Catalyst continued sulfur-resistant

The effect of suJfur poisoning on the coking tendency of alumina-supported ruthenium SNG catalyst has been studied. The clean KU/AI2O3 catalyst has exceptional coking resistance, and at 490 C and 25 atm, can tolerate steam to carbon ratios below stoichiometric (steam/carbori=0.6) with light naphtha before a continuous accumulation of carbon will occur. However, at this temperature (appropriate for SNG production), sulfur can adsorb on the active metal surfaces to a level which will cause a slow but steady accumulation of less reactive carbon. The critical sulfur coverage that adversely affected the steam to carbon ratio necessary to prevent continuous coking appears to fall just above one-half the maximum capacity of the catalyst. 

Work is continuing in an effort to find catalysts with sufficient activity and resistance to sulfur poisoning. No durability data in the presence of sulfur have been obtained as yet. 

Unlike Pt and Pt alloys, NPMCs do not suffer from the specific adsorption of anions. As shown in Fig. 8.26a, the ORR performance of a PANI-Fe-C catalyst in the kinetic range of the steady-state RDE polarization curves is virtually independent of the solution concentration of H3PO4. In the case of a Pt/C catalyst (Fig. 8.26b), a continuous ORR activity loss is observed with an increase in H3PO4 concentration due to the chemisorption of phosphate ions. Thanks to their resistance to anions (tme also of (bi)sulfate in sulfuric acid solutions), NPMCs represent an attractive alternative to Pt-based catalysts at the HT-PEFC cathode. 

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