High temperature oxidation of Cr–Mo–V tool steel in carbon dioxide

This study aims to examine the oxidation resistance and kinetics of Cr, Mo, and V containing tool steel (Calmax) when exposed in CO₂ high temperature environment by thermogravimetric measurements, X-ray diffraction analysis, and microscopic observation. The tool steel samples begin to oxidize at 480 °C while over 600 °C, the oxidation rate increases significantly. Finally, at 900 °C, the oxidation rate is significantly high. The activation energy of the oxidation was calculated as 160.1 kJ mol^?1. Microscopically, the thickness of the scale was found to increase with the exposure temperature, and the as formed scales consisted of two distinguishable oxide layers.     

High-pressure phase equilibria of some carbon dioxide–organic–water systems

Homogeneous catalysts offer better activity and selectivity than heterogeneous catalysts, but their use is limited by the need to separate them from product and reuse them. Preferential dissolution of gaseous carbon dioxide has been shown to alter phase boundaries and facilitate recovery of such homogenous catalysts. The addition of a polar organic co-solvent to a water/organic biphasic system, coupled with subsequent phase splitting induced by the dissolution of gaseous carbon dioxide creates the opportunity to run homogeneous reactions in an organic/aqueous mixture with a water-soluble catalyst. In homogeneous catalyzed reactions, the catalyst can be tuned to be soluble or insoluble with carbon dioxide present, thus allowing for high catalyst recovery.High-pressure phase equilibria for the systems containing carbon dioxide, an organic (tetrahydrofuran, acetonitrile, or 1,4-dioxane), and water were measured using a variable-volume view cell, by a method capable of rapid and facile measurement of compositions and density in both phases with no sampling or calibration. These systems are well predicted with the Peng–Robinson Equation of State with Huron–Vidal type mixing rules from correlations of the binary systems, with the modified Huron–Vidal 1 (MHV1) and Huron–Vidal–Orbey–Sandler (HVOS) model with UNIQUAC excess energy model performing the best. Applications of the phase behavior on reaction conditions and separations are addressed.     

Reduction of carbon dioxide by hydrogen on metal–carbon catalysts under supercritical conditions

The reduction of carbon dioxide with hydrogen on metal–carbon (Ru, Rh, Ir) catalysts is investigated under supercritical conditions for the first time. High selectivity (close to 100%) toward methanation with good stability of catalytic activity is observed for Ru- and Rh-containing catalyst, while the preferred reduction to CO is observed for Ir/C catalyst.     

Crystallisation kinetics and structure of modified Zn–Al–Cu alloys

The present paper reports induced glass transition dynamics appeared in porous silica (PSi) and nonporous silica (NPSi) nanoparticles. The size of these spherical particles is 5–15 nm for PSi and 15–20 nm for NPSi. PSi shows two glass transitions (Tg1 and Tg2) on heating, whereas NPSi shows one glass transition (Tg). The NPSi shows Tg at a higher temperature than PSi. PSi shows an exothermic transition on cooling, whereas NPSi shows no transition on cooling. Both Tgs appeared in PSi show dynamic behavior with the existence of positive activation energy. Both Tgs are reversible in PSi, whereas NPSi shows only one and irreversible Tg. The observed glass transitions in PSi and NPSi follow the configuron percolation model and show thermodynamic quasi-equilibrium with percolation threshold (fc) <1. The silica nanoparticles show induced glass transitions because of the presence of weak hydrogen bonds (HB) and a weak van der Waal force present in PSi, whereas the lack of porosity in NPSi shows irreversible Tg with stronger HB. The porosity of PSi makes it more reactive and dynamic due to its capillary behavior and shows its applicability in medical sciences, whereas the stability of NPSi makes it important for industrial research.     

Equilibrium and kinetics of calcium–uranyl–carbonate adsorption on silica nanoparticles

Solvent extraction studies on the purification of uranium from zirconium rich sodium diuranate (SDU) feed was carried out using n-tri butyl phosphate (TBP) as extractant and n-decanol as phase modifier. The presence of Zr in SDU leached solution leads to the formation of third phase during liquid–liquid extraction of uranium which was successfully prevented by addition of n-decanol in 30% (v/v) TBP/n-dodecane mixture. A seven stage counter current extraction of SDU feed solution followed by five stage stripping were carried out using optimum concentration of phase modifier 15% n-decanol-30% TBP in n-dodecane as solvent. Based on the findings a process flow-sheet has been developed for the purification of SDU to nuclear grade ammonium diuranate.     

