Preparation of a Novel Copper Catalyst in Terms of the Immiscible Interaction Between Copper and Chromium

Based on the metallurgical point of view, we aimed to design a new form of copper catalysts with high thermal stability and activity. Delafossite CuCrO₂ has been studied as a precursor for copper catalyst. The CuCrO₂ was reduced to fine dispersion of Cu and Cr₂O₃ particles with porous structure by the treatment in H₂ at 600 °C, which exhibited much higher activity and thermal stability for steam reforming of methanol (SRM) than those of the CuO and/or Cr₂O₃ catalysts. Sintering of Cu particles was significantly suppressed even after H₂ reduction at 600 °C. Moreover, the CuCrO₂ can be regenerated by calcination in air at 1,000 °C where the activity is also restored completely even after sintering at high temperatures. Fine porous structure generated by the reduction of CuCrO₂ and immiscible interaction between Cu and Cr₂O₃ are important in stabilizing of copper nanoparticles. Based on these findings, we propose that the CuCrO₂ is an effective precursor for a high performance copper catalyst.     

Co-precipitated ZnAl2O4 spinel precursor as potential sintering aid for pure alumina system

Ultra-fine ZnAl₂O₄ spinel hydrogel precursor synthesized from mixed salt solutions of Zn²⁺ and Al³⁺ ions using ammonium hydroxide–hexamethylenetetramine as basic media for co-precipitation was used as bonding material and sintering aid for pure alumina system. The hydrogel powder exhibited some well-defined ZnAl₂O₄ spinel phases at 800 °C. Alumina compacts were fabricated by incorporating small proportions of the precursor in alumina powder and firing at different temperatures (1350–1500 °C). The degree of densification was studied by measurement of fired shrinkage, apparent porosity, bulk density and cold crushing strength. Phase compositions and microstructural features of sintered samples were evaluated by XRD and SEM respectively. Addition of 0.2% hydrogel powder to alumina exhibited remarkable influence on development of high mechanical strength. The in situ formed ZnAl₂O₄ spinel dopant acted as a grain growth inhibitor in the alumina system.     

Reduction behaviors and catalytic properties for methanol steam reforming of Cu-based spinel compounds CuX2O4 (X=Fe,Mn, Al,La)

In this study, various Cu-based spinel compounds, i.e., CuFe₂O₄, CuMn₂O₄, CuAl₂O₄ and CuLa₂O₄, were fabricated by a solid-state reaction method. Reduction behaviors and morphological changes of these materials have been characterized by H₂ temperature-programmed reduction (H₂-TPR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Moreover, the catalytic properties for steam reforming of methanol (SRM) of these Cu-based spinel compounds were investigated. H₂-TPR results indicated that the reducibility of Cu-based spinel compounds was strongly dependent on the B-site component while the CuFe₂O₄ catalyst revealed the lowest reduction temperature (190 °C), followed respectively by CuAl₂O₄ (267 °C), CuMn₂O₄ (270 °C), and CuLa₂O₄ (326 °C). The reduced CuAl₂O₄ catalyst demonstrated the best performance in terms of catalytic activity. Based on the SEM and XRD results, pulverization of the CuAl₂O₄ particles due to gas evolution and a high concentration of nanosized Cu particles (≈50.9 nm) precipitated on the surfaces of the Al₂O₃ support were observed after reduction at 360 °C in H₂. The BET surface area of the CuAl₂O₄ catalyst escalated from 5.5 to 13.2 m²/g. Reduction of Cu-based spinel ferrites appear to be a potential synthesis route for preparing a catalyst with high catalytic activity and thermal stability. The catalytic performance of these copper-oxide composites was superior to those of conventional copper catalysts.     

Synthesis of spherical LiMn2O4 cathode material by dynamic sintering of spray-dried precursors

