Effect of siloxane on performance of the Pt-doped γ-Al2O3 catalyst for landfill gas deoxygen

Abstract

Catalytic oxidation of methane using platinum (Pt) or platinum-rhodium (Pt-Rh) doped γ-Al2O3 has been proved to be a reliable deoxygen method for landfill gas (LFG) upgrading. As siloxanes are ubiquitous in LFG, their effect on the performance of the deoxygen catalyst is an extremely important element for the design of LFG upgrading procedures. To investigate the effect of siloxanes on the deoxygen catalyst reactivity, two experiments for the simulated LFG deoxygen were designed and carried out using Pt/γ-Al2O3 as the catalyst, and octamethylcyclotetrasiloxane (D4) as the siloxane representative. The fresh and used catalysts were characterized by means of various techniques. Results of the deoxygen experiments demonstrated that the presence of siloxanes in LFG would cause deactivation of the deoxygen catalyst. For the catalyst prepared in this study, at reaction temperature of 350 °C, deoxygen conversion of the catalyst decreased to 16.6% after 7 h of running under the condition of the experiment in this study, and the light-off temperature of this used catalyst increased to 415 °C. The results of X-ray photoelectron spectroscopy (XPS) characterization indicated that compared with Pt of higher chemical states, elementary Pt presented higher catalytic deoxygen reactivity. Through various characterization techniques, the deactivation of the catalyst could be explained as that D4 was oxidized by the small amount of oxygen in the simulated LFG and converted to amorphous silicon dioxide (SiO2), which blocked the contact between the active sites of the catalyst and the gas molecules, and resulted in the catalyst failure.