【作者】 高戈；

【导师】 胡常伟；

【作者基本信息】 四川大学 ， 生物质化学与工程， 2022， 博士

【摘要】 随着化石资源日渐衰竭、其开采和利用过程中的环境污染日益加剧,开发绿色环保的可再生资源及其相关技术路线已成为研究重点。其中,木质纤维类生物质来源广泛、储量丰富,是植物通过光合作用吸收CO₂合成的有机质。因此,以木质纤维类生物质为原料制备高值化学品、高品质燃油和功能化材料,可实现从源头生成到终端消耗的CO₂循环,有助于实现我国“双碳”目标。木质纤维类生物质主要由纤维素、半纤维素和木质素组成,其中,纤维素和半纤维素作为两类多糖组分,通过水解或酶解可获得单糖（如葡萄糖、木糖）,进一步转化还可获得以呋喃醛（如糠醛、5-羟甲基糠醛）为代表的平台化合物。葡萄糖、木糖、糠醛和5-羟甲基糠醛都含有丰富的官能团,可通过加氢、脱水、氧化、酯化、分解等反应制备多种高附加值的下游化学品。若保留上述单糖和呋喃醛化合物的已有特征结构制备高附加值化学品,即可充分利用生物质天然结构、减少复杂化学键断裂或生成以及降低不必要的反应能耗。在众多糖类或呋喃醛化合物的转化方法中,催化加氢是一种常规的手段;尤其是选择性催化加氢,能够最大化反应底物的原子利用率,例如,保留单糖结构中已有多羟基官能团、呋喃醛结构中已有呋喃环结构,将其各自结构中羰基加氢,可分别制得多元醇化合物和呋喃醇化合物。当前已报道的研究工作还存在反应温度高、所需氢气压力大、有机溶剂大量使用、产物选择性较低、催化剂稳定性不佳等不足,制约了上述催化过程的实际应用。所以,亟需发展能在水相温和条件下高效高选择加氢转化单糖和呋喃醛化合物的催化反应体系。本论文围绕Pt和PtNi合金为催化活性物种,以及SBA-15和水滑石衍生物为载体,通过水热合成、等体积浸渍等方法,制备了系列金属高分散的负载型铂基催化剂,探究了催化剂在催化葡萄糖和木糖加氢制备多元醇和呋喃醇化合物、以及呋喃醛选择性加氢制备呋喃醇化合物的性能。详细研究了催化剂中金属分散度、金属物种价态分布、载体结构及性质等对单糖和呋喃醛化合物的催化加氢选择性的影响规律、以及其催化加氢反应路径和机理。通过优化催化剂结构和催化实验参数,实现了底物高效转化并较高选择性地获得目标化学品。一、PtNi/SBA-15催化糠醛和5-羟甲基糠醛中羰基选择性加氢制备呋喃醇通过水热合成法制备PtNi合金纳米颗粒,再通过含表面活性剂的浸渍法,利用SBA-15较高的比表面积和介孔孔道结构分散PtNi合金,制得PtNi/SBA-15催化剂。与常规浸渍法制备的Pt/SBA-15、Ni/SBA-15以及Pt-Ni/SBA-15催化剂相比,PtNi/SBA-15催化剂在保持SBA-15介孔结构的同时,PtNi合金纳米颗粒在载体上分散更均匀,其平均粒径约为5.8 nm,粒径分布集中于5.5～6.5 nm范围;合金态PtNi活性中心更有利于产生富含电子的Pt^δ-物种,Pt^δ-物种有助于反应底物中羰基的选择性吸附和催化加氢,促进呋喃醛化合物中羰基高选择性加氢,制得呋喃醇化合物。在接近室温（303 K）的水相温和条件下,PtNi/SBA-15催化剂能够催化糠醛选择性加氢制备糠醇（选择性77.0%）,糠醛的转化率为83.9%,其转化频数为1410 h^-1;PtNi/SBA-15催化剂也可以催化5-羟甲基糠醛选择性加氢制备呋喃二甲醇（选择性81.9%）,5-羟甲基糠醛的转化率为83.3%,其转化频数为1350 h^-1。PtNi/SBA-15催化剂在催化糠醛和5-羟甲基糠醛加氢的反应中催化稳定性高且易分离,可在五次重复使用后依旧保持较高的催化效率。二、PtNi/SBA-15催化葡萄糖和木糖转化为C₆、C₅多元醇和呋喃醇将PtNi/SBA-15催化剂拓展应用至一锅法催化葡萄糖或木糖制备C₆、C₅多元醇和呋喃醇,发现在1.5 MPa H₂气氛下,PtNi/SBA-15能够高效催化的葡萄糖和木糖转化为对应衍生的多元醇和呋喃醇,在473 K温度下反应2 h后,单糖的转化率均可>99%。反应温度可调控PtNi/SBA-15催化体系催化单糖加氢产物的选择性,在较低温条件（413～473 K）下可制备以C₆、C₅多元醇为主的产物,而在较高温条件（493～533 K）下得到以呋喃醇为主的产物。反应温度显著影响PtNi/SBA-15催化体系酸性,进而调控单糖直接加氢或先脱水再加氢的不同加氢反应路径;当温度较低时,催化体系酸性较弱,单糖易直接加氢生成对应C₆、C₅多元醇,当温度较高时,由酸催化的脱水反应优先进行,单糖先脱水生成呋喃醛,然后呋喃醛再加氢至呋喃醇。PtNi/SBA-15催化剂稳定性良好、可重复利用,PtNi/SBA-15催化体系可成功拓展至葡萄糖和木糖加氢转化反应,并为木质纤维素中单糖的一锅选择性加氢转化提供理论依据。三、水滑石衍生物负载Pt基催化剂用于糠醛高选择性加氢制备糠醇通过等体积浸渍法,利用水滑石衍生物的特殊层状结构将Pt物种高效分散,制得水滑石衍生物负载Pt基催化剂（Pt/HT）。Pt/HT催化剂呈现由多个独立片层组成的花状形貌,其独立片层直径约50 nm;Pt纳米颗粒在Pt/HT上高度分散,其平均粒径仅1.5 nm,且粒径集中分布在1～2 nm范围。通过对比由不同载体相同方法制备的Pt基催化剂,发现Pt/HT催化剂中Pt纳米颗粒更小、Pt⁰物种比例更高,则更利于选择性催化羰基加氢。在303 K的温和条件下,Pt/HT可以高效、高选择性地催化糠醛加氢至糠醇（选择性>99%）,糠醛转化率为99.9%,其转化频数为204.6 h^-1。Pt/HT对糠醛中羰基的选择性吸附促进了羰基高选择性加氢,而Pt/HT对糠醇较弱的吸附性可让糠醇生成后更易从催化剂上离去,暴露更多用于糠醛中羰基的吸附和加氢的催化活性位点,使得糠醛持续、高效选择性加氢。Pt/HT催化剂还可以在303 K的温和条件下,分别催化5-羟甲基糠醛和5-甲基糠醛选择性加氢,制备呋喃二甲醇（选择性94.5%）和5-甲基-2-呋喃甲醇（选择性>99%）,证实了Pt/HT催化体系在羰基选择性加氢过程中的普适性。Pt/HT催化剂在四次重复使用后依然保持了优秀的催化性能（糠醛的转化率>97.8%和糠醇的选择性>96.3%）。反应条件温和、催化效率高和稳定性好的Pt/HT催化体系为糠醛选择性加氢的工业化应用提供了可能。四、水滑石衍生物负载PtNi合金催化剂用于葡萄糖加氢制备多元醇通过微波辅助,水热法合成了PtNi合金纳米颗粒,并将其负载于水滑石衍生物制备了负载型PtNi合金催化剂（PtNi/HT）,微波辅助下的水热法相比于传统水热法不仅大大缩短了PtNi合金的制备时长,且制得合金纳米颗粒平均直径低至2.7 nm。PtNi合金的Pt^δ--Ni^δ+电子效应,以及水滑石衍生物载体层状双金属氢氧化物结构,均有效促进了催化葡萄糖加氢的性能。在2 MPa H₂气氛下,PtNi/HT可催化葡萄糖在393 K的水相中加氢为数种多元醇化合物,葡萄糖转化率为95.7%,多元醇总选择性为90.1%。在PtNi/HT催化体系中,反应温度可调控催化葡萄糖加氢产物的选择性;较低反应温度（333～373 K）下,葡萄糖加氢反应产物以己糖醇为主;较高反应温度（373～413 K）则有利于进行逆羟醛缩合反应断裂葡萄糖结构中的C-C键,生成C₂～C₄低碳多元醇。总结提出了PtNi/HT催化葡萄糖制备多元醇的主要反应路径:1、葡萄糖直接加氢至山梨醇;2、葡萄糖先异构化为果糖,再加氢至山梨醇和甘露醇;3、葡萄糖直接逆羟醛缩合断裂C_α-C_β键,生成赤藓糖和乙醇醛,再加氢至赤藓醇和乙二醇;4、葡萄糖先异构化为果糖或逆羟醛缩合为赤藓糖,并再进行逆羟醛缩合反应生成C₂～C₃醛酮（赤藓糖以C₂+C₂断裂,而果糖以C₃+C₃断裂）,最后,上述C₂～C₃醛酮中间体进一步加氢为C₂～C₃低碳多元醇。更多还原

