Considerable research has been conducted on monolithic catalysts for various applications. Strategies toward coating monoliths are of equal interest and importance. In this paper, the preparation of ...monoliths and monolithic catalysts have been summarized. More specifically, a brief explanation for the manufacturing of ceramic and metallic monoliths has been provided. Also, different methods for coating γ-alumina, as a secondary support, are included. Techniques used to deposit metal-based species, zeolites and carbon onto monoliths are discussed. Furthermore, monoliths extruded with metal oxides, zeolites and carbon are described. The main foci are on the reasoning and understanding behind the preparation of monolithic catalysts. Ideas and concerns are also contributed to encourage better approaches when designing these catalysts. More importantly, the relevance of monolithic structures to reactions, such as the selective oxidation of alkanes, catalytic combustion for power generation and the preferential oxidation of carbon monoxide, has been described.
In the last 30 years, C⁻C cross coupling reactions have become a reliable technique in organic synthesis due their versatility and efficiency. While drawbacks have been experienced on an industrial ...scale with the use of homogenous systems, many attempts have been made to facilitate a heterogeneous renaissance. Thus, this review gives an overview of the current status of the use of heterogeneous catalysts particularly in Suzuki and Heck reactions. Most recent developments focus on palladium immobilised or supported on various classes of supports, thus this review highlights and discuss contributions of the last decade.
Half-sandwich complexes of the platinum group metals serve as excellent precursors and find many applications in biological and catalytic applications. This review focuses on the synthesis, ...biological and catalytic applications of half-sandwich complexes of iridium, rhodium, ruthenium and osmium reported over the last three years. For the catalytic applications the focus will be on catalytic oxidation and transfer hydrogenation. In addition, for biological applications the focus will be on anticancer and antibacterial applications.
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•Reports of half-sandwich complexes of Ir, Rh, Ru, Os of the last 3 years reviewed.•A focus is on catalytic oxidation and transfer hydrogenation.•Their application as cytotoxic and antibacterial agents has also been reviewed.•Very few reports on osmium half-sandwich complexes are noted.
TiO2 catalysts with a varied composition of anatase and rutile were prepared and tested for the oxidative activation of n-octane. The rutile phase of TiO2 was found to be inactive due to its ...relatively low reducibility and surface area. The anatase phase, however, was active. Also, a mixture of anatase and rutile, with an excess of rutile, favored the formation of octene isomers during the oxidative activation of alkane. The favorable activity of TiO2 with an excess of the rutile phase was attributed to its enhanced redox properties brought about by the disorder of the TiO2 lattice at the anatase–rutile junction.
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•New arene ruthenium(II) pyridine-2-carboxaldimine complexes were prepared and characterized.•Three new crystal structure show pseudo-octahedral piano stool geometry.•The complexes ...were applied in the transfer hydrogenation of ketones.•The complexes showed good activity within high turnover numbers.•They were suitable for a wide range of aliphatic, cyclic and aromatic ketones.
The reaction of various pyridine-2-carboxaldimine ligands with the (η6-arene)Ru(μ-Cl)Cl2 dimer followed by a metathesis reaction with ammonium hexaflourophosphate, yielded the ruthenium(II) arene complex salts (η6-arene)RuCl(C5H4N-2CHN-ArPF6; where (arene=C6H6 (1), p-cymene (2), Ar=3, 5-dimethyl phenyl (a), 2,3-dimethyl phenyl (b), 2,5-dimethyl phenyl (c), 3,4-dimethyl phenyl (d)). The compounds were characterized by elemental analysis, FT- IR, UV–vis and 1H and 13C NMR. Single crystal X-ray structures for compounds 1a, 1d and 2e were also determined and showed that the ruthenium(II) centre has a pseudo-octahedral geometry and the molecule adopted a three legged piano stool geometry in which the arene ring occupies the apex and the nitrogen atoms of the N,N′-bidentate ligand and the chloride atom the base of the stool. The Ru(II) complex salts were active for the catalytic transfer hydrogenation of ketones into alcohols in the presence of NaOH using 2-propanol as the hydrogen source at 82°C. The complexes were suitable for a wide range of aliphatic, cyclic and aromatic ketones giving good turn over numbers.
The selective hydrogenation of octyne in a mixed 1‐octyne/1‐octene feed was investigated by employing Pd/Al2O3 and PdAg/Al2O3 catalysts coated with 1‐butyl‐3‐methylimidazolium dicyanamide (BMIMDCA) ...as SCILLs (Solid Catalysts with an Ionic Liquid Layer). All SCILLs were compared to an organically modified, 1‐ethylimidazole (EIM) coated catalyst to determine if there is a SCILL effect. Results of the catalysis showed that both uncoated catalysts were highly active (100 % 1‐octyne and 1‐octene conversion) in the hydrogenation reactions with dominant selectivity towards octane. No increase of 1‐octene in the reactor outflow (octene gain) was noted. Coating 1Pd/Al2O3 with BMIMDCA at four monolayers (ML) corresponding to a surface loading of 45 wt% still gave 100 % octyne conversion but now with a 54 % 1‐octene gain, as no octene was converted. Coating 1Pd9Ag/Al2O3 with only a single monolayer of BMIMDCA (14 wt%) was sufficient to give a 1‐octene gain of 84 % at an octyne conversion of 91 %. Time‐on‐stream reactions for the uncoated and SCILL systems showed stable operation during the experiments.
Catalysts have SKILLS too – the SCILL effect: Whilst all uncoated catalysts showed close to a 100 % conversion of the substrates, the optimised SCILLs (Solid Catalysts with an Ionic Liquid Layer) were able to significantly decrease octene conversion and also improve the 1‐octene gain at high octyne conversions. A 1‐octene gain was achieved with 4 ML of BMIMDCA over the monometallic Pd catalyst, whilst 1 ML of BMIMDCA was sufficient to gain 84 % 1‐octene over the bimetallic SCILL. Octane formation was effectively stopped over the bimetallic SCILL.
