CO_2氧化丙烷脱氢镓基催化剂的制备及其催化性能研究_吴佳凌.docx

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1、 C 2 氧化丙烷脱氢镓基催化剂的制备及 其催化性能研究 指导小组成员 曹勇教授 刘永梅副教授 攸 _ . 1 Abstract . 4 第一章绪论 . 9 1.1 丙烯的应用和目前供需概况 . 9 1.2 丙烧转化为丙烯的途径 . 10 1.2.1直接催化脱氢 . 10 1.2.2分子氧氧化脱氢 . 12 1.2.3二氧化碳氧化脱氢 . 13 1.3 C02氧化丙烷脱氢催化体系介绍 . 15 1_4 镓系催化体系 . 18 1.4.1镓基催化体系在低碳烧烃脱氢中的应用 . 18 1.4.2氧化镓催化剂脱氢机理的研究 . 20 1.4.3氧化镓催化剂性能的改善 . 22 1.5 制备大表面氧化

2、物催化剂的方法 . 25 1.5.1模板法制备催化剂研宄进展 . 25 1.5.2生物质模板法制备金属氧化物催化剂 . 28 1.6 本论文的指导思想 . 29 第二章实验部分 . 30 2.1 原料与试剂 . 30 2.2 催化剂表征方法 . 31 2.2.1X 射线衍射 （ XRD) . 31 2.2.2比表面测试 （ BET) . 31 2.2.3氨程序升温脱附 （ NH3-TPD) . 31 2.2.4 C 2 程序升温脱附 （ C02-TPD) . 31 2.2.5 热重分析 （ TG-DTA) . 31 2.2.6扫描电子显微镜 （ SEM) . 32 2.2.7透射电子显微镜 （

3、 TEM) . 32 2.3 活性测试 . 32 第三章大比表面 p-Ga2 3制备及其催化丙烷脱氢性能研宄 . 35 3.1 弓 It . 35 3.2 大比表面 p-Ga2 3的制备 . 36 3_3 p-Ga2 3样品的表征 . 36 3.3.1 p-Ga2 3样品的结构性质研宄 . 36 3.3.2卜 Ga2 3样品的表面酸碱性质 . 41 3.4 丙烷脱氢活性研究 . 43 3.4.1 p-Ga2 3催化活性结果 . 43 3.4.2 p-Ga2 3催化剂的稳定性和活性再生实验 . 46 3.5 其他可溶性生物质模板制备 |J-Ga2 3催化剂表征与活性结果 . 48 3.6 小结

4、. 48 第四章 Ga2 3-Ak 3固溶体用于催化丙烷脱氢制丙烯研究 . 50 4.1 引言 . 50 4.2 Ga2 3-Ak 3固溶体样品的制备 . . . 51 4.3 系列 Ga2 3-Ab 3样品的结构性质表征研宄 . 51 4.3.1结构表征 . 51 4.3.2酸碱性性质表征 . 55 4.4 丙烷脱氢活性研宄 . 56 4.4.1 Ga2 3-Ak 3固溶体催化剂的脱氢活性 . 56 4.4.2 Ga2 3-Al2 3固溶体催化剂稳定性测试 . 60 4.5 . 61 第五章总结与展望 . 62 参考文献 . 64 个人简历 . 77 硕士期间发表论文情况 . 77 賴 .

5、78 中文摘要 co2氧化丙烷脱氢镓基催化剂的制备及其 催化性能研究 关键词：丙烷、丙烯、二氧化碳、脱氢、 P-Ga2 3、 Ga2 3-Al2 3固溶体 丙烯作为重要的化工中间体，目前工业上主要来自炼油厂流化床裂解和乙烯 裂解，其收率均比较低，难以满足快速增长的需求，而由资源丰富的烷烃转化成 烯烃有望解决这一矛盾。目前己经工业化的丙烷直接脱氢工艺由于热力学上需高 温反应，能耗大，而且易导致烃类高温裂解、催化剂积碳失活，因此在工业化生 产中受到很大限制。近年来，丙烷临氧脱氢的方法作为在较低温度下获得丙烷高 转化率的新工艺被广泛研究，即将原本的吸热反应转变为热力学上有利的放热反 应。但由于 02

