Multifunctional catalyst for the conversion of CO2 to fuel
Abstract
UTSA, SWRI, and UK-CAER researchers conducted prior research on CO2 utilization in part through a UTSA-SWRI Connect seed grant. Theproject focused on converting CO2 to synthetic fuels through multiple reactions in series, including reverse water-gas shift (RWGS)and Fischer-Tropsch synthesis (FTS). For the first reaction, RWGS, a selectivity to CO of 99.8% was achieved at an elevated pressure of 20 bar, the optimal pressure for downstream FTS over commercial supported cobalt catalysts. This high selectivity was accomplished through a chemical promotion of m-ZrO2 supported Pt nanoparticles by alkali, in this case sodium. Na was found to increase the basicity of the catalyst surface, which accelerates the formation of the formate intermediate involved in the RWGS pathway. This favors CO production at the metal-support junction while attenuating methanation activity occurring on ensembles of Pt atoms located on the Pt nanoparticle surfaces. By increasing the relative rate of CO with respect to CH4 (i.e., rCO/rCH4), CO production was favored.An applied study was undertaken to further optimize the catalyst by varying the Na content. From this effort, a series of manuscripts was published over the past two years in Applied Catalysis B [1], Nanomaterials [2], and Applied Catalysis A [3]. This research confirmed that a two-stage process involving RWGS and FTS is preferable to a hybrid RWGS/FTS catalyst due to the differences in optimal conditions for each of the two reaction steps. RWGS is favored at higher temperature, whereas FTS is favored at lower temperature. The focus of the proposed research with the Office of Naval Research is on the CO conversion stage downstream from the RWGS stage.The objective is to develop mixed bed catalysts and core-shell catalysts that combine a carbon-carbon coupling function such as FTSor methanol synthesis with an aromatization function with two specific aims: increasing the aromatic content and controlling hydrocarbon chain length. Since the 1970s, various reactor configurations and catalyst combinations have been shown to increase the aromatic and branched hydrocarbon content derived from syngas. In each case, the catalysts included a CO hydrogenation catalyst (i.e., methanol synthesis or FTS catalyst), and an acid catalyst. Some configurations investigated previously include multiple reactor beds / separate catalysts, single reactor / multiple catalysts in series, single reactor / mixed bed using a physical mixture of catalysts,and single reactor with a hybrid catalyst. While important advances were made, optimal selectivity was not achieved due to a lack of control of the interplay between the chain growth function and the acid-catalyzed aromatization function. From a mechanistic standpoint, the synergy stems from the shuttling of intermediates between the two catalyst functions. Therefore, the pathlengths involvedmust be optimized to control selectivity. In this proposal, core-shell catalysts will be synthesized consisting of supported FTS (e.g., cobalt) or methanol synthesis (e.g., Cu/Zn) catalysts deposited on a metal oxide core (e.g., alumina, silica, titania, zirconia) and a shell consisting of a thin membrane of acid catalyst (e.g., zeolite HZSM-5). We will research varying the acid catalyst shell thickness with the aim of tuning selectivity such that aromatic and branched hydrocarbon contents fall within the range of the MIL-DTL-5624W standard (i.e., 8% to 25% aromatics, minimum cetane number of 40). We also aim to tune chain length to avoid heavy products (lubricants and waxes) and favor hydrocarbons found in JP5 fuel. Core-shell catalysts will be synthesized using a spin-coating preparation and characterized by adsorptive, spectroscopic, temperature-programmed, and microscopic techniques at UTSA and UK-CAER. Promising catalyst formulations will be tested using SWRI fixed bed reactors and UK-CAER continuously stirred tank reactors (CSTR). Approved for public release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 10, 2025
- Source ID
- N000142512239
Entities
People
- Gary Jacobs
Organizations
- Office of Naval Research
- United States Navy
- University of Texas at San Antonio