A series of alkali metal exchanged phosphomolybdic acid catalysts were synthesized by ion exchange, characterized by various physico-chemical techniques and used in the solvent free oxidation of ...styrene to benzaldehyde. XRD and infrared results showed that the primary structure of the Keggin ion usually present in phosphomolybdic acid is retained after metal exchange. HR-TEM analysis show a well-constructed spherical morphology of the materials with a lower degree of crystalinity. Type IV isotherms with mesoporous structure are observed from nitrogen adsorption–desorption isotherm studies and ex situ pyridine adsorption experiments reveal that Brønsted acidic sites increased after metal exchange. The K exchanged phosphomolybdic acid catalysts were most efficient in the conversion of styrene to benzaldehyde and the order of reactivity of the alkali metal exchanged phosphomolybdic acid catalysts was K > Rb > Cs. Insight into the reaction pathway by investigating the oxidation styrene oxide was obtained. The results show that phenyl acetaldehyde together with benzaldehyde are produced, providing some evidence that styrene oxidation proceeds via C=C cleavage to selectively produce benzaldehyde. The catalyst was easily recovered and was reused for up to three cycles showing stable activity.
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A series of mixed nano-metal oxides of Cu–Ni–Co on γ-alumina with different metal loadings have been synthesized through the ultrasonic cavitation-impregnation method. All the prepared catalysts were ...analyzed by BET, ICP, XRD, SEM–EDS and TEM. The heterogeneous catalytic oxidation of styrene was investigated using tert-butyl hydroperoxide (TBHP) as an oxidizing agent and acetonitrile as a solvent under mild conditions. The influence of the metal loadings, reaction temperatures, oxidizing agents and styrene/oxidant molar ratio was investigated on the styrene conversion and on the selectivity to benzaldehyde and styrene oxide.
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•Supported Cu–Ni–Co oxides were synthesized with good dispersion of the metals.•Ternary nanocatalysed approach was appropriate for styrene oxidation.•Catalysts stimulate direct oxidative cleavage of CC bond to benzaldehyde.•Enhancement in benzaldehyde selectivity is due to synergistic effect of metals.
A series of new chelating bidentate (SS) alkylimidazole-2-thione-Ru(II)/Os(II) complexes (3ai, 3aii, 3aiii, 3bii/4aiii, 4bi, 4bii), and the tridentate (SNS) ...pyridine-2,6-diylimidazole-2-thione-Ru(II)/Os(II) complexes (5bi, 5civ/6bi, 6ci, 6civ) in the forms MII(cym)(L)ClPF6 and MII(cym)(L)PF6 (M = Ru or Os, cym = η6-p-cymene, and L = heterocyclic derivatives of thiourea) respectively, were successfully synthesized. Spectroscopic and analytical methods were used to characterize the complexes and their ligands. Solid-state single-crystal X-ray diffraction analyses revealed a “piano-stool” geometry around the Ru(II) or Os(II) centers in the respective complexes. The complexes were investigated for in vitro chemotherapeutic activities against human cervical carcinoma (HeLa) and the non-cancerous cell line (Hek293) using the MTT assay. The compounds 3aii, 5civ, 5bi, 4aiii, 6ci, 6civ, and the reference drug, 5-fluorouracil were found to be selective toward the tumor cells; the compounds 3ai, 3aiii, 3bii, 4bi, 4bii, and 6bi, which were found not to be selective between normal and tumor cell lines. The IC50 value of the tridentate half-sandwich complex 5bi (86 ± 9 μM) showed comparable anti-proliferative activity with the referenced commercial anti-cancer drug, 5-fluorouracil (87 ± 15 μM). The pincer (SNS) osmium complexes 6ci (36 ± 10 μM) and 6civ (40 ± 4 μM) were twice as effective as the reference drug 5-fluorouracil at the respective dose concentrations. However, the analogous pincer (SNS) ruthenium complex 5civ was ineffective and did not show anti-proliferative activity, even at a higher concentration of 147 ± 1 μM. These findings imply that the higher stability of the chelating (SS) and the pincer (SNS) ligand architectures in the complexes improves the biological (anti-proliferative) activity of the complexes by reducing the chance of ligand dissociation under physiological conditions. In general, the pincer (SNS) osmium complexes were found to be more cytotoxic than their ruthenium analogues, suggesting that the anti-proliferative activity of the imidazole-2-thione-Ru/Os complexes depends on the ligand’s spatial coordination, the nature of the metal center, and the charge of the metal complex ions.
Cubic and rhombohedral phases of lanthanum manganite were synthesized in a high-pressure reactor. A mixture of La and Mn nitrates with ethylene glycol at a synthesis temperature of 200 °C and a ...calcination temperature of up to 1000 °C, resulted in a single-phase perovskite, LaMnO
validated using X-ray diffraction. Significant changes in unit cell volumes from 58 to 353 Å
were observed associated with structural transformation from the cubic to the rhombohedral phase. This was confirmed using structure calculations and resistivity measurements. Transmission electron microscopy analyses showed small particle sizes of approximately 19, 39, 45, and 90 nm (depending on calcination temperature), no agglomeration, and good crystallinity. The particle characteristics, high purity, and high surface area (up to 33.1 m
/g) of the material owed to the inherent PAAR reactor pressure, are suitable for important technological applications, that include the synthesis of perovskite oxides. Characteristics of the synthesized LaMnO
at different calcination temperatures are compared, and first-principles calculations suggest a geometric optimization of the cubic and rhombohedral perovskite structures.
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