Co–Cu–La catalysts for selective CO2 hydrogenation to higher hydrocarbons

Copper and lanthanum promoted cobalt catalysts for CO₂ hydrogenation to higher hydrocarbons are described. The catalysts were prepared by the self-propagating high-temperature synthesis followed by alkaline leaching. They are active in CO₂ hydrogenation at 200 °C under 10 bar pressure (CO₂ : H₂ = 1 : 3) with selectivity to C₂₊ alkanes up to 39%; no alkenes and alcohols are formed under these experimental conditions.     

Willgerodt–Kindler reaction-driven one pot solventless entry to 2-oxazolines

We report an efficient and green protocol for the synthesis of 2-oxazolines by the reaction of aromatic nitriles with β-aminoalcohols using sulfur under solvent-free conditions. The reaction occurs via the Willgerodt–Kindler mechanism followed by transamidation and dehydrosulfuration. This methodology offers several advantages such as good yields, mild and practical reaction conditions, simple work-up procedure, and broad substrate scope, which makes the process simple, convenient, and environmental-friendly.     

Application of SiO2–water nanofluid to enhance oil recovery

The present study aims to investigate effects of nanofluid flooding on EOR and also compares its performance with water flooding in field scale using the published experimental data provided from core-scale studies. The nanofluid is based on water including silica nanoparticles. The relative permeability curves of water, nanofluid and oil for a light crude oil core sample obtained in an experimental study are used in this numerical investigation. A 2D heterogeneous reservoir model is constructed using the permeability and porosity of the last layer of SPE-10 model. It has been shown that nanofluid flooding can substantially improve the oil recovery in comparison with the water flooding case. Afterward, the operational parameters of the 13 injection and production wells have been optimized in order to meet the maximum cumulative oil production. First, pattern search (PS) algorithm was implemented which has a good convergence speed, but with a high probability of trapping in local optimum points. Particle swarm optimization (PSO) approach has also been employed, which requires a large number of population (to approach the global optimum) with so many simulations. Accordingly, a hybrid PSO–PS algorithm with confined domain is proposed. The hybrid algorithm starts with PSO and depending on the distribution density of the values of each parameter, confines the searching domain and provides a proper initial guess to be used by PS. It is concluded that the hybrid PSO–PS method could obtain the optimal solution with a high convergence speed and reduced possibility of trapping in local optimums.

     

Erratum to: Nanoscale composite materials in the system SiO2–TiO2

Nanoscale composite materials based on the SiO₂–TiO₂ system were prepared in the form of co-precipitated composites and core SiO₂–shell TiO₂ composites, with specific surface area 150–650 m²/g and sorption volumes 0.1–1.0 cm³/g. It is shown that variation of phase composition and morphology permits to change their structural-adsorption properties and nanocrystallites size after thermal treatment. It is discovered that co-precipitated composite materials differ from core SiO₂–shell TiO₂ composites by a component interaction degree. It determines the difference of the titan-containing component crystallization process and alteration of their structural-absorption properties after thermal treatment. The results of the tests of composites as photocatalysts for Rhodamine B decomposition reaction, as catalysts of Hantzsch and Biginelli reaction, and as fillers in electrorheological fluids are shown.     

Cyclization of monoethanolamine to aziridine over Cs2O–P2O5/SiO2

Several commercially available supports were examined for cyclization of monoethanolamine to aziridine, and SiO₂ was found to yield the best results. The obtained results indicated that selectivity of aziridine was mainly influenced by support. The catalysts were characterized by NH₃-TPD and XRD. It was found that SiO₂ with lower acidity could inhibit the intermolecular condensations, and thus favored the formation of aziridine. The Cs₄P₂O₇ phase was confirmed as the active site in the supported cesium phosphate catalyst. The reaction parameters were also optimized and a yield of 52% aziridine was obtained over 200?h. Thus, a continuous process for the cyclization of monoethanolamine to aziridine has been established.     

