Reaction mechanism of aqueous-phase conversion of γ-valerolactone (GVL) over a Ru/C catalyst

Abstract

The present work explores the reaction pathways of γ-valerolactone (GVL) over a supported ruthenium catalyst. The conversion of GVL in aqueous phase over a 5% Ru/C catalyst was investigated in a batch reactor operating at 463K under 500-1000 psi of H 2 . The main reaction products obtained under these conditions were 2-butanol (2-BuOH), 1,4-pentanediol (1,4-PDO), 2-methyltetrahydrofuran (2-MTHF) and 2-pentanol (2-PeOH). A complete reaction network was developed, identifying the primary and/or secondary products. In this reaction network, production of 2-BuOH via decarbonylation of a ring-opened surface intermediate CH 3 CH(O*)-(CH 2 ) 2 -CO* is clearly the dominant pathway. From the evolution of products as a function of reaction time and theoretical (DFT) calculations, a mechanism for the formation of intermediates and products is proposed. The high sensitivity of 2-BuOH production to the presence of CO, compared to a much lower effect on the production of the other products indicates that the sites responsible for decarbonylation are particularly prone to CO adsorption and poisoning. Also, since the decarbonylation rate is not affected by the H 2 pressure it is concluded that the direct decarbonylation path of the CH 3 CH(O*)-(CH 2 ) 2 -CO* intermediate does not required a previous dehydrogenation step, as is the case in decarbonylation of short alcohols.

Solvent-free Hydrodeoxygenation of γ-Nonalactone on Noble Metal Catalysts Supported on Zirconia

“…The low concentrations of 1,4-nonanediol suggested that it was also an intermediate, as reported elsewhere [36,37,44]. PTHF formed from 1,4-nonanediol [36,37,44] and reacted further on Ru/ ZrO 2 and Rh/ZrO 2 , as attested by its low concentration and the decrease in the latter part of its yield profile on these two metals. A HDO study of MTHF reports its conversion to 2-pentanone and 1-pentanol as primary products [45].…”

“…Analogously, the MTHF conversion in HDO on Ru/C has been reported to increase exponentially with respect to temperature, as expected from kinetics [43]. Furthermore, in the GVL literature with Ru/C, the temperature is kept low (190 °C) when high yields of 2-butanol [36] and MTHF [44] are desired.…”

“…Thus, the amount of CH 4 obtained with Ru/ZrO 2 was much higher than with the other catalysts possibly due to a decarbonylation and methanation mechanism, as Ru metal favors decarbonylation [30,36,37]. The presence of residual Cl species has not been identified to interact with adsorbed CO species or affect their reactivity [31,33].…”

“…Secondary alcohols can form directly from GNL by decarbonylation or deoxygenation of a ring-opening surface intermediate [36]. The decarbonylation route is energetically favored on Ru [36,37]. This might explain the low yields of nonanoic acid provided by Ru as compared to the other metals.…”

Recent Advances in Ruthenium-Catalyzed Hydrogenation Reactions of Renewable Biomass-Derived Levulinic Acid in Aqueous Media

“…The authors have shown that the GVL ring-opening step through breaking the C(1)-O(2) bond ( Figure 10) proceeds rather easily with an activation energy of 25 kJ/mol and exothermicity (-31 kJ/mol), and the rate-limiting step is the hydrogenation step of the formed acyl intermediate CH 3 CH(O * )-(CH 2 ) 2 -C * -O * with an activation barrier of 146 kJ/mol and endothermicity (+74 kJ/mol) to yield 1,4-PDO. In contrast, the alternative pathway of GVL ring-opening through breaking the C(4)-O(2) bond ( Figure 10) proceeds with more difficulty with a much higher energy barrier of 122 kJ/mol, which leads to VA (Rozenblit et al, 2016). Aqueous-phase hydrogenations of GVL catalyzed by 5 wt.% Ru/C were carried out by Rozenblit et al (2016) at 200 • C under 69 bar dihydrogen pressure to obtain a conversion of GVL of 10.3 mol% and a spectrum of products with a yield of 4.95 mol% 2butanol, formed after C-C bond cleavage in a decarbonylation step of the surface acyl intermediate CH 3 CH(O * )-(CH 2 ) 2 -C * -O * obtained after GVL ring-opening, and further 4.63 mol% 1,4-PDO after hydrogenation of the acyl intermediate, 0.64 mol% 2-MTHF after dehydration of 1,4-PDO and cyclization, and 0.08 mol% 2-pentanol obtained after deoxygenation and further hydrogenation of the surface CH 3 CH(O * )-(CH 2 ) 2 -C * -O * acyl intermediate.…”