Cobalt–silica interaction and the dehydrogenation of 2-propanol

The interaction between silica and cobalt was studied on supported catalysts with low silica loading. Below a threshold cobalt level of 0.41 wt%, the catalysts were inactive for dehydrogenation of 2-propanol at 450 K. Inactivity was attributed to irreducibility of cobalt ions. Samples that were impregnated at a level below the threshold, dried, calcined, then reimpregnated below the threshold level, redried and recalcined such that the total cobalt content exceeded the threshold, were inactive. These results are not consistent with a model in which a portion of the cobalt interacts with specific silica sites, forming an irreducible species. Rather, they suggest that strongly interacting cobalt ions are incorporated into the silica surface.     

Magnesia Bricks and Magnesia Alumina Bricks

正GB/T2275-2007 1Scope This standard specifies the classification,technical requirements,test methods,quality appraisal procedures,marking,packing,transportation,storage and quality certificate of magnesia bricks and magnesia alumina bricks.This standard is applicable to burned magnesia bricks and magnesia alumina bricks for industries of     

The Microstructure and Properties of Alumina—Rich Spinel and Its Products

The paper describes the effect of chemical composition on the microstructure and properties of spinel specimens synthesized from bauxite and magnesite,The alumina-rich spinel with higher ratio of Al2O3/MgO,with smaller spinel grain,contains more titaniferous mineral and silicate phase compared to the spinel with lower Al2O3/MgO ratio.In the products obtained from alumina-rich spinel and magnesite clinker,the ratio of Al2O3/MgO of spinel decreases,ti-taniferous mineral and silicate phase in the spinel aggregate are changed,and its content tends to degradation,contrasted with original alumina-rich spinel,The products have good high temperature properties.     

Alumina–copper joining by the sintered metal powder process

Sintered metal powder process (SMPP) is one of the high technology methods in ceramic–metal joining domain. The present study examines the effect of temperature and time of metalized layer sintering on the thickness and homogeneity of the joining layer, the leakage rate in alumina–copper joining zone, and also identifies the different phases formed during sintering. The samples were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). Microstructure studies indicate that sintering the metalized layer with a holding time of 90 min at the temperature of 1530 °C, and with an applied layer thickness of 50 μm with proper plating and brazing stages lead to a completely homogeneous joining zone with an adequate thickness (about 33 μm). The results of leak tests on alumina–copper specimen in this condition was less than 10^?9 Pa l s^?1.     

High Alumina Brick

This standard specifies the classification,dimensions, technical requirement, testing method.inspection principle, package, marking, packing,transportation, storage and quality certificate.     

Cobalt Fischer�CTropsch Catalyst Regeneration: The Crucial Role of the Kirkendall Effect for Cobalt Redispersion

Redispersion of cobalt is a key process during Fischer?CTropsch catalyst regeneration. Using model catalysts we show that redispersion is a two step process. Oxidation of supported metallic cobalt nanoparticles produces hollow oxide particles by the Kirkendall effect; reduction leads to break-up of these hollow oxide shells, forming multiple metallic particles. This mechanism is to a large extent independent of the support.     

Adhesion and residual stress of plasma sprayed Alumina–titania coatings

Plasma-sprayed coatings are formed by the impacting of particles onto a fixed substrate layer-by-layer. Residual stresses inside the coatings are essential for their influencing on the coatings’ performance and durability during service life. In the present work, heat transfer and elastic–plastic residual stresses generation during plasma spraying in Al₂O₃–13wt.%TiO₂/NiCrAl (AT13) coating system were analyzed by finite element analysis (FEA). The sophisticated spraying process was simulated and the laminated structure of the coating was modeled under three-dimension. In this simulation, radial and axial compressive stresses were concentrated at the interfaces and inside the bond layer. Besides, at the specimen corner of the free edge, there were high tensile radial and axial stress concentrations. Such remarkable stresses, no matter tensile or compressive, may lead to the delamination and failure of coatings. Comparing with the numerical results, X-ray diffraction measurement was conducted on the AT13 coatings. As a result, the tested values matched well with the FEA simulated results.     

