http://www.mdpi.com/journal/ijms/special_issues/heterogeneous_catalysis/ http://www.mdpi.com/1422-0067/2/5/271/ Ab initio simulations of the Ag/a-Al2O3(0001) interface have been performed for periodic slab models. We have considered Al- and O-terminated corundum surfaces, low and high substrate coverages by silver, as well as the two preferred Ag adsorption sites. The two different terminations give rise to qualitatively different results: silver physisorption on the Al-terminated substrate and chemisorption on O-terminated one. The latter could be treated as a possible model for the defective Al-terminated substrate, where the outermost aluminium ions are removed (completely or partly). This makes O-terminated surface highly reactive towards a deposited metal, in order to restore initial corundum stoichiometry. http://www.mdpi.com/1422-0067/2/5/271/ Tue, 13 Nov 2001 00:00:00 CET International Journal of Molecular Sciences 2001-11-13 2 5 Article 271 280 1422-0067 A First-Principles Study of the Ag/a-Al2O3(0001) Interface 2001-11-13 doi: 10.3390/i2050271 Yu. F. Zhukovskii E. A. Kotomin B. Herschend K. Hermansson P. W.M. Jacobs http://www.mdpi.com/1422-0067/2/5/263/ The structure and local electron properties of Au atoms deposited on the TiN (001) surface has been theoretically analyzed using a periodic slab model and density functional based calculations. The surface is described by means of a 2x2 cell five layers thick, on which gold atoms are added. Deposition of single atoms on the surface, (θ = 0.25 ML), shows that the preferred site is on-top of Ti atoms, with a metal-surface distance of 2.49 Å. The computed adsorption energy for this site is -1.92 eV, only slightly lower than that lying between two Ti surface atoms (-1.90 eV). The on-top nitrogen sites are less favorable by about 0.4 eV. The calculations were carried out using the Perdew-Wang 91 exchange correlation functional and ultra soft pseudopotentials, with electronic states represented by a plane-wave expansion. http://www.mdpi.com/1422-0067/2/5/263/ Tue, 13 Nov 2001 00:00:00 CET International Journal of Molecular Sciences 2001-11-13 2 5 Article 263 270 1422-0067 A First Principles Density Functional Study of Au Deposition on TiN (001) Surface 2001-11-13 doi: 10.3390/i2050263 Norge Cruz Hernández Javier Fdez. Sanz http://www.mdpi.com/1422-0067/2/5/251/ This paper provides a review of recently obtained spectroscopic results, ab-initio calculations and catalytic activity tests from the authors´ laboratory of factors affecting the performance of materials used as automobile catalysts. Issues addressed include the preparation of (Ce,Zr)Ox/Al2O3 (CZA) mixed oxide supports and the use of new active metals, such as Pd and Cu, for three-way catalysts (TWCs); the performance of non-noble transition metals, such as Co or Ag, for pollution control under lean conditions; and the use of Pt/BaOx/Al2O3 (PtBa) for engine exhaust gas treatment under oscillating lean-stoichiometric conditions. http://www.mdpi.com/1422-0067/2/5/251/ Tue, 13 Nov 2001 00:00:00 CET International Journal of Molecular Sciences 2001-11-13 2 5 Article 251 262 1422-0067 New Strategies for the Improvement of Automobile Catalysts 2001-11-13 doi: 10.3390/i2050251 M. Fernández-García A. Martínez-Arias A. Iglesias-Juez A. B. Hungría J. A. Anderson J. C. Conesa J. Soria http://www.mdpi.com/1422-0067/2/5/246/ The growth of Pt deposits on Co(0001) was followed by STM and XPS. The chemical reactivity of the resulting surface was checked by CO adsorption. Pt grows as dendritic islands on the Co terraces whereas forming stripes at the Co step edges. Annealing the sample has no apparent effect on the STM pictures. However, XPS suggests that a limited dilution of Pt in Co takes place. The adsorption of CO on the surface is drastically affected by the presence of Pt even for minute traces. The adsorption energy on the Pt areas is decreased by 40 %. The maximum coverage on the Co areas is also decreased. This indicates that Pt impurities diluted in Co have a high passivating power as a consequence of the induced electronic changes. http://www.mdpi.com/1422-0067/2/5/246/ Tue, 13 Nov 2001 00:00:00 