Organic–silicate hybrid catalysts based on various defined structures for Knoevenagel condensation

Two types of organic–inorganic hybrid base catalysts are prepared. Organic-functionalized molecular sieves (OFMSs), particularly “amine-immobilized porous silicates”, are designed based on common idea to immobilize catalytic active sites on silicate surface. Silicate–organic composite materials (SOCMs), such as “ordered porous silicate–quaternary ammonium composite materials”, are the precursors of ordered porous silicates obtained during the synthesis. Both the OFMS and the SOCM are used as the catalysts for Knoevenagel condensation. Among the OFMSs, there is clear tendency that the use of molecular sieve with larger pore volume and/or surface area gives the product in higher yield. Aminopropylsilyl (AP)-functionalized mesoporous silicates such as AP-MCM-41 gives the product in high yield under mild conditions. No loss of activity is observed after repeated use for three times. The SOCMs are also active for the same reaction. The precursors of the mesoporous silicates are more active than those of microporous silicates. This material can be repeatedly used without significant loss of activity. High activity is not due to the leached species. The active sites of the SOCM catalysts are considered to be SiO⁻ moieties located on the pore-mouth. Activity of the SOCM increases when the reaction is carried out without solvent, whereas decrease in activity of the OFMS is observed in the solvent-free system.     

Role of the hydrotalcite-type precursor on the properties of CPO catalysts

New active and stable nano-structured catalysts obtained from hydrotalcite-type precursors (HT) have been synthesised as catalytic materials for the partial oxidation of methane. The prepared hydrotalcitic precursors containing carbonates or silicates as interlayer anions were calcined and the latter give rise to new mixed oxide and silicates phases. The calcined and reduced catalysts formed by mixed oxide and silicate phases were tested for the catalytic partial oxidation of methane (CPO). Finally, the role of the amount of the active metal and the amount of the excess of silicates inserted as anion were investigated.     

Formation of LiNixCo1−xO2 by decarbonization of organic gel precursors through treatment with nitric acid and hydrogen peroxide

We have used a complex sol–gel process to synthesize a family of compounds LiNi_xCo_1−xO₂ (x = 0, 0.25, 0.5, 0.75, 1). These compounds are candidates for electrode materials in high-energy-density batteries. Starting sols were prepared from xNi²⁺ + (1 − x) Co²⁺ acetates/ascorbic acid aqueous solutions by alkalizing with LiOH and NH₃. With thermal treatment in air, nickel carbonates formed in quantities roughly proportional to Ni concentration. The carbonate impurities could not be fully removed by heating in air to high temperatures. Because formation of pure layered oxides was inhibited by the presence of the carbonates, we developed a new way to remove them from just-formed precursors by treating the intermediate phases (those formed after calcination at 750 °C) with concentrated HNO₃ and H₂O₂. All resulting powders were phase pure by X-ray diffraction and were easily friable. Various electrochemical properties of compacts prepared from these powders were measured.     

Molybdocobaltate cobalt salts: New starting materials for hydrotreating catalysts

This paper deals with the use of Anderson heteropolyanions as alternative starting materials to the ammonium heptamolybdate and cobalt nitrate for the preparation of hydrotreatment oxidic precursors. Ammonium and cobalt salts of molybdocobaltate anions were synthesized and impregnated on alumina. The evolution of these compounds along the different steps of preparation of the oxidic precursors has been followed using various physical techniques such as Raman, XAS and UV–vis spectroscopies. It has been shown that the nature of the surface oxomolybdenum phase strongly depends on the nature of the starting salt. After sulfidation under H₂/H₂S, the performances of these new catalysts have been evaluated in hydrodesulfuration of thiophene. It appears that the cobalt salt of the decamolybdocobaltate anion [Co₂Mo₁₀O₃₈H₄]⁶⁻, with a Co/Mo ratio equal to 0.5, allows us to improve the catalytic conversion by comparison to reference catalysts prepared with ammonium heptamolybdate and cobalt nitrate as starting materials. It has been shown that this improvement is due to the preservation of the heteropolyanionic structure up to the drying step.     