6、的介入带来了深度氧化和氧分子插入反应等副反应，众多副产物 的生成使得产物丙烯的选择性难以提高。因此，如改用 co2作为温和氧化剂， 将丙烷脱 氢与逆水煤气变换 （ RWGS)耦合，则可以通过 C 2 除去出提高丙烷 反应活性，使丙烷脱氢反应的平衡转化率与相比直接脱氢大为提高。同时 C02 既减少了 2带来的深度氧化副反应，又可消除表面积炭，因此反应的选择性与 稳定性都将出现相应提升。由于该工艺充分利用了 C02这种温室气体，是一条 “ 绿色化学 ” 的途径。 在低碳烷烃 C02 氧化脱氢研究领域中， Ga203 作为一类新型催化剂为人们所 关注。尽管目前所报道的 Ga203催化剂的活性结果都较

7、为突出，但是积炭现象仍 然严重，一般在几小时内就会全部失活。近年来，已有相关研宄证实对于不同晶 型的 Ga203 催化剂，其表面配位不饱和 (cus)Ga 物种在 C02氧化丙烷脱氢反应中 起到至关重要的作用，且其含量随着催化剂的比表面增大而增加，因此如何方便、 快捷、环保的制备具有大比表面积的镓系催化剂对提升其催化性能至关重要。系 列研宄证实，生物质模板法是一种能够制备具有大比表面积、介孔结构金属氧化 物催化剂的有效方法，因此有望成为一种理想的、简便易行的合成大比表面镓系 脱氢催化剂的手段。 复 旦大学孩士摊论文 此外，近年来报道的一种 Ga203-Al203固溶体具有独特的表面酸性和结构性

8、 质，被广泛应用于氮氧化物的选择催化还原 （ SCR)。该固溶体相比 Ga203 具有 更大的比表面积与活性 Ga (IV)物种，且活性 Ga 物种分散度更好。同时，固 溶体表面酸性位总量随着 Ga 含量的增加而递增，但强酸位数量减少，而且在高 温下依然能保持良好的结构稳定性。本课题组此前将其用于丙烷脱氢反应，取得 了良好的催化活性与稳定性。因此，如能将生物质模板法用以合成大比表面 Ga203-Al203固溶体用于丙烷氧化脱氢反应， 则可能在反应活性和稳定性方面都 取得新的突破。 本论文分二部分，均围绕丙烷 C 2气氛下脱氢反应展开，分别以生物质模 板法制备的大比表面 p-Ga2 3材料和 G

9、a2 3-Al2 3 固溶体为催化剂体系，研宄了 它们的表面性质、活性、稳定性，并通过详细的表征研宄了其构效关系，对反应 的活性中心和催化本质进行了分析与探讨。 本论文主要内容如下： 一、大比表面 p-Ga2 3用于丙焼 C 2 气氛下脱氢研宄 用生物质模板法制备了蔗糖 /Ga203摩尔比为 1、 2、 4、 8的系列样品，分别 记为 P-Ga2 3-Sl， p-Ga203-S2， p-Ga203-S4， p-Ga203-S8,并用同样方法合成无 模板 P-Ga203样品作为参比。 XRD表征结果证明系列样品均呈现最稳定的 p-Ga203晶相，且结晶度随着蔗糖比例的增加而下降。 BET 表征研

