Effect of Nano‐Copper Oxide and Copper Chromite on the Thermal Decomposition of Ammonium Perchlorate

The catalytic effect on the thermal decomposition behavior of ammonium perchlorate (AP) of p‐type nano‐CuO and CuCr₂O₄ synthesized by an electrochemical method has been investigated using differential scanning calorimetry as a function of catalyst concentration. The nano‐copper chromite (CuCr₂O₄) showed best catalytic effects as compared to nano‐cupric oxide (CuO) in lowering the high temperature decomposition by 118 °C at 2 wt.‐%. High heat releases of 5.430 and 3.921 kJ g⁻¹ were observed in the presence of nano‐CuO and CuCr₂O₄, respectively. The kinetic parameters were evaluated using the Kissinger method. The decrease in the activation energy and the increase in the rate constant for both the oxides confirmed the enhancement in catalytic activity of AP. A mechanism based on an electron transfer process has also been proposed for AP in the presence of nano‐metal oxides.     

Synergistic effect between CuCr2O4 nanoparticles and plasticizer on mechanical properties of EP/PU/CuCr2O4 nanocomposites: Experimental approach and molecular dynamics simulation

In this research, copper chromite (CuCr₂O₄) nanoparticles (NPs) were synthesized by the sol–gel auto-combustion method. The effects of CuCr₂O₄ NPs and polyurethane (PU) on the tensile strength of the epoxy (EP) resin were studied by considering different weight percentages (wt%). The response surface methodology (RSM) coupled with central composite design (CCD) (RSM/CCD) methods were also used to optimize the Young's modulus, yield strength, and ultimate tensile strength of the EP/PU/CuCr₂O₄ nanocomposites. The composition structure and morphology of the EP/PU/CuCr₂O₄ nanocomposites were determined using the Fourier Transform Infrared spectroscopy (FT-IR), X-ray diffraction, UV–vis diffuse reflection, Scanning Electron Microscopy, X-ray energy dispersive spectroscopy, and thermogravimetric analysis. It was also shown that the RSM/CCD methods could be utilized effectively to find the optimum process variables in the tensile test of the EP/PU/CuCr₂O₄ nanocomposites. Moreover, the tensile test revealed that the presence of the CuCr₂O₄ NPs in the EP/PU matrix improved the mechanical properties. Best results were obtained with the 0.76 wt% of the CuCr₂O₄ NPs and the 2.6 wt% PU in the epoxy resin. The molecular dynamic simulation was used to illustrate the effect of the NPs on the interaction energy and mechanical properties of this nanocomposite. The calculated interaction energy for the EP/PU/CuCr₂O₄ nanocomposites was −437.96 Kcal/mol. The results showed that Young's modulus had relative agreement with the experimental results.     

十二烷基苯磺酸钠辅助尿素共沉淀制备超细铜铬黑颜料

以十二烷基苯磺酸钠为表面活性剂,采用尿素共沉淀法合成超细尖晶石型铜铬黑颜料。以铬和铜硝酸盐为原料,系统研究了沉淀剂、煅烧温度和表面活性剂等条件对铜铬黑颜料晶型、形貌和粒度的影响;并探讨了合成条件对铜铬黑颜料着色力的影响。研究表明,尿素和十二烷基苯磺酸钠可有效地控制形貌、颗粒大小及均匀性;在尿素用量为理论量4倍、表面活性剂添加量为5%、煅烧温度800℃的条件下制备出了形貌为六面体、平均粒径为300 nm、粒径分布均匀、着色力优异的超细铜铬黑颜料。     

Chemical beneficiation of coal with aqueous hydrogen peroxide/sulphuric acid solutions

The removal of sulphur and ash from coal treated with aqueous hydrogen peroxide/sulphuric acid solutions has been studied at ambient temperature, under a variety of experimental conditions. Almost complete elimination of the sulphate and the pyritic sulphur was observed in most cases, as well as substantial reduction in the ash content. The other components of the organic coal matrix were not affected to a significant extent, indicating high selectivity of the $\text{H}{}_2\text{O}{}_2\text{H}{}_2\text{SO4}$ system towards sulphur oxidation. An optimal H₂SO₄ concentration was established, above which the acid was found to have an adverse effect on the oxidation of pyrite by hydrogen peroxide.     

