Zeolites Interactions With Microwaves During Methane Non-Oxidative Coupling

Microwave-zeolite interactions during direct non-oxidative reactions of methane were studied using three HZSM-5 zeolites with different concentrations of Bronsted acid sites. The formation of C2 and aromatic hydrocarbons increased with increasing surface acidity. When compared to conventional heating, the microwave reaction produced less carbon with higher thermal stability. The increase in diffraction shifts and the decrease in surface area of microwave-reacted zeolite suggested that the carbon started depositing inside the micropores rather than on the external surfaces. Inhomogeneous carbon deposits with filamentous carbon whiskers were observed under microwave compared to homogeneous spherical carbon deposits on the conventionally reacted sample. The dielectric properties and Raman analysis suggested that the graphitic nature and the thermal stability of deposited carbon increased with zeolite surface acidity under microwave. We believe that this is a very important study for designing microwave active zeolite-based catalysts with a low affinity towards carbon formation.