铜离子交换分子筛上NO吸附的IR光谱及TPD研究

采用原位IR光谱及TPD技术研究了NO在铜离子交换分子筛上各种表面物种的生成及脱附,并与NO在Cu-ZSM-5上的分解反应性能相关联,考察了Cu-ZSM-5反应活性高的原因及O₂的生成机理。NO的吸附状态随分子筛母体种类及铜离子交换度的不同而变化,交换度较高的ZSM-5催化剂上容易形成NO-3物种,该物种对NO分解及O₂的生成具有重要作用。     

Nanocomposites based on nickel ferrites dispersed in sol–gel silica matrices

In this work, we describe the effects of thermal treatments on the structural, morphological, and textural properties of nanocomposites formed by nickel ferrite dispersed in xerogel and aerogel silica matrices. The catalytic properties for the total oxidation of an organochloro model contaminant, the chlorobenzene, are also evaluated. Wet samples with different amounts of NiFe₂O₄ in matrix were prepared by sol–gel process. Xerogels and aerogels obtained in monolithic form were prepared by controlled and hypercritical drying, respectively, and heated at temperatures between 300 and 1,100°C. The specific surface area and total pore volume of the samples change with heating mainly due to the variation on their texture. The xerogel treated at 500°C and the aerogel treated at 700°C showed the most catalytic activity, converting chlorobenzene at temperatures as low as 150°C, while the other catalysts were active only at temperatures higher than 300°C. No organic by-products were observed in the oxidation of chlorobenzene, suggesting that total oxidation takes place under the reaction conditions. A strong decrease in catalytic activity was observed for nanocomposites treated at 1,100°C, due to matrix densification, which led to the encapsulation of the ferrite particles and hindered the access of the gas to the ferrite surface.     

MnO x /ZrO2 gel-derived materials for hydrogen peroxide decomposition

Manganese-yttrium-zirconium mixed oxide nanocomposites with three different Mn loadings (5, 15 and 30 wt%) were prepared by sol–gel synthesis. Amorphous xerogels were obtained for each composition. Their structural evolution with the temperature and textural properties were examined by thermogravimetry/differential thermal analysis, X-ray diffraction, diffuse reflectance UV–vis spectroscopy and N₂ adsorption isotherms. Mesoporous materials with high surface area values (70–100 m² g⁻¹) were obtained by annealing in air at 550 °C. They are amorphous or contain nanocrystals of the tetragonal ZrO₂ phase (T-ZrO₂) depending on the Mn amount and exhibit Mn species with oxidation state higher than 2 as confirmed by temperature programmed reduction experiments. T-ZrO₂ is the only crystallizing phase at 700 °C while the monoclinic polymorph and Mn₃O₄ start to appear only after a prolonged annealing at 1,000 °C. The samples annealed at 550 °C were studied as catalysts for H₂O₂ decomposition in liquid phase. Their catalytic activity was higher than that of previously studied Mn/Zr oxide systems prepared by impregnation. Catalytic data were described by a rate equation of Langmuir type. The decrease of catalytic activity with time was related to dissolution of a limited fraction (up to 15%) of Mn into the H₂O₂/H₂O solution.     

Structural evolution of turbostratic carbon: Implications in H2 storage

Structural evolution of turbostratic carbon samples as a function of annealing temperature has been investigated in detail using small angle X-ray scattering (SAXS), solid state nuclear magnetic resonance (NMR) and Raman spectroscopic techniques. From these studies, it is established that, samples heated at lower temperatures (700 °C and 800 °C) consist carbon particles with rough surfaces forming structure of surface fractal in nature. Whereas the sample heated at higher temperature (900 °C) consists of larger clusters with nearly smooth surface as well as smaller size particles forming dense mass fractal structure. For this sample, solid state NMR and Raman Spectroscopic studies indicate an increased extent of overlapping of 2p_z orbital of carbon atoms due to improved long range ordering and clustering. Hydrogen adsorption studies further substantiated that energetically more homogeneous surface exists for particles of 900 °C heated sample as compared to those of 700 °C and 800 °C heated samples. A highest hydrogen storage capacity of 0.152 H/M has been observed at 123 K and 45 bar pressure for the sample heated at 900 °C.     

