本文關(guān)鍵詞： 鋯基氧化物 高比表面積 熱穩(wěn)定性 氧化乙苯脫氫　出處：《太原理工大學》2017年博士論文　論文類型：學位論文

【摘要】：根據(jù)國際純粹和應用化學聯(lián)合會對孔材料的定義,多孔材料可按其孔徑的大小劃分成微孔材料(孔徑2nm)、中孔或介孔材料(2nm孔徑50nm)以及大孔材料(孔徑50nm)三類。美國學者Dubinin又提出了一種孔徑介于1-2nm之間的超微孔材料。這種材料的孔徑尺寸彌補了在該區(qū)間對分子擇形有特殊需求的反應,在微孔和介孔材料之間架起了承上啟下的橋梁,具有廣闊的應用前景。金屬氧化物氧化鋯作為一種多功能兼具酸性和堿性的催化劑載體,常通過硫酸化、磷酸化或鎢酸化成為一種強的固體酸。硫化氧化鋯雖然酸性較強,但比表面較小。通常借助具有高比表面的硅基有序中孔材料負載氧化鋯應用于催化裂解、烷烴異構(gòu)化等反應,但是中孔材料的表面性能不利于四方相氧化鋯的生成,而四方相氧化鋯(t-Zr O_2)是SO42-/Zr O_2的基礎(chǔ)。因此,通過新的技術(shù)路線或已有制備工藝的改進,合成具有高熱穩(wěn)定性和高比表面的中孔-微孔多晶體結(jié)構(gòu)的四方相氧化鋯基材料,具有極大的挑戰(zhàn)性和十分重要的意義。國內(nèi)外學者對于孔材料的合成已提出了諸多成功的制備方案,并且有些技術(shù)可以達到根據(jù)實際應用需求而定向、精準合成所需類型的多孔材料。其中應用最多的是軟模板法制備孔材料,該方法又稱模板劑或結(jié)構(gòu)導向劑方法,其特點是充分利用模板劑在合成過程中所特有的模板劑效應,去制備、調(diào)控材料的孔結(jié)構(gòu)。通常認為,模板劑在所合成的液相體系中所形成的膠束的尺寸大小決定所合成材料孔徑的尺寸范圍,模板劑的種類和制備條件影響著分子篩的水熱穩(wěn)定性和多級孔材料孔徑的大小及其分布。因此,篩選性能優(yōu)越、環(huán)境友好、價廉易得的模板劑,并進一步優(yōu)化合成工藝和創(chuàng)新合成路線已成為廣大科研人員積極探索的熱點和難點。本課題采用溶劑揮發(fā)誘導自組裝的方法,以雙鏈季銨鹽陽離子表面活性劑作為軟模板(結(jié)構(gòu)導向劑),通過改變表面活性劑中碳鏈的長度(雙八烷基二甲基氯化銨、雙十二烷基二甲基氯化銨、雙十八烷基二甲基氯化銨)制備得到了孔結(jié)構(gòu)可控的氧化鋯材料,且合成過程中無需額外添加酸堿等助劑,而是通過前驅(qū)體的自身水解產(chǎn)生的酸堿性達到自我調(diào)節(jié)從而獲得相應結(jié)構(gòu)的多孔材料。以溴化十六烷基吡啶為模板劑,氧氯化鋯或丙醇鋯為鋯源前驅(qū)體,通過溶劑揮發(fā)誘導自組裝法和固液技術(shù)相結(jié)合的新策略制備出具有高比表面積的中微孔級納米晶體氧化鋯材料�？捉Y(jié)構(gòu)表征結(jié)果顯示,400℃焙燒脫模板后,其具有高的比表面積414m2/g;即使在700℃熱處理后,仍然具有較高的比表面積223m2/g。而通過單一溶劑揮發(fā)法合成的氧化鋯材料經(jīng)相應溫度熱處理后,孔結(jié)構(gòu)基本坍塌,比表面積小于50m2/g。在成功制備出微孔氧化鋯的基礎(chǔ)上,且不額外添加任何酸、堿等助劑的情況下將金屬鋁鹽引入,得到了具有超微孔結(jié)構(gòu)、高熱穩(wěn)定性以及高水熱穩(wěn)定性的氧化鋁-氧化鋯復合材料。合成得到的Al_2O_3-Zr O_2復合材料具有蠕蟲狀孔道結(jié)構(gòu),Al的含量能夠在較大范圍內(nèi)進行調(diào)節(jié),且該材料具有較高的比表面積和均一的孔徑分布。Al元素的引入使得該微孔材料具有穩(wěn)定的四方相結(jié)構(gòu),致使含有微孔結(jié)構(gòu)的此復合材料的熱穩(wěn)定性遠大于相應氧化鋯材料。當Al/Zr摩爾比為1.0時,該復合材料在800℃熱處理后仍具有微孔結(jié)構(gòu),且比表面積高達216 m2/g,顯示出高的熱穩(wěn)定性。以制備的Al_2O_3-ZrO_2復合材料為載體,采用浸漬法制備含鈷催化劑并將其應用于二氧化碳氣氛下氧化乙苯脫氫反應。研究發(fā)現(xiàn)催化劑用量為300mg,CO_2氣體流量為20m L/min,乙苯流量為0.3m L/h,550℃下連續(xù)反應10h時,隨著Al/Zr摩爾比的不斷增加,其乙苯轉(zhuǎn)化率不斷增加;當Al/Zr摩爾比為0.7時,轉(zhuǎn)化率達到最高值58.71%,其催化活性達到最大,且苯乙烯選擇性不低于96%;繼續(xù)增加Al/Zr摩爾比到1.0,乙苯轉(zhuǎn)化率為57.73%,苯乙烯選擇性不低于96%,催化活性基本維持不變。作為對比,在相同的反應條件下,對采用相同制備方案得到的Co/Al_2O_3和Co/Zr O_2催化劑進行同樣的催化性能測試,結(jié)果顯示活性鈷原子負載于Al_2O_3-Zr O_2復合材料所表現(xiàn)出的催化活性遠高于單一氧化鋯或氧化鋁孔材料為載體的相應催化劑。并且在N2氣氛下,其Al_2O_3-Zr O_2復合材料仍然顯示了較好的催化活性,是目前鋯基催化劑相關(guān)研究中鮮有報道的。鑒于此,運用此制備方案又成功制備了氧化鎂-氧化鋯復合材料。孔結(jié)構(gòu)表征顯示該產(chǎn)物具有較大的比表面積以及集中的孔分布,600℃熱處理后仍然為純四方相。在豆油和甲醇的酯交換催化反應中,以所制備的鎂鋯復合材料為催化劑進行系統(tǒng)考察,結(jié)果表明當Mg/Zr摩爾比為0.5時,經(jīng)過150℃反應6h后,催化劑對豆油的轉(zhuǎn)化率可達到99%以上,顯示出極高的酯交換反應活性。表明此復合材料將會在該催化領(lǐng)域具有較高的應用價值。該制備方案的成功運用將為今后規(guī)模化制備孔結(jié)構(gòu)可調(diào)控的高比表面積、環(huán)保易得、高熱穩(wěn)定性的多級孔鋯基復合材料提供理論依據(jù)和技術(shù)指導。
[Abstract]:According to the IUPAC definition of mesoporous materials, porous materials into microporous materials according to their pore size (2nm in diameter), divided mesoporous or mesoporous materials (2nm 50nm in diameter) and macroporous materials (50nm in diameter) three. The American scholar Dubinin proposed supermicropore between pore size between 1-2nm. The pore size of this material made in the interval has special requirements on the molecular shape selective reactions between microporous and mesoporous materials built connecting bridge, and has broad application prospects. The metal oxide zirconium oxide as a multifunctional catalyst carrier in both acidic and alkaline, often through sulfation, phosphorylation or acidification of tungsten become a