Studies of the kinetics and mechanisms of perfluoroether reactions on iron and oxidized iron surfaces

Polymeric perfluoroalkylethers are being considered for use as lubricants in high temperature applications, but have been observed to catalytically decompose in the presence of metals. X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) were used to explore the decomposition of three model fluorinated ethers on clean polycrystalline iron surfaces and iron surfaces chemically modified with oxygen. Low temperature adsorption of the model fluorinated ethers on the clean, oxygen modified and oxidized iron surfaces was molecular. Thermally activated defluorination of the three model compounds was observed on the clean iron surface at remarkably low temperatures, 155 K and below, with formation of iron fluoride. Preferential C-F bond scission occurred at the terminal fluoromethoxy, CF3O, of perfluoro-1-methoxy-2-ethoxy ethane and perfluoro-1-methoxy-2-ethoxy propane and at CF3/CF2O of perfluoro-1,3-diethoxy propane. The reactivity of the clean iron toward perfluoroalkylether decomposition when compared to other metals is due to the strength of the iron fluoride bond and the strong electron donating ability of the metallic iron. Chemisorption of an oxygen overlayer lowered the reactivity of the iron surface to the adsorption and decomposition of the three model fluorinated ethers by blocking active sites on the metal surface. Incomplete coverage of the iron surface with chemisorbed oxygen results in a reaction which resembles the defluorination reaction observed on the clean iron surface. Perfluoro-1-methoxy-2-ethoxy ethane reacts on the oxidized iron surface at 138 K, through a Lewis acid assisted cleavage of the carbon oxygen bond, with preferential attack at the terminal fluoromethoxy, CF3O. The oxidized iron surface did not passivate, but became more reactive with time. Perfluoro-1-methoxy-2-ethoxy propane and perfluoro-1,3-diethoxy propane desorbed prior to the observation of decomposition on the oxidized iron surface

Synthesis of Supported Pd-0 Nanoparticles from a Single-Site Pd2+ Surface Complex by Alkene Reduction

A surface metal-organic complex, (-AlOx)Pd(acac) (acac = acetylacetonate), is prepared by chemically grafting the precursor Pd(acac)(2) onto gamma-Al2O3 in toluene at 25 degrees C. The resulting surface complex is characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and dynamic nuclear polarization surface-enhanced solid-state nuclear magnetic resonance spectroscopy (DNP SENS). This surface complex is a precursor in the direct synthesis of size-controlled Pd nanoparticles under mild reductive conditions and in the absence of additional stabilizers or pretreatments. Indeed, upon exposure to gaseous ethylene or liquid 1-octene at 25 degrees C, the Pd2+ species is reduced to form Pd-0 nanoparticles with a mean diameter of 4.3 +/- 0.6 nm, as determined by scanning transmission electron microscopy (STEM). These nanoparticles are catalytically relevant using the aerobic 1-phenylethanol oxidation as a probe reaction, with rates comparable to a conventional Pd/Al2O3 catalyst but without an induction period. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed reaction mass spectrometry (TPR-MS) reveal that the surface complex reduction with ethylene coproduces H-2, acetylene, and 1,3-butadiene. This process reasonably proceeds via an olefin activation/coordination/insertion pathway, followed by beta-hydride elimination to generate free Pd-0. The well-defined nature of the single-site supported Pd2+ precursor provides direct mechanistic insights into this unusual and likely general reductive process

Synthesis-Dependent First-Order Raman Scattering in SrTiO 3 Nanocubes at Room Temperature

Raman spectroscopy was used to demonstrate that the lattice dynamics of SrTiO 3 (STO) nanoparticles strongly depends on their microstructure, which is in turn determined by the synthetic approach employed. First-order Raman modes are observed at room temperature in STO single-crystalline nanocubes with average edge lengths of 60 and 120 nm, obtained via sol-precipitation coupled with hydrothermal synthesis and a molten salt procedure, respectively. First-order Raman scattering arises from local loss of inversion symmetry caused by surface frozen dipoles, oxygen vacancies, and impurities incorporated into the host lattice. The presence of polar domains is suggested by the pronounced Fano asymmetry of the peak corresponding to the TO2 polar phonon, which does not vanish at room temperature. These noncentrosymmetric domains will likely influence the dielectric response of these nanoparticles