Preparation and magnetic behavior of carbon-encapsulated cobalt and nickel nanoparticles from starch

Carbon-encapsulated cobalt and nickel nanoparticles with core/shell structure have been successfully synthesized with maize-derived starch as carbon source and metal nitrate as metal precursors in flowing hydrogen. The as-prepared M@Cs materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction technique (XRD) and vibrating sample magnetometer (VSM). The effects of the metal precursors on the structure and the size of the M@Cs materials were investigated, and the magnetic properties of the M@Cs materials were measured. The results show that the structure and the size of the M@Cs materials are different in terms of the different metal precursors. The Co@Cs materials are made of the fcc-Co core and the graphitic carbon shell, of which the core diameter is in a range of 20–35 nm, while the Ni@Cs materials are composed of fcc-Ni core and the amorphous carbon shell, of which the core diameter ranges from 30 to 50 nm. The hysteresis loops of the as-made M@Cs materials show that some of the nanoparticles are in a superparamagnetic state at room temperature. A mechanism is proposed to explain the growth process of the M@Cs materials. It is believed that the starch with the helical structure is responsible for the formation of the M@Cs materials featuring the core/shell structure.     

Transformations of molecules and secondary building units to materials: a bottom-up approach

A variety of complex inorganic solids with open-framework and other fascinating architectures, involving silicate, phosphate, and other anions, have been synthesized under hydrothermal conditions. The past few years have also seen the successful synthesis and characterization of several molecular compounds that can act as precursors to form open-framework and other materials, some of them resembling secondary building units (SBUs). Transformations of rationally synthesized molecular compounds to materials constitute an important new direction in both structural inorganic chemistry and materials chemistry and enable possible pathways for the rational design of materials. In this article, we indicate the potential of such a bottom-up approach, by briefly examining the transformations of molecular silicates and phosphates. We discuss stable organosilanols and silicate secondary building units, phosphorous acids and phosphate secondary building units, di- and triesters of phosphoric acids, and molecular phosphate clusters and polymers. We also examine the transformations of metal dialkyl phosphates and molecular metal phosphates.     

Group II Tris(glycolato)silicates as Precursors to Silicate Glasses and Ceramics

Group II tris(glycolato)silicates, MSi(OCH₂CH₂O)₃ (where M = Ba, Ca, Mg), can be synthesized directly by reaction of silica with ethylene glycol and alkaline-earth (group II) oxides at 200°C. These hexa-alkoxy silicates serve as precursors to silicate glass and ceramic powders. They are readily modified by exchange with longer-chain diols into processable polymer precursors. These Theologically useful precursors may provide access to silicate or aluminosilicate powders, thin fllms, fibers, and coatings. Thus, we have examined the utility of hexacoordinate glycolatosilicates as model precursors. Pyrolysis of the compounds, MSi(OCH₂-CH₂O)₃, in air transforms them to their anticipated ceramic products, MO-SiO₂. The phase transformations and chemical changes that occur during pyrolysis were characterized using X-ray powder diffractometry (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), and scanning electron microscopy (SEM). The hexacoordinate glycolatosilicates oxidatively decompose at ∼300°C to form amorphous materials. Moderate to significant quantities of the group II carbonates, MCO₃ (15–50 wt%), form coincidentally as the amorphous intermediates trap CO₂ generated by ligand oxidation. At ∼900°C, the amorphous materials crystallize into the expected, phase-pure, MO-SiO₂.     

Cerium-containing MCM-41 materials as selective acylation and alkylation catalysts

The synthesis of Ce–MCM-41, Al–MCM-41 and Ce–Al–MCM-41-type mesoporous materials was carried out hydrothermally by refluxing the gel with magnetic stirring under atmospheric pressure for 24–36 h. The samples were characterized thoroughly in order to obtain the structural and textural properties, which reveal the presence of well-ordered M41S-type materials. The Ce–MCM-41 samples were used for catalytic acylation of alcohols, thiols, phenols and amines show good activity and selectivity including high chemoselectivity towards selective monofunctional acylation of bifunctional compounds. Quite importantly the acylation of bulky molecules such as cholesterol, ergesterol and β-sitosterol could be achieved using Ce–MCM-41 as solid catalyst. The presence of Ce along with Al in Ce–Al–MCM-41 was found to have synergistic effect as Ce–Al–MCM-41samples were more active catalysts for alkylation of naphthalene compared to either Ce–MCM-41 or Al–MCM-41 with comparable Si/Al or Si/Ce molar ratio.     

