Synthesis of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> nanoparticles by modified Pechini method and their enhanced rate capability

Layered LiNi_1/3Co_1/3Mn_1/3O₂ nanoparticles were prepared by modified Pechini method and used as cathode materials for Li-ion batteries. The pyrolytic behaviors of the foamed precursors were analyzed by use of simultaneous thermogravimetric and differential thermal analysis (TG-DTA). Structure, morphology and electrochemical performance characterization of the samples were investigated by X-ray diffraction (XRD), field emission scanning electron macroscopy(SEM), Brunauer-Emmett-Teller (BET) specific surface area and charge–discharge tests. The results showed that the samples prepared by modified Pechini method caclined at 900 °C for 10 h were indexed to pure LiNi_1/3Co_1/3Mn_1/3O₂ with well hexagonal structure. The particle size was in a range of 100–300 nm. The specific surface area was larger than that of the as-obtained sample by Pechini method. Initial discharge capacity of 163.8 mAh/g in the range 2.8–4.4 V (vs. Li/Li⁺) and at 0.1C for LiNi_1/3Co_1/3Mn_1/3O₂ prepared by modified Pechini method was obtained, higher than that of the sample prepared by Pechini method (143.5 mAh/g). Moreover, the comparison of electrochemical results at different current rates indicated that the sample prepared by modified Pechini method exhibited improved rate capability.     

Effect of the Support on the Nature of Metal-Promoter Interactions in Ru-Cs<Superscript>+</Superscript>/MgO and Ru-Cs<Superscript>+</Superscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for Ammonia Synthesis

The Ru-Cs⁺/MgO and Ru-Cs⁺/γ-Al₂O₃ catalysts, which were prepared by an impregnation method using RuOHCl₃ and Cs₂CO₃ as precursor compounds and reduced with H₂ at 450°C, are characterized by X-ray diffraction, high-resolution transmission electron microscopy (with X-ray microanalysis), and X-ray photoelectron spectroscopy (XPS). The Cs⁺/MgO(Al₂O₃) systems, Ru-Cs⁺ black, and model systems prepared by cesium sputtering onto polycrystalline ruthenium foil are studied as reference samples. It is found that, in the Ru-Cs⁺/MgO sample, cesium is present as a Cs_{2 + x}O cesium suboxide, which weakly interacts with the support, localized on the surface of Ru particles or near them. In the case of Ru-Cs⁺/γ-Al₂O₃, cesium occurs as a species that is tightly bound to the support; this is likely surface cesium aluminate, which prevents promoter migration to Ru particles. The Ru-Cs⁺/MgO sample exhibits a considerable shift of the Ru3d line in the XPS spectra toward lower binding energies, as compared to the bulk metal. It is hypothesized that this shift is due to a decrease in the electron work function from the surface of ruthenium because of the polarizing effect of Cs⁺ ions in contact with Ru particles. Based on the experimental results, the great difference between the catalytic activities of the Ru-Cs⁺/MgO and Ru-Cs⁺/γ-Al₂O₃ systems in ammonia synthesis at 250–400°C and atmospheric pressure is explained.     

Study of Fe-doped V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> catalyst for an enhanced NH<Subscript>3</Subscript>-SCR in diesel exhaust aftertreatment

Selective catalytic reduction (SCR) with ammonia has been considered as the most promising technology, as its effect deals with the NO_X. Novel Fe-doped V₂O₅/TiO₂ catalysts were prepared by sol–gel and impregnation methods. The effects of iron content and reaction temperature on the catalyst SCR reaction activity were explored by a test device, the results of which revealed that catalysts could exhibit the best catalytic activity when the iron mass ratio was 0.05%. It further proved that the VTiFe (0.05%) catalyst performed the best in denitration and its NO_X conversion reached 99.5% at 270 °C. The outcome of experimental procedures: Brunauer–Emmett–Teller surface area, X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and adsorption (H₂-TPR, NH₃-TPD) techniques showed that the iron existed in the form of Fe³⁺ and Fe²⁺ and the superior catalytic performance was attributed to the highly dispersed active species, lots of surface acid sites and absorbed oxygen. The modified Fe-doped catalysts do not only have terrific SCR activities, but also a rather broad range of active temperature which also enhances the resistance to SO₂ and H₂O.     