Spherical LiMn₂O₄ particles were successfully synthesized by dynamically sintering spherical precursor powders, which were prepared by a slurry spray-drying method. The effect of the sintering process on the morphology of LiMn₂O₄ was studied. It was found that a one-step static sintering process combined with a spray-drying method could not be adopted to prepare spherical products. A two-step sintering procedure consisting of completely decomposing sprayed precursors at low temperature and further sintering at elevated temperature facilitated spherical particle formation. The dynamic sintering program enhanced the effect of the two-step sintering process in the formation of spherical LiMn₂O₄ powders. The LiMn₂O₄ powders prepared by the dynamic sintering process, after initially decomposing the spherical spray-dried precursor at 180 °C for 5 h and then sintering it at 700 °C for 8 h, were spherical and pure spinel. The as-prepared spherical material had a high tap density (ca. 1.6 g/cm³). Its specific capacity was about 117 mAh/g between 3.0 and 4.2 V at a rate of 0.2 C. The retention of capacity for this product was about 95% over 50 cycles. The rate capability test indicated that the retention of the discharge capacity at 4C rate was still 95.5% of its 0.2 rate capacity. All the results showed that the spherical LiMn₂O₄ product made by the dynamic sintering process had a good performance for lithium ion batteries. This novel method combining a dynamic sintering system and a spray-drying process is an effective synthesis method for the spherical cathode material in lithium ion batteries.     

Effect of manganese on Cu/SiO2 catalysts for the dehydrogenation of cyclohexanol to cyclohexanone

The effect of the addition of manganese to Cu/SiO₂ catalysts for cyclohexanol dehydrogenation reaction was investigated. At reaction temperature of 250 °C, the conversion and the selectivity to cyclohexanone were both increased with the addition of manganese to Cu/SiO₂ catalyst. However, as the reaction temperature was further increased, higher loading of manganese in Cu/SiO₂ catalyst led to a decrease in the conversion of cyclohexanol. Manganese in Cu/ SiO₂ catalyst decreased the reduction temperature of copper oxide, increased the dispersion of copper metal, and decreased the selectivity to cyclohexene. It was found that the dehydration of cyclohexanol to cyclohexene occurred on the intermediate acid sites of catalyst. At high Mn loading, catalyst surface was more enriched with manganese in used catalyst compared to that in freshly calcined or reduced catalyst, which may account for the sharp decrease of the conversion at high temperature of 390 °C. Upon reduction, copper manganate on silica was decomposed into fine particles of copper metal and manganese oxide (Mn₃O₄).     

Synthesis and characterization of MgAl2O4–ZrO2 composites

Different types of dense 5–97% ZrO₂–MgAl₂O₄ composites have been prepared using a MgAl₂O₄ spinel obtained by calcining a stoichiometric mixture of aluminium tri-hydroxide and caustic MgO at 1300 °C for 1 h, and a commercial yttria partially stabilized zirconia (YPSZ) powder as starting raw materials by sintering at various temperatures ranging from 1500 to 1650 °C for 2 h. The characteristics of the MgAl₂O₄ spinel, the YPSZ powder and the various sintered products were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET surface area, particle size analysis, Archimedes principle, and Vickers indentation method. Characterization results revealed that the YPSZ addition increases the sintering ability, fracture toughness and hardness of MgAl₂O₄ spinel, whereas, the MgAl₂O₄ spinel hampered the sintering ability of YPSZ when sintered at elevated temperatures. A 20-wt.% YPSZ was found to be sufficient to increase the hardness and fracture toughness of MgAl₂O₄ spinel from 406 to 1314 Hv and 2.5 to 3.45 MPa m^1/2, respectively, when sintered at 1600 °C for 2 h.     

Preparation and characterization of CuFe2O4 bulk catalysts

This work is devoted to the investigation of the influence of the preparation process on the physical-chemical properties of a copper spinel applied as catalyst for hydrocarbon (HC) oxidation. Samples of CuFe₂O₄ mixed oxide belonging to the inverted spinel type structure have been obtained by high temperature solid state reaction and by wet chemical synthesis methods, applying nitrate and citrate precursor procedures, within the thermal range from 150 to 700 °C.The bulk catalysts were characterized by XRD, TPR, FTIR, SEM-EDX, TEM and Mössbauer spectroscopy. Propane combustion was performed as a reaction test.In this work it is demonstrated that the calcination temperature and chemical synthesis affect the crystal properties and cation distribution in the spinel structure, microstructure, surface area and reducibility; which are among the most relevant physical chemical properties for the catalytic activity. The materials obtained by wet chemical procedure, through nitrate and citrate routes, are better suited for propane combustion. This feature is assigned to the microstructure, to the presence of nanometric size particles and also to the cation distributions in the spinel sublattices of these materials.     

