In-situ IR Study On Hydrogenolysis Of Dimethyl Oxalate To Form Ethylene Glycol

The mechanism of dimethyl oxalate hydrogenolysis to ethylene glycol was studied by in situ FT-IR spectroscopy. In all, the following are primary content:adsorption and desorption of dimethyl oxalate (DMO), methyl glycolate (MG), ethylene glycol (EG), methanol (ME) on SiO2 and on Cu/SiO2 catalyst; the impact of different reactants pre-adsorption on the result during the hydrogenation of DMO and MG, respectively; the influence of different reaction temperature on the hydrogenation of MG; thermal decomposition of DMO and so on. The main results and conclusions of this paper are as follows:DMO, MG, EG, ME could be adsorbed on the surface of SiO2 through hydrogen bond between hydroxyl or carbonyl of them and hydroxyl of SiO2, they were hard to be outgased totally; the species, CH3O-M (2923-2925cm-1), CH3OC(O)(O)C-M (1667cm-1) and M-C(O)(O)C-M (1618cm-1) were formed during the adsorption of DMO on the catalyst, the species CH3O-M (2923-2925cm-1) and HOCH2(O)C-M (1689-1692cm-1) were formed during the adsorption of methyl glycolate (MG) on the catalyst, both EG and ME were strongly adsorbed on the surface of SiO2 after dissociative adsorption on the active center; the band of M-C(O)(O)C-M disappeared, only leaving the bands of DMO, MG, HOCH2(O)C-M and CH3OC(O)(O)C-M in the carbonyl region during the hydrogenolysis of DMO; combining the hydrogenation of MG, it could be deduced that, during the actual reaction process, the hydrogenolysis of DMO to form EG mainly proceed route:DMOâ†'CH3OC(O)(O)C-Mâ†'MGâ†'HOCH2(O)C-Mâ†'EG. the scheme for the mechanism of hydrogenolysis of DMO on Cu/SiO2 was firstly proposed in this paper; it showed DMO hydrogenation after H2 pre-adsorption tended to produce more EG and less residual (1754cm-1), otherwise the opposite; the result of hydrogenation of MG was in accord with it, hydrogenation at higher temperature is conductive to desorption of the residual; thermal decomposition of DMO will produce CO, CO2 and ME, among of them, CO has negative effects on the activity of catalyst.; consequently residence time of DMO should properly be kept low to avoid its thermal decomposition.