Preparation of structured egg-shell catalysts for selective oxidations by the ANOF technique

Shell-type catalysts supported on metal wires were prepared by anodic oxidation with spark discharge (the “ANOF” technique) in the presence of precursors of the catalytically active phase. Aluminium, magnesium and titanium oxide were employed as carriers, whereas nickel (also doped with lithium), chromium or molybdenum were the active components. The carrier oxides displayed regular pore structures determined by the preparation condition and influenced by the precursor of the active component, which was incorporated in the pore system of the carrier during the anodisation process. The nickel-containing catalysts were found to yield 60–90% cyclohexene selectivity in the oxidation of cyclohexane.     

Alumina ceramics with particle inclusions

Alumina composites have been prepared with particle inclusions of 0–30 wt% titanium carbonitride and/or 0–5 wt% nickel, or nickel plus molybdenum metal. The metal was added in three different ways; as metal powder, as metal oxide, or as the intermetallic compound Ti₂Ni. Pressureless sintering at 1750°C gave densities varying from 90% of theoretical density to full density. All materials were post-HIPed to full density at 1600°C before measurement of mechanical properties. Addition of metal alone increased the fracture toughness from 3·0 to 3·7 MPam^1/2, but decreased the Vickers hardness, HV 10, from 1650 to 1500. The simultaneous addition of hard titanium carbonitride inclusions compensated for the decrease in hardness and gave a further increase in fracture toughness. The alumina composites with 5 wt% metal and 30 wt% Ti(C,N) inclusions had a hardness of 1800 and a fracture toughness of about 5 MPam^1/2.     

Preparation and characterisation of mesoporous silica–alumina and silica–titania with a narrow pore size distribution

Amorphous mesoporous materials with a different degree of order in the arrangement of pores are outlined. Particularly, the synthesis of a class of mesoporous silica–alumina (MSA) materials with narrow pore size distribution and a disordered arrangement of pores is reported and discussed. Likewise, the preparation of titanium-containing ordered mesoporous silicates (Ti-MCM-41) and disordered mesoporous silica–titania (MST) are also described in detail. The structural properties of the solids are compared by means of X-ray diffraction and UV-Vis diffuse reflectance spectroscopy. The nitrogen adsorption–desorption measurements were performed and the textural properties are evaluated by the BET, DFT, BJH and t-plot methods.

The high specific surface area and pore volume, as well as the acidity, make MSA solids interesting catalysts in several petrochemical transformations, i.e. oligomerisation, alkylation, hydroisomerisation, rearrangement reactions. Besides, thanks to the width of the mesopores of such solids, the catalytic activity of titanium-containing silicates may have a potential application in the epoxidation of bulky unsaturated fine chemical substrates.     

Study of electrocatalysts for oxygen reduction based on electroconducting polymer and nickel

The properties and electrocatalytic activity were studied of composite carbon‐supported materials based on heterocyclic polymer and nickel, in particular carbon/polyaniline/nickel, carbon/polypyrrole/nickel, carbon/poly(3‐methylthiophene)/nickel, as well as their precursors, carbon/polyaniline, carbon/polypyrrole, and carbon/poly(3‐methylthiophene). The materials were characterized by means of thermogravimetric analysis (TGA), scanning electron microscopy (SEM), EDAX, and electrochemical methods, such as cyclic voltammetry and linear voltammetry using RDE. SEM show porous materials, with a particle size of around 0.3 μm. It was found that in nickel‐modified catalysts between 5 and 6 wt % of nickel is obtained. TGA and FTIR show that the modification with nickel alters the polymer bonds. Curves from cyclic voltammetry show cathodic peaks corresponding to the oxygen reduction reaction (ORR) in all materials, occurring at relatively low potentials. Based on the potential range for ORR as well as kinetic parameters obtained from linear voltammetry using RDE, it was concluded that C‐Ppy‐Ni shows the best performance for ORR in acidic medium. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hydrotreating catalysts containing zeolites and related materials—mechanistic aspects related to deep desulfurization

The deep hydrodesulfurization (HDS) of diesel fuels requires the decomposition of refractory compounds such as 4,6-dimethyldibenzothiophene (46DMDBT). There is a general agreement on the fact that the low reactivity of these compounds is due to steric hindrance of the transition state leading to C–S bond cleavage, which annihilates the effect of the promoter to a large extent. The consequence is that their so-called “direct desulfurization pathway” is particularly inhibited.