Cathodic reduction of oxygen on copper and brass

In this investigation, the electrochemical reduction of oxygen on copper and brass has been studied using the ring-disc electrode technique in solutions containing chloride, sulphate and nitrate anions and ammonium cation. The E—I curves obtained in the forward and reverse direction of polarization for copper and brass in NaCl, Na₂SO₄ and NH₄Cl solutions are similar in nature and show two waves. However in (NH₄)₂SO₄ and NH₄Cl solutions are similar in nature and show two waves. The rate of oxygen reduction is the highest in ammonium sulphate for both copper and brass whereas it is the lowest in NH₄Cl in the case of copper. In Na₂SO₄ and NaCl solutions, the rate of oxygen reduction is higher on copper than on brass. Apparent Tafel slopes for oxygen reduction obtained for copper and brass vary from 65 mV to 240 mV depending upon the medium.The two steps observed with copper disc electrode have been identified as due to the reduction of oxygen to hydrogen peroxide and reduction of H₂O₂ to OH^? ion or water depending upon the pH of the solution. In acid chloride and sulphate media no H₂O₂ was detected, which suggests direct reduction to H₂O. The diagnostic plots of I_d/I_rυs ω^{?$\text{1}\text{2}$} employed by Bockris et al indicate that in Na₂SO₄ the reduction of oxygen to H₂O₂ takes place in a parallel reaction whereas in (NH₄)₂SO₄ both direct reduction of O₂ to water (or OH^? ion) and the reduction through intermediate H₂O₂ occur.     

Reduction of nitric oxide by carbon monoxide on copper catalysts

An experimental study has been carried out of the kinetics and mechanism of the reduction of NO by reaction with CO on unsupported and supported copper catalysts. At low CO concentrations ($\text{3 <}\text{CO}\text{NO}\text{< 10}$), the kinetics of this reaction exhibit an effective reaction order of unity with respect to NO; hence, the fractional conversion is independent of the reactant level. However, relatively high CO concentrations ($\text{CO}\text{NO}\text{> 10}$) in the gas stream cause reaction inhibition. On the basis of the experimental results a reaction mechanism is proposed involving dissociative chemisorption of nitric oxide. The formation of an isocyanate (NCO) species on the copper surface is responsible for reaction inhibition. This species acts as the precursor for ammonia formation in the presence of water vapor. The dissociative chemisorption step of NO on a copper surface has an activation energy of 9.3 kcal/mole, a value unaffected by such supports as SiO₂ or CuAl₂O₄.     

Stabilization effect of Co for Mo phase in CoMoAl2O3 hydrodesulfurization catalysts studied with X-Ray photoelectron spectroscopy

The promotional effects of Co in $\text{CoMo}\text{Al}{}_2\text{O}{}_3$ hydrodesulfurization (HDS) catalysts were studied by means of X-ray photoelectron spectroscopy. The higher MoO₃-content $\text{Mo}\text{Al}{}_2\text{O}{}_3$ catalysts (10 and 20 wt% MoO₃) contain mobile Mo, which migrates from the pores to the outermost surface layers of the catalysts and segregates to form less active crystalline MoS₂ during the HDS reaction, while in the case of $\text{Mo}\text{Al}{}_2\text{O}{}_3$ (5 wt% MoO₃) catalyst: no migration of Mo was observed. It is revealed that the Co in $\text{CoMo}\text{Al}{}_2\text{O}{}_3$ catalyst inhibits the migration and segregation of Mo and that it keeps Mo effective for the HDS reaction, since no surface enrichment of Mo was observed. It is concluded that stabilization of the Mo monomolecular layer is the main role of Co. The active species of Mo is suggested to have the composition of S/Mo(IV) = 1 on the basis of the sulfur contents of the catalysts under the mild HDS reaction conditions.     