Effects of ethylene glycol addition on the properties of Ru/Al2O3 catalyst prepared by sol-gel method

Ru/Al₂O₃ catalysts were prepared by sol-gel method with an organic additive (ethylene glycol). The effect of the addition of ethylene glycol on the properties of Ru/Al₂O₃ was characterized by BET, XRD, EXAFS, and TGA/DTA. Ethylene glycol was effective to promote the phase transition of -Al₂O₃ even at 800°C calcination with high surface area. This finding is ascribed to the modified structure of aluminum alkoxide by ethylene glycol addition in the solution state. Ethylene glycol is also effective to get small particles of ruthenium after the reduction at 500°C. The EXAFS and UV-Vis spectra of Ru complex revealed that the coordination structure of Ru depended on the additive used. The ethylene glycol sol prefers to form octahedral Ru complex. This Ru complex in alumina matrix is stable up to 200°C and forms small Ru oxide particles even at 300°C calcination. This suggests that ethylene glycol coordinates to the Ru complex as well as to aluminum ion in the initial state, which is important to control the final properties of the Ru/Al₂O₃ catalyst.     

The promotion effects of Pd on Fe-Cu-Co based catalyst for higher alcohols synthesis

To increase the ability of Fe-Cu-Co based catalyst for hydrogen activation, the catalyst loaded with Pd was studied in the conversion of syngas to higher alcohols. X-ray diffraction (XRD), N₂ physisorption, H₂ temperature-programmed reduction (TPR) and H₂ temperature-programmed desorption (H₂-TPD) were applied to characterize the catalysts. The results of XRD showed that the Pd-loaded Fe-Cu-Co based samples were mainly composed of CuFe₂O₄ and CuO. After reduction, metallic Cu and Fe along with minor CuFe₂O₄ were identified, and the amount of CuFe₂O₄ decreased with the increase of the Pd content. H₂-TPR revealed that Pd facilitated the reduction of Fe-Cu-Co based catalyst. H₂-TPD confirmed that Pd enhanced the ability of Fe-Cu-Co based catalyst for H₂ activation. Therefore, the activity of the catalyst and the selectivity of alcohols were greatly improved. Over the Fe-Cu-Co based catalyst loaded with 0.5 wt.% Pd, the selectivity and the time-space yield of alcohols reached 58.7% and 1.53 g mL^− 1 h^− 1 at 350 °C, 6.0 MPa, GHSV = 10,000 h^− 1 and n(H₂)/n(CO) = 2.4.     

Efficient production of hydrogen and multi-walled carbon nanotubes from ethanol over Fe/Al2O3 catalysts

Fe/Al₂O₃ catalysts with different Fe loadings (10-90 mol%) were prepared by hydrothermal method. Ethanol decomposition was studied over these Fe/Al₂O₃ catalysts at temperatures between 500 and 800 °C to produce hydrogen and multi-walled carbon nanotubes (MWCNTs) at the same time. The results showed that the catalytic activity and stability of Fe/Al₂O₃ depended strongly on the Fe loading and reaction temperature. The Fe(30 mol%)/Al₂O₃ and Fe(40 mol%)/Al₂O₃ were both the effective catalyst for ethanol decomposition into hydrogen and MWCNTs at 600 °C. Several reaction pathways were proposed to explain ethanol decomposition to produce hydrogen and carbon (including nanotube) at the same time.     

Efficient fabrication of spinel copper ferrite with enhanced high infrared radiation properties

Rational design and exploration of high infrared radiation materials with remarkable emissivity at high temperatures are always challengeable. In the work, the spinel copper ferrite products with exceptional infrared radiation performance in the wavenumber range of 3–5 μm are massively fabricated through a simple two-step strategy including hydrothermal treatment and low temperature calcination process. Detailed physicochemical characterizations demonstrate that specific structures, compositions, optical behaviors and infrared radiant properties of resultant CuFe₂O₄ samples are enormously dependent upon the involved hydrothermal temperatures/time and annealing temperatures. The synthetic parameters were optimized as hydrothermal process at 150 °C for 16 h and subsequent calcination at 800 °C. The desirable crystallinity, hetero-composition and lower band gap energy synergistically endow the optimal CuFe₂O₄ sample with super high infrared radiation emissivity of ~0.913 evaluated at the testing temperature of 800 °C. Our contribution here will provide significant guidance for scalably low-temperature synthesis of high infrared radiation materials with superb emissivity at high temperatures.     

