Methane emission abatement by Pd-ion-exchanged zeolite 13X with ozone

Abstract

The performance of 3 wt% Pd-ion-exchanged zeolite 13X for methane emission abatement under various parameters including reaction temperature (295–435 °C), inlet ozone concentration (0–4 vol%), space velocity (12 500–62 400 h⁻¹) and inlet methane concentration (200 and 1400 ppm) were investigated. Without zeolite, gas phase reaction among methane, air and ozone gave 1–11% of methane conversion at 295–435 °C. The presence of inlet ozone (1.1–4 vol%) to the zeolite 13X system enhanced methane removal efficiency by 24–56%, giving an overall performance of 93% in this low temperature range. There existed a range of reaction temperatures where methane conversion was most enhanced by ozone in the zeolite system. Without ozone, methane oxidation showed an activation energy of 136 kJ mol⁻¹. This was reduced to 116 kJ mol⁻¹ by using 4 vol% of ozone. The enhanced methane removal efficiency was attributed to the decomposition of ozone to form atomic oxygen reacting with adsorbed methane. Higher percentage methane conversion was observed at lower space velocities under various inlet ozone concentrations. As the inlet ozone and methane concentration increased, the methane removal efficiency was limited by the number of available active sites in the zeolite, which governs the amount of adsorbed methane and atomic oxygen available for subsequent reactions. The system can be used for energy efficient green house gas and industrial effluent treatment.