The nature of silica-to-alumina ratio effect on lean methane oxidation over Pd/Beta zeolite catalysts

Abstract

The silica-to-alumina ratio (SAR) effect on lean methane oxidation over Pd/Beta catalysts was investigated. Light-off test, steady-state performance and kinetic analysis demonstrate the activity of Pd/Beta catalysts shows a volcano-shaped dependence on SAR. Pd/Beta402 presents the highest activity among all samples, regardless of the presence of water. By the employment of H2-TPR, CO-chemisorption, STEM-EDS, TGA and NH3-TPD, it is found that the activity of Pd/Beta catalysts is essentially influenced by their acidity, which is the nature of the SAR effect on methane oxidation. Increasing SAR leads to lower acidity, resulting in less formation of inactive Pd2+ and higher hydrophobicity which benefit methane oxidation. However, the larger PdO particles are formed at the same time, leading to a decrease in the amount of exposed PdO which is detrimental to methane oxidation. This work can guide the design of state-of-the-art zeolite-supported Pd-based methane oxidation catalysts.