Synthesis of micron-particle-size HZSM-5 zeolite with different Si/Al ratio and its catalytic activity for toluene methanol alkylation reaction
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摘要: HZSM-5分子筛是甲苯甲醇烷基化制对二甲苯技术中常用的催化剂之一。本研究在引入晶种调节HZSM-5分子筛形貌的同时，改变分子筛合成前驱体溶液硅铝比调控分子筛酸性位，采用一步法直接制备孔结构和酸性质均适宜的微米级HZSM-5催化剂。通过X射线衍射、N2吸附-脱附、扫描电子显微镜、NH3程序升温脱附、吡啶红外等手段对HZSM-5分子筛的物相组成、孔结构参数、微观形貌、酸性质进行表征分析，考察了其在甲苯甲醇烷基化制对二甲苯反应中的催化性能，探讨了孔结构和酸性质对催化性能的影响。结果表明：在水热晶化方法中，合成溶液中的晶种和铝含量对分子筛的酸性质和形貌结构有显著的影响，其中5 μm晶粒的HZSM-5(150)分子筛催化剂因具有更长的扩散路径和更适宜的酸性位，在甲苯甲醇烷基化评价反应中表现出60% 的对二甲苯选择性和11% 的甲苯转化率。通过对HZSM-5分子筛的孔道和酸性位的精细调节有效提高了对二甲苯选择性，为择形催化剂的设计提供新的方法和思路。Abstract: HZSM-5 molecular sieve is one of the commonly used catalysts for the alkylation of toluene with methanol to para-xylene (PX). This study introduces a one-step method to directly prepare microscale HZSM-5 catalysts with suitable pore structure and acidity. Specifically, this paper combined crystal seed regulation of the morphology of HZSM-5 and adjusted the Si/Al ratios of the precursor solution for HZSM-5 synthesis to regulate the acidic phase of the HZSM-5. It analyzed the phase composition, pore structure parameters, microstructure, and acidity of HZSM-5 molecular sieve through X-ray diffraction, N2 adsorption desorption, SEM, NH3 temperature programmed desorption, pyridine infrared spectroscopy, etc. This study investigated the catalytic performance of HZSM-5 in the alkylation of toluene with methanol to PX, and explored the effects of pore structure and acidity on the catalytic performance. Results indicate that in the hydrothermal crystallization method, the crystal seeds and aluminum content in the synthesis solution have a significant impact on the acidity and morphology structure of the HZSM-5 molecular sieve. The HZSM-5 (150)molecular sieve catalyst with 5μm grain size exhibits 60% PX selectivity and 11% toluene conversion rate in the evaluation reaction of toluene methanol alkylation due to its longer diffusion path and more suitable acidic sites. By fine-tuning the pores and acidic sites of HZSM-5 molecular sieve, the selectivity for PX has been effectively improved, providing new methods and approaches for the design of shape-selective catalysts.
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Key words:
- Si/Al ratio /
- methanol toluene alkylation /
- HZSM-5 /
- crystal seed /
- para-xylene
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图 1 不同硅铝比样品的XRD谱图
Figure 1. XRD patterns of the HZSM-5 with different Si/Al ratio samples as prepared
图 2 不同硅铝比HZSM-5样品的SEM图
Figure 2. SEM images of HZSM-5 catalysts with different Si/Al ratio as prepared
图 3 不同硅铝比HZSM-5样品的N2吸-脱附曲线和孔径分布
Figure 3. N2 adsorption-desorption isotherms and pore size distribution of HZSM-5 catalysts with different Si/Al ratio as prepared
图 4 不同硅铝比HZSM-5样品的27Al MAS NMR光谱
Figure 4. 27Al MAS NMR spectroscopy of four HZSM-5 catalysts with different Si/Al ratio
图 5 不同硅铝比HZSM-5样品的NH3-TPD曲线
Figure 5. NH3-TPD curves of the HZSM-5 catalysts with different Si/Al ratio as prepared
图 6 HZSM-5样品在350 ℃的Py-IR谱图
Figure 6. IR spectra of the HZSM-5 samples after pyridine desorption at 350 ℃
图 7 HZSM-5样品的甲苯甲醇烷基化催化性能
Figure 7. Results of the alkylation of toluene with methanol over the HZSM-5 catalysts
表 1 不同硅铝比HZSM-5样品的结构特征
Table 1. Textural properties of the HZSM-5 catalysts with different Si/Al ratio
样品 SBET/(m2·g-1) Smicro/(m2·g-1) Sexternal/(m2·g-1) Vtotal/(cm3·g-1) Vmicro/(cm3·g-1) Vmeso/(cm3·g-1) 硅铝比 XRF XPS HZSM-5(25) 407.8 231.0 176.8 0.19 0.09 0.10 32 30 HZSM-5(50) 392.7 243.2 149.5 0.18 0.10 0.08 66 101 HZSM-5(100) 373.0 234.6 138.4 0.18 0.10 0.08 124 74 HZSM-5(150) 352.6 269.3 83.3 0.19 0.11 0.08 172 78 
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