Nanoscale surface chemistry in self- and directed-assembly of organic molecules on solid surfaces and synthesis of nanostructured organic architectures

This is the published version. Copyright 2008 International Union of Pure and Applied ChemistryThis article briefly reviews the interplay of weak noncovalent interactions involved in the formation of self-assembled monolayers of organic molecules and the strong chemical binding in directed-assembly of organic molecules on solid surfaces. For a self-assembled monolayer, each molecule involves at least three categories of weak interactions, including molecule-substrate interactions, molecule-molecule interactions in a lamella, and molecule-molecule interactions between two adjacent lamellae. Basically, molecule-substrate interactions play a major role in determining molecular configuration. Molecule-molecule interactions, particularly the interactions of molecular ending functional groups between two adjacent lamellae, such as hydrogen bonds, play a dominant role in determining the molecular packing pattern in a monolayer. These weak interactions may induce or influence molecular chirality. This understanding at the atomic scale allows us to design 2D nanostructured organic materials via precisely manipulating these weak noncovalent interactions. Compared to the self-assembled monolayer formed via weak noncovalent interactions, the structure of directed-assembled monolayer/multilayers formed through strong chemical bonds is significantly dependent on the geometric arrangement and reactivity of active sites on the solid surface. In contrast to the significant role of weak intermolecular interactions in determining molecular packing in a self-assembled monolayer, strong chemical binding between molecules and reactive sites of a substrate plays a major role in determining the molecular packing pattern in a directed-assembly monolayer. Controllable chemical attachment between organic functional groups and reactive sites of the solid surface is crucial for the formation of a highly oriented organic monolayer and the following multilayer

Design of an in-house ambient pressure AP-XPS using a bench-top X-ray source and the surface chemistry of ceria under reaction conditions

A new in-house ambient pressure XPS (AP-XPS) was designed for the study of surfaces of materials under reaction conditions and during catalysis. Unique features of this in-house AP-XPS are the use of monochromated Al Kα and integration of a minimized reaction cell, and working conditions of up to 500 °C in gases of tens of Torr. Generation of oxygen vacancies on ceria and filling them with oxygen atoms were characterized in operando

Water–gas shift on gold catalysts: catalyst systems and fundamental studies

This is the published version. ©Copyright 2013 Royal Society of ChemistrySince the pioneering finding by Haruta et al. that small gold nanoparticles on reducible supports can be highly active for low-temperature CO oxidation, the synthesis, characterization, and application of supported gold catalysts have attracted much attention. The water–gas shift reaction (WGSR: CO + H2O = CO2 + H2) is important for removing CO and upgrading the purity of H2 for fuel cell applications, ammonia synthesis, and selective hydrogenation processes. In recent years, much attention has been paid to exploration the possibility of using supported gold nanocatalysts for WGSR and understanding the fundamental aspects related to catalyst deactivation mechanisms, nature of active sites, and reaction mechanisms. Here we summarize recent advances in the development of supported gold catalysts for this reaction and fundamental insights that can be gained, and furnish our assessment on the status of research progress

Development of a reaction cell for in-situ/operando studies of surface of a catalyst under a reaction condition and during catalysis

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Review of Scientific Instruments and may be found at https://aip.scitation.org/doi/10.1063/1.4946877.Tracking surface chemistry of a catalyst during catalysis is significant for fundamental understanding of catalytic performance of the catalyst since it allows for establishing an intrinsic correlation between surface chemistry of a catalyst at its working status and its corresponding catalytic performance. Ambient pressure X-ray photoelectron spectroscopy can be used for in-situ studies of surfaces of different materials or devices in a gas. To simulate the gaseous environment of a catalyst in a fixed-bed a flowing gaseous environment of reactants around the catalyst is necessary. Here, we report the development of a new flowing reaction cell for simulating in-situ study of a catalyst surface under a reaction condition in gas of one reactant or during catalysis in a mixture of reactants of a catalytic reaction. The homemade reaction cell is installed in a high vacuum (HV) or ultrahigh vacuum (UHV) environment of a chamber. The flowing gas in the reaction cell is separated from the HV or UHV environment through well sealings at three interfaces between the reaction cell and X-ray window, sample door and aperture of front cone of an energy analyzer. Catalyst in the cell is heated through infrared laser beam introduced through a fiber optics interfaced with the reaction cell through a homemade feedthrough. The highly localized heating on the sample holder and Au-passivated internal surface of the reaction cell effectively minimizes any unwanted reactions potentially catalyzed by the reaction cell. The incorporated laser heating allows a fast heating and a high thermal stability of the sample at a high temperature. With this cell, a catalyst at 800 °C in a flowing gas can be tracked readily

