Selective Catalytic Reaction Research Articles

Dispersion of barium titanate and strontium titanate nanocubes and their selective accumulations

Barium titanate (BaTiO3, BT) and strontium titanate (SrTiO3, ST) nanocube particles were prepared by a solvothermal method. The prepared particles were collected by a centrifugal separator. The X-ray diffraction (XRD) measurement and a transmittance electron microscope (TEM) observation confirmed the formation of perovskite BT and ST nanocube particles with sizes of around 17 nm. These nanocube particles were monodistributed in hexane with tri-n-butylphosphine oxide (TBPO) as dispersant, separately, and then, the accumulations composed of the BT and ST nanocubes were built up using a selective catalytic reaction between 3-bromopropylphosphonic acid (BP) and aminomethylphosphonic acid (AM) as smart glue. The TEM observation confirmed that a part of accumulations showed a hetrointerface connection between BT and ST.

Effect of selective catalytic reactor on oxidation and enhanced removal of mercury in coal-fired power plants

The present study investigated the variation of mercury (Hg) speciation within the air pollution control devices (APCDs) in bituminous coal-fired power plants. The effect of selective catalytic reduction (SCR) system, which is mainly installed for NO x removal, on elemental Hg (Hg 0) oxidation and enhancement of Hg removal within APCDs, was studied. Hg speciations in flue gas at the inlet and outlet of each APCDs, such as SCR, cold-side electrostatic precipitator (CS-ESP) and flue gas desulphurization (FGD), were analyzed. Sampling and analysis were carried out according to Ontario Hydro Method (OHM). Overall Hg removal efficiency of APCDs, on average, was about 61% and 47% with and without SCR system, respectively. In the flue gas, Hg was mainly distributed in gaseous (elemental and oxidized) form. The oxidized to elemental Hg partitioning coefficient increased due to oxidation of Hg 0 across the SCR system and decreased due to the removal of oxidized Hg (Hg 2+) across a wet FGD system. Hg 0 oxidation across the SCR system varied from 74% to 7% in tested coal-fired power plants. The comparative study shows that the installation of an SCR system increased Hg removal efficiency and suppressed the reemission of captured Hg 0 within a wet FGD system.

Mercury emission trend influenced by stringent air pollutants regulation for coal-fired power plants in Korea

Regulatory control of mercury emission from anthropogenic sources has become a global concern in the recent past. Coal-fired power plants are one of the largest sources of anthropogenic mercury emission into the atmosphere. This paper summarizes the current reducing trend of mercury emission as co-beneficial effect by more stringent regulation changes to control primary air pollutants with introducing test results from the commercial coal-fired facilities and suggesting a guideline for future regulatory development in Korea. On average, mercury emission concentrations ranged 16.3–2.7 μg Sm −3, 2.4–1.1 μg Sm −3, 3.1–0.7 μg Sm −3 from anthracite coal-fired power plants equipped with electrostatic precipitator (ESP), bituminous coal-fired power plants with ESP + flue gas desulphurization (FGD) and bituminous coal-fired power plants with selective catalytic reactor (SCR) + cold side (CS) − ESP + wet FGD, respectively. Among the existing air pollution control devices, the best configuration for mercury removal in coal-fired power plants was SCR + CS − ESP + wet FGD, which were installed due to the stringent regulation changes to control primary air pollutants emission such as SO 2, NOx and dust. It was estimated that uncontrolled and controlled mercury emission from coal-fired power plants as 10.3 ton yr −1 and 3.2 ton yr −1 respectively. After the installation of ESP, FGD and SCR system, following the enforcement of the stringent regulation, 7.1 ton yr −1 of mercury emission has been reduced (nearly 69%) from coal-fired power plants as a co-benefit control. Based on the overall study, a sample guideline including emission limits were suggested which will be applied to develop a countermeasure for controlling mercury emission from coal-fired power plants.

Structural Properties of the Bimetallic Cluster Au12Ag6 on the NOx (x=1,2,3) Adsorption Processes

AbstractIt has been shown that Au and Ag nanoparticles present catalytic properties of pollutant gases, product of the hydrocarbons combustion processes, whose efficiency is strongly dependant on their size, morphology and supporting material. The activity of Ag subnanometric particles supported on alumina in the NOx reduction mechanism, for the reaction HC-SCR (Hydrocarbon Selective Catalytic Reaction) is a good example of these catalytic properties. It is also well established that both Au and Ag nanoparticles are oxygen poisoning resistant and that in certain reactions the bimetallic combination may be more efficient than their isolated parts. In this work we present a DFT calculation of the NOx (x =1, 2, 3) adsorption energies on the Au12Ag6 cluster surface. It is also discussed the possible synergetic effect of the different configurations, forming small Ag islands composed of one to five atoms, on the surface of the bimetallic cluster. The analysis was done using DFT in the ZORA approximation.

