Experimental surface characterization methods were used to study ageing-induced changes in the active metals and washcoat oxides. The characterization techniques included both microscopic and spectroscopic methods, such as Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Several characterization techniques are available to study solid surfaces and the properties of catalysts, and no single characterization method can be used to explain the basis for the catalyst deactivation phenomena of three-way catalysts. In the proceeding sections, the characterization techniques utilized in this thesis are presented in detail. Scanning Electron Microscopy (SEM) was used in this thesis for high magnification imaging and elemental analysis. A Jeol JSM-6400 scanning electron microscope equipped with an energy dispersive spectrometer (EDS) was used for the analysis. In the pretreatment stage, flat pieces of fresh and aged catalysts were cut, and either potted in epoxy or fastened with a carbon tape in order to obtain side or top views of the catalyst respectively. Catalysts were polished down to 1 μm using diamond paste and coaled prior the analysis to avoid the accumulation of charge. The accelerating voltage and current in the measurements were 15 kV and 12 nA, respectively, and the resolution of the instrument was 3.5 nm (35 kV). SEM-EDS resources were used in the Institute of Electron Optics at the University of Oulu. Measurements of gas adsorption isotherms are widely used for determining the surface area and pore size distribution of solids. The use of nitrogen as the adsorptive gas is recommended if the surface areas are higher than 5 m2/g. The first step in the interpretation of a physisorption isotherm is to identify the isotherm type. This in turn allows for the possibility to choose an appropriate procedure for evaluation of the textural properties. Non-specific Brunauer-EmmettTeller (BET) method is the most commonly used standard procedure to measure surface areas, in spite of the oversimplification of the model on which the theory is based.
The pore size distributions can be calculated from desorption isotherms. The pores are usually classified according to their widths as micropores (diameter less than 2 nm), mesopores (diameter between 2 and 50 nm) and macropores (diameter exceeding 50 nm). Several approaches have been developed to assess the micro- and mesoporosity, and to compute pore size distribution from the adsorption-desorption data. All of these involve a number of assumptions, e .g. relating to pore shape and mechanism of pore filling. In this thesis, physisorption measurements were carried out to characterize catalysts before and after the ageings. Specific surface areas (m2/g) and pore volumes were measured according to the standard BET method, as described above, by using a Coulter Omnisorp 360CX. The specific surface areas and pore volumes were obtained from N., adsorption isotherms at -196°C by assuming the cylindrical shape of pores. Catalysts were outgassed in a vacuum at 140°C overnight before the measurements. All the BET values in this study were measured within a precision of ± 5%. Pore size distributions for micropores as well as meso- and macropores were calculated from N., -desorption isotherms by differential HK (Horva th-Kawazoe) and - BJH (Barrett-J oyner-Hallender) methods respectively. Since the monoliths showed systematically lower BET values than the crushed samples after similar ageing procedures, all the BET values presented in this thesis have been determined for the metallic monoliths with a standard shape and mass.
This book contains a brief review of absorption and catalysis, for practical purposes. This also presents some important information on adsorbents and catalysts.

Preface vii

1. Introduction 1

2. Essential Component of the Modelling Process in Chemistry 24

3. Physical and Chemical Energies 53

4. Molecular Morphology and Growth 93

5. Significance of Prostaglandins 117

6. Advances in Chemistry 159

7. Surface Chemistry 234

Index 271

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