Zeolite catalyzed conversion of oxygenates to fuels: Influence of water concentration on pore environment and kinetics of cyclohexanol dehydration
EMSL Project ID
50602
Abstract
The PNNL’s Chemical Transformations Initiative (CTI) is developing carbon-neutral chemical conversion processes to effectively transform oxygenated renewable carbon sources as feedstock to energy-dense transportation fuels. The key scientific challenge in this initiative is to develop catalytic technologies which can have distributed deployment and that operate with high reactivity and selectivity at low temperatures, typically less than 200oC. Acid-base catalysis plays an important role in eliminating the oxygen and growing the carbon-carbon chain length in condensed- phase in the presence of water, at an enhanced rate under low-temperatures. We are drawing inspiration from nature – through abstraction of principles from enzymes into inorganic catalytic systems in zeolites. The zeolites provide a confined environment that leads to an enhanced reactivity for dilute condensed-aqueous phase cyclic alcohol dehydration in HBEA and HMFI zeolites of more than an order of magnitude higher than in acidic solutions. However, the amount of water present in biomass-derived bio-oil exist only in the range of 5-30 wt%. Hence, it is critical to understand the influence of water content on the confinement-effect for cyclic alcohol dehydration. The kinetic results demonstrate that while the zeolite with the smallest pore-size MFI has the highest dehydration rate for cyclic alcohol dehydration under dilute aqueous-conditions (0.5 M), the large-pore FAU has the highest rate under water-lean conditions (7.2 M). Furthermore, the intrinsic kinetic activation parameters were shown to be dependent on the concentration of the bulk reactant-phase. As such, the dehydration kinetics and the optimum confinement for oxygenate elimination is affected by the pore environment that are dependent on the bulk-reactant phase and therefore scrutiny of these effects is called for. In this project, we propose to perform in-situ/operando characterization of reactant (alcohol) phases with solid-state nuclear magnetic resonance (NMR) from dilute conditions to neat phase. Further, we aim to investigate the temporal evolution of reactants and products under the reaction conditions. Next, the reaction mechanism of the alcohol dehydration will be studied (both E1 and E2 mechanisms) by computing the potential energy surface (PES) of the conversion. We aim to identify the critical factors and establish design principles for enhancing reactivity inside zeolite confines. This will advance our capabilities to understand, design and control catalysts for effective conversion of biomass-derived oxygenates to fuels in the presence of water.
Project Details
Start Date
2018-11-01
End Date
2019-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members
Related Publications
Wang A., Y. Chen, E.D. Walter, N.M. Washton, T. Varga, Y. Wang, and J. Szanyi, et al. 2020. "Remarkable self-degradation of Cu/SAPO-34 selective catalytic reduction catalysts during storage at ambient conditions." Catalysis Today. PNNL-SA-148098. doi:10.1016/j.cattod.2020.01.034.