Epitaxial Stabilization of Face Selective Catalysts

Abstract Selective, active, and robust catalysts are necessary for the efficient utilization of new feedstocks. Faceselective catalysts can precisely modify catalytic properties, but are often unstable under reaction conditions, changing shape and losing selectivity. Herein we report a method for synthesizing stable heterogeneous catalysts in which the morphology and selectivity can be tuned precisely and predictably. Using nanocrystal supports, we epitaxially stabilize specific active phase morphologies. This changes the distribution of active sites of different coordination, which have correspondingly different catalytic properties. Specifically, we utilize the different interfacial free-energies between perovskite titanate nanocube supports with different crystal lattice dimensions and a platinum active phase. By substituting different sized cations into the support, we change the lattice mismatch between the support and the active phase, thereby changing the interfacial free-energy, and stabilizing the active phase in different morphologies in a predictable manner. We correlate these changes in active phase atomic coordination with changes in catalytic performance (activity and selectivity), using the hydrogenation of acrolein as a test reaction. The method is general and can be applied to many nanocrystal supports and active phase combinations. Keywords Epitaxy Á Perovskite Á Platinum Á Heterogeneous catalysis Á Hydrogenation Á Acrolein Controlling the morphology of catalytic metal nanoparticles has incredible potential for improving selectivity and yield. This is because catalytic properties often depend upon the coordination of active site atoms We have recently observed that oriented oxide nanocrystal supports can epitaxially stabilize a specific orientation and morphology of the active phas

Virtual Special Issue on Catalysis at the U.S. Department of Energy’s National Laboratories

Catalysis research at the U.S. Department of Energy’s (DOE’s) National Laboratories covers a wide range of research topics in heterogeneous catalysis, homogeneous/molecular catalysis, biocatalysis, electrocatalysis, and surface science. Since much of the work at National Laboratories is funded by DOE, the research is largely focused on addressing DOE’s mission to ensure America’s security and prosperity by addressing its energy, environmental, and nuclear challenges through transformative science and technology solutions. The catalysis research carried out at the DOE National Laboratories ranges from very fundamental catalysis science, funded by DOE’s Office of Basic Energy Sciences (BES), to applied research and development (R&D) in areas such as biomass conversion to fuels and chemicals, fuel cells, and vehicle emission control with primary funding from DOE’s Office of Energy Efficiency and Renewable Energy. National Laboratories are home to many DOE Office of Science national scientific user facilities that provide researchers with the most advanced tools of modern science, including accelerators, colliders, supercomputers, light sources, and neutron sources, as well as facilities for studying the nanoworld and the terrestrial environment. National Laboratory research programs typically feature teams of researchers working closely together, often joining scientists from different disciplines to tackle scientific and technical problems using a variety of tools and techniques available at the DOE national scientific user facilities. Along with collaboration between National Laboratory scientists, interactions with university colleagues are common in National Laboratory catalysis R&D. In some cases, scientists have joint appointments at a university and a National Laboratory. This ACS Catalysis Virtual Special Issue {http://pubs.acs.org/page/accacs/vi/doe-national-labs} was motivated by Christopher Jones and Rhea Williams, who sent out the invitations to all of DOE’s National Laboratories where catalysis research is conducted. All manuscripts submitted went through the standard rigorous peer review required for publication in ACS Catalysis. A total of 29 papers are published in this virtual special issue, which features some of the recent catalysis research at 11 of DOE’s National Laboratories: Ames Laboratory (Ames), Argonne National Laboratory (ANL), Brookhaven National Laboratory (BNL), Lawrence Berkeley National Laboratory (LBNL), Lawrence Livermore National Laboratory (LLNL), National Energy Technology Laboratory (NETL), National Renewable Energy Laboratory (NREL), Oak Ridge National Laboratory (ORNL), Pacific Northwest National Laboratory (PNNL), Sandia National Laboratory (SNL), and SLAC National Accelerator Laboratory (SLAC). In this preface, we briefly discuss the history and impact of catalysis research at these particular DOE National Laboratories, where the majority of catalysis research continues to be conducted

Ethics review as a component of institutional approval for a multicentre continuous quality improvement project: the investigator's perspective

BACKGROUND: For ethical approval of a multicentre study in Canada, investigators must apply separately to individual Research Ethics Boards (REBs). In principle, the protection of human research subjects is of utmost importance. However, in practice, the process of multicentre ethics review can be time consuming and costly, requiring duplication of effort for researchers and REBs. We used our experience with ethical review of The Canadian Perinatal Network (CPN), to gain insight into the Canadian system. METHODS: The applications forms of 16 different REBs were abstracted for a list of standardized items. The application process across sites was compared. Correspondence between the REB and the investigators was documented in order to construct a timeline to approval, identify the specific issues raised by each board, and describe how they were resolved. RESULTS: Each REB had a different application form. Most (n = 9) had a two or three step application process. Overall, it took a median of 31 days (range 2-174 days) to receive an initial response from the REB. Approval took a median of 42 days (range 4-443 days). Privacy and consent were the two major issues raised. Several additional minor or administrative issues were raised which delayed approval. CONCLUSIONS: For CPN, the Canadian REB process of ethical review proved challenging. REBs acted independently and without unified application forms or submission procedures. We call for a critical examination of the ethical, privacy and institutional review processes in Canada, to determine the best way to undertake multicentre review