激光促进了烷裂解表面反应过程中的能量传递

Energy Transfer During the Processes of Laser Stimulated Surface Reaction of n-Butane Cracking

本文利用红外光谱、化学吸咐和激光表面反应技术,研究了丁烷在H-ZSM-5分子筛、SiO_2和γ-A1_2O_3表面上的激光表面反应规律;研究了不同激发模式、固体表面材料的红外特性及化学吸附能力、激光脉冲次数及脉冲间隔时间等因素对激光光能利用率的影响;证实了固体表面键激发模式的有效性,探讨了激光表面反应过程中能量吸收、积累、传递和损失的途径,提出了激光促进丁烷裂解的表面反应机理。

Infrared spectroscopy, chemisorption and pulse CO2 laser techniques have been used to investigate the behaviors of laser stimulated n- butane cracking on the surfaces of ZSM- 5 zeolite, γ- Al2O3 and SiO2 at room temperature and atmospheric pressure. A reaction mechanism of laser stimulated n-butane cracking on the solid surfaces and a model of energy transfer and relaxation in such a process are proposed based on the experimental results. This investigation has shown that the LSSR is an excellent reaction technique for n- butane cracking to ethene. Under the conditions of room temperature and atmospheric pressure, the reaction products of laser stimulated n-butane cracking on the ZSM-5 zeolite are ethane, ethene, propane and propylene, the conversion of n-butane is above 22% and the selectivity of ethene in the reaction products is above 66%. The solid surface plays an important part and the vibrational excitation of the solid surface bonds is an effective mode for LSSR. In the LSSR, the direction and rate of the energy transfer and relaxation comply with the rule of high frequency to low frequency and with the approaching principle of the vibrational frequency. The efficiency of laser photon energy in the ESS mode depends strongly on the frequency and the pulse time interval of the laser, the infrared characteristics of the solid materials and the capability of the reactant molecules. Three reaction steps (reactant chemisorption, laser excitation and surface reaction) are included in the course of LSSR. The reactivity of n-butane cracking depends essentially on the adsorbing amount of n-butane and on the rate of energy transfer from the excited solid surface bonds to the bonds to be excited in the adsorbent n-butane molecules. The selectivity of reaction products depends essentially on the chemisorption state of n-butane and the energy transfer from the excited bond to other bonds in the adsorbent n-butane molecules.