In all cases, the methane selectivity, defined as Eq. 9, was always higher than 99.98% and only traces of ethane and ethene were detected. 4(%) = (4,4 ⁄ ∑ , ⁄ ) ∗ 100 (Eq. 9) , is the product i concentration in the outlet and ν is the carbon numbers according to its chemical formula