Model and practical real-life bimetallic systems

2 Model and practical (real-life) bimetallic systems 

For model evaporated binary alloy or bimetallic systems, normally a double crucible containing ingots of the two components of the alloy are used in an evaporator and the electron beam is switched between the two metallic sources. The dwell time is varied so as to obtain a uniform distribution of each metal in the required amounts on the support. 

For practical (real) catalyst systems, precipitation, ion exchange, impregnation and sol-gel processing procedures are used. In precipitation methods, a hydroxide or a carbonate of a metal may be precipitated from a solution of a metal salt onto the support material held in the solution. Thus, a copper-silica catalyst may be prepared using a Cu-nitrate solution in which silica is suspended. Additives of any alkali cause the precipitation of copper hydroxide onto the silica support. This is then dried and normally reduced in hydrogen at moderate temperatures ( 400-500 °C) to form the catalyst. In co-precipitation techniques , the support is precipitated simultaneously with the active catalyst. In the ion-exchange method, for example, highly dispersed Pt on 

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