A heterostructured titanium silicalite-1 catalytic composite for cyclohexanone ammoximation

Submicron-sized titanium silicalite-1 is difficult to recover in industrial process because of their fineness and rapid decrease in catalytic activity due to particle agglomeration. To solve these problems, we present a heterostructured titanium silicalite-1 (TS-1) catalytic composite using bentonite clay as the catalyst support. The catalytic composite is synthesized by hydrothermal treatment which directly crystallizes TS-1 on the bentonite clay surface. The synthesized composite has been characterized using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The TS-1 crystals have been found on and between the layers of the bentonite with strong attachment. Characterizations suggest that crystallization temperature of 175 °C is the optimum hydrothermal temperature to produce TS-1 on the bentonite support with characteristics necessary to promote selective catalytic reactions. It is found that prolonged crystallization duration does not necessarily increase the crystallinity of TS-1 on the bentonite surface. The heterostructured composite is able to maintain high conversion of cyclohexanone (97%) and oxime selectivity (83%) after three reaction cycles which is contrary to the unsupported TS-1 that shows apparent decrease in activity (>10%), especially in the selectivity to oxime. The synthesized composite also has significant improvement in separation efficiency with respect to the unsupported catalytic system. Therefore, we conclude that the heterostructured TS-1 composite is a promising catalytic material for cyclohexanone ammoximation and potentially for other TS-1 related processes where catalyst recovery and reuse are required.

The control of valence state: How V/TiO 2 catalyst is hindering the deactivation using the mechanochemical method

Various experiments were conducted to improve durability against SO 2 by impregnating the same amount of vanadium in TiO 2 which had the various physical properties. According to those catalysts, the degree of deactivation by SO 2 had various results, and it was found that the production of unreacted NH 3 in selective catalytic reduction reaction should be low. Based on X-ray photoelectron spectroscopy analysis, O 2 on–off test, O 2 reoxidation test and H 2-temperature programmed reduction experiment, the redox capacity of catalyst was improved due to increasing of non-stoichiometric compounds. Such a non-stoichiometric oxide and redox capacity of catalyst can be enhanced by the ball-milling process, and the production of ammonium sulfate salt can be more easily inhibited by the superior oxidation–reduction capacity of catalyst. We found that this result is caused by producing and increasing of V x+ ( x ≤ 4), Ti y+ ( y ≤ 3) which are non-stoichiometric chemical species of catalyst.

Pd/La Complex foranti-Selective Catalytic Asymmetric Nitroaldol Reactions

A limited number of reports describe the anti-selective synthesis of chiral β-amino alcohols. This report describes the design of a simple and efficient catalyst with a broad substrate scope and practical applicability. The authors nicely demonstrate the short syntheses of two β-adrenoceptor agonists.

Vanadium Pentoxide-Coated Ultrafine Titanium Dioxide Particles Induce Cellular Damage and Micronucleus Formation in V79 Cells

Surface-treated titanium dioxide (TiO2) particles coated with vanadium pentoxide (V2O5) are used industrially for selective catalytic reactions such as the removal of nitrous oxide from exhaust gases of combustion power plants (SCR process) and in biomaterials for increasing the strength of implants. In the present study, untreated ultrafine TiO2 particles (anatase, diameter: 30–50 nm) and vanadium pentoxide (V2O5)-treated anatase particles were tested for their cyto- and genotoxic effects in V79 cells (hamster lung fibroblasts). Cytotoxic effects of the particles were assessed by trypan blue exclusion, while genotoxic effects were investigated by micronucleus (MN) assay. In addition, the generation of reactive oxygen species (ROS) was determined by the acellular method of electron spin resonance technique (ESR) and by the cellular technique of determination of thiobarbituric acid-reactive substances (TBARS). Our results demonstrate that V2O5-treated TiO2 particles induce more potent cyto- and genotoxic effects than untreated particles. Further, acellular and cellular radical formation was more pronounced with V2O5-anatase than untreated anatase. Thus, data indicate that V2O5-treated TiO2 particles were more reactive than natural anatase and capable of inducing DNA damage in mammalian cells through production of free radicals.

