With increasing concern over the environmental effects of burning fossil fuels and high CO2 emissions, the call for a more sustainable resource base has never been louder. Indeed, many developed nations now are shifting towards renewable sources of energy and storage of excess energy during non-productive periods. Additionally, several large companies have now in place measures to mitigate the excessive accumulation of CO2 in the atmosphere. These institutions achieve their goal through different carbon capture, conversion and storage schemes. Current state-of-the-art carbon capture techniques rely on toxic chemicals such as liquid mono-ethanolamine (MEA) to scrub carbon dioxide from flue gas streams. Excess renewable electric energy can be stored through water electrolysis (to obtain oxygen and hydrogen). Anticipating the market need for CO2 capture and conversion to useful products (utilizing renewable hydrogen), researchers are persistently continuing to improve a Dual Function Material (DFM) that combines the capture and conversion of CO2. In particular, CO2 is captured and converted to synthetic natural gas (CH4) at the site of its use. For traditional methanation processes, a nickel catalyst is mainly used; however, when exposed to an oxidizing environment during the CO2 capture from flue gas, it is not capable of being reduced to its catalytically active state when exposed to hydrogen at 320 °C.
Many research groups have studied Ni-containing DFMs but in all these studies the capture step was conducted in an O2-free environment. Separately, noteworthy literature has recently reported that several precious metals like Pt, Pd and Ru can dissociate H2 molecules, rendering them stronger reductants for NiO and CuO, thereby lowering the oxide reduction temperature. Therefore, in a bid to build on these recent findings, researchers from Columbia University in the City of New York: Dr. Martha Arellano-Treviño, Nisarg Kanani and Chae Jeong-Potter led by Professor Robert Farrauto proposed to incorporate combinations of small amounts of precious metal and Ni in the DFM for the O2-containing capture process and subsequent methanation. Their work is currently published in the research journal, Chemical Engineering Journal.
The focus of their study was to assess the stability and performance of a Platinum Group Metal (PGM)-promoted Ni-containing DFM when exposed to simulated flue gas conditions. To this end, the team utilized a DFM composed of an alkaline adsorbent complemented by a methanation catalyst supported on γ-Al2O3. The team operated their process at 320 °C for both CO2 capture and fuel generation upon the addition of renewable H2. Thus, the DFM isothermally captures and converts CO2 from a power plant effluent to synthetic natural gas, which is recycled to the inlet or injected into a pipeline, thereby approaching carbon neutrality.
The authors reported that the small quantities of precious metal (≤1% Pt, Pd or Ru) enhanced the reduction and activation of Ni-containing DFM towards methanation even after O2 exposure in a flue gas. Moreover, it was noted that ruthenium was most effective, while both Pt and Pd all enhance reduction of oxidized Ni. Further multiple cycles of aging corroborated the stability of the Ru-Ni dual function material.
In summary, the study presented an in-depth investigation of the dual function material for CO2 capture from O2-containing flue gas with catalytic conversion to fuel. The goal of realizing substantial economy with regard to the DFM was achieved. In a statement to Advances in Engineering, Professor Robert Farrauto, the corresponding author, highlighted that their work probed and proved the incorporation of minimal amounts of precious metals improves the methanation process for Ni catalyzed systems while bringing the overall material cost down.
Martha A. Arellano-Treviño, Nisarg Kanani, Chae W. Jeong-Potter, Robert J. Farrauto. Bimetallic catalysts for CO2 capture and hydrogenation at simulated flue gas conditions. Chemical Engineering Journal, volume 375 (2019) page 121953.