Microporous mesoporous ZSM-12 zeolites: Synthesis by using a soft template and textural, acid and catalytic properties
Microporous mesoporous ZSM-12 zeolites: Synthesis by using a soft template and textural, acid and catalytic properties
复制标题
DOI：
10.1016/j.cattod.2014.09.025
复制
发表时间：
2015-04-01
期刊：
影响因子：
5.3
通讯作者：
Urquieta-Gonzalez, Ernesto A.
中科院分区：
文献类型：
--
作者：
Carvalho, Kele T. G.;Urquieta-Gonzalez, Ernesto A.
研究了两亲性有机硅烷TPOAC{[3-（三甲氧基硅基）丙基]十八烷基二甲基氯化铵}在合成过程中的添加量和结晶时间对微孔-介孔ZSM-12 （MMZ12）分子筛的结构、酸性和催化性能的影响。采用XRD/Rietveld细化、N-2吸附、SEM、EDX和NH3-TPD对样品进行表征，并以环己烷转化为模型反应验证了其作为酸性催化剂的性能。WAXRD数据表明，由于有机硅烷对MTW核形成和晶体生长的空间限制，合成时间短和TPOAC用量增加导致ZSM-12分子筛结晶度较差。另一方面，SAXRD和N-2吸附数据证明TPOAC首先生成伪有序介孔相，根据合成条件将其转化为结晶良好的分层型MMZ12分子筛。获得的样品具有相对较宽的中孔尺寸分布，平均直径接近4.0nm，外表面积略高于唯一的微孔ZSM-12，强酸位点数量较少。与传统的ZSM-12分子筛相比，MMZ12分子筛具有相似的环己烷转化率和较低的焦炭失活率，这是由于两种相反作用的平衡，较低的强酸性和HRTEM的存在证明了微孔和介孔之间的相互连接，减少了三维内部扩散的限制。常规ZSM-12分子筛的产率和选择性与环己烷在12环h分子筛上的转化一致，而微孔-介孔分子筛的C6饱和烃产率随着介孔体积的增加而增加，不利于饱和轻烃和不饱和轻烃的产率。(C) 2014 Elsevier B.V.版权所有
The influence of the amount of amphiphilic organosilane TPOAC {[3-(trimethoxy-silyl)propyl] octadecyldimethylammonium chloride} added in the synthesis and of the crystallization time in the textural, acid and catalytic properties of microporous-mesoporous ZSM-12 (MMZ12) zeolites was investigated. XRD/Rietveld Refinement, N-2 sorption measurements, SEM, EDX, and NH3-TPD were used to sample characterization and the performance as acid catalysts verified using the transformation of cyclohexane as a model reaction. WAXRD data showed that the usage of short synthesis times and increasing amounts of TPOAC in the synthesis led to ZSM-12 zeolites with poor crystallinity due to the organosilane steric constraints to MTW nuclei formation and crystal growth. On the other hand, SAXRD and N-2 sorption data evidenced that TPOAC firstly generates a pseudo-ordered mesoporous phase, which is transformed into well-crystalline hierarchical MMZ12 zeolites tailoring the synthesis conditions. Were obtained samples with a relatively broad mesopore size distribution having mean diameters close to 4.0nm and slightly higher external surface areas and lower amounts of strong acid sites than the only microporous ZSM-12 one. The MMZ12 zeolites showed similar cyclohexane conversion and lower deactivation rate due to coke formation than a conventional ZSM-12 that were attributed to a balance of two opposite effects, a lower strong acidity and the presence of HRTEM evidenced interconnected micropores and mesopores that reduce the 3D internal diffusion limitations. The yield and selectivity on the conventional ZSM-12 were coherent with the transformation of cyclohexane on 12-ring H-zeolites, nevertheless on the microporous-mesoporous ones the yield to C6 saturated hydrocarbons increased with the increase of the mesoporous volume, then disfavoring the yield to saturated and unsaturated light hydrocarbons. (C) 2014 Elsevier B.V. All rights reserved.