Gas samples were collected in triplicates at the gas outlet of the reactor in 5.9 ml vacuum vials (Exetainer ® Evacuated Flat Bottom Vial). The composition of H 2 , CO 2 , N 2 , and CH 4 was analyzed using gas chromatography (GC, 7890A, Agilent Technologies, Santa Clara, CA, USA) equipped with a thermal conductivity detector and a fused silica capillary column (Carboxen ® 1010 PLOT, 30 m × 0.53 mm). The temperature of the oven holding the column was maintained at 35 °C with a holding time of 4 min, followed by a ramp of 25 °C/min up to 225 °C, and then maintained with a holding time of 2 min. Ar was used as the carrier gas and certified gas mix standards from Mikrolab Aarhus A/S were used for the calibration of GC.