ELECTRICAL-CONDUCTION PHENOMENA IN COKED INDUSTRIAL REFORMING CATALYSTS

Industrial Pt/Al2O3 reforming catalysts containing up to 26 wt% of car bon have been studied by admittance spectroscopy. Spectra obtained on heating in nitrogen in the range 200-500 degrees C displayed low frequ ency relaxations, which were interpreted in terms of a network of carb on islands linked by surface ionic conduction. During subsequent cooli ng, these features disappeared, suggesting that they were generated by dissociation of strongly bound water. Isothermal ac measurements in n itrogen showed that the conductance was determined by the carbon conte nt. Similar measurements made in dilute oxygen showed that the conduct ance decreased with burn-off of carbon. Analysis of gases evolved on h eating revealed aqueous and chloride species, originating from acid si tes on the catalyst support. The results suggest that electrical techn iques could be used to characterize coked reforming catalysts. Copyrig ht (C) 1997 Elsevier Science Ltd.