Page 97 - Principles of Catalyst Development
P. 97
84 CHAPTER 5
faster into understanding the principles of catalyst design. If nothing more,
the organization leads to a disciplined identification of critical features and
structure of background material. Often, missing pieces in the puzzle of
data suggest areas for further research.
Discussion on process development in Chapter 3 emphasized the
importance of defining the process need and identifying the objectives to
be achieved. If these caIl for diffusional or mechanical modifications, then
the design wiIl involve changes in preparation and formulation that optimize
the particle size, pore structure, and strength. In cases where resistance to
deactivation must be improved, the solution is found through incorporation
of chemical or structural promoters, or perhaps by changing the shape of
pores. Improvements in regeneration call for the incorporation of combus-
tion additives.
In all these situations, catalyst design is essentially modification of
existing catalyst composition and structure. The procedure may be difficult
but is a fairly straightforward application of many principles discussed
earlier. However, when an entirely new composition is required, the catalyst
designer is faced with selecting suitable materials for further testing. The
ease with which this is done depends on available research data. In the
event that no proven process technology exists as a guideline, then the
search must turn toward totally novel and untried materials. A suitable
active component must be found. Other factors such as optimal
activity, selectivity, lifetime, and formulation are subjects for future
development.
A target reaction is essential. This is easiest with chemical processes
since the critical reaction is easily identified. With petroleum and other fuel
processes, so many reactions exist that some degree of lumping into reaction
types, perhaps with model compounds, is necessary.
We now follow the original strategy of Dowden. (149) The distinct steps
in the method are shown in Fig. 5.1. These are as follows:
1. Stoichiometric analysis.
2. Thermodynamic analysis.
3. Proposed molecular mechanism.
4. Proposed surface mechanism.
5. Reaction path identification.
6. Necessary catalyst properties.
7. Search for appropriate materials.
8. Proposed catalyst(s).
Each of these steps is demonstrated with an example, selected more
for pedagogical purposes than practicality.