摘要
用浸渍法制得了不同铁含量的Fe(NO_3)_3·9H_2O/活性炭前驱态催化剂,然后在氩气中经不同温度处理,进行原位穆斯堡尔谱考察。结果表明,金属组分与载体之间存在着程度不同的相互作用,并且这种作用随着铁含量的增加而减弱。此外,这种作用还与活性炭表面的能量、位置以及α-Fe_2O_3的颗粒大小密切相关。研究发现,当催化剂热处理温度为600℃时,磁分裂Fe_3O_4向超顺磁Fe_3O_4转化,表明Fe_3O_4在活性炭表面再分散,进而推断Fe(x)(一种高分散还原态铁物类)可能是由超顺磁Fe_3O_4还原得到的。本文还就α-Fe_2O_3在活性炭表面的分散过程进行了讨论。
Fe/C catalyst precursors were prepared by impregnating activated carbon in Fe(NO3)3 · 9H2O solution of different concentrations followed by heat treatment at 350, 500, 600 and 700℃ in Ar. Mossbauer spectra of these catalyst samples with different iron contents manifested that there existed interaction between iron and activated carbon. The intensity of the interaction decreased with increasing the iron loading. From the data of Mossbauer spectra of the catalysts treated at 350℃, the amount of su-perparamagnetic α-Fe2O3 per gram of activated carbon could be counted, and which increased with the increase of iron loading. This meant that the dispersion of iron on the surface of activated carbon was not uniform, and iron would re-disperse and aggregate as iron salts decomposed.When the catalysts treated at 600℃, Fe3O4(m) was converted to Fe3O4(s), this was the further proof of the re-dispersion of iron species. In combination with the results of treatment at 700℃, it was deduced that a reduced state iron with high dispersion named as Fe(x) was probably produced by the reduction of Fe3O4 (s). Moreover, the intensity of metal-support interaction was related to the distribution of energy on the activated carbon surface, the particle size of α-Fe2O3 and the degree of reduction of α-Fe2O3. The smaller the particle size of α-Fe2O.,, the stronger the metal-support interaction was, and therefore, α-Fe2O3 was more difficult to be reduced.
