Produção de γ-valerolactona a partir de furfural sobre zeólitas Hf/Al-beta – efeito da relação de sítios ácidos de Lewis e Brønsted

Abstract

Lignocellulosic biomass has been used as a sustainable alternative to organic derivatives of fossil origin for the production of intermediates and chemicals with higher added value. In this context, γ-valerolactone (GVL), a compound used as a solvent, fuel additive or intermediate in the synthesis of fine chemical products, can be produced from bioderivated furfural. Currently, GVL is produced using high pressures in the hydrogenation in steps of levulinic acid (AL), using catalysts containing noble metals (e.g., Ru and Pd) and molecular hydrogen. As an alternative to this process, Meerwein-Ponndorf-Verley (MPV) transfer hydrogenation allows selective hydrogenation of furfural and hence AL, over Lewis (L) and Brønsted (B) acid sites, using a secondary alcohol as a hydrogen donor. As known, zeolites have high potential as heterogeneous catalysts, as their acidic and textural properties can be designed to meet specific reaction systems. Thus, type of structure, porosity and ratio of acidic L and B sites will be determining factors in the activity for this series reaction. An optimized balance of the L/B ratio can be achieved by the isomorphic substitution of structural Al3+ in the zeolite by Hf4+ atoms increasing Lewis acidity. Zeolites (Al/Hf)-Beta have been shown to be more efficient in MPV reactions than zeolites (Al/Zr)-Beta or (Al/Sn)-Beta. Thus, the objective of the work was to prepare catalysts (Al/Hf)-Beta by post-synthesis strategies and to investigate the influence of the L/B ratio, in the conversion in series of furfural to GVL, using isopropanol and carried out at atmospheric pressure, 120 °C, 150 mmol L-1 of furfural in isopropanol and 30 mg of catalyst. The precursor and modified beta zeolites were characterized by X-ray dispersive energy spectroscopy and scanning electron microscopy (SEM/EDS), X-ray diffraction (DRX), N2 physisorption, ammonia desorption at the programmed temperature (DTP-NH3) and diffuse reflectance spectroscopy in Fourier transform infrared (DRIFTS) and visible ultraviolet (DRS-UV-Vis). The results showed that the grafting treatment was efficient in the incorporation of hafnium in the beta zeolite structure, increasing the L/B acidity ratio and making it selective for the conversion into series of furfural, obtaining under the conditions used a yield at 46% GVL after 22.5 h of reaction.