Hydrogenation of furfural by noble metal-free nickel modified tungsten carbide catalysts

Abstract

Nickel-tungsten carbide catalysts convert furfural to high value products in a liquid phase catalytic reaction. The product distribution depends on the solvent and the Ni-W-ratio of the catalyst. In isopropyl alcohol a combination of Ni and W _x C enables the opening of the furan ring to yield 1,2-pentanediol. Nickel accelerates the tungsten oxide reduction in the tungsten carbide catalyst synthesis and facilitates the carbon insertion. Nickel modified tungsten carbide is a promising, noble metal-free catalyst system for the upgrading of furfural based renewable resources. Its preparation is facilitated compared to unmodified tungsten carbide catalysts.

Scheme 1. Reaction network of possible hydrogenation products starting from furfural.

Fig. 1. CO in the effluent gas stream during isothermal W_xC synthesis in a horizontal tube furnace at 700 °C in reactive gas (20% CH₄ in H₂). The reaction is starting from WO₃/SiO₂ with different mass-loadings of Ni; no Ni: blue, dashed line; increasing amounts of Ni: darker shades of orange, solid lines.

Fig. 2. X-ray diffractograms of tungsten carbide catalysts with different Ni-loadings. The Ni-loading is indicated as weight% of the WO₃/SiO₂ precursor. Catalysts are prepared in an isothermal reaction at 700 °C. Reference patterns from ICDD database, WC: 00-025-1047, W₂C: 00-35-0776, W: 00-001-1203  and Ni₁₇W₃: 03-065-4828.

Fig. 3. Reaction progress during the catalytic conversion of furfural in (a) tetrahydrofuran and (b) isopropyl alcohol as solvent. The reaction proceeds at 200 °C under 65 bar H₂, with 0.50 g 4%-Ni/W_xC/SiO₂ and 3 mL furfural.

Fig. 4. Time needed until full conversion of the intermediary product furfuryl alcohol for catalysts with different Ni-loadings. The catalyst with 10 wt% Ni consists only of Ni without a tungsten component. The reaction proceeds at 200 °C, 65 bar H₂ with 0.50 g catalyst and 3 mL furfural in isopropyl alcohol as solvent.

Fig. 5. Reaction progress during catalytic conversion of furfural with 2.5 wt% Ni/W_xC/SiO₂. The reaction proceeds at 200 °C under 65 bar H₂, with 0.5 g catalyst in isopropyl alcohol as solvent. Initially 3 mL furfural are added and after 13 h of reaction time the reactor is cooled down and depressurized to add further 3 mL of furfural before continuing the reaction.

Scheme 2. Possible orientation of furfuryl alcohol at the proposed active site for the ring opening, the boundary between Ni₁₇W₃ and W_xC. Based on the proposed reaction path by Mizugaki et al.