Operando and Kinetic Study of Low-Temperature, Lean-Burn Methane Combustion over a Pd/γ-Al2O3 Catalyst

Abstract

Operando and kinetic studies of lean-burn methane combustion were preformed on a Pd(3.3 wt %)/γ-Al2O3 catalyst in a low temperature range of 473–673 K. The reaction order with respect to oxygen decreased with temperature, and the order with respect to methane remained constant. The working catalyst is characterized using operando Raman spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (DRIFTS), and the Pd chemical states were measured with X-ray photoelectron spectroscopy (XPS). Partial oxidation of Pd atoms during reaction was identified by Raman and XPS spectroscopies. In particular, the DRIFT spectra revealed that ∼45% of Pd atoms at the top layers were transferred into PdOx species above 523 K. The reaction was assumed to occur primarily on the metallic Pd sites below 673 K, proceeding through the Langmuir–Hinshelwood mechanism, and Pd oxide may affect the adsorption and activation of reactants.