Aqueous-phase dehydration of xylose to furfural in the presence of MCM-22 and ITQ-2 solid acid catalysts

The H-MCM-22 zeolite possessing an MWW (medium-pore) framework and its delaminated counterpart, ITQ-2, with enhanced external surface area, are effective and recyclable solid acid catalysts in the batch-wise, aqueous-phase dehydration of xylose, at 170 °C. Up to 71% furfural (Fur) yield is reached at 98% conversion using a biphasic aqueous–organic solvent system (for the simultaneous extraction of Fur); using solely water as the solvent gives up to 54% Fur yield at 97% conversion. Sulfuric acid, used in an approximately equivalent amount to the total acid site concentration of the solid acids, gave 55% Fur yield at 93% conversion. Decreasing the Si/Al ratio of H-MCM-22 zeolite improves the acid properties and consequently the catalytic activity, without affecting significantly the Fur selectivity. While the delamination process considerably enhanced the external surface area of ITQ-2 in comparison to H-MCM-22, it caused modifications in the acid properties, leaving the two prepared materials with the same Si/Al atomic ratio of 24, on a comparable footing in terms of catalytic performance in the studied catalytic reaction. Nevertheless, these solid acid catalysts are fairly stable (similar Fur yields are reached in recycling runs; no structural modifications and no leaching phenomena were detected).

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► H-MCM-22 and ITQ-2 are effective catalysts in aqueous phase dehydration of xylose to furfural.
► H-MCM-22 and ITQ-2 give similar catalytic results to the industrial catalyst H2SO4.
► Recyclable solid acids with no structural modifications or leaching phenomena detected.