费托合成铁基催化剂上CO和H_2的吸附特性

Chemisorption Characteristics of CO and H_2 over Iron-based Fischer-Tropsch Synthesis Catalyst

在25～300℃和0.1～2.5MPa范围内,利用程序升温脱附及原位漫反射红外光谱考察了CO,H2及合成气在费托合成沉淀铁基催化剂上的吸附行为.程序升温脱附表明,CO在铁基催化剂表面上存在线性、孪性及桥式吸附,对H2则有强、弱两类吸附活性中心;CO吸附红外光谱表明,2170和2116cm-1处存在明显的线性吸附双峰,1623～1313cm-1处存在少量表面态吸收峰,且随温度升高,在2360和2319cm-1处出现了CO2的特征吸收峰,催化剂表面对CO的吸附受温度和压力影响;合成气共吸附反应的红外光谱表明,费托合成烃生成机理及含氧化合物生成机理可用吸附态物种的变化解释,升高温度有利于CO加氢反应进行,高温高压有利于C2+含氧化合物生成.

The adsorption behaviors of CO, H2 and syngas over precipitated iron-based Fischer-Tropsch synthesis catalyst were studied by temperature programmed desorption （TPD） and in situ diffuse reflectance FT-IR spectroscopy under the conditions of 25-300 ℃ and 0.1-2.5 MPa. CO-TPD showed that there were different adsorbed active sites over the iron-based catalyst and linear, twin and bridged CO. H2-TPD evidenced that there were two kinds of desorption peaks （strong and weak） over the catalyst. CO FT-IR demonstrated that clear double linear CO bands existed at 2170 and 2116 cm^-1 and a few surface adsorption bands occurred at 1623-1313 cm^-1. Characteristic adsorbed CO2 bands appeared with the temperature increasing at 2360 and 2 319 cm^-1. Meanwhile, the temperature and pressure had effects on CO adsorbed sites over the catalyst. Mechanisms of Fischer-Tropsch synthesis and oxygenate compound formation over the catalyst could be explained by the change of adsorbed species, In addition, increasing the temperature enhanced the CO hydrogenation, while high temperature and pressure favored the formation of C^2＋-oxygenate compound at the reaction conditions.