Relata-se um estudo sobre o processo de eletrossorção do n-propanol sobre eletrodos de platina eletrodispersa em soluções de H2SO4 1 N, a diferentes temperaturas (12 a 51 ºC) e potencíais (0,30 a 0,60 V). São abordados os aspectos relacionados com a cinética de adsorção dos possíveis intermediários formados na desidrogenação do n-propanol, bem como a determinação das constantes de velocidade em cada etapa. São apresentadas as energias de ativação do processo de adsorção para graus de cobertura, &#952; = 0 e &#952; &#8800; 0. A adsorção do álcool estudado a potencial controlado na região da dupla camada elétrica, ocorre através da desidrogenação da molécula, seguida pela ionização do hidrogênio adsorvido. A isoterma cinética de adsorção foi obtida a partir dos cronoamperogramas de desidrogenação do álcool e mostra uma variação linear de &#952; com o logaritmo do tempo de adsorção (t), para 0,25 < &#952; < 0,80. Por outro lado, a relação entre E = f (log li), onde li é a máxima corrente não estacionária obtida a t = 0, é linear com coeficiente angular igual a 2,3 (2 RT/F). Esse valor indica que no início da adsorção do n-propanol, apenas um elétron está envolvido no processo. Da mesma maneira que no metanol, supõe-se que a desidrogenação do n-propanol não ocorre através da eliminação simultânea dos dois átomos de hidrogênio ligados no carbono-&#945;, mas por duas etapas consecutivas de desidrogenação: R - CH2 - OH j1&#8594; R - .CH - OH + H+ + e- ( 1 ) R - .CH - OH j2&#8594; R - ..C - OH + H+ + e- ( 2 ) Desse modo, a corrente anódica não estacionária (j), proveniente da ionização do hidrogênio formado na desidrogenação do n-propanol é resultante da soma das correntes j>SUB>1 e j2 produzidas nas reações descritas nas equações (1) e (2). Quando o tempo de adsorção é muito curto, isto é , j2 = 0, a corrente não estacionária é determinada apenas pela adsorção da espécie R-.CH-OH. Considerando esta hipótese e as isotermas de Temkin e Elovich foi obtida uma equação que descreve o grau de cobertura pela espécie R-.CH-OH, (&#952;1) em função do tempo. &#952;1 = - Qmáx B/k2t (1-A-B ln t) + k1/k2 onde Qmáx é a carga máxima de cobertura, k1 e k2 são as constantes de velocidade de adsorção das espécies R-.CH-OH e R-..C-OH, respectivamente, A e B são as constantes da equação de Elovich. A equação precedente permitiu determinar as constantes de velocidade de adsorção k1 e k2. A partir desses valores em diferentes temperaturas foram obtidas as energias de ativação para as reações (1) e (2). Verificou-se que os tempos de máxima cobertura por R.CHOH e de inflexão, obtidos respectivamente de &#952;1= f (log t) e j-1 = f(t), são comparáveis para dada temperatura e potencial. / The kinetics and mechanism of n-propanol adsorption on a platinized platinum electrode was studied in 1 N H2SO4 at several temperatures, by means of the potential pulse method. Between 0.30 V and 0.60 V (RHE), the adsorption occurs via a dehydrogenation of the &#945;-carbon, followed by a rapid ionization of the adsorbed hydrogen atoms. The kinetic isotherms obtained by integration of the chronoamperograms show a linear variation of the surface coverage, &#952;, with logarithm of the adsorption time, tads, in the range 0.25 &#8804; &#952; &#8804; 0.80. This indicates that the adsorption rate can be expressed in tems of an Elovich equation. It is shown that the relation Eads vs log Ii, where Eads is the adsorption potential and Ii is the maximum non-stationary current at t = 0, is a straight line with a slope equal to 2.3[2RT/F], independently of the temperature. These data show that the initial adsorption step envolves a monoelectronic charge transfer, and can be represented by the following equation: R-CH2-OH j1&#8594; R-.CH-OH + H+ + e- ( 1 ) Therefore, it is assumed that the adsorption occurs via a two step consecutive reaction, given by equations (1) and (2): R-.CH-OH j2&#8594; R-..C-OH + H+ + e- ( 2 ) with the two adsorbed species R-.CH-OH and R-..C-OH characterized by their degree of coverage &#952;1 and &#952;2, respect ively. The non-stationary anodic current, j, is then the sum of currents j1 and j2 resulting from reactions described by equations (1) and (2). When the adsorption time is very short, it can be assumed that j = j1 + j2 &#8776; j1, and that &#952; = &#952; 1 + &#952;2 &#8776; &#952;1. From those assumptions, the following equation relating &#952;1 with t was obtained: &#952;1 = -Qmáx . B/[k2.t (1-A-B). ln t ] + k1/k2 (3) where Qmáx is the charge related with the maximum surface coverage, k1 and k2 the apparent rate constants of reactions (1) and (2), respectively, and A and B are constants from the Elovich equation. Equation (3) permitted the evaluation of the rate constants k1 and k2 for distinct Eads values. From the data at different temperatures, the apparent activation energies of both reactions were calculated.

