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

Abstract

• Dry reforming of methane at 400–600 °C over supported Rh catalysts was studied. • Catalyst activity depended on Rh particle size, support type, and acidic properties. • Specific activity increased with decreasing Rh particle size. • Rh/SiO 2 -TiO 2 performed the best, giving H 2 and CO yields of 1.8% and 4.2% at 400 °C. • Electron-deficient Rh δ+ species may improve the specific activity of the catalysts. Dry reforming of methane at 400–600°C was studied over Rh catalysts with different supports (SiO 2 , γ-Al 2 O 3 , α-Al 2 O 3 , TiO 2 , ZrO 2 , CeO 2 , Y 2 O 3 , SiO 2 -Al 2 O 3 , SiO 2 -MgO, SiO 2 -TiO 2 ), 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., α-Al 2 O 3 , SiO 2 -MgO) showed low activity and gradually deactivated with time on stream; in contrast, catalysts with a low density of strongly acidic sites (e.g., TiO 2 , γ-Al 2 O 3 ) showed high, stable activity. Rh/SiO 2 -TiO 2 showed the best performance, with H 2 and CO yields of 1.8% and 4.2% at 400°C and yields 37.3% and 53.1% at 600°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 δ+ 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.