Supported Metal Catalysis Research Articles

One-Dimensional Segregated Single Au Sites on Step-Rich ZnO Ladder for Ultrasensitive NO2 Sensors

Summary Here, we develop a freestanding ladder-like ZnO surface with abundant unsaturated step defects, which could efficiently anchor Au1 sites with one-dimensional assembling for the ultrasensitive NO2 detection. The dimension of the obtained ZnO hexagonal ladder could be precisely controlled through reasonably regularizing the nucleation and growth rate. Following a layer-by-layer growth mode, the obtained ZnO would adopt the step-rich evolution. These ladder-like structures could provide abundant unsaturated step defects along with their curved edge profiles to serve as susceptible centers to site-selectively immobilize isolated Au1 species (Au1-ZnO). The obtained Au1-ZnO catalysts exhibit an outstanding NO2-sensing response (12.6 to 300 ppb) at a low operating temperature (150°C). The proposed step-induced strategy will broaden the rational design of special site-trapped supported metal catalysis for gas sensors.

One Dimensional Segregated Single AU Sites on Step-Rich ZnO Ladder for Ultrasensitive NO <sub>2</sub> Sensors

Here we develop a freestanding ladder-like ZnO surface with abundant unsaturated step defects, which could efficiently anchor Au1 sites with one dimensional assembling for the ultrasensitive NO2 detection. The dimension of obtained ZnO hexagonal ladder could be precisely controlled through reasonably regularizing the nucleation and growth rate. Following a layer-by-layer growth mode, the obtained ZnO would adopt the step-rich evolution. These ladder-like structure could provide abundant unsaturated step defects along with their curved edge profiles to serve as susceptible centers to site-selectively immobilize isolated Au1 species (Au1-ZnO). The obtained Au1-ZnO catalysts exhibit an outstanding NO2 sensing response (12.6 to 300 ppb) at a low operating temperature (150 °C). The proposed step-induced strategy will broaden the rational design of special sites-trapped supported metal catalysis for gas sensors.

Self-organized macroporous thin carbon films for supported metal catalysis

An easy one step and scalable process for the synthesis of multilayer macroporous polymer and carbon films is demonstrated by using spin coated thin films of polyacrylonitrile (PAN) in N,N-dimethyl formamide (DMF) solvent followed by their carbonization. The interconnected porous carbon films were characterized by various techniques including SEM, HRTEM, Raman, XRD, BET and AFM. Phase-separation/dewetting in sub-micrometer thick films spontaneously produced a macroporous (pore diameter>50nm) polymer films with hole density in the range of 108–109percm2 and BET area of ~175m2/g. Increased porosity can be tailored under the conditions that favor greater destabilization of the spin coated films such as reduced film thickness, higher evaporation rate and lower viscosity. Further, Ag/carbon hybrid films were prepared by incorporation of a silver salt in the solution prior to spin coating. The Ag/carbon porous films show good activity in the reduction of para-nitrophenol to para-aminophanol with sodium borohydride.

The Catalytic Nanodiode: Its Role in Catalytic Reaction Mechanisms in a Historical Perspective

AbstractFor Abstract see ChemInform Abstract in Full Text.

The catalytic nanodiode. Its role in catalytic reaction mechanisms in a historical perspective

Catalytic nanodiodes, Pt/TiO 2 or Pt/GaN produce continuous flow of hot electron current during carbon monoxide oxidation for hours in the 80-150 °C temperature range at pressures of 100 Torr of O 2 and 40 Torr of CO. These observations provide proof of the Schottky diode model of oxide supported metal catalysis of many reactions that have been proposed by Schwab. Solymosi and others since the 1960s. The flow of hot electrons should influence chemistry at oxide-metal interfaces and the metal particle size dependence of catalytic activity and selectivity.

A viable route to designable chiral macromolecular supports: implications for supported metal catalysis

Chemically and structurally designed chiral microporous matrices can be obtained upon aminolysis with enantiomerically pure amino acids of an activated ester functionality pendant from the backbone of precursor cross-linked copolymers.

