高分散费-托合成铁/活性炭催化剂的研究——Ⅰ.铁/活性炭催化剂的恒温还原及其穆斯堡尔谱

STUDIES ON HIGHLY DISPERSED IRON/ACTIVATED CARBON CATALYSTS FOR FISCHER-TROPSCH SYNTHESIS——Ⅰ. MOSSBAUER SPECTROSCOPIC STUDY OF THE REDUCTION OF IRON/ACTIVATED CARBON CATALYSTS

使用原位穆斯堡尔谱研究了非担载铁氧化物和不同担载量的铁/活性炭催化剂在不同温度下的还原,详细分析了活性炭载体上高分散超顺磁铁物类的穆斯堡尔谱。还原前铁/活性炭催化剂中的铁物类为结构松散的α-Fe_2O_3和没有充分脱水的氧化铁,铁的担载量不很小时可经Fe_3O_4还原到金属态,但活性炭载体可稳定Fe^(3+)使之难以还原,在500℃氢气中大部分铁才还原为金属。铁的担载量很小时,其还原以Fe^(2+)为中间产物,0.2%Fe/AC氢气化剂在500℃氢气还原18小时生成磁分裂金属铁和超顺磁金属铁(δ=0.37mm/s,△=0,H=0),其正的同质异能移表示了铁-活性炭间的电荷转移。

The reduction of unsupported iron oxide and activated carbon (AC) supported iron catalysts in H_2 at different temperatures has been investigated with in situ Mossbauer spectroscopy. The Mossbauer spectra of highly dispersed superparamagnetic iron oxides on the AC support were analysed in detail. Before reduction the iron species in the Fe/AC catalysts are poorly crystallized α-Fe_2O_3 and hydrated iron oxide. They can be reduced to metallic iron via Fe_3O_4, when the iron loading is not very small. However, the AC support stabilizes Fe^(3+), so that not until 500℃ can most of the iron be reduced to metal by H_2. When the loading of iron is very small, the iron species are reduced to metal via Fe^(2+). The reduction of a 0.2% Fe/AC sample at 500℃ in H_2 for 18 hours results in the formation of magnetic α-Fe and superparamagnetic α-Fe(δ= 0.37mm/s, △=0, H=0). The positive isomer shift of the superparamagnetic α-Fe indicates an electron transfer between metallic iron and the AC support.