Florencia Calaza

• PhD
• Research Associate at Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)

We discuss activation and reaction of CO2 on oxide-supported Au nanoparticles in connection with the preparation and characterization of model systems for heterogeneous catalysts, referring mostly to our own studies in the field. These systems are based on crystalline oxide thin films grown on metal substrates, which allows us to characterize them...

In this work, we carried out an experimental and theoretical study on the formation of self-assembled monolayers of L-cysteine molecules on gold surfaces in the presence of methanol as a solvent. We report for the first time L-cysteine and methanol ordered structures forming a mixed self-assembled mono-layer on Au(100) surfaces under ambient condit...

Copper is one of the goldilocks metals in catalysis. Deciphering the local atomic environment and oxidation state of active centers in supported copper catalysts, as well as the design of materials to control their stability under reaction conditions remains a great challenge today. We show here that a mixed-oxide of copper delafossite with gallium...

Using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations, we conclusively demonstrate that acetaldehyde (AcH) undergoes aldol condensation when flown over ceria octahedral nanoparticles, and the reaction is desorption-limited at ambient temperature. trans-Crotonaldehyde (CrH...

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, rese...

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 distributi...

Selective C-C coupling of oxygenates is pertinent to the manufacture of fuel and chemical products from biomass and from derivatives of C1 compounds (i.e., oxygenates produced from methane and CO2). Here we report a combined experimental and theoretical study on the temperature-programmed reaction (TPR) of acetaldehyde (AcH) on a partially reduced...

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...

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...

Effective CO2 capture and reduction can be achieved through a molecular scale understanding of interaction of CO2 molecules with chemically active sites in and cooperative effects they induce with functional materials. Self-assembled arrays of parallel chains composed of Au adatoms connected by 1,4-phenylene diisocyanide (PDI) linkers decorating Au...

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 activa...

STM conductance spectroscopy and mapping has been used to analyze the impact of molecular adsorption on the quantized electronic structure of individual metal nanoparticles. For this purpose, isophorone and CO_{2}, as prototype molecules for physisorptive and chemisorptive binding, were dosed onto monolayer Au islands grown on MgO thin films. The m...

Es wurde ein Modellsystem realisiert, das mittels Elektronentransfer durch eine Metall-Isolator-Metall(MIM)-Struktur die Bildung eines CO2-Radikalanions von aus der Gasphase adsorbiertem Kohlendioxid induziert, welches anschließend zu Oxalat weiterreagiert. Dieser reversible Prozess gestattet eine Studie der involvierten Elementarschritte auf atoma...

A model system has been created to shuttle electrons through a metal-insulator-metal (MIM) structure to induce the formation of a CO2 anion radical from adsorbed gas-phase carbon dioxide that subsequently reacts to form an oxalate species. The process is completely reversible, and thus allows the elementary steps involved to be studied at the atomi...

Adsorption and reaction of acetic acid on a CeO2(1 1 1) surface was studied by a combination of ultra-high vacuum based methods including temperature desorption spectroscopy (TPD), soft X-ray photoelectron spectroscopy (sXPS), near edge X-ray absorption spectroscopy (NEXAFS) and reflection absorption IR spectroscopy (RAIRS), together with density f...

CeO2 cubes with {100} facets, octahedra with {111} facets, and wires with highly defective structures were utilized to probe the structure-dependent reactivity of acetaldehyde. Using temperature-programmed desorption (TPD), temperature-programmed surface reactions (TPSR), and in situ infrared spectroscopy, it was determined that acetaldehyde desorb...

The reactivity of MgO(0 0 1) films deposited on Ag(0 0 1) and Mo(0 0 1) in CO oxidation as a function of oxide film thickness was investigated experimentally at ambient pressure reaction conditions. MgO films grown on Mo(0 0 1) were found to be inactive in CO oxidation, whereas activity enhancement with decreasing oxide film thickness was observed...

The activation energies for the reaction of gas-phase ethylene with adsorbed acetate species on Au/ Pd(111) alloys are measured as a function of gold coverage in the alloy to probe the elementary steps in gold-palladium alloy catalyzed vinyl acetate monomer (VAM) synthesis. The activation energy decreases with increasing gold coverage in the alloy...

Cerium oxide is a principal component in many heterogeneous catalytic processes. One of its key characteristics is the ability to provide or remove oxygen in chemical reactions. The different crystallographic faces of ceria present significantly different surface structures and compositions that may alter the catalytic reactivity. The structure and...

