5 research outputs found
Response of a Model of CO Oxidation with CO Desorption and Diffusion to a Periodic External CO Pressure
We present a study of the dynamical behavior of a Ziff-Gulari-Barshad model
with CO desorption and lateral diffusion. Depending on the values of the
desorption and diffusion parameters, the system presents a discontinuous phase
transition between low and high CO coverage phases. We calculate several points
on the coexistence curve between these phases. Inclusion of the diffusion term
produces a significant increase in the CO_2 production rate. We further applied
a square-wave periodic pressure variation of the partial CO pressure with
parameters that can be tuned to modify the catalytic activity. Contrary to the
diffusion-free case, this driven system does not present a further enhancement
of the catalytic activity, beyond the increase induced by the diffusion under
constant CO pressure.Comment: 5 pages, RevTe
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 and . 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