Dehydration of Xylose into Furfural in the Presence of Crystalline Microporous Silicoaluminophosphates Se ´rgio Lima • Auguste Fernandes • Margarida M. Antunes • Martyn Pillinger • Filipa Ribeiro • Anabela A. Valente Received: 30 July 2009 / Accepted: 26 December 2009 / Published online: 16 January 2010 Ó Springer Science+Business Media, LLC 2010 Abstract Microporous silicoaluminophosphates SAPO- 5, SAPO-11 and SAPO-40 have been tested as solid acid catalysts in the dehydration of xylose into furfural (FUR) under biphasic aqueous-organic conditions, at 170 °C. For all materials, no decrease in catalytic activity is observed after three consecutive recycling runs. Furfural yields at 4 h using SAPO-11 (34–38%) are comparable with that for HMOR zeolite with Si/Al * 6 (34%), under similar reaction conditions, while H 2 SO 4 (0.03 M) gives 2% FUR. Complete xylose conversion is reached within 16–24 h, with furfural yields of up to 65%. Brønsted and Lewis acidity of the silicoaluminophosphates was determined through FTIR analysis of adsorbed pyridine, and tenta- tively correlated with the catalytic performances. Keywords Xylose Á Furfural Á Dehydration Á Silicoaluminophosphate Á Microporous Á Solid acid 1 Introduction The processing of plant biomass-derived carbohydrates into added-value products is at the core of the biorefinery concept. In particular, the acid-catalysed hydrolysis and dehydration of saccharides, which constitute the bulk of carbohydrates, into furfural (FUR) and 5-hydroxymethyl-2- furfuraldehyde (HMF) are important processes, since these are platform chemicals for generating a variety of nonpe- troleum derived products [1–3]. Sulfuric acid is commonly used in industry as the catalyst for FUR production, pre- senting several disadvantages [3]. Recent research has focussed on the replacement of the ‘‘toxic liquid’’ acid catalysts by stable, recyclable, non-toxic solid acids based on inorganic oxides [4–10]. The development of water- tolerant heterogeneous catalysts is crucial since water is the preferred solvent for the reactions mentioned above, and this can level off the surface acidity of solid acids [10]. Two of the most commonly studied types of micropo- rous solid acids are zeolites (aluminosilicates) and silico- aluminophosphates (SAPOs). In SAPOs, the introduction of Si atoms in AlPO 4 frameworks leads to the appearance of negative charges that are balanced by protons attached to Si–O–Al bridges, thereby originating Brønsted acidity. The Si substitution can be for phosphorus (SM2 mechanism) or an aluminium-phosphorus pair (SM3 mechanism) [11, 12]. The amount of silicon incorporated via SM2 is always limited, and above certain Si contents both mechanisms occur. The SM3 mechanism generates isolated pairs of Si atoms with Si in Si(1Si3Al) and Si(1Si3P) configurations [11] leading to extended Si islands and various acid site environments with variable number and strength. A higher number of acid sites are generated through the first mechanism (SM2), while the second yields less but stron- ger acid sites [12]. For these reasons, the acidity of SAPOs is sometimes considered to be more tuneable than that of zeolites [11, 12]. In a study of zeolites with different framework types (BEA, FAU, MFI, MOR) for the dehy- dration of monosaccharides, favorable shape selective S. Lima Á M. M. Antunes Á M. Pillinger Á A. A. Valente (&) Department of Chemistry, CICECO, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal e-mail: atav@ua.pt M. Pillinger e-mail: mpillinger@ua.pt A. Fernandes Á F. Ribeiro Institute of Biotechnology and Bioengineering, Instituto Superior Te ´cnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal 123 Catal Lett (2010) 135:41–47 DOI 10.1007/s10562-010-0259-6