The rates of reaction of acetate species adsorbed on a range of Au/Pd(111) alloys with gas-phase ethylene to form vinyl acetate monomer (VAM) were explored by monitoring the time dependence of the adsorbate coverages using infrared spectroscopy. It was found that the acetate species react directly to form VAM since the decrease in the coverage of a...

Enolate species are suggested to be the key intermediates in a number of organic reactions including aldol condensation, which involves C-C bond coupling and has been proposed as an important reaction in the conversion of biomass-derived feedstock to fuel and chemicals.[1] It is difficult to detect and characterize these elusive species due to thei...

The temperature-dependent adsorption and reaction of acetaldehyde (CH(3)CHO) on a fully oxidized and a highly reduced thin-film CeO(2)(111) surface have been investigated using a combination of reflection-absorption infrared spectroscopy (RAIRS) and periodic density functional theory (DFT+U) calculations. On the fully oxidized surface, acetaldehyde...

This study reports and compares the adsorption and dissociation of water on oxidized and reduced CeO{sub 2}(100) and CeO{sub 2}(111) thin films. Water adsorbs dissociatively on both surfaces. On fully oxidized CeO{sub 2}(100) the resulting surface hydroxyls are relatively stable and recombine and desorb as water over a range from 200 to 600 K. The...

The stabilization of formate and acetate surface species on Pd(111) has been studied by temperature-programmed desorption and infrared reflection absorption spectroscopy (IRRAS). In addition to the previously reported stabilization of carboxylate species by the pre-adsorption of oxygen, an even bigger stabilizing effect was observed upon the adsorp...

The surface chemistry of 1,1-difluoroethylene was studied on clean and hydrogen-covered Pd(111) using a combination of temperatureprogrammed desorption and reflection absorption infrared spectroscopy (RAIRS) to explore whether the larger infrared absorbance of 1,1-difluoroethylene than ethylene may be used to examine reactions under realistic catal...

The effect of surface hydroxyls on the adsorption of ether on ceria was explored. Adsorption of dimethyl ether (DME) and diethyl ether (DEE) on oxidized and reduced CeO2(111) films was studied and compared with Ru(0001) using RAIRS and sXPS within a UHV environment. On Ru(0001) the ethers adsorb weakly with the molecular plane close to parallel to...

One-dimensional supramolecular structures formed by adsorbing low coverages of 1,4-diisocyanobenzene on Au(111) at room temperature are obtained and imaged by scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. The structures originate from step edges or surface defects and arrange predominantly in a straight fashion on the...

The kinetics of the reaction between gas-phase ethylene and adsorbed acetate species to form vinyl acetate monomer (VAM) on a Pd(111) surface are measured using infrared spectroscopy to monitor the rate of acetate removal, as well as the rates of VAM and ethylidyne formation, at various temperatures. The results are fit using a kinetic model first...

The high adsorbate coverages that form on the surfaces of many heterogeneous catalysts under steady-state conditions can significantly lower the activation energies for reactions that involve the coupling of two adsorbed intermediates while increasing those which result in adsorbate bond-breaking reactions. The influence of the surface coverage on...

The reaction between gas-phase ethylene and adsorbed acetate species on Pd(100)-p(2 × 2)-O and Pd(100)-c(2 × 2)-O surfaces is studied using infrared spectroscopy. It is found that acetate species are removed more rapidly by gas-phase ethylene on oxygen-covered Pd(100) than on Pd(111). However, in contrast to reaction on Pd(111), where vinyl acetate...

A strategy for counting ensembles for various adsorbates on bimetallic alloys is developed. A Monte Carlo method is used to simulate the structure of a model Au/Pd(111) alloy using a gold−palladium interaction parameter ϵ/kT = 0.64 for the alloy and for a random distribution, ϵ/kT = 0.0. The method is illustrated by counting the ensembles for the a...

Bimetallic surface alloys play an important role in heterogeneous catalysis. Usually only one of the components of the alloy provides the active sites for the adsorption of the reactants. One of the effects of the second metal is to limit the size and distribution of ensembles of atoms of the active metal, changing in this way the selectivity and a...

The industrial synthesis of vinyl acetate monomer (VAM) from acetic acid, ethylene and oxygen using palladium as a catalyst is an important reaction which has been used for about thirty years, even though some controversy existed about the mechanism by which this reaction occurs. The addition of gold to the catalyst improves this process by increas...

