Current Catalysis - Volume 3, Issue 1, 2014

Fe-exchanged zeolites show great promise for the direct benzene hydroxylation to phenol, one of the most important industrial chemicals. In this review, the recent achievements on the active sites and benzene hydroxylation have been summarized and discussed. Firstly, the catalytic results that are assumed in absence of Fe ions are given; secondly, the indispensible role of Fe ions has been revealed. Four types of Fe-involved active sites reported so far have been elaborated, and each type may correpond to a variety of active-site structures. Then the catalytic mechanisms of the mono- and binuclear-Fe sites are sucessively exploited, which are found to be quite similar. The comprising Fe3+ ions are catalytically unfavorable owing to the formation of specailly stable phenolate intermediates that result in deactivation to the catalysts. The Fe2+ ions, whether in the mononuclear or binuclear sites, are potentially active for the catalytic reaction. Finally, a brief concluding remark is presented listing some unresolved problems that may seriously impede this catalytic reaction on an industrial scale.

Energy processing and fuel combustion processes generate large volumes of CO, NOx, SO2, and volatile organic compounds (VOCs). These pollutants may pollute the air and water, thus doing harm to humans, animals, plants, and buildings. Heterogeneous catalysis plays an important role in environmental remediation. Catalytic elimination of environmental pollutants is more efficient and effective than conventional incineration. In particular, metal oxide catalysts are cheap, versatile and easy to prepare. Although Co3O4 is not as popular as TiO2 (a photocatalyst) in environmental catalysis, it shows extraordinary activity in CO oxidation well below room temperature, and therefore has attracted much attention recently. Here we review the recent progress in the remediation of several environmental pollutants by various Co3O4 catalysts and furnish our perspectives.

Ethyl 2-(4-aminophenyl) acetate is an important intermediate in the synthesis of Actarit, an antiarthritic drug. In the present study, synthesis of ethyl 2-(4-aminophenyl) acetate using Novozyme 435 in toluene as a solvent has been carried out under both conventional heating and microwave irradiation. A number of commercially available lipases such as Novozyme 435, Lipozyme RM IM and Lipozyme TL IM were screened. Novozyme 435 was found to be the most active. Optimization of reaction parameters such as speed of agitation, temperature, catalyst loading and mole ratio of the reactants has been done. A synergistic effect of microwave irradiation on reaction rate and specificity of lipases was observed in comparison with the conventional heating. Kinetic modeling showed that reaction followed ping-pong bi-bi mechanism. The theoretical predictions of rates match very well with experimental rates.

Iron(III) chloride adsorbed on silica gel catalyzes the photodecomposition of dichloromethane under near-UV irradiation, functioning through photodissociation to produce chlorine atoms that initiate a radical chain. While the photocatalytic activity under these conditions is similar to that of FeCl4macr heterogenized on an ion exchange resin, under solar irradiation the FeCl3/silica system is considerably more effective.

Fluoride-free Hiyama cross-coupling reactions of phenyltrimethoxysilane with aryl halides were performed in water using sodium hydroxide as the activator at 110 °C. The reactions, catalyzed by PVP stabilized colloidal palladium nanoparticles, show enhanced rate under microwave heating and proceed quickly (6 min).The progress of the reactions was monitored by GC-MS and parameters such as catalyst concentration, effect of base, recyclability etc. were investigated. Excellent yields were obtained with a variety of substrates and the products, after isolation, were characterized by 1H NMR.

Revisiting the iodine mediated N-Boc (N-tert-butoxycarbonyl) protection of amines revealed that the reaction can be performed using a lower quantity of iodine as a catalyst within a shorter reaction time. In addition to various aliphatic and aromatic amines the reaction was found to be equally effective and selective for the N-Boc protection of amino acid, guanidine, thiourea and N-(diaminomethylene)-1,1,1-trifluoromethanesulfonamide. The operational simplicity, high yield, mild and solvent free nature are the other features of this process. In addition to reassessing the reported reaction conditions and duration our study also demonstrates the further generality and versatility of this process.

Sulfonated carbon/silica composites derived from biomaterials viz. glucose, maltose, cellulose, chitosan and starch exhibited high catalytic activity for the one-pot synthesis of Hantzsch 1,4-dihydropyridines under solvent-free conditions, and for one-pot synthesis of 2,4,5-trisubstituted imidazoles and 2-arylbenzimidazoles under liquid phase catalysis. The activity of sulfonated carbon/silica composites derived from starch was found to be superior to other sulfonated carbon/ silica composites. The excellent conversions showed that the catalyst has strong and sufficient acidic sites, which are responsible for its catalytic performance. Moreover, these solid acid catalysts owned the advantages of high selectivity and recyclability.

N-alkylation of different amines with benzyl alcohol in the presence of easily prepared heterogeneous catalysts based on ruthenium hydroxide supported on zeolite NaY and Mordenite were investigated. All the reactions showed moderate to excellent yields especially for aliphatic primary amines without the addition of any co-catalysts such as bases and stabilizing ligands. Primary amines were converted into a mixture of secondary and tertiary amines, while secondary amines were unreactive under our experimental conditions. Catalysts were recovered after the reaction and reused without considerable loss of catalytic activities for the N-alkylation of benzyl alcohol and characterized by powder X-ray diffraction, BET volumetric surface area measurements, TEM and SEM microscopies.

