Catalysts “live” from the active centers on their surface; these can be tiny platinum particles, acid centers, iron crystal surfaces, liquid vanadium oxide islands, finely dispersed nickel metal, etc. These are where the accelerated reactions occur. If these are no longer available to the gas, the catalyst will no longer function. Typical toxins for active centers are sulfates, dust, siloxanes (vitrification), chlorine, phosphorus, soot, etc. The purity of the feed gas is therefore crucial; this is why fine purification processes are used. In the damage analysis, the poisoning is identified, and in cases of reversible deactivation, regeneration may be worthwhile.