10、宄发现，随 着蔗糖加入量的增加，系列样品的比表面显著增加，其中 p-Ga203-S4 的比表面 最大，为 98 m2/g。 SEM、TEM 表征中可以看出蔗糖模板法制备的 p-Ga2 3催 化剂具有海绵状的表面结构。而NH3-TPD 结果显示，蔗糖模板法制备的四个样 品的表面酸性位数目是传统方法制备样品的 2 3倍。 773 K 常压下的活性测试中，无论在有、无 C02 气氛下，生物质模板法制备 的系列 P-Ga203催化剂的活性都显著高于无模板的 p-Ga203,而 C02气氛下整体 活性高于无C02气氛下的活性。系列催化剂的活性变化趋势为 P-Ga203-S4 p-Ga2 3-S8 p-G

11、a2 3-S2 p-Ga203-Sl P-Ga2 3， 其中 P-Ga2 3-S4 催化剂的丙 烷起始转化率为43.7 %,几乎为传统方法制备的 p-Ga2 3 (23.8%)的 2倍。经 过活性再生测试，发现模板法制备的 P-Ga203催化剂活性再生能力强， P-Ga203-S4三轮再生后其初始活性依然有 37.6 %。其他可溶性糖源 (如葡萄糖、 果糖等 ） 生物质模板制备的催化剂都取得了相比无模板 p-Ga203更高的丙烷转 2 复 SJ： 学頌士雜论文 化率，证明了生物质模板法制备 P-Ga203催化剂的灵活性与通用性，为未来发 展新型氧化镓催化剂提供了新的思路。 二、 Ga2 3-A

12、l2 3 固溶体用于催化丙烷脱氢反应的研宄 米用生物质模板法制备了系列大比表面 Ga2 3-Ah 3 样品，鹿糖： Ga: A1 摩尔比分别为 0:l:l、 2:l:l、 4:l:l、 8:l:l、 12:l:l、 8:1.6:0.4、 8:0.4:1.6d3SSOGalAll、 S2GalAll、 S4GalAll、 S8GalAll 等以此类推。通过 XRD 表征可知系列样品中 Ga2 3与Ah 3都形成了固溶体，且大部分固溶体均与 Y_Ga2 3和 Y-A丨 2 3的特 征峰相似，而 S12-Gal-All 样品除 Y-A1203的衍射峰外还出现了 p-Ga203的转晶 衍射峰。 BET

13、 研宄发现无模板的 SOGalAll 样品由于铝的存在已经能够获得相当 大的比表面 （ 135 m2/g)，而蔗糖模板法能够在此基础上对其进一步提高，其中 S8-Gal-All 材料能获得高达187m2/g 的比表面。 SEM、 TEM 研究结果表明蔗糖 模板法制备的系列 Ga203-A 丨 203呈现出海绵状多孔形貌，且平均粒径略小于传统 方法制备的 Ga203-Al203 固溶体。NH3-TPD 实验表明随着蔗糖量的增加，固溶 体催化剂的弱酸酸位数目出现先增加后减小的趋势， S8-Gal-All 样品的弱酸酸 位数目达到最高，而系列样品的表面中强酸性位数目则无明显变化规律。 在常压及 77

14、3K 条件下，分别测试了有、无 C02气氛的系列 Ga2 3-Ab 3固 溶体的丙烷脱氢活性，发现蔗糖比例的不同会对催化剂活性产生显著影响。在两 种气氛下，丙烷初始转化率都为 S8-Gal-All S4-Gal-All S2-Gal-All S0-Gal-AllS12-Gal-AU，C02气氛下虽然初始活性较无 CO2 气氛下低，但整 体稳定性较高。对于不同 Ga/Al 摩尔比催化剂， Ga 含量越低，催化剂失活越慢。 此外，为考察固溶体催化剂的反应稳定性，对 S8-Gal-AU 催化剂进行了在线反 应 50 h 的活性测试， C02气氛下、 773 K 反应50 h 后仍然表现出 19.3

15、%的丙烷 转化率。 3 Abstract Dehydrogenation of propane to propylene in the presence of carbon dioxide over novel gallium oxide based catalysts Keywords: propane, propylene, CO2, Dehydrogenation, p-Ga2 39 Ga2 3-Ah 3 solid solution Propylene is currently an important building block of the chemical industry,

