Catalytic cooperation at the interface of physical mixtures of CaO and MgOcatalysts during steam gasification of naphthalene

Oxides CaO, MgO and a physical mixture of 10% CaO + 90% MgO were used as ca talysts for the steam gasification of naphthalene. A synergistic effect in the conversion was observed with the mixture. Catalysts were characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and XPS techniques. Basicity was significant for CaO as compared to MgO and th e mixture, but did not correlate with catalytic activity. Bidentate carbona te-type formation, which remained even in the presence of steam at high tem perature (1033 K), was observed on CaO. Carbonates on MgO and on the mixtur e are unidentate and disappeared when steam was present. Formates, carboxyl ic and aldehydic groups also were formed, at 723 K on MgO and at 423 K on t he mixture and on CaO. These species disappeared at 873 and 1033 K for the mixture and CaO, respectively, thus indicating their greater stability on C aO than on the mixture and on the MgO. Deposition of carbonaceous matter on solids was observed. The order of the deposited content is mixture < MgO < CaO. No indication of mutual contamination by the metal composing the oxid es was observed. A higher carbonate removal and less carbonaceous matter de position were observed in CaO when in the mixture, as compared with CaO alo ne, suggesting a beneficial effect of MgO in the mixture. The synergistic e ffect observed using the 10% CaO + 90% MgO mixture was related to the inhib ition of carbonaceous matter and carbonate formation on the catalysts. This inhibition is due to a catalytic cooperation between both oxides, as two s eparate phases. The presence of MgO is assumed to avoid the formation of st able bidentate carbonates on CaO, promoting instead unidentate species form ation, this facilitates the gasification of naphthalene by steam. Copyright (C) 2001 John Wiley & Sons, Ltd.