CET International Journal of Molecular Sciences 2001-11-13 2 5 Article 246 250 1422-0067 CO Adsorption on Co(0001)-Supported Pt Overlayers 2001-11-13 doi: 10.3390/i2050246 P. Légaré B. Madani G. F. Cabeza N. J. Castellani http://www.mdpi.com/1422-0067/2/5/230/ Alumina supported CuCl2, the basic catalyst for ethylene oxychlorination, has been investigated by UV-Vis spectroscopy, EPR, EXAFS and XANES in a wide range (0.25-9.0 wt%) of Cu concentration. We have evidenced that, at low Cu content, the formation of a surface aluminate species takes place. The formation of this surface copper aluminate stops at 0.95 wt% Cu / 100 m2; at higher Cu concentrations excess copper chloride precipitates directly from solution during the drying step forming an highly dispersed CuCl2.H2O, phase, overlapping progressively the surface aluminate. Depletion tests and IR spectroscopy of adsorbed NO have demonstrated that the latter is the only active phase. A complete catalytic cycle has then been performed on CuCl2/Al2O3 catalyst. EPR, XANES and EXAFS, have been used to demonstrate that the ethylene oxychlorination reaction: C2H4 + 2HCl + ½ O2 --> C2H4Cl2 + H2O follows a three steps mechanism: (i) reduction of CuCl2 to CuCl (2CuCl2 + C2H4 --> C2H4Cl2 + 2CuCl), (ii) oxidation of CuCl to give an oxychloride (2CuCl + ½ O2 --> Cu2OCl2) and (iii) closure of the catalytic circle by rechlorination with HCl, restoring the original CuCl2 (Cu2OCl2 + 2HCl --> 2CuCl2 + H2O). Finally, we have shown that time resolved, in situ, spectroscopy is a very promising technique to investigate the interplay between catalyst activity and oxidation state of copper. http://www.mdpi.com/1422-0067/2/5/230/ Tue, 13 Nov 2001 00:00:00 CET International Journal of Molecular Sciences 2001-11-13 2 5 Article 230 245 1422-0067 The CuCl2/Al2O3 Catalyst Investigated in Interaction with Reagents 2001-11-13 doi: 10.3390/i2050230 Carlo Lamberti Carmelo Prestipino Luciana Capello Silvia Bordiga Adriano Zecchina Giuseppe Spoto Sofia Diaz Moreno Andrea Marsella Barbara Cremaschi Marco Garilli Sandro Vidotto Giuseppe Leofanti http://www.mdpi.com/1422-0067/2/5/221/ The H2/O2 reaction on a polycrystalline palladium foil has been studied. The experimental methods used were Laser-Induced Fluorescence (LIF) and microcalorimetry. The reaction was also simulated with the Chemkin software package. The water production maximum occurs at 40% H2 and the OH desorption has its maximum at 10% H2, at a total pressure of 100 mTorr (13 Pa) and a catalyst temperature of 1300 K. It is concluded, in agreement with the simulations, that the main water-forming reaction at these experimental conditions is OH+H→H2O. From the water production maximum the quotient of the initial sticking coefficient for hydrogen and oxygen (SH2(0)/SO2(0)) is calculated to be 0.75(±0.1). http://www.mdpi.com/1422-0067/2/5/221/ Tue, 13 Nov 2001 00:00:00 CET International Journal of Molecular Sciences 2001-11-13 2 5 Article 221 229 1422-0067 The H2/O2 Reaction on a Palladium Model Catalyst Studied with Laser-Induced Fluorescence and Microcalorimetry 2001-11-13 doi: 10.3390/i2050221 Åsa Johansson Michael Försth Arne Rosén http://www.mdpi.com/1422-0067/2/5/211/ The density functional theory (DFT) based hybrid-method B3LYP has been used to study the interaction of the nitromethane molecule (CH3NO2) with the Au(111) surface. The perfect Au(111) surface has been represented by a rather large cluster model, Au22, that was in turn used to extract information about the preferred adsorption geometry of the CH3NO2 species. In order to extract energetic information about the stability of adsorbed nitromethane, calculations were also performed for the gas-phase CH3NO2 molecule. The results obtained here are used to interpret experimental data. The computed geometry for adsorbed CH3NO2 agrees with the structure proposed from a previous experimental work. http://www.mdpi.com/1422-0067/2/5/211/ Tue, 13 Nov 2001 00:00:00 CET International Journal of Molecular Sciences 2001-11-13 2 5 Article 211 220 1422-0067 The Adsorption of Nitromethane on the Au (111) Surface 2001-11-13 doi: 10.3390/i2050211 J. R. B. Gomes F. Illas