Caracterización fundamental de superficies metálicas a condiciones relevantes para la catálisis

Heterogeneous catalysis involves chemisorption, reactions of chemisorbed species, and desorption of the products formed. The enthalpies and entropies for these elementary steps and their transition states provide the thermodynamic context that allows rigorous interpretations of the rates and selectivities of chemical reactions mediated by surfaces. The measurement of rates and/or thermodynamic properties at conditions relevant for catalysts and in the absence of mass and heat transport limitations are required for the proper reactor and catalyst design. Different challenging examples are provided, in which chemical rates and/or thermodynamic properties are measured under rigorous kinetic or thermodynamic conditions, giving information regarding the nature of the active metal surfaces and their role at reaction conditions. Among the cases to be presented are the alkane oxidation reactions on noble metals, Pd-PdO phase transition and its consequences for catalysis, and the surface characterization of metals by H2 chemisorption at elevated temperatures. Alkane-O2 (CH4 and C2H6) reactions are highly exothermic and tend to occur within the length scale of conductive or convective heat and mass transfer, which lead to severe gradients within undiluted catalyst pellets and reactors. Extensive dilution within the pellets and reactor has been used to get kinetic and isotopic data for Alkane-O2 reactions on supported Pt, Rh and Pd. These data have shown that CO and H2 do not form via direct alkane partial oxidation but instead via sequential combustion-reforming pathways. Alkane-O2 reactants form CO2 and H2O on Pt in three kinetic regimes (KR), each with distinct rate equations, kinetically-relevant steps, most abundant surface intermediates (MASI), and cluster size effects. Transitions among these regimes are determined by the prevalent steady-state coverages of chemisorbed oxygen (O*), which are given by O2 pressure when O2 dissociation is equilibrated and by O2 to Alkane ratios when it is irreversible. Mechanistic interpretations remain valid for other metals such as Pd, and the difference in reactivity among metals is correlated to O* binding strengths when O* is involved in the kinetically-relevant steps. On Pd and Rh, however, the clusters undergo phase transition to PdO and RhO2, leading to an additional kinetic regime characterized by an abrupt increase in reactivity caused by the transition from metal to oxide. Ex-situ O2 uptake measurements, at equilibrium, were performed to correlate the oxygen content during the phase transition with the measured rates at reaction conditions. Another example is given by the use of dissociative H2 chemisorption methods at conditions relevant for catalysis as a thermodynamic probe instead of mere site counting technique, in which differential enthalpies and entropies of adsorption are obtain to probe the non-uniformity of cluster surfaces. H-atoms formed via H2 dissociation are attractive titrants because of the reversible nature of the adsorption processes and the well-defined adsorption stoichiometry, but also because of the ubiquitous involvement of H-atoms in hydrogenation-dehydrogenation catalysis.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The Conversion Rate of R&D into Technological Innovation in Family-Managed Firms Under Vulnerability

This paper primarily questions whether under vulnerability, decision-makers will be able to turn R&D into technological innovation more efficiently in order to increase the likelihood of firm survival (Palmer & Wiseman, 1999), using divergences between current firm performance and both historical and social performance as indicators of aspirations gaps (Lant, 1992; Wiseman & Gómez-Mejia, 1998). Then, we look whether the level family management and the level of slack may moderate the effect of performance below aspiration levels on the relationship between R&D intensity and the likelihood of obtaining technological innovation.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

First-principles investigation of morphotropic transitions and phase-change functional responses in BiFeO3-BiCoO3 multiferroic solid solutions

We present an ab initio study of the BFCO solid solution formed by multiferroics BiFeO3 (BFO) and BiCoO3 (BCO). We find that BFCO presents a strongly discontinuous morphotropic transition between BFO-like and BCO-like ferroelectric phases. Further, for all compositions such phases remain (meta)stable and retain well-differentiated properties. Our results thus suggest that an electric field can be used to switch between these structures, and show that such a switching involves large phase-change effects of various types, including piezoelectric, electric, and magnetoelectric ones.Comment: Submitte

First-Principles Calculations at Constant Polarization

We develop an exact formalism for performing first-principles calculations for insulators at fixed electric polarization. As shown by Sai, Rabe, and Vanderbilt (SRV) [N. Sai, K. M. Rabe, and D. Vanderbilt, Phys. Rev. B {\bf 66}, 104108 (2002)], who designed an approximate method to tackle the same problem, such an approach allows one to map out the energy landscape as a function of polarization, providing a powerful tool for the theoretical investigation of polar materials. We apply our method to a system in which the ionic contribution to the polarization dominates (a broken-inversion-symmetry perovskite), one in which this is not the case (a III-V semiconductor), and one in which an additional degree of freedom plays an important role (a ferroelectric phase of KNO$_3$). We find that while the SRV method gives rather accurate results in the first case, the present approach provides important improvements to the physical description in the latter cases.Comment: 4 pages, 4 figure

