Electrocatalyst materials for fuel cells based on the polyoxometalates—K7 or H7[(P2W17O61)Fe(H2O)] and Na12 or H12[(P2W15O56)2Fe4(H2O)2]

Free acids of the iron substituted heteropoly acids (HPA), H₇[(P₂W₁₇O₆₁)Fe^III(H₂O)] (HFe1) and H₁₈[(P₂W₁₅O₅₆)₂Fe^III₂(H₂O)₂] (HFe2) were prepared from the salts K₇[(P₂W₁₇O₆₁)Fe^III(H₂O)] (KFe1) and Na₁₂[(P₂W₁₅O₅₆)₂Fe^III₄(H₂O)₂] (NaFe4), respectively. The iron-substituted HPA were adsorbed on to XC-72 carbon based GDLs to form HPA doped GDEs after water washing with HPA loadings of ca. 1 μmol. The HPA was detected throughout the GDL by EDX. Solution electrochemistry of the free acids are reported for the first time in sulfate buffer, pH 1-3. The hydrogen oxidation reaction was catalyzed by KFe1 at 0.33 V, with an exchange current density of 38 mA/cm². Moderate activity for the oxygen reduction reaction was observed for the iron substituted HPA, which was dramatically improved by selectively removing oxygen atoms from the HPA by cycling the fuel cell cathode under N₂ followed by reoxidation to give a restructured oxide catalyst. The nanostructured oxide achieved an OCV of 0.7 V with a Tafel slope of 115 mV/decade. Cycling the same catalysts in oxygen resulted in an improved catalyst/ionomer/carbon configuration with a slightly higher Tafel slope, 128 mV/decade but a respectable current density of 100 mA/cm² at 0.2 V.     

Selective oxidation of methanol to dimethoxymethane over acid-modified V2O5/TiO2 catalysts

Selective oxidation of methanol to dimethoxymethane (DMM) was conducted in a fixed-bed reactor over an acid-modified V₂O₅/TiO₂ catalyst. The influence of the acid modification on its structure, redox and acidic properties, and catalytic performance for methanol oxidation were investigated. The results indicated that the content of vanadia in the catalyst exhibits a vital influence on the dispersion of vanadium species, while the acid modification can enhance its surface acidity. Proper amounts of the acid (W() = 15%) and V₂O₅ (W(V₂O₅) = 15%) components loaded in the acid-modified V₂O₅/TiO₂ catalyst are able to build a bi-functional circumstance that is favorable for the formation of DMM with high activity and selectivity. As a result, for the selective oxidation of methanol, the H₂SO₄-modified V₂O₅/TiO₂ catalyst gives a much higher DMM yield at 150 °C than the unmodified one.     

HDS reactivities of dibenzothiophenic compounds in a LC-finer LGO and H2S/NH3 inhibition effect

The hydrodesulfurization (HDS) reactivities and the inhibition effects of H₂S and NH₃ were experimentally investigated for 11 difficult-to-remove sulfur compounds contained in LC-finer light gas oil using a commercial NiMo/Al₂O₃ hydrotreating catalyst. Among these sulfur compounds, 4-MDBT was the most reactive while 4,6-DMDBT was the least reactive. It was found that the presence of methyl groups away from the sulfur atom slightly enhanced the HDS reactivities of the methyl substituted DBTs. The observed low reactivity of 4,6-DMDBT was mainly caused by the steric hindrance of the two methyls at the 4 and 6 positions. Both H₂S and NH₃ significantly inhibited the HDS reaction rates for all 11 sulfur species of interest, while 4,6-DMDBT was one of the most inhibited species. At the same concentration (1.0 vol%), H₂S showed a stronger inhibition effect than NH₃. Measurable catalyst deactivation was observed in the course of the experiment that had a relatively even effect on the HDS of all reactants investigated in this study.     

Efficient oxidative desulfurization (ODS) of model fuel with H2O2 catalyzed by MoO3/γ-Al2O3 under mild and solvent free conditions

An efficient process to remove organic sulfur compounds from model fuel has been explored. Dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (4, 6-DMDBT) can be completely oxidized into their corresponding sulfones by H₂O₂ over 14 wt.% MoO₃/γ-Al₂O₃ catalyst under mild conditions in 15 min. The effects of solvent, initial sulfide concentration, loading of MoO₃ and amount of catalyst on oxidative removal of DBT were studied. The employments of solvents have decreased the reaction rate of DBT, which can be attributed to the competitive adsorption between the sulfide and solvent. The oxidative reactivity increases in the order of thiophene (Th) < benzothiophene (BT) < DBT < 4, 6-DMDBT. The catalyst can be regenerated by methanol washing at 333 K.     