Relata-se um estudo sobre o processo de eletrossorção do n-propanol sobre eletrodos de platina eletrodispersa em soluções de H2SO4 1 N, a diferentes temperaturas (12 a 51 ºC) e potencíais (0,30 a 0,60 V). São abordados os aspectos relacionados com a cinética de adsorção dos possíveis intermediários formados na desidrogenação do n-propanol, bem como a determinação das constantes de velocidade em cada etapa. São apresentadas as energias de ativação do processo de adsorção para graus de cobertura, &#952; = 0 e &#952; &#8800; 0. A adsorção do álcool estudado a potencial controlado na região da dupla camada elétrica, ocorre através da desidrogenação da molécula, seguida pela ionização do hidrogênio adsorvido. A isoterma cinética de adsorção foi obtida a partir dos cronoamperogramas de desidrogenação do álcool e mostra uma variação linear de &#952; com o logaritmo do tempo de adsorção (t), para 0,25 < &#952; < 0,80. Por outro lado, a relação entre E = f (log li), onde li é a máxima corrente não estacionária obtida a t = 0, é linear com coeficiente angular igual a 2,3 (2 RT/F). Esse valor indica que no início da adsorção do n-propanol, apenas um elétron está envolvido no processo. Da mesma maneira que no metanol, supõe-se que a desidrogenação do n-propanol não ocorre através da eliminação simultânea dos dois átomos de hidrogênio ligados no carbono-&#945;, mas por duas etapas consecutivas de desidrogenação: R - CH2 - OH j1&#8594; R - .CH - OH + H+ + e- ( 1 ) R - .CH - OH j2&#8594; R - ..C - OH + H+ + e- ( 2 ) Desse modo, a corrente anódica não estacionária (j), proveniente da ionização do hidrogênio formado na desidrogenação do n-propanol é resultante da soma das correntes j>SUB>1 e j2 produzidas nas reações descritas nas equações (1) e (2). Quando o tempo de adsorção é muito curto, isto é , j2 = 0, a corrente não estacionária é determinada apenas pela adsorção da espécie R-.CH-OH. Considerando esta hipótese e as isotermas de Temkin e Elovich foi obtida uma equação que descreve o grau de cobertura pela espécie R-.CH-OH, (&#952;1) em função do tempo. &#952;1 = - Qmáx B/k2t (1-A-B ln t) + k1/k2 onde Qmáx é a carga máxima de cobertura, k1 e k2 são as constantes de velocidade de adsorção das espécies R-.CH-OH e R-..C-OH, respectivamente, A e B são as constantes da equação de Elovich. A equação precedente permitiu determinar as constantes de velocidade de adsorção k1 e k2. A partir desses valores em diferentes temperaturas foram obtidas as energias de ativação para as reações (1) e (2). Verificou-se que os tempos de máxima cobertura por R.CHOH e de inflexão, obtidos respectivamente de &#952;1= f (log t) e j-1 = f(t), são comparáveis para dada temperatura e potencial. / The kinetics and mechanism of n-propanol adsorption on a platinized platinum electrode was studied in 1 N H2SO4 at several temperatures, by means of the potential pulse method. Between 0.30 V and 0.60 V (RHE), the adsorption occurs via a dehydrogenation of the &#945;-carbon, followed by a rapid ionization of the adsorbed hydrogen atoms. The kinetic isotherms obtained by integration of the chronoamperograms show a linear variation of the surface coverage, &#952;, with logarithm of the adsorption time, tads, in the range 0.25 &#8804; &#952; &#8804; 0.80. This indicates that the adsorption rate can be expressed in tems of an Elovich equation. It is shown that the relation Eads vs log Ii, where Eads is the adsorption potential and Ii is the maximum non-stationary current at t = 0, is a straight line with a slope equal to 2.3[2RT/F], independently of the temperature. These data show that the initial adsorption step envolves a monoelectronic charge transfer, and can be represented by the following equation: R-CH2-OH j1&#8594; R-.CH-OH + H+ + e- ( 1 ) Therefore, it is assumed that the adsorption occurs via a two step consecutive reaction, given by equations (1) and (2): R-.CH-OH j2&#8594; R-..C-OH + H+ + e- ( 2 ) with the two adsorbed species R-.CH-OH and R-..C-OH characterized by their degree of coverage &#952;1 and &#952;2, respect ively. The non-stationary anodic current, j, is then the sum of currents j1 and j2 resulting from reactions described by equations (1) and (2). When the adsorption time is very short, it can be assumed that j = j1 + j2 &#8776; j1, and that &#952; = &#952; 1 + &#952;2 &#8776; &#952;1. From those assumptions, the following equation relating &#952;1 with t was obtained: &#952;1 = -Qmáx . B/[k2.t (1-A-B). ln t ] + k1/k2 (3) where Qmáx is the charge related with the maximum surface coverage, k1 and k2 the apparent rate constants of reactions (1) and (2), respectively, and A and B are constants from the Elovich equation. Equation (3) permitted the evaluation of the rate constants k1 and k2 for distinct Eads values. From the data at different temperatures, the apparent activation energies of both reactions were calculated.