Enhanced physical and chemical adsorption of carbon dioxide using bimetallic copper–magnesium oxide/carbon nanocomposite

Mixed Cu and Mg oxides on nitrogen-rich activated carbon (AC) from Nypha fruticans biomass were characterized and their CO₂ adsorption performance was measured. Highly dispersed CuO and MgO nanoparticles on AC was obtained using an ultrasonic-assisted impregnation method. The optimum adsorbent is 5%CuO–25%MgO/AC having good surface properties of high surface area, pores volume and low particles agglomeration. The higher content of MgO of 5%CuO–25%MgO/AC adsorbent contributes to less metal carbide formation which increases their porosity, surface area and surface basicity. XPS analysis showed some amount of nitrogen content on the surface of the adsorbent which increased their surface basicity towards selective CO₂ adsorption. The presence of moisture accelerated the CO₂ chemisorption to form a hydroxyl layer on the surfaces. The 5%CuO–25%MgO/AC adsorbent successfully adsorbed CO₂ via physisorption and chemisorption of 14.8 and 36.2 wt%, respectively. It was significantly higher than fresh AC with better selectivity to CO₂.     

Modeling the high-pressure phase equilibria of carbon dioxide–triglyceride systems: A parameterization strategy

The group contribution equation of state (GC-EOS) has been used in several published works to correlate or predict the high-pressure phase equilibria of a variety of systems of practical interest. Nevertheless, quantitative and even qualitative disagreement among predictions and experimental data has been detected in mixtures of CO₂ with heavy compounds, such as triglycerides, when operating at high pressure. For instance, phase split up to indefinitely high pressures has been computed, when the observed experimental behavior shows full miscibility at sufficiently high pressure. In the present work, we study the influence on calculated critical lines and solubilities (Pxy diagrams) of the group-based interaction parameters k_ij, for the interactions of CO₂ with both, the triglyceride (TG) group and the paraffinic groups. Based on such study, we propose a parameterization procedure that improves upon the conventional parameter regression practice. The distinguishing feature of such procedure is the repeated observation of the global phase equilibrium behavior, studying in particular the effect of the group–group interaction parameters on critical lines, on the composition of the phases at equilibrium along liquid–liquid–vapor lines, and on selected isothermal or isobaric phase equilibrium diagrams. For the case of the non-randomness parameter, we use a universal positive value, more consistent with its physical meaning.     

First assessment of Li_2O–Bi_2O_3 ceramic oxides for high temperature carbon dioxide capture

The capacity to capture CO_2 was determined in several stoichiometric compositions in the Li_2O–Bi_2O_3 system. The compounds(Li_7BiO_6, Li_5BiO_5, Li_3BiO_4 and LiBiO_2 phases) were synthesized via solid-state reaction and characterized by X-ray diffraction, scanning electron microscopy and N2 adsorption techniques.The samples were heat-treated at temperatures from 40 to 750 °C under the CO_2 atmosphere to evaluate the carbonate formation, which is indicative of the capacity of CO_2 capture. Moreover, Li_7BiO_6 shows an excellent CO_2 capture capacity of 7.1 mmol/g, which is considerably higher than those of other previously reported ceramics. Li_7BiO_6 is able to react with CO_2 from 240 °C to approximately 660 °C showing a high kinetic reaction even at CO_2 partial pressure values as low as 0.05.     

A two-dimensional microporous metal–organic framework for highly selective adsorption of carbon dioxide and acetylene

Solvothermal reaction of 3-aminoisonicotinic acid(Haina) and Cu(NO_3)_2·2.5H_2O gave a novel twodimensional(2D) microporous metal–organic framework, [Cu(aina)_2(DMF)]·DMF(1, DMF = N,N-dimethylformamide). Single-crystal X-ray crystallographic study of compound 1 revealed that Cu(II)ions are linked by ainaàligands forming square grid-like layers, which stack together via multiple hydrogen bonding interactions. The solvent-free framework of 1a displayed considerable porosity(void = 46.5%) with one-dimensional(1D) open channels(4.7 ? ? 4.8 ?) functionalized by amino groups.Gas sorption measurements of 1 revealed selective carbon dioxide(CO_2) and acetylene(C_2H_2) adsorption over methane(CH_4) and nitrogen(N_2) at ambient temperature.     