【Abstract】 With the exhaustion of fossil resources and the related environmental issues,exploring renewable resources and developing the utilization technologies have been the research focus worldwide.Lignocellulosic biomass is the organic matter synthesized by plants absorbing CO₂ through photosynthesis.Therefore,the carbon recycle from source generation to terminal consumption can be realized by using lignocellulosic biomass as raw material to prepare high-value chemicals,high-quality fuels and functional materials,contributing to achieve the Chinese carbon peaking and carbon neutrality goals.Lignocellulosic biomass is mainly composed of cellulose,hemicellulose and lignin.Among them,the cellulose and hemicellulose as two kinds of polysaccharide components,can be converted to monosaccharides（such as glucose and xylose）via hydrolysis or enzymatic hydrolysis.Then,glucose and xylose could be further converted to furaldehyde platform compounds（such as furfural,5-hydroxymethylfurfural）.Glucose,xylose,furfural and 5-hydroxymethylfurfural（HMF）can be used to prepare a variety of high-value downstream chemicals through hydrogenation,dehydration,oxidation,esterification and decomposition.Retaining the characteristic structures of the monosaccharides and furaldehydes to prepare high value-added chemicals,the energy consumptions for breaking or forming complex chemical bond can be reduced,making full use of the natural structures of biomass.Catalytic hydrogenation is a common method for the conversion of monosaccharides or furaldehydes into valuable chemicals,which can maximize the atomic utilization rate of the reaction substrates.For example,polyols can be prepared by reserving the existing polyhydroxyl groups and hydrogenating the aldehyde groups in monosaccharide.There are still some shortcomings in the reported catalysis process,such as high reaction temperature,high hydrogen pressure,large amount of organic solvents,low product selectivity and moderate catalyst stability,which restrict the practical application.Therefore,it is important to develop an efficient catalytic system with high product selectivity under mild conditions in aqueous phase.In this paper,series of supported platinum-based catalysts with high metal dispersion were prepared by hydrothermal synthesis and impregnation.In detail,Pt and PtNi alloys were active species,while SBA-15 and hydrotalcite-derivatives were selected as carriers.Then,the catalytic performances of these catalysts in the hydrogenation of glucose,xylose,furfural and HMF have been evaluated.The effects of metal dispersion,metal species,carrier structure and properties on the hydrogenation selectivities of monosaccharides and furaldehydes were studied,and the reaction path and mechanism of catalytic hydrogenation were illustrated.The catalyst structures and experimental parameters were optimized to achieve the efficient conversion and high selectivity of target chemicals.I.PtNi/SBA-15 catalyzed selective hydrogenation of furfural and 