(6q) Combined Quantum and Classical Computational Approaches for Investigating Complex Surface Interactions Impacting Heterogeneous Catalysis

2^nd Year Post-Doctoral Associate

Post-Doctoral Project: â??Ab initio design of semiconductor materials for the heterogeneous photo-electrocatalytic reduction of CO₂â?Â Under the supervision of Prof. Emily A. Carter, Department of Mechanical and Aerospace Engineering, Princeton University

Ph.D. Dissertation: â??Development of multi-scale computational techniques for modeling phase formation in Pd-based oxide catalystsâ? Under the joint supervision of Prof. Michael J. Janik and Prof. Adri C. T. van Duin, Department of Chemical Engineering, Pennsylvania State University

Research Interests:

I am interested in research that employs atomistic simulation techniques at both electronic and classical levels of theory, with a particular focus on applying such methods to address issues related to energy conversion, storage, and utilization. I began academic research as an undergraduate under the supervision of Prof. William F. Schneider at the University of Notre Dame. There I was introduced to ab initio simulation techniques while completing an undergraduate thesis entitled â??Ab initio insights into ionic-liquid/CO₂ binding trends for CO₂ capture applications.â? My training in atomistic simulation continued at the Pennsylvania State University, where I completed my Ph.D. in Chemical Engineering under the advisement of Prof. Michael J. Janik and Prof. Adri C. T. van Duin. My graduate research included the joint application of quantum and classical simulation techniques for investigating phase formation affecting the overall activity of oxide-supported metal catalysts, with a particular emphasis on identifying design principles for methane conversion catalysts. I am currently a post-doctoral associate under the advisement of Prof. Emily A. Carter at Princeton University, where I am conducting ab initio investigations of heterogeneous catalytic mechanisms for CO₂ reduction over semiconductor photo-electrodes. The aforementioned projects have led to 15 total publications (7 first-authored, 1 joint first-authored, 5 second-authored, and 2 co-authored), many of which were written with experimental collaborators.

Future Research Directions:

Through my previous research experiences, I have become well versed in both quantum and classical simulation techniques, which I will continue to apply in research aiding the development of sustainable energy technologies. I intend to integrate computational techniques I have learned from the Carter, Janik, and van Duin groups into my independent research program. I foresee that my group will collaborate with experimental researchers in the fields of catalysis, materials science, and surface characterization. In particular, my research plan consists of three principal focus areas:

(1) Extending multi-physical simulation methodologies to the emerging field of heterogeneous catalysis over photo-electrode surfaces. Combined quantum/classical simulation techniques will be used to assess the structural evolution of catalytically active photo-electrode surfaces that are in contact with a reactive aqueous environment. Full consideration of the reactive environment is essential, as the nature of active sites on the surface will be affected by structural changes induced by interaction with the solvent, and a reactive force field approach will be indispensable for assessing the complexities of the surface-solvent interface. Once the overall surface morphology is understood, ab initio methods will be used to elucidate the electronic structure of excited states that are accessible to photo-excited electrons involved in the catalytic mechanism. These studies will be relevant for H₂O splitting and CO₂ reduction applications.

(2) Applying quantum and classical simulation techniques in tandem to assess strong metal/support interactions impacting the catalytic behavior of metal oxides. I will continue to use combined quantum and classical simulation methods to characterize metal/support interactions leading to emergent catalytic behavior. My previous research determined the origin of highly active sites derived from unique interactions between Pd nanoclusters and a CeO₂ support. Preliminary results, obtained by an undergraduate student under my supervision, indicate that similar interaction trends occur between other metal/support pairs, thus affecting sintering rates and cluster size distributions. My group will further explore these trends, with the objective of developing novel and concrete optimization principles informing the rational design of oxide-supported metal catalysts.

