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Bernhardt L. Trout
Current Research

Overview
Our research focuses on the development and application of molecular based computational and theoretical methods for the design of chemical systems and processes. The overall objective is to develop a theoretical understanding of important chemical systems in order to advance beyond empirical approaches which are based on heuristics and conceptual understanding. Our theories must be verifiable and predictive. The projects described below, incorporate the development and use of Monte Carlo simulations, molecular dynamics methods, ab initio and density functional theory calculations, QM/MM methods, and first-principles molecular dynamics.

Water in Inhomogeneous Environments
Nucleation of Hydrate Clathrates and Ice: Hydrate-clathrates are ice-like materials, in which cages of water molecules arrange themselves in regular patterns around small guest molecules, such as CO2 and/or methane. They are involved in the sequestration and ocean storage of CO2, and they host vast resources of natural gas. The current understanding of nucleation, the labile cluster hypothesis, is merely conceptual at best. It states that under hydrate-forming conditions, solid cages of water molecules are formed first, and these then connect with each other to build the lattice. We have developed a new approach to study nucleation based on the Landau Free Energy method, combined with the choice of suitable order parameters that we developed. Using this method to study CO2-hydrate clathrates, we showed that the labile cluster hypothesis is not feasible. More importantly, we developed a new theory, the local structuring hypothesis, in which the critical nucleus (~18 ‰ in diameter) must be formed completely via local fluctuations. We intend to extend this theory to the study of methane hydrates, to heterogeneous nucleation, and to the development of kinetic inhibitors to be using in gas pipelines.

Stabilization of Therapeutic Proteins via Solvent Formulation: Therapeutic proteins, which are used to treat an enormous variety of diseases, are generally stored in aqueous media before they are used. Unfortunately, they degrade over time from the oxidation of sulfur atoms in methionine residues. We hypothesize that local structuring of solvent in addition to solvent accessibility controls the rates of oxidation of various sites, and we are developing theories to be used to add benign solutes which will stabilize these proteins.

Modeling of the Dissolution of CO2 under Hydrate-Forming Conditions: We have developed the first verifiable macroscopic model that can describe the dissolution of droplets of CO2 in the ocean. This has been accomplished by using molecular simulations to compute model-independent transport properties, such as diffusivities.

Modeling of the Phase Behavior of Hydrate-Clathrates: We have used ab initio methods to compute 18,000 points on the methane-water potential energy hypersurface with high accuracy. In order to accomplish this, we developed a method to correct calculations performed using small basis sets (~1 min./calc.) to those using large basis sets (~1 day/calc.). We have validated this potential for use in making predictions by computing accurately the phase behavior of methane-hydrates. We have also developed an analytical method for fitting phase data. We have shown that our analytical method is not only simpler than the numerical methods currently used by hundreds of researchers but also gives more meaningful physical understanding than those methods.

Theoretical Heterogeneous Catalysis
Understanding Stratospheric Heterogeneous Catalysis Responsible for Ozone Depletion: Ice in the stratosphere, normally thought to be chemically inactive, is an extremely good catalyst for activating chlorine, which is a key component in cycles leading to ozone depletion. We have used order parameters to characterize the degree of disorder on ice surfaces as a function of temperature and adsorbate concentration, and we have helped to explain the high uptake of HCl. We have concluded that HCl is most likely molecularly adsorbed. In future work, we wish to study HCl uptake on nitric acid trihydrate and futher reactions involving HCl.

Reactions of Sulfur Oxides on Metal Surfaces: Sulfur plays a key role in deactivating automotive catalysts and components of fuel cells. In particular, it can (reversibly) form metal sulfides under reducing conditions, and (irreversibly) form sulfates from metal oxides under lean conditions. We have been quantifying the rates of elementary reactions involving sulfur poisoning and plan to continue to do so. Our objective is to use this understanding in order to develop more sulfur resistant catalysts.

Development of Measures of Reactivity of Solid Acid Catalysts: No scale currently exists to quantify solid acidity, such as Br¯nsted acidity in zeolites. Furthermore, simple measures, such as the energy of adsorption of bases, sometimes correlates to reactivity and sometimes does not. We are performing quantum density functional theory calculations on periodic models of chabazite in order to develop a measure of solid acidity and to address the question of whether different acid sites in a particular zeolite have different activities.

Further details

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