Shape selective methanol to olefins over highly thermostable DDR catalysts

ZSM-58, having a DDR topology, is shown to be a very attractive catalyst for the direct formation of propylene and ethylene via conversion of methanol. A performance similar to the state of the art SAPO-34 catalysts is achieved, while no olefins longer than C₄ are formed. In addition, ZSM-58 has a much higher thermostability than SAPO catalysts. Mainly propylene, ethylene and linear butenes (trans-but-2-ene and butadiene) are formed when materials with the DDR topology are used as catalysts during the MTO process. The ratio propylene/ethylene can be tuned by changing the reaction conditions or the degree of catalyst coking. An optimum in performance, in terms of stability and selectivity, is found for catalysts containing one acid site (one Al) per accessible cavity. Deactivation of the catalysts takes place due to formation of coke and homogeneous blocking of the catalysts porosity. Activity is fully recovered after regeneration in air.