Vilcocq Léa, Paez Ana, Freitas Victoria D S, Veyre Laurent, Fongarland Pascal, Philippe Régis
Catalysis, Polymerisation, Processes, Materials (CP2M), UMR 5128 - CNRS, Université Claude-Bernard Lyon 1 CPE-Lyon Villeurbanne F-69616 France
RSC Adv. 2021 Dec 10;11(62):39387-39398. doi: 10.1039/d1ra08193d. eCollection 2021 Dec 6.
Xylose is a major component of hemicelluloses. In this paper, its hydrogenation to xylitol in aqueous medium was investigated with two Ru/TiO catalysts prepared with two commercial TiO supports. A strong impact of the support on catalytic performance was evidenced. Ru/TiO-R led to fast and selective conversion of xylose (100% conversion in 2 h at 120 °C with 99% selectivity) whereas Ru/TiO-A gave a slower and much less selective transformation (58% conversion in 4 h at 120 °C with 17% selectivity) with the formation of several by-products. Detailed characterization of the catalysts with ICP, XRD, FTIR, TEM, H chemisorption, N porosimetry, TPR and acid-base titration was performed to elucidate the role of each support. TiO-R has a small specific surface area with large ruthenium nanoparticles in weak interaction with the TiO support and no acidity, whereas TiO-A is a mesoporous material with a large specific surface area that is mildly acidic, and bears small ruthenium particles in strong interaction with the TiO support. The former was very active and selective for xylose hydrogenation to xylitol whereas the latter was less active and poorly selective. Moreover, careful analysis of the reaction products also revealed that anatase TiO can catalyze undesired side-reactions such as xylose isomerisation to various pentoses, and therefore the corresponding unexpected polyols (arabitol, ribitol) were produced during xylose conversion by hydrogenation. In a first kinetic approach, a simplified kinetic model was built to compare quantitatively intrinsic reaction rates of both catalysts. The kinetic constant for hydrogenation was 20 times higher for Ru/TiO-R at 120 °C.
木糖是半纤维素的主要成分。本文研究了在水介质中使用两种由商业TiO载体制备的Ru/TiO催化剂将木糖氢化为木糖醇的过程。结果表明载体对催化性能有很大影响。Ru/TiO-R能使木糖快速、选择性地转化（在120℃下2小时内转化率达100%，选择性为99%），而Ru/TiO-A的转化速度较慢且选择性低得多（在120℃下4小时内转化率为58%，选择性为17%），并生成多种副产物。通过电感耦合等离子体质谱（ICP）、X射线衍射（XRD）、傅里叶变换红外光谱（FTIR）、透射电子显微镜（TEM）、氢化学吸附、氮孔隙率测定、程序升温还原（TPR）和酸碱滴定对催化剂进行了详细表征，以阐明每种载体的作用。TiO-R比表面积小，钌纳米颗粒大，与TiO载体相互作用弱且无酸性，而TiO-A是一种具有大比表面积的介孔材料，呈弱酸性，且钌颗粒小，与TiO载体相互作用强。前者对木糖氢化为木糖醇非常活跃且具有选择性，而后者活性较低且选择性差。此外，对反应产物的仔细分析还表明，锐钛矿型TiO能催化不希望发生的副反应，如木糖异构化为各种戊糖，因此在木糖氢化转化过程中会生成相应的意外多元醇（阿拉伯糖醇、核糖醇）。在初步的动力学研究中，建立了一个简化的动力学模型来定量比较两种催化剂的本征反应速率。在120℃下，Ru/TiO-R的氢化动力学常数高出20倍。