Inhibition of CoMo/HMS catalyst deactivation in the HDS of 4,6-DMDBT by support modification with phosphate

A series of CoMoS catalysts supported on hexagonal mesoporous silica (HMS) modified with different amounts of phosphate (0.5, 1.0, 1.5 and 2.0 wt.%) were prepared in order to study the influence of phosphate on catalyst deactivation. The catalysts were characterized by a variety of techniques (X-ray fluorescence, N₂ adsorption-desorption at 77 K, FT-IR study of the framework vibration and NO adsorption, NH₃-TPD, H₂-TPR, XPS, ³¹P NMR and TPO/TGA). The sulfided catalysts were tested in the deep hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) performed in a fixed-bed flow reactor at 598 K, P = 5.0 MPa and WHSV = 46.4 h⁻¹. The catalyst with the largest phosphate content (2.0 wt.%) showed the best catalytic response linked with its low deactivation during on-stream reaction and a larger sulfidation degree of Co species. It was found that coking behavior is closely related with the location of the active sites in the support structure being a lower coke formation on the catalysts having active phases located within support structure. The catalysts modified with a large amount of phosphorous (1.5 and 2.0 wt.% of P₂O₅) were more susceptible to coking and produced a more polymerized coke than P-free sample, as confirmed by TPO/TGA experiments. The presence of P₂O₅ favours the sulfidation degree of Co species and the creation of medium strength acid sites leading to the enhancement of the 4,6-DMDBT HDS reaction toward the isomerization route.     

Characterization and catalytic performance of Au/Ti-HMS catalysts on the oxidative desulphurization using in situ H2O2: Effect of method catalysts preparation

Au/Ti-HMS was prepared by in situ method, NH₃ deposition–precipitation (NH₃ DP) and urea deposition–precipitation (Urea DP), respectively. The catalysts were characterized by a series of techniques including ICP, powder XRD, N₂ sorption, UV–visible spectroscopy, TEM and H₂-TPR. Using n-octane containing BT, DBT and 4,6-DMDBT as model compound, the performance of the catalysts in oxidative desulfurization (ODS) using in situ generated H₂O₂ from H₂ and O₂ were investigated. The results show that preparation method influences porous structure of the support and gold particles size. In situ sample has maintained the intrinsic structure of Ti-HMS, whereas, the gold particles are not as uniform and small as that of DP sample. NH₃ DP sample still possesses the wormhole structure of HMS despite the absence of typical XRD peak. The mesoporous structure of urea DP sample has been damaged seriously. Au³⁺ on outer surface of the support is easier to be reduced than that in pores, as confirmed by H₂-TPR. In addition, the three samples exhibit different catalytic activities in ODS using in situ H₂O₂ as oxidant. For the removal of BT and DBT, Au/Ti-HMS (NH₃ DP) exhibits the highest catalytic activities. Regarding the removal of 4,6-DMDBT, the optimum catalyst is Au/Ti-HMS (In situ); however, Au/Ti-HMS (Urea DP) nearly loses catalytic activity.     

Polyoxometalate-based ionic liquids as catalysts for deep desulfurization of fuels

In order to obtain the ultra low-sulfur diesel, deep desulfurization of diesel oil has become a vital subject of environmental catalysis studies. Extraction and catalytic oxidation desulfurization (ECODS) system is one of the most promising desulfurization processes. A series of Keggin-type POM-based ionic liquids hybrid materials [MIMPS]₃PW₁₂O₄₀·2H₂O (1-(3-sulfonic group) propyl-3-methyl imidazolium phosphotungstate), [Bmim]₃PW₁₂O₄₀ (1-butyl 3-methyl imidazolium phosphotungstate), [Bmim]₃PMo₁₂O₄₀ (1-butyl 3-methyl imidazolium phosphomolybdate) and [Bmim]₄SiW₁₂O₄₀ (1-butyl-3-methyl imidazolium silicotungstate) have been developed in this study, and the reaction has performed using the POM-ILs materials as catalysts, H₂O₂ as oxidant, and ionic liquid (IL) as solvent. Through experimental evaluations, [MIMPS]₃PW₁₂O₄₀·2H₂O was found to be the best catalyst, with an S-removal of 100% at 30 °C for 1 h. The main factors affecting the process including temperature, catalyst dosage, and O/S (H₂O₂/DBT) molar ratio were investigated in detail. Under the optimal conditions, DBT (dibenzothiophene) and 4,6-DMDBT (4,6-dimethyl-dibenzothiophene) could achieve high desulfurization efficiency. Moreover, the reaction system also exhibited high activity in actual diesel oil, which could be reduced from 1113 ppm to 198 ppm. The reaction system could recycle 8-times with a slight decrease in activity.     

