摘要
用原位穆斯堡尔谱研究了Fe-K-Cr/C体系催化剂在脱氧反应前后铁组分的价态变化。通过与反应结果相关联,初步认为该催化剂在脱氧反应中铁的化学形态是决定其高CO选择性的关键,α-Fe和Fe_3C等还原态铁的存在是导致产物中高CO/(CO+CO_2)比的前提;而且催化剂的稳定性取决于还原态铁对氧化气氛的稳定性。K,Cr等助催化剂明显增强了这种稳定性。此外,推断在脱氧反应温度下(约700℃),还原态铁加速了反应C+CO_2→2CO的进行,从而使气体产物中CO/(CO+CO_2)比增大。
The valence change of iron species in Fe-K-Cr/C catalyst before and after deoxidation was studied by using in-situ Mossbauer spectrometer. The heal treatment temperature of catalysts influences greatly the CO/CO2 ratio of the product. It is demonstrated that the chemical states of iron are the decisive factors for the CO selectivity, iron in reduced state, such as Fe3C, α-Fe, is the prerequisite to obtain high CO/CO2 ratio and the iron in oxidized state is favourable to form CO2. The study on the stability of Fe-K-Cr/C, Fe-K/C and Fe/C catalysts presents an order as Fe-K-Cr/>Fe-K/C>Fe/C. The catalyst stability depends on the extent of stability of the reduced iron to the oxidizing atmosphere. The coordinated effect of the promoters K and Cr is to improve the stability of the reduced state iron. It is deduced that the reduced state iron at deoxidation temperature (about 700℃)may accelerate the C + CO2→2CO reaction and thus increases the CO/CO 2 ratio in the product.
