【摘要】：近年來(lái),由于化石能源的不斷枯竭和環(huán)境污染日益加劇,迫使人類(lèi)尋找新型生物質(zhì)能源。生物質(zhì)包括纖維素、半纖維素和木質(zhì)素等,其中木質(zhì)素含量約占25%左右,目前每年以造紙工業(yè)廢液等形式排放到自然界,不僅污染環(huán)境,而且木質(zhì)素的高附加值化未能實(shí)現(xiàn)。本論文,以木質(zhì)素模型化合物為研究對(duì)象,可以在一定程度上,探尋提高木質(zhì)素附加值有效途徑,因此,開(kāi)展木質(zhì)素模型化合物的催化轉(zhuǎn)化研究具有重要的科學(xué)意義和應(yīng)用價(jià)值。首先,以納米金屬作為催化劑,探究香草醛經(jīng)氧化酯化合成香草酸甲酯產(chǎn)品的過(guò)程。采用沉積沉淀法制備了納米金、鉑、鈀負(fù)載的固體催化劑,其中針對(duì)納米金催化劑的制備,采用了三種不同方法合成Au/Al_2O_3,Au-R/Al_2O_3,Au-h/Al_2O_3催化劑,并將上述催化劑應(yīng)用于催化香草醛與甲醇間的氧化酯化反應(yīng)。研究發(fā)現(xiàn),以Au-h/Al_2O_3為催化劑、氧氣為氧化劑、140℃反應(yīng)4小時(shí)后,香草醛的轉(zhuǎn)化率為98.1%,主產(chǎn)物香草酸甲酯的選擇性高達(dá)為99.1%。同時(shí)對(duì)Au-h/Al_2O_3催化劑做了5次循環(huán)實(shí)驗(yàn),發(fā)現(xiàn)香草酸甲酯的收率仍保持96.1%以上,說(shuō)明催化劑在該反應(yīng)具有較高的穩(wěn)定性。進(jìn)而,考察在甲醇溶液中異香草醛、茴香醛、丁香醛、3,4,5-三甲氧基苯甲醛于氧氣氣氛下發(fā)生氧化酯化情況,發(fā)現(xiàn)納米金負(fù)載三氧化二鋁效果也較佳,對(duì)應(yīng)芳香酯可達(dá)70.2-98.0%的收率。其次,還將不同制備方法的納米金催化劑用于香草醇的氧化酯化過(guò)程,研究發(fā)現(xiàn),在分子氧的存在下,經(jīng)適當(dāng)時(shí)間后香草醇和甲醇可以發(fā)生催化氧化酯化反應(yīng);其中,以Au-h/Al_2O_3為催化劑、氧氣為氧化劑,在140℃反應(yīng)4小時(shí)以后,香草醇轉(zhuǎn)化率高達(dá)99.4%,不過(guò),產(chǎn)物當(dāng)中2-甲氧基-4-甲氧甲基苯酚的選擇性為17.0%,香草醛的選擇性為31.9%,香草酸甲酯的選擇性為49.9%;繼續(xù)延長(zhǎng)反應(yīng)時(shí)間至10、12小時(shí),則香草醇接近全部轉(zhuǎn)化,轉(zhuǎn)化率分別為99.4%、99.9%,目標(biāo)產(chǎn)物香草酸甲酯的選擇性分別為94.8%、99.6%。結(jié)果表明,在A(yíng)u-h/Al_2O_3催化劑促進(jìn)下的氧化反應(yīng)歷程中,香草醇首先被氧化為香草醛,進(jìn)而轉(zhuǎn)化為香草酸甲酯。最后,通過(guò)對(duì)催化劑進(jìn)行XRD、BET、TEM、SEM、TPD和NMR等表征測(cè)試,對(duì)反應(yīng)數(shù)據(jù)做出了合理的解釋。進(jìn)而,基于實(shí)驗(yàn)現(xiàn)象和對(duì)比試驗(yàn)結(jié)果,在總結(jié)催化反應(yīng)規(guī)律的基礎(chǔ)上,提出了香草醇和甲醇的氧化酯化的反應(yīng)機(jī)理。
[Abstract]:In recent years, due to the continuous depletion of fossil energy and environmental pollution, human beings are forced to look for new biomass energy. Biomass includes cellulose, hemicellulose and lignin, in which lignin content accounts for about 25%. At present, it is discharged into nature in the form of waste liquid from papermaking industry every year, which not only pollutes the environment, but also fails to realize the high addition value of lignin. In this paper, taking lignin model compounds as the research object, we can explore the effective ways to improve the added value of lignin to a certain extent. Therefore, it is of great scientific significance and application value to carry out the catalytic transformation of lignin model compounds. Firstly, using nano-metal as catalyst, the process of oxidative esterification of vanillin to methyl vanillic acid was studied. Solid catalysts supported on gold, platinum and palladium were prepared by deposition and precipitation method. Au/Al_2O_3,Au-R/Al_2O_3,Au-h/Al_2O_3 catalysts were synthesized by three different methods for the preparation of gold nanoparticles, and the catalysts were applied to the oxidative esterification of vanillin with methanol. It was found that the conversion of vanillin was 98.1% and the selectivity of methyl vanillic acid was 99.1% after reaction at 140 鈩，

本文編號(hào)：2508490