The Meerwein–Ponndorf–Verley–Oppenauer reaction between 2-hexanol and cyclohexanone on magnesium phosphates

Various magnesium phosphates were tested as catalysts for the vapour-phase Meerwein–Ponndorf–Verley–Oppenauer (MPVO) reaction between 2-hexanol and cyclohexanone. Some of the solids studied are as selective as MgO in this reaction. Others are also active in the dehydration of the alcohols. The activity and selectivity of the catalysts are related to their structure and surface chemical properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nano-sulfated titania (TiO ) as a new solid acid catalyst for Friedel–Crafts acylation and Beckman rearrangement in solvent-free conditions

A novel protocol for the highly selective N-monoalkylation of the sulfamate ester moiety has been developed. This reaction proceeded efficiently using alkyl halides, benzyl halides and α-halo ketones as the electrophile in the presence of KF-Al₂O₃ as a cost-effective and robust catalyst. This approach provides new access to N-monoalkylated Topiramate (anticonvulsant drug) derivatives which are potentially of great importance in medicinal chemistry.     

Phosphorus-containing activated carbon as acid support in a bifunctional Pt–Pd catalyst for tire oil hydrocracking

A bifunctional Pt–Pd catalyst supported on phosphorus-containing activated carbon has been prepared, characterized and tested in the hydrocracking of a hydrotreated tire pyrolysis oil. The product has a very interesting composition: 48–78 wt% naphtha and 19–42 wt% diesel fractions, with moderate amounts of aromatics (< 40 wt%) and sulfur (< 250 ppm). The challenge was to prepare a stable, porous, selective and acid carbonaceous catalyst from a waste (olive stone), which has been confirmed from the catalytic properties and product distribution point of view. In fact, phosphate groups in the activated carbon are stable hydrocracking sites, with comparable performance to that of the acid sites present in amorphous SiO₂–Al₂O₃.     

Multi walled carbon nanotubes supported N-heterocyclic carbene–cobalt (ΙΙ) as a novel,efficient and inexpensive catalyst for the Mizoroki–Heck reaction

In this paper, an N-heterocyclic carbene–cobalt complex (NHC–Co^2 +) was immobilized onto the surface of multi-walled carbon nanotubes (MWCNTs) via direct grafting amination approach for the first time. The resultant composite (Co-–NHC@MWCNTs) was characterized by FT-IR, TGA, XRD, ICP-OES, FE-SEM, TEM and CHN analyses. It was demonstrated that Co–NHC@MWCNTs can act as an efficient and inexpensive catalyst for Heck reactions in normal conditions which provided the corresponding products in moderate to good yields. More importantly, this phosphine and palladium-free catalyst can be reused for at least six successive runs without any discernible decrease in its catalytic activity and no remarkable changes were observed in catalyst structure.     

FeVO4 nanorods supported TiO2 as a superior catalyst for NH3–SCR reaction in a broad temperature range

In this work, a catalyst with FeVO₄ nanorods supported on TiO₂ was prepared and applied for NH₃–SCR reaction. A significantly enhanced low temperature catalytic activity has been achieved in the presence of 10% H₂O with the active window shifting by 15 °C to lower temperatures, compared to the classical catalyst with FeVO₄ nanoparticles supported TiO₂. For the catalyst containing FeVO₄ nanorods, enhanced redox ability and enriched surface active oxygen species originated from its unique crystal structure and predominantly exposed reactive crystal facets (− 2 1 0) on the catalyst surface are responsible for its improved low temperature catalytic activity.     

Synthesis of poly(lactic acid)–poly(ethylene glycol) copolymers using multi-SO3H-functionalized ionic liquid as the efficient and reusable catalyst

Poly(lactic acid)–poly(ethylene glycol) copolymers were synthesized under the catalysis of multi-SO₃H-functionalized ionic liquid. Compared to the ordinary ionic liquids and the traditional Lewis acid catalysts, the ionic liquids with multi-sulfonic acid groups were more catalytically active, and the reaction conversion rate reached up to 97.8 %. The molecular weight of the resulting copolymer was 5.69 × 10⁴ g mol^?1 and the degree of crystallinity was 42.9 %. The copolymers were also of higher hydrophilicity and better mechanical properties. The reaction kinetics of copolymerization was analyzed. The intrinsically high catalytic activity of multi-SO₃H groups originated from the lower activation energy and the higher free acidity. The recovering catalytic activity of the multi-SO₃H ionic liquid catalyst was higher, suggesting that it is a recyclable, environmentally friendly catalyst.     

