Semihydrogenation of Acetylene on Indium Oxide: Proposed Single-Ensemble Catalysis

Indium oxide catalyzes acetylene hydrogenation with high selectivity to ethylene (>85 %); even with a large excess of the alkene. In situ characterization reveals the formation of oxygen vacancies under reaction conditions, while an in depth theoretical analysis links the surface reduction with the creation of well-defined vacancies and surrounding In3O5 ensembles, which are considered responsible for this outstanding catalytic function. This behavior, which differs from that of other common reducible oxides, originates from the presence of four crystallographically inequivalent oxygen sites in the indium oxide surface. These resulting ensembles are 1) stable against deactivation, 2) homogeneously and densely distributed, and 3) spatially isolated and confined against transport; thereby broadening the scope of oxides in hydrogenation catalysis

Reactivity descriptors for ceria in catalysis

Ceria has been very successfully employed in oxidation catalysis, whereas its application in other reactions has been less intensively investigated. The catalytic activity of ceria can be further enhanced by the use of dopants, and it exhibits structure sensitivity for numerous processes. The rich chemistry of cerium oxide is gathered and discussed in the present work, where the nature of each step of the most common reactions performed on it is assessed. Chemically intuitive computational and experimental descriptors, namely acid-base, redox, and structural features, are put forward to correlate the observed trends among the different doped and undoped facets. We have attempted to generate a robust framework that maps the chemically sound descriptors to the experimental fingerprints and theoretically calculated parameters

Mechanism of ethylene oxychlorination over ruthenium oxide

The oxychlorination of ethylene is an industrially relevant process within the manufacture of polyvinyl chloride (PVC). Although RuO2 is the best performing catalyst for the Deacon process (4HCl + O2? 2H2O + 2Cl2), experiments demonstrate a modest activity in the selective oxychlorination to vinyl chloride, favouring oxidation and polychlorinated saturated products. From the computational modelling three main contributions are found to control the performance: (i) coverage effects that alter the configuration of intermediates; (ii) the monodimensional arrangement of the active sites, in which the reaction of coadsorbed species works on a ‘‘first-come, first-served” basis; and (iii) the high reactivity of the oxygen species. Competition between oxidation and chlorination processes results in variable selectivity, depending on the reaction conditions (particularly temperature and reactant partial pressures), which influence the surface composition. From the analysis of the complex reaction network, the essential requirements for a good oxychlorination catalyst are formulated

Prevalencia del síndrome de apnea obstructiva del sueño en pacientes con disfunción sinusal

Introducción y objetivos. El síndrome de apnea-hipopnea del sueño (SAHS) ha sido relacionado con varias enfermedades cardiovasculares. Podría incluso estar implicado en la etiopatogenia de la disfunción sinusal (DS), aunque se desconoce la asociación real entre las 2 enfermedades. Pretendemos conocer la prevalencia del SAHS en enfermos diagnosticados de DS. Pacientes y método. Entre junio de 2002 y diciembre de 2004 se ha estudiado a 38 pacientes consecutivos diagnosticados de DS mediante registro Holter de 24 h. Todos fueron interrogados acerca de si presentaban síntomas relacionados con SAHS y se les hizo una polisomnografía respiratoria con un equipo validado. Resultados. La edad media de los 38 pacientes fue de 67 ± 10 años, el 68% era varón y el 58%, hipertenso. En el Holter la frecuencia máxima fue de 87 ± 6 lat/min, la mínima de 35 ± 3 lat/min y la media de 48 ± 3 lat/min. El 63% de los pacientes requirió marcapasos por DS sintomática. El 39% tenía somnolencia diurna excesiva (escala de Epworth [ESS] > 9). La polisomnografía demostró que sólo un 13% tenía un índice de apnea-hipopnea/h (IAH) normal y que el 31,6% (intervalo de confianza del 95%, 16,8-46,4) tenía un SAHS (IAH > 10 y ESS > 9). Conclusiones. Considerando que la prevalencia del SAHS en la población general es de alrededor del 3%, los resultados de nuestro estudio muestran que el SAHS es 10 veces más frecuente en pacientes con DS que en la población general, lo que indica una asociación entre las 2 enfermedades

Mechanism and microkinetics of methanol synthesis via CO2 hydrogenation on indium oxide

Indium oxide has emerged as a highly effective catalyst for methanol synthesis by direct CO2 hydrogenation. Aiming at gathering a deeper fundamental understanding, mechanistic and (micro)kinetic aspects of this catalytic system were investigated. Steady-state evaluation at 5 MPa and variable temperature indicated a lower apparent activation energy for CO2 hydrogenation than for the reverse watergas shift reaction (103 versus 117 kJ mol!1), which is in line with the high methanol selectivity observed. Upon changing the partial pressure of reactants and products, apparent reaction orders of !0.1, 0.5, !0.2, and !0.9 were determined for CO2, H2, methanol, and water, respectively, which highlight a strong inhibition by the latter. Co-feeding of H2O led to catalyst deactivation by sintering for partial pressures exceeding 0.125 MPa, while addition of the byproduct CO to the gas stream could be favorable at a total pressure below 4 MPa but was detrimental at higher pressures. Density Functional Theory simulations conducted on In2O3(1 1 1), which was experimentally and theoretically shown to be the most exposed surface termination, indicated that oxygen vacancies surrounded by three indium atoms enable the activation of CO2 and split hydrogen heterolytically, stabilizing the polarized species formed. The most energetically favored path to methanol comprises three consecutive additions of hydrides and protons and features CH2OOH and CH2(OH)2 as intermediates. Microkinetic modeling based on the DFT results provided values for temperature and concentration-dependent parameters, which are in good agreement with the empirically obtained data. These results are expected to drive further optimization of In2O3-based materials and serve as a solid basis for reactor and process design, thus fostering advances towards a potential large-scale methanol synthesis from CO2

Multistep π dimerization of tetrakis(n-decyl)heptathienoacene radical cations: a combined experimental and theoretical study

Radical cations of a heptathienoacene a,b-substituted with four n-decyl side groups (D4T7C+) form exceptionally stable p-dimer dications already at ambient temperature (Chem. Comm. 2011, 47, 12622). This extraordinary p-dimerization process is investigated here with a focus on the ultimate[D4T7C+]2 p-dimer dication and yet-unreported transitoryspecies formed during and after the oxidation. To this end, we use a joint experimental and theoretical approach that combines cyclic voltammetry, in situ spectrochemistry and spectroelectrochemistry, EPR spectroscopy, and DFT calculations. The impact of temperature, thienoacene concentration, and the nature and concentration of counteranions on the p-dimerization process is also investigated in detail. Two different transitory species were detected in the course of the one-electron oxidation: 1) a different transient conformation of the ultimate [D4T7C+]2 p-dimer dications, the stability of which is strongly affected by the applied experimental conditions, and 2) intermediate [D4T7]2C+ p-dimer radical cations formed prior to the fully oxidized [D4T7]2C+ p-dimer dications. Thus, this comprehensive work demonstrates the formation of peculiar supramolecular species of heptathienoacene radical cations, the stability, nature, and structure of which have been successfully analyzed. We therefore believe that this study leads to a deeper fundamental understanding of the mechanism of dimer formation between conjugated aromatic systems