Cobalt ferrite for direct cracking of methane to produce hydrogen and carbon nanostructure: Effect of temperature and methane flow rate

Cobalt ferrite (CoFe₂O₄) was used as a catalyst for direct methane cracking. The reaction was accomplished in a fixed bed reactor at normal atmospheric pressure, while gas flow rate (20–50 mL/min) and reaction temperature (800–900 °C) were varied. The fresh CoFe₂O₄ morphology is sponge-like particle with inverse spinel structure as revealed from SEM and XRD results. The methane conversions and hydrogen formation rate were increased with reaction temperature, while catalyst stability and induction period decreased. Increases of gas flow rate > 20 mL/min led to a decrease the overall catalytic activity of CoFe₂O₄ for methane cracking. The XRD results of spent catalysts revealed that CoFe alloy was the active phase of methane cracking. TGA analysis showed that the largest amount of deposited carbon was 70.46 % at (20 mL/min, 900 °C), where it was 34.40 % at (50 mL/min, 800 °C). The deposited carbon has the shape of spherical carbon nanostructures and/or nano sprouts as observed with SEM. Raman data confirmed the graphitization type of the deposited carbon.     

High oxygen-reduction activity of silk-derived activated carbon

Activated carbon prepared from silk fibroin, which is free of metal elements, showed a high catalytic activity for the oxygen-reduction reaction (ORR). The activated carbon had a very high onset potential of E_onset = 0.83 V (vs. RHE) in oxygen-saturated 0.5 M H₂SO₄ at 60 °C. The ORR on the activated carbon proceeded by a four-electron process in the high-electrode-potential region; this gradually decreased to a 3.5-electron reaction below about 0.6 V (vs. RHE). Only about 1% of nitrogen atoms (mostly quaternary) remained in the activated carbon by heat-treatment at up to 1200 °C are responsible for the high catalytic activity. The open circuit voltage of a polymer electrolyte fuel cell using the activated carbon as the cathode and a platinum/carbon black anode under pure oxygen and hydrogen gases, respectively, both at one atmosphere, was 0.96 V at 27 °C.     

Sorption-enhanced steam methane reforming over Ni/Al2O3/KNaTiO3 bifunctional material

The performance of a new lab-made bifunctional material Ni/Al₂O₃/KNaTiO₃ for producing high purity H₂ via sorption-enhanced steam methane reforming (SESMR) was investigated. A series of bifunctional materials with 10 wt% Ni loading but different wt% ratios of KNaTiO₃ and Al₂O₃ was prepared by wetness impregnation method. All the materials were calcined at 700 °C for 3 hours and screened for their catalytic activity in a continuous flow fixed-bed reactor. The material containing 50 wt% each of KNaTiO₃ and Al₂O₃ (designated as HM) was found to be the best choice. The optimum process parameters for the production of high purity H₂ were determined: temperature = 700 °C, steam to carbon (S/C) molar ratio = 6 and gas-hourly space velocity (GHSV) = 2000 cm³ g^-1 h^-1. The values of CH₄ conversion, H₂ yield and H₂ purity were 87, 87 and 90%, respectively, at the optimum reaction conditions. The adsorption capacity of HM was found to be 14.7 wt%. With a breakthrough time of 10 min, the material was stable for 8 adsorption-desorption cycles. The regeneration of HM was achieved with N₂ gas at the same reaction temperature. Overall, the activity of this material for SESMR was very promising.     

Hydrogen production over partial oxidation of methane using NiMgAl spinel catalysts: A kinetic approach

NiMgAl–based catalysts were synthesized by coprecipitation, sol–gel, and impregnation methods, calcined at 700 °C for 4 h and tested in partial oxidation of methane in a temperature range of 500–800 °C. The fresh and used unsupported and supported samples were characterized by X-ray diffraction, nitrogen physisorption with Brunauer-Emett-Teller (BET) analysis, and H₂–temperature-programmed reduction. X-ray diffraction analysis showed, for all samples, the formation of spinel phases MgAl₂O₄ and/or NiAl₂O₄ with crystallite sizes of 6–14 nm. H₂–temperature-programmed reduction analysis showed reduction of two Ni²⁺ species (in octahedral and tetrahedral sites of a spinel structure) into metallic nickel known to be responsible for the methane activation. The 10 wt % Ni/MgAl₂O₄ impregnated catalysts exhibited the highest activity and stability in the partial oxidation of methane reaction, which led mainly to syngas (CO + H₂) at 800 °C with a methane conversion close to the thermodynamic equilibrium (95%). A kinetic model revealed that the oxidation of methane occurs on a thin layer of the catalytic bed in which oxygen is consumed and is followed by the production of CO and H₂ by methane steam reforming and water gas shift reactions.     

