Integração numérica de leis de velocidade diferenciais com o uso do SCILAB

In this work, we applied the free open source SCILAB software for the numerical integration of differential rate law equations to obtain the concentration profiles of chemical species involved in the kinetics of some complex reactions. An automated method was applied to construct the system of ordinary differential equations (ODE) from the postulated chemical models. The solutions of the ODEs were obtained numerically by standard SCILAB functions. We successfully simulated even complex chemical systems such as pH oscillators. This communication opens up the possibility of using SCILAB in simulations and modeling by our chemistry undergraduate students

Mechanistic aspects of glycerol electrooxidation on Pt(111) electrode in alkaline media

Glycerol electrooxidation reaction (GEOR) in alkaline media was studied on the Pt(111) electrode with in situ FTIR and electrochemical methods. Cyclic voltammogram profiles display strong electrode deactivation after the first potential scan. Chronoamperometric pulses demonstrate that the deactivation is a result of the reaction intermediates yielded during the faradaic process. In situ FTIR shows evidence that the strongly adsorbed intermediate formed during GEOR is an acyl species which remains present on the surface within the potential window studied.This work was supported by CNPq (projects 474590/2013-5 and 456758/2014-3), FAPESP (project 2013/13749-0) and Capes for the financial support

The role of adsorbates in electrocatalytic systems: An analysis of model systems with single crystals

The use of single crystal electrodes as model catalysts has been widely applied for the study of several reactions. The known structure of the surface provides a system with controlled electronic properties that helps in the understanding of the mechanism of reactions. In this model system, any modification, including the adsorption of anions, organic molecules or foreign atoms, generate changes in the electronic properties of the surface and, thus, in the adsorption energy of the species involved in the studied reaction. The adsorbate can hinder the surface and diminish the activity or prevent the oxidation of the surface and improve the catalysis. The changes in electronic properties can modify the adsorption energy and enhance or worsen the catalytic activity. The effect of any adsorbed species will depend on the structure of the surface, the nature of the species and the studied reaction.CAA and JSG thank FAPESP through projects 2018/06677e6 and 2018/10292e2. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) d Finance Code 001. JMF thanks the MCINN (FEDER) project PID2019-105653 GB-100 (Spain)

Integração numérica de leis de velocidade diferenciais com o uso do SCILAB Numerical integration of differential rate laws by means of SCILAB

<abstract language="eng">In this work, we applied the free open source SCILAB software for the numerical integration of differential rate law equations to obtain the concentration profiles of chemical species involved in the kinetics of some complex reactions. An automated method was applied to construct the system of ordinary differential equations (ODE) from the postulated chemical models. The solutions of the ODEs were obtained numerically by standard SCILAB functions. We successfully simulated even complex chemical systems such as pH oscillators. This communication opens up the possibility of using SCILAB in simulations and modeling by our chemistry undergraduate students

Electrochemical features of Pt(S)[n(110) × (100)] surfaces in acidic media

Experiments have been carried out in sulfuric and perchloric acid solutions on Pt(S)[n(110) × (100)] electrodes. The comparison between the two different electrolytic media reveals an important influence of the anion in the voltammetric features. Total charge curves have been obtained with the CO charge displacement method in combination with voltammetric measurements. From these curves, the dependence of the pztc with the step density and the strength of the anion adsorption have been analyzed. The problem of the so-called third peak is treated for a series of electrodes that contain (110) terraces, revealing the requirement of (110) domains for occurrence of this adsorption state.Financial support from the MEC (Spain) through project CTQ2010-16271 (Feder) is gratefully acknowledged

Oxide formation as probe to investigate the competition between water and alcohol molecules for OH species adsorbed on platinum

The creation of defects on the surface of Pt(111) and Pt(100) and the dissolution of Pt were used as probes to investigate the oxidation of the surface in the absence and in the presence of methanol, ethanol, glycerol and ethylene glycol. Electrochemical and Graphite Furnace Atomic Absorption Spectrometry showed that in the presence of ethanol, glycerol and ethylene glycol, in the same potential window, the formation of defects is decreased in comparison to the oxidation of platinum in the absence of these alcohols. Since both the oxidation of the alcohols and the oxidation of the surface depend on PtOH formation, the competition for this species can displace the potential at which the oxidation of the surface oxidation to PtO is favored in the presence of ethanol, glycerol and ethylene glycol. On the other hand, the presence of methanol does not influence the oxidation and subsequent disordering of the surface, possibly because this reaction takes place in parallel with platinum oxidation to PtO.This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES), Finance Code 001. The authors also thank FAPESP (projects 2013/13749–0 and 2016/23878-0) and CNPq for PIC/PIBIC (R.A.G. Oliveira and J.M. Roquetto) and DAI (N. Akiba) scholarships and projects 474590/2013–5 and 456758/2014–3. The authors are grateful to the Multiuser Central Facilities (UFABC) for experimental support

The influence of stepped Pt[n(111)×(110)] electrodes towards glycerol electrooxidation: Electrochemical and FTIR studies

In situ Fourier Transform Infrared (FTIR) spectroscopy and cyclic voltammetry were combined for the first time to study the influence of Pt steps sites, belonging to the series of Pt(S)[n(111)x(111)], over the glycerol electrooxidation reaction (GEOR) in acid media. The spectroelectrochemical studies exhibited that the adsorption and electrooxidation process of glycerol at Pt surfaces are quite sensitive to the monoatomic ‘defect’ added on the well-ordered surface. The presence of (110) steps on the (111) terraces plays a significant role in the CV profiles with the presence of two peaks well-defined on the positive-going scan at 0.57 and 0.70 V, which the first one can be related to the (111) oriented terraces, and the second one to the (110) oriented ‘defects’. The in situ FTIR detached the presence of three well-discernible bands (ν(CO), ν(COL) and ν(CO2)) which give us new insights about glycerol electrooxidation mechanism and its dependence with the surface structure. The Pt(111) has shown the higher electroactivity towards GEOR, while Pt(110) has demonstrated greater ability in breaking C–C bond to convert into CO2. Moreover, for the Pt(111) and Pt(554) electrodes, the C–C seems to break only during the positive scan. On the other hand, at the beginning of the reverse scan, the incomplete oxidation prevails for Pt(111) and Pt(554) and, thus, being more selective to form only C3 products as dihydroxyacetone, glycolic acid and glyceric acid.Authors gratefully acknowledge financial support from FAPESP, Brazil (process numbers 2013-16930-7, 2013-13749-0, 2018-10292-2), FAPEAL, Brazil (process number 60030 1076/2016), CNPq, Brazil and CAPES, Brazil. Also, Prof. Juan M. Feliu acknowledges MINECO, Spain, through project n.o CTQ2016-76221-P