Oxidative desulfurization of thiophene derivatives with H<Subscript>2</Subscript>O<Subscript>2</Subscript> in the presence of catalysts based on MoO<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> under mild conditions

The catalysts based on MoO₃/Al₂O₃ were synthesized and tested using aqueous hydrogen peroxide as the oxidant in the oxidative desulfurization of thiophene, benzothiophene (BT) and dibenzothiophene (DBT) into the corresponding sulfones. Among catalysts tested, 15%(MoO₃–WO₃)/Al₂O₃ prepared by a conventional impregnation method was considerably active for the oxidation of thiophene, BT and DBT, which could achieve higher than 99.2% conversions at lower reaction temperature (≤338 K). The use of hexadecyltrimethyl ammonium bromide as the phase-transfer reagent in small amounts could promote the reaction efficiently.     

Catalytic efficiency of cesium and potassium salts of dodecatungstophosphoric acid supported on silica and comparison with H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>/SiO<Subscript>2</Subscript>

Pure tungstophosphoric acid, potassium tungstophosphate, and cesium tungstophosphate with varying extent of substitution of protons by Cs or K ions x (x = 1, 2, 2.5, and 3) have been prepared and are supported on silica by the wet impregnation method. The extent of loading was fixed at 20 wt %. For the sake of comparison, unloaded Cs _x and K _x (x = 1) salts of tungstophosphoric acid were prepared by the precipitation method. The supported catalysts were characterized by FT-IR, XRD, specific surface area measurements, and catalytic conversion of tert-butanol. The results revealed that the catalytic conversion of tert-butanol proceeds mainly via dehydration yielding isobutene. The Cs₁PW/SiO₂, HPW/SiO₂, and K₁PW/SiO₂ catalysts were more active than their unsupported samples. The previous solids showed greater catalytic activity and stability. Unexpectedly, substitution of one proton of tungstophosphoric acid by a cesium or potassium ion exerted no measurable effect on the catalytic activity of the treated solids, in spite of decreasing the Brønsted acidity of Cs₁PW/SiO₂ and K₁PW/SiO₂ indicating that the acidity of HPW/SiO₂ decrease may be due to the interaction between HPW and the SiO₂ surface. On the other hand, significant decrease in the catalytic activity took place upon increasing the cation content (x) to x = 2, 2.5, and 3.     

FePO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> Catalysts for Propylene Glycol Oxidation

FePО₄/SiO₂ supported catalysts with a different content of iron phosphate are prepared. The properties of the catalyst are changed by the introduction of alkali metal compounds (Na or Cs) on its surface. The samples obtained are characterized by X-ray diffraction, low-temperature nitrogen adsorption, temperatureprogrammed reduction by hydrogen, and temperature-programmed desorption of ammonia. The catalytic properties are investigated in the reaction of gas-phase propylene glycol oxidation. It is shown that the selectivity of methylglyoxal formation on the unmodified catalysts is determined by the state of the supported active component and by its reduction–oxidation ability under the action of a reaction mixture.     

Promotional effect of cobalt addition on catalytic performance of Ce<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript> mixed oxide for diesel soot combustion

A series of Co-modified Ce_0.5Zr_0.5O₂ catalysts with different concentrations of Co (mass %: 0, 2, 4, 6, 8, 10) was investigated for diesel soot combustion. Ce_0.5Zr_0.5O₂ was prepared using the coprecipitation method and Co was loaded onto the oxide using the incipient wetness impregnation method. The activities of the catalysts were evaluated by thermogravimetric (TG) analysis and temperature-programmed oxidation (TPO) experiments. The results showed the soot combustion activities of the catalysts to be effectively improved by the addition of Co, 6 % Co/Ce_0.5Zr_0.5O₂ and that the 8 % Co/Ce_0.5Zr_0.5O₂ catalysts exhibited the best catalytic performance in terms of lower soot ignition temperature (T_i at 349°C) and maximal soot oxidation rate temperature (T_m at 358°C). The reasons for the improved activity were investigated by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), H₂ temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). These results revealed that the presence of Co could lower the reduction temperature due to the synergistic effect between Co and Ce, thereby improving the activity of the catalysts in soot combustion. The 6 % Co catalyst exhibited the best catalytic performance, which could be attributed to the greater amounts of Co³⁺ and surface oxygen species on the catalyst.     