Selective Catalytic Reduction of NO x Over Nano-Sized Gold Catalysts Supported on Alumina and Titania and Over Bimetallic Gold–Silver Catalysts Supported on Alumina

The reduction of NO with octane under lean conditions was examined over gold supported on alumina and titania and over alumina supported bimetallic gold–silver catalysts. The silver loading was either 1.2 or 1.9 wt% whereas 0.3, 1 or 5 wt% gold was used. The catalysts were characterized by means of EDXS, N₂-adsortion, UV–Vis and TEM to correlate recorded results with different preparation methods. UV–Vis measurements indicated that gold was present in the form of fine Au particles, single Au ions and small (Au)_n ^δ+ clusters on the catalysts and silver was mainly present in the form of single Ag ions. The highest NO to N₂ reduction activity was recorded over the 0.3Au–Al₂O₃ catalyst. The Au–TiO₂ catalysts did not result in significant NO to N₂ reduction.     

Research on the Influence of Zircon Additive on the Properties of Sintered High Alumina Refractories

The influence of zircon particle size and adding quan-tity on the properties of high alumian refractories have been researched,The phase composition and microstructure were analysed by SEM and X-ray diffraction,The research il-lustrated that high alumina refractories can be greatly im-proved by adding proper quantity of zircon micro powder to form dense corundum-mullite-zirconia matrix.     

Colloidal Stability and Sintering of Yttria–Silica and Yttria–Silica–Alumina aqueous suspensions

The aim of this work was to produce dense yttrium silicate materials by slip casting, with more than 90% of Y₂SiO₅ phase. The rheological behaviour of concentrated aqueous slips was studied considering the effect of the dispersing additives, solids content and pH. The densification kinetics was examined as a function of temperature and time, and the reactions were analysed in the light of the equilibrium phase diagrams. Deflocculation of the slips was achieved by either an electrostatic mechanism using tetraethylammonium hydroxide, thus requiring a high concentration of base, and by a polyelectrolyte through an electrosteric mechanism, which provided more reliable results. In the binary system Y₂O₃–SiO₂, a very low grade of sintering was obtained at 1600°C. The use of alumina allows sintering through a liquid phase, reaching 90% theoretical density.     

Silica-Supported Cobalt Catalysts for Fischer–Tropsch Synthesis: Effects of Calcination Temperature and Support Surface Area on Cobalt Silicate Formation

Cobalt silicate formation reduces the activity of the catalyst in Fischer–Tropsch synthesis (FTS). In this article, the effects of calcination temperature and support surface area on the formation of cobalt silicate are explored. FTS catalysts were prepared by incipient wetness impregnation of cobalt nitrate precursor into various silica supports. Deionized water was used as preparation medium. The properties of catalysts were characterized at different stages using FTIR, XRD and BET techniques. FTIR-ATR analysis of the synthesized catalyst samples before and after 48 h reaction identified cobalt species formed during the impregnation/calcination stage and after the reduction/reaction stage. It was found that in the reduction/reaction stage, metal-support interaction (MSI) added to the formation of irreducible cobalt silicate phase. Co/silica catalysts with lower surface area (300 m²/g) exhibited higher C₅₊ selectivity which can be attributed to less MSI and higher reducibility and dispersion. The prepared catalysts with different drying and calcination temperatures were also compared. Catalysts dried and calcined at lower temperatures exhibited higher activity and lower cobalt silicate formation. The catalyst sample calcined at 573 K showed the highest CO conversion and the lowest CH₄ selectivity.     

Cobalt Particle Size Effects in the Fischer–Tropsch Synthesis and in the Hydrogenation of CO2 Studied with Nanoparticle Model Catalysts on Silica

We have investigated the effect of cobalt nanoparticle size in Fischer–Tropsch synthesis (CO/H₂) and have compared it to data obtained for carbon dioxide hydrogenation (CO₂/H₂) using model catalysts produced by colloidal methods. Both reactions demonstrated size dependence, in which we observed an increase of the turnover frequency with increasing average particle size. In both case, a maximum activity was found for cobalt particles around 10–11 nm in size. Regarding the selectivity, no size-dependent effect has been observed for the CO₂ hydrogenation, whereas CO hydrogenation selectivity depends both on the temperature and on the size of the particles. The hydrogenation of CO₂ produces mainly methane and carbon monoxide for all sizes and temperatures. The Fischer–Tropsch reaction exhibited small changes in the selectivity at low temperature (below 250 °C) while at high temperatures we observed an increase in chain growth with the increase of the size of cobalt particles. At 250 °C, large crystallites exhibit a higher selectivity to olefin than to the paraffin equivalents, indicating a decrease in the hydrogenation activity.     

