High resolution transmission electron microscopic (HRTEM) determination of the preferentially exposed faces onγ-Al2O3 andη-Al2O3

High resolution transmission electron microscopy has been used to examine the crystallites in -Al₂O₃ and -Al₂O₃. -Al₂O₃ has been found to be nearly hexagonally shaped crystallites whose identity distances and angles of fringe patterns indicate that (110) planes are preferentially exposed. -Al₂O₃ showed preferentially exposed surfaces of (100), (110) and super imposed (111)/(211). This information is valuable to the catalyst researcher trying to model the surfaces of these two supports.     

Grinding kinetics of calcined alumina

Conclusions If it is necessary to obtain a mineral powder with a high dispersion (_mean 1 ), it is technically-undesirable and economically unsuitable to increase the quantity of grinding bodies by more than four times with respect to the weight of -Al₂O₃.Silicone oil is a suitable surface active agent for carrying out effective dry grinding of -Al₂O₃.With the dry grinding of -Al₂O₃ using metal grinding bodies, the iron pickup is approximately ten times greater than with wet grinding. During the dry grinding of -Al₂O₃ with an addition of silicone oil, and corundum grinding bodies, the rate of grinding is the same as with wet grinding using metal grinding bodies.Translated from Ogneupory, No. 8, pp. 71–72, August, 1971.     

Effect of the crystalline from of Al2O3 on the interaction and sintering of large-crystal quartzite and disperse alumina

It is established that the amount of mullite and the value of the open porosity of specimens increase in the sequence -Al₂O₃(+)-Al₂O₃-Al₂O₃Al₂O₃ · 3H₂O. The apparent density and the ultimate compressive strength increase in the reverse direction. Active modifications of alumina (hydrargillite, -Al₂O₃) stimulate mullite formation, which is accompanied by an increase in the open porosity to 40% and a decrease of the mechanical strength to 8–12.5 MPa, and high (up to 12%) linear shrinkage. High-quality, dense, strong refractories can be produced in a single firing from coarse-grained quartzite and finely disperse corundum and alumina in the form of -Al₂O₃.Translated from Ogneupory, No. 10, pp. 18 – 20, October, 1994.Eastern Institute of Refractories.     

Reduction of NO by H2 and CO on PdO-MoO3/γ-Al2O3 of low molybdena loading

The activity and selectivity in the catalytic reduction of NO by a mixture of CO and H₂ of three PdO-MoO₃/-Al₂O₃ catalysts are compared in the presence of varying amounts of oxygen at reaction temperatures from 100 to 550°C. The catalysts were prepared by different methods and contain about 2% Mo and 2% Pd. Results are compared with those for PdO/-Al₂O₃, PdO-MoO₃/-Al₂O₃ containing 2% Pd and 20% Mo, and a commercial Pt-Rh catalyst. The PdO-MoO₃/-Al₂O₃ catalysts are more active for the selective reduction of NO to N₂ and N₂O than PdO/-Al₂O₃ under slightly oxidizing conditions at temperatures from 300 to 550°C. At these reaction conditions, the fresh PdO-MoO₃/-Al₂O₃ catalysts are comparable with a commercial Pt-Rh catalyst. The improved activity of PdO-MoO₃/-Al₂O₃ relative to PdO/-Al₂O₃ is believed to be due to the interaction between Pd and Mo. The effect of O₂ on the activity and selectivity of these catalysts is different in the reduction of NO by H₂, by CO, and by a mixture of H₂ and CO. The results using the mixture of reductants cannot be inferred from the results with the single reductants.     

Catalytic Decomposition of Hydrazine over Supported Molybdenum Nitride Catalysts in a Monopropellant Thruster

The catalytic decomposition of hydrazine over a series of MoN_x/-Al₂O₃ catalysts with different Mo loadings was investigated in a monopropellant thruster (10 N). When the Mo loading is equal to or higher than the monolayer coverage of MoO₃ on -Al₂O₃, the catalytic performance of the supported molybdenum nitride catalyst is close to that of the conventionally used Ir/-Al₂O₃ catalyst. The MoN_x/-Al₂O₃ catalyst with a loading of about 23 wt% Mo (1.5 monolayers) shows the highest activity for hydrazine decomposition. There is an activation process for the MoN_x/-Al₂O₃ catalysts at the early stage of hydrazine decomposition, which is probably due to the reduction of the oxide layer formed in the passivation procedure.     