Transport of amorphous and semi-crystalline, oriented, annealed and non-annealed PET films has been studied using pure and mixed gas/vapor feeds to understand the influence of flavor molecules on the efficacy of the barrier material. Methanol has been used as the flavor molecule simulant, and pure methanol vapor sorption studies show swelling and relaxation effects in the polymer. Multi-component transport of O2/methanol and O2/CO¬2/methanol mixtures, performed at different activities of methanol, shows that vapor induced plasticization leads to increases in O2 and CO2 permeability. Annealed, semi-crystalline PET is shown to be most resistant to plasticization effects. It has been shown that the non-annealed film is less stable despite similar crystallinity as the annealed film due to the presence of orientation related stress in the material. Presence of crystals also restricts the chain motion, and helps suppress the plasticization effects. The results have been compared with the predictions of the dual mode model for multi-component mixtures. Plasticization effects at the high activities have been analyzed within the framework of the free volume theory. It has been proposed that only the densified domains of a glassy polymer be considered when evaluating fractional free volume change due to swelling in the polymer-penetrant system. The free volume parameter- BA has been evaluated for O2 and CO2 in PET and is found to be different from that for other high permeability polymers.

This report summarises the work done on monohydroxy aliphatic alcohol upgrading using Au/TiO2 catalysis. The catalysts were initially tested using a plug-flow CO oxidation reactor; complete conversion of a stream of CO flowing over the catalyst bed at a GHSV of approximately 79,500 hr-1 was typically achieved without any required external heating. TEM analysis showed that the freshly prepared catalyst does not contain detectable Aunano clusters, while the spent CO oxidation catalyst had clearly visible nanoparticles with an average size of approximately 1.6 nm. XRD analyses showed that the final pH to which the deposition-precipitation procedure was adjusted had a major role in determining the average nanocluster size. Alcohols were oxidised using the 1% Au/TiO2 catalyst in a plug-flow reactor, with the alcohol vapour being produced by sparging a blended stream of helium and oxygen (typically made up to a total flowrate of 100 ml min-1). The temperature of the alcohol could be adjusted, thereby controlling the vapour mole fraction of alcohol. For methanol oxidation, the primary reaction pathway across the entire range of studied feed compositions was combustion. The onset of combustion occurred dramatically, in the range of 140-160°C. For ethanol oxidation, acetaldehyde selectivity increases and overall conversion decreases as the oxygen content of the feed stream decreases. The kinetics of the catalysed ethanol oxidation showed a compensation effect, described by the equation ln(A) = 0.2032EA + 2.6102 (EA in kJ mol-1). Propanol oxidation demonstrated the highest selectivity towards a value added product (propanaldehyde), with propanaldehyde being formed in significant quantities. However, combustion was still favoured at high temperatures when large excesses oxygen were present. The thermokinetic data calculated for n-propanol oxidation did not exhibit the compensation effect observed in ethanol oxidation; the EA for this reaction was stable at approximately 38 kJ mol-1. In the anaerobic catalysed reactions of ethanol and n-propanol, an oily layer was collected above the water meniscus in a cold trap. This oil could potentially be formed via poly-aldol condensation reactions of the aldehydes produced during oxidation. Though other researchers suggest these condensation reactions typically end in a cyclic dehydration into aromatic compounds, electrospray mass spectrometry found no indication of such products. Control reactions performed using unloaded TiO2 and porous Au (obtained by in-situ reduction of Au2O3) produced different product distributions, all requiring substantially higher reaction temperatures. This suggests that there must be a synergistic effect between the Au and TiO2 substrate which facilitates reactions. Furthermore, the product distributions of the 1% Au/TiO2 catalysed reactions were significantly different from results published by other researchers performing similar oxidations on Au(111) single crystals, where substantially higher selectivity towards value-added products (formaldehyde, acetaldehyde, and propanaldehyde) is typically observed.