(3) Developing accelerated simulation methodologies for modeling kinetically limited processes with the ReaxFF potential. I have developed various methods tailored to the classical ReaxFF potential for assessing the thermodynamic stability of active sites on catalytic surfaces. These methods, however, are not able to identify kinetic limitations present in the system, as processes involving significant kinetic barriers require prohibitively long simulation timescales to model. However, various well-known computational â??tricksâ? are available for accelerating kinetic sampling during a simulation. Some have been implemented in the literature for ReaxFF already, such as parallel replica dynamics, meta-dynamics, and bond-boost methods. My group will continue to develop such methods for ReaxFF, and in particular will implement an â??on-the-flyâ? kinetic Monte Carlo technique (OF-kMC) for simulating phase formation on catalyst surfaces. During OF-kMC simulations, reaction barriers are calculated directly as the state of the system evolves, thus allowing the simulation to explore phase space without the restriction of having pre-defined reaction paths. ReaxFF is uniquely suited for this, as the required barrier calculations, which typically are prohibitively expensive at the quantum level, become computationally tractable at the ReaxFF level.

Teaching Interests:

My previous teaching experiences have prepared me to serve as the instructor for both undergraduate and graduate courses traditional to the Chemical Engineering core; namely, thermodynamics, transport phenomena, and reaction engineering. While a graduate student at Penn State, I served as a Teaching Fellow for ChE 220 Introduction to Chemical Engineering Thermodynamics. As a Teaching Fellow, I co-instructed â?? with a ChE faculty member (Prof. Scott Milner) â?? a core undergraduate thermodynamics course, where I was responsible for developing and implementing a significant portion of the class material. I served as a Teaching Assistant for ChE 544 Transport Phenomena, which is a core graduate transport course covering momentum, heat, and mass transport. Although I have never formally taught reaction kinetics, I am confident that I can do so given my primary background in catalysis research. In addition to teaching traditional ChE courses, I assisted my advisors, Prof. Mike Janik and Prof. Adri van Duin, in teaching their co-instructed graduate elective course, titled Atomistic Simulations for Engineers, for two semesters. I was responsible for designing and delivering lectures covering quantum mechanical simulation techniques. As a ChE faculty member, I hope to design a similar graduate course for introducing students to atomistic simulation techniques covering both quantum and classical methodologies.

Selected Publications:

Review Article:

Senftle, T. P.; Hong, S.; Islam, M. M.; Kylasa, S. B.; Zheng, Y.; Shin, Y. K.; Junkermeier, C.; Engel-Herbert, R.; Janik, M. J.; Aktulga, H. M.; Verstraelen, T.; Grama, A.; van Duin, A. C. T., â??The ReaxFF reactive force-field: development, applications and future directions.â?Â npj Computational Materials 2016, 2, 15011.

Research Articles:

Senftle, T. P.; van Duin, A. C. T.; Janik, M. J., â??The role of site stability in describing methane activation on Pd_xCe_1-xO_δ.â?Â ACS Catalysis 2015, 5 (10), 6187-6199.

Strayer, M. E.; Senftle, T. P.; Winterstein, J. P.; Vargas-Barbosa, N. M.; Sharma, R.; Janik, M. J.; Mallouk, T. E., â??Strong adsorption of late transition metal nanoparticles correlates with sintering resistance on niobium and silicon oxides.â?Â Journal of the American Chemical Society 2015, 137 (51), 16216-16224.

Addou, R.*; Senftle, T. P.*; Oâ??Connor, N.; Janik, M. J.; van Duin, A. C. T.; Batzill, M., "Influence of hydroxyls on Pd atom mobility and clustering on rutile TiO₂(011)-(2Ã?1).â?Â ACS Nano 2014, 8(6), 6321-6333. *Equal author contribution.

Senftle, T. P.; Meyer, R. J.; Janik, M. J.; van Duin, A. C. T., â??Development of a ReaxFF potential for Pd/O and application to palladium oxide formation.â?Â Journal of Chemical Physics 2013, 139 (4), 044109-15.

Book Chapter:

Senftle, T. P.; van Duin, A. C. T.; Janik, M. J., â??Application of computational methods to supported metal-oxide catalysis.â?Â Computational Catalysis 2014, Royal Society of Chemistry, 157-191.