Oxidation of CH4 and C3H8 over combustion synthesized nanosize metal particles supported on α-Al2O3

Abstract

The catalytic oxidation of both CH₄ and C₃H₈ over combustion synthesized nanosize Pt, Pd, Ag and Au particles supported on α-Al₂O₃ was investigated using the temperature programmed reaction technique in a packed-bed tubular reactor. Complete CH₄ oxidation occurs over 1% Pd/Al₂O₃ and 1% Pt/Al₂O₃ at 350 and 425 °C, respectively, whereas complete oxidation of C₃H₈ over 1% Pt/Al₂O₃ and 1% Pd/Al₂O₃ gives CO₂ and H₂O at 175 and 300 °C. Supported Ag and Au both show CH₄ and C₃H₈ conversion at much higher temperatures. The rate and turnover frequency (TOF) of CH₄ oxidation over 1% Pd/Al₂O₃ at 300 °C are 33.33 µmol g⁻¹ s⁻¹ and 0.34 s⁻¹, respectively. Similarly, those of C₃H₈ oxidation over 1% Pt/Al₂O₃ at 150 °C are 116.67 µmol g⁻¹ s⁻¹ and 1.21 s⁻¹, respectively. The CH₄ oxidation over supported Pt and Pd particles follows first-order kinetics with respect to CH₄. The values of the rate constant (k) are 225 and 210 cm³ g⁻¹ s⁻¹ over 1% Pt/Al₂O₃ and 1% Pd/Al₂O₃ at 300 and 400 °C, respectively. Activation energy (E_a) values are 95.5 and 128.4 kJ mol⁻¹ for supported Pd and Pt, respectively.