Describes method for removing carbonaceous deposits from an Fe catalyst without substantially oxidizing the Fe or even appreciably reducing any of the Fe oxide in the catalyst. The ultimate state of oxidation of the Fe, coke, and H2 present in the system may be controlled by a suitable control of pressure, temperature, and rate and composition of the oxidizing gas. The system may be operated at pressures ranging from close to vacuum to 100 atm. or more and temperatures 800°-2000° F., provided temperatures, pressures, and gas feed are properly correlated. Relatively low pressures, about atmospheric, and high temperatures above 1,300° F. generally favor the desired reactions. Formulas are derived. Diagrams.