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When Fritz Haber was looking for a catalyst to make ammonia, the approach amounted to little more than intelligent trial and error. In the case of the Haber process some 200,000 possible catalysts were tried.
This time-consuming approach reflected the lack of understanding of how catalysts worked, and in particular the structure and behaviour of the surface of materials, essential areas of understanding for the development of heterogeneous catalysts
By the 1960s some useful techniques had been developed to enable research into surface structures to be carried out, and additional techniques continue to be added. Of particular importance to the development of new, improved catalysts is the ability to characterise the structure of the catalyst, and to identify precisely the processes occurring during reaction. This understanding aids the design of more effective catalysts.
Summary of techniques
Low Energy Electron Diffraction One of the earliest techniques. Provides information on the arrangement of atoms on the surface of a single crystal. Continues to be an important technique.
Scanning Electron Microscopy In use from the 1960s. Allows images of minute particles to be generated and so enables the study of their behaviour
Low Energy Electron Microscopy This is an extremely sensitive surface technique in which a beam of low energy electrons strikes the surface, and reflected electrons can be "focussed" and used to form an image.
X-Ray Spectroscopy

UV Spectroscopy
Analysis of the electrons emitted from the surface following impact by X-rays or UV provides information about the surface
Infra Red Spectroscopy Enables the study of molecules bonded to the surface of a material.
Scanning Tunnelling Microscopy (STM) Developed in the last 15 years. Generates a "contour map" of the surface with sufficient resolution to show individual atoms
Synchrotron Radiation Particle accelerators can provide the X-rays necessary to obtain very detailed information about surface structure

 

 

 

 

 

 


 

 

 

 

 

 

 

 

 

 

 

 


 

 

Catalytic Surfaces
Cleanliness

Methods of studying surfaces rely on using very clean samples, with cleaning and operation taking place under high vacuum. Without vacuum, clean metal surfaces can be prepared but they do not remain clean for long. Each atom on a metal surface exposed to gas at 1 atm and 25oC is struck about 100,000,000 times per second, and will soon hold adsorbed atoms or molecules.