16、which is mainly produced from steam cracking and FCC. However the propylene production from these sources barely matches with its rapid increasing consumption. Therefore, transformation of the relatively cheap and abundant propane into propylene seems to be an alternative to slove this problem. Ther

17、mal dehydrogenation of propane to propylene (DHP), although industrialized, requires high reaction temperature due to the thermodynamics limits. This drawback makes the process not only extremely energy intensive, but also severe coking and consequent deactivation which restrict the further applicat

18、ion of this technique. Meanwhile oxidative dehydrogenation of propane by molecular oxygen (ODHP), which allows the endothermic reaction to be exothermic, permits high conversion of propane at lower temperature. However, introduction of oxygen leads to side-reaction such as over-oxidation and inserti

19、on of molecular oxygen, significantly decreasing its selectivity to propylene. Employment of CO2 as weak oxidant instead of O2 would couple the DHP with reverse water-gas shift (RWGS), which consumes H2 by C 25 leading to the enhancement of DHP equilibrium conversion. In confrast to ODH, by-products

20、 are remarkably suppressed, and selectivity to propylene is greatly promoted in the CO2-DHP. Besides, CO2 can stabilize the catalysts via elimination of coke and as green house gas has been effectively utilized, CO2-DHP is recognized as a “green chemistry” route. In the field of CO2-DH of light alka

21、nes, Ga2 3 receives considerable attentions as a new class of catalysts. Although Ga2 3-based catalysts are reported to be active in some cases, they suffer heavily from coke, which renders the catalysts to deactivate rapidly in a few hours commonly. Over the years, a number of studies have establis

22、hed that the population of the catalytically relevant (cus) Ga species is a strong function of the surface area of Ga2 3 among different Ga2 3 polymorphs. In this sense, one may rationalize that simply increasing the surface area of Ga2 3 can lead to an improvement in the PDH activity. Alternatively

23、, biomass has been widely employed as a simple and convenient carbon template precursor in synthesis of high surface area metallic oxide, which could be a new alternative for the preparation of Ga2 3. Moreover, a new class of Ga2 3-Ah 3 solid solution reported, with unique acidic and structural prop

24、erties, has been frequently applied to the selective catalytic reduction (SCR) of NOx. In contrast to those of AI2O3, the total amount of acid site of the Ga2 3-Al2 3 solid solution increases with the enhancement of Ga concentration, but the amount for strong acid site decreases accordingly. The sol

25、id solution is also fairly stable in crystalline structure against heat treatment. Previous work in our group indicated that the catalytic dehydrogenation of propane in the presence or absence of CO2 over a series of Ga2 3-Ah 3 mixed oxides had favorable results. Therefore, we attempt to prepare hig

26、h surface area Ga2 3-Ala 3 mixed oxides materials using eco-friendly biomass as a non-surfactant template to improve the performance for catalyzing propane dehydrogenation in the presence of CO2. This dissertation is divided into two parts according to the catalyst systems studied in the current CO2

27、-DHP process: p-Ga2 3 catalysts and Ga2 3-Ab 3 solid solutions. The activity, stability and regeneration behavior for the two catalyst systems have been systematically studied, and the structural-activity relationships have been carefully analyzed via detailed characterizations. The activity centers

28、 as well as the origin of the catalytic performance have been discussed in depth. The main content of this dissertation is as follows: 1) Studies on p-Ga2 3 for CO2-DHP Biomass-template samples with sucrose/Ga2 3 molar ratio at 1， 2, 4, and 8 were synthesized， denoted as p- Ga2 3-Sl， p- Ga2 3-S2, p-

29、 Ga2 3-S4, and p- Ga2 3-S8, respectively. For comparison purpose， a corrventicmal P_ Ga2 3 sample was prepared. The characteristic peaks of p* Ga2 3 are observed for all samples in the XRD measurement, demonstrating that the most stable form of Ga2 3 was achieved via the sucrose-template synthesis.

