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On methanol to hydrocarbons reactions in a hierarchically structured ZSM-5 zeolite catalyst
Catalysis Today ( IF 5.3 ) Pub Date : 2017-09-18 , DOI: 10.1016/j.cattod.2017.09.032
Heejoong Kim , Hoi-Gu Jang , Eunhee Jang , Sung Jun Park , Taehee Lee , Yanghwan Jeong , Hionsuck Baik , Sung June Cho , Jungkyu Choi

Two type ZSM-5 catalysts (Si/Al ratio of ∼30) with different mesoporosity were synthesized by using a structure directing agent of tetra-n-butylphosphonium hydroxide. In particular, the molar compositions of ethanol and water in the synthetic precursor were changed in order to acquire the two type ZSM-5 catalysts. The resulting ZSM-5 catalysts were formed via the interconnection of very thin pillars or lamellae; (1) ∼6 nm thick with marked mesoporosity (H_30; high mesoporous ZSM-5) and (2) ∼13 nm thick without any considerable mesoporosity (L_30; low mesoporous ZSM-5). The pyridine-based acid titration reveals that H_30 had internal Brønsted acid sites similar to those in the commercially available ZSM-5 with a Si/Al ratio of 75 (referred to as C_75), though H_30 contained a large amount of external Brønsted acid sites. The methanol to hydrocarbons (MTH) reaction performance of these two ZSM-5 catalysts demonstrates that H_30 preferred to produce propene over ethene compared to C_75, while L_30 showed a very poor MTH performance mainly due to the lower amount of internal Brønsted acid sites. More desirably, a very short diffusional length (∼18,600 times lower than that in C_75) in H_30 considerably disfavored the aromatic dealkylation that is known to produce ethene. With this, H_30 allowed for achieving the ratio of propene to ethene as high as ∼9.1, which is, to the best of our knowledge, a highest value among the MTH results on ZSM-5 catalysts without any co-feed. Furthermore, ceria-doped H_30 not only enhanced the stability for the MTH reaction via a passivation of the external Brønsted acid sites, but also improved a propene to ethene ratio up to ∼15.0.



中文翻译:

ZSM-5分子筛催化剂中甲醇与碳氢化合物的反应

利用四-n结构导向剂合成了两种介孔率不同的ZSM-5型催化剂(Si / Al比为〜30)。-丁基氢氧化hydroxide。特别是,为了获得两种ZSM-5催化剂,改变了合成前体中乙醇和水的摩尔组成。所得的ZSM-5催化剂是通过非常薄的支柱或薄片相互连接而形成的。(1)约6 nm厚,具有明显的介孔率(H_30;高介孔ZSM-5),(2)约13 nm厚,没有明显的介孔率(L_30;低介孔ZSM-5)。基于吡啶的酸滴定法表明,H_30具有类似于商业上可获得的ZSM-5的内部布朗斯台德酸位,Si / Al比为75(称为C_75),尽管H_30包含大量外部布朗斯台德酸位。这两种ZSM-5催化剂的甲醇转化为碳氢化合物(MTH)的反应性能表明,与C_75相比,H_30较丙烯更优选生产丙烯。而L_30的MTH性能非常差,主要是因为内部的布朗斯台德酸性位点较少。更期望地,在H_30中非常短的扩散长度(比C_75的扩散长度低约18,600倍)大大不利于已知产生乙烯的芳族脱烷基化。这样一来,H_30可使丙烯与乙烯的比例达到约9.1,这是据我们所知,在没有任何共进料的ZSM-5催化剂上,MTH结果中的最高值。此外,掺杂二氧化铈的H_30不仅通过外部布朗斯台德酸位的钝化增强了MTH反应的稳定性,而且还提高了丙烯与乙烯的比例,最高可达约15.0。在H_30中比C_75低600倍)明显不利于已知可产生乙烯的芳族脱烷基反应。这样一来,H_30可使丙烯与乙烯的比例达到约9.1,这是据我们所知,在没有任何共进料的ZSM-5催化剂上,MTH结果中的最高值。此外,掺杂二氧化铈的H_30不仅通过外部布朗斯台德酸位的钝化增强了MTH反应的稳定性,而且还提高了丙烯与乙烯的比例,最高可达约15.0。在H_30中比C_75低600倍)大大不利于已知可产生乙烯的芳族脱烷基反应。这样一来,H_30可使丙烯与乙烯的比例达到约9.1,这是据我们所知,在没有任何共进料的ZSM-5催化剂上,MTH结果中的最高值。此外,二氧化铈掺杂的H_30不仅通过外部布朗斯台德酸位的钝化增强了MTH反应的稳定性,而且还提高了丙烯与乙烯的比例,最高可达约15.0。

更新日期:2017-09-18
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