resumo
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 degrees 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). (C) 2012 Elsevier B.V. All rights reserved.
palavras-chave
12-TUNGSTOPHOSPHORIC ACID; SELECTIVE PREPARATION; ZEOLITE; TRANSFORMATION; CONVERSION; MECHANISM; ADSORPTION; PRECURSOR; BENZENE
categoria
Chemistry; Environmental Sciences & Ecology
autores
Antunes, MM; Lima, S; Fernandes, A; Pillinger, M; Ribeiro, MF; Valente, AA
nossos autores
Anabela Tavares Aguiar Valente
Investigador Principal
Maria Margarida Feitor Pintão Moreno Antunes
Investigador Júnior
Martyn Pillinger
Investigador Principalagradecimentos
This work was partly funded by the FCT, POCTI and FEDER (project POCTI/QUI/56112/2004). The authors thank Dr U. D. Morales (Instituto de Tecnologia Quimica, CSIC, Universidad Politecnica de Valencia) for the valuable help with the recipe of ITQ-2; Marta A. C. Ferro for help with the TEM studies, and acknowledge the Portuguese network of electron microscopy, the RNME, FCT Project REDE/1509/RME/2005; Prof. C.P. Neto (University of Aveiro) for helpful discussions; Dr. F. Domingues (University of Aveiro) for access to HPLC equipment. S.L. (SRFH/BPD/23765/2005) and M.M.A. (SFRH/BD/61648/2009) are grateful to the FCT for grants.