Various issues were considered to circumvent the difficulty to eliminate the HDS-resistant molecules and therefore to reach deep desulfurization. Two of them at least consist in designing new hydrotreating catalysts (in addition to the improvement of the alumina-supported conventional catalysts): (i) catalysts with improved hydrogenation properties; (ii) bifunctional catalysts containing an acid component. The main findings obtained with the first class of catalysts are summarized. On these catalysts HDS was found very sensitive to the inhibition by aromatics. The studies regarding the second category of catalysts are analyzed in more detail. Several techniques were used to introduce acid components, including mesoporous materials, in hydrotreating catalysts: physical mixing, binding, deposition of sulfide precursors on an acid–alumina support, deposition of sulfide precursors on an acidic support. Most of these catalysts were found more active than conventional catalysts in the HDS of compounds such as 46DMDBT. The various interpretations of the effect of the acid component are reported and discussed. It is however generally accepted that the improvement of the reactivity, on this category of catalysts, of the HDS-resistant compounds is due to their acid-catalyzed isomerization and disproportionation into more reactive derivatives. When acidic materials were used directly as supports it was difficult to obtain a good association of, for instance, molybdenum, with promoters. Nevertheless, in certain cases catalysts were obtained which were more active than conventional catalysts in the HDS of compounds such as 46DMDBT or of gas oils containing such impurities. However although the catalysts containing acid components proved efficient in hydrotreating various kinds of oils, they suffer several drawbacks such as deactivation by coke deposition and inhibition of HDS by aromatics. Moreover nitrogen impurities which inhibit HDS even with conventional catalysts may also impede seriously their use in practice.     

Nanophase catalytic oxides: I. Synthesis of doped cerium oxides as oxygen storage promoters

Doped CeO₂ materials were synthesized with the aim to improve the performance of CeO₂ as oxygen storage promoter in gas catalytic reactions. The coprecipitation method was used for the synthesis of fine oxalate precursors of high homogeneity and well defined composition. The chemical and morphological properties of both the coprecipitated oxalates and the calcined oxides were examined. The influence of doping of different metal cations into the CeO₂ structure on the oxygen storage capacity in particular was investigated. Some of the doped oxides Ce_0.9M_0.1 O_{2 − δ} (M = Ca, Nd, Pb, etc.) give an increased oxygen storage capacity, 20–40% higher than the undoped. Their redox activity also remarkably increased.     

Stabilisation of active nickel catalysts in partial oxidation of methane to synthesis gas by iron addition

Mixed LaNi_xFe_(1−x)O₃ perovskite oxides (0≤x≤1) have been prepared by a sol–gel related method, characterised by X-ray diffraction (XRD), specific surface area measurements, transmission electron microscopy (TEM) coupled to an energy dispersive X-ray spectrometer (EDS). These systems are the precursors of highly efficient catalysts in partial oxidation of methane to synthesis gas. Studies on the state of these systems after test show the stabilisation of active nickel by increasing the amount of iron. These systems permit to control the reversible migration of nickel from the structure to the surface. The best mixed perovskite for the partial oxidation of methane is LaNi_0.3Fe_0.7O₃.     

Role of CeO2 in Ni/CeO2–Al2O3 catalysts for carbon dioxide reforming of methane

Ni catalysts supported on γ-Al₂O₃, CeO₂ and CeO₂–Al₂O₃ systems were tested for catalytic CO₂ reforming of methane into synthesis gas. Ni/CeO₂–Al₂O₃ catalysts showed much better catalytic performance than either CeO₂- or γ-Al₂O₃-supported Ni catalysts. CeO₂ as a support for Ni catalysts produced a strong metal–support interaction (SMSI), which reduced the catalytic activity and carbon deposition. However, CeO₂ had positive effect on catalytic activity, stability, and carbon suppression when used as a promoter in Ni/γ-Al₂O₃ catalysts for this reaction. A weight loading of 1–5 wt% CeO₂ was found to be the optimum. Ni catalysts with CeO₂ promoters reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and stronger dispersion of nickel. The stability and less coking on CeO₂-promoted catalysts are attributed to the oxidative properties of CeO₂.     

