Current Catalysis - Volume 2, Issue 1, 2013

When the yield of a heterogeneously photocatalyzed reaction is seen to pass through maximum as the mass of catalyst is increased in a suspension, this behavior may be attributable to a regime in which back-reflection most often occurs after a single photon-particle encounter, while absorption requires multiple internal reflections. This was modeled with a double exponential equation, which predicts that the yield will pass through a maximum with increasing catalyst mass when the catalyst has low absorptivity, but approach an asymptotic limit when the absorptivity is high. The rate of photodecomposition of chloroform, catalyzed by the chloride form of a polystyrene anion exchange resin (low absorptivity), was found to pass through a maximum as the amount of resin was increased, while catalysis by the CuCl4 2- form of the resin (higher absorptivity) caused an increase in the rate of decomposition with catalyst mass to an asymptotic value.

The Cu-Fe mixed oxide catalysts with different Cu:Fe mass ratios were prepared by a solution technique. The catalysts were characterized by Ar physisorption, PXRD, TPD-MS, SEM-EDX and were tested for the CO-PROX reaction. According to PXRD and SEM-EDX microanalysis data, the active Cu-Fe mixed oxide catalysts, where the Cu:Fe mass ratio ranges from 1:1 to 1:5.67, contain the delafossite CuFeO2 phase, which is formed at the pretreatment stage in the gas mixture used for the CO-PROX reaction. The Cu-Fe mixed oxide catalyst with the mass ratio of Cu:Fe = 1:3 showed 100% CO conversion at 408 K and the low H2 conversion (4 %) at this temperature, giving >80 % selectivity to CO oxidation. The blocking of the active sites at the catalyst surface by water, which is detected with TPDMS, could explain the high selectivity to CO oxidation.

Novel monotosylated ethylenediamine was synthesized from ethylenediamine and its application to ruthenium(II)-transfer hydrogenation of aldehydes in water is described. The transfer hydrogenation reaction could afford excellent conversion rates (up to 100%).

The increase in the global contamination of freshwater systems with industrial and natural chemical compounds is one of the key problems facing the world today. We report a simple fabrication strategy for hierarchical mesoporous NiO nanocrystals (NCs) with sheet-like morphologies using the hydrothermal method. This fabrication strategy introduces the controlled synthesis of scalable and high-yield mesoporous NiO nanosheets with high surface areas. The mesoporous NiO nanosheets were characterized by small- and wide-angle X-ray diffraction, nitrogen adsorption/desorption, scanning electron microscopy, and transmission electron microscopy. The as-prepared Ni(OH)2 sheets retained their hexagonal sheet morphologies during mild thermal treatment when converted to disordered mesoporous NiO NCs. The physical characteristics of the NiO nanosheets, such as intra-crystal mesoporosity, large surface area, and large pore volume, enabled phenolic pollutants such as o-aminothiophenol to access the active sites of the nanosheets. The NiO nanocatalyst with sheet-like morphology induced high catalytic efficiency and excellent reusability even after extended reutilization. In addition, the mechanistic pathway of phenolic pollutant transformation was demonstrated theoretically using density functional theory. The theoretical study provides insights into the changes in the molecular structure throughout the transformation mechanism of organic pollutants using the mesosporous NiO nanosheets.

Palladium supported TiO2 catalysts (2 %wt. of Pd) were prepared by different methods and studied in the gas phase reaction of partial oxidation of methanol. A comparative study of classical methods of preparation with those prepared in liquid phase was done. The catalysts were characterized by different methods such as: ICP, XRD, XPS, H2- chemisorption, N2-physisorption and TEM. The results showed that the preparation method changes the catalytic properties of the materials: both catalysts prepared by chemical reduction with hydrazine (aqueous and microemulsion) showed better catalytic performances than their classical counterparts (wet impregnation and sol gel). The activity of the catalysts is strongly influenced by the palladium particle size which seems to play a crucial role in the reaction mechanism.

A systematic optimization study of reaction conditions of alkyne hydration, catalyzed by mercury(II) ptoluensulfonamidate is described. Hydration takes place under catalytic conditions by using from 0.01 to 0.2 equivalents of the easily available and inexpensive mercury(II) p-toluensulfonamidate in a hydroalcoholic solution, under mild and neutral conditions. Different reaction parameters like temperature, concentration of substrates, equivalents of water and catalyst, portionwise addition of the catalyst, thermal, microwave and ultrasound activation conditions and solvent type have been studied and optimized.

Zn(II) and Co(II) organometallic complexes I and II involving 1,2-ethylenediamine were first synthesized from the reaction of the ligand 1,2-ethylenediamine with Zn(OAc)2· 2H2O and Co(OAc)2·4H2O in ethanol, then they were used to catalyze the Henry reaction, and good catalytic results (64-99%) were achieved.

We investigated an efficient production of ethyl esters (biodiesel) by enzymatic transesterification of triolein. This triacylglyceride was synthesized from oleic acid and glycerol by acid catalysis and then subjected to enzymatic transesterification by Candida antarctica lipase. This biocatalytic process afforded high yields of biodiesel (93% by 1H NMR, 90.4% by GC, 24 h, at 32 °C) which were dependent on reaction time. The yield of biodiesel was determined by 1H NMR and GC-FID analyses. The 1H NMR methodology developed for the quantification of biodiesel in unpurified reaction mixtures showed good correlations between the signal areas of peaks associated with the -methylene protons of the triolein (δ2.31) and those of the ethyl oleate ( δ2.28) in residual oil. Monoacyloleate (MAO), diacyloleate (DAO) and triacyloleate (TAO) could also be detected and quantified in the crude biodiesel using 1H NMR spectroscopic and GC-FID chromatographic methods. The enzymatic transesterification produced low amounts of monoacyloleate (2-MAO, 0.8% by GC) and diacyloletate (1,2-DAO, 1.3% by GC). Another advantage of the biocatalytic reaction was the production of high purity glycerol that was easily removed by decanting.

Catalytic hydroamination of terminal alkynes with amines is the most attractive C-N bond forming method. Intermolecular hydroamination of terminal alkynes with aromatic amine has been carried out using Cu- exchanged SiO2/Al2O3 as a heterogeneous catalyst. SiO2/Al2O3 with Si/Al ratio 12.5 has been prepared by novel sol-gel method using tetraethyl orthosilicate and aluminium sec-butoxide as Si and Al precursors respectively. The catalyst has been extensively characterized using various physicochemical and spectroscopic techniques viz., X-ray diffraction analysis, BET surface area, NH3-TPD, FTIR of adsorbed pyridine and 29Si and 27Al NMR. The catalyst showed very high conversion up to 97% and turnover number of 335 for intermolecular hydroamination of terminal alkynes with amines. The reaction proceeded smoothly with highly selective Markonikov addition product.

A simple, efficient and ecofriendly protocol for the synthesis of pyrazoles and β-enaminones using halogen free Bronsted acidic ionic liquid N-methyl-2-pyrrolidone hydrogen sulfate as a reusable catalyst has been developed. The prepared ionic liquids were characterized by different techniques like NMR and their Bronsted acidity was measured using infrared spectroscopy using pyridine as a probe molecule and monitoring the band in the range of 1350-1600 cm-1 arising from its ring vibration modes. Present catalytic system is simple, works at ambient conditions and requires shorter reaction time to furnish excellent yield of the desired products under solvent free conditions for majority of substrates. The ionic liquid shows very good catalytic activity and reusability up-to six recycles and gave good to excellent yields of the desired products.