Response of a catalytic reaction to periodic variation of the CO pressure: Increased CO_2 production and dynamic phase transition

We present a kinetic Monte Carlo study of the dynamical response of a Ziff-Gulari-Barshad model for CO oxidation with CO desorption to periodic variation of the CO presure. We use a square-wave periodic pressure variation with parameters that can be tuned to enhance the catalytic activity. We produce evidence that, below a critical value of the desorption rate, the driven system undergoes a dynamic phase transition between a CO_2 productive phase and a nonproductive one at a critical value of the period of the pressure oscillation. At the dynamic phase transition the period-averged CO_2 production rate is significantly increased and can be used as a dynamic order parameter. We perform a finite-size scaling analysis that indicates the existence of power-law singularities for the order parameter and its fluctuations, yielding estimated critical exponent ratios $\beta/\nu \approx 0.12$ and $\gamma/\nu \approx 1.77$. These exponent ratios, together with theoretical symmetry arguments and numerical data for the fourth-order cumulant associated with the transition, give reasonable support for the hypothesis that the observed nonequilibrium dynamic phase transition is in the same universality class as the two-dimensional equilibrium Ising model.Comment: 18 pages, 10 figures, accepted in Physical Review

High-energy resolution core level photoelectron spectroscopy and diffraction: Powerful tools to probe physical and chemical properties of solid surfaces

Since the seventies, core level spectroscopy has played a key role in elucidating the geometric and electronic structure of solid surfaces. Due to their high localization, core electrons are extremely sensitive to the chemical state and to the local environment, and for this reason can be used for the identification of local configurations. The high energy resolution now attainable with this technique (below 100meV) and the reduced data acquisition time (down to few ms per spectrum) has opened the possibility to probe the physical and chemical properties of a large variety of low-dimensional systems and to shed light on complex processes taking place on solid surfaces. The characterization of the properties of mono- and bi-metallic materials, the investigation of the atomic and molecular interactions on solid surfaces and the recent findings on epitaxial graphene outline the potential of high energy resolution core level photoelectron spectroscopy and photoelectron diffraction as precious tools in determining nanoscale electronic, geometrical and chemical properties