The direct synthesis of dimethyl ether (DME) from synthesis gas (STD) via methanol as an intermediate is a promising option for implementation of the Power-to-X concept, involving the storage of renewable electrical energy via hydrogen or synthesis gas in synthetic fuels or chemicals. The STD reaction shifts the equilibrium conversion dictated by thermodynamics to higher values compared to methanol synthesis alone at given conditions. Notwithstanding, proper catalyst materials and a suitable configuration have to be found that would support high CO-conversion as well as high DME-selectivity. In this work, different catalyst configurations obtained by combining CuO/ZnO/Al2O3 (CZA) for methanol synthesis with zeolite H-ZSM-5 (Z) for its dehydration are investigated via simulation based on a crystallite-pore network model, able to describe e.g. the polycrystalline anisotropic zeolite. In this way, hybrid particles with proximity of the two catalysts in both, the micrometer-scale (medium proximity, CZA+Z) and in the sub-micrometer-scale (close proximity, CZA&Z) as well as structured core@shell particles (CZA@Z) were investigated for a tubular reactor. Moreover, their planar (coated) counterparts, namely the hybrid layered systems with medium (CZA#Z) and close proximity (CZA&/Z) and a structured double layer system (CZA//Z) were investigated for a wall-coated microchannel reactor. The performance of these systems in the STD reaction was studied focusing on the influence of the CZA/Z ratio and the operational parameters (temperature, GHSV, feed composition). According to this study, hybrid particles with close proximity of the two catalysts as well as the double layer structures showed the best performance in terms of CO-conversion and DME-selectivity.

The direct synthesis of dimethyl ether (DME) from synthesis gas via methanol as an intermediate is a promising process for realizing a decentralized, small-scale Power-to-X concept. The efficient realization of this coupled process depends to a large extent on the appropriate catalyst configuration, i.e. the combination of the catalyst for methanol formation with the one for the subsequent dehydration step. In this work, two catalyst configurations were compared in terms of CO-conversion and DME-selectivity using modelling and experiments. Catalysts for methanol formation (Cu/ZnO/Al2O3, CZA) and dehydration (Zeolite H-ZSM-5, Z) prepared via flame spray pyrolysis and hydrothermal synthesis, respectively, were combined in the form of hybrid pellets (CZA&Z) and CZA-core@zeolite-shell (CZA@Z) particles. During the synthesis of the CZA@Z system, alteration of the CZA core in terms of CuO-reducibility and activity in methanol synthesis were found after individual steps of calcination and hydrothermal shell synthesis. In contrast, the preparation of the CZA&Z system presents an easy and tunable method with promising catalytic properties in terms of CO-conversion and DME-selectivity, once the proper mass ratio of the two catalysts was set. From modelling, for the same CZA/Z ratio in general higher CO-conversion was found for the CZA&Z system as compared to the CZA@Z, while the latter system shows higher DME-selectivity.