Effects of metal-support interactions on the hydrogenation of CO over PdSiO2 and PdLa2O3

A study of CO hydrogenation over $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$ has been carried out for the purpose of identifying the effects of Pd dispersion, Pd morphology, and support composition on the catalytic activity of supported Pd. The specific activity of each catalyst for methanol and methane synthesis was determined from microreactor studies carried out at a fixed set of reaction conditions. Palladium dispersion was measured by H₂O₂ titration, and the morphology of the Pd crystallites, as expressed by the distribution of Pd(100) and Pd(111) planes, was determined from in situ infrared spectra of adsorbed CO. The crystallite morphology of the $\text{Pd}\text{SiO}{}_2$ catalysts is the same, independent of Pd weight loading: 90% of the surface is comprised of Pd(100) planes and 10% of the surface is comprised of Pd(111) planes. By contrast, the crystallite morphology of the $\text{Pd}\text{La}{}_2\text{O}{}_3$ catalysts changes with Pd loading. Primarily Pd(100) planes are exposed at low-weight loadings while Pd(111) planes are exposed at high-weight loadings. The Pd dispersion has little effect on the methanol turnover frequency over both $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$, for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over $\text{Pd}\text{SiO}{}_2$, but increases with decreasing dispersion over $\text{Pd}\text{La}{}_2\text{O}{}_3$. It is further observed that the Pd morphology influences the specific activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ is a factor of 7.5 greater than that of $\text{Pd}\text{SiO}{}_2$.     

Thermal Decomposition of AMMO/AP Composite Propellants

Thermal decomposition of AMMO/AP composite propellants was studied by DTA, TGA and DSC in helium atmosphere. The effects of accelerated aging at 347 K for 370 days on decomposition kinetics were also measured. AMMO/AP propellant showed two different decomposition steps, which were mainly the AMMO binder decomposed region and the reaction of AP dominated region. These regions were separated at around 20 % weight loss point at the condition used in this study. AMMO binder decomposition and AP decomposition were strongly related each other. The heat generated by the AMMO binder decomposition initiated and accelerated the thermal decomposition of AP. Although both Fe₂O₃ and CFe activated the thermal decomposition of AMMO/AP propellants, CFe mainly accelerated the decomposition of AMMO binder and Fe₂O₃ catalyzed the AP reactions which consisted of the AP decomposition and the reaction between decomposed AP and decomposed AMMO binder. AMMO/AP composite propellants were thermally stable even after aging at 347 K for 370 days.     

Platinum catalysts supported on graphitized carbon black—I: Characterization of the platinum by titrations and differential calorimetry

A graphitized carbon black and samples resulting from its oxidation in air at 798 K over different periods of time have been used as supports for platinum catalysts. Platinum dispersion and mean diameter of platinum particles have been determined by O₂-H₂, H₂-O₂ and O₂-CO titrations and by differential calorimetry of the O₂-H₂ reaction. Comparison of titration results does not permit an unambiguous choice of $\text{Pt}\text{O}$ or $\text{Pt}\text{CO}$ ratios to be used in the titration stoichiometries. However, results from the calorimetric study suggest that the $\text{Pt}\text{O}$ ratio should be taken as one. Dispersion increases with increasing burn-off of the support, the surface area of the support being the principal factor conditioning the platinum dispersion, although there is also a smaller contribution due to the increase in surface heterogeneity.     