Synthesis of spherical spinel LiMn2O4 with commercial manganese carbonate

Spherical spinel LiMn₂O₄ particles were successfully synthesized from a mixture of manganese compounds containing commercial manganese carbonate by sintering of the spray-dried precursor. Different preparation routes were investigated to improve the tap density and to enhance the electrochemical performance of LiMn₂O₄. The structure and morphology of the LiMn₂O₄ particles were confirmed by X-ray diffraction (XRD) and scanning electron microscopy. The results showed that hollow spherical LiMn₂O₄ particles could be obtained when only commercial MnCO₃ was used as the manganese source. These particles had a low tap density (ca.0.8 g/cm³). Perfect micron-sized spherical LiMn₂O₄ particles with good electrochemical performance were obtained by spray-drying a slurry composed of MnCO₃, Mn(CH₃CHOO)₂ and LiOH, followed by a dynamic sintering process and a stationary sintering process. The as-prepared spherical LiMn₂O₄ particles comprised hundreds of nanosize crystal grains and had a high tap density(ca. 1.4 g/cm³). The galvanostatic charge-discharge measurements indicated that the spherical LiMn₂O₄ particles had an initial capacity of 121 mAh/g between 3.0 and 4.2 V at 0.2 C rate and still delivered a reversible capacity of 112 mAh/g at 2 C rate. The retention of capacity after 50 cycles was still 96% of its initial capacity at 0.2 C. All the results showed that the as-prepared spherical LiMn₂O₄ particles had an excellent electrochemical performances. The methods we used for preparing spherical LiMn₂O₄ are energy-saving and suitable for industrial application.     

Preparation,characterization, and catalytic behavior of Rh-Mn double oxide on SiO2

Rh double-oxide compound (MnRh₂O₄) was formed by air calcination treatment of manganese oxide-promoted Rh/SiO₂ catalyst at 900 °C, and characterized by Rietveld analysis of the X-ray diffraction pattern. The MnRh₂O₄ particles on SiO₂ were reduced to smaller Rh metal particles by H₂ treatment at 300 °C, and this catalyst system exhibited a strong Rh-MnO _x interaction behavior in catalytic studies of ethane hydrogenolysis and cyclohexane dehydrogenation reactions.     

Highly active and selective Cu/SiO2 catalysts prepared by the urea hydrolysis method in dimethyl oxalate hydrogenation

Cu/SiO₂ catalysts have been successfully prepared via urea hydrolysis method. The catalysts have been systematically characterized by X-ray diffraction, high-resolution transmission electron microscopy, N₂-physisorption and H₂ temperature-programmed reduction. The results demonstrated the presence of copper nanoparticles and their high dispersion on the SiO₂ support. Catalysts with different copper loadings were prepared, and their performances in the hydrogenation of dimethyl oxalate to ethylene glycol were studied. A 100% conversion of dimethyl oxalate and maximum 98% selectivity of ethylene glycol were reached with 15.6 wt.% copper loading at 200 °C and 2 MPa. Furthermore, under the same reaction conditions, the catalyst can maintain the selectivity of 90% when the reduction temperature reduced from 350 °C to 200 °C. The high activity and selectivity over the catalyst may be ascribed to the homogenously distribution of copper nanoparticles on the large surface.     

CO2 hydrogenation to methanol over Cu/ZnO/ZrO2 catalysts prepared via a route of solid-state reaction

Cu/ZnO/ZrO₂ catalysts were prepared by a route of solid-state reaction and tested for the synthesis of methanol from CO₂ hydrogenation. The effects of calcination temperature on the physicochemical properties of as-prepared catalysts were investigated by N₂ adsorption, XRD, TEM, N₂O titration and H₂-TPR techniques. The results show that the dispersion of copper species decreases with the increase in calcination temperature. Meanwhile, the phase transformation of zirconia from tetragonal to monoclinic was observed. The highest activity was achieved over the catalyst calcined at 400 °C. This method is a promising alternative for the preparation of highly efficient Cu/ZnO/ZrO₂ catalysts.     

Oxygen storage capacity of promoted Rh/CeC2 catalysts. Exceptional behavior of RhCu/CeO2

The effect of various additives (V, Cr, Mn, Fe, Co, Ni, Cu and Pb) on the oxygen storage capacity (OSC) of CeO₂ and Rh/CeO₂ catalysts was investigated. Copper is an excellent promoter of OSC conferring to Rh a very high resistance to sintering (900°C, 2% O₂).     

