In Situ Formation of Silicon Carbide Nanofibers on Cordierite Substrates

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.     

Synthesis and Toluene Adsorption/Desorption Property of Beta Zeolite Coated on Cordierite Honeycomb by an In Situ Crystallization Method

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.     

In Situ Measurements of Frictional Bridging Stresses in Alumina Using Fluorescence Spectroscopy

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.     

Toward Practical Application Of H2 Generation From Ammonia Decomposition Guided by Rational Catalyst Design

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 H_2, besides other inherent advantages. This holistic optimization of catalysts is expected to pave the way for application of NH₃ as H₂ storage media.     

氨浸法回收铜冶炼污泥中的铜

以大冶有色金属公司铜冶炼污泥为原料,研究了氨浸法回收铜的工艺路线,并用加热的方法驱氨,使铜以氢氧化铜的形式析出,氧化铜的最大回收率达89.1％.     

Investigation on Foam Self‐Generation Using In Situ Carbon Dioxide (CO2) for Enhancing Oil Recovery

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.     

Selective NOx Reduction During the H2 + NO + O2 Reaction Under Oxygen-Rich Conditions Over Pd/V2O5/Al2O3: Evidence for In Situ Ammonia Generation

Under oxygen-rich conditions in H₂ + NO + O₂ mixtures, Pd/V₂O₅/Al₂O₃ catalysts are active and highly selective (～80%) for NO_x reduction to N₂. In situ DRIFT spectroscopy and reactor data show that the system operates via formation of NH_x 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.     

合成氨吹除气氢回收技术应用

比较几种氢气回收方法的优劣,确定选用膜分提氢技术回收合成氨系统合成塔吹除气中的氢气,作为合成氨原料气使用,达到了节能降耗的目的。     

Photocatalytic Disinfection of E. coli Using Silver-Doped TiO2 Coated on Cylindrical Cordierite Honeycomb Monolith Photoreactor Under Artificial Sunlight Irradiation

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.

Graphical Abstract

     

Reduction of CuO in H2: In Situ Time-Resolved XRD Studies

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.     

Co-generation of Ammonia and H2 from H2O Vapor and N2 Using a Membrane Electrode Assembly

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.     

泡沫镍上原位合成硒化镍与电解水性能研究

过渡金属硒化物已被认为是一类极具发展前景的电解水催化剂。以泡沫镍为基底和镍源,通过一步水热法在泡沫镍上负载硒化镍制备电催化剂(记为Ni-Se@NF)。扫描电镜图表明,在泡沫镍表面原位生长合成了一层纳米颗粒;X射线衍射和X射线光电子能谱表征证明该层纳米颗粒为Ni_(0.85)Se和Ni_3Se_2。在1 mol·L~(-1)KOH电解质中,对Ni-Se@NF电极进行了双催化电解水性能测试。Ni-Se@NF电极的析氢电流密度10 mA·cm~(-2)时的超电势为153 mV,析氧电流密度50 mA·cm~(-2)时的超电势为340 mV,并表现出良好的稳定性。     

Laser-Assisted Growth of Superconducting MgB2 Films in an In Situ Annealing Process Using a Stoichiometric Target

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.     

氨分解制氢工艺对浮法玻璃生产的影响浅析

浮法玻璃生产中锡槽内氢气作为还原气体,具有很重要的作用,氨分解制氢工艺因较为经济而被广泛应用。那么该工艺制氢对浮法玻璃生产有什么影响呢？本文就此提出一些看法进行探讨。     

The Effect of Yttrium on Oxygen Grain-Boundary Transport in Polycrystalline Alumina Measured Using Ni Marker Particles

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.     

Time-Resolved In Situ X-ray Diffraction in the Crystallization of VOHPO4 ⋅ 0.5H2O

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%).     

Preparation and Characterization of Polysiloxane@CeO2@PMMA Hybrid Nano/Microspheres via In Situ One-Pot Process

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.     

Effects of Noble Metal Promoters on In Situ Reduced Low Loading Ni Catalysts for Methane Activation

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.