Design of a new reactor-like high temperature near ambient pressure scanning tunneling microscope for catalysis studies

This is the published version. ©Copyright 2013 American Institute of PhysicsHere, we present the design of a new reactor-like high-temperature near ambient pressure scanning tunneling microscope (HT-NAP-STM) for catalysis studies. This HT-NAP-STM was designed for exploration of structures of catalyst surfaces at atomic scale during catalysis or under reaction conditions. In this HT-NAP-STM, the minimized reactor with a volume of reactant gases of ∼10 ml is thermally isolated from the STM room through a shielding dome installed between the reactor and STM room. An aperture on the dome was made to allow tip to approach to or retract from a catalyst surface in the reactor. This dome minimizes thermal diffusion from hot gas of the reactor to the STM room and thus remains STM head at a constant temperature near to room temperature, allowing observation of surface structures at atomic scale under reaction conditions or during catalysis with minimized thermal drift. The integrated quadrupole mass spectrometer can simultaneously measure products during visualization of surface structure of a catalyst. This synergy allows building an intrinsic correlation between surface structure and its catalytic performance. This correlation offers important insights for understanding of catalysis. Tests were done on graphite in ambient environment, Pt(111) in CO, graphene on Ru(0001) in UHV at high temperature and gaseous environment at high temperature. Atom-resolved surface structure of graphene on Ru(0001) at 500 K in a gaseous environment of 25 Torr was identified

Integration of surface science, nanoscience, and catalysis

This is the published version. Copyright 2010 International Union of Pure and Applied ChemistryThis article briefly reviews the development of surface science and its close relevance to nanoscience and heterogeneous catalysis. The focus of this article is to highlight the importance of nanoscale surface science for understanding heterogeneous catalysis performing at solid–gas and solid–liquid interfaces. Surface science has built a foundation for the understanding of catalysis based on the studies of well-defined single-crystal catalysts in the past several decades. Studies of catalysis on well-defined nanoparticles (NPs) significantly promoted the understanding of catalytic mechanisms to an unprecedented level in the last decade. To understand reactions performed on catalytic active sites at nano or atomic scales and thus reach the goal of catalysis by design, studies of the surface of nanocatalysts are crucial. The challenges in such studies are discussed

Shape control of bimetallic nanocatalysts through well-designed colloidal chemistry approaches

This is the published version. ©Copyright 2012 Royal Society of ChemistrySynthesis of bimetallic nanomaterials with well controlled shape is an important topic in heterogeneous catalysis, low-temperature fuel cell technology, and many other fields. Compared with monometallic counterparts, bimetallic nanocatalysts endow scientists with more opportunities to optimize the catalytic performance by modulating the charge transfer between different metals, local coordination environment, lattice strain and surface element distribution. Considering the current challenges in shape controlled synthesis of bimetallic nanocatalysts, this tutorial review highlights some significant achievements in preparing bimetallic alloy, core–shell and heterostructure nanocrystals with well-defined morphologies, summarizes four general routes and some key factors of the bimetallic shape control scenarios, and provides some general ideas on how to design synthetic strategies to control the shape and exposing facets of bimetallic nanocrystals. The composition and shape dependent catalytic behaviours of bimetallic nanocrystals are reviewed as well

