Twenty-five years of diesel particulate filter (DPF) developments have shown that high-volume ceramic materials are well suited for the harsh requirements of exhaust after treatment. Nevertheless, problems regarding filter reliability and durability associated with the regeneration of the filter have limited their serious application until only recently. To extend useful filter life, the present study has examined the growth of silicon carbide (SiC) nanofibers by a simple carbothermal reduction process on cordierite support surfaces using cheap raw materials such as kaolin, talc, and carbon black. Transmission electron microscopy confirms the crystalline (β - SiC) nature of the nanofibers (10–20 nm diameter). The growth of these nanofibers increases the support-specific surface area restricting the agglomeration of noble metal catalyst particles that otherwise occurs in wash-coat sintering. As a result, fewer particles are needed to perform the catalyst role (at reduced cost) and the support structure can host the catalyst for prolonged times at higher temperatures. As the future will see increasing economic competition in filter fabrication routes and materials, this new design of catalytic DPF promises to play a significant role. 相似文献
The beta zeolite on cordierite ceramic monolith was synthesized by an in situ crystallization method and characterized by XRD, N2 adsorption/desorption, SEM and NH3‐TPD techniques. Toluene adsorption/desorption was used as probe test for the control of cold‐start emissions and treatment of volatile organic compounds. The presence of beta on the supports was confirmed by XRD, SEM, and N2 adsorption/desorption measurements. The zeolite crystals grow both into the cordierite macropores and on the surface of the monolith channels, which form an integrated network ensuring a strong adherence. The highly dispersed beta on supports, demonstrated by larger surface area and adsorption capacity of N2, resulted in a significant increase of the total acidity, and thus a greater adsorption capacity for toluene. Furthermore, it could trap larger amounts of toluene to higher temperature and show considerable activity for toluene cracking and oxidation. These are attributed to the greater acidity and stronger acid sites of in situ synthesized beta. 相似文献
Fracture of a large-grained alumina polycrystal has been examined in situ by optical microscopy. Concurrently, local bridging stresses, as generated by friction or tension of unbroken ligaments in the wake of the crack path, were measured by piezospectroscopy. Stress measurements were performed both at fixed sites as a function of the external load and at a fixed external load along the crack profile. Frictional stresses were similar/congruent50 MPa, while unbroken ligaments between the crack faces were found to support tensile stresses up to similar/congruent100 MPa. The maximum bridging stress was dictated by the weak (intrinsic) interface bonding of the polycrystal. Average bridging stresses, either theoretically calculated from R -curve data or experimentally measured by piezospectroscopy on frictional/bridging sites, were similar. Such a circumstance enables us to explain the fracture behavior of polycrystalline alumina by considering crack-wake shielding as the main micromechanism contributing to toughening. 相似文献
This perspective article focuses on the recent advances in the rational design of catalyst for NH3 decomposition at different length scales, from catalyst nanoparticles to reactor design. For an overall optimum performance, all scales should be optimized in a concerted manner. The study of the mechanism of reaction has given guidelines for the catalyst design. As far as reactor design is concerned, a structured reactor is beneficial for this reaction because it minimizes the inhibiting effect of produced H2, besides other inherent advantages. This holistic optimization of catalysts is expected to pave the way for application of NH3 as H2 storage media. 相似文献
