Modeling the Interactions of Adsorbates with Metal Surfaces and the Development of New Sorbents for Post-Combustion CO2 Capture

Dr. John Kitchin
Chemical Engineering Department
Carnegie Mellon University

Abstract The interactions of molecules with metallic surfaces are fundamental to the ability of metals to catalyze reactions. One often thinks of a metal like platinum as the catalyst, but under reaction conditions the reactivity of the metal surfaces is modified by the molecules that adsorb on them. We have used quantum chemical calculations to probe the adsorption behavior of atomic adsorbates such as C, N, O, and S on late transition metal surfaces such as Rh, Ir, Pd, Pt, Cu, Ag, and Au(111). There are remarkable similarities in the adsorption behavior of these adsorbates that can be interpreted in terms of a simple adsorbate-induced surface electronic structure modification mechanism that is common to all the adsorbates and surfaces. The variations between the adsorbates and metals are readily explained in terms of the size of the metal and adsorbate orbitals and the geometry dependent overlap of these orbitals. We have constructed a new Solid State Table of these orbital radii from the quantum chemical calculations that can be used in conjunction with a simple model to rapidly estimate the electronic structure of metal and alloy surfaces with adsorbates on them.

The capture and sequestration of CO2 from fossil energy power generation is one technological solution to minimizing the amount of CO2 that enters the atmosphere, and may help mitigate the effects of fossil energy power generation on climate change. Sorbents are an attractive option compared to solvents for capturing CO2 from the flue gas of air-fired power plants because sorbents often have lower heat capacities than solvents, thus reducing the energy needed to regenerate the sorbent due to heating. We have examined the role of moisture in the capture mechanism of CO2 on amidine based sorbents, the role of the support in parasitic moisture sorption and the capture capacity of two amidines, DBU and DBN. A thermodynamic framework for evaluating the CO2 capacity under different capture and regeneration conditions has been developed to show that each amidine is an optimal sorbent for different conditions. We have also used quantum mechanical calculations to explore the range of CO2 capacities that might be possible from functionalized amidines. These functional groups modify the electronic and geometric environment around the CO2 binding site through steric hindrance, hydrogen bonding and electron withdrawing/donating effects. We will discuss how these results could be integrated in developing new CO2 sorbents.

BIO John Kitchin completed his B.S. in Chemistry at North Carolina State University. He completed aM.S.in Materials Science and a PhD in Chemical Engineering at the University of Delaware in 2004 under the advisement of Dr. Jingguang Chen and Dr. Mark Barteau. He received an Alexander von Humboldt postdoctoral fellowship and lived in Berlin, Germany for 1 ½ years studying alloy segregation with Karsten Reuter and Matthias Scheffler in the Theory Department at the Fritz Haber Institut. Professor Kitchin began a tenure-track faculty position in the Chemical Engineering Department at Carnegie Mellon University in January of 2006. At CMU, Professor Kitchin’s research focuses on CO2 capture, adsorption behavior, and electrochemical energy conversions. He is coordinating a major research effort within the National Energy Technology Laboratory Institute for Advance Energy Solutions (NETL-IAES) in CO2 capture, sequestration and risk management that includes more than 25 faculty members and theirgraduate students. Professor Kitchin also uses computational methods to study adsorbate-adsorbate interactions on transition metal surfaces, which is funded by DOE-BES. Finally, his research group is developing electrochemical energy conversion technologies including fuel cells, electrochemical gas separations and hybrid hydrogen generation/CO2 sorbent regeneration systems. He was awarded a DOE Early Career award in 2010 to investigate multifunctional oxide electrocatalysts for the oxygen evolution reaction in water splitting using experimental and computational methods.