Tetra-σ attachment of allyl cyanide on Si(111)−7×7

This is the published version. Copyright 2002 American Physical SocietyThe investigation of allyl cyanide adsorption on Si(111)−7×7 using high-resolution electron-energy-loss spectroscopy (HREELS), x-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS) reveals a tetra-σ binding mode through two [2+2]-like cycloaddition reactions. The HREELS spectra of chemisorbed monolayer show the absence of C=C, C≡N, and C(sp2)—H stretching modes coupled with the appearance of C=N stretching mode at ∼1590 cm−1, demonstrating that both the C=C and C≡N of allyl cyanide directly participate in binding with the surface to form C—C and C=N bonds, respectively. This binding configuration was further confirmed in our XPS and UPS studies. The imine-containing skeleton formed on the surface can possibly be employed as a molecular template for a further modification of Si surfaces and syntheses in vacuum

Action of bimetallic nanocatalysts under reaction conditions and during catalysis: evolution of chemistry from high vacuum conditions to reaction conditions

This is the published version. Copyright 2012 Royal Society of ChemistryBimetallic catalysts are one of the main categories of metal catalysts due to the tunability of electronic and geometric structures through alloying a second metal. The integration of a second metal creates a vast number of possibilities for varying the surface structure and composition of metal catalysts toward designing new catalysts. It is well acknowledged that the surface composition, atomic arrangement, and electronic state of bimetallic catalysts could be different from those before a chemical reaction or catalysis based on ex situ studies. Thanks to advances in electron-based surface analytical techniques, the surface chemistry and structure of bimetallic nanoparticles can be characterized under reaction conditions and during catalysis using ambient pressure analytical techniques including ambient pressure XPS, ambient pressure STM, X-ray absorption spectroscopy and others. These ambient pressure studies revealed various restructurings in the composition and arrangement of atoms in the surface region of catalysts under reaction conditions or during catalysis compared to that before reaction. These restructurings are driven by thermodynamic and kinetic factors. The surface energy of the constituent metals and adsorption energy of reactant molecules or dissociated species on a metal component are two main factors from the point of view of thermodynamics. Correlations between the authentic surface structure and chemistry of catalysts during catalysis and simultaneous catalytic performance were built for understanding catalytic mechanisms of bimetallic catalysts toward designing new catalysts with high activity, selectivity, and durability

An inventory of glacier changes between 1973 and 2011 for the Geladandong Mountain area, China.

This is the publisher's version, also available electronically from http://www.the-cryosphere-discuss.net/7/507/2013/tcd-7-507-2013.htmlThe snow and ice of the Geladangong Mountain area supply the headwaters of the Yangtze River, and long-term changes to glaciers and ice masses in this region due to a warming climate are of great concern. An inventory of glacier boundaries and changes over decades for the Geladandong Mountain area in China has been conducted using remote sensing imagery from Landsat (MSS, TM, ETM+), CERBES CCD, and GIS techniques. Variations in glacier extent has been measured using a~series of digital images since 1973, including Landsat MSS in 1973, Landsat TM in 1992, Landsat ETM+ in 2004, and CBERS CCD in 2011. All Landsat data are snow-free outside the glacier boundaries, allowing an unsupervised classification method to be used to extract glacier area. For the CBERS CCD data, some areas were covered by clouds and snow, requiring an initial unsupervised classification method to divide glacier, clouds and snow from other land types, followed by a supervised visual interpretation to extract glacier area. The results show a decrease in glacier ice cover in the study area during the past 38 yr. From 1973 to 2011, glacier area decreased from 107 105 hectares to 94 220 hectares, or a change of −12%. The speed at which ice cover is being lost has been decreasing during the past 38 yr. The rate of glacier area loss was 0.47% yr−1 from 1973–1992, 0.19% yr−1 from 1992–2004, and 0.14% yr−1 from 2004–2011. While most of the glaciers are shrinking, some are expanding. For the 1973 to 2004 period, retreating glaciers exposed 14 447 hectares of land, and advancing glaciers spread over 2682 hectares that were not covered by ice in 1973. The net glacier area decrease is 11 765 hectares from 1973–2004. For the 1973 to 2011 period, glaciers expanded over 3791 hectares, and retreated from 16 504 hectares