Effects of rhodium catalyst support and particle size on dry reforming of methane at moderate temperatures

Dry reforming of methane at 400-600 degrees C was studied over Rh catalysts with different supports (SiO2, gamma-Al2O3, alpha-Al2O3, TiO2, ZrO2, CeO2, Y2O3, SiO2-Al2O3, SiO2-MgO, SiO2-TiO2), Rh particle sizes (1.5-15.6 nm), and acidic properties (acidic site density, 0.37-3.40 mmol g(-1)). Catalysts with a high density of strongly acidic sites (e.g., alpha-Al2O3, SiO2-MgO) showed low activity and gradually deactivated with time on stream; in contrast, catalysts with a low density of strongly acidic sites (e.g., TiO2, gamma-Al2O3) showed high, stable activity. Rh/SiO2-TiO2 showed the best performance, with H-2 and CO yields of 1.8% and 4.2% at 400 degrees C and yields 37.3% and 53.1% at 600 degrees C, respectively. Catalyst activity depended strongly on Rh particle size; specific activity increased with decreasing particle size, indicating that Rh-catalyzed dry reforming of methane is structure-sensitive. The support type influenced not only the dispersion and reducibility of the Rh particles but also the specific activity of the catalysts. CO temperature-programmed desorption and FT-IR suggested that electron-deficient Rh delta+ species were generated by electronic interactions between the Rh particles and the support, and the number of these species strongly influenced the overall catalytic activity.