Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong, People's Republic of China.
Philos Trans A Math Phys Eng Sci. 2013 Jun 3;371(1994):20110590. doi: 10.1098/rsta.2011.0590. Print 2013 Jul 13.
Polycyclic aromatic hydrocarbons (PAHs) are known to be present in many astrophysical objects and environments, but our understanding of their formation mechanism(s) is far from satisfactory. In this paper, we describe an investigation of the catalytic conversion reaction of acetylene gas to PAHs over pyroxene and alumina. Crystalline silicates such as pyroxenes (with general formula [Mg, Fe]SiO₃) and alumina (Al₂O₃) are observed astrophysically through their infrared spectra and are likely to promote grain surface chemical reactions. In the experiments reported here, gas-phase PAHs were produced by the catalytic reaction of acetylene over crystalline silicates and alumina using a pulsed jet expansion technique and the gaseous products detected using time-of-flight mass spectrometry. In a separate experiment, the catalytic formation of PAHs from acetylene was further confirmed with acetylene gas at atmospheric pressure flowing continuously through a fixed-bed reactor. The gas effluent and carbonaceous compounds deposited on the catalysts were dissolved separately in dichloromethane and analysed using gas chromatography-mass spectrometry. Among the samples studied, alumina showed higher activity than the pyroxene-type grains for the acetylene reaction. It is proposed that formation of the PAHs relies on the Mg²⁺ ions in the pyroxenes and Al³⁺ ions in alumina, where these ions act as Lewis acid sites. X-ray diffraction, Fourier transform infrared and high-resolution transmission electron microscopy techniques were used to characterize the structure and physical properties of the pyroxene and alumina samples.
多环芳烃（PAHs）已知存在于许多天体物理物体和环境中，但我们对其形成机制的理解还远远不够。在本文中，我们描述了对乙快气体在辉石和氧化铝上催化转化为 PAHs 的反应的研究。结晶硅酸盐，如辉石（通式为[Mg，Fe]SiO₃）和氧化铝（Al₂O₃），通过它们的红外光谱在天体物理学中被观察到，并且可能促进颗粒表面的化学反应。在本文报道的实验中，通过使用脉冲喷射扩展技术使乙快气体在结晶硅酸盐和氧化铝上发生催化反应，产生气相 PAHs，并使用飞行时间质谱法检测气态产物。在另一个实验中，通过在大气压下使乙快气体连续流过固定床反应器，进一步证实了乙快气体催化生成 PAHs。气体流出物和沉积在催化剂上的含碳化合物分别溶解在二氯甲烷中，并使用气相色谱-质谱法进行分析。在所研究的样品中，氧化铝对乙快反应的活性高于辉石型颗粒。据提议，PAHs 的形成依赖于辉石中的 Mg²⁺离子和氧化铝中的 Al³⁺离子，其中这些离子充当路易斯酸位。使用 X 射线衍射、傅里叶变换红外和高分辨率透射电子显微镜技术对辉石和氧化铝样品的结构和物理性质进行了表征。
