Catalyst Technology

Catalyst performance is determined mainly by the choice of metal. Catalyst activity and selectivity, however, can be modified by the appropriate choice of support material and metal location / dispersion within the pore structure of the support. Other catalyst preparation factors include metal loading, reduced/unreduced form, pH and choice of PGM salt precursor. Reaction pressure, temperature, agitation and solvent will further affect catalyst performance and hence process yield and economics.

Choice of Metal Location

Catalyst performance can be altered significantly by the appropriate choice of support material, metal location and dispersion within the pore structure of the support. Johnson Matthey has developed techniques to deposit the metal selectively in the desired location.

Eggshell shows palladium located on the exterior surface.
Intermediate shows palladium located deeper within the pore structure.
Uniform shows palladium evenly dispersed throughout the support structure.

The catalysts are designed with different metal locations for reactions performed under different conditions of pressure and temperature.

Hydrogenation reactions are generally first order with respect to hydrogen. Thus the reaction rate is directly proportional to hydrogen pressure .With intermediate and uniform catalyst types; an increasing proportion of the metal becomes accessible as the pressure increases. When all the metal is available, the catalyst properties closely parallel those of an eggshell catalyst. Therefore at higher pressures, intermediate and uniform catalysts have a higher activity than eggshell ones because of their intrinsic greater metal dispersion due to metal located deeper within the pore structure. Thus, eggshell catalysts would be chosen for high activity at low hydrogen pressure and uniform catalysts at high pressure.