Decoupling microporosity and nitrogen content to optimize CO2 adsorption in melamine–resorcinol–formaldehyde xerogels

Selected melamine–resorcinol–formaldehyde (MRF) xerogels have been synthesized and analyzed to determine the influence of nitrogen (N) incorporated into the gel structure and resorcinol-to-catalyst (sodium carbonate) and resorcinol-to-formaldehyde molar ratios. The aforementioned factors were varied, and their effect on gel properties was characterized, allowing for a better understanding of how gel characteristics can be tailored and their impact on gel performance. MRF gels, produced in this study, were characterized using volumetric and gravimetric analyses to determine porous structure and quantify CO₂ capture capacities and kinetics, allowing determination of heats of adsorption and activation energies for CO₂. MRF10_200_0.25 has exhibited the largest CO₂ capacity (1.8 mmol/g at 0 °C) of the sample tested. Thermal stability was tested by proximate analysis, and MRF xerogels exhibited high thermal stability; however, it was found that volatile matter increases as [M] increases, particularly for [M] 20%w/w and higher. Working capacity was determined from a series of cycling studies, and capacities of 0.55, 0.58, and 0.56 mmol/g at 60 °C were observed for [M] of 10, 20, and 30%w/w, respectively. The measured heat of adsorption showed that incorporation of nitrogen functionalities results in a low energy penalty, demonstrating that the adsorption mechanism is still driven by physical forces. The results obtained indicate that the family of materials studied here offer potential routes for carbon capture materials, through a combination of micropore structure development and incorporation of favorable Lewis acid–base interactions.     

Gas hydrate formation in the system C2H6–H2–H2O at pressures up to 250 MPa

Decomposition curves of gas hydrates formed in the ethane–hydrogen–water system were studied in the pressure interval 2–250 MPa. Gas hydrates synthesized at low (up to 5 MPa) pressures were also studied with use of X-ray powder diffraction and Raman spectroscopy. It was shown that ethane–hydrogen mixtures with hydrogen contents 0–30 mol.% form cubic structure I gas hydrates. Higher hydrogen concentration most probably results in appearance of another hydrate phase. We speculate that the gas mixtures with the hydrogen content above 60 mol.% form cubic structure II double hydrate of hydrogen and ethane at temperatures below ≈280 K and pressures above 25 MPa.     

Electrochemical reduction of UO2 to U in a LiCl–KCl-Li2O molten salt

An electrochemical reduction of UO₂ to U in a LiCl–KCl-Li₂O molten salt has been investigated in this study. A diagram showing equilibrium potentials (relative to Cl₂/Cl^?) plotted versus the negative logarithms of oxide-ion activity (pO^2?) was constructed. The crushed UO₂ pellets in the cathode basket of an electrolytic reducer were successfully reduced to U. The reduction of UO₂ is proved to proceed mainly through chemical reaction with in situ generated Li and K at the cathode. The control of cathode potential is essential to prevent the deposition and subsequent vaporization of K metal at the cathode for the applications of a LiCl–KCl-Li₂O molten salt as an electrolyte for the metal production from its oxide sources.     

Enhancing CO2 Electroreduction to Methane with a Cobalt Phthalocyanine and Zinc–Nitrogen–Carbon Tandem Catalyst

Developing copper-free catalysts for CO₂ conversion into hydrocarbons and oxygenates is highly desirable for electrochemical CO₂ reduction reaction (CO₂RR). Herein, we report a cobalt phthalocyanine (CoPc) and zinc–nitrogen–carbon (Zn-N-C) tandem catalyst for CO₂RR to CH₄. This tandem catalyst shows a more than 100 times enhancement of the CH₄/CO production rate ratio compared with CoPc or Zn-N-C alone. Density functional theory (DFT) calculations and electrochemical CO reduction reaction results suggest that CO₂ is first reduced into CO over CoPc and then CO diffuses onto Zn-N-C for further conversion into CH₄ over Zn-N₄ site, decoupling complicated CO₂RR pathway on single active site into a two-step tandem reaction. Moreover, mechanistic analysis indicates that CoPc not only generates CO but also enhances the availability of *H over adjacent N sites in Zn-N₄, which is the key to achieve the high CH₄ production rate and understand the intriguing electrocatalytic behavior which is distinctive to copper-based tandem catalysts.     

Influence of the composition of acrylamide–acrylonitrile–2-acrylamido-2-methylpropanesulfonic acid terpolymer on its resistance to high temperatures and salts

The influence of the ratio of the acrylamide, acrylonitrile, and 2-acrylamido-2-methylpropanesulfonic acid monomeric units in the terpolymer on its resistance to elevated temperatures and sensitivity to calcium salts was studied. The influence of the terpolymer composition on the chemical transformations occurring under the conditions of thermal and hydrothermal treatment was studied by TGA and IR spectroscopy. The degree of hydrolysis of the terpolymers influences their resistance to CaCl₂. The resistance of the terpolymers to CaCl₂ additions at their concentrations of up to 7 wt % is preserved at the content of 2-acrylamido-2-methylpropanesulfonic acid units higher than 20 mol %. The revealed features allow optimization of the structure of polymer systems used in drilling lubricants.     

