Dans un contexte de forte demande en carburants, la diversification des charges pétrolières et la sévérité des normes actuelles sur les carburants conduisent à des modifications des unités industrielles de raffinage en vue de leur optimisation. L’approche proposée dans cette thèse consiste à améliorer la description des cinétiques des réactions d’hydrotraitement des gazoles pour pouvoir prédire les effets de changements de conditions opératoires et de charge dans un simulateur du procédé industriel. La cinétique a été étudiée pour 7 charges de compositions initiales différentes sur catalyseur commercial CoMo/Al2O3 pour des températures comprises entre 320°C et 380°C à 45MPa de pression. La méthodologie adoptée a permis de balayer une gamme de soufre final allant de 5000 ppm jusqu’à quelques ppm correspondant à l’HDS ultra-profonde. Un réacteur parfaitement agité continu (Mahoney-Robinson) a été utilisé pour mesurer les vitesses de réaction. Des techniques analytiques (Sulf UV, CPG-SCD, CPG-NCD, HPLC) ont été mises au point pour quantifier les espèces soufrées, azotées et aromatiques présentes dans les gazoles. L’influence de H2, H2S, des familles de réactivité a pu ainsi être observée. Un modèle cinétique de forme Langmuir-Hinshelwood à deux sites (voies hydrogénante et désulfuration directe) pour l’HDS des espèces soufrées individuelles a été établi. Il intègre 188 paramètres cinétiques pour 33 composés et a donné des résultats satisfaisants. L’H2S est le composé le plus inhibiteur pour la voie DDS et les composés di- et tri-aromatiques pour la voie d’hydrogénation. Enfin, un modèle pour l’HDA et l’HDN des différentes familles identifiées est également proposé. / In the context of a growing demand for fuel, the diversity of feedstocks and the severity of the actual specifications have led to major modifications in the industrial refinery processes for their optimization. The approach of this thesis consists in improve the kinetic descriptions of the hydrotreatment reactions of gas oils to predict the effects of operating conditions and gas oil nature changes in an industrial process simulator. The kinetic has been studied for 7 gas oils with different initial compositions over a CoMo/Al2O3 commercial catalyst for 320-380°C range of temperature and 45MPa total pressure. The methodology used in this work has permitted to cover a total sulfur range from 5000ppm to few ppm corresponding to the deep HDS. A continuous stirred tank reactor (Mahoney-Robinson) has been used to measure the reactions rates. Analytic technics (Sulf UV, CPG-SCD, CPG-NCD, HPLC) have been set to quantify the sulfur, nitrogen and aromatic species present in the gas oils. The influence of H2, H2S, individual sulfur species or reactivity groups of sulfur species, groups of aromatic and nitrogen compounds have been observed. A bi sites kinetic model (hydrogenation and direct desulfurization pathways) for the HDS of the individual sulfur species resulting from a Langmuir-Hinshelwood mechanism has been established with 188 parameters for 33 compounds and has given satisfying results. The H2S is the most inhibiting compound for the direct desulfurization and the di- and tri-aromatics for the hydrogenation. At last, a model for the HDA and HDN of the different identified families is presented as well.