Highly Selective and Active Niobia-Supported Cobalt Catalysts for Fischer–Tropsch Synthesis

The performance of Co/Nb₂O₅ was compared to that of Co/γ-Al₂O₃ for the Fischer–Tropsch synthesis at 20 bar and over the temperature range of 220–260 °C. The C₅₊ selectivity of Nb₂O₅-supported cobalt catalysts was found to be very high, i.e. up to 90 wt% C₅₊ at 220 °C. The activity per unit weight cobalt was found to be similar for Nb₂O₅ and γ-Al₂O₃-supported catalysts at identical reaction temperature. However, due to the low porosity of crystalline Nb₂O₅, the cobalt loading was limited to 5 wt% and consequently the activity per unit weight of catalyst was lower than of Co/γ-Al₂O₃ catalysts with higher cobalt loadings. This low activity was largely compensated by increasing the reaction temperature, although the C₅₊ selectivity decreased upon increasing reaction temperature. Due to the high intrinsic C₅₊ selectivity, Nb₂O₅-supported catalysts could be operated up to ~250 °C at a target C₅₊ selectivity of 80 wt%, whereas γ-Al₂O₃-supported catalysts called for an operation temperature of ~210 °C. At this target C₅₊ selectivity, the activity per unit weight of catalyst was found to be identical for 5 wt% Co/Nb₂O₅ and 25 wt% Co/Al₂O₃, while the activity per unit weight of cobalt was a factor of four higher for the niobia-supported catalyst.     

Effect of the Mesostructuration of the Beta Zeolite Support on the Properties of Cobalt Catalysts for Fischer–Tropsch Synthesis

The effect of mesostructuration of beta zeolite and of metal loading on the properties of cobalt-based catalysts for Fischer–Tropsch synthesis was studied in this work. The most active catalyst was the mesostructured beta zeolite-supported cobalt (10%), which also showed a low selectivity to methane and the lowest olefin/paraffin ratio.     

n-Pentane Isomerization Over Pt- and Ni–Pt-Promoted Sulfated Zirconia Catalysts Supported on Alumina

Two series of sulfated zirconia catalysts promoted with Pt and Pt–Ni, respectively, were prepared and extruded with different amount of alumina binder (0, 20, 33, and 60 wt%). The catalytic activities of the two series of catalysts, SZPtA and SZNiPtA, were measured for n-pentane isomerization reaction. The reaction reaches its maximum conversion at 20 wt% of alumina for both catalyst series. Adding alumina beyond 20 wt% reduces the overall conversion and modifies the selectivity for both catalysts series from i-C4 towards i-C5 suggesting that the reaction mechanism changed from a monomolecular to a bimolecular one. However, only SZNiPtA catalysts maintain a higher catalytic activity at higher amounts of alumina. Such difference between the two catalyst series can be attributed to the combining effect of Ni and Pt promotion of the SZNiPtA catalysts and not to their acidic properties.     

Processing Red Mud Produced at the Eti Alüminyum A.Ş. Seydişehir Alumina Refinery to Recover Gallium and Vanadium and Obtain Iron Oxide Pigments

Theoretical Foundations of Chemical Engineering - It is demonstrated that Bayer–hydrogarnet technology can be developed and applied to process red mud for separating important components such...     

Low-Temperature Ammonia Oxidation Over Pt/γ-Alumina: The Influence of the Alumina Support

Deactivation of a Pt/-alumina catalyst used for low-temperature ammonia oxidation was studied using positron-emission profiling (PEP). Evidence is presented that irreversibly adsorbed nitrogen and oxygen species deactivate the catalyst. This deactivation is further accelerated by preadsorption of oxygen on the catalyst. Ammonia strongly interacts with the alumina support. A steady state of the ammonia oxidation reaction is reached after the alumina sites are saturated with ammonia. PEP experiments show that spillover of oxygen to the support is not significant during the ammonia oxidation.     

Influence of Synthesized Super Al2O3 Powder on the Properties of Alumina Castable

The in fluence of three different Al2O3 powder on self-flowing alumina castable was studied.Maximum compaction of sample was computed by Andresen Equation.The result showed that the Al2O3 powder.which has much smaller particle size,could improve the microstructure and the mechanical properties of castable under room temperature and high temperature.With the same powder size,the room tem perature strength of the castable added with Al2O3 powder properties of which were altered by adding mineralizing agent,was higher than that of the castable added with common Al2O3 powder ,but the flowability of these three different castable was almost the same.