In situ carbon dioxide (CO2) foam flooding has proved to be economically feasible in the oil field, but its self‐generation behavior in the bulk scale/porous media is far from understood. In this study, the optimum in situ CO2‐foaming agent was first screened, and then in situ foam was investigated in the bulk. In situ foam flooding was conducted to evaluate the displacement characteristics and enhanced oil recovery of this system. The results showed that the foaming agent comprising 0.5% sodium dodecyl sulfonate (SDS) + 0.5% lauramido propyl hydroxyl sultaine (LHSB) gave the best foam properties and that the in situ CO2 foam with a slow releasing rate is effective both in bulk scale and in porous media, allowing a considerable enhancement of oil recovery in sand packs with different permeabilities. 相似文献
Under oxygen-rich conditions in H2 + NO + O2 mixtures, Pd/V2O5/Al2O3 catalysts are active and highly selective (~80%) for NOx reduction to N2. In situ DRIFT spectroscopy and reactor data show that the system operates via formation of NHx species on the highly dispersed V2O5 component. Both NH3 and NH4+ are formed, with the latter dominant. The role of the palladium component is also discussed. 相似文献
In this paper, TiO2 and Ag-doped TiO2 photocatalysts were coated on the cylindrical cordierite honeycomb monolith (CHM) to evaluate their photocatalytic disinfection against Escherichia coli (E. coli) bacteria under artificial sunlight irradiation. The X-ray diffraction (XRD) patterns showed a single-phase anatase structure for TiO2 samples calcined at 500 °C for 2 h. With the presence of Ag, the bandgap of TiO2 becomes narrower, and the absorption edge shifts toward the visible region. 6 mol% Ag-doped TiO2 (6Ag-T) showed a reduction of bandgap energy to 2.2 eV. TiO2 and Ag-doped TiO2 solutions were prepared and coated on the channels’ surface of CHM for antibacterial applications. Although monolithic TiO2 caused a slight decrease in the number of alive E. coli, Ag dopant showed significant improvement in antibacterial properties. 6 mol% Ag-doped TiO2 coated on CHM (6Ag-T/S10/M) showed strong antibacterial effectiveness against E. coli that the bacterial cell concentration dropped to zero after 1 h of exposure. Impressively, reusability tests with these materials showed superior performance, where the antibacterial remains unchanged after five or seven successive operation cycles.
CuO is used as a catalyst or catalyst precursor in many chemical reactions that involve hydrogen as a reactant or product. A systematic study of the reaction of H2 with pure powders and films of CuO was carried out using in situ time-resolved X-ray diffraction (XRD) and surface science techniques. Oxide reduction was observed at atmospheric H2 pressures and elevated temperatures (150-300 °C), but only after an induction period. High temperature or H2 pressure and a large concentration of defects in the oxide substrate lead to a decrease in the magnitude of the induction time. Under normal process conditions, in situ time-resolved XRD shows that Cu1+ is not a stable intermediate in the reduction of CuO. Instead of a sequential reduction (CuO Cu4O3 Cu2O Cu), a direct CuO Cu transformation occurs. To facilitate the generation of Cu1+ in a catalytic process one can limit the supply of H2 or mix this molecule with molecules that can act as oxidant agents (O2, H2O). The behavior of CuO-based catalysts in the synthesis of methanol and methanol steam reforming is discussed in the light of these results. 相似文献
The direct electrochemical synthesis of NH3 from nitrogen and water vapor without the use of a fossil carbon source is highly desired. This synthesis is a viable option to store energy and produce fertilizer precursors. Here, a new Pt-free membrane electrode assembly is presented. An electrochemical membrane reactor demonstrates the feasibility of co-generating NH3 and H2 directly from nitrogen and water vapor at ambient conditions. An unprecedented high NH3-specific current efficiency of up to 27.5% using Ti as cathodic catalyst is reported. The co-generation can be tuned by the balance of process parameters. 相似文献
A superconducting MgB2 film with a superconducting transition temperature of ∼36 K was successfully prepared on an MgO substrate by pulsed-laser ablation from a stoichiometric MgB2 target. A multilayer deposition process involving interposed Mg-rich layers was performed at 200°C by controlling the laser energy density in order to maintain the correct stoichiometry, and followed by an in situ annealing process at temperature ranging from 700° to 900°C. It was found that smooth, fine-grained films with superconducting transition temperatures of 24–36 K could be obtained from in situ annealing of the as-deposited multilayer at 900°C without excess Mg addition. 相似文献
