Preparation of silica xerogel beads embedded with Fe2O3 nanoparticles and their characterization

摘要

Fe2O3 nanoparticles immobilized on SiO2 xerogel beads were prepared using a sol-gel-based method. Two different acid catalysts, namely citric acid and acetic acid, were used to modify the preparative conditions and materials with desirable surface characteristics and pore structure. Three sets of samples with 1, 5, and 10 wt% Fe2O3 dispersed on silica beads were synthesized. A decrease in the specific surface area from 457.1 to 144 m(2)/g and pore volume from 0.558 to 0.172 cm(3)/g was observed when the iron content was increased from 1 to 10 wt% in the case of acetic acid-catalyzed sample. A similar decreasing trend was observed in citric acid-catalyzed samples due to the precipitation of Fe2O3 in the pores. XRD studies revealed the presence of both alpha-Fe2O3 and gamma-Fe2O3 phases in the 1000 degrees C calcined samples. The Mossbauer data showed that the fraction of alpha-Fe2O3 decreased while gamma-Fe2O3 increased in samples with Fe content. Structural investigations carried out by Mossbauer spectroscopy also revealed the oxidation state of Fe in the sample as + 3. From scanning electron micrographs (SEM), sub-micron size particles of Fe2O3 homogeneously dispersed on SiO2 having faceted geometry could be revealed. TPR results of these samples showed a good interaction of Fe2O3 particles with the silica support with a distinct reduction profile compared to bulk Fe2O3 and indicated that Fe2O3 nanoparticles were homogeneously distributed throughout SiO2 surface and within the mesoporous structure of SiO2. Catalytic activity measurement of these catalysts towards sulfuric acid decomposition reactions at 800 degrees C showed a constant yield of similar to 55% of SO2 at a WHSV of 27 g acid g(-1) h(-1). The catalyst showed a good stability for more than 12 h at 800 degrees C for continuous operation.