Dimethyl Ether—Reforming Catalysts for Hydrogen Production

This article reviews our recent works on dimethyl ether steam reforming (DME SR) over nanocomposite catalysts of copper-based spinel oxide and solid-acid catalyst. A series of Cu-based spinels was prepared by citric acid complexation method and their catalytic performance was studied in terms of activity, selectivity, and stability. The influence of preparation conditions, such as calcination temperature, reduction temperature, and chemical composition, and reforming conditions, such as steam-to-carbon ratio and reaction temperature, was systematically studied. Effect of type of solid-acid catalyst was also reported. Zeolite-based composites and alumina-based ones are highly active in temperature ranges of <300 °C and >300 °C, respectively. The composite of CuFe₂O₄ and alumina treated thermally in air at 700–800 °C exhibited excellent activity and stability in DME SR. Upon H₂ reduction, phase separation of copper spinel to metallic copper nanoparticles and host oxides proceeds. The high dispersion of the Cu particles (Cu¹⁺-rich surface of ca. 70%) on the hosts, and the strong chemical interaction between them could be observed. The H₂-rich reformate (>70% H₂) could be attained for longer than 800 h at 375 °C, showing the good potential for practical use in H₂ and fuel cell applications. Doping Ni to CuFe₂O₄ significantly enhanced the stability of the catalyst, in accordance with the alloying effect. Regeneration of the degraded catalysts could be obtained by simple heat-treatment since carbon deposits were removed, and spinel structures were reconstructed.     

Thermal analysis applied in the crystallization study of SrSnO3

SrSnO₃ was synthesized by the polymeric precursor method with elimination of carbon in oxygen atmosphere at 250 °C for 24 h. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After calcination at 500, 600 and 700 °C for 2 h, samples were evaluated by X-ray diffraction (XRD), infrared spectroscopy (IR) and Rietveld refinement of the XRD patterns for samples calcined at 900, 1,000 and 1,100 °C. During thermal treatment of the powder precursor ester combustion was followed by carbonate decomposition and perovskite crystallization. No phase transition was observed as usually presented in literature for SrSnO₃ that had only a rearrangement of SnO₆ polyhedra.     

Diesel soot oxidation by nitrogen dioxide,oxygen and water under engine exhaust conditions: Kinetics data related to the reaction mechanism

Experimental studies on diesel soot oxidation under a wide range of conditions relevant for modern diesel engine exhaust and continuously regenerating particle trap were performed. Hence, reactivity tests were carried out in a fixed bed reactor for various temperatures and different concentrations of oxygen, NO₂ and water (300–600 °C, 0–10% O₂, 0–600 ppm NO₂, 0–10% H₂O). The soot oxidation rate was determined by measuring the concentration of CO and CO₂ product gases. The parametric study shows that the overall oxidation process can be described by three parallel reactions: a direct C–NO₂ reaction, a direct C–O₂ reaction and a cooperative C–NO₂–O₂ reaction. C–NO₂ and C–NO₂–O₂ are the main reactions for soot oxidation between 300 and 450 °C. Water vapour acts as a catalyst on the direct C–NO₂ reaction. This catalytic effect decreases with the increase of temperature until 450 °C. Above 450 °C, the direct C–O₂ reaction contributes to the global soot oxidation rate. Water vapour has also a catalytic effect on the direct C–O₂ reaction between 450 °C and 600 °C. Above 600 °C, the direct C–O₂ reaction is the only main reaction for soot oxidation. Taking into account the established reaction mechanism, a one-dimensional model of soot oxidation was proposed. The roles of NO₂, O₂ and H₂O were considered and the kinetic constants were obtained. The suggested kinetic model may be useful for simulating the behaviour of a diesel particulate filter system during the regeneration process.     

An effect of heat processing on catalytic activity of a system MnO x ,SiO2/TiO2/Ti

An effect of annealing in air at temperatures 250, 350, 500, and 700°C on composition, surface structure, and catalytic activity in CO oxidation of a system MnO _x ,SiO₂/TiO₂/Ti formed by combining methods of plasma electrolytic oxidation and impregnation was examined.     

