Solution combustion synthesis of cerium-, iron-, and tungsten-promoted alumina for conversion of sugarcane leaves to furfural

Abstract

The valorization of abundant agricultural wastes such as sugarcane leaves into furfural is significant and challenging. The solution combustion method (SC) was used to synthesize cerium-, iron-, and tungsten-promoted alumina and the effect of metal loadings (1, 5, 10, and 20 wt.%) on the one-pot conversion of sugarcane leaves to furfural was investigated. The prepared catalysts were characterized by X-ray diffraction (XRD), N2-physisorption, scanning electron microscopy (SEM), and ammonia temperature-programmed desorption (NH3-TPD). The XRD results showed that SC-derived catalysts were gamma-phase alumina and suggested the highly dispersed of metals on the alumina surface. The specific surface area and pore volume of unpromoted alumina were 189 m2/g and 0.24 cm3/g, respectively. These monotonically increased to 272 m2/g and 0.31 cm3/g with increasing tungsten loading. In contrast for cerium and iron, the specific surface of cerium increased to 212 and 245 and then decreased to 169 and 214 m2/g, with increasing cerium and iron loading, respectively. Moreover, the pore size distribution was narrow with the average pore diameter around 4-5 nm for all series. The SEM images indicated the aggregation of uniform small particles and EDS analysis of tungsten-promoted alumina indicated a high dispersion of tungsten on alumina. The NH3-TPD results showed that the acidity of tungsten-promoted alumina catalysts was increased with increasing tungsten loading but decreased for cerium-, and iron-promoted alumina catalysts. The highest furfural yield (29.3 mg per 1 g of sugarcane leaves) was achieved at 170°C, 10 bars of N2, and 5 h using 5Ce-Al. Furthermore, the effect of reaction times was investigated for tungsten-promoted aluminas and the amount of sulfate impregnation on 10W-Al was also investigated. This work suggested that metal-oxide catalysts play an important role in reducing reaction time, and this work illustrated the advantage of solution combustion for synthesizing solid acid catalysts which can be used in the valorization of biomass.

-