resumo
The acid-catalysed, aqueous phase dehydration of xylose (a monosaccharide obtainable from hemicelluloses, e.g., xylan) to furfural was investigated using vanadium phosphates (VPO) as catalysts: the precursors, VOPO4 center dot 2H(2)O. VOHPO4 center dot 0.5H(2)O and VO(H2PO4)(2), and the materials prepared by calcination of these precursors, that is, gamma-VOPO4, (VO)(2)P2O7 and VO(PO3)(2), respectively. The VPO precursors were completely soluble in the reaction medium. In contrast, the orthorhombic vanadyl pyrophosphate (VO)(2)P2O7, prepared by calcination of VOHPO4 center dot 0.5H(2)O at 550 degrees C/2 h, could be recycled by simply separating the solid acid from the reaction mixture by centrifugation, and no drop in catalytic activity and furfural yields was observed in consecutive 4 h-batch runs (ca. 53% furfural yield, at 170 degrees C). However, detailed catalytic/characterisation studies revealed that the vanadyl pyrophosphate acts as a source of active water-soluble species in this reaction. For a concentration of(VO)(2)P2O7 as low as 5 mM, the catalytic reaction of xylose (ca. 0.67 M xylose in water, and toluene as solvent for the in situ extraction of furfural) gave ca. 56% furfural yield, at 170 degrees C/6 h reaction. (C) 2011 Elsevier Ltd. All rights reserved.
palavras-chave
LIQUID-PHASE DEHYDRATION; N-BUTANE OXIDATION; SOLID ACID CATALYSTS; SELECTIVE OXIDATION; MALEIC-ANHYDRIDE; PHOSPHATE CATALYSTS; REACTIVITY; TEMPERATURE; PERFORMANCE; CONVERSION
categoria
Biochemistry & Molecular Biology; Chemistry
autores
Sadaba, I; Lima, S; Valente, AA; Granados, ML
nossos autores
Anabela Tavares Aguiar Valente
Investigador Principalagradecimentos
This work was partially funded by the Spanish Ministry of Science and Innovation (MICINN: ENE-2009-12743-C04-01), 'Consejeria de Educacion' of the Autonomous Government of Madrid (CAM: CARDENER-CM) and the Portuguese Fundacao para a Ciencia e a Tecnologia (FCT), POCI and FEDER (project POCI/QUI/56112/2004).1. I. Sadaba is grateful to the Spanish National Research Council (CSIC) for a JAE-Predoc and for the financial support for the stay at CICECO, University of Aveiro. S. Lima is grateful to the FCT for post-doctoral grant. The authors wish to express their gratitude to Dr. F. Domingues (Department of Chemistry. University of Aveiro) for access to HPLC equipment and to Doctor Martyn Pillinger (CICECO, University of Aveiro) for helpful discussions.