Gas chromatography: Gas-chromatography was performed on a Bruker Scion GC/MS, with a thermal conductivity detector 15 (column: molecular sieve 5A 75 m × 0.53 mm, oven temperature 70 °C, flow rate 25 ml min -1 , detector temperature 200 °C) with Argon as carrier gas. The GC was calibrated by direct injection of known amounts of H2 gas.