Catalytic Combustion of Methane with Ozone Using Pd-Exchanged Zeolite X: Experimental Investigation and Kinetics Model

The authors experimentally investigated the catalytic combustion of methane on a 3-wt%-Pd-ion-exchanged zeolite 13X catalyst under various reaction temperatures, ozone/methane concentration ratios, and gas hourly space velocities. A model based on Langmuir-Hinshelwood kinetics was developed to analyze the performance of the system. Without the catalyst, the activation energy for methane oxidation with ozone is 148kJ/mol. Adding catalysts but using oxygen only as oxidant, the activation energy reduces to 114kJ/mol. Adding ozone to the system greatly reduces the activation energy to 63kJ/mol. The enhanced methane conversion by adding ozone with catalysts could be attributed to the decomposition of ozone to atomic oxygen species. With the catalyst, at temperatures below 400 degrees C, methane conversion is mainly achieved by reaction with ozone. Adding ozone at this low temperature range can enhance the energy efficiency of methane conversion. Reaction with oxygen becomes increasingly important at higher temperature and becomes the dominant mechanism at above 500 degrees C.