Active sites and reaction mechanisms for deuteration of acrolein on TiO2-, Y2O3-, ZrO2-, CeO2 and Na/SiO2- supported platinum catalysts

Acrolein–deuterium reactions on low-and high-temperature-reduced Pt/TiO2, Pt/Y2O3, Pt/ZrO2 and Pt/CeO2 in comparison with Pt/SiO2 and Na/Pt/SiO2 have been investigated in order to understand promotion in supported-metal catalysis by isotope tracing and infrared studies. The products on Pt/TiO2, Pt/Y2O3, Pt/ZrO2 and Pt/CeO2 were propanal and allyl alcohol but only propanal was formed over Pt/SiO2 and Na/Pt/SiO2. The similarity of the d-electron density of platinum in high-temperature-reduced Pt/TiO2, Pt/Y2O3, Pt/ZrO2 and Pt/CeO2, and Na/Pt/SiO2 was not reflected in the reaction profiles, suggesting the contribution of the periphery of suboxides on Pt particles and/or the boundary/interface of Pt particles on support. η4-Adsorbate was suggested to be an intermediate for allyl alcohol formation on Pt/TiO2 and Pt/Y2O3 by IR spectra and isotope distributions in the products. On Pt/TiO2, Pt/Y2O3, Pt/ZrO2 and Pt/CeO2 reduced at both low and high temperatures, the active sites and reaction environments (surface D/H ratio) for the formations of propanal and allyl alcohol were different for the two products. The reaction mechanisms are discussed in connection with the promoting effects and the SMSI state of catalysts.

The equilibrium shape and surface energy anisotropy of clean platinum

We have measured the equilibrium shape of clean platinum by monitoring the changes in the shape of a series of micrometer-sized platinum droplets during annealing at 1200°C in 10 −7 Torr of oxygen. The droplets start out with a rounded shape and a wavy surface. Upon annealing for 24 h or more, the particles are converted to nearly spherical shapes with distinct facets in the (100) direction and smaller facets in the (111) direction. At equilibrium, the facets only cover 16% of the particle's surface. The rest of the surface is stepped or kinked. The equilibrium particle shape is also independent of particle size for particles in the size range explored here ( d > 1 micrometer). Initially, the particles show a series of hill and valley structures around the (100) facets. However, the hill and valley structures disappear after a long anneal. After a long anneal, the particles also assume an epitaxial relation with the support. From the data, we estimatethat the surface energy of platinum only varies by about 92 erg/cm 2 with crystal face, with Pt(100) having the lowest surface energy, Pt(111) having a slightly higher surface energy, and all of the other faces of platinum having essentially the same surface energy. By comparison, previous workers have shown that heats of adsorption of simple gases often vary by 350 erg/cm 2 with crystal face. The implication, therefore, is that in platinum the variations in surface energy with orientation are small enough that particle shape control in supported metal catalysis is feasible. Consequences to the stability of various single crystal faces are also discussed.

A scanning tunneling microscopy study of the surface morphology of supported gold particles

Scanning tunneling microscopy (STM) was used to examine the surface structure of supported gold particles. STM images of annealed gold particles showed that particles larger than 150 Å have a polyhedral shape and a relatively smooth surface morphology. However, the surfaces of the particles smaller than 60 Å remained highly corrugated even after long annealing times. We believe that the difference in morphology of large and small particles may have some important implications for supported metal catalysis.

STM of Gold on Graphite

ABSTRACTScanning Tunnelling Microscopy was used to examine the surface structure of gold films and supported gold particles. It was found that freshly evaporated gold films have a relatively smooth surface morphology. However, after 1 hr of annealing, a series of dendrites were clearly visible on the surface of the films. With additional annealing, the dendrites got larger, until the film broke into particles. STM images of annealed gold particles showed that annealed gold particles larger than 150 Å have a polyhederal shape and a smooth surface morphology. However, the surfaces of the particles smaller than 60 Å remained highly corrugated even after a long anneal. We believe that the difference in morphology of large and small particles may have some profound implications in supported metal catalysis.

Perspective on the use of gas Adsorption for Particle-Shape Control in Supported Metal Catalysis

AbstractThis paper explores the possibility of using gas adsorption for particle-shape control in supported metal catalysis. Calculations are done to identify the kinds of shape changes which are possible due to treatment in an appropriate adgas. Experiments are done to try to verify the concepts. The results show that gas adsorption can be used for particle shape control in supported metal catalysis.