A Heterobimetallic Pd/La/Schiff Base Complex for anti‐Selective Catalytic Asymmetric Nitroaldol Reactions and Applications to Short Syntheses of β‐Adrenoceptor Agonists

A Heterobimetallic Pd/La/Schiff Base Complex for <i>anti</i>‐Selective Catalytic Asymmetric Nitroaldol Reactions and Applications to Short Syntheses of β‐Adrenoceptor Agonists

Activation and functionalization of benzylic derivatives by palladium catalysts

Palladium-catalyzed transformations of aryl halides and pseudo-halides involving carbonylation, carbon-carbon and carbon-heteroatom bond-forming reactions, etc. are very well documented, and have already been reviewed several times. The metal-catalyzed activation of benzylic derivatives is much less described. However, during the last decades, a number of papers have shown the interest offered by benzylic derivatives (halides, carbonates, acetates, phosphonates) in selective catalytic reactions for organic synthesis, most of them in the presence of palladium catalysts. The purpose of this tutorial review is to highlight selected examples of palladium-catalyzed transformations involving reactive benzylic derivatives.

Syn-Selective Catalytic Asymmetric Nitro-Mannich Reactions

This communication highlights the first syn-selective catalytic asymmetric nitro-Mannich reaction. The catalyst consists of a hetero­bimetallic Cu-Sm-Schiff base complex synthesized from a dinucleating Schiff base ligand in two steps. The scope is broad with a variety of N-Boc imines affording high yields, syn selectivities, and enantioselectivities, including imines with electron-donating, electron-withdrawing, and hetero­aryl substituents. Even isomerizable alkyl N-Boc imines and use of nitropropane instead of nitro­ethane afford high yields and selectivities. The synthetic utility is demonstrated by converting one of the products into syn-1,2-diamines in two steps and with excellent yields.

On selectivity of catalytic reactions with multi-centered adsorption

Modeling of kinetics, stereo-, regio- and enantioselectivity of reactions representing different typical cases of multiphase heterogeneous organic catalysis is usually discussed within the framework of ideal surfaces, neglecting the polyatomic nature of reacting molecules. However, there is a number of cases when the real adsorption geometry of large organic molecules, especially in catalysis on nanoparticles, should be accounted for. Particularly challenging is the description of selectivity as a function of conversion when conventional models often fail to capture experimental behavior. Data on chemoselective hydrogenation of α,β-unsaturated aldehydes along with numerical simulations are used to illustrate importance of multicentred adsorption considerations in understanding selectivity behavior.

Syn-Selective Direct Catalytic Asymmetric Mannich-Type Reactions of Aromatic and Heteroaromatic Hydroxy Ketones Promoted by Y[N(SiMe3)2]3/Linked-BINOL Complexes

Abstract Full details of syn-selective catalytic asymmetric direct Mannich-type reactions of aromatic and heteroaromatic hydroxy ketones promoted by Y[N(SiMe3)2]3/linked-BINOL complexes are described. From a screening of various rare-earth metals and linked-BINOL derivatives, a Y[N(SiMe3)2]3/TMS-linked-BINOL (1.7/1) complex was determined to be the most effective. Mannich-type reactions of aromatic and heteroaromatic hydroxy ketones with aryl and alkenyl N-diphenylphosphinoylimines, catalyzed by 0.1 molar amount of Y[N(SiMe3)2]3 and 0.059 molar amount of TMS-linked-BINOL, afforded syn-β-amino-α-hydroxy ketones in good yields (78–98%), high diastereoselectivity (syn/anti = 81/19–96/4), and high enantioselectivity (86–98% ee).

Highly anti-Selective Catalytic Aldol Reactions of Amides with Aldehydes

Barium phenoxide-catalyzed, highly anti-selective direct-type aldol reactions of amides with aldehydes have been developed. In the presence of a slight excess amount of an amide, the desired reactions proceeded smoothly under mild conditions, and a wide range of aromatic, heterocyclic, α,β-unsaturated aldehydes were applicable to afford the desired adducts in high yields with high anti-selectivities. A catalytic, enantioselective reaction of an amide with an aldehyde using a chiral ligand is also described.

Highly Selective Catalytic Cross-Aldol Reactions of Chloral with Aliphatic Aldehydes

An efficient synthetic method for β-trichloromethyl-β-hydroxy aldehydes is described. Using piperidine or L-prolinamide as the catalyst, direct cross-aldol reactions of chloral with aliphatic aldehydes occur smoothly at room temperature. The cross-aldol condensation products are isolated in high yields (up to 95%), and a moderate to high enantioselectivity (up to 88% ee) is observed in the case of L-prolinamide.

