Catalysis

TiO 2 is an effective and well-known photocatalyst for water and air purification, but its practical applications in visible light-assisted chemical reactions are hindered mainly by its poor visible light absorption capacity. Nitrogen-doped TiO 2 (N-doped TiO 2) has attracted considerable attention as a photocatalyst, and rapid progress has been made in enhancing the photocatalytic efficiency of TiO 2 under visible light irradiation. N-doped TiO 2 exhibits broad absorption in the visible region, which can allow the utilization of a large part of the solar spectrum. This might be useful for environmental and energy applications, such as the photocatalytic degradation of organic pollutants, solar cells, sensors, and water splitting reactions. This review focuses on the major developments in the synthesis of N-doped TiO 2 and its possible applications in the photocatalytic degradation of organic pollutants and environmental remediation under visible light irradiation.

High-level composite, ab initio and density functional theory (DFT) procedures have been employed to study O–H bond dissociation energies (BDEs), as well as radical stabilization energies (RSEs) in the oxygen-centred radicals that are formed in the dissociation of the O–H bonds. Benchmark values are provided by Wn results up to W3.2 and W4.x. We are able to recommend revised BDE values for FO–H (415.6 ± 3 kJ mol–1), MeC(O)O–H (459.8 ± 6 kJ mol–1) and CF3CH2O–H (461.9 ± 6 kJ mol–1) on the basis of high-level calculations. We find that Gn-type procedures are generally reliable and cost-effective, and that some contemporary functionals and double-hybrid DFT procedures also provide adequate O–H BDEs/RSEs. We note that the variations in the O–H BDEs are associated with variations in the stabilities of not only the radicals but also the closed-shell precursor molecules. Most substituents destabilize both species, with σ-electron-withdrawing groups having larger destabilizing effects, whil...

Effect of platinum nanoparticle size on catalytic reduction of nitrate in liquid phase was examined under ambient conditions by using hydrogen as a reducing agent. For the size effect study, Pt nanoparticles with sizes of 2, 4 and 8 nm were loaded silica support. TEM images of Pt nanoparticles showed that homogeneous morphologies as well as narrow size distributions were achieved during the preparation. All three catalysts showed high activity and were able to reduce nitrate below the recommended limit of 50 mg/L in drinking water. The highest catalytic activity was seen with 8 nm platinum; however, the product selectivity for N2 was highest with 4 nm platinum. In addition, the possibility of PVP capping agent acting as a promoter in the reaction is highlighted.

An efficient and direct procedure has been developed for the preparation of amidoalkyl naphthols by a one-pot condensation of aryl aldehydes, β-naphthol and urea or amides, in the presence of potassium dodecatungstocobaltate trihydrate [K5CoW12O40 · 3H2O, (1 mol%)] as a heterogeneous catalyst. The reactions were carried out in 1,2-dichloroethane at room temperature or under solvent-free media at elevated temperature. The present methodology offers several advantages such as excellent yields, simple procedure and the catalyst exhibited remarkable reusability.

A green and sustainable method for the oxidation of 1,3-dihydrobenzo[c] thiophenes to sulfones using metalloporphyrin complexes Two efficient methods are reported for the oxidation of 1,3-dihydrobenzo[c]thiophenes to sulfones in good to high yields using H 2 O 2 in the presence of catalytic amounts of porphyrin-based catalysts in ethanol or acetonitrile as solvents at room temperature. The presence of electron-donating or electron-withdrawing groups, in the benzene ring of 1,3-dihydrobenzo[c]thiophene, is well tolerated.

... 18. K. Hattori, H. Sajiki and K. Hirota. Tetrahedron 57 (2001), p. 4817. Article | PDF (166 K) | View Record in Scopus | Cited By in Scopus (46). 19. ND Zelinsky, K. Packendorff and L. Leder-Packendorf. Chem. Ber. 66 (1933), p. 872. Full Text via CrossRef. 20. ...

Abstract: A novel and general biomimetic
non-heme Fe-catalyzed asymmetric
epoxidation of aromatic alkenes by
using hydrogen peroxide is reported
herein. The catalyst consists of ferric
chloride hexahydrate (FeCl3·6H2O),
pyridine-2,6-dicarboxylic acid (H2-
ACHTUNGTRENUNG(pydic)),and readily accessible chiral
N-arenesulfonyl-N’-benzyl-substituted
ethylenediamine ligands. The asymmetric
epoxidation of styrenes with this
system gave high conversions but poor
enantiomeric excesses (ee),whereas
larger alkenes gave high conversions
and ee values. For the epoxidation of
trans-stilbene (1a),the ligands (S,S)-N-
(4-toluenesulfonyl)-1,2-diphenylethyl-
ACHTUNGTRENUNGenediamine ((S,S)-4a) and its N’-benzylated
derivative ((S,S)-5a) gave opposite
enantiomers of trans-stilbene
oxide,that is,( S,S)-2a and (R,R)-2a,
respectively. The enantioselectivity of
alkene epoxidation is controlled by
steric and electronic factors,altho ugh
steric effects are more dominant. Preliminary
mechanistic studies suggest
the in situ formation of several chiral
Fe-complexes,such as [FeCl(L*)2-
ACHTUNGTRENUNG(pydic)]·HCl (L*=(S,S)-4a or (S,S)-5a
in the catalyst mixture),which were
identified by ESIMS. A UV/Vis study
of the catalyst mixture,which consisted
of FeCl3·6H2O,H 2ACHTUNGTRENUNG(pydic),and (S,S)-
4a,suggested the formation of a new
species with an absorbance peak at l=
465 nm upon treatment with hydrogen
peroxide. With the aid of two independent
spin traps,we could confirm
by EPR spectroscopy that the reaction
proceeds via radical intermediates. Kinetic
studies with deuterated styrenes
showed inverse secondary kinetic isotope
effects,with values of kH/kD=0.93
for the b carbon and kH/kD=0.97 for
the a carbon,w hich suggested an unsymmetrical
transition state with stepwise
O transfer. Competitive epoxidation
of para-substituted styrenes revealed
a linear dual-parameter Hammett
plot with a slope of 1.00. Under
standard conditions,epoxidat ion of 1a
in the presence of ten equivalents of
H2
18O resulted in an absence of the isotopic
label in (S,S)-2a. A positive nonlinear
effect was observed during the
epoxidation of 1a in the presence of
(S,S)-5a and (R,R)-5a.

.

Methods of intensification of the process of liquid-phase cyclohexane oxidation in the presence of complex catalytic systems, catalytic solutions and individual catalysts have been considered in the article. Quantitative and qualitative influences of binary catalytic systems which contain cobalt naphthenate and organic modifiers of different nature have been determined. The research confirmed the assumption of complexation involving components of the catalytic solutions in the reaction mixture. The structural formula of possible intermediate catalytic complex has been built.

Cyclohexanone is an important intermediate in the manufacture of polyamides in chemical industry, but direct selective hydrogenation of phenol to cyclohexanone under mild conditions is a challenge. Hydrogenation of phenol to cyclohexanone has been investigated in the presence of the composite catalytic system of Pd/C-heteropoly acid. 100% conversion of phenol and 93.6% selectivity of cyclohexanone were achieved within 3 h under 80 °C and 1.0 MPa hydrogen pressure. It has been found that a synergetic effect of Pd/C and heteropoly acid enhanced the catalytic performance of the composite catalytic system which suppressed the hydrogenation of cyclohexanone to cyclohexanol. Graphic Abstract HO C Cl H H Cl P d / C + H P A O Stainless steel reactor