Poisoning of Ru/C by homogeneous Brønsted acids in hydrodeoxygenation of 2,5-dimethylfuran via catalytic transfer hydrogenation

Abstract

It has been proposed that the combination of metal and acid sites is critical for effective ring opening of biomass-derived furans to linear molecules, a reaction that holds promise for the production of renewable polymer precursors and alkanes. In this work, we use 2,5-dimethylfuran (DMF) as a model compound to investigate hydrogenolysis and hydrogenation pathways using a combination of H2SO4 and Ru-mediated catalytic transfer hydrogenation in 2-propanol. Acid-catalyzed hydrolytic ring opening of DMF to 2,5hexanedione (HDN) occurs readily at 80 °C with a selectivity of 89% in 2-propanol. Over Ru/C, HDN is fully converted after only 2 h at 80 °C, forming a mixture of both ring-closed products (~68% total yield), i.e., 2,5-dimethyltetrahydrofuran (DMTHF) and 2,5-dimethyl-2,3-dihydrofuran (DMDHF), as well as ring opened products (~28% total yield), i.e., 2,5-hexanediol (2,5-HDL) and 2-hexanol (HOL). Rather than observing sequential hydrolysis/hydrogenation reactions, we observe severe suppression of metal chemistry when having both Ru/C and H2SO4 in the reaction system. While minor leaching of Ru occurs in the presence of mineral acids, X-ray photoelectron spectroscopy coupled with CO chemisorption studies suggest that the primary cause of the lack of Ru-mediated chemistry is poisoning by strongly adsorbed sulfate species. This hypothesis is supported by the observation of Ru-catalyzed chemistry when replacing H2SO4 with Nafion, a solid Brønsted acid, as sulfonic acid groups tethered to the polymer backbone cannot adsorb on the metal sites.

Insight into the hydrogenation of pure and crude HMF to furan diols using Ru/C as catalyst

“…HMF may be obtained by the dehydration of model compounds, including monosaccharides, such as glucose [8][9][10][11] and fructose [11][12][13][14][15], polysaccharides, such as inulin [12,13,16], starch [11,15] and cellulose [11,15,17,18] and, more advantageously, real lignocellulosic biomasses, such as corn stover, pinewood, switchgrass and poplar [14,19]. The presence of different reactive groups (an aldehyde group, a hydroxyl group and a furan ring) makes HMF a very important platform-chemical, precursor of bio-fuels, such as 2,5-dimethylfuran (DMF) [20,21], 5-ethoxymethylfurfural (EMF) [22] and long chain alkanes [23]. In addition, it is possible to convert HMF into interesting monomers, such as 2,5-furandicarboxylic acid (FDCA) [24,25], 2,5-bis (hydroxymethyl)furan (BHMF) [26][27][28], 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) [29][30][31] and caprolactone [32] and many more valuable products [33][34][35].…”

Catalytic Hydrogenation/Hydrogenolysis of 5‐Hydroxymethylfurfural to 2,5‐Dimethylfuran

“…Undesirable high Brønsted acidity cause side reactions, [24,48, 55] such as etherification and acetalization with 2‐propanol as a solvent [35] . It was also observed that Brønsted acids in Co/Al‐Beta suppress the yield of DMF in HMF transformation [17] analogously as observed over Ru/C and sulphuric acid [59] . Weak acid sites determined by ammonia TPD were active and selective in HMF transformation to DMF over Ru/MoO x /C (Table 1, entry 21), while Ru/C exhibited no acidity [52] .…”

“…[35] It was also observed that Brønsted acids in Co/Al-Beta suppress the yield of DMF in HMF transformation [17] analogously as observed over Ru/C and sulphuric acid. [59] Weak acid sites determined by ammonia TPD were active and selective in HMF transformation to DMF over Ru/MoO x /C ( Table 1, entry 21), while Ru/C exhibited no acidity. [52] As a comparison the main product was DHMTHF with the yield of 91 % over Ru/CeO x in HMF transformation at 130°C under 20 bar hydrogen in 1-butanol-water mixture as a solvent.…”

“…Transformation of HMF to DMF is scientifically an interesting reaction with a complex reaction network and this reaction has been intensively studied [14–62] . In the first step HMF is hydrogenated to BHMF followed by its hydrogenolysis to methylfurfuryl alcohol (MFA) and further hydrogenolyses to DMF.…”

Catalytic Hydroconversion of 5‐HMF to Value‐Added Chemicals: Insights into the Role of Catalyst Properties and Feedstock Purity

“…For instance, a poisoning effect of H 2 SO 4 on Ru/C catalyst was observed by Gilkey et al in the hydrodeoxygenation of DMF via CTH in 2-propanol. [93] It is believed that the efficient ring-opening of furans to linear molecules requires a combination of metal and acid sites. However, severe suppression of metal chemistry was observed when having both Ru/C and H 2 SO 4 in the reaction system.…”