Direct synthesis of furfuryl alcohol from furfural: catalytic performance of monometallic and bimetallic Mo and Ru phosphides†
The catalytic properties of monometallic and bimetallic Ru and Mo phosphides were evaluated for their ability to selectively hydrogenate furfural to furfuryl alcohol. Monometallic MoP showed high selectivity (98%) towards furfuryl alcohol, while RuP and Ru2P exhibited lower selectivity at comparable conversion. Bimetallic promotional effects were observed with Ru1.0Mo1.0P, as the pseudo-first order reaction rate constant for furfural hydrogenation to furfuryl alcohol, k1, was at least 5× higher than MoP, RuP, and Ru2P, while maintaining a 99% selectivity. Composition-directed catalytic studies of RuxMo2−xP (0.8 < x < 1.2) provided evidence that Ru rich compositions positively influence k1, but not the selectivity. The rate constant ratio k1/(k2 + k3) for furfuryl alcohol production compared to methyl furan (k2) and tetrahyrofurfuryl alcohol (k3) followed the trend of Ru1.0Mo1.0P > Ru1.2Mo0.8P > MoP > Ru0.8Mo1.2P > RuP > Ru2P. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to examine the configuration of adsorbed furfural on the synthesized catalysts, but the results were inconclusive and no correlation could be found with the selectivity due to the possible IR inactive surface modes with furfural adsorption. However, gas phase density functional theory calculations suggested the x = 1.0 material in RuxMo2−xP (0.8 < x < 1.2) had the most favorable furfural adsorption energy. Experimentally, we also observed that the solvent greatly influenced both the conversion and selectivity, where isopropanol provided the highest selectivity to furfuryl alcohol. Finally, recycling experiments showed a 12% decrease in k1 after 3 cycles without any regeneration, but the activity could be fully recovered through a re-reduction step.
- This article is part of the themed collection: 2019 Catalysis Science & Technology HOT Articles