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

Abstract

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 O-intermediates were likely to be Ni sites.

Dehydra-Decyclization of Tetrahydrofuran on H-ZSM5: Mechanisms, Pathways, and Transition State Entropy

“…They note a higher reactivity for the ring-opening of tetrahydrofurfuryl alcohol and 2-MTHF, compared with THF and THP. Other recent reports have also elucidated C–O bond rupture as the rate-limiting step in the hydrogenolysis of 2-MTHF and THP on different metal phosphides. − While the reaction pathways, product identity, and distribution for hydrogenolysis are different from dehydra-decyclization, the first step for both chemistries involves C–O bond activation and, to that extent, it is expected that the trends involving molecular substitution and this reaction step are similar.…”

A cobalt phosphide catalyst for the hydrogenation of nitriles

“…Metal phosphides are less common metals that extend beyond traditional metal (0) and metal oxide materials. Although metal phosphides have recently emerged as new electro-and photo-catalysts for the hydrogen evolution reaction [33][34][35][36][37] and hydrotreatment catalysts in the petroleum industry, [38][39][40][41] their catalysis for organic synthesis remains largely unexplored despite their unique characteristics. [42][43][44][45][46] Therefore, nano-Co 2 P reported here can be categorized as a new class of catalyst for the hydrogenation of nitriles that is quite different from conventional catalysts of modied metal nanoparticles, sponge metals and metal complexes.…”

In Situ Methods for Identifying Reactive Surface Intermediates during Hydrogenolysis Reactions: C–O Bond Cleavage on Nanoparticles of Nickel and Nickel Phosphides

“…Kinetic studies demonstrate that Ni, Ni 12 P 5 , and Ni 2 P catalyze two parallel pathways: rupture of the hindered and unhindered C−O bonds (tertiary ( 3 C−O) and secondary ( 2 C−O), respectively, where x C indicates that C is bound to x non-H atoms) to form primary or secondary alcohols and aldehydes (Scheme 1). 20,21 The addition of phosphorus to Ni increases the selectivity toward cleaving the 3 C−O bond in MTHF by decreasing the relative activation enthalpy barrier (ΔH ⧧ ) of 3 C−O bond rupture to that of 2 C−O bond rupture; 20 however, without direct spectroscopic evidence, it is not clear if the addition of phosphorus influences the binding configurations of intermediates and thus ΔH ⧧ because rate measurements occur on heterogeneous supported nanoparticles while DFT calculations use single crystal surfaces. Scheme 1 illustrates the numerous reactive intermediates that may exist on the catalyst surface, including adsorbed MTHF and sequentially dehydrogenated intermediates that lead to kinetically relevant C−O bond rupture, as calculated by DFT (Figures S1−S3 for Ni, Ni 12 P 5 , and Ni 2 P, respectively) and detailed in previous work.…”