【作者】 刘莉；

【导师】 曲虹霞； 俞马宏；

【作者基本信息】 南京理工大学 ， 化学工程（专业学位）， 2021， 硕士

【摘要】 等级孔沸石分子筛由于具有孔道结构多、传质阻力小、传输速率大等优点广泛应用于催化反应。目前,微孔SSZ-13是NH₃ selective catalytic reduction（NH₃-SCR）有效的商业催化剂,但存在扩散阻力大,高温下NH₃氧化过度等问题。因而等级孔SSZ-13逐渐引起了人们的关注,确定多孔沸石中的介孔在NH₃-SCR催化反应中的功能与作用至关重要。本论文采用双模板法,利用N,N,N-三甲基-1-金刚烷基氢氧化铵（TMAda OH）作为结构引导剂与C₁₆H₃₃-[N⁺-methylpiperdine](C₁₆MP)作为介孔剂,制备了一种孔隙可控的等级孔SSZ-13分子筛。对其结晶过程研究,发现C₁₆MP的引入改变了结晶凝胶中有机物和无机物之间的相互作用力,使分子筛的形貌由层状生长向块状堆叠演变。在诱导期和结晶初期,无定形蠕状前驱体溶解并重新结晶为CHA核,随后部分介孔向微孔转化。Horvath-Kawazoe（HK）与Barrett-Joyner-Halenda（BJH）孔径分布曲线表明,C₁₆MP可能诱导SSZ-13先形成较小的2 nm左右的晶内介孔,36 h处0.38 nm CHA特征微孔逐渐形成,48 h处,晶内介孔逐渐生长至3 nm。通过控制双模板TMAda OH/C₁₆MP的比例,孔尺度与孔径分布随之改变。SSZ-13（15:5）不仅具有CHA微孔结构,还包括3nm的晶内介孔与10 nm左右处的晶间介孔。随着C₁₆MP含量的增加,等级孔SSZ-13中4Si物种的含量增加,而Si/Al比值保持不变,说明介孔的引入对铝的分布产生了一定的影响。对等级孔Cu-SSZ-13催化剂进行脱硝活性研究,发现低温下,Cu-SSZ-13（20:0）由于微孔的限域NO活化表现出较好的NH₃-SCR催化性能。而高温下微介孔Cu-SSZ-13（15:5）的活性仅下降8%,是微孔催化剂的一半（16%）,主要是因为介孔的存在抑制非选择性氨氧化副反应的发生。高空速200000 h^-1下,微介孔Cu-SSZ-13（15:5）具有较高的催化活性,在温度窗口300-510°C内可保持90%以上的NO_x转化率。在800°C,水热老化8 h的严苛条件下,Cu-SSZ-13（15:5）仍可在270-540°C范围内保持90%以上催化活性。为了进一步分析等级孔Cu-SSZ-13出色的活性和水热稳定性的原因,对催化剂中铜活性位和酸性位点的性质进行研究。相较于Cu-SSZ-13（20:0）,Cu-SSZ-13（15:5）具有较高Cu²⁺/[Cu（OH）]⁺占比,与较少的Cu O_x簇。微孔和介孔之间的相互作用提高了NO和NH₃的吸附能力。介孔中Bronsted酸（B酸）与Lewis酸（L酸）分布范围较为广泛,包括弱酸,中强酸,强酸。此外,介孔提高了催化剂中的酸总量,但是对于不同含量的微介孔催化剂,B酸与L酸在介孔中的分布情况基本相似。更多还原

【Abstract】 Hierarchical zeolites are widely used in catalytic reactions due to the advantages of multiple pore structures,low mass transfer resistance and high transfer rates.Recently,the small-pore SSZ-13 is an effective commercial catalyst for NH₃ selective catalytic reduction（NH₃-SCR）,but suffers from the high diffusion resistance and the excessive oxidation of NH₃at high temperature.Therefore,the hierarchical SSZ-13 has gradually attracted people’s attention,and it is crucial to determine the role and function of the mesopore of porous zeolite catalysis for NH₃-SCR.In this paper,a pore-controllable hierarchical SSZ-13 was assembled using dual-template combining N,N,N-trimethyl-1-adamantammonium hydroxide（TMAda OH）as the structure-directing agent with C₁₆H₃₃-[N⁺-methylpiperdine](C₁₆MP)as the mesoporogen.The crystallization process was studied and it was found that the introduction of C₁₆MP leads to the transition of morphology of SSZ-13 from layered stacking to blocky stacking since the arrangement of organic and inorganic species in the crystallization gel.During induction and early crystallization stage,amorphous porous material dissolves and recrystallizes into CHA nucleus,followed by partial mesopores to micropores transformation.The Horvath-Kawazoe（HK）and Barrett-Joyner-Halend（BJH）pore size distribution curves indicate that C₁₆MP may induce SSZ-13 to form smaller intracrystal mesopores of about 2 nm first,and 0.38 nm CHA characteristic micropores gradually form at 36 h.At 48 h,the intracrystal mesopores gradually grow to 3 nm.Different dimensions and sizes of mesopores are created by controlling the ratio of dual-template TMAda OH/C₁₆MP.For SSZ-13（15:5）,it not only has the CHA microporous structure,but also includes 3 nm intracrystal mesopores and intercrytsal mesopores around 10 nm.With the increase of C₁₆MP,the content of 4Si species in the hierarchical SSZ-13 increases while the Si/Al ratio is maintained unchanged,suggesting that aluminum distribution may be regulated by the mesoporogen.The hierarchical pore Cu-SSZ-13 catalyst was studied for NH₃-SCR and it was found that at low temperature,Cu-SSZ-13（20:0）exhibits better NH₃-SCR catalytic performance due to the confined NO activation of the micropores.In contrast,the activity of hierarchical Cu-SSZ-13（15:5）at high temperature decreases only 8%,which is half（16%）of the microporous catalyst,mainly because the presence of mesopores inhibited the occurrence of non-selective ammonia oxidation side reactions.At a high space velocity of 200000 h^-1,the micro-mesoporous Cu-SSZ-13（15:5）has the high catalytic activity,and it can maintain more than 90%NO_x conversion within the temperature window of 300-510°C.Under the severe condition of hydrothermal aging at 800°C for 8 h,Cu-SSZ-13（15:5）can still maintain more than 90%catalytic activity in the range of 270-540°C.In order to further analyze the reason for the excellent activity and hydrothermal stability of hierarchical Cu-SSZ-13,the properties of copper active sites and acid sites in the catalyst were studied.Compared with Cu-SSZ-13（20:0）,Cu-SSZ-13（15:5）has a higher Cu²⁺/[Cu（OH）]⁺ratio and fewer Cu O_xclusters.The interaction between micropore and mesopore improves the adsorpbility of NO and NH₃.The distribution of Bronsted acid sites（B acid sites）and Lewis acid sites（L acid sites）in mesopores are relatively wide,including weak acid,medium strong acid,and strong acid.In addition,mesopores increase the total amount of acid in the catalyst,but the distributions of B acid and L acid in the mesopores are essentially similar for different micro-mesoporous catalysts.更多还原