Oxidative gas phase carbonylation of methanol to dimethyl carbonate over chloride-free Cu-impregnated zeolite Y catalysts at elevated pressure

Abstract Incipient wetness impregnation of zeolite Y with copper(II) nitrate solution and inert activation at 650 °C led to active catalysts for the oxidative carbonylation of methanol to dimethyl carbonate in the gas phase. Activities were measured under elevated pressure (0.4–1.6 MPa) with feed compositions of CO/MeOH/O 2  = 40/20/6–1.5 vol.% (balanced by N 2 ) over zeolite Y loaded with 10–17 wt.% copper. It could be shown that inert activation at 650 °C enhanced the activity, and that Cu loading of 14–17 wt.% gave the best performance. By combined XRD, TEM, TPR and DRIFT characterization it was found that the inert activation initiated dispersion of crystalline CuO, auto-reduction of Cu 2+ to Cu + and redistribution of copper ions with enrichment inside the supercages of the zeolite. The O 2 content of the feed was found to control the selectivity to dimethyl carbonate. Dimethyl carbonate selectivities of 70–75% were achieved within the temperature range of 140–170 °C at an O 2 content of 1.5 vol.%. This allowed space-time yields of dimethyl carbonate up to 632 g l cat −1  h −1 at methanol conversions of 5–12%. Formation of the main side product, dimethoxymethane, was surprisingly affected by CO, which is not in line with suggested reaction pathways. A mechanism is proposed including formation of surface carbonate structures as common intermediate.