Hydroconversion mechanism of biomass-derived γ-valerolactone

Abstract

The hydroconversion mechanism of γ-valerolactone (GVL) was studied over a Co/SiO 2 and a Pt/aluminosilicate catalyst. The reaction was carried out at 250 °C, 30 bar, and WHSV= 1 g GVL •g cat. -1 •h -1 . The Co/SiO 2 catalyst had moderate hydrogenation activity and Lewis acidity, whereas the Pt/aluminosilicate catalyst had high hydrogenation activity and Brønsted acidity. Diffuse Reflectance Fourier Transform Spectroscopic (DRIFTS) results suggested that the GVL ring was bounded more strongly to the stronger acid Pt/aluminosilicate that to the weaker acid Co/silica catalyst. The Pt/aluminosilicate catalyst was substantiated to open the GVL ring in a protonation/deprotonation process giving pentenoic acid (PE) intermediate and pentanoic acid (PA) as main final product. Over Co/SiO 2 catalyst 2-methyl-tetrahydrofuran (2-MTHF) and pentanol were the major products of GVL conversion. It was substantiated that latter transformation proceeded in consecutive hydrogenation and dehydration steps via 2hydroxy-5-methyl-tetrahydrofuran and 1,4-pentanediol (1,4-PD) intermediates. The oxygen atoms of GVL were shown to establish H-bonds with the silanol groups of the Co/SiO 2 catalyst. The  CO frequency of the adsorbed GVL depends on the adsorption interaction of the GVL and the silica surface. Three distinct  CO bands were distinguished by DRIFTS. Quantum chemical calculations gave the structures of the three adsorbed GVL species. Operando DRIFTS examination of the catalytic reaction suggested that in the structure that was activated for hydrogenation/hydrogenolysis both the ring and the carbonyl oxygen were bound to silanol groups.

Conversion of γ‐Valerolactone to Ethyl Valerate over Metal Promoted Ni/ZSM‐5 Catalysts: Influence of Ni0/Ni2+ Heterojunctions on Activity and Product Selectivity

“…Thus, such band position is also described for metal ketoenol chelate complexes of β‐diketones and it is likely that particularly Ni 2+ Lewis sites as present in Mo−Ni/HZ5 favour the formation of such species . Such types of intermediates were also postulated for the hydroconversion of GVL over Co/SiO 2 …”

“…The characteristic ν (C=O) band of GVL is observed at 1786 cm À 1 shifting to lower wavenumbers due to adsorption. [46] Thus, additional bands around 1765, 1741, and 1694 cm À 1 appear which indicate weak and strong interactions of GVL with the catalyst surface, respectively. [46,47] By inspecting the OH region of the FTIR spectra, it can be seen that the OH groups at the surface are involved in this interaction with GVL ( Figure S4).…”

“…[46] Thus, additional bands around 1765, 1741, and 1694 cm À 1 appear which indicate weak and strong interactions of GVL with the catalyst surface, respectively. [46,47] By inspecting the OH region of the FTIR spectra, it can be seen that the OH groups at the surface are involved in this interaction with GVL ( Figure S4). Interestingly, an additional broad band around 1558 cm À 1 is observed on MoÀ Ni/HZ5, possibly stemming from an enolatelike adsorbed species.…”

“…[48,49] Such types of intermediates were also postulated for the hydroconversion of GVL over Co/SiO 2 . [46] After the pre-adsorption of GVL, ethanol was injected into the IR cell to initiate the reaction of GVL ring opening to EV. The reaction progress was followed for 40 min, while the cell was permanently flushed with 5 % H 2 /He.…”

“…According to the above results and discussions, a plausible reaction mechanism for GVL ring opening can be proposed which is in good agreement with results reported in other studies. [17,46,51] It is worth noticing that the reaction proceeds through two pathways as depicted in Scheme 2, with path I being more predominant over all studied catalysts. This is obviously due to the fact that all catalysts possess both Brønsted as well as Lewis acid sites which favour reaction path I.…”