Kinetic and Infrared Spectroscopy Study of Hydrodeoxygenation of 2‑Methyltetrahydrofuran on a Nickel Phosphide Catalyst at Atmospheric Pressure

Understanding the reactions of heteroatomic cyclic compounds is essential for developing good catalysts for the upgrading of bio-oils into liquid fuels. The present study presents the reaction network of 2-methyltetrahydrofuran (2-MTHF, C₅H₁₀O), a bio-oil model compound, on silica-supported nickel phosphide at 0.1 MPa and 300 °C. Contact time experiments showed that 2-MTHF reacted to first form 1-pentanol and 2-pentanol, then <i>n</i>-pentanal, 2-pentanone, and 1- and 2-pentenes, and finally <i>n</i>-pentane. The observation is consistent with a reaction network in which adsorption of 2-MTHF is followed by rate-determining ring-opening steps on the more hindered side (path I) or the more open side (path II) to first produce adsorbed alcohols. The alcohols then transform into adsorbed aldehyde, ketone, and pentene species which can simply desorb or react to produce the final product <i>n</i>-butane (decarbonylation of adsorbed <i>n</i>-pentanal) or <i>n</i>-pentane (hydrogenation of adsorbed pentenes). Kinetic modeling of the proposed reaction network gave good agreement with the experimental data and predicted that path I intermediates would be more numerous than path II intermediates on the surface. A series of in situ FTIR results gave further support for the mechanism with the presence of the CO and CC bands of the adsorbed aldehyde/ketone and alkene species. Transient experiments gave evidence for the model calculations that predicted more plentiful path I surface species

Reactions of 2‑Methyltetrahydropyran on Silica-Supported Nickel Phosphide in Comparison with 2‑Methyltetrahydrofuran

The reactions of 2-methyltetrahydropyran (2-MTHP, C₆H₁₂O) on Ni₂P/SiO₂ provide insights on the interactions between a cyclic ether, an abundant component of biomass feedstock, with a transition-metal phosphide, an effective hydrotreating catalyst. At atmospheric pressure and a low contact time, conditions similar to those of a fast pyrolysis process, 70% of products formed from the reaction of 2-MTHP on Ni₂P/SiO₂ were deoxygenated products, 2-hexene and 2-pentenes, indicating a good oxygen removal capacity. Deprotonation, hydrogenolysis, dehydration, and decarbonylation were the main reaction routes. The reaction sequence started with the adsorption of 2-MTHP, followed by ring-opening steps on either the methyl substituted side (Path I) or the unsubstituted side (Path II) to produce adsorbed alkoxide species. In Path I, a primary alkoxide was oxidized at the α-carbon to produce an aldehyde, which subsequently underwent decarbonylation to 2-pentenes. The primary alkoxide could also be protonated to give a primary alcohol which could desorb or form the final product 2-hexene. In Path II, a secondary alkoxide was oxidized to produce a ketone or was protonated to a secondary alcohol that was dehydrated to give 2-hexene. The active sites for the adsorption of 2-MTHP and <i>O</i>-intermediates were likely to be Ni sites