Combination of hydrotalcite-like-compound-derived Ni-Fe/Mg/Al and ceria-supported Rh catalysts for fuel reforming in exhaust gas recirculation system of gasoline engine

Abstract

Hydrotalcite-like-compound-derived Ni-Fe/Mg/Al catalyst, which is known to have high catalytic performance on reforming when activated by pre-reduction with H2, was combined with small amount of noble metal to obtain self-activation ability (startability) in toluene reforming with model exhaust gas of gasoline engine of automobiles. Rh is found to be the most effective noble metal from the viewpoints of the inherent reforming activity, good promotion of reduction of NiFe, and stability. Physical mixing of Rh/CeO2 and Ni-Fe/Mg/Al powders before shaping to granules gave higher activity in the startability test (reaction without pre-reduction) than other combination methods of Rh/CeO2 + Ni-Fe/Mg/Al, although the activity increase from Rh/CeO2 was much smaller than the potential activity of Ni-Fe/Mg/Al catalyst induced by pre-reduction with H2. Direct addition of Rh to Ni-Fe/Mg/Al by impregnation gave inferior performance to the mixture catalyst, because of the lower activity of Rh on hydrotalcite-derived oxide support than that of Rh on CeO2 support. The characterization with XRD, TEM-EDX and XAS showed that the reduction degrees of Ni, Fe and even Rh were small during the startability test. The Ni and Fe species only located near Rh species were probably reduced by reforming products from toluene formed over Rh.