Composition of Pd-La/α-Al2O3 catalysts

The objective of this study is to investigate the structure of the Pd-La/-Al₂O₃ catalyst. X-ray diffraction (XRD) and temperature-programmed reduction (TPRd) were used as characterization techniques. Contrary to the assertions in the literature, XRD studies conducted on La/-Al₂O₃ composite oxides and Pd-La/-Al₂O₃ catalysts show that Pd catalyzes the solid state reaction between A1₂O₃ and Al₂O₃ to form LaAlO₃. TPRd studies conducted on Pd/-Al₂O₃, Pd/La₂O₃, Pd/LaAlO₃, and Pd-La/-Al₂O₃ catalysts suggest that Pd in the Pd-La/-Al₂O₃ catalyst interacts more strongly with LaAlO₃ than with -Al₂O₃. Reaction studies were conducted to investigate the activity of Pd/-Al₂O₃, Pd/La₂O₃, Pd/LaA10₃, and Pd-La/-Al₂O₃ catalysts for nitric oxide (NO) reduction. These studies show that Pd/LaAlO₃ catalysts are most active for NO removal at stoichiometric and under net reducing conditions.     

Synergistic Catalysis of Carbon Dioxide Hydrogenation into Methanol by Yttria-Doped Ceria/γ-Alumina-Supported Copper Oxide Catalysts: Effect of Support and Dopant

Methanol synthesis from carbon dioxide hydrogenation was studied over ceria/-alumina- and yttria-doped ceria (YDC)/-alumina-supported copper oxide catalysts to seek insight into the catalysis at metal–support interfaces. It was found that, in comparison with Cu/-Al₂O₃, the Cu/CeO₂/-Al₂O₃ and Cu/YDC/-Al₂O₃ catalysts exhibited substantial enhancement in activity and selectivity toward methanol formation. The extent of enhancement was augmented by increased ceria loading on -alumina and with increased yttria doping into ceria. The enhancement is inferred to result from the synergistic effect between copper oxide and surface oxygen vacancies of ceria.     

Anisotropic structure analysis for cobalt oxides on α-Al2O3(0001) by polarized total-reflection fluorescence extended X-ray absorption fine structure

Anisotropic structure analyses for [CoO_x]/-Al₂O₃ (0001) and [Co₃O₄]_n /-Al₂O₃ (0001) which were derived from Co₂(CO)₈/-Al₂O₃ (0001) were performed by a polarized total-reflection fluorescence extended X-ray absorption fine structure (EXAFS) technique. Both s- and p-polarized EXAFS data revealed that the cobalt atoms of [CoO_x] were located on three-fold hollow sites of -Al₂O₃ (0001) in a monomer form and that a thin spinel structure [Co₃O₄] grew with the (001) plane parallel to -Al₂O₃ (0001).     

On the Promotion of Ag/γ-Al2O3 by Cs for the SCR of NO by C3H6

The promotion of Ag/-Al₂O₃ by adding alkali metals (Li, Na, K, Cs) for selective catalytic reduction of NO with C₃H₆ was studied in this work. The activity of NO reduction was enhanced by addition of Cs to Ag/-Al₂O₃ in the presence of excess oxygen and SO₂. The stability and growth of silver oxide particles were promoted and the dispersion of silver particles on -Al₂O₃ was improved by the addition of 0.5 wt% Cs and 1 wt% Cs to 2 wt% Ag/-Al₂O₃, respectively. The results were confirmed by H₂ TPR, UV-Vis DRS, TEM, and XPS.     