Conformation and packing analysis of polysaccharides and derivatives: 6. Detailed refinement of tri-O-ethylamylose-solvent complexes TEA1-C1 and TEA1-DCM1

The crystal structures of two tri-O-ethylamylose polymorphs, with chloroform (TEA1-C1) and with dichloromethane (TEA1-DCM1) inside the crystal lattice, have been investigated. Both polymorphs are very similar: they crystallize in an orthorhombic unit cell, space group P2₁2₁2₁. The chain conformations are 4₃ helices with a 4.005 Å rise per residue. The X-ray diffraction diagrams can be indexed with $\text{a = 16.76 ± 0.02}\text{A}\text{?}$, $\text{b = 14.28 ± 0.03}\text{A}\text{?}$, $\text{c = 16.02 ± 0.03}\text{A}\text{?}$ (fibre repeat) for TEA-C1 and $\text{a = 16.52 ± 0.02}\text{A}\text{?}$, $\text{b = 13.95 ± 0.02}\text{A}\text{?}$, $\text{c = 16.02 ± 0.02}\text{A}\text{?}$ (fibre repeat) for TEA1-DCM1. Two chains pass through the unit cell, and four solvent molecules are located in the interstitial spaces of the unit cell with close Cl … O interatomic contact distances.     

Ca3SiO5 and its fluorine-stabilized aristotype: Synthesis,stability and postulated structure of Ca6−0.5xSi2O10−xFx

Single crystal structural studies disclose hexagonal symmetry, $\text{a = 7.099 ± 0.003}\text{A}\text{?}$, $\text{c = 5.687 ± 0.002}\text{A}\text{?}$. The structure has been refined in space groups P6₃mc and finally in P6₃/mmc. The ideal cell contents are Ca₆Si₂O₁₀; any fluorine present is postulated to substitute randomly for oxygen with concommitant Ca omission. The close structural relations between this phase and Ca₃SiO₅ are described.     

Synthesis and Characterization of Antibacterial Activity of Spinel Chromium-Substituted Copper Ferrite Nanoparticles for Biomedical Application

Metal ferrite nanoparticles (NPs) attracted much attention due to their superparamagnetic, catalytic properties and surface area to volume ratio. Among these spinel ferrite NPs have shown immense potential in nanomedicine. The objective of present research work was the synthesis of chromium-substituted spinel copper ferrite NPs [(CuCr_xFe_2?xO₄ (0.0?≤?x?≤?1.0)] by coprecipitation method and characterization of their antibacterial activity against E. coli. The synthesized ferrite NPs were characterized by X-ray diffraction, FT-IR, UV- Vis diffuse reflectance, SEM, Brunauer-Emmett-Teller (BET) and Barrett–Joyner–Halenda (BJH) techniques. XRD analysis confirmed that the all the samples were cubic spinel in structure with crystal size of 43.3–20.2 nm. It has been found that as the amount of dopant (Cr) increases, size of the NPs decreased. The E_g values were found in the range of 1.20–1.80 eV for CuCrxFe_2???xO₄ (0.0?≤?x?≤?1.0) NPs as analyzed by UV–Visible diffuse reflectance spectroscopy. The BET surface area of Cr-substituted ferrite NPs decreases as Cr content increased while the pore diameter increases when moved from CuFe₂O₄ to CuCrFeO₂ analyzed by BJH. The antibacterial activity increases as the concentration of dopant (Cr) increased. It has been found that CuCr_xFe_2?xO₄ NPs inhibit bacterial growth in a size dependent manner i.e., small size NPs (CuCr_xFe_2?xO₄; 20.2 nm; x?=?1.0) exhibit strong antibacterial activity (MIC; 2.5 mg/ml), whereas large size NPs (CuCr_xFe_2?xO_4; 43.3 nm; x?=?0.0) inhibit bacterial growth at concentration of more 16 mg/ml. SEM micrograph shows that CuCr_xFe_2?xO₄ NPs get adhered to bacterial cell surfaces and damaged the cell membrane due to interaction between NPs and cell membrane. Cells treated with CuCr_xFe_2?xO₄ NPs were irregular and abnormal in shape with distorted cell membrane. CuCr_xFe_2?xO₄ NPs severely damaged E. coli cells might be because of formation of pits, indentation, deformation and distortion of cell wall and membrane, indicating significant loss of membrane integrity that may lead to cell death.     

