The catalytic effect of H2 in the dehydrogenation coupling production of ethylene glycol from methanol using a dielectric barrier discharge

The catalytic effect of H-2 in the one-step synthesis of ethylene glycol (EG) from methanol dehydrogenation coupling reaction using dielectric barrier discharge (DBD) was studied by in-situ optical emission spectroscopy and online chromatographic analysis. The influence of discharge frequency, methanol and H-2 flow rates as well as reaction pressure was investigated systematically. Results show that, in the non-equilibrium plasma produced by DBD, H-2 dramatically improved not only the conversion of methanol but also the selectivity for EG. Using the reaction conditions of 300 degrees C, 0.1 MPa, input power 11 W, discharge frequency 12.0 kHz, methanol gas flow rate 11.0 mL/min, and H-2 flow rate 80-180 mL/min, the reaction of the CH3OH/H-2 DBD plasma gave a methanol conversion close to 30% and a selectivity for EG of more than 75%. The change of the EG yield correlated with the intensity of the H-alpha spectral line. H atoms appear to be the catalytically active species in the reaction. In the DBD plasma, the stable ground state H-2 molecule undergoes cumulative collision excitation with electrons before transitioning from higher energy excited states to the first excited state. The spontaneous dissociation of the first excited state H-2 molecules generates the catalytically active H atom. The discharge reaction condition affects the catalytic performance of H-2 by influencing the dissociation of H-2 molecules into H atoms. The catalytic effect of H-2 exhibited in the non-equilibrium plasma may be a new opportunity for the synthesis of chemicals. (C) 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.