Abstract
The catalytic upgrading of bio-based platform molecules is a promising approach for biomass valorization. However, most solid catalysts are not thermally or chemically stable, and are difficult to prepare. In this study, a stable organic phosphonate–hafnium solid catalyst (PPOA–Hf) was synthesized, and acid–base bifunctional sites were found to play a cooperative role in the cascade transfer hydrogenation and cyclization of ethyl levulinate (EL) to γ-valerolactone (GVL). Under relatively mild reaction conditions of 160 °C for 6 h, EL was completely converted to GVL with a good yield of 85%. The apparent activation energy was calculated to be 53 kJ/mol, which was lower than other solid catalysts for the same reaction. In addition, the PPOA-Hf solid catalyst did not significantly decrease its activity after five recycles, and no evident leaching of Hf was observed, indicating its high stability and potential practical application.
Highlights
Nowadays, with the continuous development of human society, the demand for energy and fine chemicals is increasing [1]
As a biomass-derived versatile platform molecule, γ-valerolactone (GVL) can be used as a green solvent for biomass conversion and organic transformations [6]. It can be employed for producing biofuels and fuel additives (e.g., 2-methyltetrahydrofuran) [7], and as a key intermediate in the synthesis of fine chemicals (e.g., pentenoic acid and α-methylene-γ-valerolactone (MeGVL)), as shown in Scheme 1 [8,9]
Cascade hydrogenation and cyclization were deemed in recent years as the key step in catalytically upgrading levulinic acid and its esters to GVL [17,18]
Summary
With the continuous development of human society, the demand for energy and fine chemicals is increasing [1]. As a biomass-derived versatile platform molecule, γ-valerolactone (GVL) can be used as a green solvent for biomass conversion and organic transformations [6] It can be employed for producing biofuels and fuel additives (e.g., 2-methyltetrahydrofuran) [7], and as a key intermediate in the synthesis of fine chemicals (e.g., pentenoic acid and α-methylene-γ-valerolactone (MeGVL)), as shown in Scheme 1 [8,9]. GVL can be prepared from lignocellulose via sequential catalytic pathways involving various reactions such as hydrolysis, isomerization, dehydration, etherification, esterification, hydrogenation, and lactonization [10,11,12,13,14,15,16] Amongst these conversion processes, cascade hydrogenation and cyclization were deemed in recent years as the key step in catalytically upgrading levulinic acid and its esters to GVL [17,18]
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