect of the support upon the behavior of Cu in NO decomposition exemplified on Cu-ZSM-5 containing Zr

ZSM-5 containing Zr in the lattice was prepared following the procedure for ZSM-5 using ZrCl₄ as zirconium precursor. Zr was substituted for Si in the ZSM-5 lattice and then this zeolite was loaded with Cu. Loading these catalysts with Cu was carried out following Iwamoto’s procedure. An increase in Zr results in a decrease in Cu loading, although the exchange solutions were the same. The increased Zr loading and, hence, decreased Cu loading resulted in a decreased NO decomposition activity relative to the Zr-free ZSM-5 loaded with Cu. NO conversions, obtained on Cu-ZSM-5 zeolites in which zirconium replaced Si, were below 40%, which is about 30% lower than those recorded on Cu-exchanged pure zeolites. The amount of NO₂ detected in the reaction products proved that, for total conversions lower than 20%, the reaction of NO takes place almost exclusively without decomposition to N₂ and O₂. The catalysts were characterized by DRIFTS and NO-DRIFTS, Raman spectroscopy, O₂ — TPD and XPS. The OH region observed in DRIFTS changed with an increase in Zr loading and, hence, Cu(II)–O–Cu(I) species cannot be formed. This may play a role in the decreased activity. Raman spectra showed that increased Zr also results in increased CuO which may lead to the decreased activity. Although the exposure of the samples with high Zr content to NO results in the apparent redispersion of CuO to isolated sites within the ZSM-5, the Cu moves to locations which are inactive and/or inaccessible to NO and, hence, the activity does not increase even though the Cu is dispersed. The formation of NO₂ follows the mechanism proposed by Shelef.     

Diastereoselective hydrogenation of a prostaglandinic intermediate over chirally modified Pt/Al2O3

Liquid phase diastereoselective hydrogenation of a prostaglandin-F intermediate has been studied over two commercial 5% Pt/Al₂O₃ catalysts. More specifically, the effect of metal dispersion and pore diameter on the reaction, as well as the conditions which allow to improve the diastereoselectivity and eventually orient towards the synthesis of the natural-like compound have been examined. The catalysts were characterized by nitrogen sorption isotherms, XRD, H₂-chemisorption, and XPS. It has been found that the characteristics of the catalysts (especially the textural properties) and the nature of the solvent strongly influence the catalytic behavior. In the presence of acetic acid as a solvent, it is possible to direct the formation of allylic alcohol to the (11S,15S) configuration which corresponds to the natural-like diastereoisomer compound.     

TG and DTA investigation of ZrO2–SO 4 2– catalysts exposed to hexane, methylcyclopentane and cyclohexane

ZrO₂– catalysts with different sulfur contents were analysed with thermal methods coupled with mass spectrometry after exposure to mixtures of hexane, methylcyclopentane, and cyclohexane in argon. The reaction of the hydrocarbons led to carbonaceous deposits, but an important part of hydrocarbon remained chemisorbed as well. Heating these samples in He atmosphere provoked the decomposition of these deposits with evolution of CO₂ and CO, and also of SO₂ and SO. At the same time, COS was evidenced in the reaction products. The release of these molecules occurred below the activation temperature of the catalysts. The behavior of the catalysts depended both on reactant molecule and sulfur content. The analyses clearly evidenced the oxidation ability of ZrO₂–SO catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of LaCoO3 perovskite deposition on ceria-based supports on total oxidation of VOC

Supported LaCoO₃ perovskites with 10 wt.% loading were prepared by impregnation of different supports containing ceria with a solution of La and Co nitrates and citric acid. All precursors were calcined at 700 °C for 5 h. XRD investigations indicated the perovskite formation via “citrate” precursor only on ceria support. All catalysts were tested for toluene total oxidation in the temperature range 100–600 °C. In spite of a large surface area, alumina-supported perovskites showed a lower global activity. It appears then the necessity of the presence of a perovskite phase for good oxidative activity. In terms of reaction rates higher reaction rates per perovskite weight were observed for all supported catalysts when compared to bulk LaCoO₃.     

Iron oxide colloids and their heterogenization by silica sol–gel entrapment: Catalytic and magnetic properties

Fe₃O₄ colloids modified by the chiral ligand cinchonidine were prepared with the goal of obtaining a magnetic and catalytic nano-material and were subsequently embedded in silica to form a heterogeneous catalyst. The systems were characterized by TEM and XRD measurements, while the Mössbauer technique was applied for measuring the magnetic properties of the Fe₃O₄ colloids. The hyperfine magnetic field distribution was consistent with one type of Fe oxide, namely, the magnetite (Fe₃O₄). These colloids, both as ‘quasi-homogenous catalysts’ (or soluble heterogeneous catalysts) and embedded in silica (heterogeneous catalysts) were employed in the selective hydrogenolysis of complex bicyclo[2.2.2]oct-7-enes (bicyclo[2.2.2]oct-2-enes when unsubstituted).     

Synphos modified Pt nanoclusters, their heterogenization by silica sol-gel entrapment, and catalytic activity in hydrogenolysis of bicyclo[2.2.2]oct-7-enes and hydrogenation of ethyl pyruvate

Platinum (Pt) colloids modified by the chiral ligand synphos were prepared with the goal of obtaining a catalytic nanomaterial and were subsequently embedded in silica to form a heterogeneous catalyst. The systems were characterized by (31)P-NMR, x-ray diffraction, molecular modeling and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) measurements. These colloids, both as 'quasi-homogeneous catalysts' (or soluble heterogeneous catalysts) and embedded in silica (heterogeneous catalysts) were employed in the selective hydrogenolysis of highly sterically constrained bicyclo[2.2.2]oct-7-enes and hydrogenation of ethyl pyruvate.     

Asymmetric Carbon‐Carbon Bond Forming Reactions Catalysed by Metal(II) Bis(oxazoline) Complexes Immobilized using Supported Ionic Liquids

A series of bis(oxazoline) metal(II) complexes has been supported on silica and carbon supports by non‐covalent immobilisation using an ionic liquid. The catalytic performance of these solids was compared for the enantioselective Diels–Alder reaction between N‐acryloyloxazolidinone and cyclopentadiene and the Mukaiyama‐aldol reaction between methyl pyruvate and 1‐methoxy‐1‐trimethylsilyloxypropene. In both reactions the enantioselectivity was strongly influenced by the choice of support displaying enantioselectivies (ee values) up to 40% higher than those conducted under homogeneous reaction conditions.     

Trivalent Ce2O3 and CeO2−x intermediate oxides induced by laser irradiation of CeO2 powders

A strong non-stoichiometry of pure fcc CeO₂ was induced by laser irradiation. The increase of laser power and/or energy density had a saturable effect on particle size growth. The possibility of CeO₂ reduction to A-Ce₂O₃ by laser irradiation was demonstrated. Particles of stable Ce₇O₁₂ phase were observed in all specimens irradiated at low laser-power densities. An epitaxial relationship between triclinic Ce₁₁O₂₀ and cubic Ce₁₂O₂₂ phases was found. The controversial C-Ce₂O₃ phase was detected at the limits of a bcc particle. An unknown bcc phase of acicular morphology, strongly related to C-Ce₂O₃, was also registered. The dose dependence of CeO₂ structural modifications obtained by laser irradiation as a function of laser energy density variation could be explained by a simple defect aggregation model implying lattice defects (oxygen vacancies and Ce³⁺ ions).