Conformal sulfated zirconia monolayer catalysts for the one-pot synthesis of ethyl levulinate from glucose

The primary goal of this preparation method was synthesis of uniformly coated ZrO2/SBA-15 materials exhibiting high dispersion and accessibility of zirconium using a layerwise deposition method to minimize growth of large crystallites. SBA15 was prepared the original method by Zhao et al.1 First 10g of SBA-15 was dried at 300°C for 4 hours. Then the dried SBA-15 and 58.5g of zirconium precursor (70% zirconium propoxide in propanol, Sigma-Aldrich) were added to 300ml of dry hexane in a round bottom flask. The amount of zirconium precursor is based on the number of hydroxyl groups of SBA15 calculated according to thermal gravimetric analysis. So that each hydroxyl group could react with zirconium propoxide and a uniform layer would graft on SBA-15. The mixture was refluxed at 69°C overnight and then filtered and washed 3 times with hexane in order to remove any unreacted precursor. Afterwards, the material was rehydrated by adding it to 300ml deionized water under stirring for 4h to fully hydrolyze any residual propoxide groups. Finally the catalyst was filtered and dried at 80°C overnight. To get SBA-15 with 2 and 3 monolayers, the same procedure was repeated 2 and 3 times respectively. A subsequent step of sulphation with H2SO4 was made by adding the ZrO2/SBA-15 catalysts to a 0.075M aqueous sulphuric acid solution (volume 10 ml acid per g sample) for 5h, after which the sample was filtered and dried at 80°C overnight. As a final step of preparation, the materials were calcined at 550°C for 3h.