Having represented a catalyst supplier for a number of years I can answer this question. Also there are a couple of WAI papers that I wrote that I am sure WAI will be glad to provide ,probably for a minor fee.
I would like some info before I try to answer this - what type - manufacture - oven and model(s) are we talking about?
What type catalysts are in the oven? Who made them?
What are the dimensions?
Do you have pressure drop across the cat and what is it?
When were the cats last reactivated?
Have they ever been reactivated?
Provide some of this information first and I might be able to help.