strong solid acid. Although the sulfated zirconia strong acid, but smaller specific surface. Usually by silicon substrate with high surface area mesoporous materials supported zirconium oxide used in Catalytic cracking, isomerization reaction, but the surface properties of mesoporous materials is not conducive to the formation of tetragonal zirconia, and tetragonal zirconia (t-Zr O_2) is the foundation of SO42-/Zr O_2. Therefore, the improved preparation of new or existing technical route system, synthesis of mesoporous - high thermal stability and high the surface of the microporous crystal structure of tetragonal zirconium based material phase oxidation, is of great challenge and great significance. Domestic and foreign scholars for the synthesis of mesoporous materials has made many successful preparation scheme, and some technology can be achieved according to the actual application requirements and orientation precision required for the synthesis of porous material type. Which is the most widely used in preparing porous material by soft template method, this method is also called template or structure directing agent method, which is characterized by the template effect and make full use of the unique template in the synthesis process, to By controlling the pore structure of the material. Generally, the size range of size determines the size of the template in the synthesis of liquid phase system of micelles formed by the synthetic aperture material, preparation conditions of template agent and system affects the hydrothermal stability of zeolite and hierarchical porous materials hole size and distribution of diameter. Therefore, screening of superior performance, environment friendly, template agent is cheap, and further optimize the synthetic route and innovation has become a hot and difficult scientific research personnel to actively explore the method in this paper. By evaporation induced self-assembly, as soft template with double chain quaternary ammonium cationic surfactants (structure oriented agent), by changing the surface active agent in the carbon chain length (double eight alkyl two methyl ammonium chloride, didodecyl dimethyl ammonium chloride two, double eighteen alkyl two methyl ammonium chloride) were prepared by controlled pore structure The zirconia material, and the synthesis process without addition of acid and other additives, but pH produced by precursor hydrolysis to regulate themselves so as to obtain porous material corresponding to the structure. In sixteen alkyl pyridine bromide as template, zirconium or zirconium propoxide as zirconium precursor, were induced by the new the strategy of self-assembly and solid technology combined with the preparation of high specific surface area of the porous nano crystal zirconia material by solvent evaporation. The pore structure characterization results show that 400 degrees off the template after roasting, which has a high specific surface area of 414m2 /g; even after heat treatment at 700 DEG C, still has a high the specific surface area of 223m2/g. and the single zirconia materials synthesized by solvent evaporation method with corresponding temperature after heat treatment, the basic structure of hole collapse, a surface area of less than 50m2/g. in the prepared porous zirconia based on, and not Any additional acid, alkali and other