V.I. Pârvulescu

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, H-2 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

A polynuclear complex, {[Cu(bpe)2](NO3)}, with interpenetrated diamondoid networks: synthesis, properties and catalytic behavior

A polynuclear complex {[Cu(bpe)2](NO3)} (1), with five-fold interpenetrated diamondoid nets, was synthesized following a hydrothermal procedure, starting from a copper(II) salt, Cu(NO3)2·2.5H2O, and using a molar ratio Cu(NO3)2 : monoethanolamine : bpe : H2O of 1 : 3 : 1 : 500. The well stirred mixture was introduced into a Teflon-lined stainless steel autoclave, heated at 423 K, and kept at this temperature for 3 days. Red single crystals containing complex 1 were fully characterized by chemical analysis, FTIR, single-crystal X-ray diffraction, powder XRD, DR-UV-Vis, TG–heat flow analysis, sorption isotherms of N2 at 77 K, and X-ray photoelectron spectroscopy (XPS). The characterization results indicated that these crystals corresponded to a copper–organic network with a microporous-like structure in which part of the channels are blocked by water molecules and nitrate ions. The synthesis led to a structure in which all the Cu ions were well stabilized as a Cu(I) species, although the precursor was a Cu(II) compound. This structure exhibits remarkable properties: high thermal stability and capacity to totally exchange NO3− anions, without causing any damage to the microporous texture. The catalytic behavior was investigated in NO decomposition and NO reduction with hexane in the presence of O2, revealing very interesting and high catalytic activity. Cu was well preserved in a Cu(I) state after the catalytic tests, which provided new information about the mechanism of NO reaction on copper.

Diastereoselective hydrogenation of a prostaglandin intermediate over ru supported on different molecular sieves

Summary Hydrogenation of a prostaglandin intermediate has been carried out on some Rumolecular sieves prepared via deposition of RuCl3. Characterization of these catalysts using different tools like WAXS, XPS or EXAFS indicated differences due to both the different metal loading and the different structure and topology of the investigated molecular sieves (L, APO-34 and ZSM-5). The prostaglandin intermediate has two kinds of unsaturation, a double C=C bond and a prochiral C=O bond. Therefore hydrogenation could imply two different selectivities. On simple Ru-molecular sieves, hydrogenation occurs with different reaction rates and selectivities as a function of the catalysts characteristics. Thus, d.e. of about 100% for a selectivity to the alcohol of 99% were obtained for Ru(12wt.%)-L. However, on these catalysts only the epi configuration was obtained. Modification of the catalysts using L (+) tartaric acid leads to the increase of the reaction rate and the decrease of the d.e. Adding of the pivalic acid to the reaction mixture determined a supplementary increase of the reaction rate. More important in this case is the change of the stereoselectivity, the main product becoming the natural configuration.

Gas-solid oxidations with RuO2TiO2 and RuO2SiO2 membranes

Abstract The activity of the RuO 2 TiO 2 and RuO 2 SiO 2 membrane catalysts in oxidation with air of the isopropylic alcohol was determined at temperatures ranging from 40 to 120°C. The RuO 2 TiO 2 and RuO 2 SiO 2 membranes were prepared by the sol-gel process and supported on microporous glass membranes. The catalysts were characterized by scanning electron microscopy, IR spectroscopy and X-ray diffraction studies.

Chapter 12 Plasma-assisted NOX abatement processes: a new promising technology for lean conditions

Abstract This chapter deals with the removal of nitrogen oxides from gas streams by using non-equilibrium (non-thermal) plasma generated in atmospheric pressure electrical discharges. The advantage of using non-thermal plasma for promoting chemical reactions is its energy selectivity: most of the electrical energy dissipated in the discharge is used to produce high-energy electrons, and not spent on heating the entire gas stream. Typical electron temperatures in these discharges are 2–10 eV, while the background gas remains close to room temperature. The high-energy electrons seldom collide directly with the pollutant molecules, however, they excite, dissociate and ionize the background gas molecules. Thus, chemically active species are generated, which in turn, react with the pollutant molecules and decompose them. Different types of electrical discharges will be discussed with respect to NO x removal: corona discharges, dielectric barrier discharges (DBD), dielectric packed-bed discharges, and microwave discharges. Two issues of utmost importance will be emphasized throughout this chapter, namely: energy efficiency/energy consumption and by-product formation. In order to improve the efficiency for NO x removal by non-thermal plasma, different electrode geometries and electrode shapes have been investigated. The effect of the discharge gap length and of structured electrodes or multipoint electrodes, which enhance the local electric field, will be addressed. The discharges can be operated in d.c, a.c. or in pulsed mode. Comparisons between those operation modes will be discussed, as well as the influence of voltage polarity, amplitude and frequency. In pulsed discharges, the effect of pulse width and pulse repetition rate on NO x removal will be considered. Other experimental parameters found important for NO x decomposition are the gas flow rate, NO x initial concentration, reactor length, etc. The gas mixture containing the nitrogen oxides is very important as well. Experiments and modeling carried out for N 2 /NO x mixtures, or with addition of O 2 , H 2 O, CO 2 and hydrocarbons will be discussed. Typical hydrocarbon additives investigated are ethane, propene, propane, 2-propene-l-ol, 2-propanol, etc. As compared to the case without hydrocarbons, NO oxidation occurs much faster when hydrocarbons are present. The reaction paths for NO removal change significantly, in fact the chemical mechanism itself is completely different from that of without hydrocarbon additives. Another additive investigated extensively is ammonia, used especially in corona radical shower systems. The combination of non-thermal plasma and heterogeneous catalysis will be addressed as well. Single stage plasma-catalytic systems, with the catalysts placed in the discharge zone, and two stage systems, with the catalysts placed downstream of the plasma will be discussed. Single-stage reactors have the advantage of reactions on the catalyst surface with short-lived active species generated in the discharge. In two-stage systems, or plasma enhanced selective catalytic reduction (PE-SCR) systems, the oxidation of NO to NO 2 in the plasma increases the catalyst performance at low temperature (below 450–500 K).

