疏水SBA-15负载高分散Pd催化剂制备及蒽醌加氢性能

Hydrogen peroxide is widely accepted as a green oxidant and, today, is almost exclusively produced by the sequential hydrogenation and oxidation of an alkyl-anthraquinone dissolved in a mixed solvent (working solution) known as the AO process. Catalytic hydrogenation of alkyl-anthraquinone in the working solution is a key step of the hydrogen peroxide production by the AO process. Since the Pd catalysts used commonly in industry show the relatively low selectivity, the hydrogenation are limited at the conversion of alkyl-anthraquinone lower than 60%, together with a requirement for periodic replacement of active alumina, to keep the smaller concentration of degradation products. It results in the use of a large amount of the working solution and formation of a large amount of spent active alumina which is harmful to environment. Hence, enhancement of the selectivity of catalysts, with maintenance of the high activity would be an effective route for solving the problems mentioned above. In this project, highly dispersed Pd catalysts will be prepared on hydrophobic SBA-15 silica with highly ordered mesopores and good thermal stability as supports for hydrogenation of 2-alkylanthraquinone. The pore size, acidity and alkalinity and hydrophilicity/hydrophobicity of SBA-15 will be adjusted to improve diffusion and adsorption of reactant as well as the diffusion and desorption of target product. And the confinement effect of ordered mesopores will be used to decrease the size of Pd particles. It is expected that all above would bring the benefits of enhancements in the selectivity and activity of catalyst. Also, the effects of the pore size and surface properties of SBA-15 (including acidity, alkalinity and hydrophilicity/hydrophobicity), and the distribution of Pd particles in the channels of support on the micro- and meso- structure of catalyst and hydrogenation behaviors of alkyl-anthraquinone will be systematically studied. The adjustment mechanism of the structure and properties of SBA-15 and size of Pd particles will be clarified. And the preparation method of Pd catalyst having the high selectivity and activity will be proposed through investigation works made in this project, which will give interesting information for the development of supported Pd catalysts with the high performance in large-scale production.

过氧化氢是应用广泛的绿色氧化剂，其主要生产方法是蒽醌法。该法的核心步骤是烷基蒽醌的氢化。目前普遍使用的Pd催化剂选择性较低，需要限制烷基蒽醌转化率低于60%和频繁更换活性氧化铝再生剂，才能维持较低的降解物量。这导致大量工作液无效循环、产生大量废氧化铝造成严重的环境污染等问题。因此，提高催化剂的选择性并维持其高活性，是解决上述问题的关键。本项目拟以介孔高度有序、热稳定性好的SBA-15分子筛为载体制备Pd催化剂。通过调控载体的孔尺寸和表面酸碱性及疏水性、利用有序介孔的限域作用固定Pd颗粒，强化反应/产物的扩散和吸/脱附性能、减小Pd的颗粒尺寸，进而提高催化剂的选择性和活性。拟通过系统研究SBA-15孔尺寸、表面酸碱性和疏水性以及Pd分布对催化剂的微介观结构及其烷基蒽醌加氢性能的影响规律，阐明载体结构和表面性质及Pd颗粒尺寸和分布的调控机制，发展高选择性、高活性负载型Pd加氢催化剂的制备方法。

烷基蒽醌（AQ）氢化是蒽醌法生产绿色氧化剂过氧化氢的核心步骤。本项目通过深入分析AQ加氢反应特征，提出通过调控载体结构和表面性质强化反应/产物的扩散和吸/脱附性能、进而提高催化剂选择性并维持其高活性的策略，以解决降解物多及由此引发的低效和高污染问题。.通过调整水热条件、溶胀剂和共溶剂种类及用量，可大幅改变SBA-15的孔尺寸和形貌。其中，加入共溶剂正癸烷可增加SBA-15孔径，同时减小SBA-15的颗粒尺寸至约300 nm并形成单分散形貌。活性组分Pd的电子和表面性质不受载体孔径影响、粒径略减小。2-乙基蒽醌、2-叔丁基蒽醌和2-戊基蒽醌加氢反应活性分别提高2.2、1.6和1.5倍，活性蒽醌选择性超过99%。.通过调整一步合成配方中铝和镁的用量，可实现对SBA-15载体酸和碱性的调控。碱性催化剂的加氢速率和TOF及选择性均较高且随镁含量增加而显著增加，酸性催化剂的规律则相反。.采用后/共缩聚接枝、惰性气氛中焙烧和氟化剂后处理均可实现对SBA-15亲/疏水性的调控。通过改变接枝顺序和预水解时间，可调控疏水基团的分布。外表面接枝的疏水功能化催化剂的活性最高，2-乙基蒽醌、2-叔丁基蒽醌和2-戊基蒽醌的加氢速率分别为0.20、0.08和0.05 molH2Pd-1min-1。与未疏水功能化的催化剂相比，分别提高了33.3%,、60.0% 和150.0%。而且，疏水功能化催化剂均表现了高的蒽醌加氢选择性。.分别采用“水热一锅法”和双溶剂浸渍法将Pd颗粒引入载体孔道，利用载体孔道的限域效应实现了对Pd粒径尺寸和分布的调控。限域使Pd颗粒得以均匀而高度的分散，EAQ加氢速率增加约100 %。但限域使Pd利用率下降，导致TOF值略有下降、副产物收率略有增加。.综上，单独调变载体结构和表面性质都可显著改善Pd/SBA-15催化剂的烷基蒽醌加氢性能。因此，进一步研究应将两者相结合。