Highly anti-Selective Catalytic Aldol Reactions of Amides with Aldehydes

Barium phenoxide-catalyzed, highly anti-selective direct-type aldol reactions of amides with aldehydes have been developed. In the presence of a slight excess amount of an amide, the desired reactions proceeded smoothly under mild conditions, and a wide range of aromatic, heterocyclic, alpha,beta-unsaturated aldehydes were applicable to afford the desired adducts in high yields with high anti-selectivities. A catalytic, enantioselective reaction of an amide with an aldehyde using a chiral ligand is also described.

Heterogeneous hydroxylation catalyzed by multi-walled carbon nanotubes at low temperature

In this paper, multi-walled carbon nanotubes (MWCNTs) were directly used as catalysts for the hydroxylation of aromatic hydrocarbons at low temperature (50–70 °C). Without the assistance of any solvent or additive, high selectivity was still obtained. The catalysts were characterized by X-ray powder diffraction, infrared spectra, Raman spectra, and transmission electronic microscopy. These results prove that MWCNT was a highly-active, highly-selective, and well-reproductive heterogeneous catalyst. The curved sp 2-hybridized carbon surfaces of MWCNT played an important role in these selective catalytic reactions. The reactions were proposed to occur via an oxene attacking process. The active oxygen species were generated through the interaction between the hydrogen peroxide and the MWCNTs and subsequently consumed by the aromatic hydrocarbons. This process was repeated in the catalytic reactions.

A Low Cost ZSM-5 Zeolite Obtained from Rice Hull Ash

The high pure synthetic zeolite have a large application in industry and agriculture, being nowadays in majority imported in Brazil. The biomass like rice hull ash (RHA), a rice industry waste, can be real advantageous in manufacture of different materials, since that is produced in large scale in the country. The silica extraction from RHA by alkaline leaching is a low energetic coast process and high efficiency, obtaining high pure silica with high reactive amorphous structure, very interesting for zeolite production. In this work was developed a economically feasible route for the production of high purity and crystallinity ZSM-5 zeolite, free of expensive template, starting from a low value intake, a industrial waste, producing a high value materials. The extracted silica from RHA in sodium silicate form is precipitated in the proper zeolite formation reactional mixture. The ZSM-5 have a lot of industrial applications due your high selectivity in catalytic reactions and high thermal and acid stability.

Preparation of new bis(oxazoline) ligand bearing non-covalent interaction sites and an application in the highly asymmetric Diels–Alder reaction

New asymmetric bis(oxazoline) (Box) ligand bearing amide group at the oxazoline 4-position, ( S, S)-2,2′-methylenebis(4- tert-butylcarbamoyl-2-oxazoline) ( 1S ), was designed and synthesized for selective catalytic reaction. The crystal structure of the ternary copper complex, consisting of 1S and N-benzoyl-N-phenyl-hydroxylamine, demonstrated interligand interactions, such as hydrogen bonding and CH- π interaction. Catalytic performance of the copper complex with 1S was investigated for an asymmetric Diels–Alder reaction using benzylidene-2-acetylpyridine and 1,3-cyclohexadiene (CHD). The reaction product was enantio-pure endo-(pyridin-2-yl)(3-phenylbicyclo[2,2,2]oct-5-ene-2-yl)methanone (BPCD), of which crystal structure was analyzed by the X-ray method. No stereo- and enantio-isomer of BPCD was detected by chiral HPLC analysis. Introduction of hydrogen bonding site into 1S can promote the Diels–Alder reaction even though using poor reactive CHD. Without 1S , this reaction did not give any product. Addition of 2-propanol to this reaction system inhibited the formation of BPCD, indicating that the designed interligand interaction sites, especially hydrogen bonding, play an important role for catalytic performance.

Heterogeneous Reductive Isomerization Reaction Using Catalytic Pd/C and H2

[reaction: see text] A highly selective catalytic reductive isomerization reaction is described. The extremely mild and neutral reaction conditions (10% Pd/C, H2, and MeOH at 0 degrees C) tolerate a wide range of functional groups and generally result in excellent yields. Mechanistic studies suggest that this reaction does not proceed via a stepwise reduction/elimination sequence or a pi-allylpalladium intermediate.