Effect of Nano‐support and Type of Active Metal on Reforming of CH4 with CO2

Two series of Co and Ni based catalysts supported over commercial (ZrO₂, CeO₂, and Al₂O₃) nano supports were investigated for dry reforming of methane. The catalytic activity of both Co and Ni based catalysts were assessed at different reaction temperatures ranging from 500—800 °C; however, for stability the time on stream experiments were conducted at 700 °C for 6 h. Various techniques such as N₂ adsorption‐desorption isotherm, temperature‐programmed reduction (H₂‐TPR), temperature‐programmed desorption (CO₂‐TPD), temperature‐programmed oxidation (TPO), X‐ray diffraction (XRD), thermogravimetric analysis (TGA) were applied for characterization of fresh and spent catalysts. The catalytic activity and stability tests clearly showed that the performance of catalyst is strongly dependent on type of active metal and support. Furthermore, active metal particle size and Lewis basicity are key factors which have significant influence on catalytic performance. The results indicated that Ni supported over nano ZrO₂ exhibited highest activity among all tested catalysts due to its unique properties including thermal stability and reducibility. The minimum carbon deposition and thus relatively stable performance was observed in case of Co‐Al catalyst, since this catalyst has shown highest Lewis basicity.     

Effects of calcination and activation temperature on dry reforming catalysts

The effect of calcination temperatures on dry reforming catalysts supported on high surface area alumina Ni/γ-Al₂O₃ (SA-6175) was studied experimentally. In this study, the prepared catalyst was tested in a micro tubular reactor using temperature ranges of 500, 600, 700 and 800 °C at atmospheric pressure, using a total flow rate of 33 ml/min consisting of 3 ml/min of N₂, 15 ml/min of CO₂ and 15 ml/min of CH₄. The calcination was carried out in the range of 500–900 °C. The catalyst is activated inside the reactor at 500–800 °C using hydrogen gas. It was observed that calcination enhances catalyst activity which increases as calcination and reaction temperatures were increased. The highest conversion was obtained at 800 °C reaction temperature by using catalyst calcined at 900 °C and activation at 700 °C. The catalyst characterization conducted supported the observed experimental results.     

Effect of Calcination Temperature on the Structure and Catalytic Properties of MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Ca<Subscript>2</Subscript>O<Subscript>3</Subscript> in the Reaction of CO and Ethane Oxidation

Effect of the calcination temperature of the MnOx/Ga2O3 system on its structural and catalytic properties in the reaction of oxidation of CO and hydrocarbons. The dependences of the catalytic activity of MnO _x /Ga₂O₃ in the reactions of CO and ethane oxidation on the calcination temperature exhibit an extremal behavior. The maximum values of activity are observed upon calcination of the system at 700°C, i.e., at the temperature that is limiting for the existence of a solid solution of manganese ions in γ-Ga₂O₃. The structural changes occurring with increasing calcination temperature are accompanied by a substantial decrease in the specific surface area of a sample. The observed rise in the specific catalytic activity (by a factor of ~7 upon an increase in the preliminary-calcination temperature from 600 to 800°C) confirms that the thermal activation effect exists for the given system.     

Effect of the microstructure of the supported catalysts CuO/TiO<Subscript>2</Subscript> and CuO/(CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>) on their catalytic properties in carbon monoxide oxidation

The effect of the microstructure of titanium dioxide on the structure, thermal stability, and catalytic properties of supported CuO/TiO₂ and CuO/(CeO₂-TiO₂) catalysts in CO oxidation was studied. The formation of a nanocrystalline structure was found in the CuO/TiO₂ catalysts calcined at 500°C. This nanocrystalline structure consisted of aggregated fine anatase particles about 10 nm in size and interblock boundaries between them, in which Cu²⁺ ions were stabilized. Heat treatment of this catalyst at 700°C led to a change in its microstructure with the formation of fine CuO particles 2.5–3 nm in size, which were strongly bound to the surface of TiO₂ (anatase) with a regular well-ordered crystal structure. In the CuO/(CeO₂-TiO₂) catalysts, the nanocrystalline structure of anatase was thermally more stable than in the CuO/TiO₂ catalyst, and it persisted up to 700°C. The study of the catalytic properties of the resulting catalysts showed that the CuO/(CeO₂-TiO₂) catalysts with the nanocrystalline structure of anatase were characterized by the high-est activity in CO oxidation to CO₂.     

Enhancement of the catalytic performances and lifetime of Ni/γ-Al2O3 catalysts for the steam toluene reforming via the combination of dopants: inspection of Cu,Co, Fe,Mn, and Mo species addition

In this work, the influence of metallic dopant addition in 10 wt % Ni/γ-Al₂O₃ catalyst on the material physico-chemical properties and catalytic activity for the toluene steam reforming was studied. Seventeen doped Ni/γ-Al₂O₃ catalysts were synthesized by the sol–gel process. The aim of this study was to determine which elements were the most suitable for the doping of 10 wt % Ni/γ-Al₂O₃ catalysts. The influence of the dopants was studied through different physico-chemical techniques. It appeared that some dopants showed lower catalytic performances due to high carbon deactivation. On the contrary, some dopants increased the resistance to coking while also improving the catalytic activity. Different mechanisms were proposed to explain these modifications of catalytic behavior. Among all doped Ni/γ-Al₂O₃ catalysts, the samples that combined Mn + Mo or Co + Mo dopants showed the best catalytic performances at 650 °C. Both samples showed high toluene reforming activity and low amounts of carbon deposit.     