The grain-boundary transport of oxygen in polycrystalline α-Al2O3 (undoped and 500 ppm Y3+-doped) was studied in the temperature regime of 1100°–1500°C by monitoring the oxidation of a fine, uniform dispersion of Ni marker particles (0.5 vol%). The annealing treatments were carried out in a high-purity O2 atmosphere (>99.5%). The Ni particles, which are visibly oxidized to nickel aluminate spinel, were used to determine the depth of oxygen penetration. The thickness of the reaction zone was measured as a function of heat-treatment time and temperature, and a comparison of the oxidation rate constants and activation energies for undoped and Y3+-doped alumina was made. The results indicate that the presence of Y3+ slows oxygen grain-boundary transport in alumina by a variable factor of from 15 to 3 in the temperature regime of 1100°–1500°C. The values of the activation energy for undoped and Y3+-doped alumina were determined to be 430±40 and 497±8 kJ/mol, respectively. 相似文献
The liquid-phase isopropylation of isobutylbenzene (IBB) with 2-propanol to 3-isobutylcumene (3-IBC) and 4-isobutylcumene (4-IBC) using zeolite H-beta as a catalyst is reported. The zeolite H-beta-catalyzed isopropylation of isobutylbenzene is found to be more selective for 4-isobutylcumene (52 wt%) than using the conventional catalyst, AlCl3 (19 wt%). 相似文献
In this study, polysiloxane@CeO2@PMMA microspheres were successfully synthesized by controllable one-pot process, in which CeO2 nanoparticles were stabilized in the surface of PMMA nano/microsphere using an in situ precipitation method. The core–shell structure of the synthesized product were confirmed by FT-IR, XRD and electronic microscope analysis. The size of polysiloxane@CeO2@PMMA nano/microspheres were about 550 nm via microscopy analysis. Moreover, the novel hybrid nanocomposites eliminated the yellowish coloration problem of CeO2 and had good dispersibility. In addition, the transmittance of the multifunctional films based on polysiloxane@CeO2@PMMA microspheres owned good transmittance of visible light and can block harmful UV rays, which can be attributed to nano-CeO2 accession. Hence, such green synthesized route can be considered as a simple common method for preparing UV-shielding multifunctional materials. 相似文献
The commercial potential for a given catalytic process may be influenced by requirements on metal loading, in particular where noble metals are used. In an effort to substantially decrease the amount of catalyst material used for methane activation and catalytic partial oxidation (CPO), the effect of 0.005 wt% noble metal (Rh, Ru, Pd or Pt) on 0.5 wt% Ni/γ-Al2O 3 catalysts have been studied at temperatures below 1,173 K and 1 atm. The successful catalysts were activated directly by in situ reduction, without a calcination step, to promote formation of a highly dispersed (supported) metal phase from nitrate precursors. The obtained metal particles were not observable by XRD (size < 2–3 nm). This activation procedure had a decisive effect on catalyst activity, as compared to a catalyst which was calcined ex situ before in situ reduction. Adding a noble metal caused a significant drop in the ignition temperature during temperature programmed catalytic partial oxidation (TPCPO). The ignition temperature for partial oxidation coincides well with the temperature for methane dissociation, and is likely correlated to the reducibility of the noble metal oxide. Methane partial oxidation over 0.5 wt% Ni catalysts, both with and without promoter, yielded high selectivity to synthesis gas (>93%) and stable performance for continued operation, but synthesis gas production at temperatures below 1,073 K required a promoter when the catalyst was ignited by TPCPO. Ignition of the CPO reactions by introducing the feed at a high furnace temperature (1,073 K) also enabled formation of synthesis gas, but the reaction was then less stable than obtained with the TPCPO procedure. A dual bed concept attempted to beneficially use the activation and combustion properties of the noble metal followed by the reforming properties of Ni. However, it was concluded that co-impregnated catalysts yielded as high, or even higher conversion of methane and selectivity to synthesis gas. 相似文献