効率的な電極触媒による硝酸塩のアンモニアへの還元のための触媒の探索とメカニズムの研究

Tohoku University博士（環境科学）thesi

Understanding the Nanotube Growth Mechanism: A Strategy to Control Nanotube Chirality during Chemical Vapor Deposition Synthesis

For two decades, single-wall carbon nanotubes (SWCNTs) have captured the attention of the research community, and become one of the flagships of nanotechnology. Due to their remarkable electronic and optical properties, SWCNTs are prime candidates for the creation of novel and revolutionary electronic, medical, and energy technologies. However, a major stumbling block in the exploitation of nanotube-based technologies is the lack of control of nanotube structure (chirality) during synthesis, which is intimately related to the metallic or semiconductor character of the nanotube. Incomplete understanding of the nanotube growth mechanism hinders a rationale and cost-efficient search of experimental conditions that give way to structural (chiral) control. Thus, computational techniques such as density functional theory (DFT), and reactive molecular dynamics (RMD) are valuable tools that provide the necessary theoretical framework to guide the design of experiments. The nanotube chirality is determined by the helicity of the nanotube and its diameter. DFT calculations show that once a small nanotube 'seed' is nucleated, growth proceeds faster if the seed corresponds to a high chiral angle nanotube. Thus, a strategy to gain control of the nanotube structure during chemical vapor deposition synthesis must focus on controlling the structure of the nucleated nanotube seeds. DFT and RMD simulations demonstrate the viability of using the structures of catalyst particles over which nanotube growth proceeds as templates guiding nanotube growth toward desired chiralities. This effect occurs through epitaxial effects between the nanocatalyst and the nanotube growing on it. The effectiveness of such effects has a non-monotonic relationship with the size of the nanocatalyst, and its interaction with the support, and requires fine-tuning reaction conditions for its exploitation. RMD simulations also demonstrate that carbon bulk-diffusion and nanoparticle supersaturation are not needed to promote nanotube growth, hence reaction conditions that increase nanoparticle stability, but reduce carbon solubility, may be explored to achieve nanotube templated growth of desired chiralities. The effect of carbon dissolution was further demonstrated through analyses of calculated diffusion coefficients. The metallic nanocatalyst was determined to be in viscous solid state throughout growth, but with a less solid character during the induction/nucleation stage

Co₃Mo₃N—An efficient multifunctional electrocatalyst

Efficient catalysts are required for both oxidative and reductive reactions of hydrogen and oxygen in sustainable energy conversion devices. However, current precious metal-based electrocatalysts do not perform well across the full range of reactions and reported multifunctional catalysts are all complex hybrids. Here, we show that single-phase porous Co(3)Mo(3)N prepared via a facile method is an efficient and reliable electrocatalyst for three essential energy conversion reactions; oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) in alkaline solutions. Co(3)Mo(3)N presents outstanding OER, ORR, and HER activity with high durability, comparable with the commercial catalysts RuO(2) for OER and Pt/C for ORR and HER. In practical demonstrations, Co(3)Mo(3)N gives high specific capacity (850 mA h g(Zn)(−1) at 10 mA cm(−2)) as the cathode in a zinc-air battery, and a low potential (1.63 V at 10 mA cm(−2)) used in a water-splitting electrolyzer. Availability of Co and Mo d-states appear to result in high ORR and HER performance, while the OER properties result from a cobalt oxide-rich activation surface layer. Our findings will inspire further development of bimetallic nitrides as cost-effective and versatile multifunctional catalysts that will enable scalable usage of electrochemical energy devices

Exploring the Mechanistic Landscape of Nitric Oxide Oxidation and Ammonia Selective Catalytic Reduction of Nitric Oxide on Cu-Zeolites via Kinetic and Spectroscopic Characterization

Increasingly stringent regulations to reduce emissions of nitrogen oxides (NOx) from exhausts of heavy-duty diesel engines has set the stage to delve into a detailed investigation of engine after-treatment catalysts in order to understand the chemistry during their operation and design the next generation of catalytic formulations to meet future requirements. Small-pore Cu- and Fe-exchanged SSZ-13 catalysts with chabazite (CHA) topology are able to sustain high catalytic rates for selective catalytic reduction (SCR) even after exposure to harsh hydrothermal conditions present in diesel exhaust. Probing the redox behavior and the active site requirements for standard SCR on Cu-SSZ-13 catalysts using a combination of infrared (FTIR) and x-ray absorption (XAS) spectroscopies, kinetic measurements and density functional theory (DFT) calculations forms the basis for this dissertation

Present and future of surface-enhanced Raman scattering

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article

Summaries of FY 1997 Research in the Chemical Sciences

The objective of this program is to expand, through support of basic research, knowledge of various areas of chemistry, physics and chemical engineering with a goal of contributing to new or improved processes for developing and using domestic energy resources in an efficient and environmentally sound manner. Each team of the Division of Chemical Sciences, Fundamental Interactions and Molecular Processes, is divided into programs that cover the various disciplines. Disciplinary areas where research is supported include atomic, molecular, and optical physics; physical, inorganic, and organic chemistry; chemical energy, chemical physics; photochemistry; radiation chemistry; analytical chemistry; separations science; heavy element chemistry; chemical engineering sciences; and advanced battery research. However, traditional disciplinary boundaries should not be considered barriers, and multi-disciplinary efforts are encouraged. In addition, the program supports several major scientific user facilities. The following summaries describe the programs