Catalytic removal of soot particles over MnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> catalysts prepared by the auto-combustion method

Soot removal for exhaust gas from diesel engine has been addressed due to the more stringent legislation and environmental concerns. MnCo₂O₄ catalysts were systematically prepared using glucose as a fuel via the auto-combustion method and applied for soot removal. The as-prepared samples were characterized by X-ray diffraction (XRD), O₂-temperature-programmed oxidation (TPO) reaction and H₂-temperature-programmed reduction reaction (H₂-TPR). The catalytic activities for soot combustion were evaluated by micro activity test (MAT) with a tight contact mode between soot and catalysts. Compared with catalysts prepared by the solid state method without glucose, auto-combustion method in the presence of glucose can decrease the synthetic temperature, avoiding high temperature treatment and sintering. The catalysts prepared with glucose could catalyze soot oxidation effectively and the derived values of T₁₀, T₅₀, and T₉₀ were 326, 408, and 468 °C in a tight contact mode, respectively, showing a significant drop of T₁₀, T₅₀, and T₉₀ by 156, 177, and 178 °C for non-catalytic reaction.     

Thermal and structural investigation of SnO<Subscript>2</Subscript>/Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> obtained by the polymeric precursor method

SnO₂-based materials are used as sensors, catalysts and in electro–optical devices. This work aims to synthesize and characterize the SnO₂/Sb₂O₃-based inorganic pigments, obtained by the polymeric precursor method, also known as Pechini method (based on the metallic citrate polymerization by means of ethylene glycol). The precursors were characterized by thermogravimetry (TG) and differential thermal analysis (DTA). After characterization, the precursors were heat-treated at different temperatures and characterized by X-ray diffraction. According to the TG/DTA curves basically two-step mass loss process was observed: the first one is related to the dehydration of the system; and the second one is representative to the combustion of the organic matter. Increase of the heat treatment temperature from 500 to 600°C and 700°C resulted higher crystallinity of the formed product.     

Hydrogenolysis of glycerol to propanediols over heteropolyacids promoted AgCu/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Various amounts and different types of heteropolyacids promoted 5Ag15Cu/Al₂O₃ catalysts were prepared by impregnation method and analyzed through many techniques. The synthesized catalysts were evaluated for hydrogenolysis of glycerol to propanediols. The results demonstrated that heteropolyacids loading facilitated the reduction, promoted the dispersion, enhanced the acidity, and increased Broensted acid sites of the AgCu catalysts, which benefited the generation of 1,3-propanediol. Compared with phosphotungstic acid and phosphomolybdic acid, silicotungstic acid promoted AgCu catalyst had a better performance for 1,3-propanediol due to the better Cu dispersion and higher Broensted acidity. In addition, when the reaction was performed at 220 °C under 3.5 MPa for 8 h, the chosen 5Ag15Cu-10HSiW/Al₂O₃ achieved a 69.6% glycerol conversion with 35.6% 1,2-propanediol selectivity and 21.5% 1,3-propanediol selectivity.     

Effect of calcination temperature on the physicochemical and catalytic properties of FeSO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> in hydrogen sulfide oxidation

The effect of calcination temperature on the state of the active component of iron-containing catalysts prepared by the impregnation of silica gel with a solution of FeSO₄ and on their catalytic properties in selective H₂S oxidation to sulfur was studied. With the use of thermal analysis, XPS, and Mössbauer spectroscopy, it was found that an X-ray amorphous iron-containing compound of complex composition was formed on the catalyst surface after thermal treatment in the temperature range of 400–500°C. This compound contained Fe³⁺ cations in three nonequivalent positions characteristic of various oxy and hydroxy sulfates and oxide and sulfate groups as anions. Calcination at 600°C led to the almost complete removal of sulfate groups; as a result, the formation of an oxide structure came into play, and it was completed by the production of finely dispersed iron oxide in the ?-Fe₂O₃ modification (the average particle size of 3.2 nm) after treatment at 900°C. As the calcination temperature was increased from 500 to 700°C, an increase in the catalyst activity in hydrogen sulfide selective oxidation was observed because of a change in the state of the active component. A comparative study of the samples by temperature-programmed sulfidation made it possible to establish that an increase in the calcination temperature leads to an increase in the stability of the iron-containing catalysts to the action of a reaction atmosphere.     

