Polyoxometalate modified SAPO-34: A highly stable and selective catalyst for methanol conversion to light olefins

Highly stable and selective SAPO-34 catalysts were synthesized with direct synthesis incorporation of tungstophosphoric acid (HPW) and silver salt of HPW (AgPW) in SAPO-34 framework. The physicochemical properties of synthesized SAPO-34 samples were investigated using various analyses, including XRD, FTIR, UV-vis/DRS, NH3-TPD, ICP-AES, FESEM, BET and TGA. Furthermore, the catalytic performances of SAPO-34 samples in the reaction of methanol to olefins (MTO) were studied at 450 degrees C and 1atm. Incorporation of a moderate amount of HPW (HPW/Al2O3 = 0.010) as a Bronsted acid promoter in the SAPO-34 framework significantly reduced the SAPO-34 crystals size, enhanced the BET surface area and boosted the acidic properties. MTO catalytic tests revealed that the existence of a higher amount of Bronsted acid site as an active site could promote the light olefins selectivity and lifetime of HPW-modified SAPO-34 samples. The best HPW-SAPO-34 sample had a 375 min lifetime and 95.34% selectivity to light olefins, while the unmodified SAPO-34 represented 185 min and 83.28% of catalytic lifetime and selectivity to light olefins, respectively. AgPW-SAPO-34 with AgPW/Al2O3 = 0.010 illustrated superior catalytic performance and a lower deactivation rate due to the small well-defined crystals, the highest BET surface area and sufficient created Bronsted acid sites with a lower strength than the other synthesized samples. The AgPW-SAPO-34 sample showed a 403 min lifetime and 96.61% light olefins selectivity in the MTO process.