We propose a molecular wire that is made from alternating bis(1,2-bis(diphenylphosphino)ethane)tungsten(0) centers linked by 1,4-phenyldiisocyanide ligands. Aryl isocyanides coordinate with greater Π back donation with Pt, than with Au or Pd. Π back donation ensures that Π conjugation is preserved between the molecule and the electrode surface, red...

The surface chemistry of vinyl acetate monomer (VAM) on clean and oxygen-covered Pd(100) is explored experimentally in ultrahigh vacuum using reflection absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD), combined with density functional theory (DFT) calculations. Both RAIRS...

The adsorption of vinyl acetate is studied on Au/Pd(111) alloys as a function of alloy composition using temperature-programmed desorption and reflection–adsorption infrared spectroscopy. Vinyl acetate adsorbs weakly on gold sites on the alloy with a heat of adsorption of ∼55kJ/mol, which is independent of the size of the gold ensembles. In contras...

The surface composition of a Au/Pd(1 1 1) alloy formed by depositing five monolayers of gold onto clean Pd(1 1 1) at 300 K in an ultrahigh vacuum and heating to various temperatures is measured from an analysis of the low-energy electron diffraction (LEED) intensity versus energy curves and by low-energy ion scattering (LEIS). The LEIS and LEED dat...

The reaction pathway for the palladium-catalyzed synthesis of vinyl acetate from acetic acid, ethylene and oxygen is investigated using reflection–absorption infrared spectroscopy by monitoring the rate of acetate titration by gas-phase ethylene. This reveals that acetate species are removed by reaction with gas-phase ethylene resulting in vinyl ac...

The formation of alloys by adsorbing gold on a Pd(111) single crystal substrate and subsequently annealing to various temperatures is studied in an ultrahigh vacuum by means of Auger and X-ray photoelectron spectroscopy. The nature of the alloy surface is probed by CO chemisorption using temperature-programmed desorption and reflection-absorption i...

The adsorption of acetic acid is studied as a function of gold content by temperature-programmed desorption and reflection–absorption infrared spectroscopy on Au/Pd(111) alloys formed by depositing 5 ML of gold onto a Pd(111) surface and heating to various temperatures. For mole fractions of gold greater than ∼0.5, acetic acid adsorbs molecularly a...

The adsorption of ethylene on gold–palladium alloys formed on a Pd(111) surface is investigated using a combination of temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). Various alloy compositions are obtained by depositing four monolayers of gold on a clean Pd(111) surface and annealing to various temp...

The surface chemistry of vinyl acetate on clean Pd(1 1 1) is explored experimentally in ultrahigh vacuum using reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) combined with density functional theory (DFT) calculations. The relative intensities of the vibrational features of a vinyl acetate overlayer a...

The reaction pathways for acetylene trimerization and hydrogenation, and ethylene hydrogenation, catalyzed by palladium, are explored using a range of surface-sensitive techniques. Reflection–absorption infrared spectroscopy (RAIRS) and low-energy electron diffraction (LEED) show that ethylene is di-σ-bonded on clean Pd(111), but forms a π-bonded s...

(Chemical Equation Presented) Finding the right pathway: Reaction of isotopomers of ethylene with acetate species (see scheme) adsorbed on a Pd(111) surface in ultrahigh vacuum has shown that vinyl acetate is produced by insertion of ethylene into the acetate species to form an acetoxyethyl intermediate, which decomposes by β-hydride elimination to...

The reaction pathway of vinyl acetate synthesis is scrutinized by reacting gas-phase ethylene (at an effective pressure of 1 x 10-4 Torr) with eta2-acetate species (with a coverage of 0.31 +/- 0.02 monolayer) on a Pd(111)-O(2x2) model catalyst surface in ultrahigh vacuum. It is found that the 1414 cm-1 infrared feature due to the symmetric OCO stre...

Alumina supported molybdenum oxide was prepared using ammonium heptamolybdate and molybdenum acetate as different precursors. The catalysts were characterized by BET, AAS, SEM-EDAX, XRD, TPR and surface acidity measurements. The characterization results and the catalytic behavior in oxydehydrogenation of propane were similar irrespective of precurs...

A conformational study on N-acetyl-l-isoleucine-N-methylamide was carried out using ab initio (RHF/3-21G and RHF/6-31G(d)) calculations. All backbone and side-chain conformations in this compound were explored. N-acethyl-l-isoleucine-N-methylamide displayed a significant molecular flexibility. Also a different conformational behaviour was obtained...