Effectiveness in catalytic washcoats with multi-step mechanisms for catalytic combustion of hydrogen

The effect of intra-phase diffusion for channel-flow oxidation reactors with washcoats ranging in thickness from 10 to is explored in combination with a detailed surface chemistry for low-temperature H₂ oxidation over supported Pd/PdO_x catalysts. A numerical model of a porous catalyst washcoat is developed to assess how local conditions influence catalyst effectiveness when considering a detailed multi-step surface mechanism, and this washcoat model is integrated into a channel flow reactor model to assess if and when effectiveness correlations may apply for channel flow reactors. The Pd-H₂-O₂ surface chemistry mechanism, which is validated against experimental measurements in an annular flow reactor, implements thermodynamically consistent interaction potentials of surface species and predicts non-linear behavior of conversion with respect to H₂ concentrations at the low equivalence ratios of the current study, particularly at lower temperatures where surface chemistry dominates overall reaction rates. The catalytic washcoat model further indicates that conversion and similarly catalyst effectiveness are strongly dependent upon the site fractions of vacancies available for H₂ adsorption, which vary strongly with flow conditions and at higher conversions with depth in the porous washcoat. This leads to difficulty in developing simple models for catalyst washcoat effectiveness based upon any parameter such as a Thiele modulus. Furthermore the results suggest that care should be taken in interpreting kinetic data for oxidation reactions even when relatively thin washcoats are employed for reaction rate studies.     

Studies of the activation process over Pd perovskite-type oxides used for catalytic oxidation of toluene

Calcined and reduced catalysts Pd/LaBO₃ (B = Co, Fe, Mn, Ni) were used for the total oxidation of toluene. Easiness of toluene destruction was found to follow the sequence based on the T₅₀ values (temperature at which 50% of toluene is converted): Pd/LaFeO₃ > Pd/LaMnO_3+δ > Pd/LaCoO₃ > Pd/LaNiO₃. In order to investigate the activation process (calcination and reduction) in detail, the reducibility of the samples was evaluated by H₂-TPR on the calcined catalysts. Additionally, characterization of the Pd/LaBO₃ (B = Co, Fe) surface was carried out by X-ray photoelectron spectroscopy (XPS) at each stage of the global process, namely after calcination, reduction and under catalytic reaction at either 150 or 200 °C for Pd/LaFeO₃ and either 200 or 250 °C for LaCoO₃. The different results showed that palladium oxidized entities were totally reduced after pre-reduction at 200 °C for 2 h (2 L/h, 1 °C/min). As LaFeO₃ was unaffected by such a treatment, for the other perovskites, the cations B are partially reduced as B³⁺ (B = Mn) or B²⁺ even to B⁰ (B = Co, Ni). In the reactive stream (0.1% toluene in air), Pd⁰ reoxidized partially, more rapidly over Co than Fe based catalysts, to give a Pd²⁺/Pd⁴⁺ and Pd⁰/Pd²⁺/Pd⁴⁺ surface redox states, respectively. Noticeably, reduced cobalt species are progressively oxidized on stream into Co³⁺ in a distorted environment. By contrast, only the lines characteristic of the initial perovskite lattice were detected by XRD studies on the used catalysts. The higher activity performance of Pd/LaFeO₃ for the total oxidation of toluene was attributed here to a low temperature of calcination and to a remarkable high stability of the perovskite lattice whatever the nature of the stream which allowed to keep a same palladium dispersion at the different stages of the process and to resist to the oxidizing experimental conditions. On the contrary, phase transformations for the other perovskite lattices along the process were believed to increase the palladium particle size responsible of a lower activity.     

希夫碱类金属配合物催化剂催化氧化烯烃研究进展

分析了希夫碱金属配合物的结构特点及其催化氧化烯烃的研究现状,阐述了用于均相催化氧化的希夫碱、固载型希夫碱金属配合物催化剂的分类及其在氧化烯烃领域的应用研究。通过分析希夫碱类小分子金属配合物催化氧化烯烃的缺陷,得出非均相的负载型希夫碱类金属配合物催化剂是目前主要发展方向的结论。     

Rh oxide reducibility and catalytic activity of model Pt–Rh catalysts

Pt and Rh were impregnated by different methods into the washcoat to investigate the differences in Rh oxidation state and catalytic activity of the samples. Both fresh and laboratory aged samples were studied. Clear differences in catalytic activity were noticed between the catalysts with different Pt and Rh addition methods. The best oxidation activity for fresh catalysts was achieved with the catalyst having both Pt and Rh deposited into the Ce–Zr mixed oxide. However, this state was observed to be unstable, and hence, this particular catalyst was dramatically deactivated in air ageing at high temperature. After ageing, the catalyst having both Pt and Rh impregnated lastly into the entire calcined washcoat matrix had the best activity in all three reactions, carbon monoxide and hydrocarbon oxidation and nitrogen oxide reduction. According to XPS studies, Rh was in easily reducible form in all the fresh samples. After ageing, the highest portion of reducible Rh was observed in the sample having also the best catalytic activity.     

