Role of Phosphorus in Transition Metal Phosphides for Cleaving Hindered C-O Bonds in 2-Methyltetrahydrofuran
AIChE Annual Meeting
2023
2023 AIChE Annual Meeting
Annual Student Conference: Competitions & Events
Undergraduate Student Poster Session: Catalysis and Reaction Engineering
Monday, November 6, 2023 - 10:00am to 12:30pm
Biomass can be upgraded into higher value chemicals, such as α,Ï-diols, via C-O hydrogenolysis. However, this process requires the selective activation of sterically hindered C-O bonds. Here, we observe a model biomass-derived molecule, 2-methyltetrahydrofuran (MTHF). The molecule has two C-O cleavage pathways, the unhindered (2C-O) cleavage and hindered (3C-O) cleavage. Previous work examining C-O hydrogenolysis in MTHF demonstrated that an increase in P content to Ni shifts selectivity towards 3C-O cleavage. Ni2P (P62m spacegroup) showed the greatest selectivity towards 3C-O cleavage over 2C-O cleavage in comparison to Ni15P5 and pure Ni. Alongside this, other transition metals were also compared to their pure metal counterparts to investigate selectivity trends. A shift in selectivity towards hindered 3C-O cleavage was seen for almost all transition metals investigated when P was added. Here we examine hindered 3C-O cleavage using simulated models and calculating free energy barriers (ÎG) for Ni2P using Density Functional Theory (DFT). Here we now more closely investigate structural effects on selectivity by modeling Ni2P in both the Pnma and Fm3m spacegroups while comparing our results to previous work to determine if structural effects play a role in selectivity. It was found that Ni2P(010) was the optimal surface for Pnma and Ni2P(001) was the optimal surface for Fm3m among various Miller Indices. Probe molecules when then adsorbed to the catalyst surface to determine the likely preferred binding site for MTHF C-O cleavages. During our adsorbate calculations, it was observed that the Fm3m surface restructured, rendering it unsuitable for conducting chemical reactions due to its instability. Comparing our reaction coordinate diagram to previous work, it was found that the 3CâO activation barrier was lower than 2CâO activation in Ni2P, making 3C-O cleavage more favorable, as was seen in the prior work. Additionally, the previous relative energy difference (ÎÎE) calculated for Ni2P P62m was 44 kJ mol-1, and our Ni2P Pnma ÎÎE was 17 kJ mol-1. This suggests that structure does play a role in selectivity. Future work will include completing free energy difference (ÎÎG) calculations to further prove this suggestion true.