Sub-Nanometer Catalyst Clusters for Propane Dehydrogenation

Propane dehydrogenation (PDH) is used to produce propene, which is the primary building block for many commercial plastics. The catalyst most commonly used for this reaction is platinum. Due to rising demand for propene, an alternative catalyst is being sought due to platinum’s high cost. Alternatives might involve very small platinum particles as well as particles composed of different atoms. For this purpose, we have performed a computational study of the PDH reaction with a 4 atom platinum cluster (Pt4) and several different 4-atom transition metal cluster (TM4) catalysts on a graphene support. We have computed the equilibrium structures of the Pt4 and TM4 clusters on both single-and double-vacancy sites and have calculated the complete PDH reaction pathway for each case. This allowed us to study the effect of the graphene support on catalytic activity. We have also calculated the PDH reaction pathway for larger Ptx clusters, where x = 5-14, in order to study the effect of particle size on catalytic activity. These results help clarify the relationship between the PDH activation energy and the propane binding energy and overall reaction energy and may aid in the design of new potential catalysts for the PDH reaction

Propane Dehydrogenation Using Transition Metal Cluster Catalysts

Our research seeks to determine the propane dehydrogenation (PDH) reaction pathways using various transition-metal cluster catalysts. We are studying the first step of the reaction, in which a C-H bond is broken. This has been previously shown to be the rate-limiting step of the PDH reaction. We are calculating the PDH activation energy (Ea) using the Vienna Ab-Initio Simulation Package (VASP) in conjunction with the nudged elastic band algorithm. Thus far, we have studied Pt, Ta, and Ni clusters ranging in size from 2-10 atoms. Our goal is to better understand the dependence of Ea on metal type and cluster size

Sub-Nanometer Catalyst Clusters for Propane Dehydrogenation

Propane dehydrogenation (PDH) is used to produce propene, which is the primary building block for many commercial plastics. The catalyst most commonly used for this reaction is platinum. Due to rising demand for propene, an alternative catalyst is being sought due to platinum’s high cost. Alternatives might involve very small platinum particles as well as particles composed of different atoms. For this purpose, we have performed a computational study of the PDH reaction with a 4 atom platinum cluster (Pt4) and several different 4-atom transition metal cluster (TM4) catalysts on a graphene support. We have computed the equilibrium structures of the Pt4 and TM4 clusters on both single-and double-vacancy sites and have calculated the complete PDH reaction pathway for each case. This allowed us to study the effect of the graphene support on catalytic activity. We have also calculated the PDH reaction pathway for larger Ptx clusters, where x = 5-14, in order to study the effect of particle size on catalytic activity. These results help clarify the relationship between the PDH activation energy and the propane binding energy and overall reaction energy and may aid in the design of new potential catalysts for the PDH reaction

Surface-Dependence of Interfacial Binding Strength between Zinc Oxide and Graphene Investigated from First Principles

There is an increasing interest in hybridized materials for applications such as improving the structural integrity of known and commonly used materials. Recent experiments have suggested that the adhesion of zinc oxide (ZnO) nanowires with carbon fibers can significantly improve the interfacial shear strength of fiber-reinforced composites. We have carried out a systematic study of the interaction between ZnO and graphene based on density functional theory, with a focus on the effect of the surface orientation and termination of ZnO. The most thermodynamically stable hexagonal phase of ZnO is modeled by a cluster with (001), (100), and (110) facets, and the (001) surface is constructed to have both Zn-rich and O-rich terminations. The interaction has been explored through varying both the orientation and the binding sites of the interacting surfaces. The interfacial binding strength is calculated by scanning the potential energy surface while bringing the ZnO cluster incrementally closer to graphene. Results from these energy scans will be presented and discussed along with simple physical arguments to rationalize the observed behavior

