Influence of Si distribution in framework of SAPO-34 and its particle size on propylene selectivity and production rate for conversion of ethylene to propylene
Influence of Si distribution in framework of SAPO-34 and its particle size on propylene selectivity and production rate for conversion of ethylene to propylene
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DOI：
10.1039/b911659a
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发表时间：
2009-01-01
影响因子：
3.3
通讯作者：
Baba, Toshihide
中科院分区：
文献类型：
--
作者：
Iwase, Yasuyoshi;Motokura, Ken;Baba, Toshihide
为了研究SAPO-34颗粒尺寸（在其骨架中具有固定的Si摩尔分数）和Si摩尔分数（在具有固定颗粒尺寸的SAPO-34骨架中）对丙烯选择性和乙烯转化为丙烯的生产速率的影响，使用四乙基氢氧化铵或吗啉作为结构剂通过水热合成制备SAPO-34。乙烯的转化在473 K下使用SAPO-34进行。丙烯的选择性，丙烯的生产速率，和催化剂的寿命的强烈影响的催化剂的晶体尺寸。具有类似于2.5 μ m粒径的SAPO-34具有最高的丙烯选择性（类似于80%），直到乙烯的高转化率（类似于70%），而具有较小颗粒的SAPO-34具有较长的催化剂寿命，这意味着催化剂失活被抑制。在固定粒径的SAPO-34骨架中Si的摩尔分数对丙烯选择性的影响很小，表明SAPO-34的酸强度与Si的摩尔分数无关，并且SAPO-34中所有质子的行为是等效的。此外，通过NH3-TPD（程序升温脱附）光谱的测量确定的质子的酸强度不依赖于Si摩尔分数或SAPO-34颗粒尺寸。该结果在正丁烷的裂化速率中也是明显的，正丁烷的裂化速率随着SAPO-34中质子数的增加而成比例地增加。通过将Si 4+引入到SAPO-34晶格中而产生的质子数成比例地增加，直到一个Si原子引入到SAPO-34的每个笼中，但是随着Si 4+进一步引入到晶格中而不继续增加。
To investigate the effect of SAPO-34 particle size (with a fixed Si mole fraction in its framework) and that of the Si mole fraction (in a SAPO-34 framework with fixed particle size) on propylene selectivity and production rate for the conversion of ethylene to propylene, SAPO-34 was prepared by hydrothermal synthesis using tetraethyl ammonium hydroxide or morpholine as a structural agent. The conversion of ethylene was carried out at 473 K using SAPO-34. The selectivity for propylene, the rate of propylene production, and the lifetime of the catalyst were strongly influenced by the catalyst crystal size. The SAPO-34 with a similar to 2.5 mu m particle size had the highest selectivity for propylene (similar to 80%) up to a high conversion of ethylene (similar to 70%), while SAPO-34 with smaller particles had a longer catalyst lifetime, implying that catalyst deactivation was suppressed. The mole fraction of Si in the SAPO-34 framework with fixed particle size had little influence on the selectivity for propylene, indicating that the acid strength of SAPO-34 is independent of the Si mole fraction and all protons in SAPO-34 behave equivalently. Furthermore, the acid strength of protons determined by the measurements of NH3-TPD (temperature-programmed desorption) spectra did not depend on either the Si mole fraction or the SAPO-34 particle size. This result was also evident in the cracking rate of n-butane, which increased proportionally with increasing number of protons in SAPO-34. The number of protons generated by the incorporation of Si4+ into the SAPO-34 lattice increased proportionally, up to one Si atom introduced into every cage of SAPO-34, but did not continue to increase with further introduction of Si4+ into the lattice.