Elucidation of reaction mechanisms under far from thermodynamic equilibrium regime

Author(s)

Raphael Nagao de Sousa

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos
• Defense date: 06 dez. 2013

Examining board members

Hamilton Brandão Varela de Albuquerque; Pedro Henrique Cury Camargo; Janaina de Souza Garcia; Sergio Antonio Spinola Machado

• Advisor: Hamilton Brandão Varela de Albuquerque

Abstract

The spontaneous formation of self-organized spatiotemporal patterns under far from thermodynamic equilibrium conditions is a characteristic behavior in reaction-transport systems. Indeed, this spatial structuration can be understood as a collective behavior of a large number of individual elements in the system. Consequently the pattern emerges as a result of the interaction between the local dynamic of these subunits and the spatial coupling. Multistable, excitable and oscillatory nonlinear dynamics are typical examples of complex temporal patterns usually associated to the spatial structuration. In this doctoral thesis, two work fronts are presented using the nonlinear chemical dynamics in the elucidation of reaction mechanisms under far from thermodynamic equilibrium regime: (a) the investigation of the chemical nature and effect of the drift in the transient time-series in electrochemical oscillators. The analysis of the temporal evolution of the bifurcation parameter was based on an empiric method of stabilization, being the slow accumulation of oxygenated species the main responsible for the drift; (b) the decoupling of the parallel electrochemical routes for CO2 production by a combination of experiments, modeling and numerical simulations during the oscillatory electro-oxidation of methanol on polycrystalline platinum. The effect of perchlorate and sulfate anions in the parallel reactions was investigated by the global production of CO2 and HCOOCH3. Remarkably, sulfate anions inhibited more strongly the catalytic activity from direct pathway in contrast to the small alteration in the indirect pathway. In parallel to the two work fronts, an experimental setup was built in order to obtain a spatiotemporal evolution of a electrochemical reaction with a multichannel data acquisition system. A description of the confection process of the cell and the multichannel working electrode, data treatment and some preliminary experimental results are included as an additional chapter. The main idea of this thesis converges in the obtainment of chemical kinetic information which is not observed in conditions close to the thermodynamic equilibrium. This interpretation might be used as an alternative methodology in the study of electrocatalysis in complex chemical reactions. (AU)

• FAPESP's process: 09/00153-6 - Spatio-temporal self-organization in electrocatalysis
• Grantee: Raphael Nagao de Sousa
• Support type: Scholarships in Brazil - Doctorate