Air-stable zirconocene bis(perfluorobutanesulfonate) as a highly efficient catalyst for synthesis of α-aminophosphonates via Kabachnik–Fields reaction under solvent-free condition

Zirconocene bis(perfluorobutanesulfonate) [Cp₂Zr(OSO₂C₄F₉)₂·2H₂O] was successfully synthesized by treatment of Cp₂ZrCl₂ with C₄F₉SO₃Ag, and was found to have the nature of air-stability, water tolerance, high thermal stability and strong Lewis acidity. This complex showed high catalytic efficiency for the synthesis of α-aminophosphonates via Kabachnik–Fields reaction of aldehydes/ketones, amines and diethyl phosphite under mild and solvent-free conditions. Furthermore, it can be reused without loss of activity in a test of five cycles. Compared with our previously reported complex of Cp₂Zr(OSO₂C₈F₁₇)₂·3H₂O·THF, this complex showed better catalytic activity.     

Comparison of the morphology of alkali–silica gel formed in limestones in concrete affected by the so-called alkali–carbonate reaction (ACR) and alkali–silica reaction (ASR)

The morphology of alkali–silica gel formed in dolomitic limestone affected by the so-called alkali–carbonate reaction (ACR) is compared to that formed in a siliceous limestone affected by alkali–silica reaction (ASR). The particle of dolomitic limestone was extracted from the experimental sidewalk in Kingston, Ontario, Canada that was badly cracked due to ACR. The siliceous limestone particle was extracted from a core taken from a highway structure in Quebec, affected by ASR. Both cores exhibited marked reaction rims around limestone particles. The aggregate particles were polished and given a light gold coating in preparation for examination in a scanning electron microscope. The gel in the ACR aggregate formed stringers between the calcite crystals in the matrix of the rock, whereas gel in ASR concrete formed a thick layer on top of the calcite crystals, that are of the same size as in the ACR aggregate.     

Preparation of a mesoporous ceria–zirconia supported Ni–Fe catalyst for the high temperature water–gas shift reaction

A Ni–Fe/ceria–zirconia catalyst with ordered mesostructure was prepared by the hard-template method employing mesoporous silica (KIT-6) as a template to impart its highly ordered structure to the ceria–zirconia mixed oxide support. Catalytic activities of the Ni–Fe/CeO₂–ZrO₂ catalyst for the water–gas shift reaction were superior to those of a commercial Fe–Cr-based catalyst. The ordered structure of Ni–Fe/CeO₂–ZrO₂ catalyst became more stable compared to one prepared without zirconia due to structural stabilization of the mixed oxide by added zirconia in the framework. Alloying of Ni and Fe and enhanced mobility of lattice oxygen in the oxide support may promote its catalytic activity and selectivity for the water–gas shift reaction.     

Manipulation of Lewis acid–base complexation in the Zr-centered quaternary system for monodisperse spherical zircons

Zircon (ZrSiO₄) is a distinctive material widely investigated and applied for its superb physicochemical advantages. To date, great challenges remain in the synthesis of high-quality zircon powders for their stringent crystallization requirements at elevated temperature and inherent preferential growth along the [200] direction. Herein we, for the first time, present monodisperse spherical zircon (MSZ) powders synthesized via a facile one-step hydrothermolysis at 200 °C by rationally manipulating the Lewis acid–base complexation of zirconium with competitive ions (Lewis basic R ligands) in a Zr–OH–R–F quaternary system. Systematical investigations were revealed encircling the complexation of Zr⁴⁺ with the R ligands from various sources, which involve the adjusting acids (HR), Zr/Si reactants and halogen-containing mineralizers. Sufficient acidity from the adjusting acid and weak enough Zr–R affinity are confirmed as two paramount factors modulating the crystallization and growth of high-quality MSZ crystals, which undergo a unique metamorphic morphological transition from monolayered, to multilayered, to donut-shaped and ultimately to micrometer-sized spherical particles. The hydrothermal zircons are first confirmed as Zr-deficient (Zr/Si ratios <1.0) zirconium silicates as (ZrO₄)_1–xSi[(OH)_1–y·R_y]_4x, rather than the Si-deficient Zr(SiO₄)_1–x[(OH)·R]_4x as initially proposed and hitherto generally accepted. The MSZ powders exhibit fair thermal stability and terrific monodispersity even after calcination at 1100 °C, superior photoreflectance and much lower thermal conductivity (0.18–0.48 W m^?1 K^?1) over non-spherical zircons. The novel MSZ powders provide arresting prospects to extend the applications of zircon in many traditional and emerging fields.     