Characterization and electrocatalytic properties of PtRu/C catalysts prepared by impregnation-reduction method using Nd2O3 as dispersing reagent

A simple impregnation-reduction method introducing Nd₂O₃ as dispersing reagent has been used to synthesize PtRu/C catalysts with uniform Pt-Ru spherical nanoparticles. X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis have been used to characterize the composition, particle size and crystallinity of the catalysts. Well-dispersed catalysts with average particle size about 2 nm are achieved. The electrochemically active surface area of the different PtRu/C catalysts is determined by the CO_ad-stripping voltammetry experiment. The electrocatalytic activities of these catalysts towards methanol electrooxidation are investigated by cyclic voltammetry measurements and ac impedance spectroscopy. The in-house prepared PtRu/C catalyst (PtRu/C-03) in 0.5 M H₂SO₄ + 1.0 M CH₃OH at 30 °C display a higher catalytic activity and lower charge-transfer resistance (R_t) than that of the standard PtRu/C catalyst (PtRu/C-C). It is mainly due to enhanced electrochemically active specific surface, higher alloying extent of Ru and the abundant Pt⁰ and Ru oxides on the surface of the PtRu/C catalyst.     

Raising Co/Al2O3 catalyst lifetime in Fischer–Tropsch synthesis by using a novel dual-bed reactor

Accelerated deactivation of 15 wt.% Co/Al₂O₃ catalyst in Fischer–Tropsch synthesis (FTS) in a single-bed and a dual-bed reactor is reported. Water was found to have a remarkable effect on the deactivation of Co/Al₂O₃ catalyst during FTS. Synthesis at higher temperatures and lower space velocities resulted in higher values of P_H2O/(P_CO + P_H2) and P_H2O/P_CO and higher catalyst deactivation rates. Water-induced back-oxidation of cobalt, cobalt–alumina interactions, irreducible cobalt aluminates formation and refractory coke formation are the main sources of deactivation. When the water to carbon monoxide plus hydrogen ratio P_H2O/(P_CO + P_H2) is greater than about 0.55 or water to carbon monoxide ratio P_H2O/P_CO is greater than about 1.5, it is not uncommon to find rapid catalyst deactivation. Separation of water and heavy hydrocarbons between the two catalytic beds of the dual-bed reactor, resulted in 62% lower catalyst deactivation rate than that of the single-bed reactor. The amount of refractory coke formation on the catalysts of the dual-bed reactor is 34% lower than that of the single-bed reactor. It was revealed that activity recovery of the used catalysts of the dual-bed is higher than that of the single-bed reactor.     

Effect of double doping on crystal structure and electrical conductivity of CaO and WO3-doped Bi2O3

The atomic arrangement of WO₃-doped Bi₂O₃ was found similar to that of the fluorite structure. However, the electrical conductivity of WO₃-doped Bi₂O₃ is significantly lower than that of commonly used Y₂O₃-doped Bi₂O₃. The structure and electrical conductivity of samples formulated as (Ca_xW_0.15Bi_0.85−x)₂O_3.45−x (x = 0, 0.1, 0.2 and 0.3) were investigated. The as-sintered (W_0.15Bi_0.85)₂O_3.45 and (Ca_0.1W_0.15Bi_0.75)₂O_3.35 exhibit similar single tetragonal structure that is isostructural with 7Bi₂O₃·2WO₃. Therefore, (W_0.15Bi_0.85)₂O_3.45 and (Ca_0.1W_0.15Bi_0.75)₂O_3.35 formed a superstructure consisting of 10 enlarged cubic fluorite subcells. However, the as-sintered samples consist of a tetragonal structure and tetragonal CaWO₄ for x = 0.2 and 0.3 because the oxygen vacancy concentration increases. The conductivities of (Ca_xW_0.15Bi_0.85−x)₂O_3.45−x (x = 0, 0.1, 0.2 and 0.3) did not exhibit linear dependence with x value. The best conductivity is 2.35 × 10⁻² S cm⁻¹ at 700 °C for x = 0.1 that is higher than that of Ca-free (W_0.15Bi_0.85)₂O_3.45. The higher conductivity of (Ca_0.1W_0.15Bi_0.75)₂O_3.35 than (W_0.15Bi_0.85)₂O_3.45 may result from the higher anion vacancy concentration and more symmetrical structure.     