30、The sucrose derived p- Ga2 3 samples show obviously lowers crystalline, as reflected from their broadened peaks and decreased diffraction signals relative to that for conventional p- Ga2 3. Besides, the sucrose-template approach can afford the production of a series of mesoporous samples with favora

31、ble textural properties and enhanced surface areas. The SEM and TEM analysis reveals that conventional p- Ga2 3 presents a solid bulk structure and smaller average particle size， while the sucrose-template samples display distinct sponge-like morphology and higher sucrose/ Ga2 3 ratio possesses high

32、er porosity. Specifically* the total acidity of the four sucrose-derived samples is approximately 1-2 times higher than that of the conventional p- Ga2 3 measured by NH3-TPD experiments. The dehydrogenation of propane over the p- Ga2 3 samples in the presence/ absence of CO2 was investigated at 773

33、K. Activities in the presence of CO2 are generally superior to those in the absence of CO2. In both conditions, the initial propane conversions follow the sequence: p-Ga2 3-S4 p-Ga2 3-S8 p-Ga2 3-S2 p-Ga2 3-Sl p-Ga2 3. Worth mentioning is that over p- Ga2 3-S4 with the highest specific surface area,

34、a conversion of propane (43.7%) approximately twice that of conventional p- Ga2 3 (23.8%) can be achieved. As far as the stability is concerned, regeneration for (3- Ga2 3-S4 is tested， and after the third regenerations, the propane conversion maintains 37.6 %. It is important to highlight here that

35、 this approach is not limited to the use of sucrose as the carbohydrate-based carbon sources. The present findings may provide new opportunities for the rational design of new mesostructured gallium oxide catalyst systems for advanced applications. 2) Studies on Ga2 3-Al2 3 solid solution for CO2-DH

36、P Prepare biomass-template Ga2 3-Al2 3 solid solution with sucrose/Ga/Al ratio at 0:1:1， 2:1:1, 4:1:1， 8:1:1， 12:1:1， 8:1.6:0.4， 8:0.4:1.6， denoted as SOGalAll， S2GalAll, S4GalAll, S8GalAll etc. XRD reveals the samples all formed Ga2 3-Ah 3 solid solutions. The characteristic peaks of the samples ar

37、e similar with y- Ga2 3 and y- AI2O3 except for S12GalAll, which presents a p- Ga2 3 crystalline phase style. Besides, the sucrose-template approach can afford the production of a 复肚学顼士 m论文 series of mesoporous samples with favorable textural properties and enhanced surface areas that enlarge the no

38、n-template SOGalAll (135 m2/g) to S8-Gal-All (187 m2/g). The SEM and TEM analysis reveals that series sucrose-template Ga2 3-Al2 3 samples appear to a spongy porous morphology, and the average particle diameter is smaller than the non-template preparing Ga2 3-Ab 3 solid solution. NH3-TPD experiment

39、further suggests the number of weak acid sites increased initially and then decreased with the increment in sucrose content, and the maximum value was achieved over sample S8-Gal-All. The catalytic activities of the Ga2 3-Al2 3 solid solutions were monitored on a continuous micro-reactor at 773 K an

40、d 1 atm. Activities both in the presence/absence of CO2 were analyzed， showing composition effect has a great impact on the DHP activity. In both conditions, the initial propane conversions follow the sequence: S8-Gal-All S4-Gal-All S2-Gal-All SO-Gal-All S12-Gal-All. Activities in the presence of CO

41、2 are generally more stable than those in the absence of C 2, though higher initial propane conversions were achieved in the absence of CO2. Moreover，it was discovered that sample with lower Ga2 3 content deactivates more slowly. Taking into account the application potential， the Ga2 3-Al2 3 solid solution was accessed by 50 h on-stream activity test, and SI 2-Gal-All showed conversion of propane as high as 19.3% at 50 h. 7 第 一 章 绪 论 1.1丙烯的应用和目前供需概况 丙烯是一种重要的石油化工原料，主要用于生产聚丙