Ward Antony J, Lesic Rebecca A, Fisher Keith, Proschogo Nicholas, Fábos Viktória, Masters Anthony F, Maschmeyer Thomas
Laboratory of Advanced Catalysis for Sustainability, School of Chemistry F11, University of Sydney, Sydney 2006, (Australia), Fax: (+61) 2 9351 3329.
Chemistry. 2014 Nov 10;20(46):15169-77. doi: 10.1002/chem.201403709. Epub 2014 Sep 1.
Amorphous silica plays an important role in heterogeneous catalysis as a support and is frequently presumed to be "inert". The structure of the supported catalyst is key to understanding the stability and reactivity of catalytic systems. To provide vital insights into the surface reactivity of silica, Polyhedral oligomeric silsesquioxanes (POSSs) can act as realistic homogeneous molecular models for silica surfaces. Here, we report novel reactivities associated with the silica surface, derived from our insights obtained by means of such model systems with potentially significant implications in catalysis when employing silica-supported catalysts. In this work, the gas-phase reactivities of two cyclohexyl-substituted POSSs, namely the completely condensed triganol prism [Si6cy6O9] (a6b0), and the incompletely-condensed partial cube [Si7cy7O9(OH)3] (a7b3), with cy = c-C6H11, were studied by using atmospheric pressure chemical ionisation (APCI) and collision-induced decomposition (CID) spectroscopies. Silsesquioxane a6b0, containing three-membered rings, was found to be much more reactive, undergoing novel CH2-insertion on reaction with gas phase molecules-a reaction not observed for a7b3, containing only four-membered rings. Both silsesquioxanes displayed the ability to trap ammonia formed in situ within the mass spectrometer from N2 in the instrument. This work also demonstrates the applicability of APCI and the role of CID in elucidating reactive POSS structures, highlighting novel gas-phase reactivities of POSS.
无定形二氧化硅在多相催化中作为载体发挥着重要作用，并且通常被认为是“惰性的”。负载型催化剂的结构是理解催化体系稳定性和反应活性的关键。为了深入了解二氧化硅的表面反应活性，多面体低聚倍半硅氧烷（POSS）可作为二氧化硅表面实际的均相分子模型。在此，我们报告了与二氧化硅表面相关的新型反应活性，这些反应活性源自我们通过此类模型体系获得的见解，在使用二氧化硅负载型催化剂时，这些见解可能对催化具有重要意义。在这项工作中，通过大气压化学电离（APCI）和碰撞诱导分解（CID）光谱研究了两种环己基取代的POSS的气相反应活性，即完全缩合的三棱柱[Si6cy6O9]（a6b0）和不完全缩合的部分立方体[Si7cy7O9(OH)3]（a7b3），其中cy = c-C6H11。发现含有三元环的倍半硅氧烷a6b0反应活性更高，在与气相分子反应时会发生新的CH2插入反应——这是仅含有四元环的a7b3未观察到的反应。两种倍半硅氧烷都显示出能够在质谱仪中捕获仪器内由N2原位形成的氨的能力。这项工作还证明了APCI的适用性以及CID在阐明活性POSS结构中的作用，突出了POSS的新型气相反应活性。
