硼改性HZSM-5对催化MTP反应活性影响

水热晶化一步合成了BHZSM-5分子筛，投料SiO₂/Al₂O₃=100、200，其中，B₂O₃/Al₂O₃=1，研究了其甲醇制丙烯（MTP）催化活性。硼改性提高了丙烯选择性，并有利于稳定活性。硼修饰引起合成样品的强B酸量减少；水热（480℃）环境条件下，BHZSM-5的强B酸量保留量约50%，相比HZSM-5，酸性位点保留较多，显示增强的水热稳定性；同时骨架Al分布发生了变化：位于晶体直孔道和正弦孔道的Al稳定，孔道交叉口的Al易于脱除，有利于基于烯烃循环机理的MTP活性。水热处理空速由1 h^-1增加到9 h^-1，B酸量进一步下降，晶体孔道交叉口的Al脱除更多。

Effects of boron modification on the activity of HZSM-5 toward MTP

BHZSM-5 zeolite was synthesized using one-step hydrothermal crystallization by changing SiO₂/Al₂O₃ (100 and 200) with B₂O₃/Al₂O₃=1. The catalytic activity for methanol to propylene (MTP) was studied. Boron modification lead to increased propylene selectivity and improved stability. Boron modification reduced the amount of the strong Brønsted (B) acid sites. Subjected to hydrothermal treatment at 480 ℃, BHZSM-5 remained 50% of the amount of the strong B acid sites, higher than that of HZSM-5, showing enhanced hydrothermal stability. The distribution of the framework Al also changed. The Al located in the straight and the sinusoidal channels of the ZSM-5 crystal was stable whereas those at the channel intersections was easy to be removed, favoring the MTP activity via the olefin cycle mechanism. As the hydrothermal treatment velocity was increased from 1 h^-1 to 9 h^-1, the B acid sites amount of the BHZSM-5 further decreased and more Al at the intersections was removed.