New catalyst systems for the polymerization of substituted acetylenes: M(CO)6—Lewis acid—hv (M=W,Mo)

Summary A new catalyst system prepared by UV irradiation of a toluene solution of W(CO)₆ and a Lewis acid polymerized phenylacetylene (e.g., polymer yield 50%, M _n 5.0×10⁴ with SnCl₄ (0.5 equivalent to W(CO)₆) as Lewis acid). This catalyst afforded high molecular weight polymers M _n 4×10⁵ – 5×10⁵) from phenylacetylenes with ortho-substituents (e.g., o-Me₃Si and o-CF₃). The Mo(CO)₆-based counterpart was rather effective to acetylenes having electron-withdrawing groups (e.g., ClC Cph). Polymerization of phenylacetylene occurred as well when SnCl₄ was added after UV irradiation of a toluene solution of W(CO)₆ and the monomer; this suggests that the polymerization proceeds via metal carbenes having coordinated SnCl₄.     

Study on the role of tannic acid–calcium oxide adduct as a green heat stabilizer as well as reinforcing filler in the bio-based hybrid polyvinyl chloride–thermoplastic starch polymer composite

In this study, we prepared a green heat stabilizer tannic acid–calcium oxide (TA–CaO) adduct in a green method and its efficacy was studied in a bio-based polyvinyl chloride-thermoplastic starch polymer matrix. The composite was prepared in a green pathway by melt mixing. CaO in the prepared complex also acted as a reinforcing filler in the composite. The addition of TA–CaO adduct in place of lead carbonate improved all the physical and chemical properties of the composite. The tensile strength and flexural strength improved to 102% and 127%, respectively, in comparison with similar percentage of lead carbonate and TA–CaO adduct. The composite with 15 phr loading of TA–CaO showed improved properties compared with other TA–CaO loaded composites.     

Condensation–cyclization reaction for one-pot synthesis of 1,3-thiazolidin-4-one derivatives by poly(p-phenylenediamine) grafted on LDHs as a catalyst with green tool

The three-component reaction between amine, carbonyl compound and thioglycolic acid is now considered as a major strategy for synthesis of 1,3-thiazolidin-4-ones, which consists of the following steps: (i) condensation of aldehyde and amine which results the formation of an imine; (ii) the reaction between thioglycolic acid and the imine which is followed by an intramolecular cyclization reaction, which leads to the formation of the final product. In this way, if no suitable catalyst is employed, the completion of the reaction will not be achieved. Hence, it is of great importance to select an appropriate catalyst so that these compounds can be successfully synthesized. Herein, we employed LDHs@PpPDA as a versatile catalyst for the fabrication of novel derivatives of 1,3-thiazolidin-4-one.     

Preparation of high-magnetization Fe3O4–NH2–Pd (0) catalyst for Heck reaction

A magnetically separable Fe₃O₄–NH₂–Pd (0) catalyst was easily synthesized by immobilizing Pd nanoparticles on the surface of magnetic Fe₃O₄–NH₂ microspheres. It was found that the combination of Fe₃O₄ and triethylene tetramine (TETA) could give rise to structurally stable catalytic sites. Furthermore, the high-magnetization Fe₃O₄–NH₂–Pd(0) catalyst can be recovered by magnet and reused for six runs for Heck reaction without significant loss in catalytic activity.     

Palladium nanoparticle supported on metal–organic framework derived N-decorated nanoporous carbon as an efficient catalyst for the Suzuki coupling reaction

A novel catalyst made of Pd nanoparticles supported on the N-doped nanoporous carbon, which was derived from Al-based metal−organic frameworks, was successfully fabricated for the first time. The prepared catalyst was characterized by transmission electron microscopy, scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy and N₂ adsorption. The as-obtained catalyst showed high catalytic activity for the Suzuki –Miyaura coupling reactions. The coupling reactions can be conducted at room temperature. The yields of the products were in the range from 90% to 99%. The catalyst can be recycled and reused at least 6 consecutive cycles without any significant loss in catalytic activity.     

IrO2–SnO2 mixtures as electrocatalysts for the oxygen reduction reaction in alkaline media

In this work, SnO₂ + IrO₂ mixed oxides are studied as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media by means of voltammetric techniques under controlled mass transfer conditions thanks to the use of rotating (ring) disk electrodes (RDE/RRDE). The oxides, prepared by sol–gel methodology, are supported on the disk electrodes using a thin layer of anionic exchange polymer as gluing agent. The amount of deposited polymer was optimized to avoid any limitation due to the diffusion of reactant/products across the film thickness. The mixed oxides were prepared at the following mole fractions of IrO₂: $ x_{{{\text{IrO}}_{ 2} }} $  = 0.15, 0.31, 0.55, 0.73, and 1. The role of composition was studied in terms of the reaction pathways and the relevant fraction of H₂O₂ production, together with the potentials of the onset of ORR. The fraction of sites able to give proton/hydroxyl and electron transfers is also determined and discussed. The results point to the best performance of low-Ir containing mixtures and to their low sensitivity to the presence of methanol, a key feature in the case of crossover in alkaline direct alcohol fuel cells.