Precursor effects on ZrW2O8 formation kinetics

The synthesis of ZrW₂O₈ from different kinds of mixtures containing ZrO₂–WO₃, ZrO(NO₃)₂·2H₂O–WO₃, ZrCl₂O·8H₂O–WO₃, and ZrO₂–(NH₄)₁₀W₁₂O₄₁·5H₂O was investigated, and the kinetics was analyzed using JMA equation. It was found that ZrO(NO₃)₂·2H₂O, ZrCl₂O·8H₂O H₂O and (NH₄)₁₀W₁₂O₄₁·5H₂O that were used as inorganic precursors formed ZrO₂ and WO₃ after firing above 500 °C. The content of ZrW₂O₈ obtained by firing the mixtures is influenced by the kinds of precursors as well as mixing methods. The formation rate of ZrW₂O₈ depends on homogeneity related to mixing methods as well as the particle size of starting powders. Phase-pure ZrW₂O₈ is obtained from the ZrCl₂O·8H₂O–WO₃ mixtures at 1200 °C for 4 h, which is much shorter time than in the case of conventional ZrO₂–WO₃ mixtures. In the reaction kinetics of ZrO₂–WO₃ system, the Avrami exponent (n) is ∼0.5 above 1175 °C, indicating that the reaction is controlled by the diffusion-controlled reaction.     

Mixtures of carbon and Ni/Al2O3 as catalysts for the microwave-assisted CO2 reforming of CH4

In this work, the microwave-assisted CO₂ reforming of CH₄ over mixtures of carbonaceous materials and an in-lab prepared Ni/Al₂O₃ was studied. Ni/Al₂O₃ is not heated by microwave radiation, and for this reason, microwave receptors, such as carbonaceous materials, must be mixed with this catalyst. In order to evaluate the role of the carbonaceous component of the blend, two different carbonaceous materials were used: an activated carbon, FY5, and a metallurgical coke, CQ. The carbonaceous component acted not only as microwave receptor but also as catalyst and, consequently, it influenced the catalytic activity of the mixture. FY5 + Ni/Al₂O₃ was found to be a better catalyst than CQ + Ni/Al₂O₃, since FY5 on its own showed a better catalytic activity than CQ. Ni/FY5, which consists of Ni impregnated directly onto the microwave receptor, was also evaluated as a catalyst. It was found that the catalytic activity of the mixture FY5 + Ni/Al₂O₃ was better than that of Ni/FY5. Finally, the influence of the heating device on the catalytic activity of FY5 + Ni/Al₂O₃ was studied. Conversions over FY5 + Ni/Al₂O₃ and microwave heating were found to be similar to conversions over Ni/Al₂O₃ and conventional heating.     

Effects of preparation conditions in hydrothermal synthesis of highly active unsupported NiMo sulfide catalysts for simultaneous hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

Unsupported NiMo sulfide catalysts were prepared from ammonium tetrathiomolybdate (ATTM) and nickel nitrate by using a hydrothermal synthesis method involving water, organic solvent and hydrogen. The activity of these catalysts in the simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was much higher than that of the commercial NiMo/Al₂O₃ sulfide catalysts. Interestingly, the unsupported NiMo sulfide catalysts showed higher activity for hydrogenation (HYD) pathway than the direct desulfurization (DDS) pathway in the HDS of DBT. The same trends were observed for the HDS of 4,6-DMDBT. Morphology, surface area, pore volume and the HDS activity of unsupported NiMo sulfide catalyst depended on the catalyst preparation conditions. Higher temperature and higher H₂ pressure and addition of an organic solvent were found to increase the HDS activity of unsupported NiMo sulfide catalysts for both DBT and 4,6-DMDBT HDS. Higher preparation temperature increased HYD selectivity but decreased DDS selectivity. High-resolution TEM images revealed that unsupported NiMo sulfide prepared at 375 °C shows lower number of layers in the stacks of catalyst with more curvature and shorter length of slabs compared to that prepared at 300 °C. On the other hand, higher preparation pressure increased DDS selectivity but decreased HYD selectivity for HDS of 4,6-DMDBT. HRTEM images showed higher number of layers in the stack for the NiMo sulfide prepared under an initial H₂ pressure of 3.4 MPa compared to that under 2.1 MPa. The optimal Ni/(Mo + Ni) ratio for the NiMo sulfide catalyst was 0.5, higher than that for the conventional Al₂O₃-supported NiMo sulfide catalysts. This was attributed to the high dispersion of the active species and more active NiMoS generated. The present study also provides new insight for controlling the catalyst selectivity as well as activity by tailoring the hydrothermal preparation conditions.     