Ru-MCM-41 catalysts for diastereoselective hydrogenation

Abstract Ru-MCM-41 catalysts were prepared by deposition of several complexes from their solvents: of Ru acetylacetonate from its ether solution, of cis -dichlorobis(2,2 ′ -bipyridine) Ru in chloroform, of di-μchlorobis(( p -cymene)chloro Ru(II)) in chloroform and of dichloro(1,5-cyclooctadiene) Ru(II) dissolved in pyridine. The catalysts were characterized as prepared and after several reactions cycles by: adsorption–desorption isotherms of N 2 at 77 K, XRD, FTIR, and XPS. The above catalysts were used in the liquid phase hydrogenation of a F prostaglandin intermediate. A strong leaching of Ru was observed, but after four cycles the catalysts remained unchanged in activity and diastereoselectivity. The stereoselectivity was found to be influenced by the nature of the precursor complex. In the presence of the catalyst prepared from di-μchlorobis(( p -cymene)chloro Ru(II)) the natural-like product was obtained.

Hydrogenation of vinylbenzenes on Pd–Tm/Al2O3 and Tm/Al2O3 catalysts

Pd–Tm/γ-Al 2 O 3 catalysts containing 0.1% Pd–1% Tm, 0.3% Pd–1% Tm and 0.5% Pd–1.% Tm, respectively have been obtained by successive impregnation of γ-Al 2 O 3 , first with palladium and then with thulium. Introduction of Tm leads to an increase in the conversion of vinylbenzenes compared to that with monometallic Pd/γ-Al 2 O 3 catalysts. For monocomponent Pd/γ-Al 2 O 3 catalysts, turnover frequency (TOF) is unchanged. For bicomponent Pd–Tm/γ-Al 2 O 3 catalysts, if one considers that the reaction occurs only on the Pd particles, then introduction of Tm seems to increase the TOF. However, by taking Tm into consideration when calculating the TOF, then the bicomponent catalysts are seen to behave as the monocomponent catalysts. This behaviour is highlighted also by using the Koros–Nowak criterion. If Tm is not considered to be an active species, vinylbenzene hydrogenation appears to be controlled by mass transfer processes. However, the texture characteristics of the bicomponent catalysts are not sufficiently modified by Tm introduction to support such a hypothesis. On the contrary, by considering the Tm participation in the reaction, the slope of the Koros–Nowak dependence is included in a range typical for kinetically controlled reactions.

New evidences for the fluoride contribution in synthesis of gallium phosphates

Gallium phosphates were prepared by hydrothermal synthesis under autogeneous pressure. Gel compositions with formulas Ga 2 O 3 .x P 2 O 5 .y HF.z Py(Pr 3 N).70 H 2 O with x=0.5 till 1; y=1 till 5, z=1.7 till 3.4 for Py and 1.5 till 3 for Pr 3 N were obtained under vigorous stirring by successive dissolution in a phosphoric acid/water solution of Ga 2 O 3 , hydrofluoric acid and template. These materials were characterized by XRD, N 2 adsorption-desorption isotherms at 77 K, TG-DTA, FTIR, NH 3 -DRIFT, XPS, SEM, MAS-NMR. The increase of the F/Ga gel composition ratios was found to enhance the crystallinity of the samples and, in certain limits, to improve the thermal stability.

Diastereoselective hydrogenation of a prostaglandin intermediate over Ru supported on MCM-41 and MCM-48

Ru-MCM-41 and MCM-48 catalysts were prepared via deposition of Ru from various precursors RuCl3.3H2O, [Ru(NH3)6]Cl2 and Ru(acac)3. The samples were characterised using several techniques: adsorption and desorption curves of N2 at 77K, TPO, TPR, XRD, XPS, Mossbauer spectroscopy, and TEM. After deposition and activation the support keeps the structural features of the MCM materials, but Ru exists in different dispersion and reduction states both inside of the MCM pores and on the amorphous part of the material depending on the precursor nature. The distribution of the metal inside and on the external surface controls the selectivity to allylic alcohol. But the diastereoselectivity in this reaction was found to be influenced by the interaction occurring inside of the MCM pore lattice and by the solvent.

Modified ruthenium exchanged zeolites for enantioselective hydrogenation

Abstract Preparation of modified ruthenium molecular sieves has been investigated in two steps-depositionof ruthenium and modifying of ruthenium molecular sieves in presence of ligands. As support sieve there were used two molecular sieves with large pore apertures and low acidity strength (zeolite L and APO-34). Correlation of in situ UV-VIS ruthenium deposition measurements with catalyst characterisation revealed that ruthenium deposition takes place not only through ionic exchange but also through adsorption of ruthenium hydrolysed species. Modifying of the ruthenium molecular sieves catalysts with ligands has as effect a diminution of electronic charge on metal. The experimental data indicate that the presence of ligand favours an enantioselective hydrogenation of D-fructose to D-mannitol even if the yields are not very high.