5-hydroxymethylfurfural to furfuryl alcohol and 2,5-dihydroxymethylfuranPtNi alloy nanoparticles were prepared by hydrothermal synthesis method,and then SBA-15 with high specific surface area and mesoporous channel structure was employed to disperse PtNi alloy to obtain PtNi/SBA-15 catalyst by impregnation method.Compared with Pt/SBA-15,Ni/SBA-15 and Pt-Ni/SBA-15 catalysts prepared by the conventional impregnation method,PtNi/SBA-15 catalyst maintained the SBA-15 mesoporous structure,resulting in the PtNi alloy nanoparticles（5.8 nm of average particle size）dispersed more evenly on the support.The PtNi alloys favored the generation of electron-rich Pt^δ-species,which was conducive to the selective adsorption and catalytic hydrogenation of aldehyde groups of the reaction substrates.PtNi/SBA-15 catalyst catalyzed 83.9%of furfural into furfuryl alcohol with 77.0%of selectivity at room temperature（303 K）in aqueous phase,and the conversion frequency is 1410 h^-1.PtNi/SBA-15 catalyst could also catalyze the selective hydrogenation of HMF to 2,5-dihydroxymethylfuran（DHMF,selectivity:81.9%）,where the conversion of HMF is 83.3%and the conversion frequency is 1350 h^-1.PtNi/SBA-15 catalyst exhibited high catalytic stability during five recycles in the catalytic hydrogenation of furfural and 5-hydroxymethylfurfural.II.PtNi/SBA-15 catalyzed the conversion of glucose and xylose to C₆,C₅ polyols and furfuryl alcoholsPtNi/SBA-15 catalyst was applied to the one-pot catalytic of glucose or xylose to C₆,C₅ polyols and furfuryl alcohols.After 2 h reaction at 473 K,the conversion of monosaccharides could be>99%under 1.5 MPa H₂ atmosphere.The selectivities of the hydrogenation products over PtNi/SBA-15 catalytic system were controlled by reaction temperature.The reaction temperature significantly affected the acidity of PtNi/SBA-15 catalytic system,and then regulated the reaction paths of monosaccharides hydrogenation.At low temperature（413-473 K）,the catalytic system is less acidic,and monosaccharides are easy to be directly hydrogenated to C₆,C₅polyols.At high temperature（493-533 K）,the acid-catalyzed dehydration reaction takes precedence,and the monosaccharides are firstly dehydrated to form furaldehyde,and then furaldehyde is hydrogenated to furfuryl alcohols.PtNi/SBA-15 catalyst system can be successfully extended to the hydrogenation of glucose and xylose,and provide theoretical basis for the selective hydrogenation of monosaccharides in lignocellulose.III.Hydrotalcite-derived Pt-based catalyst for the highly selective hydrogenation of furfural to furfuryl alcoholThe hydrotalcite-derived Pt-based catalyst（Pt/HT）was prepared by incipient impregnation method,and the Pt species were efficiently dispersed by the special layered structure of hydrotalcite derivative.The Pt/HT catalyst presented a flower-like morphology composed of multiple independent lamellae with about 50 nm diameter.Pt nanoparticles were highly dispersed on Pt/HT,with the average particle size of only1.5 nm,and the particle sizes were concentrated in the range of 1～2 nm.Comparing to the other Pt-based catalysts prepared by the same method with