Ordered Au Nanoparticle Array on Au(111) through Coverage Control of Precursor Metal−Organic Chains

Metal–organic overlayer structures formed by 1,4-phenylene-diisocyanide (PDI) and Au adatoms on Au(111) in UHV, their stability in air, and the tip-induced Au nanoparticle formation on PDI–Au(111) surfaces in air were investigated using scanning tunneling microscopy (STM) and vibrational spectroscopy. This study reveals that the distribution of Au nanoparticles created during tip-induced release of Au atoms from molecule-Au adatom complexes shows strong dependence on the PDI coverage. Ordered Au nanoparticle arrays form in the medium-coverage regime, while more disordered distributions are observed at low and saturation coverages. The different distributions of Au nanoparticles are a direct consequence of the coverage-dependent assembly of (PDI–Au)n chains, their different stability in air, and a templating effect of the Au(111) surface, which is most pronounced for medium coverage, where phases of densely packed (PDI–Au)n chains and disordered PDI–Au assemblies are confined, respectively, to the fcc and hcp regions of the (22 × √3) surface reconstruction of Au(111). The Au nanoparticles nucleate preferentially in the disordered or defective regions of the PDI–Au precursor overlayer, and their formation requires ambient air and high negative tip-bias, suggesting an electrochemical initiation of Au release from the molecule–Au adatom complexes.Fil: Ghalgaoui, Ahmed. University Of Graz. Institute Of Physics; AustriaFil: Doudin, Nassar. University Of Graz. Institute Of Physics; AustriaFil: Calaza, Florencia Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina. Fritz-Haber-Institut der Max-Planck-Gesellschaft; AlemaniaFil: Surnev, Svetlozar. University Of Graz. Institute Of Physics; AustriaFil: Sterrer, Martin. University Of Graz. Institute Of Physics; Austri

Mechanism of the acetonitrile hydrogenation to amines over a platinum catalyst investigated by in situ infrared spectroscopy and DFT modeling

The mechanism of the hydrogenation of acetonitrile (CH3CN and CD3CN) to amines over a platinum filmand Pt/Al2O3 catalyst was investigated by in situ infrared spectroscopy. The reaction was studied under realisticconditions -liquid phase with toluene as solvent- using a flow-through cell-microreactor in attenuated total reflection(ATR) mode developed in our research group. Reaction intermediates were identified combining infrared spectra withtheoretical modeling by DFT. A sequential hydrogenation mechanism is proposed. Acetonitrile linearly and 2-foldchemisorbed on platinum sites is hydrogenated to form an imine surface intermediate (CH3CH=NH), which ishydrogenated to ethylamine. In turn, this imine intermediate can condense producing diethylamine and triethylamineand ammonia as a by-product. The time-evolution of the IR signals were modeled using a proposed microkineticmechanism and intrinsic kinetic constants were obtained under chemical control.Fil: Vogt, Lautaro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Quaino, Paola Monica. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Calaza, Florencia Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Collins, Sebastián Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina255th American Chemical Society National Meeting and ExpositionNew OrleansEstados UnidosAmerican Chemical Societ

Adsorption and Decomposition of Glycerol on Pristine and Oxygen Modified Au(111) Surfaces

Research on biomass derived raw materials for conventional catalytic processes, especially those directed to replace human dependence on fossil-based energy, is a high priority academic topic worldwide. Glycerol, the ubiquitous by-product of biodiesel manufacture, is seen as a promising building block due to its versatile functionality. Hence, research efforts to valorize it by selective partial oxidation are widespread. Fundamental knowledge of the interaction of glycerol with metal surfaces in the presence of oxygen is of extreme importance to rationally design new catalytic materials. In this work, a complete study of glycerol interaction with pristine and oxygen modified Au(111) surfaces is presented, by means of X-ray photoelectron and infrared reflection absorption spectroscopies, aided by temperature programmed desorption (TPD) experiments using mass spectrometry. On the clean Au(111) surface, glycerol adsorbs at 150 K through weak interactions between the oxygen atoms from OH groups and gold atoms. No thermal activation is observed and only molecular desorption is detected in TPD at 293 K. On the other hand, when the Au surface is precovered with oxygen atoms in the form of chemisorbed oxygen, glycerol adsorbs in a slightly different geometry and is activated even at low temperatures. The observation of spectral features related to C=O bonds clearly corroborates the activation of the alcohol groups toward partial oxidation intermediates. Possible products desorbing from the surface due to this activation are identified as dihydroxyacetone, hydroxypiruvic, tartronic and formic acid, as well as H2O and CO2.Fil: Calaza, Florencia Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Baltanas, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Sterrer, Martin. Institute Of Physics, University Of Graz; AustriaFil: Freund, Hans-Joachim. Dept Of Chemical Physics, Fritz-haber-institut Der Mpg; Alemani

Combining IR Spectroscopy and Monte Carlo Simulations to Identify CO Adsorption Sites on Bimetallic Alloys

