An efficient catalyzed liquid-phase selective oxidation of p-cymene to tertiary cymene hydroperoxide (TCHP) and its derivative p-methylacetophenone (PMAP) was achieved over a nanostructured ruthenium-cerium oxide (Ru/CeO₂) composite catalyst with remarkable activity using a green molecular oxygen oxidant. Both of the composite catalysts were prepared from CeO₂ oxide with different particles sizes [i.e., bulk CeO₂ (Ru/b-CeO₂) and nanosized CeO₂ (Ru/n-CeO₂)]. The n-Ru/CeO₂ exhibited high catalytic activity for the free-radical driven oxyfunctionalization reaction of the inert CH bond in p-cymene to afford up to 55% conversion within 5 h at 65% TCHP and 26% PMAP selectivity. The combined ratio of the TCHP/PMAP selectivity was dependent on the reaction time and the amount of p-cymene conversion. An increase in the reaction time resulted in converted large amount of TCHP to PMAP. The better catalytic performance of the Ru/n-CeO₂ catalyst compared to Ru/b-CeO₂ was partially due to the catalyst redox and oxygen vacancies effect. Both the reduced and oxidized forms of Ru/n-CeO₂ were investigated to gain insight into the active form of the catalyst. The reduced Ru/n-CeO₂ catalyst exhibited poor performance compared to the high catalytic performance of the oxidized form. This result demonstrated the significant concomitant effect of the balanced Ru⁴⁺/Ru³⁺ and Ce⁴⁺/Ce³⁺ redox combination to facilitate the free-radical driven mechanism via the excitation of O₂ to activate the substrate inert CH. The Ru/n-CeO₂ catalyst was highly recyclable with consistent activity after its sequential re-use. The catalytic performance of Ru/n-CeO₂ was correlated to its structural characteristics based on the results from complimentary techniques, such as powder XRD, Raman spectroscopy, HRTEM, BET SA nitrogen physisorption, FESEM, H₂-TPR and EDX. According to the characterization results, the enhanced catalytic performance of the Ru NPs loaded on CeO₂ with nanosized particles was due to intrinsic metal-metal oxide interactions, enhanced redox cycles and high oxygen mobility resulting from structural defects of n-CeO₂ that form oxygen vacancies compared to dispersed on the bulk CeO₂ with large particles. The catalytic activity exhibited by Ru/CeO₂ provides encouraging results to add to the class of active and stable catalysts for the activation of typical alkyl aromatic hydrocarbons, such as the p-cymene inert CH bond, for the selective introduction of an oxygen atom.

中文翻译：

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钌-铈氧化物纳米复合材料的界面结构效应对其催化氧化生物萜衍生的对-丁烯的催化活性

的有效催化的液相选择性氧化p -cymene〜叔伞花烃氢过氧化物（TCHP）及其衍生物p甲基苯乙酮（PMAP）经一个纳米结构的钌-氧化铈（RU /实现的CeO ₂），使用了显着的活性复合催化剂绿色分子氧氧化剂。两种复合催化剂均由具有不同粒径[即本体CeO ₂（Ru / b-CeO ₂）和纳米级CeO ₂（Ru / n-CeO ₂）]的CeO ₂氧化物制备。所述Ñ -Ru /的CeO ₂用于惰性CH键的自由基驱动oxyfunctionalization反应表现出高的催化活性p -cymene，得到高达55％的转化率5小时内，在65％TCHP和26％PMAP选择性。TCHP / PMAP选择性的总比值取决于反应时间和对-Cymene转化量。反应时间的增加导致大量的TCHP转化为PMAP。与Ru / b-CeO ₂相比，Ru / n-CeO ₂催化剂具有更好的催化性能，部分原因在于催化剂的氧化还原和氧空位效应。研究了Ru / n-CeO ₂的还原形式和氧化形式，以深入了解催化剂的活性形式。还原的Ru / n-CeO与氧化形式的高催化性能相比，图_2的催化剂表现出较差的性能。该结果证明了平衡的Ru ⁴⁺ / Ru ³⁺和Ce ⁴⁺ / Ce ³⁺氧化还原组合的显着伴随作用是通过O ₂的激发来促进自由基驱动机制，以活化底物惰性CH。连续使用后，Ru / n-CeO ₂催化剂具有较高的可回收性和稳定的活性。Ru / n-CeO ₂的催化性能基于互补技术的结果，例如粉末XRD，拉曼光谱，HRTEM，BET SA氮物理吸附，FESEM，H ₂ -TPR和EDX ，将其与结构特征相关联。根据表征结果，具有纳米颗粒的负载在CeO ₂上的Ru NPs增强的催化性能是由于固有的金属-金属氧化物相互作用，增强的氧化还原循环和形成氧的n -CeO _2的结构缺陷导致的高氧迁移率所致。与分散在具有大颗粒的块状CeO ₂上相比，空位较大。Ru / CeO ₂表现出的催化活性在为选择性引入氧原子而活化典型的烷基芳香烃（例如对甲基异丙基惰性CH键）的活性和稳定催化剂类别中提供令人鼓舞的结果。