Thermal Methods Applied to the Glass Transition of Mixed Network AlPO4–BPO4–SiO2 Glasses

Glass transition effect of mixed network AlPO₄–BPO₄–SiO₂ glasses was studied. DTA/DSC and TMA measurements has been applied in the research. It has been found that glass transition effect has structurally sensitive properties. Glass transition temperature T _g, changes of specific heat (Δc _p)and thermal expansion coefficient (α) accompanying the process depend on the nature and the number of components forming the glassy framework. Character of chemical bonds combining them into the glass structure has an influence on the glass transition effect. Its course is dependent on the flexibility of the structure of glasses. This revised version was published online in July 2006 with corrections to the Cover Date.     

New approach to simplify the equation for the excess Gibbs free energy of aqueous solutions of electrolytes applied to the modelling of the NH3–CO2–H2O vapour–liquid equilibria

A new, simple, empirical equation for G^E (excess Gibbs free energy) of electrolyte solutions is proposed in which, contrary to the commonly used Pitzer equation, binary and ternary interaction parameters relate to the interactions of electrolytes in a solution rather than to the interactions of real species in a solution (i.e., anions, cations and nondissociated molecules). Such an approach radically reduces the number of parameters in the new equation for G^E as compared with the Pitzer equation and consequently significantly simplifies their calculation. The efficiency of the new approach is demonstrated on the example of modelling the vapour–liquid equilibria of the industrially important and widely investigated NH₃–CO₂–H₂O system.     

Julia–Kocienski approach to trifluoromethyl-substituted alkenes

A Julia–Kocienski approach to trifluoromethyl-substituted alkenes was evaluated in the reactions of 1,3-benzothiazol-2-yl, 1-phenyl-1H-tetrazol-5-yl, and 1-tbutyl-1H-tetrazol-5-yl 2,2,2-trifluoroethyl sulfones with aldehydes. Among the various conditions tested, the best yields were obtained with 1-phenyl-1H-tetrazol-5-yl 2,2,2-trifluoroethyl sulfone, in CsF-mediated, room temperature olefinations in DMSO. Aromatic aldehydes gave (trifluoromethyl)vinyl derivatives in 23–86% yields, with generally moderate stereoselectivity. Straightforward synthesis of the Julia–Kocienski reagent, and conversion to trifluoromethyl-substituted alkenes under mild reaction conditions, are the advantages of this approach.     

Convenient approach to Si–H-containing polymers

New synthetic routes to organosilicon polymers containing SiH₂ groups and organic -electron units in the polymer main chain are described. These polymers are expected to be useful precursors for ceramics. The polymer backbone is formed by condensation of ,-bis(trifluoromethylsulfonyloxy)-substituted organo-silicon compounds containing SiH₂ groups with the organometallic dinucleophiles Li₂C₂, Li₂C₄, and 1,4-BrMg–C₆H₄–MgBr. We could confirm the formation of the silicone polymers at low temperatures, in short reaction times, and with high yields. The structural characterization is based on ²⁹Si, ¹³C, and ¹H NMR spectroscopy. The narrow ²⁹Si NMR signals of the products indicate the regular alternating arrangement of the building blocks in the polymer backbone resulting from the fact that the condensation reactions are not accompanied by exchange processes analogous to metal halogen exchange. Weight-average molecular weights in the range of M_w = 10000–20000, relative to polystyrene standards, were found by GPC. The pyrolytic behaviour of [H₂Si–H₂Si–C C–]_n 2a is compared with the behaviour of the methylated derivative [Me₂Si–Me₂Si–C C–]_n.     

Well-dispersed porous Fe–N–C catalyst towards the high-selective and high-efficiency conversion of CO2 to CO

In this study, through direct pyrolysis of a nitrogen-rich metal-organic framework of Fe-BTT at different temperatures and followed by acid treatment, we prepared a series of Fe–N–C_T (T = 800–1000 °C) composite catalysts with uniform cubic morphology and homogeneously distributed active sites. Acid leaching leads to the removal of excess Fe NPs and the exposure of more pyridinic N and porphyrin-like Fe–N_x sites and creates a higher specific surface area. Structural and electrochemical performance test results showed that Fe–N–C₉₀₀ catalyst exhibited the highest selectivity for CO product at –1.2 V vs. Ag/AgCl, with 496 mV of overpotential and 86.8% of Faraday efficiency, as well as excellent long-term stability, due to the good inheritance from rich-N Fe–BTT precursor.     