The atomic distribution on the surface of alloys dictates the nature of the ensembles available as possible active sites during catalytic reactions. In the present work, an infrared spectroscopic study of carbon monoxide adsorption on the surface of AuPd/Pd(111) alloys, combined with Monte Carlo simulations of the surface and bulk atomic distribution, identifies the correct distribution of available surface adsorption sites. For gold coverages >0.9 monolayers (ML), CO adsorbs weakly on top of Au atoms and with higher adsorption energy on top of Pd atoms (CO top ), distributed mostly as monomers on the surface. For ? Au = 0.8-0.4 ML, Pd-CO top is the predominant species, even though several other sites with multiple coordination are available. The simulations show no perfect ordering of the surface but a slight tendency to form lines of Pd atoms, thus favoring the appearance of bridge but not 3-fold hollow sites. Using 13 CO: 12 CO isotopic mixtures, the frequency shifts due to chemical and intermolecular coupling effects has been determined for the CO top IR signal. These effects mostly cancel each other out, so that only small frequency shifts are seen, implying the presence of significant electronic/ligand effects. At ? Au < 0.5 ML, hollow sites are experimentally observed in agreement to the simulated model surfaces. Their IR absorption bands are tentatively distinguished as fcc and hcp hollow sites by correlating with the simulated distribution of Au and Pd atoms on subsurface sites, where for ? Au < 0.5 ML an enrichment by Au atoms is seen in the near-surface region.Fil: Manzi, Sergio Javier. Universidad Nacional de San Luis; ArgentinaFil: Brites Helú, Mariela Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Tysoe, Wilfred T.. University Of Wisconsin Milwaukee;Fil: Calaza, Florencia Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Cooperative Chemisorption-Induced Physisorption of CO2 Molecules by Metal-Organic Chains

Effective CO2 capture and reduction can be achieved through a molecularscale understanding of interaction of CO2 molecules with chemically active sites and thecooperative effects they induce in functional materials. Self-assembled arrays of parallelchains composed of Au adatoms connected by 1,4-phenylene diisocyanide (PDI) linkersdecorating Au surfaces exhibit self-catalyzed CO2 capture leading to large scale surfacerestructuring at 77 K (ACS Nano 2014, 8, 86448652). We explore the cooperativeinteractions among CO2 molecules, Au-PDI chains and Au substrates that are responsiblefor the self-catalyzed capture by low temperature scanning tunneling microscopy (LTSTM),X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy(IRAS), temperature-programmed desorption (TPD), and dispersion corrected densityfunctional theory (DFT). Decorating Au surfaces with Au-PDI chains gives the interfacialmetalorganic polymer characteristics of both a homogeneous and heterogeneouscatalyst. Au-PDI chains activate the normally inert Au surfaces by promoting CO2 chemisorption at the Au adatom sites even at <20 K. The CO2 δ- speciescoordinating Au adatoms in-turn seed physisorption of CO2 molecules in highly ordered two-dimensional (2D) clusters, which grow with increasing dose to a fullmonolayer and, surprisingly, can be imaged withmolecular resolution on Au crystal terraces. The dispersion interactions with the substrate force the monolayerto assume a rhombic structure similar to a high-pressure CO2 crystalline solid rather than the cubic dry ice phase. The Au surface supported Au-PDI chains providea platform for investigating the physical and chemical interactions involved in CO2 capture and reduction.Fil: Feng, Min. Chinese Academy Of Sciences; República de China. University Of Pittsburgh; Estados UnidosFil: Petek, Hrvoje. University of Pittsburgh; Estados UnidosFil: Shi, Yongliang. University of Science and Technology of China; ChinaFil: Sun, Hao. University of Science and Technology of China; ChinaFil: Zhao, Jin. University of Science and Technology of China; ChinaFil: Calaza, Florencia Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Sterrer, Martin. Fritz-Haber-Institute der Max-Plank-Gesellschaft; AlemaniaFil: Freund, Hans. University Of Graz; Austri

Coupling of Acetaldehyde to Crotonaldehyde on CeO 2-x (111): Bifunctional Mechanism and Role of Oxygen Vacancies

Selective C-C coupling of oxygenates is pertinent to the manufacture of fuel and chemical products from biomass and from derivatives of C 1 compounds (i.e., oxygenates produced from methane and CO 2 ). Here we report a combined experimental and theoretical study on the temperature-programmed reaction (TPR) of acetaldehyde (AcH) on a partially reduced CeO 2-x (111) thin film surface. The experiments have been carried out under ultra-high-vacuum conditions without continuous gas exposure, allowing better isolation of active sites and reactive intermediates than in flow reaction conditions. AcH does not undergo aldol condensation in a typical TPR procedure, even though the enolate form of AcH (CH 2 CHO) is readily produced on CeO 2-x (111) with oxygen vacancies. We find however that a tailored "double-ramp" TPR procedure is able to successfully produce an aldol adduct, crotonaldehyde (CrA). Using density functional theory calculations and microkinetic modeling we explore several possible C-C coupling pathways. We conclude that the double-ramp procedure allows surface oxygen vacancy dimers, stabilized by adsorbate occupation, to form dynamically during the TPR. The vacancy dimers in turn enable C-C coupling to occur between an enolate and an adjacent AcH molecule via a bifunctional enolate-keto mechanism that is distinct from conventional acid-or base-catalyzed aldol condensation reactions. The proposed mechanism indicates that CrA desorption is rate-limiting while C-C coupling is facile.Fil: Zhao, Chuanlin. Louisiana State University;Fil: Watt, Charles. University of Princeton; Estados Unidos. Oak Ridge National Laboratory;Fil: Kent, Paul R.. Oak Ridge National Laboratory;Fil: Overbury, Steven H.. Oak Ridge National Laboratory;Fil: Mullins, David R.. Oak Ridge National Laboratory;Fil: Calaza, Florencia Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Savara, Aditya. Oak Ridge National Laboratory;Fil: Xu, Ye. Louisiana State University

