Abstract:

Fe₃O₄/C-SO₃H was a magnetic carbon-based solid acid catalyst. It was prepared with Fe₃O₄, biomass carbon and sulfonic acid source, in which Fe₃O₄ was the magnetic core and biomass carbon （glucose, starch, sucrose） was the raw material. Firstly, Fe₃O₄/C was prepared by the carbonization reaction taken place between Fe₃O₄ and biomass. Then, sulfonation of Fe₃O₄/C with p-toluenesulfonic acid was carried out, and thus Fe₃O₄/C-SO₃H was prepared. The synthesis of octyl glucoside was used as a probe reaction. The activity of the catalyst was measured by the conversion of glucose and the catalyst acid content. The influencing factors such as biomass carbon type, carbonization temperature, carbonization time, acid type, sulfonation temperature and sulfonation time were investigated. The catalyst was characterized by FT-IR, XRD, TG, SEM and Vibrating Sample Magnetometer （VSM）. The results show that, the optimum preparation conditions of Fe₃O₄/C-SO₃H are as follows: Starch is the best biomass carbon source among glucose, starch and sucrose; the mass ratio of Fe₃O₄ to starch is 1:10; carbonization temperature is 190 ℃; carbonization time is 8 h; among the three sulfonic acid sources （p-toluenesulfonic acid, dodecylbenzene sulfonic acid and concentrated sulfuric acid）, p-toluenesulfonic acid is the best; the mass ratio of Fe₃O₄/C to p-toluenesulfonic acid is 1:0.6; the sulfonation temperature is 250 ℃; the sulfonation time is 4 h. Under the optimized conditions, the acid content of the catalyst is 1.17 mmol/g, and the glucose conversion is 97.9%. XRD results show that the crystal structure of magnetic Fe₃O₄ particles does not significantly change after carbonization and sulfonation, and the catalyst still retains good magnetic properties. FT-IR analysis shows that sulfonic groups are successfully loaded on the carrier Fe₃O₄/C. Thermogravimetric analysis shows that Fe₃O₄/C-SO₃H has good thermal stability below 300 ℃. SEM shows that magnetic Fe₃O₄ particles are irregular spherical particles with uniform size distribution and agglomeration. After carbonization, Fe₃O₄ are encapsulated by starch, and the particle size becomes larger, and there is a certain pore structure. The Fe₃O₄/C-SO₃H catalyst also has a certain core-shell structure, and the particle size is approximately 30 nm. The VSM curves show that the magnetic strength of Fe₃O₄/C and Fe₃O₄/C-SO₃H is much smaller than that of Fe₃O₄, but Fe₃O₄/C-SO₃H can be separated from the system rapidly by simple magnetic attraction. It shows that the final magnetic properties of Fe₃O₄/C-SO₃H meet the requirements of magnetic separation and recovery.

Key words: magnetic catalyst, solid acid catalyst, octyl glucoside