Catalyst Characterisation

• Catalyst Composition
  • Bulk composition
  • Surface composition
  • Phase composition
  • Metal crystallite compositions
• Support materials & composition
• Metal crystallite size
• Catalyst architecture
• Surface area and Porosity
• Pore systems and blockage
• Surface segregation
• Conditioning
• Sintering
• Fouling
• Poisoning
• Zeolites

Catalyst Composition

Surface composition (top)
XPS provides the average composition to a depth of 3nm or so plus chemical species.  SIMS on the other hand identifies molecular species lifted off the outermost layer of the surface but is not quantitative.  STEM analysis complements this when used to analyse the edge of particles of individual phases within a catalyst.

Metal crystallite compositions (top)
These are often most effectively measured on a crystallite-by-crystallite basis by high resolution analytical STEM. In some cases different compositions will result in changes in the metal lattice parameters that can be measured by XRD.

Pore systems and blockage (top)
Porosity can be characterised by adsorption isotherms, usually with nitrogen. Apart from closed pores and macropores (>50 nm), total pore volume and pore size distribution can be measured. The size distribution is often important to ensure efficient transport of reactants and products to and from the active surface. In some catalyst systems, smaller sizes are also used to limit unwanted reactions. Reaction byproducts and feedstock impurities can result in loss of loss of activity through pore blockage. Pore volume and size distribution can be used to detect such processes by comparing used catalysts with fresh.

Surface segregation (top)
Data from bulk composition analysis, TEM/STEM analysis of sub volumes, XPS and SIMS provide a body of knowledge over a wide range of length scales from which surface segregation effects in complex multiphase systems can be deduced.

Fouling (top) 
Fouling will typically result in porosity reduction and narrowing of pores. These can be investigated by nitrogen adsorption methods (BET surface area, pore size and pore size distribution)