Mechanochemical activation as a tool of increasing catalytic activity

The role of structure–energy properties of mechanically induced defects in the crystal structure of heterogeneous catalysts is considered. The main concepts of the mechanochemical activation effect on the activity and selectivity of catalysts are discussed. The wasteless and energy-saving methods of preparation of some catalysts are presented. Rigorous experimental proofs of the influence of defects in the crystal structure of catalysts on their specific catalytic activity are obtained. High performance of mechanochemical catalysis application for hydrogenation, oxidation, amination and hydroalumination processes is shown. For the first time catalytic reactions under the conditions of mechanochemical activation at elevated temperature and increased pressure of gases are carried out.     

Polymer-immobilized manganese(III)-Schiff base complexes for catalytic epoxidation of olefins

Polymer-linked manganese(III)-salen-type Schiff base complexes were prepared by the copolymerization of functionalized Schiff base, styrene, and divinylbenzene at various mixing ratios (1:10:0–1:12:4), followed by introduction of Mn(III) ion. The materials catalyzed epoxidation of cyclohexene with iodosylbenzene in CH₂Cl₂ as rapidly as the monomer complexes. The maximum total turnover reached 170, which is about 13 times higher than that of the monomer. The lifetime of polymer catalysts is discussed in terms of cross-linking and solvent effects.     

A comparison between hexaaluminates and perovskites for catalytic combustion applications

Hexaaluminates and perovskites are two promising candidates for use in catalytic combustion applications. In the present study two hexaaluminates, LaMnAl₁₁O₁₉ and LaCoAl₁₁O₁₉, were compared with two perovskites, LaMnO₃ and LaCoO₃, with respect to their thermal stability and catalytic activity for combustion of methane and gasified biomass. The results showed that the hexaaluminates retained a much higher surface area even after calcination at 1200 °C compared to the perovskites. LaMnAl₁₁O₁₉ showed the highest catalytic activity of all catalysts. LaCoAl₁₁O₁₉ generally showed low activity. Of the two perovskites, LaCoO₃ was the most active, and the initial test run the activity for biomass combustion were close to that one of LaMnAl₁₁O₁₉ even though its surface area was only one tenth of the hexaaluminate's. However, it was severely deactivated in the second test run. Similar deactivation but less severe was also found for the other catalyst.     

Advanced technology catalytic combustor for high temperature ground power gas turbine applications

We report results from a lean burn ultra-low emission catalytic combustor. In a sub-scale rig, atmospheric testing with methane demonstrated NO_x<3, CO<5, and UHC<1 ppm, with stable combustion at inlet temperatures of 400–500°C (750–1020°F) and combustor discharge temperatures of 1150–1540°C (2100–2800°F). Catalyst temperatures were held well below metal substrate material limits, while combustor discharge temperatures of up to 1540°C (2800°F) were achieved.     

MCr2O4 (M=Co,Cu, and Zn) nanospinels for 2-propanol combustion: Correlation of structural properties with catalytic performance and stability

The correlation between structure and activity of MCr₂O₄ nanospinels (M=Co, Cu, and Zn) synthesized by a sol–gel combustion method was investigated for the oxidation of 2-propanol. The catalysts were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), N₂ adsorption/desorption, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Wide-angle XRD patterns show that the samples are pure spinel phases with cubic structure for CoCr₂O₄ and ZnCr₂O₄, and tetragonal structure for CuCr₂O₄. FTIR spectra confirmed the spinel structure of samples. The spinels were tested for total oxidation of 2-propanol as a model reaction for the catalytic combustion of oxygenated organic pollutants. ZnCr₂O₄ exhibited the highest activity and stability than the others toward the combustion of 2-propanol. The higher activity of ZnCr₂O₄ was ascribed to existence of excess surface oxygen on catalyst, active Cr³⁺–Cr⁶⁺ pair sites, and synergistic effect between ZnO and ZnCr₂O₄ confirmed by TPR and XPS techniques. The high stability of ZnCr₂O₄ and CuCr₂O₄ was explained by the existence of stable Cr⁶⁺ species on the surface of catalysts. The study showed that ZnCr₂O₄ could be used as a promising catalyst in the catalytic conversion of organic compounds.     

