Texture of zirconia obtained by forced hydrolysis of ZrOCl2 solutions

The structure and surface properties of ZrO₂ strongly depend on its preparation. In the present work the impact of prolonged aging at basic conditions (pH = 9, T = 100°C, t = 48 h), on the phase composition and textural properties, obtained by calcination of the precipitate, was investigated using several techniques conjointly (DTA/TG, DSC, XRD, porosimetry). The thermal effects accompanying the ZrO₂·xH₂O gel formation, the coalescence of the particles and crystallization were evaluated and discussed in terms of the structural differences between the aged and non-aged samples. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cr－Ag／γ－Al_2O_3催化剂在CO氧化反应中Ag的助催化作用

Ｃｒ－Ａｇ／γ－Ａｌ_２Ｏ_３催化剂在ＣＯ氧化反应中Ａｇ的助催化作用陈平，朱波，钟依均，罗孟飞，李少华，吴红丽（杭州大学催化研究所杭州３１００２８）（杭州大学中心实验室杭州）关键词氧化铬，氧化银，氧化铝，负载催化剂，还原特性，一氧化碳，氧化活性催化燃烧...     

Model-free kinetics applied to regeneration of coked alumina

Thermogravimetry is proposed to study the alumina catalyst regeneration deactivated by coke, after being used in the transformation of styrene in a fixed bed continuous flow reactor. The model-free kinetic approach has been applied to data for the thermal oxidation of carbonaceous deposits on the catalyst. The activation energy (E) was calculated as a function of a (conversion) and T (temperature), by using Vyazovkin model-free kinetic method, allowing to estimate time required to remove coke at a given temperature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of Pore-expansion Agent on the Structure and Performance of Activated Alumina Synthesized from Waste Aluminum Sludge

1 INTRODUCTION The reactivity of activated alumina adsorbent is closely related to its specific surface area: the larger the specific surface area, the better its activity and adsorbent capability are. However, in reality, the prac- tically available specific surface area or effective spe- cific area has relationship with its pore structure[1]. Since many reactant molecules are difficult to enter the pores to react with whose radius is shorter than certain critical value, the increase of p…     

Gas Phase Catalysis by Metal Nanoparticles in Nanoporous Alumina Membranes

Nanoporous alumina membranes, loaded with palladium and ruthenium nanoparticles of various size, were used for gas phase hydrogenation of 1, 3‐butadiene and for oxidation of carbon monoxide, respectively. Those membranes contain 10⁹ ‐ 10¹¹ pores per cm², all running perpendicular to the surface. Membrane discs of 20 mm in diameter and only 60 μm thick, incorporated in a reactor in which the reactants can be pumped in a closed circuit through the pores, turned out to very actively catalyze hydrogenation of butadiene (Pd) and oxidation of CO (Ru). The activity of the Pd catalysts depends characteristically on the particles size, the gas flow, and of the educts ratio. As could be expected, larger particles are less active than smaller ones, whereas increasing gas flows in case of hydrogenation accelerates the reactions. Excessive hydrogen reduces selectivity with respect to the various butenes, but favours formation of butane.     

Si-tolerance of iron doped Pt/alumina catalyst in the total oxidation of VOC

Summary In the present study the effects of addition of iron on the catalytic activity and Si tolerability of Pt/g-Al₂O₃in the total oxidation of volatile organic compounds were investigated. Preliminary results showed that there is a noticeable improvement effect on Si-tolerance of catalyst, particularly for short term poison exposure. Bulk analysis of deposited silicon on the catalyst surface indicated that both Pt/g-Al₂O₃and iron-doped pellets had roughly the same silicone uptakes. Deactivation of catalyst was reversible and much faster for iron doped sample. The promoting effects of iron were related to its electronegativity and, to blocking of fewer Pt sites when iron is present at the surface of the catalyst.     

