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Oxides CaO, MgO and a physical mixture of 10% CaO + 90% MgO were used as catalysts 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 the mixture, but did not correlate with catalytic activity. Bidentate carbonate-type formation, which remained even in the presence of steam at high temperature (1033 K), was observed on CaO. Carbonates on MgO and on the mixture are unidentate and disappeared when steam was present. Formates, carboxylic and aldehydic groups also were formed, at 723 K on MgO and at 423 K on the mixture and on CaO. These species disappeared at 873 and 1033 K for the mixture and CaO, respectively, thus indicating their greater stability on CaO 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 oxides was observed. A higher carbonate removal and less carbonaceous matter deposition were observed in CaO when in the mixture, as compared with CaO alone, suggesting a beneficial effect of MgO in the mixture. The synergistic effect observed using the 10% CaO + 90% MgO mixture was related to the inhibition of carbonaceous matter and carbonate formation on the catalysts. This inhibition is due to a catalytic cooperation between both oxides, as two separate phases. The presence of MgO is assumed to avoid the formation of stable bidentate carbonates on CaO, promoting instead unidentate species formation; this facilitates the gasification of naphthalene by steam.

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