Electrochemical and spectroscopic properties of 1:2 Ni complexes of 1,3-substitued (CH3, OCH3) phenyl-5-phenylformazans

In this study, new 1:2 nickel complexes of 1-[o-, m-, p-(methyl, metoxyphenyl)]-3-(p-metoxyphenyl)-5-phenylformazans were synthesized. Their structures were elucidated and spectral behaviors were investigated with the use of elemental analysis, GC–mass, ¹H NMR, ¹³C NMR, IR, and UV–vis spectra. The redox characteristics of these compounds have been investigated in nonaqueous dimethylsulfoxide at platinum and ultramicro platinum (10 μm) electrodes. Through controlled potential electrolysis, the oxidation products of each class of compounds can be separated and identified. The oxidation mechanism is suggested and it is proved. It was observed the oxidation mechanism take place in a single step two-electron or one-electron transfer to a disproportionation or dimerization reactions following the radical formation step. Eventually the relation between their absorption properties and electrochemical properties was examined.     

Nickel cuprate supported on cordierite as an active catalyst for CO oxidation by O2

The physicochemical, surface and catalytic properties of 10 and 20 wt% CuO, NiO or (CuO–NiO) supported on cordierite (commercial grade) calcined at 350–700 °C were investigated using XRD, EDX, nitrogen adsorption at −196 °C and CO oxidation by O₂ at 220–280 °C. The results obtained revealed that the employed cordierite preheated at 350–700 °C was well-crystallized magnesium aluminum silicate (Mg₂Al₄Si₅O₁₈). Loading of 20 wt% CuO or NiO on the cordierite surface followed by calcination at 350 °C led to dissolution of a limited amount of both CuO and NiO in the cordierite lattice. The portions of CuO and NiO dissolved increased upon increasing the calcination temperature. Treating a cordierite sample with 20 wt% (CuO–NiO) followed by heating at 350 °C led to solid–solid interaction between some of the oxides present yielding nickel cuprate. The formation of NiCuO₂ was stimulated by increasing the calcination temperature above 350 °C. However, raising the temperature up to ≥550 °C led to distortion of cuprate phase. The chemical affinity towards the formation of NiCuO₂ acted as a driving force for migration of some of copper and nickel oxides from the bulk of the solid towards their surface by heating at 500–700 °C. The S_BET of cordierite increased several times by treating with small amounts of NiO, CuO or their binary mixtures. The increase was, however, less pronounced upon treating the cordierite support with CuO–NiO. The catalytic activity of the cordierite increased progressively by increasing the amount of oxide(s) added. The mixed oxides system supported on cordierite and calcined at 450–700 °C exhibited the highest catalytic activity due to formation of the nickel cuprate phase. However, the catalytic activity of the mixed oxides system reached a maximum limit upon heating at 500 °C then decreased upon heating at temperature above this limit due to the deformation of the nickel cuprate phase.     

The synthesis and optical characterization of quinoxalines bearing 2,2′:6′,2″-terpyridine

4′-(4-{2-[6,7-Bis-dodecyloxy-3-(2-p-substituted phenyl-vinyl)-quinoxalin-2-yl]-vinyl}-phenyl)-[2,2′:6′,2″] terpyridine was prepared by the Horner–Wadsworth–Emmons (HWE) reaction of 4-[2,2′:6′,2″]terpyridin-4′-yl-benzaldehyde and quinoxaline derivatives. The absorption and fluorescence maximum of these compounds were observed at 398–443 nm and 484–586 nm, respectively. The compounds were characterized by ¹H NMR spectroscopy and MALDI-TOF-MS, and their recognition properties for metal ions were evaluated using both absorption and emission spectroscopy.     

Calcium zirconate: preparation, properties and application to the solid oxide galvanic cells

Stoichiometric, and doped with a small amount of CaO, calcium zirconate dense samples were prepared. X-ray analysis revealed that the solid solution was formed in the concentration range up to x=0.06 in the {xCaO+(1−x)CaZrO₃} mixture. The activity of CaO in the solid solution was determined by the emf method at the temperatures 1073 and 1273 K. The electrical conductivity was measured using both dc four-probe and ac impedance spectroscopy methods. The maximum conductivity values were observed for the sample with x=0.06. This sample was used for further investigation. The oxygen-ion transference number, estimated by the emf method, appeared to be close to unity. The partial electronic (electron and electron hole) conductivities, deduced from current–potential curves following the polarisation method, were found to be very small with respect to total electrical conductivity. Then, the sample was tested as an electrolyte in solid oxide galvanic cells. In this way, the values of the standard free enthalpy of formation of cobalt and nickel silicates at the temperatures 1073 and 1273 K were determined and compared with those obtained by other authors.