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功能化氧化石墨烯负载贵金属制备Pickering乳液用于肉桂醛选择性加氢反应
论文作者:童鞋论文网  论文来源:www.txlunwenw.com  发布时间:2019/10/12 8:24:52  

摘要:肉桂醛选择性加氢作为最典型的反应之一,广泛用于合成药物,香水和化工中间体。尽管使用水作为溶剂更加环保,但是在水和肉桂醛之间存在不混溶性,因此导致差的传质。因此,高效环保的催化肉桂醛选择性C=C加氢是目前的研究热点。另一方面,由于肉桂醛中的C=O的键能比C=C的键能大,而且二者具有共扼作用,使得C=O上选择性加氢比C=C键难。除了活性金属对肉桂醛选择性C=O加氢有着影响外,肉桂醛分子在催化剂上的吸附取向对选择性也是一种重要的影响因素。本文利用有机硅烷功能化氧化石墨烯负载贵金属制备Pickering乳液用于水为介质的肉桂醛选择性C=C和C=O加氢反应中。

(1) 利用三甲氧基甲基硅烷对氧化石墨烯进行疏水改性后负载Pd纳米粒子制备Pd/GO-Si催化剂。采用XRD、TEM、FT-IR、XPS、Raman、TG等技术手段对催化剂进行表征。将催化剂,水与肉桂醛进行超声,搅拌,制备Pickering乳液,用光学显微镜对Pickering乳液体系进行表征。将制备好的Pickering乳液体系用于肉桂醛选择性C=C加氢反应中。实验结果表明,在80 °C,2 MPa H2下反应20min,肉桂醛(CAL)的转化率可达99%,氢化肉桂醛(HCAL)的选择性可达84%,催化效果明显好于Pd/GO催化剂。Pd/GO-Si催化剂对不同底物仍然具有非常好的催化效果,并且具有良好的重复使用性。优异的催化活性是由于Pickering乳液增加催化剂与反应物之间的接触面积以减少非均相催化体系中的传质阻力,同时,对催化剂表面进行疏水改性,增加反应物分子在催化剂表面的吸附量,提高了催化活性。

(2) 用甲基,丙基,苯基,己基,辛基,十二烷基,十六烷基和氨丙基有机硅烷分别对氧化石墨烯进行改性后分别负载Pt纳米颗粒制得Pt/GO-Si催化剂。采用XRD、TEM、FT-IR、XPS、TG等技术手段对催化剂进行表征。将催化剂,水与肉桂醛进行超声,搅拌,制备Pickering乳液,用光学显微镜对乳液体系进行表征。将制备好的Pickering乳液体系用于肉桂醛选择性C=O加氢反应中。实验结果表明,在40 °C,2 MPa H2下反应2 h,由三甲氧基辛基硅烷改性后制备出的催化剂Pt/GO-Si-C8表现出最佳的活性,肉桂醛的转化率达到91%,肉桂醇的选择性达到84%,高于其他硅烷改性后的催化剂。这是由于适中的碳链长度会控制肉桂醛在催化剂表面的吸附方向,使得醛基直接接触Pt纳米粒子,从而提高催化活性。

As one of the most fundamentalreactions,selective hydrogenation of cinnamaldehyde is extensively used in thesynthesis of pharmaceuticals, perfumes and chemical intermediates. Most of thesolvents employed in the selective hydrogenation of cinnamaldehyde are organiccompounds. Although the use of water as a solvent is more eco-friendly, howeversuffering from immiscibility between water and cinnamaldehyde, thus resultingin a poor mass transfer. Therefore, the efficiently and eco-friendly catalyticcinnamaldehyde selective C=C hydrogenation reaction is a research hotspot. Onthe other hand, since the bond energy of C=O in cinnamaldehyde is larger thanthat of C=C, and the two have a conjugate effect, selective hydrogenation onC=O is more difficult than C=C bond. In addition to the effect of the activemetal on the selective C=O hydrogenation of cinnamaldehyde, the adsorptionmethod of the cinnamaldehyde molecules on the catalyst is also an importantfactor influencing the selectivity of the unsaturated aldehyde. In this paper,organosilane functionalized graphene oxide-loaded noble metal nanoparticlesstabilized Pickering emulsions were used in water-based cinnamaldehydeselective C=C and C=O hydrogenation reactions.

(1) A Pd/GO-Si catalyst was prepared byloading Pd nanoparticles on graphene oxide hydrophobically modified by usingtrimethoxymethylsilane. The catalyst was characterized through severaltechnologies including XRD, TEM, FT-IR, XPS, Raman, TG. The catalyst, water andcinnamaldehyde were ultrasonicated and stirred to prepare a Pickeringemulsions, and the Pickering emulsions system was characterized by an opticalmicroscope. The prepared Pickering emulsion system was used in thecinnamaldehyde selective C=C hydrogenation reaction. The experimental resultsshowed that the conversion of cinnamaldehyde (CAL) can reach 99% at 80 °C, 2MPa H2 for 20 min, the selectivity of hydrogenated cinnamaldehyde (HCAL) reached84%, and the catalytic effect was better than Pd/GO catalyst. The Pd/GO-Sicatalyst still had a very good catalytic effect on different substrates and hasgood reusability. The excellent catalytic activity was due to the fact that thePickering emulsion increased the contact area between the catalyst and thereactant to reduce the mass transfer resistance in the heterogeneous catalyticsystem. At the same time, the hydrophobic modification of the catalyst surfaceincreased the adsorption amount of the reactant molecules on the surface of thecatalyst, thereby improving the catalytic activity.

(2) Pt/GO-Si catalysts were prepared byseparately loading Pt nanoparticles on graphene oxide modified by using methyl,propyl, phenyl, hexyl, octyl, dodecyl, hexadecyl and aminopropyl organosilanes.The catalyst was characterized through several technologies including XRD, TEM,FT-IR, XPS,TG. The catalyst, water and cinnamaldehyde were ultrasonicated andstirred to prepare a Pickering emulsion, and the emulsion system wascharacterized by an optical microscope. The prepared Pickering emulsion systemwas used in a cinnamaldehyde selective C=O hydrogenation reaction. Theexperimental results showed that the catalyst Pt/GO-Si-C8 prepared by themodification of trimethoxyoctylsilane exhibits the best activity at 40 °C, 2MPa H2 for 2 h, and the conversion of cinnamaldehyde reached 93%, theselectivity of cinnamyl alcohol reached 85%, higher than other silane modifiedcatalysts. This was because the moderate carbon chain length controlled theadsorption direction of cinnamaldehyde on the catalyst surface, so that thealdehyde group directly contacted the Pt nanoparticles, thereby improving thecatalytic activity.

关键词:氧化石墨烯;肉桂醛;选择性加氢;Pickering乳液;钯;铂

Graphene oxide; Cinnamaldehyde; Selectivehydrogenation; Pickering emulsion; Palladium; Platinum

上一篇:一种表面润湿性可控的碳纳米管负载钯催化剂及其催化性能研究     下一篇:多功能分子筛催化剂的研制及催化芳烃烷基化的研究
 
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