Pt and Pt–Ru nanoparticles decorated polypyrrole/multiwalled carbon nanotubes and their catalytic activity towards methanol oxidation

Conducting polymer composite films comprised of polypyrrole (PPy) and multiwalled carbon nanotubes (MWCNTs) [PPy–CNT] were synthesized by in situ polymerization of pyrrole on carbon nanotubes in 0.1 M HCl containing (NH₄)S₂O₈ as oxidizing agent over a temperature range of 0–5 °C. Pt nanoparticles are deposited on PPy–CNT composite films by chemical reduction of H₂PtCl₆ using HCHO as reducing agent at pH = 11 [Pt/PPy–CNT]. The presence of MWCNTs leads to higher activity, which might be due to the increase of electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces allowing higher dispersion and utilization of the deposited Pt nanoparticles. A comparative investigation was carried out using Pt–Ru nanoparticles decorated PPy–CNT composites. Cyclic voltammetry demonstrated that the synthesized Pt–Ru/PPy–CNT catalysts exhibited higher catalytic activity for methanol oxidation than Pt/PPy–CNT catalyst. Such kinds of Pt and Pt–Ru particles deposited on PPy–CNT composite polymer films exhibit excellent catalytic activity and stability towards methanol oxidation, which indicates that the composite films is more promising support material for fuel cell applications.     

Synthesis of homogeneous La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> solid solutions by the Pechini method and their activity in methane oxidation

Homogeneous La_{1 − x} Ca _x MnO₃ solid solutions have been synthesized by the Pechini method (using polymer-solid compositions). Their microstructure, stability at high temperatures, and catalytic activity in methane oxidation are reported. A continuous series of solid solutions stable in air up to 1100°C forms in the system, and the particle surface is enriched with calcium. A distinctive microstructural feature of the particles is their microporosity. The catalytic activity of all calcium-containing samples (except for x = 0.7) below 700°C is lower than that of lanthanum manganite and decreases under the action of the reaction medium, which can be due to the decrease in the amount of weakly bound oxygen on the surface because of the enrichment of the surface with calcium and the formation of strongly bound surface carbonates. The higher activity and stability of the La_0.3Ca_0.7MnO₃ sample (calcined at 1100°C) above 500°C can be due to the formation of nanosized areas with an Mn₃O₄ structures on the perovskite particle surface in the reaction medium.     

TGA-MS study of the decomposition of phosphorus-containing ionic liquids trihexyl(tetradecyl)phosphonium decanoate and trihexyltetradecylphosphonium bis[(trifluoromethyl)sulfonyl] amide

The phosphorus-containing ionic liquids (IL) decompose where ion pairs fall apart. Trihexyl(tetradecyl)phosphonium decanoate, sold as Cyphos IL 103, and Trihexyltetradecylphosphonium bis[(trifluoromethyl)sulfonyl] amide, sold as Cyphos IL 109, decompose in 200–475 °C range in air and the fragments containing organophosphorus are found here among other major fragments of hydrocarbon arms. Black residues are found after heating in air to 740 °C in TG in 5.0 and 0.6 mass/% for Cyphos IL 103 and 109, respectively. They were presumably containing P₂O₅ after oxidation. Not all the phosphorus can be counted for at 740 °C and falls short of calculated values of 10.9 and 9.3 mass/%, if residues contain nothing else but P₂O₅. Among the fragments the authors found in MS the organophosphorus fragments from decomposition of the cationic C₃₂ H₆₈ P + including P with 3–4 hydrocarbon attached as well as the major fragments of linear hydrocarbon arms. Water evolves early at lower temperature and continues to 740 °C. CO₂ comes from oxidation of carbon at high temperatures. The SO, SO₂, CF₃, CF₂CF₂ evolve in sulfur and fluorine containing anion in Cyphos IL 109. H₃PO₄ is detected, which is most likely from the reaction product of P₂O₅ and water. No P₂O₅ was found. Ash content examined by inductively coupled plasma spectroscopy (ICP) found that the phosphorus P in the ashes after burning in air to 700 °C and found 3200 ppm (or 0.62 mass/%) and 30 ppm (0.003 mass/%) in Cyphos IL 103 and 109, respectively.