additives under the condition of the metal aluminum salt has been introduced, with super microporous structure, high thermal stability and high hydrothermal stability of alumina zirconia composite materials. Al_2O_3-Zr O_2 composites were synthesized with wormlike pore structure, the content of Al can be adjusted in a large range, and the the material has high specific surface areas and uniform pore size distribution of.Al element into the microporous material with stable tetragonal structure, the thermal stability of the composite material containing porous structure is far greater than the corresponding zirconia material. When the Al/Zr molar ratio is 1, the composite material has porous structure in 800 degree heat after the treatment, and the specific surface area of up to 216 m2/g, showed high thermal stability. Al_2O_3-ZrO_2 composites were prepared by the carrier, was prepared by impregnation and the cobalt catalyst For the oxidative dehydrogenation of ethylbenzene under carbon dioxide atmosphere. The study found that the amount of catalyst is 300mg, CO_2 gas flow rate of 20m L/min, 0.3m L/h 10h, ethylbenzene flow, continuous reaction at the temperature of 550 DEG C, with the increase of the molar ratio of Al/Zr, the conversion of ethylbenzene increases; when the Al/ Zr molar ratio was 0.7, the conversion rate reached the highest value 58.71%, the catalytic activity and selectivity of styrene reached a maximum of not less than 96%; with the increase of Al/Zr molar ratio to 1, the ethylbenzene conversion rate was 57.73%, the selectivity of styrene is not less than 96%, the catalytic activity remained unchanged. In contrast, under the same reaction conditions, catalytic performance test of the same with the same preparation plan Co/Al_2O_3 and Co/Zr O_2 results showed that the activity of catalyst, catalytic activity of cobalt atom load in Al_2O_3-Zr O_2 composites showed much higher than that of single zirconia or alumina material The material for the corresponding catalyst carrier. And in the atmosphere of N2, the Al_2O_3-Zr O_2 composites still showed good catalytic activity, is currently little research in zirconium base catalyst are reported. In view of this, Magnesium Oxide - zirconia composite materials were prepared by using the preparation and characterization of pore structure were successfully. The result shows have a larger surface area and pore size distribution of 600 DEG C after heat treatment is still a pure tetragonal phase. In soybean oil and methanol transesterification reaction, the magnesium zirconium composite material prepared by the catalysts were investigated, the results show when the Mg/Zr molar ratio is 0.5, after 150 DEG C 6H after the transformation of catalyst oil ratio can reach more than 99%, showing a very high transesterification activity. This indicates that the application of composite material will have a higher value in the field of catalysis. The preparation of the successful application will be In the future, large-scale production of porous structure with adjustable surface area, environmental protection and high thermal stability will provide theoretical basis and technical guidance for multistage Kong Gaoji composite materials.

【學位授予單位】：太原理工大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TQ134.12;TB383.4

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