Selective production of aromatics from alkylfurans over solid acid catalysts

Solid acid catalysts were studied at temperatures near 523K for the production of benzene, toluene, and p-xylene by the reaction of ethylene with furan, 2-methylfuran, and 2,5-dimethylfuran, respectively, through the combination of cycloaddition and dehydrative aromatization reactions. Catalysts containing Brønsted acid and Lewis acid sites (i.e., WO_x-ZrO₂, niobic acid, zeoliteY, silica-alumina) were more active than catalysts containing predominantly Lewis acid sites (γ-Al₂O₃, TiO₂), which indicates the importance of Brønsted acidity in the production of aromatics. Microporosity is not required for this reaction, because amorphous solid acids and homogeneous Brønsted acids demonstrate significant activity for p-xylene production. The production of p-xylene from 2,5-dimethylfuran proceeded at higher rates compared with the production of toluene and benzene from 2-methylfuran and furan, respectively. Both WO_x-ZrO₂ and niobic acid demonstrate superior activity for aromatics production than does zeoliteY. WO_x-ZrO₂ demonstrates a turnover frequency for p-xylene production that is 35times higher than that demonstrated by zeoliteY. In addition, mesoporous materials such as WO_x-ZrO₂ offer higher resistance to deactivation by carbon deposition than do microporous materials. Results from Raman spectroscopy and the trend of turnover frequency with varying tungsten surface densities for a series of WOx-ZrO2 catalysts are consistent with previous investigations of other acid-catalyzed reactions; this suggests that the high reactivity of WO_x-ZrO₂ is mainly associated with the presence of subnanometer WO_x clusters mixed with zirconium, which reach a maximum surface concentration at intermediate tungsten coverage.