Tailoring the acidity of ZSM-5 via surface passivation: Catalytic assessment on dimethyl ether to olefins (DTO) process

In the present study, four different samples having different acidity were synthesized. Two MFI-type zeolites having silicon-to-aluminum ratio equal to 25 and 50 were prepared. Besides, two additional samples were obtained by external passivation of each parent zeolite with a layer of Silicalite-1, leading to a core–shell structure. Each sample was characterized to assess textural properties, structure, composition, and acidity, and then tested for dimethyl ether (DME) conversion at different reaction temperatures between 300 and 375 ◦C. The analysis of produced mixture revealed the simultaneous presence of hydrocarbons and methanol. DME conversion grew by increasing the temperature. Propylene was the most abundant hydrocarbon detected during all the time-onstream analyses. Especially at 375 ◦C, the investigated samples having greater acidity showed faster deactivation due to coking. Samples with lower acidity were thus more stable but, on the other hand, they presented higher methanol selectivity and lower hydrocarbons yield.