BaTi<Subscript>1–x</Subscript>Zr<Subscript>x</Subscript>O<Subscript>3</Subscript> nanopowders prepared by the modified Pechini method

The results reported here based on a study of BaTi_1–xZr_xO₃ (x=0, 0.2 and 1) nanometric powders prepared by the modified Pechini method. The powder samples annealed from 600 to 1000°C/2 h were characterized by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The decomposition reactions of resins were studied using thermal analysis measurements. The barium titanate zirconate system presented just one orthorhombic phase. Furthermore, this study produced BaTiO₃ powders with a tetragonal structure using shorter heat treatments and less expensive precursor materials than those required by the traditional methods.     

Temperature-programmed reduction of lightly yttrium-doped Au/CeO<Subscript>2</Subscript> catalysts

The reducibility of Au catalysts on CeO₂ supports doped with 1 and 2.5 mass% Y₂O₃ by two types of preparation methods (impregnation and co-precipitation) has been studied by temperature-programmed reduction and compared with that of pure Au/CeO₂. The kinetic parameters of reduction were determined simulating each reduction process. The capacities of these catalysts to retain oxygen have been evaluated by temperature-programmed desorption. The catalytic activities in water gas shift reaction were determined measuring CO conversion between 413 and 623 K. The catalytic performances of all these catalysts were explained in terms of mobility of the oxygen ions of the CeO₂ lattice.     

Kinetics and mechanism of carbon monoxide oxidation on the supported metal complex catalyst PdCl<Subscript>2</Subscript>-CuCl<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The kinetics of carbon monoxide oxidation with atmospheric oxygen on a PdCl₂-CuCl₂/γ-Al₂O₃ catalyst was studied at T = 27°C and an N₂-O₂-CO mixture pressure of 1 atm. The catalyst was prepared by cold impregnation. Three groups of mechanistic hypotheses are considered, and two of them are demonstrated to be consistent with kinetic data, although they differ in the roles of water and oxygen in carbon monoxide oxidation.     

Promoted porous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia decomposition

Transition metal catalysts have been considerably used for NH₃ decomposition because of the potential application in CO_x-free H₂ generation for fuel cells. However, most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components. Here, we adopted an efficient method, aerosol-assisted self-assembly approach (AASA), to prepare the optimized cobalt-alumina (Co₃O₄-Al₂O₃) catalysts. The Co₃O₄-Al₂O₃ catalysts exhibited excellent catalytic performance in the NH3 decomposition reaction, which can reach 100% conversion at 600 °C and maintain stable for 72 h at a gaseous hourly space velocity (GHSV) of 18000 cm³ g_cat^?1 h^?1. The catalysts were characterized by various techniques including transmission electron microscope (TEM), scanning electron microscope (SEM), nitrogen sorption, temperature-programmed reduction by hydrogen (H₂-TPR), ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction (XRD) to obtain the information about the structure and property of the catalysts. H₂-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species, which influences the redox properties of the catalysts. It is found that even a low content of alumina (10 at%) is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components, which ensures the high activity and superior stability of the cobalt-alumina catalysts.     

Ru/Ni/MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> catalysts for steam reforming of methane: effects of Ru content on self-activation property

The effects of Ru on the self-reducibility of Ru-doped Ni/MgAl₂O₄ catalysts, which do not need pre-reduction treatment with H₂, were investigated in the steam reforming of methane (SRM). The Ru-promoted Ni/MgAl₂O₄ catalysts with various amounts of Ru (0–0.5 wt%) were prepared by stepwise impregnation and co-impregnation methods using hydrotalcite-like MgAl₂O₄ support. For comparison, Ru/MgAl₂O₄ catalysts with the same amount of Ru were also prepared by the impregnation method. The catalysts were characterized by the N₂-sorption, XRD, H₂-TPR, H₂-chemisorption, and XPS methods. Ni/MgAl₂O₄ catalyst in the presence of even the trace amount of Ru (Ru content ≥0.05 wt%) showed higher conversion without pre-reduction as compared to Ru/MgAl₂O₄ catalysts in SRM under the same conditions. The self-activation of Ru–Ni/MgAl₂O₄ catalysts is mainly attributed to the spillover of hydrogen, which is produced on Ru at first and then reduces NiO species under reaction conditions. Besides, Ru doping makes the reduction of NiO easier. The stepwise impregnated Ru/Ni/MgAl₂O₄ catalyst produced superior performance as compared to co-impregnated Ru–Ni/MgAl₂O₄ catalyst for SRM.     