From Hartree–Fock and Heitler–London to chemical orbitals

For chemistry the theoretical representation of the forces connecting atoms in molecules was and is a central problem. The Atomic Orbital and the Molecular Orbital are basic building blocks in the Heitler–London (HL) and in the Linear Combination of Atomic Orbitals–Molecular Orbital (LCAO-MO) methods, which have lead to the construction of modern Valence Bond and Hartree–Fock methods (and related extensions). However, accurate predictions from non semi-empirical methods often require enormous amount of computer power, if applied to molecules of reasonable size and current chemical interest. We have critically re-examined the two basic methods and suggested a few extensions. Merging of the Hartree–Fock with the Heitler–London algorithms, as recently proposed in the Hartree–Fock–Heitler–London (HF–HL) method, reduces the length of the expansions needed in AO or MO ab initio models in the computation of binding energy; this simplification allows easy interpretation of the resulting wave function. The HF–HL method is exemplified with systematic computations on ground and excited state of the hydrides and homonuclear diatomic molecules with atoms of the first and second period of the periodic table. Further, we show that the HF–HL method is derivable from a wave function constructed with a new type of orbital, the Chemical orbital (CO), which embodies the characterization of MO near equilibrium, AO at dissociation and at the united atom. Preliminary computations with CO are included. The new method provides the conceptual origin of both the HF and VB approaches, thus the foundation of an 80 years effort in variational quantum chemistry.     

Synthesis and characterization of Na2O–CaO–SiO2 glass–ceramic

The Na₂O–CaO–SiO₂ ternary glass–ceramic with the composition of 49 mass% Na₂O, 20 mass% CaO, and 31 mass% SiO₂ was prepared by the conventional method. The ternary glass–ceramic was characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques. The Na₂CaSiO₄ phase, having the cubic crystal system, with the crystallite size of 25.14 nm and lattice parameter of 0.7506 nm was determined from the XRD pattern. The activation energy of the glass–ceramic calculated from the DTA curves was found to be 162.02 kJ mol^?1. The Avrami exponent was found to be ~2 indicating a one-dimensional growth process. The mass loss percent from ambient temperature to 1,173 K is less than 1 %. The density was calculated to be 2,723 kg m^?3. The fine-grained microstructure with the particle sizes less than 1 μm was confirmed by the scanning electron microscope micrograph.     

Erratum to: Sol–gel synthesis of mesoporous WO3–TiO2 composite thin films for photochromic devices

Mesoporous WO₃–TiO₂ composite films were prepared by a sol gel based two stage dip coating method and subsequent annealing at 450, 500 and 600 °C. An organically modified silicate based templating strategy was adopted in order to obtain a mesoporous structure. The composite films were prepared on ITO coated glass substrates. The porosity, morphology, and microstructures of the resultant products were characterized by scanning electron microscopy, N₂ adsorption–desorption measurements, μ-Raman spectroscopy and X-ray diffraction. Calcination of the films at 450, and 500 °C resulted in mixed hexagonal (h) plus monoclinic phases, and pure monoclinic (m) phase of WO₃, respectively. The degree of crystallization of TiO₂ present in these composite films was not evident. The composite films annealed at 600 °C, however, consist of orthorhombic (o) WO₃ and anatase TiO₂. It was found that the o-WO₃ phase was stabilized by nanocrystalline anatase TiO₂. The thus obtained mesoporous WO₃–TiO₂ composite films were dye sensitized and applied for the construction of photochromic devices. The device constructed using dye sensitized WO₃–TiO₂ composite layer heat treated at 600 °C showed an optical modulation of 51 % in the NIR region, whereas the devices based on the composite layers heat treated at 450, and 500 °C showed only a moderate optical modulation of 24.9, and 38 %, respectively. This remarkable difference in the transmittance response is attributed to nanocrystalline anatase TiO₂ embedded in the orthorhombic WO₃ matrix of the WO₃–TiO₂ composite layer annealed at 600 °C.