Zhu Lihua,Cao Maohong,Zhou Hua,Zhang Nuowei,Zheng Jinbao,Li Yunhua,Chen Bing H.
Abstract
A series of CaO/Al 2 O 3 base catalysts with different crystal phases is prepared via thermal treatment. The as-prepared base catalysts are tested through Baeyer–Villiger oxidation of cyclohexanone to ε-caprolactone in liquid-phase using a mixture of aqueous hydrogen peroxide and benzonitrile as oxidant. The corresponding results show that the CaO/Al 2 O 3 catalysts with high thermal treatment temperature (e.g. 900 °C) exhibit excellent activity as well as stability. Upon these, the catalysts are characterized by TG–DTG, XRD, N 2 -physisorption, SEM and CO 2 -TPD techniques. The characterization results clearly suggest that such a stable and efficient catalytic performance is beneficial from the formation of calcium aluminate phase, thus overcoming one of base catalyst application barriers, that Ca or CaO species loss (leach) from CaO-based catalysts during reactions. Correspondingly, it can be inferred that the treatment of the catalysts at different temperatures results in the diverse distribution of basic strength. Furthermore, it is also demonstrated that the suitable base strength (medium strength is good for the reaction selected in the work) plays a critically role in the improvement of catalytic performance. Finally, the effects of operation conditions on catalytic activity and product selectivity are also determined and discussed. Graphical Abstract
Yujiao Zhang,Shengli Niu,Kuihua Han,Yingjie Li,Chunmei Lu
Calcium oxide is one of the most promising heterogeneous catalysts for biodiesel production . However, an inherent drawback of CaO is the leaching of active species into the reaction solution with the degraded reusability . To strengthen the stability, different supports are composited with the SrO–CaO oxide through the hydrothermal method and mass ratio of SrO to CaO are optimized to get the best outcome of the catalyst. Meanwhile, various characterization methods, including TG , XRD , SEM-EDX, CO 2 -TPD, XPS , ATR-FTIR and ICP-AES, are used to explore the physicochemical properties of catalysts. The 0.4-SrO-CaO-Al 2 O 3 catalyst shows the best catalytic capability in transesterification of palm oil with methanol to produce biodiesel , where the FAME yield of 98.16% is achieved with the molar ratio of methanol to oil of 18:1 and catalyst concentration of 7.5 wt% at 65 °C for 3 h. Besides, ascribed to the greatly reduced leaching out of the active species , this catalyst presents the satisfying reusability and the FAME yield is slightly decreased to 92.61% for the fifth reused cycle. Therefore, this modification method for SrO–CaO–Al 2 O 3 is feasible for enhancing the catalytic stability in transesterification .
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