Synthesis characterization and catalytic evaluation of Ni/ZrO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> aerogels catalysts

The Ni/ZrO₂/SiO₂ aerogels catalysts were synthesized via three different routes: (i) impregnation ZrO₂–SiO₂ composite aerogels with a aqueous solution of Ni(NO₃)₂, (ii) impregnation SiO₂ aerogels with a mixed aqueous solution of Ni(NO₃)₂ and ZrO(NO₃)₂ · 2H₂O, (iii) one-pot sol–gel procedure from precursors Ni(NO₃)₂/ZrO(NO₃)₂ · 2H₂O/Si(OC₂H₅)₄. These catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), ammonia temperature-programmed desorption (NH₃-TPD), N₂ adsorption–desorption isotherms and Fourier transform infrared (FT-IR). The Liquid-phase hydrogenation of maleic anhydride (MA) was performed over these catalysts. The results revealed that the different preparation routes result in a difference between the obtained samples, concerning the crystal structure and composition, surface acidity, mixed level of each component, texture, and catalytic selectivity.     

Monolithic FeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia oxidation and nitrous oxide decomposition

(1.2–8.3)%FeO_х/Al₂O₃ monolith catalysts have been prepared by impregnating alumina with aqueous solutions of iron(III) nitrate and oxalate and have been tested in NH₃ oxidation and in the selective decomposition of N₂O in mixtures resulting from ammonia oxidation over a Pt–Rh gauze pack under conditions of nitric acid synthesis (800–900°C). In the case of the support calcined at 1200°C, the catalyst is dominated by bulk Fe₂O₃ particles localized on the Al₂O₃ surface. The activity of these samples in both reactions decreases with a decreasing active component content, thus limiting the potential of Fe₂(C₂O₄)₃ · 5H₂O, an environmentally friendlier but poorly soluble compound, as a substitute for Fe(NO₃)₃ · 9H₂O. Decreasing the support calcination temperature to 1000°C or below leads to the formation of a highly defective Fe–Al–O solid solution in the (1.2–2.7)%FeO_х/Al₂O₃ catalysts. The surface layers of the solid solution are enriched with iron ions or stabilize ultrafine FeO_х particles. The catalytic activity of these samples in both reactions is close to the activities measured for ~8%FeO_х/Al₂O₃ samples prepared using iron nitrate.     

Study on the oxygen exchange capacities of Ce<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript> pyrochlore

Ce₂Sn₂O₇ pyrochlore was synthesized by a hydrothermal method. X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the composition and valence state of the sample. The oxygen exchange property of the Ce₂Sn₂O₇ phase was measured by an oxidation reaction in sealed air atmosphere and a followed reduction reaction in 5% H₂-95% N₂ atmosphere. Gas chromatography (GC) was used to analyze the oxygen change in the reaction. The results show that Ce₂Sn₂O₇ sample has excellent oxygen absorption capacity at 250°C as Ce³⁺ ions are oxidized to Ce⁴⁺ ions. The oxidized sample can be reduced by 5% H₂-95% N₂. The refreshed sample remains the capacity of oxygen absorption, while the oxygen exchange capacity degrades with the reduction times.     

Heteroatom effect on hydrodesulphurization activity of TiO<Subscript>2</Subscript>-supported molybdenum heteropolyoxometalates of Anderson type

The properties of the Mo-containing samples (6 wt % Mo) prepared by mechanochemical mixing of Fe, Co, or Ni heteropolymolybdates of Andersen type and the TiO₂ support are reported. A detailed characterization of the surface properties has been performed by BET scanning electron microscopy, IR, XPS and thermo programmed reaction methods and by testing of catalysts in the thiophene conversion. The effects of the mixing time and the nature of heteroatom on the properties of the samples are shown. The nanosized particles are formed when mechanochemical synthesis is running 30 min. The Ni-containing catalyst reveals the highest and the most stable activity compared to Co- and Fe-containing catalysts. Their hydrodesulphurization activity is compared to those of alumina and titania catalysts synthesized by the conventional impregnation method.