Computational Environmental Catalysis at the University of Notre Dame
The goal of research in the Schneider group is to develop molecular-level understanding, and ultimately to direct molecular-level design, of chemical reactivity at surfaces and interfaces. This heterogeneous chemistry is a key element of virtually every aspect of the energy enterprise, and is fundamental to environmental processes on the earth and in the atmosphere. Examples range from the preparation of clean fuels from crude oil or coal, to the transformation of chemical to electrical energy in fuel cells, to the remediation of exhaust from fossil fuel combustion, to even the sequestration of CO2 via mineralization. While the processes and technologies of interest are very different when viewed macroscopically, at the molecular level unifying chemical and physical phenomena emerge.
First-principles simulations based on density functional theory (DFT) allow this reactivity to be probed at the molecular scale, providing insight and guidance for the development of improved catalytic materials and processes. Understanding gained at the molecular level allows us to better control-and ultimately to tailor-chemical systems to perform functions more cleanly, efficiently, and durably. The problems we address cut across the traditional boundaries of chemical engineering, chemistry, physics, environmental science, and materials science, and our work both draws on and impacts all of these fields.
Collaborations with research groups in academia and at the National Laboratories are important for validating and applying our results, and interactions with industry are critical for guidance and ensuring relevance to practical catalysis and environmental chemistry.
Adsorbate coverage can have a significant impact on the structures, energetics, kinetics, and statistics (orders) of surface reactions. In this project, we are interested in developing quantitative models of reactive surfaces and particles at finite coverage, combining DFT-based first principles thermodynamics, Monte Carlo, and microkinetics. Work is carried out in collaboration with experimental colleagues Fabio Ribeiro and Nick Delgass at Purdue.
J. M. Bray and W. F. Schneider, “Coverage-dependent adsorption at a low symmetry surface: DFT and statistical analysis of oxygen chemistry on kinked Pt(321),” Topics Catal., 2013, in press. doi:10.1007/s11244-013-0165-4
J.-S. McEwen, J. M. Bray, C. Wu, and W. F. Schneider, “How Low Can You Go: Minimum Energy Pathways for O2 Dissociation on Pt(111),” Phys. Chem. Chem. Phys., 2012, 14, 16677-16685. doi:10.1039/C2CP42225E
Their wide range of chemical tunability make ionic liquids great candidates for absorption-based gas separations. In this project, we are using DFT simulations to design in silico ionic liquids with reactivity optimally tuned for separating CO2 from pre- or post-combustion gas mixtures. Work is carried out in collaboration with the Brennecke group, which is synthesizing and characterizing these functionalized ionic liquids, and the Maginn group, which is applying classical simulations to predict the physical properties of the materials. Most recently, we have been investigating ionic solids that actually change phase (melt) in the presence of CO2 as a way to further facilitate gas separations.
C. Wu, T. P. Sentfle, and W. F. Schneider, “First-Principles-Guided Design of Ionic Liquids for CO2 Capture,” Phys. Chem. Chem. Phys., 2012, 14, 13163-13170. doi:10.1016/10.1039/c2cp41769c
B. E. Gurcan, J. C. de al Fuente, E. M. Mindrup,
L. E. Ficke, B. F. Goodrich, E. A. Price, W. F. Schneider, and J. F. Brennecke,
“Equimolar CO2 Absorption by Anion-Functionalized Ionic Liquids,” J. Am. Chem. Soc., 2010, 132, 2116-2117.
Cluster expansions provide a powerful formalism for mapping DFT-computed energies onto an accurate lattice-gas Hamiltonian that can be evaluated for very large arrays of atoms. In this collaborative project with Chris Wolverton at Northwestern University, we are developing cluster expansions for metal-metal and metal-adsorbate interactions at surfaces. These expansions can be used to predict surface structure and ordering, and we are pursuing novel approaches to couple them with microscopically detailed microkinetic models of, for instance, temperature-programmed desorption.
W. Chen, P. Dalach, W. F. Schneider, and C. Wolverton, “Interplay Between Subsurface Ordering, Surface Segregation, and Adsorption on Pt-Ti(111) Near-Surface Alloys,” Langmuir, 2012, 28 4683-4693. doi:10.1021/la204843q
D. J. Schmidt, W. Chen, C. Wolverton, and W. F. Schneider, “Performance of Cluster Expansions of Coverage-Dependent Adsorption of Atomic Oxygen on Pt(111),” J. Chem. Theory Comp., 2012, 8 264-273. doi:10.1002/ct200659c
NOx is a by-product of combustion in air, and catalytic removal of NOx from the exhaust of high efficiency diesel engines, coal combustion, or turbines, is problematic. The challenge is to reduce small amounts of NOx to N2 in an over-whelmingly large background of O2. Remarkably, Cu-exchanged zeolites have this ability, but the mechanism of function is not well understood or well quantified. In this collaboration with researchers at Purdue, Argonne National Lab, and at Cummins, we are developing atomistic models of these zeolite catalysts, answering questions about the nature and state of the Cu catalytic active site, its interactions with NOx, and the mechanism of activity. This collaboration brings together DFT theory with state-of-the-art characterization and quantification of activity, advancing both the science and technology of SCR.
J.-S. McEwen, T. Anggara, W. F. Schneider, V. F. Kispersky, J. T. Miller, W. N. Delgass, and F. H. Ribeiro, “Integrated operando X-ray absorption and DFT characterization of Cu-SSZ-13 exchange sites during the selective catalytic reduction of NOx with NH3,” Catal. Today, 2012, 184, 129-144. doi:10.1016/j.cattod.2011.11.037
Predicting new and better catalysts is a grand challenge in materials design. In this project with Purdue University, we are exploring a "Discovery Informatics" approach, developing kinetic models from precise experiments and, using information from DFT and other sources, "inverting" these models to predict and discover better catalysts. We have chosen water-gas shift as a practically important but sufficiently simple (!) reaction for testing this approach.
A. A. Phatak, W. N. Delgass, F. H. Ribeiro, and
W. F. Schneider, “DFT Comparison of Water Dissociation Steps on Cu, Au,
Ni, Pd and Pt,”
J. Phys. Chem. C, 2009, 113, 7269-7276. doi:10.1021/jp810216b
Catalytic NO oxidation is of great practical importance, but current Pt catalysts are expensive and susceptible to degradation in the catalytic environment. Metal oxides could be cheaper and possess greater stability. Recent experimental results indicate that doped perovskite oxides s based on LaCoO3 may possess the desired high catalytic activity. In this project with collaborators at the University of Michigan and General Motors, supported through the NSF GOALI program, we are attempting to uncover the molecular origins of this activity, to contrast it with the more traditional Pt catalysts, and through simulations to guide the design of highly active and sulfur tolerant catalysts.
S. O. Choi, M. Penninger, C. H. Kim, W. F. Schneider, and L. T. Thompson, “Experimental and Computational Investigation of Effect of Sr on NO Oxidation and Oxygen Exchange for La1-xSrxCoO3 Perovskite Catalysts,” ACS Catal., 2013, 3, 2719-2728. doi:10.1021/cs400522r
Z. Chen, C. H. Kim, L. T. Thompson, and W. F. Schneider, “LDA+U Evaluation of the Stability of Low-Index Facets of LaCoO3 perovskite,” Surf. Sci., 2013, 619, 71-76. doi:10.1016/j.susc.2013.09.12