Electrochemical behavior and its electrocatalytic properties of chemically modified electrode with Keggin-type [SiNi(H2O)W11O39]

A monolayer of Keggin-type heteropolyanion [SiNi(H₂O)W₁₁O₃₉]⁶⁻ was fabricated by electrodepositing [SiNi(H₂O)W₁₁O₃₉]⁶⁻ on cysteamine modified gold electrode. The monolayer of [SiNi(H₂O)W₁₁O₃₉]⁶⁻ modified gold electrode was characterized by atomic force microscopy (AFM) and electrochemical method. AFM results showed the [SiNi(H₂O)W₁₁O₃₉]⁶⁻ uniformly deposited on the electrode surface and formed a porous monolayer. Cyclic voltammetry exhibited one oxidation peak and two reduction peaks in 1.0 M H₂SO₄ in the potential range of −0.2 to 0.7 V. The constructed electrode could exist in a large pH (0-7.6) range and showed good catalytic activity towards the reduction of bromate anion (BrO₃⁻) and nitrite (NO₂⁻), and oxidation of ascorbic acid (AA) in acidic solution. The well catalytic active of the electrode was ascribed to the porous structure of the [SiNi(H₂O)W₁₁O₃₉]6⁻ monolayer.     

Low temperature sintering and microwave dielectric properties of Ce2(WO4)3 ceramics

Ce₂(WO₄)₃ ceramics have been synthesized by the conventional solid-state ceramic route. Ce₂(WO₄)₃ ceramics sintered at 1000 °C exhibited ?_r = 12.4, Qxf = 10,500 GHz (at 4.8 GHz) and τ_f = −39 ppm/°C. The effects of B₂O₃, ZnO–B₂O₃, BaO–B₂O₃–SiO₂, ZnO–B₂O₃–SiO₂ and PbO–B₂O₃–SiO₂ glasses on the sintering temperature and microwave dielectric properties of Ce₂(WO₄)₃ were investigated. The Ce₂(WO₄)₃ + 0.2 wt% ZBS sintered at 900 °C/4 h has ?_r = 13.7, Qxf = 20,200 GHz and τ_f = −25 ppm/°C.     

Co-doped ceria-based solid solution in the CeO2-M2O3-CaO, M = Sm, Gd system

The Pechinni method (A) as well as hydrothermal treatment (B) of co-precipitated CeO₂-based gels with NaOH solution were used to synthesise pure CeO₂, and CeO₂-based solid solutions with formula Ce_1−xM_xO₂, Ce_1−x(M_0.5Ca_0.5)_xO₂ M = Gd, Sm for 0.15 < x < 0.3 nanopowders. The thermal evolution of CeO₂-based precursors during heating them up to 1000 °C was monitored by thermal (TG, DTA) analysis and X-ray diffraction method. All nanopowders and samples sintered were found to be pure CeO₂ or ceria-based solutions with fluorite-type structure. The microstructure of CeO₂-based sintered samples at 1500 °C (A) or 1250 °C (B) was observed for 2 h under the scanning electron microscope. The electrical properties of singly Ce_1−xM_xO₂ or doubly doped CeO₂-based samples with formula Ce_1−x(M_0.5Ca_0.5)_xO₂, M = Gd, Sm, 0.15 < x < 0.30 were investigated by means of the ac impedance spectroscopy method throughout the temperature range of 600-800 °C. It has been stated that partial substitution of calcium by samarium or calcium by gadolinium in the Ce_1−x(M_0.5Ca_0.5)_xO₂, M = Gd, Sm solid solutions leads to ionic conductivity enhancement comparable with only samaria- or gadolina-doped ceria. The CeO₂-based samples with small-grained microstructures obtained from powders synthesised by hydrothermal method exhibited better ionic conductivity than samples with the same composition obtained from powders synthesised by the Pechinii method. The stability of the electrolytic properties of selected co-doped ceria sinters in fuel gases (H₂, CH₄) as well as exhaust gases from diesel engine was also investigated. The co-doped Ce_0.8(Sm_0.5Ca_0.5)_0.2O₂ or Ce_0.85(Gd_0.5Ca_0.5)_0.15O₂ dense samples would appear be to more adequate oxide electrolytes than Ce_1−xM_xO₂, M = Sm, Gd and x = 0.15 or 0.2 for electrochemical devices operating at temperatures ranging from 600 to 700 °C.     

