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Surface science approach to heterogeneous catalysis: CO hydrogenation on transition metals
A221 629
Surface Science 117 (1982) 629-638 North-Holland Publishing Company
A NOVEL METHOD J.P. COAD,
G. TAPPIN
OF INTERFACE
EXPOSURE
and J.C. RIVIlkRE
Materials Developmerlr Diotsion, A ERE, Ham~eN, UK Received
13 September
1981; accepted
for publication
17 November
1981
A method has been found of removing intact an oxide scale from the underlying metal, without recourse to chemical treatment; since the removal occurs by separation along a line of weakness, it often leads to exposure of interfaces that would not otherwise be accessible. The method consists of coating the oxidised specimen with a suitable material, in this case nickel, by sputter ion plating at an elevated temperature. The thickness of the nickel coating and the temperature of plating are chosen so that on cooling, the stored elastic energy in the nickel is greater than the fracture energy of the we%cest region in the scale. When nickel is then removed from the edges of the specimen, the remaining nickel coating peels away from the metal taking the scale with it. In the case of Fe/Si alloys oxidised in CO*. the line of weakness, as revealed by surface analysis by XPS. was either at the interface between the magnetite scale and the layer of accumulated oxidised silicon adjacent to the metal, or at the interface between the inner and outer oxides. The method may have general applications in the study of spalling.
639
Surface Science 117 (1982) 639-658 North-Holland Publishing Company
SURFACE SCIENCE APPROACH TO HETEROGENEOUS CO HYDROGENATION ON TRANSITION METALS H.P. BONZEL and H.J. KREBS Institul fir Grenzfliichenforschung und Vakuumphysik, Kemforschungsanlage Jiilich, Fed. Rep. of Germany Received
14 September
1981; accepted
for publication
20 October
CATALYSIS:
Jiilich GmbH, D-51 70
1981
Modern surface sensitive electron spectroscopies and other surface analytical techniques have in recent years been extensively applied to the study of Ha and CO adorption on transition metals. This work has now been extended to include the heterogeneous reaction between adsorbed H, and CO on these metals. The combination of surface analysis (carried out under ultra-high vacuum conditions) and reaction rate measurements in the range of 100 mbar to 1 bar total pressure is being practiced. This approach yields information on changes of the surface composition of the catalyst as well as data on reaction kinetics and the possible time dependence of the reaction rate. Low surface area samples - either single or polycrystalline - are used for these studies. In the present paper the results obtained by this approach will be reviewed and discussed in the light of the adsorption data. Recent advances in the direction of studying either poisoned or promoted catalytic surfaces will also be mentioned.
Surface Science 117 (1982) 629-638 North-Holland Publishing Company
A NOVEL METHOD J.P. COAD,
G. TAPPIN
OF INTERFACE
EXPOSURE
and J.C. RIVIlkRE
Materials Developmerlr Diotsion, A ERE, Ham~eN, UK Received
13 September
1981; accepted
for publication
17 November
1981
A method has been found of removing intact an oxide scale from the underlying metal, without recourse to chemical treatment; since the removal occurs by separation along a line of weakness, it often leads to exposure of interfaces that would not otherwise be accessible. The method consists of coating the oxidised specimen with a suitable material, in this case nickel, by sputter ion plating at an elevated temperature. The thickness of the nickel coating and the temperature of plating are chosen so that on cooling, the stored elastic energy in the nickel is greater than the fracture energy of the we%cest region in the scale. When nickel is then removed from the edges of the specimen, the remaining nickel coating peels away from the metal taking the scale with it. In the case of Fe/Si alloys oxidised in CO*. the line of weakness, as revealed by surface analysis by XPS. was either at the interface between the magnetite scale and the layer of accumulated oxidised silicon adjacent to the metal, or at the interface between the inner and outer oxides. The method may have general applications in the study of spalling.
639
Surface Science 117 (1982) 639-658 North-Holland Publishing Company
SURFACE SCIENCE APPROACH TO HETEROGENEOUS CO HYDROGENATION ON TRANSITION METALS H.P. BONZEL and H.J. KREBS Institul fir Grenzfliichenforschung und Vakuumphysik, Kemforschungsanlage Jiilich, Fed. Rep. of Germany Received
14 September
1981; accepted
for publication
20 October
CATALYSIS:
Jiilich GmbH, D-51 70
1981
Modern surface sensitive electron spectroscopies and other surface analytical techniques have in recent years been extensively applied to the study of Ha and CO adorption on transition metals. This work has now been extended to include the heterogeneous reaction between adsorbed H, and CO on these metals. The combination of surface analysis (carried out under ultra-high vacuum conditions) and reaction rate measurements in the range of 100 mbar to 1 bar total pressure is being practiced. This approach yields information on changes of the surface composition of the catalyst as well as data on reaction kinetics and the possible time dependence of the reaction rate. Low surface area samples - either single or polycrystalline - are used for these studies. In the present paper the results obtained by this approach will be reviewed and discussed in the light of the adsorption data. Recent advances in the direction of studying either poisoned or promoted catalytic surfaces will also be mentioned.