H-SAPO-34分子筛磷改性机理及作用

Effect and Mechanism of Phosphorus Modification on H-SAPO-34 Molecular Sieves

选取n（Si）/n（Si＋Al＋P）为0.120和0.086两种H-SAPO-34分子筛进行磷改性,制备出一系列（n（P）/n（Si）为0.33～1.67）磷改性H-SAPO-34分子筛样品.采用XRD、XRF、SEM、BET、NH3-TPD和29Si NMR、27Al NMR、31P NMR手段分析磷改性H SAPO 34分子筛的物相、孔结构和酸性以及骨架元素Si、P、Al的化学配位,并通过脉冲微反实验考察磷改性对H-SAPO-34分子筛催化甲醇制烯烃（MTO）反应活性和烃产物分布及选择性的影响.结果表明,对H-SAPO-34进行磷改性时,在高温水蒸气作用下,磷氧化物能够均匀分布在H-SAPO-34分子筛晶体的外表面,并随机与表面的骨架Al、P发生化学配位,引起骨架结构中的P-O-Al键和Si-OH-Al键断裂;随着n（P）/n（Si）增加,表面骨架铝的配位数提高,促进了AlPO4鳞石英相生成,以及Si-O-Al键断裂和Si（OSi）4无定形相析出,伴随着孔结构破坏、相对结晶度下降以及酸量降低.采用n（P）/n（Si）为0.33～1.33范围内的磷改性H-SAPO-34分子筛催化MTO反应,随着n（P）/n（Si）的增加,产物中C4、C5烃的含量有所下降,C2烃的含量明显增加,择形性提高,乙烯选择性提高.

A series of P-modified H-SAPO-34 with n（P）/n（Si） in the range of 0.33- 1.67 were prepared by saturating impregnation of H-SAOPO-34, whose n（Si）/n（Si＋Al＋P） were 0. 120 and 0.086, respectively, and characterized by means of XRD, XRF, SEM, BET, NHa-TPD and 29Si NMR, 27A1 NMR, 31p NMR to investigate the effects of phosphorus modification on the phase, pore structure and acidity and chemical coordinates of Si, A1 and P in framework of P-modified H-SAPO-34. Catalytic performances of those samples in methanol to olefin （MTO） reaction, such as catalytic activity, carbon number distribution of hydrocarbon products and their selectivity, were evaluated by the experiments in pulse-feed micro-reactor. The results showed that during the phosphorus modification of H-SAPO-34 under the conditions of 100% steam and 550℃, the loaded phosphorus oxides were distributed uniformly on the surface of H-SAPO-34 crystal and coordinated with surface framework A1 and P atoms in probability to promote the cleavage fracture of P-O-A1 and Si-OH-A1 bonds. With the increase of phosphorus oxide loadings （n（P）/n（Si））, the coordinate number of surface framework A1 with phosphorus oxides increased and precipitation of A1PO2 tridymite and the formation of Si（OSi）4 amorphous phase and the cleavage fracture of Si--OH--A1bonds were accelerated, along with the decrease of relative crystallinity and acid capacity and decline of pore structure. By using the P-modified H-SAPO-34 of n（P）/n（Si） in the suitable range of 0.33--1.33 as catalyst, the shape-selectivity in MTO reaction was enhanced with the increase of n（P）/n（Si）, that is, in hydrocarbon product C4, C5 contents decreased and C2 content increased, and the ethylene selectivity increased.