Chaitanya K. Narula

Bio: Chaitanya K. Narula is an academic researcher from Oak Ridge National Laboratory. The author has contributed to research in topics: Boron nitride & Catalysis. The author has an hindex of 26, co-authored 139 publications receiving 3279 citations. Previous affiliations of Chaitanya K. Narula include University of Michigan & University of New Mexico.

CO Oxidation on Supported Single Pt Atoms: Experimental and ab Initio Density Functional Studies of CO Interaction with Pt Atom on θ-Al2O3(010) Surface

Abstract: Although there are only a few known examples of supported single-atom catalysts, they are unique because they bridge the gap between homogeneous and heterogeneous catalysis. Here, we report the CO oxidation activity of monodisperse single Pt atoms supported on an inert substrate, θ-alumina (Al2O3), in the presence of stoichiometric oxygen. Since CO oxidation on single Pt atoms cannot occur via a conventional Langmuir–Hinshelwood scheme (L–H scheme) which requires at least one Pt–Pt bond, we carried out a first-principles density functional theoretical study of a proposed pathway which is a variation on the conventional L–H scheme and inspired by the organometallic chemistry of platinum. We find that a single supported Pt atom prefers to bond to O2 over CO. CO then bonds with the oxygenated Pt atom and forms a carbonate which dissociates to liberate CO2, leaving an oxygen atom on Pt. Subsequent reaction with another CO molecule regenerates the single-atom catalyst. The energetics of the proposed mechanism ...

Single-Phase PrOy−ZrO2 Materials and Their Oxygen Storage Capacity: A Comparison with Single-Phase CeO2−ZrO2, PrOy−CeO2, and PrOy−CeO2−ZrO2 Materials

Abstract: High-surface-area PrOy−ZrO2 mixed oxide, crystallized in the cubic fluorite structure, is synthesized for the first time as a single-phase material over a wide range of composition by sol−gel processing X-ray powder diffraction shows that the material remains single phase even after thermal treatment in air to 900 °C The oxygen storage capacity of PrOy−ZrO2, where praseodymium undergoes Pr3+ ↔ Pr4+ interconversion, is assessed by temperature-programmed reduction with H2 The results show that there is little oxygen storage capacity unless the PrOy concentration exceeds 25 mol % A comparison of oxygen storage capacity from similarly prepared single-phase CeO2−ZrO2, PrOy−CeO2, and PrOy−CeO2−ZrO2 materials is presented Measurements of lattice parameter and reducibility suggest that there are preferred associations that lead to PrOy−ZrO2 and CeO2−ZrO2 rather than PrOy−CeO2 in the ternary mixed oxide An evaluation of model Pd catalysts, using PrOy−ZrO2 and CeO2−ZrO2 as support materials, in functional tes

Materials chemistry issues related to advanced materials applications in the automotive industry

Abstract: The driving force behind the research on advanced materials has largely been aerospace and defense applications. In such applications the customer-induced limitations and infrastructural economic factors are secondary to the application-oriented parameters. Automobiles, on the other hand, represent the primary consumers of advanced materials in civilian applications. Automobiles are high-technology, low-cost machines which need to be robust for various climatic conditions and driver behavior. Advanced materials play an important role in the design and fabrication of various components of automobiles, and the use of new materials continues to increase. Recent interest in developing highly fuel efficient vehicles with low emissions has focused efforts toward materials, designs, and devices and is spurring research into advanced materials for weight reduction. The goal is to achieve fuel efficiency by weight reduction and a more efficient powertrain. In this review article, we summarize the efforts of the 19...

Synthesis of boron nitride ceramics from poly(borazinylamine) precursors

Abstract: Several simple monomeric boron and nitrogen reagents have been utilized as starting materials in high-temperature pyrolyses or chemical vapor deposition schemes to prepare hexagonal boron nitride. However, extensive applications and demands for new forms (films, gels, foams, fibers) have recently led to searches for improved syntheses and processing techniques for BN. The authors preliminary studies indicate that an oligomeric borazinylamine gel can be prepared in high yield, and this gel provides a useful precursor for the formation of hexagonal boron nitride. It is also very important to note that this chemistry provides a system which is adaptable to sol-gel processing. Although several features require additional study, it is apparent that the amine cross-linking of borazene fragments offers a beneficial and important advance in the use of borazenes as sources for BN. It is interesting to note that some investigators have suggested that the presence of silica in boron nitride improves its processing characteristics as well as prevents hydrolysis of boron nitride. Therefore, the presence of organosilicon in their synthesis may prove beneficial. Additional studies of chemicall modified borazenes and other cross-linking reagents are in progress.

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Abstract: Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Boron Nitride Nanotubes and Nanosheets

Abstract: Hexagonal boron nitride (h-BN) is a layered material with a graphite-like structure in which planar networks of BN hexagons are regularly stacked. As the structural analogue of a carbon nanotube (CNT), a BN nanotube (BNNT) was first predicted in 1994; since then, it has become one of the most intriguing non-carbon nanotubes. Compared with metallic or semiconducting CNTs, a BNNT is an electrical insulator with a band gap of ca. 5 eV, basically independent of tube geometry. In addition, BNNTs possess a high chemical stability, excellent mechanical properties, and high thermal conductivity. The same advantages are likely applicable to a graphene analogue-a monatomic layer of a hexagonal BN. Such unique properties make BN nanotubes and nanosheets a promising nanomaterial in a variety of potential fields such as optoelectronic nanodevices, functional composites, hydrogen accumulators, electrically insulating substrates perfectly matching the CNT, and graphene lattices. This review gives an introduction to the rich BN nanotube/nanosheet field, including the latest achievements in the synthesis, structural analyses, and property evaluations, and presents the purpose and significance of this direction in the light of the general nanotube/nanosheet developments.

Thermally stable single-atom platinum-on-ceria catalysts via atom trapping

Abstract: Catalysts based on single atoms of scarce precious metals can lead to more efficient use through enhanced reactivity and selectivity. However, single atoms on catalyst supports can be mobile and aggregate into nanoparticles when heated at elevated temperatures. High temperatures are detrimental to catalyst performance unless these mobile atoms can be trapped. We used ceria powders having similar surface areas but different exposed surface facets. When mixed with a platinum/aluminum oxide catalyst and aged in air at 800°C, the platinum transferred to the ceria and was trapped. Polyhedral ceria and nanorods were more effective than ceria cubes at anchoring the platinum. Performing synthesis at high temperatures ensures that only the most stable binding sites are occupied, yielding a sinter-resistant, atomically dispersed catalyst.

Atomic cobalt on nitrogen-doped graphene for hydrogen generation

Abstract: Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts.