From 1-D to 3-D zeolite structures: performance assessment in catalysis of vapour-phase methanol dehydration to DME

A series of molecular sieves from silico-aluminate (zeolites) to silico-aluminophosphate (SAPO-34) were synthesised, characterized and tested as catalysts for DME production via vapour-phase methanol- dehydration also benchmarking with a commercial gAl2O3. Both high methanol conversion and DME yield were achieved on zeolites but catalyst stability and coke formation was strongly dependent upon the channels configuration. 1-dimensional channels structures with large openings and/or side pockets suffered of high carbon deposition, causing catalyst deactivation whilst the 2-dimensional small pore channel system of FER structure ensures a high resistance to deactivation by inhibiting coke deposition. 3-dimensional structures showed a pronounced tendency to deposit heavier molecules in the coke phase, strongly affecting the catalytic performances. In fact, carbon deposit phase mainly consists in poly- substituted benzenes with a substitution level depending on the channel system (size and topology). Considering catalytic performances in terms of methanol conversion, DME selectivity and deactivation, ferrierite (Si/Al 1⁄4 8.4) exhibited the best performances being a reliable catalyst for DME production via vapour-phase methanol dehydration.