Abstract: A mobile catalyst treatment unit and process of operating same involves a closed gas processing loop supported on a normally mobile carrier such as a flat truck bed or trailer which is connectable with the inlet and outlet of a catalytic reactor. The normal process gas is cut off from the catalytic reactor so as to isolate the catalyst and to place the gas processing loop into communication with the reactor. Thereafter, the catalytic reactor can be purged of reducing gases and then treated with an oxidizing gas to burn off carbonaceous materials from the catalyst surface, in the process known as regeneration, or the catalyst can be treated with a reducing gas in the process known as reduction, or the catalyst can be heated for startup purposes, or cooled down for purposes of unloading or other mechanical work on the reactor or treated with other treatment gases such as hydrogen sulfide for sulfiding and the like.