Abstract
Ethanol is an important C2 platform molecule for producing value-added chemicals and distillate hydrocarbon fuels (e.g., jet and diesel). Among these, catalytic upgrading of ethanol to butenes can generate valuable commodity chemicals (e.g., 1-butene) and provide C4 olefin intermediates that can be further upgraded to jet/diesel fuels. Two-dimensional (2D) zeolites offer hierarchical mesoporous structures, leading to improved mass transport and reduced diffusion length, which can help to address the coking challenges faced by ethanol conversion to hydrocarbons over three-dimensional (3D) zeolites. In this study, we investigate the acid-catalyzed conversion of ethanol to 1-butene over the Brønsted acid sites (BAS) in 2D-pillared MFI zeolite (2D-PMFI) using ab initio molecular dynamics (AIMD) simulations, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and calorimetric measurements. A detailed thermodynamic analysis, using quasi-harmonic approximation (QHA), on the Gibbs free-energy pathway of ethanol conversion shows that the consideration of entropy is critical to accurately capture the detailed thermodynamic profiles. Employing the Blue Moon ensemble method, the formation of framework-bound butoxide from ethoxy and ethene is found to be the likely rate-determining step (RDS), proceeding via a stepwise mechanism. The reactivity of 2D-PMFI can be further tuned by manipulating RDS through careful control of the number of BAS and operating temperatures. The calculated vibrational density of states (VDOS) validate the structural models of adsorbed ethanol by comparing with the experimental DRIFTS measurements. Overall, our study provides mechanistic insights into ethanol upgrading over the 2D-PMFI and shows the importance of evaluating entropic effects in such a confined system.
| Original language | English |
|---|---|
| Pages (from-to) | 28437-28447 |
| Number of pages | 11 |
| Journal | Journal of Physical Chemistry C |
| Volume | 124 |
| Issue number | 52 |
| DOIs | |
| State | Published - Dec 31 2020 |
Funding
The authors gratefully acknowledge funding for this research, provided by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy (EERE), Bioenergy Technologies Office (BETO), at the Pacific Northwest National Laboratory (PNNL), and in collaboration with the Chemical Catalysis for Bioenergy Consortium (ChemCatBio), a member of the Energy Materials Network (EMN). The views expressed in the article do not necessarily represent the views of the U.S. Department of Energy or the United States Government. PNNL is operated by Battelle for U.S. DOE under Contract DE-AC05-76RL01830. Computational Resources were provided by user proposals at the National Energy Research Scientific Computing Center (NERSC) located at the Lawrence Berkley National Laboratory (LBNL) and at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research under Contract No. DE-AC02-76SF00515 and located at PNNL. The experimental work is sponsored by the U.S. DOE, Office of EERE, BETO, under contract DE-AC05-00OR22725 with UT-Battelle, LLC, and in collaboration with ChemCatBio, a member of EMN. F.P.-G. and Z.W. were supported by the U.S. DOE, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Catalysis Science Program. A portion of the research including the in situ DRIFTS study was conducted at the Center for Nanophase Materials Sciences (CNMS), a U.S. DOE Office of Science User Facility.