【作者】 李航；

【导师】 张旭斌； 靳登超；

【作者基本信息】 天津大学 ， 化学工程， 2020， 硕士

【摘要】 苯二酚作为一种重要的化工中间体,在医药、染料、农药等诸多方面有着广泛地应用。苯酚羟基化作为一种绿色、高效的苯二酚生产工艺,受到了研究者们的广大关注。金属掺杂MFI型分子筛(主要包括TS-1、Fe-ZSM-5等)在该反应中表现出优越的催化性能。本文合成了不同金属掺杂的MFI型分子筛,研究了不同金属掺杂在苯酚羟基化中的催化性能,并通过脱硅后处理法在分子筛中引入介孔,进一步地提高了样品在反应中的催化活性。本文的主要工作如下:(1)通过一步水热法制备了S-1、ZSM-5、TS-1、Fe-S-1和Fe-TS-1,并使用X射线衍射(XRD)、氮气吸附脱附、场发射扫描电子显微镜(SEM)、傅里叶变换红外光谱(FT-IR)、紫外可见吸收光谱(UV-vis)等表征手段对这些材料的物化性能进行了全面的研究。在通过苯酚羟基化反应对这些样品进行催化性能的测试后,发现S-1和ZSM-5没有催化活性,骨架Fe和骨架Ti为苯酚羟基化反应的活性位点。相比于单金属掺杂的TS-1、Fe-S-1及其混合物,以双金属掺杂的Fe-TS-1作为催化剂的反应拥有更高的转化率和选择性,说明骨架Fe和骨架Ti在苯酚羟基化反应中存在协同效应。Fe-TS-1在五次反应后催化性能与第一次反应时相差不大,表现出了良好的循环稳定性。(2)合成了不同铁含量的Fe-TS-1,并以氢氧化钠作为碱性介质对所有样品进行了脱硅后处理,为样品引入了多级孔结构。通过各种表征手段,发现通过调节Fe的含量可以实现介孔的可控性,Fe含量越多,脱硅处理后所形成的介孔体积越少,介孔孔径也越小,说明铁物种在脱硅过程中可以有效地保护分子筛的骨架结构。研究发现样品中的少量氧化铁对于骨架并无明显的保护作用,铁物种对骨架的保护主要是由样品中的骨架铁所引起的。(3)通过脱硅法制备了一系列的多级孔MFI型分子筛,并将这些分子筛作为催化剂进行了苯酚羟基化反应。反应结果表明,脱硅处理为样品引入的大量介孔可以有效地提高其催化性能。其中,Fe-TS-1(50)-D表现出最优的催化性能,在苯酚双氧水摩尔比为1:1的情况下,苯酚的转化率可达到45.2%,苯二酚的选择性可以达到95.2%。在经过五次循环反应后,Fe-TS-1(50)-D仍然表现出良好的催化性能且晶体结构和金属分布基本不变,说明样品在脱硅处理后依旧拥有良好的循环稳定性。更多还原

【Abstract】 Dihydroxybenzenes are important chemical intermediates,which can be widely used in medicine,dyes,pesticides,etc.Phenol hydroxylation,as an environmental-friendly and efficient technology to produce dihydroxybenzenes,is recognized by many researchers.Metal-containing MFI-type zeolites,mainly including TS-1,Fe-ZSM-5,etc.,show good catalytic performance in the reaction.In this work,different metal-containing MFI-type zeolites were synthesized,and the catalytic activity of these samples in phenol hydroxylation was studied.In order to improve the catalytic activity of the samples,desilication method was used to introduce mesopores into the zeolites.The main works of this article are as follow:（1）S-1,ZSM-5,TS-1,Fe-S-1 and Fe-TS-1were synthesized through a one-step hydrothermal method.The physicochemical properties of the prepared samples were investigated by X-ray diffraction,N₂ adsorption-desorption,Field-emission scanning electron microscopy,Fourier transform infrared spectroscopy,Ultraviolet visible spectroscopy,etc.The catalytic performance of these samples was evaluated by conducting phenol hydroxylation experiments.It is found that S-1 and ZSM-5 showed no catalytic activity,while framework Fe and framework Ti were considered the active sites for phenol hydroxylation.Compared to TS-1,Fe-S-1 and their mixture,Fe-TS-1 showed higher conversion and selectivity,indicating there might be a synergistic effect between framework Ti and framework Fe in phenol hydroxylation.After the reaction was conducted five times,the catalytic performance of Fe-TS-1 was similar to that in the first reaction,which illustrated the sample owned good stability.（2）Fe-TS-1 samples with different iron content were prepared,and were desilicated by Na OH as the alkali media,which introduced mesopores into the samples.It is found that the manipulation of mesopores can be achieved by changing the amount of Fe.The more amount of iron species,the smaller volume and diameter of mesopores would be,indicating that the iron species could protect the structure of zeolite during Na OH desilication.By comparing the physicochemical properties of the acid-treated samples and the untreated samples after desilication process,the iron oxides,which could be removed by acid treatment,were found to show no protection to the skeleton structure of the zeolite.The protective effect of iron species on the structure was mainly caused by the framework Fe of the sample.（3）A series of hierarchical MFI-type zeolites were prepared through desilication and used as catalysts in phenol hydroxylation.The reaction results showed that the desilication process could effectively improve the catalytic performance by introducing abundant mesopores.Among all the samples,Fe-TS-1（50）-D showed the best catalytic performance with a phenol conversion of 45.2%and a dihydroxybenzenes selectivity of 95.2%,when the phenol/H₂O₂ molar ratio was 1:1.Fe-TS-1（50）-D still showed an excellent catalytic performance and basically unchanged metal distribution after the reaction was conducted five times,which confirmed the good stability and reusability of the sample.更多还原