Reduction of NO by H2 on PdO-MoO3/γ-Al2O3 of low molybdena loading

The catalytic activity and selectivity of three PdO-MoO₃/-Al₂O₃ catalysts containing about 2% Pd and 2% Mo were studied for the reduction of NO by h₂ in the presence of varying amounts of oxygen at temperatures from 50 to 550 °C. The results are compared with those for PdO/-Al₂O₃, PdO-MoO₃/-Al₂O₃ containing 2% Pd and 20% Mo, and a commercial Pt-Rh catalyst. In the absence of oxygen, the conversion of NO to N₂ and N₂O is higher on the three catalysts than it is on PdO/-Al₂O₃ at 500 and 550 °C. In the presence of oxygen, the yields of N₂ and N₂O are generally lower on two of the PdO-MoO₃/-Al₂O₃ catalysts than on PdO/-Al₂O₃.     

Phase transitions and dimensional and morphological changes in an “Aluminum Hydroxide-Alumina” system under a shock-wave action

A method is proposed to study the sequence of phase transitions in powdered materials under a shock-wave action. It is shown that the aluminum hydroxide-alumina system has the following sequence of phase transformations under a shock-wave action: bayerite boehmite -Al₂O₃ -Al₂O₃. It is found that there are no transitional high-temperature modifications of alumina. A method is developed for obtaining a submicron alumina powder, which allows obtaining materials with a controlled phase composition, including a thermodynamically stable -modification of Al₂O₃. The specific features of the morphological structure and the phase and structural characteristics of powders after a shock-wave action are considered.Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 1, pp. 110–119, January–February, 2005.     

Study of the V2O5-Al2O3 interaction during ultra-high intensity grinding

Ultrahigh intensity grinding of mechanical mixtures of V₂O₅ with -Al₂O₃ at ambient temperature was found to create vanadyl complexes with ESR spectral parameters identical to those of vanadia-alumina samples prepared by impregnation methods.No interaction was found after intensive grinding of -Al₂O₃ with V₂O₄.     

Ultrafine α-Al2O3. Explosive Method of Synthesis and Properties

An explosive method for producing ultrafine -Al₂O₃ is developed and optimal synthesis parameters are determined. Particles of ultrafine -Al₂O₃ have a spherical shape and are separated from one another. The size distribution is log-normal (number-averaged size 70 nm and variance 1.9). Special features of phase transitions in ultrafine aluminum oxide under shock-wave action are studied. Results of x-ray phase analysis suggest stabilization of the new high-pressure phase -Al₂O₃ with a face-centered cubic lattice with a parameter a = 8.53 Key words: metastability, corundum, shock-wave synthesis, surface, modification.     

The Preferential Oxidation of CO: Selective Combinatorial Activity and Infrared Studies

From EXAFS (extended X-ray absorption fine structure) analysis, gold was found to have mainly oxygen in its nearest coordination shell in the fresh Au/-Al₂O₃ catalyst prepared by AuCl₃ impregnation and vacuum drying at room temperature. After thermal treatment under helium, chlorine appeared within the nearest neighbors of gold and more chlorine showed up as the treatment temperature was increased from 323 to 473K. No reduced Au species was observed up to 473K under He. However, the gold became reduced during CO oxidation at 373K and above. The precursor AuCl₃ was found to deposit on -Al₂O₃ via bonding to surface hydroxyl groups. This catalyst showed nearly 100% CO conversion at 573K, but a very low activity at 373 K under the conditions used in this study. Neither the residual chlorine nor the extent of reduction can explain the low activity at lower temperatures.     

Mesitylene solvated platinum atoms in the preparation of efficient supported catalysts for the dehydrogenation of methylcyclohexane to toluene

Mesitylene solvated platinum atoms have been conveniently used for the deposition of active Pt particles on -Al₂O₃ supports. The so prepared catalysts have been compared with traditionally obtained Pt/-Al₂O₃ catalysts in the dehydrogenation of methylcyclohexane to toluene, at 200 and 250 °C, showing, at low Pt loadings, a much greater specific activity.     