Studies of a CuY zeolite as a redox catalyst

The stability and behavior of CuY in the redox cycles with $\text{CO}\text{O}{}_2$, $\text{H}{}_2\text{O}{}_2$, and $\text{CO}\text{NO}$ have been studied using a microbalance operating in the flow mode and with a standard (BET) volumetric system. When CO was used as a reducing agent CO₂ was produced, thus removing oxygen from the zeolite lattice, but when H₂ was used only some of the H₂ consumed was evolved as H₂O. The rest was retained as lattice OH groups, but this was minimal when H₂ was used after treating the sample with CO. Oxidation with NO produced only N₂. At 500 °C the sample was stable and could be reversibly oxidized and reduced through many cycles using either $\text{CO}\text{O}{}_2$ or $\text{NO}\text{CO}$. In all cases the ratio $\text{O}\text{Cu}$ was close to 0.5, i.e., $\text{1e}\text{Cu}$. Treatment in CO at higher temperatures did not affect the reversible nature of the oxidation, but now the valence change was substantially larger; it approached $\text{2e}\text{Cu}$. The crystallinity of the exchanged zeolite was studied using X-ray diffraction and by measurement of the pore filling with liquid N₂. No significant changes could be detected after the different treatments, even those performed at 750 °C. Temperature-programmed reduction, temperature-programmed oxidation, and X-ray diffraction studies were made and the different maxima are reported. CuO and Cu ^o appeared in the oxidized and reduced samples, respectively, after treatment at 750 °C in CO but not at lower temperatures. Subsequent redox cycles at 500 °C did not appear to affect the size or amount of Cu ^o crystallites. CuY was active in the oxidation of CO with O₂ or NO. Its activity was lower than that of FeY zeolite when it exhibited an oxygen-carrying capacity of 0.5 $\text{O}\text{Cu}$. Treatment with CO at 750 °C, however, reversed the situation. Kinetic results showed that the fresh CuY catalyst was close to zero order in CO and fractional order in O₂ with an activation energy of 15 kcal/mole. After treatment at 750 °C in CO, the rate law became dependent upon the $\text{CO}\text{O}{}_2$ ratio. It was close to first order in CO and zero order in O₂ under oxidizing conditions ($\text{CO}\text{O}{}_2\text{≤ 2}$), but the orders were reversed under reducing conditions ($\text{CO}\text{O}{}_2\text{> 2}$). The activation energies were 12 and 15 kcal/mole, respectively. The data suggested that the Cu²⁺ with bound oxygen are the species active in the oxidation reaction.     

Effect of carboxylic acids on the cathodic reduction of benzophenone in N,N-dimethyl-formamide. Polarographic and CNDO/2 studies

Effect of eight carboxylic acids on the polarographic reduction of benzophenone in N,N-dimethylformamide has been studied. In the presence of these acids, a new cathodic wave (“pre-wave”) appears at more positive potentials than the original wave of benzophenone. Linear correlation has been found between ΔE_{$\text{1}\text{2}$} and the pK^DMF_a values of acids, where ΔE_{$\text{1}\text{2}$}  (E^pre-wave_{$\text{1}\text{2}$}  E^{original wave}_{$\text{1}\text{2}$}). It is suggested that in all the cases investigated the reduction proceeds via a hydrogen-bonded complex formed between the carbonyl compound and the acid in the double-layer. The structural aspects of the benzophenoneformic acid adduct have been solved using CNDO/2 method.     