In this study, benzoin methyl ether and benzoin ethyl ether were highly selectively synthesized in one-pot reaction using the reusable NiAlCe-hydrotalcite catalysts, where the benzoin ether compounds are traditionally obtained in two steps through condensation and etherification. The high crystallinity NiAlCe-hydrotalcites with different Ni2+/Al3+/Ce3+ ratios were facilely synthesized by the coprecipitation method under a constant pH value. The reaction parameters (e.g., different Ni2+/Al3+/Ce3+ ratios, reaction time, temperature, amount and the stability of catalyst) were studied in details and it was found that the Ni2+/Al3+/Ce3+ ratios, reaction temperature and the reaction medium play crucial influence on the catalytic activity and products distribution. 99.2% selectivity of benzoin methyl ether was achieved at 85.4% conversion of benzaldehyde and 98.3% selectivity was obtained at 63.7% conversion using a NiAlCe-hydrotalcite catalyst with the Ni2+/Al3+/Ce3+ ratio of 22:10:1, respectively. Besides, NiAlCe-hydrotalcite catalysts were easily recycled through a simple separation process and show high stability over three consecutive runs.

The [RuIII(hedtra)(H2O)] (hedtra3- = N-hydroxyethylethylenediaminetriacetate) mediated oxidative degradation of methylene blue (MB) in the presence of H2O2 has been achieved under ambient conditions. Based on the results of spectral studies a catalytic pathway involving activation of the dye, MB through its coordination to the ruthenium centre of Ru(hedtra) complex has been suggested. The catalytic-active intermediate [RuIII(hedtra)(OOH)]- was also found to be operative at high H2O2 concentration in effecting MB degradation under the specified conditions. Results of the catalytic studies have been discussed with reference to the data reported for the corresponding Ru(edta) (edta4- = ethylenediamineteraacetate) complex.

Manganese oxide supported on alumina and zirconia has been prepared by precipitation-impregnation method. The materials have been characterized by FT-IR, P-XRD, BET, TPD-NH3, TGA, SEM and TEM techniques for their textural properties. The catalytic activity of these materials has been explored in the synthesis of dihydropyrimidinones via.,Biginelli reaction. A rod like morphology is observed for zirconia containing 5% manganese oxide. These materials exhibited good catalytic activity in terms of isolated yield (>97%) and selectivity (100%) for the synthesis of dihydropyrimidinones. Acidity of the catalysts and the tetragonal phase of zirconia were found to play an important role in catalyzing this reaction. The catalyst with 5%Mn/ZrO2 exhibited distinctly different catalytic activity. The catalyst is reusable without losing its activity upto 5 cycles.

The kinetics of silver (I) catalyzed oxidation of l-ascorbic acid (H2A) by peroxodiphosfate (PDP) in acetate buffers has been studied. Triple distilled water was employed to eliminate suspected trace metal-ion catalysis of Cu (II) or Fe (III). The kinetics was monitored ceremetrically and the rate has been found to be independent of substrate concentration. A plausible reaction mechanism has been suggested. Results were analysed graphically in view of complex rate equation. The role of the catalyst has been via AgI/AgII redox cycle, Ag (II) confirming the presence of by the addition of 2,2’-bipyridyl where brown-orange color of AgI(bipy)2 complex of transient life time was observed.

Polyethylene glycol (PEG) nanotubes with an array structure were prepared by penetrating a PEG solution into anodic aluminum oxide (AAO) templates with a pore diameter of 200 nm. Nitrogen-doped carbonaceous nanotubes array were also successfully fabricated by annealing the polymer nanotube arrays in NH3 atmosphere. Their morphology and structure were charactarized by XRD, SEM, TEM, and XPS respectively. The results show that the structure of carbonaceous nanotubes array is uniformly sustained. Their electrocatalytic performance was tested by using rotating disk electrode (RDE) technique. The results indicate the new carbon-based metal-free catalyst shows a high catalytic activity and an excellent methanol tolerance for the oxygen reduction reaction (ORR).

Photocatalyzed decolorization of an azo dye Acid Yellow 29 has been examined under UV -light irradiation by monitoring the change in absorption intensity as a function of irradiation time under a variety of conditions. The reaction was carried out in an immersion well photochemical reactor using titanium dioxide (TiO2) as photocatalyst. The effect of operating parameters such as catalyst type, catalyst quantity, substrate concentration, pH and electron acceptors (H2O2 and KBrO3,) on decolorization efficiency have been discussed. The photodecolorization of the dye Acid Yellow 29 was also examined under sunlight and the decolorization efficiency was compared with UV-light source. The maximum decolorization of the dye was observed at pH 3.2 with catalyst loading of 2.0 gL-1. Addition of KBrO3 as electron acceptor showed pronounced effect for the decolorization of the dye under investivation. Results demonstrated that the TiO2 mediated photocatalytic process can effectively decolorize Acid Yellow 29 under UV-light radiations.