INFLUENCE OF THE CHOICE OF THE TEMPLATE ON THE SHORT-TERM AND LONG-TERM STABILITY OF SAPO-34 ZEOLITE
INFLUENCE OF THE CHOICE OF THE TEMPLATE ON THE SHORT-TERM AND LONG-TERM STABILITY OF SAPO-34 ZEOLITE
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DOI：
10.1021/j100020a060
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发表时间：
1995-05-18
影响因子：
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通讯作者：
BARTHOMEUF, D
中科院分区：
文献类型：
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作者：
BRIEND, M;VOMSCHEID, R;BARTHOMEUF, D
关于模板[四乙基氢氧化铵(TEAOH)或吗啉]的分解和随后几个小时至两年的水化-脱水循环，研究了SAPO-34(Chabasite结构)。用X射线衍射仪、红外光谱、Al-27和Si-29MAS核磁共振、N-2吸附等手段表征了相关的结构变化。模板分解导致Al-27和Si-29的MAS核磁共振峰移动，反映了它与骨架的相互作用。无模板剂材料在室温下水合导致Si-OH-Al键断裂，部分失去结晶度，形成Q(1)、Q(2)和Q(3)Si物种(Si(OT)(N)(OH)(4-n))。材料在大约1到2天的水合后脱水，可以可逆地产生。无模板材料的初始结晶度、硅环境和孔隙率。长达2年的长期水化表明，以吗啉为模板剂合成的沸石不能完全恢复其结晶度，最终不能恢复其孔隙度。相比之下，TEAOH材料更稳定，保持了高达80%的初始结晶度和70%的孔隙率。在用TEAOH合成硅岛的过程中，模板的影响与硅岛的形成有关，而吗啉则提供了大部分的孤立硅。这限制了TEAOH样品中的Si-OH-Al键的数量，即水攻击骨架的点的数量。
SAPO-34 (chabasite structure) is studied with regard to decomposition of the template [tetraethylammonium hydroxide (TEAOH) or morpholine] and subsequent hydration-dehydration cycles over a period of few hours up to 2 years. XRD, IR, Al-27 and Si-29 MAS NMR, and N-2 adsorption an used to characterize the related structural changes. The template decomposition results into shifts in Al-27 and Si-29 MAS NMR peaks reflecting its interaction with the framework. Hydration of the template-free materials leads at room temperature to a breaking of Si-OH-Al bonds, giving a partial loss of crystallinity and the formation of Q(1), Q(2), and Q(3) Si species (Si(OT)(n)(OH)(4-n)). Dehydration of the materials after about 1 or 2 day hydration gives reversibly the. initial crystallinity, the Si environment, and the porosity for the template-free materials. Long-term hydration, up to 2 years, shows that zeolites synthesized with morpholine as a template do not recover their full crystallinity and eventually none of their porosity. By contrast, TEAOH materials-are more stable, keeping up to 80% of the starting crystallinity and 70% of their porosity. The influence of the template is correlated to the formation, during synthesis of Si islands with TEAOH, while morpholine gives a larger part of isolated Si. This restricts in the TEAOH sample the number of Si-OH-Al bonds, i.e., of points where water attacks the framework.