Deactivation and regeneration of hybrid catalysts in the single-step synthesis of dimethyl ether from syngas and CO2

Synthesis of dimethyl ether (DME) has been studied in a single reaction step, from H-2 + CO and H2 + CO2, in a fixed bed reactor on CuO-ZnO-Al2O3/gamma-Al2O3 and CuO-ZnO-Al2O3/NaHZSM-5 hybrid catalysts. It has been proven that water content in the reaction medium (which is higher when CO2 is fed) contributes to efficiently decreasing deactivation by coke in both catalysts and, consequently, when water is in the feed deactivation is insignificant for 30 h reaction. Nevertheless, water also decreases the activity of gamma-Al2O3 acid function, due to its high adsorption capacity on the acid sites. Due to its importance in the viability of the industrial process, a study has been carried on the regeneration of both catalysts by coke combustion under controlled conditions (in order to avoid CuO sintering). For this study, the catalysts have been used under severe deactivation conditions. It has been proven that gamma-Al2O3 does not have a suitable hydrothermal stability and that CuO-ZnO-Al2O3/NaHZSM-5 catalyst has an excellent performance and is suitable for using it in uninterrupted reaction-regeneration cycles. (c) 2005 Elsevier B.V. All rights reserved.