Reinvestigation of the system C4A.nH2O  C4A.Co2.nH2O

The system C₄A.nH₂O  C₄A.CO₂.nH₂O has been reinvestigated at 22°, 100 % and 65 % relative humidity. Formation conditions, composition and crystallographic properties of the phases C₄A.nH₂O, C₄A.1/2CO₂.nH₂O, C₄A.CO₂nH₂O and their dehydration products have been studied by X-ray and elektron diffraction, infrared and Raman spectroscopy, dynamic weight-loss curves and differential thermal analysis. Only very limited solid solution occurs in the system. X-ray single crystal studies showed the quaternary compound C₄A.1/2CO₂.12H₂O to be trigonal with space group R3c or R$\text{3}$c, lattice parameters $\text{a}{}_{\mathrm{o}}\text{=5.77}\text{a}\text{?}\text{,}\text{C}{}_{\mathrm{<mtext>o</mtext>}}\text{=49.16}\text{a}\text{?}$. C₄A.CO₂11H₂O is triclinic with $\text{a}{}_{\mathrm{o}}\text{=5,}{}_{\mathrm{o}}\text{=5.74}\text{A}\text{?}\text{,}\text{C}{}_{\mathrm{o}}\text{=7.86}\text{A}\text{?}\text{α=92.61°, β=101.96°, δ=120.09°}$. Indexed powder diffraction data of both compounds are given.     

Infrared spectroscopic studies of the hydration products of the system CaOAl2O3CaSO4SiO2

Hardened pastes in this system were studied by infrared spectroscopy. The anhydrous mixes, which had bulk compositions C₆A$\text{S}$₃S_0–4 and C_6–10A$\text{S}$₃S₂, contained C₄A₃$\text{S}$ and other phases. Addition of silica to the bulk composition C₆A$\text{S}$₃ inhibited ettringite formation, unless the lime content was also increased. These results confirm ones previously obtained by X-ray diffraction and thermal analysis.     

Methane Combustion Over Copper Chromites Catalysts Prepared by the Sol–Gel Process

Abstract  

Methane combustion was performed over a series of copper chromites (CuCr₂O₄) catalysts prepared by the sol–gel process (SG). The results were compared with those obtained over commercial CuCr₂O₄. The samples were characterised by elemental analysis, thermal analysis, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The as-synthesised CuCr₂O₄ sample exhibited higher specific surface area (248 m² g⁻¹) with respect to commercial solids (42 m² g⁻¹). The surface properties were established using XPS. Simultaneously, an increase in the atomic Cr⁶⁺/Cr³⁺ ratio (0.56 for SG catalyst vs. 0.39 for commercial sample) and a decreasing surface copper concentration (8.3%, for SG specimen vs. 17.6% for commercial catalyst) are observed. XPS study revealed also that Cu²⁺/(Cu° + Cu⁺) ratio of copper species remained constant (ca. 5) in both catalysts. Structure transformations of CuCr₂O₄ under reduction-reoxidation conditions showed that the reduction of copper and/or chromium cations from the CuCr₂O₄ and from delafossite (CuCrO₂) structure (CuCr₂O₄↔CuCrO₂ + Cu + Cr₂O₃↔Cu + Cr₂O₃) were different. This has lead to a difference in catalytic properties of the catalysts. Catalytic activity of SG catalysts was superior to that of commercial CuCr₂O₄ tested under the same conditions. Complex hysteresis behaviour for CuCr₂O₄ catalysts ramped over a temperature range of 220–850 °C where the stables active phases were obtained only after the first ramp of heating under reactants. No catalysts deactivation was further observed after several cycles of heating and cooling. The stabilisation of catalytic activity was attributed to the formation of mixed crystalline phases containing both copper and chromium species.     

Nanocrystalline Transition Metal Oxides as Catalysts in the Thermal Decomposition of Ammonium Perchlorate

Nanocrystalline transition metal oxides (NTMOs) have been successfully prepared by three different methods: novel quick precipitation method (Cr₂O₃ and Fe₂O₃); surfactant mediated method (CuO), and reduction of metal complexes with hydrazine as reducing agent (Mn₂O₃). The nano particles have been characterized by X‐ray diffraction (XRD) which shows an average particle diameter of 35–54 nm. Their catalytic activity was measured in the thermal decomposition of ammonium perchlorate (AP). AP decomposition undergoes a two step process where the addition of metal oxide nanocrystals led to a shifting of the high temperature decomposition peak toward lower temperature. The kinetics of the thermal decomposition of AP and catalyzed AP has also been evaluated using model fitting and isoconversional method.