The aim of this review is to discuss the most relevant chemical routes for converting furfural to chemicals and to biofuels and additives.

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This review is aimed to be a brief tutorial covering the deactivation of solid catalysts in the liquid phase, with specific focus on leaching, which can be especially helpful to researchers not familiarized with catalytic processes in the liquid phase.

Two series of Fe−Ce catalysts were prepared following two different methods:  coprecipitation from Fe and Ce nitrate solutions and physical mixing of pure Fe and Ce precursors. Evidence of the presence of a chemical interaction between Fe and Ce was found in the calcined state of the coprecipitated catalysts. Such evidence was obtained with different techniques. The Fe−Ce interaction occurs through the formation of hematite-like and cubic ceria-like solid solutions. In the hematite-like solid solution, Ce cations are dissolved in the hematite structure, whereas in the cubic ceria-like solid solution Fe cations are dissolved in the ceria structure. Such interactions were absent in the samples prepared by the physical mixing. It is suggested that the Fe−Ce interaction present in the calcined state results in a strong Fe−Ce interaction in the final catalyst that defines their better catalytic properties. When tested in the Fischer−Tropsch synthesis of hydrocarbons from CO + H2 gas mixtures, the coprecipitation method series showed higher CO conversion rates, higher hydrocarbon formation rates, and a higher degree of olefinicity than the pure Fe catalyst sample and the Fe−Ce samples prepared by physical mixing.

Furfural can be converted into maleic anhydride (73 % yield) through selective gas phase oxidation at 593 K with O2 by using VOx/Al2O3 (10 atV nm−2) as solid catalysts. The use of lower temperatures and/or O2 pressures result in the additional formation of furan (maximum 9 % yield). Mechanistically, furfural (C5H4O2) is oxidized stepwise to furan (C4H4O), 2‐furanone (C4H4O2), and finally, maleic anhydride (C4H2O3). The specific structure of the supported vanadium oxides and reaction conditions (temperature and reactants pressures) all influence furfural oxidation catalysis. We have found that Al2O3‐supported polyvanadates are intrinsically more active (2.70 mmol h−1 g‐at V−1) than monovanadates (VO4) and V2O5 crystals (0.89 and 0.70 mmol h−1 g‐at V−1, respectively) in maleic anhydride and furan formation rates (553 K, 1.6 kPa furfural, 2.5 kPa O2). Our alternative approach enables the use of biomass instead of petroleum to synthesize maleic anhydride and furan from furfural. The potential variety of industrial applications is of enormous interest for the development of future biorefineries.

This review revises the advances in the chemocatalytic processes for producing renewable carboxylic acids for the synthesis of bio-based polymers and proposes the actions to overcome the problems threatening their technical and economic viability.

This investigation explores the selective liquid-phase oxidation of furfural to maleic acid (MA) using hydrogen peroxide as an oxidant and titanium silicalite (TS-1) as a catalyst. The effect of temperature and of the concentration of H 2 O 2 , furfural and catalyst on the MA yield was studied. The highest yield, 78 mol%, was obtained under the following reaction conditions: 4.6 wt% of furfural, 4.6 wt% of catalyst, a H 2 O 2 /furfural mol ratio of 7.5, corresponding to 12.3 wt% of H 2 O 2 , 323 K and 24 hours of reaction. To reduce the amount of H 2 O 2 employed, a two-step sequence of reactions was conducted using TS-1 and Amberlyst 70 consecutively as catalysts in the first and second steps, respectively. In this case, a H 2 O 2 / furfural mol ratio ¼ 4.4 was required, which is quite close to the stoichiometric ratio (3.0), and a maleic acid yield close to 80% was obtained under 4.6 wt% of furfural, 4.6 wt% of catalyst and 28 h of reaction at 323 K; after 52 h of reaction, the MA yield reached 92%. Fresh and used catalysts were characterised by X-ray diffraction (XRD), Raman spectroscopy, total reflection X-ray fluorescence (TXRF), X-ray photoelectron spectroscopy (XPS), N 2 adsorption-desorption isotherms and thermogravimetric analysis.Ti was largely incorporated within the silicalite framework, but the presence of some TiO 2 anatase was also confirmed. Ti leaching was observed, especially during the first run but became much less important in successive cycles. Leaching affects both anatase and Ti species within the silicalite framework. Notwithstanding the leaching, when using pure furfural, TS-1 could be reused for six runs without noticeable deactivation, whereas when using furfural directly derived from biomass, weak but visible deactivation occurred upon reutilisation; this deterioration must be related to the presence of some organic products other than furfural.

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