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• Rapid copper sintering occurring under realistic conditions of direct dimethyl ether synthesis. • No copper oxidation under a wide range of dimethyl ether synthesis conditions. • Strong effect of water on copper sintering and crystallite size. Dimethyl ether is one of the most promising environmentally optimized alternatives to the conventional fossil fuels and an important platform molecule for chemical industry. Catalyst deactivation is one of the most important challenges of the single-step dimethyl ether synthesis from syngas. Because of the lack of direct characterization techniques working under harsh reaction conditions, the information about deactivation mechanisms of bifunctional Cu/ZSM-5 catalysts is rather contradictory. In this paper, a combination of synchrotron-based in-situ time-resolved X-ray diffraction and X-ray absorption spectroscopy operating under high pressure and temperature alongside with the conventional ex-situ characterization uncovered very rapid copper sintering occurring under realistic conditions of direct dimethyl ether synthesis. Copper sintering was strongly affected by the presence of water either produced by the reaction or co-fed to the reactor. No copper oxidation was observed under a wide range of experimental conditions. [ABSTRACT FROM AUTHOR]

Abstract: Hierarchical porous composite with a core–shell structure possessing FAU-type zeolite core (zeolite X) and LTA-type zeolite shell (zeolite A) has been prepared. The intimate growth of zeolite shell is achieved by in situ crystallization of the LTA zeolite crystals with size of 1μm on large single FAU-type crystals with size of about 60–90μm. Direct visualization of the core–shell material is provided by X-ray microbeam measurements using synchrotron radiation on a single crystal complemented with field emission scanning electron microscopic study. The nitrogen sorption data confirmed that the access to large single FAU-type core is controlled by the defect-free LTA-type shell. Sorption measurements showed that about 98% of core crystals are covered by the LTA shells. Further the FAU–LTA core–shell material is used as a host for the stabilization of platinum clusters. The Pt location, mean size and distribution have been studied by CO chemisorption followed by FT-IR spectroscopy. High loading of platinum accessible to CO molecules in the core–shell material is achieved. The use of the FAU–LTA matrix allowed the stabilization of two different sizes of Pt clusters. Additional advantage of the core–shell material is the protection of the clusters from thermal sintering and poisoning, which is of significant importance for future catalysts. [Copyright &y& Elsevier]