Grigoreva Anna, Kolobova Ekaterina, Pakrieva Ekaterina, Mäki-Arvela Päivi, Carabineiro Sónia A C, Gorbunova Alina, Bogdanchikova Nina, Murzin Dmitry Yu, Pestryakov Alexey
Research School of Chemistry & Applied Biomedical Sciences, National Research Tomsk Polytechnic University, 634050 Tomsk, Russia.
Johan Gadolin Process Chemistry Centre, Åbo Akademi University, 20500 Turku/Åbo, Finland.
Nanomaterials (Basel). 2021 Feb 12;11(2):469. doi: 10.3390/nano11020469.
Herein, it has been shown that betulin can be transformed into its biologically active oxo-derivatives (betulone, betulinic and betulonic aldehydes) by liquid-phase oxidation over supported silver catalysts under mild conditions. In order to identify the main factors determining the catalytic behavior of nanosilver catalysts in betulin oxidation, silver was deposited on various alumina supports (γ-alumina and boehmite) using deposition-precipitation with NaOH and incipient wetness impregnation methods, followed by treatment in H or O. Silver catalysts and the corresponding supports were characterized by X-ray diffraction, nitrogen physisorption, inductively coupled plasma optical emission spectroscopy, photoelectron spectroscopy and transmission electron microscopy. It was found that the support nature, preparation and treatment methods predetermine not only the average Ag nanoparticles size and their distribution, but also the selectivity of betulin oxidation, and thereby, the catalytic behavior of Ag catalysts. In fact, the support nature had the most considerable effect. Betulin conversion, depending on the support, increased in the following order: Ag/boehmite < Ag/boehmite (calcined) < Ag/γ-alumina. However, in the same order, the share of side reactions catalyzed by strong Lewis acid centers of the support also increased. Poisoning of the latter by NaOH during catalysts preparation can reduce side reactions. Additionally, it was revealed that the betulin oxidation catalyzed by nanosilver catalysts is a structure-sensitive reaction.
在此已表明，在温和条件下，通过负载型银催化剂上的液相氧化，桦木醇可转化为其生物活性氧代衍生物（桦木酮、桦木酸和桦木酮醛）。为了确定决定纳米银催化剂在桦木醇氧化中催化行为的主要因素，采用氢氧化钠沉积沉淀法和初湿浸渍法将银负载在各种氧化铝载体（γ-氧化铝和勃姆石）上，随后在氢气或氧气中进行处理。通过X射线衍射、氮物理吸附、电感耦合等离子体发射光谱、光电子能谱和透射电子显微镜对银催化剂及相应载体进行了表征。结果发现，载体的性质、制备和处理方法不仅预先决定了银纳米颗粒的平均尺寸及其分布，还决定了桦木醇氧化的选择性，从而决定了银催化剂的催化行为。事实上，载体的性质影响最为显著。取决于载体，桦木醇的转化率按以下顺序增加：Ag/勃姆石＜Ag/勃姆石（煅烧）＜Ag/γ-氧化铝。然而，同样按此顺序，载体强路易斯酸中心催化的副反应份额也增加。在催化剂制备过程中用氢氧化钠对后者进行中毒处理可减少副反应。此外，还发现纳米银催化剂催化的桦木醇氧化是一个结构敏感反应。
