A highly efficient SAPO-34 catalyst for improving light olefins in methanol conversion: Insight into the role of hierarchical porosities and tailoring acid properties based on in situ NH3-poisoning

Hierarchical SAPO-34 with diverse porosity resulted from primary nanocrystals aggregating were hydrothermally synthesized by precisely modulating Si/Al molar ratios of the gel precursors, the developed mesoporosity along with the reserved inherent microporosity endows the catalysts excellent performances in MTO reaction. Furthermore, the weakened strong acid sites modified by in-situ NH3 poisoning pretreatment can be further improved the catalytic efficiency and significantly enhanced the even selectivity toward light olefins. [Display omitted] •Hierarchical SAPO-34 zeolites were prepared using TEAOH as a sole template.•The fabricated mesopore structure offers excellent MTO catalytic performances.•The relationship between acid strength and light olefins selectivity was revealed.•Synergistic effect of acid and pore structure in lifting light olefin selectivity in MTO.•A universal strategy (NH3 poisoning) for lifting light olefins selectivity in MTO. Hierarchical SAPO-34 zeolites with tunable porosity were hydrothermally synthesized by modulating the Si/Al molar ratios of the gel precursors, and the morphologies of SAPO-34 crystals gradually evolve from well-dispersed ultra-small nanocrystals to compactly polycrystalline aggregates, and to analogous polycrystallinites but adhered with minute amorphous debris by increasing the Si/Al ratio ranging from 0.20 to 0.67. The catalytic tests during methanol-to-olefins (MTO) reaction indicate that the Hier-SAPO-34-0.20 (Si/Al = 0.20) catalyst constructed by loosely nano-sized crystals centered at 50 nm presents prominent catalytic performances with about 2.5 times prolonged catalytic longevity and around 10 % improvement for the selectivity toward light olefins (ethylene and propylene) as compared to a reference catalyst. More interestingly, when Hier-SAPO-34-0.20 catalyst was in situ pretreated with NH3 flowing, the selectivity of light olefins can be greatly increased by 18.1 % at the initial stage and the corresponding even selectivity with time-on-stream can be elevated by 6.9 %. It founds that in situ NH3-poisoned catalysts with improved light olefins selectivity are also suitable for ZSM-5 zeolite. These results reveal that the weakened strong acid sites modified by NH3-poisoning play a pivotal role in suppressing the undesired hydrogen transfer reactions and thus giving a high selectivity for light olefins. This work highlights the importance of acidity fine-tailoring by in-situ NH3-poisoning strategy on hiera