A Comparative Study of 4-Methylphenol Hydrodeoxygenation Over High Surface Area MoP and Ni₂P

Abstract

Unsupported, high surface area MoP and Ni₂P catalysts were synthesized by adding citric acid (CA) to solutions of ammonium heptamolybdate and diammonium hydrogen phosphate or nickel nitrate and diammonium hydrogen phosphate, respectively, followed by drying (397 K), calcination (773 K), and reduction in H₂ (923 K). The addition of CA increased the surface area, decreased the particle size, and increased the CO uptake of the MoP and Ni₂P catalysts. At 623 K and 4.4 MPa, the Ni₂P was 2.3 times more active than the MoP on a mass basis and 6 times more active on a site basis for the hydrodeoxygenation of 4-methylphenol. However, the Ni₂P catalysts deactivated due to non-selective carbon deposition on the catalyst surface. Oxidation was excluded as a potential cause of deactivation over the Ni₂P catalysts. The rate of deactivation was well described by an exponential decay law. Deactivation was eliminated by operation at higher H₂ pressures (5.3 and 6.1 MPa) but the hydrogenation selectivity of the Ni₂P increased at these conditions. No deactivation was observed over the MoP catalysts at the conditions of the present study.