A First-Principle Study of Small Neutral and Anionic Silver Halide Clusters

Silver halide is a material that was traditionally used in photographic films. In recent years, there has been a revived interest in using small clusters of silver halides for photocatalytic and photovoltaic applications. We present the results of a theoretical study of neutral and anionic AgnXn (X = F, Cl, and Br, and n = 1-6) clusters. Quantum-mechanical calculations were performed using Density Functional Theory (DFT) in search of the lowest-energy isomers of the neutral and anionic clusters with applied symmetry constraints. The optimal configurations are compared across the series of AgF, AgCl, and AgBr. The variation in binding energies, bond lengths, charge distributions, HOMO-LUMO gaps, and electron affinities will be discussed as a function of cluster size and composition. The study of these clusters allows us to gain a better understanding of the structure and function of these materials in current and future applications

Propane Dehydrogenation Using Transition Metal Cluster Catalysts

Our research seeks to determine the propane dehydrogenation (PDH) reaction pathways using various transition-metal cluster catalysts. We are studying the first step of the reaction, in which a C-H bond is broken. This has been previously shown to be the rate-limiting step of the PDH reaction. We are calculating the PDH activation energy (Ea) using the Vienna Ab-Initio Simulation Package (VASP) in conjunction with the nudged elastic band algorithm. Thus far, we have studied Pt, Ta, and Ni clusters ranging in size from 2-10 atoms. Our goal is to better understand the dependence of Ea on metal type and cluster size

Screening Single-Atom Catalysts for Propane Dehydrogenation

Recent interest in so-called single-atom catalysts raises the question of how single transition metal atoms differ in reactivity from small atomic clusters and bulk systems. As a first step toward more extensive modeling of propane dehydrogenation catalysis by transition metal atoms on a graphene support, we have studied the interaction of transition metal atoms with propane using density functional theory as implemented in the VASP program. The climbing-image nudged elastic band algorithm was used to identify the minimum energy pathway for the rate-limiting step of this reaction. We compared the calculated activation energies for this reaction step with simple properties of the transition metal atoms, such as electron affinity and ionization energy, that might be correlated with the activation energies. While certain atoms stand out as promising catalysts, this survey reveals other interesting properties of this reaction, such as spin state changes, that merit further study

Altering the Activity of a Ni4 Catalyst for Propane Dehydrogenation Using a Nitrogen-Doped Graphene Support

Propane dehydrogenation (PDH) is used to produce propene, which is the primary building block for many commercial plastics. The catalyst used most commonly for this reaction is platinum. Due to a rising demand for propene, an alternative to platinum is being sought because of its high cost. For this purpose, we are performing a computational study of a 4-atom nickel cluster (Ni4) on a graphene support. We have calculated the propane binding energy, overall reaction energy, and activation energy for the first step of the PDH reaction, which we believe to be the rate-determining step. We have introduced varying numbers of nitrogen atoms into the graphene sheet to study the effect of nitrogen doping on the behavior of the Ni4 catalyst. We will attempt to find the dependence of the PDH activation energy on the propane binding energy and the reaction energy. The results will aid in the design of new potential catalysts for the PDH reaction

Single-Electron Activation of CO2 on Graphene-Supported ZnO Nanoclusters: Effects of Doping in the Support

Use of solar energy to convert the greenhouse gas CO2 into useful chemicals or fuels could not only reduce the accumulation of CO2 in the atmosphere but also provide a solution to sustainable energy development. There has been much interest in understanding the mechanistic role of graphene when added to semiconductor nanostructures to reduce CO2because of the observation of enhanced photocatalytic activities in recent experiments. In this work, we investigate the adsorption and single-electron activation of CO2 on ZnO nanoclusters with and without a modified graphene support using a first-principles approach, with a special focus on the effect of the support. The formation of the CO2– anion is identified under simulated photoexcitation conditions and is energetically more favorable than for previously studied oxide photocatalysts. The calculated results suggest that single-heteroatom doping in graphene has a significant impact on the catalytic activity of ZnO. The electronic coupling between the support and the semiconductor cluster plays a critical role in the activation of CO2 on the supported ZnO cluster. n-type doping helps to retain the photoexcited electron on ZnO and facilitates CO2reduction on ZnO, whereas p-type doping enhances charge transfer from the photoexcited ZnO to graphene and would be useful for reductions occurring on graphene