High-pressure phase equilibria for the carbon dioxide–2-methyl-1-butanol,carbon dioxide–2-methyl-2-butanol,carbon dioxide–2-methyl-1-butanol–water,and carbon dioxide–2-methyl-2-butanol–water systems

High-pressure vapor–liquid equilibria for the binary carbon dioxide–2-methyl-1-butanol and carbon dioxide–2-methyl-2-butanol systems were measured at 313.2 K. The phase equilibrium apparatus used in this work is of the circulation type in which the coexisting phases are recirculated, on-line sampled, and analyzed. The critical pressure and corresponding mole fraction of carbon dioxide for the binary carbon dioxide–2-methyl-1-butanol system at 313.2 K were found to be 8.36 MPa and 0.980, respectively. The critical point of the binary carbon dioxide–2-methyl-2-butanol was also found 8.15 MPa and 0.970 mole fraction of carbon dioxide. In addition, the phase equilibria of the ternary carbon dioxide–2-methyl-1-butanol–water and carbon dioxide–2-methyl-2-butanol–water systems were measured at 313.2 K and several pressures. These ternary systems showed the liquid–liquid–vapor phase behavior over the range of pressure up to their critical point. The binary equilibrium data were all reasonably well correlated with the Redlich–Kwong (RK), Soave–Redlich–Kwong (SRK), Peng–Robinson (PR), and Patel–Teja (PT) equations of state with eight different mixing rules the van der Waals, Panagiotopoulos–Reid (P&R), and six Huron–Vidal type mixing rules with UNIQUAC parameters.     

Peculiarities of sorption isotherm and sorption chemisms of caesium by mixed nickel–potassium ferrocyanide based on hydrated titanium dioxide

The effect of ⁶⁰Co source γ-radiation on β-carotene and chlorophyll-b solutions and on methyl blue dye fixed on cotton fabric has been investigated by colorimetric measurements. For the three reactive pigments, the result obtained shows that the power-law function can be used to predict the value of color difference according to γ-radiation dose. This same behaviour was observed during examination of many other published data. Based on these observations, the power-law function has been proposed as an empirical distribution for modeling the color variation of biologic molecules as a function of irradiation dose.     

High resolution N2 adsorption isotherms at 77.4 K and 87.3 K by carbon blacks and activated carbon fibers--analysis of porous texture of activated carbon fibers by αs-method

The standard α(s)-data of N(2) at 87.3 K by graphitized and nongraphitized carbon black samples (GCB-I and NGCB) (cf.Figs. 3 and 4) have been determined on the basis of the high resolution adsorption isotherms of N(2) at 87.3 K, which were repeatedly measured in the pressure range of p/p(o)=5×10(-8)-0.4. The high resolution adsorption isotherms of N(2) by two kinds of activated carbon fibers (ACF-I and ACF-II) were measured from p/p(o)=10(-7) to p/p(o)=0.995 at 77.4 K and from p/p(o)=10(-7) to p/p(o)=0.4 at 87.3 K. Combination of the adsorption isotherms by ACF-I and ACF-II with the standard α(s)-data by NGCB at 77.4 K and 87.3 K make it possible to construct the high resolution α(s)-plots from very low filling (1%) to complete filling (100%). The high resolution α(s)-plots of N(2) at 77.4 K and 87.3 K were analyzed. On the basis of the analyzed result, the porous textures of ACF-I and ACF-II will be discussed.     

Simultaneous effect of carbon and water on NOx adsorption on a stabilized Pt–Ba/Al2O3 catalyst

The influence of the presence of H₂O on the contact between carbon, used as model soot, and a model four-way catalyst (1% Pt–10% BaO/Al₂O₃) was investigated. NO_x adsorption/TPD cycles at 300 °C together with XRD, XPS and DRIFTS characterizations showed that only surface nitrate species are destabilized by the carbon present in the catalytic bed, leading to a decrease of the NO_x storage capacity and carbonate species formation. In another way, injection of water in the reactive gas flow decreases also the NO_x storage capacity of the catalyst, but promotes the formation of stable nitrate species. A non-cumulative effect of carbon and water was observed. It was proposed that a competition between the destabilization, by carbon, of weakly bonded surface nitrate species and the enhancement of bulk nitrate species formation in the presence of water occurs.     