Effect of Ta2O5 additions on phase formation during synthesis and sintering of β-alumina based ceramics

Conclusions We demonstrated the effect of the Ta₂O₅ additive on the process of phase formation during the synthesis of the powders and during sintering of -alumina ceramics (as compared to stoichiometric sodium polyaluminate Na₂O·5Al₂O₃). The presence of the additive increases the quantity of -Al₂O₃ phase and stabilizes it during low-temperature isothermal synthesis; during high-temperature sintering, it hinders the formation of the nonconducting -Al₂O₃ phase; this is one of the main conditions required for obtaining -alumina ceramics having a high ionic conductivity.Translated from Ogneupory, No. 2, pp. 13–15, February, 1991.     

The effect of steam treatment on MeO/Al2O3 model catalysts (Me = Ni,Co, Cu,Fe)

To study the influence of steam on the solid state reaction between MeO (Me = Ni, Co, Cu or Fe) and Al₂O3, MeO/-Al₂O₃ and MeO/-Al₂O₃ model catalysts were kept in either N₂/20% O₂ or N₂/O₂/30% H₂O at 500–1000°C. The samples were subsequently analyzed with RBS and FTIR. Surprisingly, nickel, cobalt and copper volatilized when MeO/-Al₂O₃ or MeAl₂U₄/-Al₂O₃ samples were annealed in the presence of 0.3 atm steam at 1000°C. Especially copper was found to volatilize very rapidly in the presence of steam, even at a temperature as low as 800°C. FTIR spectra of steam-treated NiO/-Al₂O₃ samples showed the incorporation of hydroxyl groups in the nickel oxide layer. This observation and an excellent agreement with thermochemical calculations support our conclusion that the volatile species are metal hydroxides. The solid state reaction of MeO with-Al₂O₃ was found to proceed at a much higher rate in the presence of 0.3 atm steam at 500–800°C, presumably as a result of an enhanced surface mobility of Me and Al ions along the grain boundaries and the surfaces of the internal pores of the-Al₂O₃ support, when steam is present.     

Correlation between ionic conductivity and7Li-NMR of polyether-polyurethane networks containing lithium perchlorate

Summary The effect of temperature on the ionic conductivity and the⁷Li NME line width of a polyether-polyurethane network containing lithium perchlorate was studied. A treatment of the results based on free-volume principles yielded a linear correlation between the logarithm of the reduced conductivity, _T /_{T 0}, and the logarithm of the reduced⁷Li NMR line width, _T/_{T 0}, for a given reference temperature, T_o=323 K.     

Study of elementary reactions of free radicals formed on oxide and platinum containing catalysts

The formation of alkylperoxy radicals on catalysts CuCr₂O₄/ -Al₂O₃, Pt /--Al₂O₃ and on alumina upon the interaction of amines and alcohols with oxygen has been observed applying the matrix isolation ESR technique. Surface-generated gas phase radicals are shown to initiate a radical chain reaction. The efficiency of the yield of radicals depends on the catalyst mass and its arrangement in a reactor: the desorption of radicals into the gas phase occurs primarily from the outer geometrical surface of catalyst granules.     

Novel and Ideal Zirconium-Based Dense Membrane Reactors for Partial Oxidation of Methane to Syngas

A novel and ideal dense catalytic membrane reactor for the reaction of partial oxidation of methane to syngas (POM) was constructed from the stable mixed conducting perovskite material of BaCo_0.4Fe_0.4Zr_0.2O_3– and the catalyst of LiLaNiO/-Al₂O₃. The POM reaction was performed successfully. Not only was a short induction period of 2 h obtained, but also a high catalytic performance of 96–98% CH₄ conversion, 98–99% CO selectivity and an oxygen permeation flux of 5.4–5.8 mlcm^–2min^–1 (1.9–2.0 molm^–2S^–1Pa^–1) at 850°C were achieved. Moreover, the reaction has been steadily carried out for more than 2200 h, and no interaction between the membrane material and the catalyst took place.