Theoretical study of ferroelectric potassium nitrate

We present a detailed study of the structural behavior and polarization reversal mechanism in phase III of KNO$_3$, an unusual ferroelectric material in which the nitrate groups rotate during polarization reversal. This material was one of several studied in a previous work [O. Di\'eguez and D. Vanderbilt, Phys. Rev. Lett. {\bf 96}, 056401 (2006)] where methods were described for computing curves of energy versus electric polarization. In the present work we extend and systematize the previous first-principles calculations on KNO$_3$, and analyze in detail a two-parameter model in which the energy of the system is written as a low-order expansion in the polarization and the nitrate group orientation. We confirm that this model reproduces the first-principles results for KNO$_3$ very well and construct its parameter-space phase diagram, describing regions where unusual triple-well potentials appear. We also present first-principles calculations of KNO$_3$ under pressure, finding that its energy-versus-polarization curves change character by developing a first-derivative discontinuity at zero polarization.Comment: Replaced with extended versio

ORGANIZATIONAL TRAINING IN MANUFACTURING FIRMS AND ADVANCED MANUFACTURING TECHNOLOGIES

The introduction of new microelectronic technologies in the manufacturing process forces companies to adapt human resource strategy to the changes in the workplace. While this subject has been widely researched from an operations management perspective, research from a human resource management viewpoint has been less frequent. The aim of this article is to gain insight into some of the factors that determine personnel training efforts in companies introducing advanced manufacturing technologies (AMTs.) The study provides empirical evidence from a sector with high rates of technological modernisation.Training, human resources, metal-mechanic sector, companies, Advanced Manufacturing Technologies, AMT.

Models of public-private partnerships in megaprojects: the Spanish case

This article provides a literature review of PPP Models, where the clarification of this current confusion and ambiguity constitute the fundamental issue addressed by our research. The systematization of the PPP models is performed by applying six classification criteria based on organizational and financial aspects and focused on the Spanish experience. Additionally, a comparative study of the various schemes applied in European countries is carried out, whereby the concession model implemented successfully in Spain is studied in greater detail. To this end, a megaproject, the first metro line of Seville (Spain) forms the basis of a case-study. When the megaproject is viable through user fees, the public sector can use PPPs to defer payments and as a way to control their deficits and debt without cutting investments in infrastructures and public services. Nevertheless, certain drawbacks should be borne in mind, such as the expenditure commitments of future budgets, the higher cost of private funding, and the necessity for transparency and accountability of PPP contractual arrangements to be improved. Therefore, the aim of this article is to analyze the various forms of PPPs in megaprojects in order to determine the potential efficiency gains that can be achieved in the implementation of these models

Risk management in megaprojects.

Despite its high relevance to the success of megaprojects, risk management remains one of the least developed research issues. Risk management is a process composed of several phases. This paper is focused on the first of these phases: risk identification. Our purpose is to establish the state of the art in risk management in megaprojects, systematize the risks studied in the literature, as well as to identify potential areas of further research. To this end, a systematic review is carried out. Academic journals and conference papers published from 2000 onwards in main databases (WoK, Scopus and ABI) have been examined. A qualitative analysis has been performed by using ATLAS.ti together with a checklist. To the best of the authors’ knowledge, no previous systematic revision of papers on risk management in megaprojects has ever been carried out, although certain authors have emphasized its importance. The contribution of this research includes: a bibliometric analysis of the papers that focus on risk management in megaprojects; a systematization and classification of the risks; tw†o matrices comprised of the proposed risk categorization, first in relation to the sector studied, and second related with the different stakeholders; and an identification of gaps in the research in risk management in megaprojects. The systematization of the risks helps managers towards their identification within the megaproject, and to follow the subsequent steps in the risk management process. Moreover, the matrix developed on the transfer of risks can enable managers to analyse who would be the best partner to support each risk. Furthermore, from an academic point of view, potential areas for future lines of research are presented

Wannier-based definition of layer polarizations in perovskite superlattices

In insulators, the method of Marzari and Vanderbilt [Phys. Rev. B {\bf 56}, 12847 (1997)] can be used to generate maximally localized Wannier functions whose centers are related to the electronic polarization. In the case of layered insulators, this approach can be adapted to provide a natural definition of the local polarization associated with each layer, based on the locations of the nuclear charges and one-dimensional Wannier centers comprising each layer. Here, we use this approach to compute and analyze layer polarizations of ferroelectric perovskite superlattices, including changes in layer polarizations induced by sublattice displacements (i.e., layer-decomposed Born effective charges) and local symmetry breaking at the interfaces. The method provides a powerful tool for analyzing the polarization-related properties of complex layered oxide systems