n—BuLi／THF体系希夫碱末端化学改性SSBR的研究

采用2种希夫碱化合物对以n-BuLi/THF引发体系合成的溶液聚合丁二烯-苯乙烯共聚物（SSBR）进行末端化学改性。研究结果表明,改性后的SSBR其物理机械性能及抗湿滑性能良好,滚动阻力有所降低,说明用希夫碱化合物改性SSBR可以制备低滚动阻力橡胶。     

Numerical study of on-board fuel reforming in a catalytic plate reactor for solid-oxide fuel cells

A pseudo-transient numerical model is used for the simulation of a multi-functional catalytic plate reactor (CPR). The work mainly addresses the problems associated with on-board reforming for solid-oxide fuel cells. Heat management is achieved by indirectly coupling partial oxidation with reforming. Water management is achieved by partially recycling the anode stream from a solid-oxide fuel cell. The model uses detailed heterogeneous chemistry for reforming and oxidation reactions occurring on the catalyst beds.     

Promoting effect of electroactive polymer supports on the catalytic performances of palladium-based catalysts for nitrite reduction in water

Conducting polymers, polypyrrole and polyaniline, were used as supports for Pd in order to obtain catalysts with higher performances than a classical Pd/Al₂O₃ catalyst for application in water treatment. The supports and the catalysts were characterized by elemental analysis, Fourier transformed infra-red spectroscopy (FTIR), transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD) and by their activity in nitrite reduction. It was demonstrated that these conducting polymers can be advantageously used as support for noble metals such as palladium. Indeed, the redox properties of these supports allow the deposition of a part of palladium directly in the reduced state and also a direct reduction of nitrite, even if this reduction is not complete. The Pd/polyaniline and Pd/polypyrrole catalysts are much more active than the classical Pd/Al₂O₃ catalyst with less ammonium ions. These better performances were explained by the redox and ion-exchange properties of the conducting polymers allowing the exchange between the hydroxides produced and the dopant anion of the conducting polymer. The ion-exchange property of the polymer depends on its oxidation state which is directly linked to the polymerization conditions and then can be easily modulated.     

A novel nanocomposite catalytic cathode for direct methanol fuel cells

We report a new nanocomposite catalytic cathode composed of iron phthalocyanine, platinum, carbon black and Nafion^® (FePc-Pt/C-Nafion^®) which exhibited enhanced catalytic activity for the oxygen reduction reaction (ORR) in the presence of methanol compared with usual Pt/C based electrodes. The catalytic cathode was prepared by depositing Pt colloidal nanoparticles (d_av = 2.2 nm) on a FePc/C support to form a FePc-Pt/C powder and ultrasonically treating a mixture of Nafion^® and the FePc-Pt/C powder in ethanol, followed by loading the mixture on a glassy carbon electrode and drying at 120 °C. In an O₂-saturated H₂SO₄ solution (0.5 M) with methanol (0.5 M), the onset potential (0.92 V vs RHE) over the FePc-Pt/C-Nafion^® electrode shifted by more than 240 mV toward positive relative to that over an electrode prepared with a commercial Pt/C catalyst and Nafion^®. A new kind of catalytic sites constructed by FePc nanocrystals and Pt nanoparticles was found in the FePc-Pt/C-Nafion^® electrode for the first time, which exhibited higher specific activity for ORR than Pt as calculated based on the hydrogen desorption charge.     

Zeolite-based materials for novel catalytic applications: Opportunities, perspectives and open problems

Zeolites and related materials (including a wide range of microporous and mesoporous materials with ordered pore structure) have been one of the areas in the field of materials and catalysis with the largest impact on science, technology and industrial processes. We discuss here some recent developments in this field, with particular references how to tailor and design zeolite and related material properties to control/enhance the catalytic performances. Four main topics have been addressed. (i) The recent progress and perspectives in the field of tailored syntheses, with selected examples showing the trend and prospects to develop new structures, control the location of active sites, and the crystal size and morphology, including nanoarchitecture of the final catalysts. (ii) The development and prospects of two-dimensional zeolites presenting an extended view/concept of zeolite structures integrating the classical 3D frameworks and the various lamellar forms. (iii) The progresses in the design and synthesis of hierarchical zeolites, with discussion on the still existing challenges related to the synthesis, characterization and catalytic application. (iv) Novel opportunities and needs in terms of zeolite multifunctional design for catalytic applications, with a discussion of the critical issues related to the use in the field of fine chemicals, organic industrial syntheses and biorefinery, and the prospects for the use in two novel challenging areas of the direct conversion of CO₂ to light olefins and methane to methanol.     