Acid–base features of ex-hydrotalcites Mg-containing and Mg-free mixed oxides

CuNiAl and MgCuNiAl mixed oxides (Cu²⁺/Ni²⁺ = 0.29 and 0.32 mol/mol) were obtained from layered double hydroxide precursors (M²⁺/Al³⁺ = 2 mol/mol) synthesized by pH-controlled co-precipitation. After structural and textural characterization (by X-ray diffraction and N₂ physisorption, respectively), the acid and basic features of the mixed oxides were investigated by adsorption microcalorimetry. NH₃ and CO₂ were used for probing the acid and basic features, respectively. By the use of temperature-programmed technique, the redox features of the oxides were investigated as well. The behaviour of the oxides as catalysts for the conversion of 4-methylpentan-2-ol at 448, 473, and 523 K under atmospheric pressure was studied in a fixed-bed reactor. The dehydration products distribution and the relative extents of the dehydration and dehydrogenation reactions are discussed in terms of the possible occurrence, depending on the lack or presence of Mg in the oxide and the reaction temperature, of either acid–base-governed E1 and E2 mechanisms or Cu-promoted reaction pathways.     

Effects of the preparation method and calcination temperature on Cu–Cr–Mg–Al catalysts for the dehydrogenation of cyclohexanol

Novel dioxomolybdenum(VI) complexes bearing bis(ferrocenylcarbaldimine) ligands were prepared in good yield and characterized by spectroscopy and elemental analysis. The complexes were found to be excellent catalysts for the homogeneous epoxidation of cyclohexene and styrene using tert-butyl hydroperoxide (TBHP) as oxidant. The complexes can be recovered and reused.     

Predominating stable adsorption and direct electrochemistry of glucose oxidase on carbon nanotubes by oxygen-containing groups

Stable adsorption and direct electrochemistry of glucose oxidase (GOx) occurred on nitric acid (HNO3)-treated multi-walled carbon nanotubes (MWNTs) instead of as-received MWNTs, demonstrating the critical roles of oxygen-containing groups in stableadsorption and direct electrochemistry of GOx on carbon nanotubes (CNTs).     

Pyrolysis and combustion kinetics of microcapsules containing carbon nanofibers by thermal analysis–mass spectrometry

The thermal properties of microcapsules containing carbon nanofibers (CNFs) suspended in ethyl phenylacetate (EPA) were investigated by thermogravimetric analysis coupled with mass spectrometry (TGA–MS). The pyrolysis of these microcapsules consisted of two stages. During the first one (100–150 °C), the emissions of aromatic compounds coming from the decomposition of EPA were identified. In the second one (150–290 °C), NH₂–CO coming from primary amide decomposition was mainly detected.A multiple-step model was used to predict the thermal decomposition of the synthesized microcapsules under both inert and oxidant atmospheres. Furthermore, pyrolysis and combustion kinetic parameters such as pre-exponential factor and activation energy of these microcapsules were estimated by nonlinear regression. An excellent agreement between experimental and predicted data was observed and confirmed from the statistical point of view.     

Electrochemical characterization of sodium and potassium doped lanthanum–titanium mixed oxides prepared by sol–gel method

Varying amounts of Na and K doped lanthanum–titanium oxides were synthesized by gel entrapment technique. These ceramics were characterized by X-ray diffraction. Microstructural investigations revealed grain growth in the doped material compared to undoped sample. Dielectric relaxations of these compounds were investigated in the temperature range 250–900 °C. A high degree of dispersion of the permittivity of un-doped lanthanum–titanium oxide and K and Na doped lanthanum–titanium oxide was observed in the frequency range <100 kHz which was attributed to oxygen vacancies. An increase in the permittivity values were observed with 1 % Na and K doped samples. The permittivity values further deteriorated with the dopant concentration. Using the Cole–Cole model, an analysis of the dielectric loss with frequency was performed, assuming a distribution of relaxation time. The dielectric loss was found to decrease by doping K in lanthanum–titanium oxide matrix. The dc conductivity studies showed that a temperature dependent hopping type mechanism is responsible for electrical conduction in the system.