Abstract
High surface area SiO2 samples were synthesized by one-step hydrolysis and co-condensation at different pH (between 3.0 and 6.0) using tetraethyl orthosilicate as the Si source and formamide as the drying additive. The effects of the presence of H2O, formamide and NH3 solution on the hydrophobic nature, textural properties and catalytic functionality of SiO2 were investigated. The physico-chemical properties of the samples were measured by XRD, FTIR, SEM, TEM, N-2-physisorption and NH3-TPD techniques. It was observed that the use of formamide led to the formation of strong Si-O-Si bonds and the samples possessed a high surface area (325-853 m(2) g(-1)), large pore size (42.5 angstrom) and large pore volume (0.875 cm(3) g(-1)). The characterization results also indicated that SiO2 sample prepared in the absence of water at pH = 3 possessed fewer surface hydroxyl groups, leading the sample to have predominantly hydrophobic nature. An increase in water content in the SiO2 precursor solutions resulted in an increase in the average particle size with a more hydrophilic nature. All synthesized SiO2 samples were tested for partial oxidation of methanol at a temperature range of 200-400 degrees C. The sample synthesized at pH = 3 without water offer 90% conversion at 400 degrees C; however the SiO2 sample synthesized with low water content (100 mmol) at pH= 4 offered the best selectivity (83%) to methyl formate and formaldehyde with moderate methanol conversion (72%). The SiO2 sample prepared at pH = 6 with more water content offered less methanol conversion (60%) and low selectivity toward oxygenated products. It is evident that SiO2 samples that possessed better textural properties and moderate hydrophobicity performed better in partial methanol oxidation.