http://www.mdpi.com/1422-0067/2/5/197/ The catalytic properties of LaCoO3 in aqueous oxidation are explored as a function of doping. Both Sr substitution for La and Fe/Ni substitution for Co are studied. The reaction of interest is the aqueous epoxidation of crotyl alcohol with hydrogen peroxide. The reaction products are measured using GC, and the decomposition of hydrogen peroxide is studied using the volume of oxygen evolved during reaction. Strong variations in the activity to epoxide formation are observed, with Fe-doped samples being rather inactive in the reaction. SR VUV photoemission is used to explore the surface reactivity of the ceramic catalysts in aqueous solution, using H2O as a probe molecule. These measurements are complemented by XANES measurements designed to probe the local defect structure and XPS measurements of surface composition. We relate the observed catalytic activity to the defect structure of the doped materials. In Ni-doped materials, oxygen vacancies appear to be the predominant defect, whereas in Fe-doped samples, electron holes are stabilized on Fe, leading to very different catalytic behaviour. Surface studies in combination with AA measurements reveal some dissolution of the catalyst into solution during the reaction. The surface reactivity to water is influenced by the TM d electron count, with water binding more strongly to Fe-doped materials than to those containing Ni. The influence of these factors on the rate of the unwanted hydrogen peroxide decomposition reaction and hence on activity in epoxidation is discussed. http://www.mdpi.com/1422-0067/2/5/197/ Tue, 13 Nov 2001 00:00:00 CET International Journal of Molecular Sciences 2001-11-13 2 5 Article 197 210 1422-0067 Electronic Structure and Reactivity of TM-Doped La1-xSrxCoO3 (TM=Ni, Fe) Heterogeneous Catalysts 2001-11-13 doi: 10.3390/i2050197 S. C. Grice W. R. Flavell A. G. Thomas S. Warren P. G. D. Marr D. E. Jewitt N. Khan P. M. Dunwoody S. A. Jones http://www.mdpi.com/1422-0067/2/5/183/ Some aspects of the reaction mechanisms in multistep selective (amm)oxidation reactions over oxide surfaces are discussed evidencing some of the challenges for surface science and theory in describing these reactions, and for applied catalysis in order to have a more in deep identification of the key factors governing surface reactivity and which may be used to improve catalytic performances. In particular, the role of chemisorbed species in the modification of the surface reactivity and the presence of multiple pathways of reaction are evidenced by comparing the behavior of V-based catalysts in C3-C4 alkanes and alkene oxidation. http://www.mdpi.com/1422-0067/2/5/183/ Tue, 13 Nov 2001 00:00:00 CET International Journal of Molecular Sciences 2001-11-13 2 5 Article 183 196 1422-0067 Reaction Mechanism and Control of Selectivity in Catalysis by Oxides: Some Challenges and Open Questions 2001-11-13 doi: 10.3390/i2050183 Gabriele Centi Siglinda Perathoner http://www.mdpi.com/1422-0067/2/5/167/ TS-1 and Fe-MFI systems have been chosen as cases studies for describing the behavior of single-site catalysts. We will report a concise review of the firmly established knowledge and of the open problems concerning the structure and the reactivity of Ti and Fe sites in TS-1 and Fe-MFI in partial oxidation catalysts. Some new experimental and theoretical results will also be described. http://www.mdpi.com/1422-0067/2/5/167/ Tue, 13 Nov 2001 00:00:00 CET International Journal of Molecular Sciences 2001-11-13 2 5 Article 167 182 1422-0067 The Role of Isolated Sites in Heterogeneous Catalysis: Characterization and Modeling 2001-11-13 doi: 10.3390/i2050167 Silvia Bordiga Alessandro Damin Gloria Berlier Francesca Bonino Gabriele Ricchiardi Adriano Zecchina Carlo Lamberti http://www.mdpi.com/1422-0067/2/5/165/ n/a http://www.mdpi.com/1422-0067/2/5/165/ Fri, 09 Nov 2001 00:00:00 CET International Journal of Molecular Sciences 2001-11-09 2 5 Editorial 165 166 1422-0067 Papers from Euroconference on Molecular Mechanism of Heterogeneous Catalysis Held in San Feliu de Guixols (Spain) in June 2001 2001-11-09 doi: 10.3390/i2050165 Francesc Illas Josep Manel Ricart