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

Abstract

Butadiene is an important monomer for rubbery and hard polymeric materials, and it can be produced efficiently from biomass-derived tetrahydrofuran (THF) using solid-acid zeolite catalysts. In this work, electronic structure calculations, kinetic experiments, and microkinetic modeling were applied to investigate the THF dehydra-decyclization reaction to butadiene as well as its retro-Prins fragmentation to the side product propene on a Brønsted acid site within H-ZSM5. A comprehensive reaction network consisting of 15 elementary surface reactions was investigated, and a microkinetic model was parametrized using computed energetics to compare with experimental kinetic data. Among the proposed reaction pathways, THF dehydra-decyclization primarily proceeds via an alkenol intermediate species, 2-buten-1-ol, while retro-Prins fragmentation to propene occurs through a direct pathway. Two other alkenol species that could be involved in the reaction network, 3-buten-1-ol and 3-buten-2-ol, do not substantially contribute to THF conversion. While multiple elementary steps were found to be kinetically relevant, the Brønsted acid-catalyzed ring opening of THF is the predominantly rate-limiting surface reaction. The apparent activation energies (ca. 30 kcal mol–1 for both butadiene and propene in the temperature range of 220–270 °C), reaction orders, and selectivity, as well as absolute rates predicted by the model are in agreement with experimental values, provided that the modeled entropy of activation is calculated to account for translational freedom for transition states that exhibit complete proton transfer from the solid acid site.

Catalysis-in-a-Box: Robotic Screening of Catalytic Materials in the Time of COVID-19 and Beyond

“…For the case of 2-MTHF dehydra-decyclization, however, the kinetic parameters obtained on the micro-flow reactor were directly compared with measurements performed on a traditional PBR as described in our earlier work. 44 Minimal catalyst deactivation was observed after initial transients for alcohol dehydration kinetics under the investigated conditions, and the rates reported here are steady-state values. Replicate experiments were carried out using randomized reactor temperature sequencing to minimize any systematic errors.…”

“…Error bars in (A) to (C) represent the 95% CI on multiple injections from the same experimental run to measure steady-state rates; error bars in (D) represent 95% CI on replicate independent measurements on fresh/recalcined catalyst beds. The references indicated in the insets 38 , 40 , 44 , [45 , 46 , 47 , 48 , 49 , 50 are also listed in the last column of Table 1 . …”

“… a These measurements were performed on a traditional packed bed reactor as described in Li et al. 44 …”

Catalysis-in-a-Box: Robotic Screening of Catalytic Materials in the Time of COVID-19

“…For the case of 2-MTHF dehydra-decyclization, however, the kinetic parameters obtained on the micro-flow reactor were directly compared with measurements performed on a traditional packed bed reactor as described in our earlier work. 37 Minimal catalyst deactivation was observed after initial transients for alcohol dehydration kinetics under the investigated conditions, and the rates reported here are steadystate values. Replicate experiments were carried out using randomized reactor temperature sequencing to minimize any systematic errors.…”

Resonance-Promoted Formic Acid Oxidation via Dynamic Electrocatalytic Modulation

“…This involved establishing the rate and current at a fixed applied potential, followed by an instantaneous change to potentiodynamic operation, and finally returning to the same potentiostatic condition. We have previously demonstrated the utility of such bracketing strategies, 19,40 allowing us to account for deactivation and other parasitic phenomena that readily corrupt kinetic measurements.…”