Supports and Modified Nano-particles in Designing Model Catalysts

In order to design catalytic materials, we need to understand the essential causes for material properties resulting from its composite nature. In this paper we discuss two, at first sight, diverse aspects: a) the effect of the oxide-metal interface on metal-nanoparticle properties and b) the consequences of metal particle modification after activation on the selectivity of hydrogenation reactions. However, those two aspects are intimately linked. The metal-nanoparticles electronic structure changes at the interface as a catalyst is brought to different reaction temperatures due to morphological modifications in the metal and, as we will discuss, those changes the chemistry leading to changes in the reaction path. As the morphology of the particle varies, facets of different orientation and size are exposed which may lead to a change in surface chemistry as well. We use two specific reactions to address those issues in some detail. To the best of our knowledge the present paper reports the first observations of this kind for well-defined model systems. The changes of the electronic structure of Au nanoparticles due to their size and interaction with a supporting oxide are revealed as a function of temperature using CO2 activation as a probe. The presence of spectator species (oxopropyl) as formed during an activation step of acrolein hydrogenation, strongly controls the selectivity of the reaction towards hydrogenation of the unsaturated C-O vs. the C-C bond on Pd(111) when compared with oxide supported Pd nanoparticles.Fil: Obrien, C. P.. US Army Research Laboratory; Estados UnidosFil: Dostert, K. H.. Fritz-Haber Institut der Max-Planck Gesellschaft; AlemaniaFil: Hollerer, M.. University of Graz; AustriaFil: Stiehler, Christian. Fritz-Haber Institut der Max-Planck Gesellschaft; AlemaniaFil: Calaza, Florencia Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina. Fritz-Haber Institut der Max-Planck Gesellschaft; AlemaniaFil: Schauermann, S.. Fritz-Haber Institut der Max-Planck Gesellschaft; AlemaniaFil: Shaikhutdinov, S.. Fritz-Haber Institut der Max-Planck Gesellschaft; AlemaniaFil: Sterrer, M.. University of Graz; AustriaFil: Freund, H. J.. Fritz-Haber Institut der Max-Planck Gesellschaft; Alemani

Toward an Understanding of Selective Alkyne Hydrogenation on Ceria: On the Impact of O Vacancies on H 2 Interaction with CeO 2 (111)

Ceria (CeO2) has recently been found to be a promising catalyst in the selective hydrogenation of alkynes to alkenes. This reaction occurs primarily on highly dispersed metal catalysts, but rarely on oxide surfaces. The origin of the outstanding activity and selectivity observed on CeO2 remains unclear. In this work, we show that one key aspect of the hydrogenation reaction—the interaction of hydrogen with the oxide—depends strongly on the presence of O vacancies within CeO2. Through infrared reflection absorption spectroscopy on well-ordered CeO2(111) thin films and density functional theory (DFT) calculations, we show that the preferred heterolytic dissociation of molecular hydrogen on CeO2(111) requires H2 pressures in the mbar regime. Hydrogen depth profiling with nuclear reaction analysis indicates that H species stay on the surface of stoichiometric CeO2(111) films, whereas H incorporates as a volatile species into the volume of partially reduced CeO2–x(111) thin films (x ∼ 1.8–1.9). Complementary DFT calculations demonstrate that oxygen vacancies facilitate H incorporation below the surface and that they are the key to the stabilization of hydridic H species in the volume of reduced ceria.Fil: Werner, Kristin. Dept Of Chemical Physics, Fritz-haber-institut Der Mpg;Fil: Weng, Xuefei. Dept Of Chemical Physics, Fritz-haber-institut Der Mpg;Fil: Calaza, Florencia Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Sterrer, Martin. Institute Of Physics, University Of Graz;Fil: Kropp, Thomas. Institut Fur Chemie, Humboldt-universitat;Fil: Paier, Joachim. Universitat Zu Berlin / Institut Fur Chemie, Humboldt-u;Fil: Sauer, Joachim. Universitat Zu Berlin / Institut Fur Chemie, Humboldt-u;Fil: Wilde, Markus. Institute Of Industrial Science-the University Of Tokyo;Fil: Fukutani, Katsuyuki. Institute Of Industrial Science-the University Of Tokyo;Fil: Shaikhutdinov, Shamil. Dept Of Chemical Physics, Fritz-haber-institut Der Mpg;Fil: Freund, Hans-Joachim. Dept Of Chemical Physics, Fritz-haber-institut Der Mpg