Metal-support interaction and charge distribution in ceria-supported Au particles exposed to CO

Understanding how reaction conditions affect metal-support interactions in catalytic materials is one of the most challenging tasks in heterogeneous catalysis research. Metal nanoparticles and their supports often undergo changes in structure and oxidation state when exposed to reactants, hindering a straightforward understanding of the structure-activity relations using only ex situ or ultrahigh vacuum techniques. Overcoming these limitations, we explored the metal-support interaction between gold nanoparticles and ceria supports in ultrahigh vacuum and after exposure to CO. A combination of in situ methods (on powder and model Au/CeO2 samples) and theoretical calculations was applied to investigate the gold/ceria interface and its reactivity toward CO exposure. X-ray photoelectron spectroscopy measurements rationalized by first-principles calculations reveal a distinctly inhomogeneous charge distribution, with Au+ atoms in contact with the ceria substrate and neutral Au0 atoms at the surface of the Au nanoparticles. Exposure to CO partially reduces the ceria substrate, leading to electron transfer to the supported Au nanoparticles. Transferred electrons can delocalize among the neutral Au atoms of the particle or contribute to forming inert Auδ− atoms near oxygen vacancies at the ceria surface. This charge redistribution is consistent with the evolution of the vibrational frequencies of CO adsorbed on Au particles obtained using diffuse reflectance infrared Fourier transform spectroscopy

Properties of Nitrogen/Silicon Doped Vertically Oriented Graphene Produced by ICP CVD Roll-to-Roll Technology

Simultaneous mass production of high quality vertically oriented graphene nanostructures and doping them by using an inductively coupled plasma chemical vapor deposition (ICP CVD) is a technological problem because little is understood about their growth mechanism over enlarged surfaces. We introduce a new method that combines the ICP CVD with roll-to-roll technology to enable the in-situ preparation of vertically oriented graphene by using propane as a precursor gas and nitrogen or silicon as dopants. This new technology enables preparation of vertically oriented graphene with distinct morphology and composition on a moving copper foil substrate at a lower cost. The technological parameters such as deposition time (1–30 min), gas partial pressure, composition of the gas mixture (propane, argon, nitrogen or silane), heating treatment (1–60 min) and temperature (350–500 °C) were varied to reveal the nanostructure growth, the evolution of its morphology and heteroatom’s intercalation by nitrogen or silicon. Unique nanostructures were examined by FE-SEM microscopy, Raman spectroscopy and energy dispersive X-Ray scattering techniques. The undoped and nitrogen- or silicon-doped nanostructures can be prepared with the full area coverage of the copper substrate on industrially manufactured surface defects. Longer deposition time (30 min, 450 °C) causes carbon amorphization and an increased fraction of sp3-hybridized carbon, leading to enlargement of vertically oriented carbonaceous nanostructures and growth of pillars

Effect of fluorine on terrace-ledge-kink morphology and valence state of copper and titanium ions in CaCu3Ti4O12

Ceramic CaCu3Ti4O12 (ССТО), Ca0.98Cu3Ti4O11.96F0.04 (CΔCTOF), and CaCu3Ti4O11.92F0.08 (CCTOF) were synthesized by the solid-state reaction technique. Fluorine stimulates the formation of Cu-depleted grains, Cu3+ ions, and Cu-rich composites CuO-xCCTO-yTiO2-zSiO2-wСaF2 (w < z < y < x < 1), which include parts of grinding bodies. The observed structures are distinct from simple grain boundaries of the perovskite phase. They exhibit a terrace-ledge-kink (TLK) morphology and, in some cases, the presence of twinning planes, both independent of fluorine content. They are responsible for the nanoscale barrier layer capacitance (NBLC) component of the dielectric response of both CCTO and CuO ceramics. Changes in the unit cell parameter a, and titanium and copper valences indicate that Ca2+ ions occupy part of Cu vacancies in the grains of CCTO and CCTOF. In CΔCTOF, Ti3+ ions in the copper sublattice were found for the first time using NMR. The maximum ε′1kHz = 6.9 × 104 demonstrates CΔCTOF and the minimum tan δ = 0.045 is characteristic of CCTOF

Microstructure, chemical composition, and dielectric response of CaCu3Ti4O12 ceramics doped with F, Al, and Mg ions

Ceramics with nominal chemical composition CaCu3Ti4O12 (CCTO), CaCu3Ti3.96Al0.04O11.96F0.04 (CCTOAF), and Ca0.98Mg0.08Cu2.94Ti3.96Al0.04O11.96F0.04 (CCTOMAF) were prepared by the solid-state reactions technique. Using SEM, EDX, XPS, EPR, NMR, and complex impedance spectroscopy, the microstructure, elements distribution, chemical composition of grains and grain boundaries, and the dielectric response of ceramics were investigated. In the ССТО, CCTOAF, and CCTOMAF series, the average grain size increases, the degree of copper segregation at the grain boundaries is inversely related to grain size, and the dielectric loss decreases from 0.071 to 0.047 and 0.030, respectively, while dielectric permittivity ε′ at 1 kHz is 5.6 × 104, 7.1 × 104, and 4.3 × 104, respectively. Additives of Al, Mg, F and milled particles (ZrO2, Al2O3, and SiO2) can either partially introduce into the perovskite structure or form low-melting eutectics at the grain boundaries, causing abnormal grain growth. The presence of copper ions in various oxidation states, as well as evidence of exchange spin interactions between them, was confirmed in all samples

Surface Composition of a Highly Active Pt 3

Currently, platinum is the most widely used catalyst for low temperature proton exchange membrane fuel cells (PEMFC). However, the kinetics at the cathode are slow, and the price of platinum is high. To improve oxygen reduction reaction (ORR) kinetics at the cathode, platinum can be alloyed with rare earth elements, such as yttrium. We report that Pt3Y has the potential to be over 2 times more active for the ORR compared with Pt inside a real fuel cell. We present detailed photoemission analysis into the nature of the sputtered catalyst surface, using synchrotron radiation photoelectron spectroscopy (SRPES) to examine if surface adsorbates or impurities are present and can be removed. Pretreatment removes most of the yttrium oxide in the surface leaving behind a Pt overlayer which is only a few monolayers thick. Evidence of a substochiometric oxide peak in the Y 3d core level is presented, this oxide extends into the surface even after Ar+ sputter cleaning in-situ. This information will aid the development of new highly active nanocatalysts for employment in real fuel cell electrodes