different supports,it was found that the small Pt nanoparticles and high proportion of Pt⁰ species on Pt/HT catalysts were favorable for selective hydrogenation of carbonyl.At 303 K,Pt/HT catalyzed the hydrogenation of furfural to furfuryl alcohol with high efficiency and selectivity（selectivity:>99%）,where the furfural conversion was 99.9%and the conversion frequency was 204.6 h^-1.The selective adsorption of the carbonyl group in furfural on Pt/HT promoted the highly selective hydrogenation of the carbonyl group,while the weak adsorption of furfuryl alcohol on Pt/HT benefited to the rapid desorption of furfuryl alcohol,exposing more catalytic active sites for the continuous and efficient selective hydrogenation of furfural.In addition,Pt/HT catalyst could also catalyze the selective hydrogenation of HMF and 5-methylfurfural at 303 K,respectively,to produce DHMF（selectivity 94.5%）and 5-methyl-2-furanmethanol（selectivity>99%）,confirming the general applicability of Pt/HT catalyst system in the selective hydrogenation of carbonyl.The Pt/HT catalyst maintained excellent catalytic performance after four runs（furfural conversion>97.8%and furfuryl alcohol selectivity>96.3%）.The Pt/HT catalytic system with mild reaction conditions,high catalytic efficiency and good stability provides a possibility for the industrial application of selective hydrogenation of furfural.IV.Hydrotalcite-derived PtNi alloy catalyst for glucose hydrogenation to polyols PtNi alloy nanoparticles were synthesized by microwave-assisted hydrothermal method,and then dispersed on hydrotalcite derivatives to prepare supported PtNi alloy catalyst（PtNi/HT）.The microwave-assisted hydrothermal method not only greatly shortened the preparation time of PtNi alloy,but also decreased the average diameter of the alloy nanoparticles（2.7 nm）.The Pt^δ--Ni^δ+electron effect of PtNi alloy and the layered double hydroxides structure of hydrotalcite derivative support effectively promoted the catalytic performance of glucose hydrogenation.PtNi/HT could catalyze the hydrogenation of glucose to several polyols in aqueous phase at 393 K in 2 MPa H₂ atmosphere,where the conversion of glucose is 95.7%and the total selectivity of polyols is 90.1%.In the PtNi/HT catalytic system,the selectivities of glucose hydrogenation products were controlled by reaction temperature.At lower reaction temperature（333～373 K）,hexitol was the main product of glucose hydrogenation.While higher reaction temperature（373～413 K）was favorable for the retrograde aldol condensation reaction to break the C-C bond in the glucose structure and generate C₂～C₄ low carbon polyols.Besides,the main reaction paths of glucose to polyols catalyzed by PtNi/HT were summarized:1.direct hydrogenation of glucose to sorbitol;2.glucose isomerization into fructose,and then hydrogenation to sorbitol and mannitol;3.breaking the C_α-C_βbond of glucose to forming erythritose and glycolaldehyde,and further hydrogenation to erythritol and ethylene glycol;4.breaking the C_α-C_βbond of fructose and erythritose（erythritose:C₂+C₂,while fructose:C₃+C₃）,and then hydrogenation to C₂～C₃ low carbon polyols.更多还原