Mössbauer spectroscopy of supported bimetallic catalysts: 1∶5 FeM/SiO2 (M=Ru,Rh, Pd,Ir, Pt)

Mössbauer spectra of SiO₂-supported bimetallic FeM (M=Ru, Rh, Pd, Ir, and Pt) with FeM=15 arter treatments such as reduction, exposure to CO and passivation in air are described and compared with previous results obtained on 11 FeM/SiO₂ catalysts.     

FeRu/TiO2 and Fe/TiO2 catalysts after reduction and Fischer-Tropsch synthesis studied by Mössbauer spectroscopy

A series of TiO₂-supported bimetallic FeRu catalysts with different Fe:Ru ratios (; 101; 31; 11; 13) has been studied by means of in situ Mössbauer spectroscopy. The influence of reduction and Fischer-Tropsch synthesis on the state of iron in the FeRu/TiO₂ catalysts will be derived.     

The outermost atomic layer of thin films of fluorinated polymethacrylates

In this paper, we investigate the surface properties of a series of copolymers of perfluoroalkyl methacrylate (CH2 = C(CH3)COOCH2CnF(2n + 1), n = 1, 6, or 10) and methyl methacrylate (MMA) and of blends of perfluorooctyl-end-capped poly(methyl methacrylate) (PMMA) and pure PMMA. The introduction of perfluoroalkyl groups significantly lowers the polymer surface energy as determined by the acid-base approach. X-ray photoelectron spectroscopy (XPS) confirms a higher fluorine concentration in the surface region (the outer 3.8 nm) as compared to in the bulk. The fluorine density in the outermost atomic layer is quantitatively determined by low-energy ion scattering (LEIS). A linear relationship is found between the fluorine density in the outermost atomic layer and the surface energy of the partially fluorinated polymethacrylates, irrespective of the length of the perfluoroalkyl chain. This linearity confirms Langmuir's "principle of independent surface action". Deviation from this linear relationship exists for both highly and sparsely fluorinated polymethacrylates and can be ascribed to the local (surface) ordering of the fluorinated tails and MMA units, respectively. This study may offer one further step toward a deeper understanding of the correlations between macroscopic surface properties and microscopic surface chemical composition.     

How important is Mössbauer spectroscopy in catalysis?

Hyperfine Interactions - Applications of Mössbauer spectroscopy in catalysis are reviewed with the emphasis on the type of information obtained and the performance of Mössbauer...     

An improved error bound for a finite element approximation of a model for phase separation of a multi-component alloy

Using the approach of Rulla (1996 SIAM J. Numer. Anal. 33, 68-87)for analysing the time discretization error and assuming moreregularity on the initial data, we improve on the error boundderived by Barrett and Blowey (1996 IMA J. Numer. Anal. 16,257-287) for a fully practical piecewise linear finite elementapproximation with a backward Euler time discretization of amodel for phase separation of a multi-component alloy.     

Catalyst characterization: Mössbauer spectroscopy in relation to other techniques

For the purpose of catalyst characterization. Mössbauer spectroscopy has matured into a routinely used tool, which is most effective when used in combination with other spectroscopies in a problem-oriented research strategy.Extended abstract.     

Methanol from synthesis gas over bimetallic FePd catalysts

Bimetallic FePd/SiO₂ catalysts exhibit higher activities in the formation of methanol from synthesis gas than Pd/SiO₂. The catalysts are a complex mixture of bcc and fcc FePd alloy, α-Fe and some unreduced iron.     

Aspects of dissociative chemisorption and promotion in catalysis

Catalysis is a cyclic event in which reactants adsorb on the catalyst, react on the surface and desorb into the gas phase, leaving empty adsorption sites behind for the next catalytic cycle. Very often, at least one of the participating reactants has to dissociate. This paper qualitatively reviews the electronic interactions between an adsorbed molecule and the surface that lead to dissociation, and discusses in more detail how alkali metal promoters enhance this interaction by lowering the electrostatic surface potential. As a dissociating molecule generally needs an ensemble of several metal atoms, the kinetics of the dissociation reaction depends sensitively on the surface coverage, as is illustrated for the dissociation of NO on rhodium.     

Materials analysis with Rutherford Backscattering Spectrometry; Application to catalysts

Rutherford Backscattering Spectrometry (RBS) is shown to be a powerful tool in the analysis of model catalysts. The surface coverage of various metals on thin SiO₂ layers on Si and thin Al₂O₃ layers on Al can be accurately measured while simultaneously depth profiles of the metals are obtained. The scattering technique is briefly reviewed and several applications concerning the preparation of model catalysts by wet chemical methods are presented.