Catalytic combustion, as an alternative to conventional thermal combustion, has received considerable attention during the past decade. Research efforts have been promoted by the need to meet governmental demands concerning pollution and the wish to use energy sources more efficiently. The two main advantages offered by catalytic combustors over flame combustors apply to these goals: Catalytic combustion can be carried out over a wide range of fuel concentrations in air and at low temperatures. These low temperatures result in attaining NO, emission levels substantially lower than possible with conventional combustors.

Catalytic Materials for High-Temperature Combustion

The bases of IR spectroscopic methods for the characterization of the surface acidity, of the Lewis type and of the Bronsted type, of solid, simple and mixed oxides are briefly reviewed. The results are described and a systematization is proposed. The surface acidity is essentially associated with the ionicity/covalency of the element–oxygen bond, mainly affected by the size and charge of the cation.

The surface acidity of solid oxides and its characterization by IR spectroscopic methods. An attempt at systematization

The topotactic transformation of boehmite (AlOOH) taking place under calcination and leading to γ-alumina (γ-Al2O3) has been investigated theoretically and a step-by-step mechanism for the structural transformation is proposed This mechanism reveals two major steps First, the structural collapse of boehmite occurs, after hydrogen transfers and water extraction Then, through an aluminum migration process, the γ-alumina characteristics appear The proposed mechanism demonstrates the existence of an equilibrium structure for γ-alumina containing 25−31% of tetrahedral aluminum sites in agreement with nuclear magnetic resonance (NMR) results Temperature effects on the thermodynamic stability of the different structures involved in the mechanism has been investigated Theoretically simulated X-ray diffraction (XRD) patterns confirm the validity of our model structures According to this mechanism, a coherent skeleton of γ-alumina inherited from the original AlOOH network is constructed This skeleton can be

Theoretical Study of the Dehydration Process of Boehmite to γ-Alumina

A survey is made of high-temperature membranes and several possible applications of membrane reactors for integration in power generation cycles with CO2 capture. Current performance and limitations of relevant inorganic membranes are presented and discussed. Integrated H2, O2 or CO2 membrane separation is analysed and it is concluded that development of power plant concepts including membrane technology is not yet fully explored. Significant design optimisation would be required in order to identify efficient, feasible and environmentally sound technical solutions. In addition, further development and validation of performance of membranes in real applications are needed.

High-temperature membranes in power generation with CO2 capture

https://dspace.library.uu.nl/bitstream/handle/1874/14690/J.Catal.-v.Dillen-2003.pdf?sequence=1

Synthesis of supported catalysts by impregnation and drying using aqueous chelated metal complexes

Sintering of pseudo-boehmite, acicularγ-Al2O3 produced by dehydration of pseudo-boehmite, andγ-Al2O3 ex alum was investigated. The sintering process was studied by X-ray diffraction, transmission electron microscopy with selected area electron diffraction and BET surface area measurements. The solid state reaction toα-Al2O3 causes a steep drop of the surface area to less than 10 m2g−1. The acicular pseudo-boehmite andγ-Al2O3 supports exhibit an intermediate state where the acicular particles assume a rod-like shape and the surface area falls from about 300 to 100 m2g−1. It was established that reaction to α-Al2O3 and, hence, sintering proceeds via a nucleation and growth mechanism. The rate-limiting step is nucleation of α-Al2O3. Consequently, the contacts between the elementary alumina particles dominate the sinter process. The contact between the acicular elementary particles of pseudoboehmite andγ-Al2O3 studied leads to the reaction to α-Al2O3 to be almost complete after keeping samples for 145 h at 1050 °C. Decomposition of alum produces very small particles showing negligible mutual contacts. Consequently an elevated thermal stability is exhibited. Treatment of the alumina ex alum with water and drying results in a xerogel in which contact between elementary particles is much more intimate. Accordingly, treatment at 1050 °C causes a sharp drop in surface area.

Sintering of pseudo-boehmite and γ-Al2O3

Elements such as lanthanum, zirconium, thorium and cerium are known to raise the thermostability of γ-Al2O3. Among these elements lanthanum is the most effective. Three procedures have been used to apply lanthanum homogeneously to the surface of pseudo-boehmite and γ-Al2O3, namely, incipient wetness impregnation, deposition-precipitation from a homogeneous solution, and specific adsorption of a La(EDTA)-complex. The latter procedure results in supports covered homogeneously with lanthanum. The minimum amount of lanthanum required to render the catalyst supports thermostable, depends on the procedure to apply the lanthanum. The specific adsorption procedure offers the possibility to obtain thermostable supports with loadings as low as 0.5 wt % La.

J. W. Geus

Papers

Sintering of pseudo-boehmite and γ-Al2O3

Application of lanthanum to pseudo-boehmite and γ-Al2O3