Insignificant impact of designed oxygen release from high capacity Li[(Ni1/2Mn1/2)xCoy(Li1/3Mn2/3)1/3]O2 (x + y = 2/3) positive electrodes during the cycling of Li-ion cells

The properties of graphite/Li[(Ni_0.5Mn_0.5)_xCo_y(Li_1/3Mn_2/3)_1/3]O₂ (x + y = 2/3, y = 1/12 and 1/6) Li-ion cells are reported. There is an extended plateau near 4.5 V during the first charging of the cells that corresponds to the simultaneous removal of Li and oxygen from the Li[(Ni_0.5Mn_0.5)_xCo_y(Li_1/3Mn_2/3)_1/3]O₂ (x + y = 2/3, y = 1/12 and 1/6) electrodes. The release of this oxygen directly within a Li-ion cell has been a cause for concern. However, it was found that subsequent to O₂ release, Li-ion cells delivered a high reversible positive electrode specific capacity near 250 mAh/g at C/30 between 2.5 and 4.8 V, the cells did not display increased irreversible capacity relative to counterparts having Li metal negative electrodes and the cells retained 85% of their initial capacity after 70 cycles at C/6 between 2.5 and 4.6 V. Therefore, the O₂ released during the first charge does not significantly impact the electrochemical properties of graphite/Li[(Ni_0.5Mn_0.5)_xCo_y(Li_1/3Mn_2/3)_1/3]O₂ (x + y = 2/3) lithium-ion cells.     

Mechanical properties of Al2O3-Cr2O3/Cr3C2 nanocomposite fabricated by spark plasma sintering

The fine grains of Al₂O₃-Cr₂O₃/Cr-carbide nanocomposites were prepared by employing recently developed spark plasma sintering (SPS) technique. The initial materials were fabricated by a metal organic chemical vapor deposition (MOCVD) process, in which Cr(CO)₆ was used as a precursor and Al₂O₃ powders as matrix in a spouted chamber. The basic mechanical properties like hardness, fracture strength and toughness, and the nanoindentation characterization of nanocomposites such as Elastics modulus (E), elastic work (W_e) and plastic work (W_p) were analyzed. The microstructure of dislocation, transgranular and step-wise fracture surface were observed in the nanocomposites. The nanocomposites show fracture toughness of (4.8 MPa m^1/2) and facture strength (780 MPa), which is higher than monolithic alumina. The strengthening mechanism from the secondary phase and solid solution are also discussed in the present work. Nanoindentation characterization further illustrates the strengthening of nanocomposites.     

Synthesis, characterization and performance of CuO/La2O3 composite catalyst for ammonia catalytic oxidation

This work considers the oxidation of ammonia (NH₃) by selective catalytic oxidation (SCO) over a CuO/La₂O₃ composite catalyst at temperatures between 150 and 400 °C. A CuO/La₂O₃ composite catalyst was prepared by co-precipitation of copper nitrate and lanthanum nitrate at various molar concentrations. This study also considers how the concentration of influent NH₃ (C₀ = 1000 ppm), the space velocity (GHSV = 92,000 l/h), the relative humidity (RH = 12%) and the concentration of oxygen (O₂ = 4%) affect the operational stability and the capacity for removing NH₃. The catalysts that were characterized using FTIR, XRD, UV-Vis, BET and PSA, have shown that the catalytic behavior is related to the copper (II) oxide, while lanthanum (III) oxide may serve only to provide active sites for the reaction during a catalyzed oxidation run. The experimental results show that the extent of conversion of ammonia by SCO in the presence of the CuO/La₂O₃ composite catalyst was a function of the molar ratio. The ammonia was removed by oxidation in the absence of CuO/La₂O₃ composite catalyst, and around 93.0% NH₃ reduction was achieved during catalytic oxidation over the CuO/La₂O₃ (8:2, molar/molar) catalyst at 400 °C with an oxygen content of 4.0%. Moreover, the effect of the reaction temperature on the removal of NH₃ in the gaseous phase was also monitored at a gas hourly space velocity of under 92,000 h^− 1.     

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.