Regeneration of metallic catalysts

The results of studies related to the regeneration of catalysts poisoned by sulfur are described. The regeneration studies were performed in two parts. One part was devoted to oxidation processes involved in the removal of sulfur from metal surfaces using an Auger electron spectrometer for surface analysis, equipped with quadrupole mass analyzer for gas-phase analysis. In this part, a molecular beam of oxygen strikes the surface of a metal (Ni) which has previously been covered (partially or fully) with an adsorbed sulfur layer. Direact dosing of the surface facilitated accurate determination of the resultant SO/sub 2/ partial pressure originating from the surface of the dosed sample. Kinetics of SO/sub 2/ formation were investigated at various regions of temperature (room temperature to approx. 500/sup 0/C), oxygen partial pressure (approx. 10/sup -8/ torr to subatmospheric), and fractional sulfur coverage (half to a full sulfur layer). The second part of the studies was carried out to evaluate regeneration potential for catalysts employed at practical conditions. Nickel catalysts supported on alumina and zirconia employed in the conversion of CO to hydrocarbons were placed in a plug flow reactor. Each catalyst was poisoned by sulfur, e.g., H/sub 2/S either in an H/sub 2/ stream ormore » in the CO+H/sub 2/ reactant stream with H/sub 2/S/H/sub 2/ concentrations ranging from 1 to 10 ppM and the catalyst activity was investigated. The catalyst was then exposed to oxygen diluted by a carrier gas and at moderate temperatures, 300 to 500/sup 0/C. Complete recovery of activity was obtained when adequate exposure times were employed.« less