【作者】 姜超；

【导师】 褚海斌；

【作者基本信息】 内蒙古大学 ， 化学， 2022， 硕士

【摘要】 甘油是酯交换生产生物柴油的主要副产物,通过简单的催化反应将甘油选择性氧化为高附加值的化学品,是实现资源可持续利用的一种绿色可行性策略。本研究以高活性的Pt为主要催化氧化活性位点,利用Sn改性分子筛和片状氧化铈的高比表面积、酸碱性质、氧空位、缺陷位点等特点,设计制备了高效Pt基催化剂,实现催化甘油氧化的高活性和对二羟基丙酮、乳酸等特定产物的高选择性。同时对分子筛酸性性质的调控方法及其在催化反应中的作用机制、金属间相互作用、氧空位对催化活性的影响机制等进行了研究,主要研究内容及结论如下:（1）水热合成一系列不同Sn含量的Sn-MFI分子筛,以其为载体制备了PtCu/Sn-MFI双功能催化剂,该催化剂以接力式反应的方式将甘油转化为二羟基丙酮。其中,以Cu作促进剂的Pt位点氧化甘油的伯羟基为甘油醛,载体中的路易斯酸性位点——Sn位点再催化甘油醛重排为二羟基丙酮,Cu和Sn的协同作用使得该催化剂将甘油高效转化为二羟基丙酮。在该催化剂中,Pt与Cu之间的电子相互作用及晶格畸变和PtCu合金的形成大大提高了催化剂的催化活性。同时,本工作通过控制Sn的含量,调控分子筛Lewis酸和Br（?）nsted酸的比例,阻断了二羟基丙酮继续转化为乳酸的反应路径,实现对二羟基丙酮的高选择性（66.7%）和高产率（38.7%）。（2）以层状氢氧化铈为前体,以不同温度煅烧得到了超薄片状氧化铈（LCeO-T,T为煅烧温度）,通过表征分析发现,煅烧温度越高,组成LCeO的氧化铈颗粒越大,Ce³⁺含量越高,其相应的氧空位越多。以LCeO-T为载体,通过Na BH₄还原法负载铂制备Pt/LCeO-T催化剂。在对反应条件进行优化后,5%Pt/LCeO-400℃在无碱条件下,对甘油醛的选择性可达61.7%;1.5%Pt/LCeO-600℃在碱性条件下,对乳酸的选择性可达63.2%,且其催化活性和乳酸选择性均显著高于短棒状氧化铈、长棒状氧化铈和纳米立方体状氧化铈负载的Pt催化剂,这可能与LCeO较大的比表面积、更加丰富的氧空位和缺陷等特点有关。最后还将Sn-MFI引入Pt/LCeO催化剂中,提高了其在无碱条件下的催化活性,并将甘油氧化的主产物甘油醛转化为二羟基丙酮,再次证明了Sn-MFI对甘油醛异构化反应的催化作用,体现其普适性。更多还原

【Abstract】 In the process of transesterification production of biodiesel,glycerol is the main by-product of transesterification production of biodiesel.Selective oxidation of glycerol into high value-added chemicals through simple catalytic reaction is a feasible green strategy to achieve sustainable resource utilization.Herein,Pt with high activity as the main catalytic oxidation active site,based on the characteristics of Sn-modified zeolite and flake ceria,such as high specific surface area,acid-base properties,oxygen vacancy and defect sites,a series of high-efficiency Pt-base catalyst were designed and prepared.These catalysts have high activity to catalyze the oxidation of glycerol and high selectivity to specific products such as dihydroxyacetone and lactic acid.At the same time,the method for regulating acidic properties of zeolite,the mechanism of acid site of zeolite in catalytic reaction,intermetallic interaction and the influence mechanism of oxygen vacancy on catalytic activity were studied.The main research contents and conclusions are as follows:（1）A series of Sn-MFI with different Sn contents were synthesized by hydrothermal method.PtCu/Sn-MFI bifunctional catalyst which converted glycerol to dihydroxyacetone in a relay reaction mode was prepared by using Sn-MFI as a carrier.In this catalyst,Pt sites with Cu as promoter oxidize the primary hydroxyl of glycerol to glyceraldehyde.Then the Sn Lewis acid sites catalyze glyceraldehyde rearrangement into dihydroxyacetone.The synergistic effect of Cu and Sn makes the catalyst efficiently catalyze the conversion of glycerol into dihydroxyacetone.In this catalyst,the electron interaction between Pt-Cu and the formation of lattice distortion and PtCu alloy greatly improve the catalytic activity of the catalyst.At the same time,by controling the content of Sn,the ratio of Lewis acid and Br（?）nsted acid in zeolite was adjusted,the reaction path of dihydroxyacetone further conversion to lactic acid was blocked and the high selectivity（66.7%）and high yield（38.7%）of dihydroxyacetone were achieved.（2）Using layered cerium hydroxide（LCe H）as the precursor,ultra-thin lamellar ceria nanosheet（LCeO-T,T is the calcination temperature）was obtained by calcination at different temperatures.Through characterization analysis,it was found that with the increase of calcination temperature,the size of cerium oxide particles composed of LCeO increased and the content of Ce³⁺increased which means the oxygen vacancy concentration may also increase.Pt/LCeO-T catalysts were prepared with LCeO-T as supporter through the reduction of Na BH₄.Under the optimized reaction conditions,the selectivity of glyceraldehyde can reach 61.7%in base-free condition over5%Pt/LCeO-400℃catalyst and the selectivity of lactic acid can reach 63.2%in base condition over the 1.5%Pt/LCeO-600℃catalyst.The catalytic activity and lactic acid selectivity of 1.5%Pt/LCeO-600℃were significantly higher than short rod-like ceria,long rod-like ceria and nano-cubic ceria supported Pt catalysts.This may be related to the larger specific surface area,more abundant oxygen vacancies and defects of LCeO.Finally,Sn-MFI was introduced into Pt/LCeO catalyst,which improved the catalytic activity of the catalyst under the base-free condition and successfully converted the main product of glycerol oxidation from glyceraldehyde into dihydroxyacetone.That proved the catalytic effect of Sn-MFI on the isomerization of glyceraldehyde again and reflects its universality.更多还原