Catalytic combustion: from reaction mechanism to commercial applications

The present commercial applications of catalytic combustion are briefly reviewed. Difficulties still hinder the commercial development of this type of combustion as an NO_x control technique. The problems are addressed by both academia and industry. The relevant activities of Gaz de France and GASTEC, both involved in several projects supported by the European Union, are described.     

Surface modification of low density polyethylene films by homogeneous catalytic ozonation

Low density polyethylene films were treated by ozone to generate peroxides on the surfaces. The peroxides generated are capable of initiating radical graft polymerization of hydrophilic vinyl monomers onto the polymers, resulting in hydrophilic surfaces. Results of ozonation revealed that molecular ozone instead of hydroxyl radicals was the main oxidant for peroxide generation. A novel approach, aqueous ozonation with the addition of a soluble transitional metal salt, FeCl₃, as a homogeneous catalyst, was proposed and proved to be successful in this study. The addition of FeCl₃ could increase peroxide generation by 22.7%, compared to its non-catalyzed counterpart. An optimum catalyst concentration, 0.04 g/L, was determined. Also, the effects of pH, ozonation time and applied ozone dose on peroxide generation were investigated. The loss in tensile strength of the films would be 15% or less if the applied ozone dose was not over 2 wt.%. The functional groups generated on the film surfaces were characterized by FTIR, the contact angle and surface roughness of the film were also examined before and after ozonation.     

Development of a novel catalytic burner for natural gas combustion for gas stove and cooking plate applications

On the request of Gaz de France Research Department, Catator AB has designed, constructed and evaluated a catalytic burner, based on Catator's patented wire mesh catalysts, for natural gas combustion in gas stoves or cooking plates. The results have shown that burner operation results in extremely low NO_x emissions (1–3 mg NO_x/kWh), acceptable CO-levels (0–15 mg CO/kWh), relatively high thermal efficiencies over a broad range of power inputs (40–50% for 1–4 kW) and a long catalyst life-time (>10 000 h). Other advantages of this burner design are its compactness and ease of cleaning. The critical concern is the high emissions of unburned hydrocarbons measured at slow cooking mode (<1 kW), which is believed to be overcome by developing and implementing an appropriate heat-exchanger with the burner.     

Mathematical model and numerical simulations of catalytic flow reversal reactors for industrial applications

A mathematical model and computer program have been developed for the study and the design of Catalytic Flow Reversal Reactors (CFRR). It combines a transient two-dimensional heterogeneous model with a numerical method allowing the fast formulation of new reactor configurations during the design phase. The program has been validated with experiments performed for the oxidation of lean methane emissions. It is shown that the dynamic behaviour of the CFRR can be predicted accurately for a wide range of conditions including small reactor diameter and low air flow rate if the radial effects related to the thermal insulation are taken in account. Experiments were also accurately predicted for two different heat removal systems: hot air withdrawal and an internal heat exchange, both in the mid-section of the reactor.     

加氢脱硫催化过程的动力学研究进展

简述了加氢脱硫催化剂的发展历程,介绍了加氢脱硫的反应机理,并在此基础上讨论了抑制剂对加氢脱硫反应动力学的影响。对国内外各种加氢脱硫反应的动力学模型进行了综述,并指出了这些模型存在的不足,以及加氢脱硫动力学的研究方向和面临的挑战。     

Performances of a catalytic foam trap for soot abatement

A catalytic trap for soot particles was prepared by deposition of Cu–V–K–Cl catalyst on a ceramic foam. Catalytic trap performances were evaluated by treating the exhaust of a gas oil burner under different operating conditions. The results obtained showed that ceramic foam is a particularly suitable support for this application since it yields low gas pressure drop, good soot collection efficiency (“deep bed” filtration mechanism), high thermal shock resistance and good contact throughout the filter between soot particles and catalyst surface. In addition, the catalytic foam trap is able to spontaneously regenerate at operating conditions comparable to those typical of diesel engine exhaust and after more than 70 test hours it retains its activity towards soot oxidation.