Y2O3, La2O3, Sm2O3对氧化铝瓷烧结及力学性能的影响

研究了3种稀土氧化物对氧化铝陶瓷烧结性能和力学性能的影响.结果表明 含Y2O3,La2O3,Sm2O3的添加剂促进了氧化铝瓷的烧结,提高了氧化铝瓷的力学性能.Y2O3和Sm2O3掺量为0.50%,La2O3掺量为0.75%时氧化铝瓷在1600或1620 ℃保温2 h烧结,相对密度达98.9%以上,强度超过439 MPa,断裂韧性达5.15 MPa·m1/2以上.微观结构分析表明,Y2O3,La2O3,Sm2O3抑止氧化铝晶粒生长,细化晶粒,使晶粒尺寸较均匀形成致密化结构.     

Preparation of Nano-Sized γ-Al2O3 Supported Iron Catalyst for Fischer-Tropsch Synthesis by Solvated Metal Atom Impregnation Methods

Two types of small iron clusters supported on γ-Al2O3-RT(dehydroxylated at room temperature) and γ-Al2O3-800 (dehydroxylated at 800 ℃) were prepared by solvated metal atom impregnation (SMAI) techniques. The iron atom precursor complex, bis(toluene)iron(0) formed in the metal atom reactor, was impregnated into γ-Al2O3 having different concentrations of surface hydroxyl groups to study the effect of surface hydroxylation on the crucial stage of iron cluster formation. Catalysts prepared in this way were characterized by TEM, M(o)ssbauer, and chemisorption measurements, and the results show that higher concentration of surface hydroxyl groups of γ-Al2O3-RT favors the formation of more positively charged supported iron cluster Fen/γ-Al2O3-RT, and the lower concentration of surface hydroxyl groups of γ-Al2O3-800 favors the formation of basically neutral supported iron cluster Fen/γ-Al2O3-800. The measured results also indicate that the higher concentration of surface hydroxyl groups causes the rapid decomposition of precursor complex, bis(toluene)iron(0), and favors the formation of relatively large iron cluster. Consequently, these two types of catalysts show different catalytic properties in Fischer-Tropsch reaction. The catalytic pattern of Fen/γ-Al2O3-RT in F-T reaction is similar to that of the unreduced α-Fe2O3 and that of Fen/γ-Al2O3-800 is similar to that of the reduced α-Fe2O3.     

Influence of the exchange‐correlation functional in all‐electron calculations of the vibrational frequencies of corundum (α‐Al2O3)

The equilibrium structural parameters, high‐ and low‐frequency dielectric tensors, Born effective charges, and Γ‐point vibrational frequencies of bulk Al₂O₃ corundum are calculated by using the periodic, ab initio program CRYSTAL, which adopts an all‐electron Gaussian‐type basis set. The effect of basis set and the performance of three different functionals, i.e., LDA, PW91, and B3LYP, are discussed. The mean absolute deviation from the measured frequencies is as small as 7 cm^?1 for both the LDA and B3LYP functionals, indicating that these functionals perform extremely well in this case. The mean absolute deviation increases to 18 cm^?1 when the PW91 functional is used. All three functionals reproduce the equilibrium geometry of corundum to a high level of accuracy, with LDA and B3LYP outperforming PW91 slightly. The comparison of the current all‐electron calculations with previous plane‐wave, pseudo‐potential calculations shows an overall similar performance. The results of isotopic substitution for both Al and O are also presented. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Adsorption of benzene on the V2O5/γ-Al2O3 catalyst

Adsorption of benzene on the V₂O₅/-Al₂O₃ catalysts was studied in the temperature interval from 443 to 493 K and at partial pressures of the adsorbate ranging from 1 to 400 Pa. The adsorption isotherms were plotted. The isosteric heats and various entropy characteristics of adsorption were determined. Mobility of benzene in the adsorption layer is restricted compared to the model of ideal dimeric gas. The adsorbed amounts of benzene and chlorobenzene are compared.