Wire-mesh honeycomb catalysts for selective catalytic reduction of NO with NH3

Both flat and corrugated wire mesh sheets were coated with aluminum powder by using electrophoretic deposition (EPD) method. Controlled thermal sintering of coated samples yielded uniform porous aluminum layer with a thickness of 100 μm that was attached firmly on the wire meshes. Subsequent controlled calcination formed a finite thickness of Al₂O₃ layer on the outer surface of each deposited aluminum particles, which resulted in the formation of Al₂O₃/Al double-layered composite particles that were attached firmly on the wire surface to form a certain thickness of porous layer. A rectangular-shaped wire-mesh honeycomb (WMH) module with triangular-shaped channels was manufactured by packing alternately the flat sheet and corrugated sheet of the Al₂O₃/Al-coated wire meshes. This WMH was further coated with V₂O₅-MoO₃-WO₃ catalyst by wash-coating method to be applied for the selective catalytic reduction (SCR) of NO with NH₃. With an optimized catalyst loading of 16 wt%, WMH catalyst module shows more than 90% NO conversion at 240 °C and almost complete NO conversion at temperatures higher than 300 °C at GHSV 5,000 h⁻¹. When compared with conventional ceramic honeycomb catalyst, WMH catalyst gives NO conversion higher by 20% due to reduced mass transfer resistance by the existence of three dimensional opening holes in WMH.     

Nickel-niobia interaction induced by the reduction of NiNb2O6 supported on SiO2

Nickel niobate (NiNb₂O₆) supported on SiO₂ was prepared by a chemical mixing method using mixed Ni and Nb citrate solutions. X-ray diffraction study showed that the NiNb₂O₆ compound was reduced to Ni metal and NbO₂ after H₂ treatment at 600 ° C, and a strong Ni-niobia interaction was induced after the decomposition of the compound: the ethane hydrogenolysis activity was suppressed severely after high temperature reduction at 600 ° C, and recovered by O₂ treatment at 500 ° C followed by low-temperature reduction at 200 ° C. The selectivity of cyclohexane dehydrogenation was improved significantly by the Ni-niobia interaction, if compared with unpromoted Ni/SiO₂ catalyst, and the structural change and catalytic behaviors were compared with those of Rh double oxides such as RhNbO₄.     

Characterization of fused Fe-Cu based catalyst for higher alcohols synthesis and DRIFTS investigation of TPSR

Fused Fe-Cu based catalyst for higher alcohols synthesis (HAS) is characterized by XRD, TG-DTA, H₂-TPD and DRIFTS of CO adsorption. The results of XRD reveal that the fused Fe-Cu based catalyst consists of Cu₂O, CuFeO₂ and CuFe₂O₄ species. After reduction, the metallic Fe and Cu are the main species, but minor CuFeO₂ and CuFe₂O₄ species are also present. H₂-TPD shows that in comparison with the pure Fe- or Cu-based sample, the ability of Fe-Cu based catalyst for activation of H₂ is higher and the stronger metal-hydrogen bonds are formed. DRIFTS of CO adsorption indicates that CO is adsorbed on both metal and metal ion sites, where the dissociation of CO to C* and O* species and the formation of CO₂ are observed. In situ DRIFTS investigation of CO + H₂-TPSR over the Fe-Cu based catalyst shows that the dissociative activation of H₂ is more difficult than the activation of CO, and carbonaceous and hydrocarbon fragment species only appears after the dissociative activation of H₂. In addition, HAS over the Fe-Cu based catalyst is very complicated, where various intermediates including = CH₂, − CHO, − OOCH, − OH and − C(= O)-R exist.     

Synthesis and electrochemical characterization of nano-CeO2-coated nanostructure LiMn2O4 cathode materials for rechargeable lithium batteries

LiMn₂O₄ spinel cathode materials were coated with 0.5, 1.0, and 1.5 wt.% CeO₂ by a polymeric process, followed by calcination at 850 °C for 6 h in air. The surface-coated LiMn₂O₄ cathode materials were physically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron microscopy (XPS). XRD patterns of CeO₂-coated LiMn₂O₄ revealed that the coating did not affect the crystal structure or the Fd3m space group of the cathode materials compared to uncoated LiMn₂O₄. The surface morphology and particle agglomeration were investigated using SEM, TEM image showed a compact coating layer on the surface of the core materials that had average thickness of about 20 nm. The XPS data illustrated that the CeO₂ completely coated the surface of the LiMn₂O₄ core cathode materials. The galvanostatic charge and discharge of the uncoated and CeO₂-coated LiMn₂O₄ cathode materials were measured in the potential range of 3.0-4.5 V (0.5 C rate) at 30 °C and 60 °C. Among them, the 1.0 wt.% of CeO₂-coated spinel LiMn₂O₄ cathode satisfies the structural stability, high reversible capacity and excellent electrochemical performances of rechargeable lithium batteries.