CAREER: Simulation of Metal Nanoparticle Interactions with Doped Carbon Supports

University Of Alabama Tuscaloosa, Tuscaloosa AL

Investigators

Abstract

0747690 Turner Scientific Merit: Many electronic, chemical, and physical properties are known to depend upon system size, especially when the length scale approaches nanometer or sub-nanometer dimensions. This revelation has driven a significant amount of the scientific and engineering research over the past few decades, especially with regards to electronic materials, biological processes, and catalysis. With regards to catalysis, it is recognized that the activity of a catalyst is not a pure function of its surface area. In fact, as the size of the catalyst shrinks, the catalyst behaves less like a bulk metal, and characteristics such as the morphology of the particles and the nature of the support begin to play a significant role. The primary goal of a catalyst search is to identify materials with specific chemical activity. However, a secondary goal is for the catalyst to maintain its activity during reacting conditions, which may include high temperatures, high or low pH, interactions with adsorbates, or the presence of an electrical current in electrochemical applications. Harsh reacting conditions may quickly result in a loss of chemical activity, due to catalyst poisoning, sintering, or dissolution of the catalyst or its support material. In order to maintain activity, these detrimental processes must be mitigated, either by tightly controlling the reaction conditions or by altering the intrinsic properties of the catalyst/support material. As such, a computational investigation will be performed to understand how the interactions between metal clusters and carbon support materials might be manipulated in order to preserve or enhance catalyst function. This project is built upon the premise that catalyst sintering is (in part) related to the interaction of the catalyst with its support material. There are two primary mechanisms that are used to describe the sintering process: coalescence and Ostwald ripening. Since both processes involve the diffusion of the catalyst particles on the support (either as single atoms or as clusters), the catalyst stability should be significantly improved by reducing the inherent mobility of the catalysts. In other words, if the particles are somehow pinned or anchored to the support, sintering should decrease. This is the route that will be explored here. Attention will be focused on the interactions of Pt, Pd, Ru, Rh, and Au metal atoms and clusters with (doped) carbon supports. These metal/support combinations can be found in a wide range of catalytic and electrochemical applications in industry, including fuel cell catalysis, decarbonylation reactions, reductive amination, alcohol synthesis, etc. Due to the high price (and limited quantities) of these precious metals, it is particularly important to maintain their original activity under reacting conditions for extended periods of time. This is one of the central challenges of catalysis. The modeling will be primarily performed using electronic structure calculations to predict a variety of physical and chemical properties of the metal/support systems. In particular, characterization of the structure and activity of Pt, Pd, Ru, Rh, and Au catalyst particles on pristine and doped carbon supports will be performed. Various dopant schemes will be investigated, and these will be compared with typical carbon support chemistry (carboxyl groups, hydroxyl groups, Stone-Wales defects, etc.). Along with this, the propensity of the catalyst particles for sintering, as a function of temperature and as a function of electric field strength (pertinent to electrochemical applications) will be investigated with ab initio MD simulations. Finally, the metal particles will be analyzed with respect to their catalytic activity by calculating the reaction mechanisms of standard probe reactions, such as CO oxidation. Broader Impacts: The education and outreach plan has been given significant attention, and a high impact strategy has been developed for disseminating the science outcomes. The outreach activities involve K-12 students by partnering with the McWane Science Center in Birmingham, AL to create a new science exhibit. Also, undergraduate students will participate in this project through the UA Computer Based Honors Program. Finally, faculty at HBCU programs will be included in summer workshops, as well as other audiences through the more traditional avenues (graduate courses, conference presentations, and journal publications).