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Performance of hierarchical HZSM-5 zeolites prepared by NaOH treatments in the aromatization of glycerol

机译：NaOH治疗在甘油芳族化芳族化中制备的分层HZSM-5沸石的性能

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摘要

A series of hierarchical HZSM-5 zeolites were prepared by post-synthesis modification of conventional bulk crystals of HZSM-5 zeolite with sodium hydroxide (NaOH) solution at different concentrations. These micro-mesoporous composite molecular sieves were characterized by powder X-ray diffraction, transmission electron microscopy, nitrogen adsorption, Fourier transform infrared (FT-IR) spectroscopy techniques and pyridine FT-IR to investigate the changes in crystallinity, acidity, morphology and textural property of HZSM-5 zeolite before and after alkaline treatment. The catalytic performances of these hierarchical HZSM-5 zeolites were evaluated by the aromatization of glycerol with methanol as the solvent, which was a promising route for converting renewable glycerol and methanol into high value aromatics. Substantial mesoporosity with sizes centered at around 4 nm could be generated for HZSM-5 zeolites after treatment with mild NaOH solution (<= 0.4 M), coupled with improved retained microporosity, resulting in great improvements in catalytic lifetime and selectivity to benzene, toluene and xylene (BTX) aromatics during the reaction of glycerol to aromatics. Although the larger mesopore surface areas were achieved when treated with NaOH concentrations that were higher than 0.5 M, the HZSM-5 structure was partly damaged, leading to the reduction of catalytic lifetime and selectivity to BTX aromatics. The HZSM-5 treated with 0.3 M NaOH solution was found to be the optimum catalyst for the transformation of glycerol/methanol to aromatics, producing a nearly two-fold increase in BTX aromatics (carbon yields of 25.18%) and three-fold improvement in catalyst lifetime (12.5 h) when compared to the parent microporous HZSM-5 (13.9% carbon yields of BTX aromatics and catalyst lifetime of 4 h). These improved catalytic performances are mainly attributed to the optimized bimodal micro-mesoporous HZSM-5 zeolite during the alkali treatment, which retained sufficient micropores that have the capacity for aromatization and also more mesopores were created that would shorten the average diffusion path lengths, increase the accessibility to the acid sites and facilitate the transportation of large molecules, e.g., glycerol and carbon precursors, during the aromatization of glycerol.
机译：通过在不同浓度下用氢氧化钠（NaOH）溶液的HzSM-5沸石的常规散装晶体后常规散装晶体后的合成改性来制备一系列分层HZSM-5沸石。这些微介孔复合分子筛通过粉末X射线衍射，透射电子显微镜，氮吸附，傅里叶变换红外（FT-IR）光谱技术和吡啶FT-IR来研究结晶度，酸度，形态学和纹理的变化碱性处理前后HZSM-5沸石的性质。通过用甲醇作为溶剂的甘油芳香化评价这些等级HZSM-5沸石的催化性能，这是将可再生甘油和甲醇转化为高价值芳烃的有希望的途径。在用温和的NaOH溶液（<= 0.4m）处理后，可以为HzSM-5沸石产生大约4nm的大小的尺寸尺寸，与改善的保留微孔隙相结合，导致催化寿命和对苯，甲苯的选择性的大改善二甲苯（BTX）甘油在甘油对芳烃反应过程中的芳烃。尽管在用高于0.5μm的NaOH浓度处理时实现了较大的中孔表面区域，但是HZSM-5结构部分受损，导致催化寿命和对BTX芳烃的选择性的降低。发现用0.3M NaOH溶液处理的HZSM-5是用于将甘油/甲醇转化为芳烃的最佳催化剂，产生近似两倍的BTX芳烃（碳产量为25.18％）和三倍的改善与亲本微孔HZSM-5相比，催化剂寿命（12.5H）（13.9％的BTX芳烃碳产率和4小时的催化剂寿命）。这些改善的催化性能主要归因于在碱处理期间优化的双峰微介孔HzSM-5沸石，其保留了足够的微孔，其具有芳族化能力，并且产生更多的中孔，这将缩短平均扩散路径长度，增加在甘油芳族化期间，对酸部位的可用性并促进大分子的运输，例如甘油和碳前体。

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  • 来源
    《RSC Advances》 |2015年第78期|共8页
  • 作者

    Xiao Weiyin; Wang Fei; Xiao Guomin;

  • 作者单位

    Southeast Univ Sch Chem &

    Chem Engn Nanjing 211189 Jiangsu Peoples R China;

    Southeast Univ Sch Chem &

    Chem Engn Nanjing 211189 Jiangsu Peoples R China;

    Southeast Univ Sch Chem &

    Chem Engn Nanjing 211189 Jiangsu Peoples R China;

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  • 正文语种 eng
  • 中图分类 化学;
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