Synthesis of RUB-13 zeolite and its catalytic performance in the conversion of methanol to olefins
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摘要: 采用水热法合成RUB-13分子筛,探讨了有机模板剂(OSDA)、硅源、晶化温度和水硅比等制备条件对RUB-13分子筛晶体结构的影响,考察了RUB-13分子筛在甲醇制烯烃(MTO)反应中的催化性能。结果表明,采用1,2,2,6,6-五甲基哌啶(PMP)为有机模板剂、白炭黑为硅源,在晶化温度为170℃的条件下,选择H2O/Si比为100和80时可分别合成出高纯度的低硅铝比(Si/Al=100)和高硅铝比(Si/Al=200)的RUB-13分子筛晶体,且晶粒呈棒状形貌。H-Al-B-RUB-13(Si/Al=200)分子筛用于催化甲醇制烯烃反应时,在400℃下表现出高的低碳烯烃选择性(C2-5=选择性达97.8%,丙烯选择性为54.5%),优于传统的H-SAPO-34和H-ZSM-5分子筛催化剂。Abstract: RUB-13 zeolites were synthesized by hydrothermal method. The effect of organic structure-directing agent (OSDA), silica source, crystallization temperature and Si/H2O ratio on the crystal structure was investigated and the catalytic performance of H-RUB-13 in the conversion of methanol to olefins (MTO) was evaluated. The results indicate that with 1, 2, 2, 6, 6-pentamethylpiperidine (PMP) as OSDA and fumed silica as silica source, pure and highly crystalline RUB-13 zeolites with a Si/Al ratio of 100 or 200 can be successfully synthesized by crystallization at 170 ℃, with a H2O/Si ratio of 100 or 80 in the synthesis gel, respectively. The crystals of the synthesized RUB-13 zeolites display a thin rod-like morphology. As a catalyst in MTO, the high-silica H-Al-B-RUB-13 (Si/Al=200) zeolite exhibits unprecedentedly high selectivity to light olefins at 400 ℃ (54.5% to propene and 97.8% to C2-5=), much better than the traditional H-SAPO-34 and H-ZSM-5 zeolites under similar conditions.
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图 6 不同硅铝比的H-Al-B-RUB-13分子筛催化剂上MTO反应过程中的甲醇转化率和产物选择性
Figure 6 Methanol conversion and product selectivity with time on stream for MTO over the H-Al-B-RUB-13 zeolites with different Si/Al ratios
(a): H-Al-B-RUB-13(Si/Al=100); (b): H-Al-B-RUB-13(Si/Al=200) the reactions were carried out at 400 ℃, with a methanol weight space velocity of 1.0 h-1
表 1 不同硅铝比H-Al-B-RUB-13分子筛的组成结构和酸性
Table 1 Constitution and acidity of the H-Al-B-RUB-13 zeolites with different Si/Al ratios synthesized under optimized conditions
Zeolite Si/Al ratio Si/B ratio Acidity by NH3-TPD/ (μmol·g-1) gel bulk gel bulk weak strong H-Al-B-RUB-13(Si/Al=100) 100 70 4 20 71 89 H-Al-B-RUB-13(Si/Al=200) 200 171 4 18 34 56 note:the elemental compositions of the synthesis gel and the bulk H-Al-B-RUB-13 zeolite were determined by ICP-OES, the amounts of weak and strong acid sites were determined as the quantities of ammonia desorbed at 120-250 and 250-550 ℃ during the NH3-TPD, respectively -
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