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- W2776697029 abstract "Dimethyl ether (DME), which can be produced from both renewable (e.g. biomass) and fossil resources, is considered as a clean alternative fuel. The direct synthesis of DME from syngas is much more thermodynamically and economically favourable than the two-step route which involves methanol synthesis followed by methanol dehydration. Methanol synthesis requires a copper based metallic catalyst, while methanol dehydration occurs on an acidic catalyst. ZSM-5 zeolite is currently the most interesting acidic system for methanol dehydration. The main challenges of direct DME synthesis over hybrid Cu-ZnO-Al2O3/ZSM-5 remains, however, quite low selectivity and catalyst deactivation which reduced the DME productivity. The present work is directed on the solution of these problems by variation of the size of zeolite crystals. The hybrid catalysts were prepared by mechanical mixing of Cu-ZnO-Al2O3 with ZSM-5 zeolites with different Si/Al ratios ratios and crystallite sizes from several μm to 50 nm by variation of the temperature of crystallization. DME, methanol and CO2 were major reaction products over hybrid catalysts. The catalysts containing zeolite nanocrystallites exhibited much better catalytic performance. Decrease of zeolite crystals resulted in the higher activity, selectivity to DME and stability of the catalyst. The increase of the activity is the result of the shift of the equilibrium in the direction of DME formation with decrease of the distance between CuZnAl and zeolite crystals. Higher selectivity over catalyst with small crystals is the result of the fast dehydration of intermediate methanol which transforms partially into side products in the case of the large crystals. Investigation of the fresh and used catalysts by TEM and IR spectroscopy of adsorbed Py and CO was indicative of copper sintering and spectacular copper migration during the reaction. Copper migration led ion exchange of Cu2+ species with the external protons of zeolites. As a result, both metal and acidic functions were affected and the rate of DME synthesis has been notably reduced. Small crystals of ZSM-5 had lower contribution of the external acid sites determined by lutidine adsorption which explains higher stability of composites." @default.
- W2776697029 created "2018-01-05" @default.
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- W2776697029 date "2015-01-01" @default.
- W2776697029 modified "2023-09-26" @default.
- W2776697029 title "Effect of the size of zeolite crystals on dimethyl ether synthesis from syngas over CuZnAl/ZSM-5" @default.
- W2776697029 hasPublicationYear "2015" @default.
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