Isomerization of Norbornadiene to Quadricyclane Using Ti-Containing MCM-41 as Photocatalysts
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Isomerization of Norbornadiene to Quadricyclane Using Ti-Containing MCM-41 as Photocatalysts Ji-Jun Zou Æ Ming-Yue Zhang Æ Bin Zhu Æ Li Wang Æ Xiangwen Zhang Æ Zhentao Mi
Received: 21 November 2007 / Accepted: 11 February 2008 / Published online: 5 March 2008 Springer Science+Business Media, LLC 2008
Abstract Heterogeneous Ti-containing MCM-41 materials were prepared for the photocatalytic isomerization of norbornadiene to quadricyclane with the aim of replacing homogeneous sensitizers. Chemical grafting produces quantum-size TiO2 crystallites highly dispersed in the pore of MCM-41. Isomorphous substitution generates Ti species in the framework of MCM-41, but some non-framework species are formed with increasing Ti content. It is found that Ti-containing MCM-41 materials show significantly higher photocatalytic activity than bulk TiO2, and the framework Ti species are more active than the surfacedispersed species. Keywords Photocatalyst Ti–MCM-41 Norbornadiene Quadricyclane Isomerization
1 Introduction Photocatalytic valance isomerization of norbornadiene(NBD, bicyclo[2.2.1]hepta-2,5-diene) to quadricyclane(QC, tetracyclo[3.2.0.02,7.04,6]heptane) has been regarded as an effective way to store solar energy for decades [1–3]. In this reaction, about 89 kJ of energy is stored in one mole of QC molecules due to its highly-strained structure. The stored energy can be released through the inverse reaction under specific conditions. J.-J. Zou M.-Y. Zhang B. Zhu L. Wang (&) X. Zhang Z. Mi Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China e-mail: [email protected] J.-J. Zou e-mail: [email protected]
QC is a liquid with melting point of -40 C, density of 0.98 g/mL (20 C), and combustion heat of 44.9 MJ/kg [4]. It is stable under atmospheric conditions, thus can be easily stored, transported and handled. During combustion, the strained energy released can significantly increase the heat value. So QC has been considered as a potential high-energy density liquid fuel for the replacement or additives of current hydrocarbon fuels. It is reported that the H2O2/QC mixture shows higher specific impulse than the mixture based on RP-1 that is a widely used rocket fuel [4, 5]. It is also considered as a nontoxic high energy fuel in satellite control system to replace the highly toxic hydrazine [6]. The isomerization of NBD to QC occurs under irradiation, but the reaction has to be assisted with sensitizers or photocatalysts because the NBD molecules cannot absorb solar energy directly. The sensitizer-catalytic isomerization has been widely investigated. Many sensitizers like Michler’s Ketones, benzenzophenone, CuCl2 and Ru compounds have been used for this reaction [7–9]. Although these sensitizers show high activity and selectivity, they, unfortunately, suffer from some drawbacks. The sensitizers are not stable under irradiation and prone to decompose. Homogenous sensitizers are soluble in the re
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