This study investigated the effects of temperature and humidity on the photocatalytic oxidation of volatile organic compound (VOCs) over titanium dioxide. Benzene, methyl tert-butyl ether (MTBE), perchloroethylene (PCE), and toluene were selected to investigate the influences of temperature and humidity on photocatalytic conversion. Among these four VOCs, benzene and MTBE were selected for the investigation of reaction pathways and kinetics. This work employed a self-designed annular packed-bed photocatalytic reactor to determine the conversion and reaction rates during photocatalytic degradation of VOCs. Degussa P-25 TiO2 was used as the photocatalyst and a 15 W near-UV lamp (350 nm) served as the light source. Benzene conversions increased with temperature below 160 ºC, but decreased above 160 ºC. Moreover, the conversions of MTBE increased with temperature from 30 to 120 ºC, and the thermocatalytic reaction began above 120 ºC. The conversions of PCE decreased as the temperature increased from 120 to 200 ºC. Toluene conversions almost remained constant at 100~200 ºC. Based on the gas-solid catalytic reaction theory, raising the reaction temperature could promote the chemical reaction rate and reduce reactant adsorption on TiO2 surfaces. The overall reaction rate increased with temperature, indicating that the reduction of reactant adsorption did not affect the overall reaction, and thus the chemical reaction was the rate-limiting step. As the chemical reaction rate gradually increased and the reactant adsorption decreased with temperature, the rate-limiting step could shift from the chemical reaction to the reactant adsorption, while the overall reaction rate decreased with temperature. Additionally, the competitive adsorption between VOCs and water for the active sites on TiO2 resulted in VOCs influent concentration and humidity promoting or inhibiting the reaction rate. The mineralization of benzene and the selectivity of CO and CO2 were not obviously affected under various temperatures, humidities, and influent benzene concentrations. The benzene mineralization ratios ranged from 0.85 to 1.0, to which CO and CO2 contributed approximately 5~20% and 80~95%, respectively. Temperature and humidity variation did not influence the photocatalytic reaction pathway of benzene. Acetone (AC) and tert-butyl alcohol (TBA) were two major organic products for the photocatalysis of MTBE. The addition of water transferred the reaction pathway from producing AC to TBA, while the temperature increase transferred the reaction pathway from producing TBA to AC. A modified bimolecule Langmuir-Hinshelwood kinetic model was developed to simulate the temperature and humidity related promotion and inhibition of the photocatalysis of benzene and MTBE. The competitive adsorption of VOCs and water on the active sites resulted in VOCs influent concentration and humidity promoting or inhibiting the reaction. The reaction rate constant increased with temperature while the adsorption equilibrium constants decreased, confirming that increasing reaction temperature enhanced the chemical reaction, but reduced the adsorption of VOCs and water. Furthermore, the correlation developed here was also used for determining the apparent activation energy of photocatalytic oxidation of VOCs and the adsorption enthalpies of benzene, MTBE, water vapor, and oxygen.

Semiconductor photocatalysis has received considerable attention in recent years as an alternative for treating water polluted with hazardous organic chemicals. The process, as a means of removal of persistent water contaminants such as pesticides, which exhibit chemical stability and resistance to biodegradation, has attracted the attention of many researchers. To a lesser extent, it has also been studied for decontamination of water containing toxic metals. Precious and common metals enter waters through washing, rinsing, pickling and surface treatment procedures of industrial processes, such as hydrometallurgy, plating and photography. As a result we are living in an environment with a multitude of potentially harmful toxic metal ions. In contrast, the demand for metals increases significantly with the development and growth of industry. Even though research on the photocatalytic recovery of waste and noble metals has escalated in the past 10 years, the practical implementation of these processes is not yet justified. The successful implementation of large scale reactors, for industrial application, has to consider several reactor design parameters that must be optimised, such as reactor geometry and the utilization of radiated energy. In this study the effect of various parameters such as initial platinum(IV)chloride concentrations, initial sacrificial reducing agent (ethanol) concentrations, catalyst (TiO2) concentration, pH, temperature and light intensity has been investigated as a first step towards optimising a photocatalytic batch and photocatalytic flow reactor. Langmuir–Hinshelwood kinetics has been applied to calculate the photocatalytic rate constant kr as well as the adsorption equilibrium constant Ke for both the initial platinum(IV) dependency as well as the initial ethanol concentration dependency. The results in this study may be used in future work for the optimisation and comparison of both batch and flow reactors towards the industrial implementation of these processes. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

Semiconductor photocatalysis has received considerable attention in recent years as an alternative for treating water polluted with hazardous organic chemicals. The process, as a means of removal of persistent water contaminants such as pesticides, which exhibit chemical stability and resistance to biodegradation, has attracted the attention of many researchers. To a lesser extent, it has also been studied for decontamination of water containing toxic metals. Precious and common metals enter waters through washing, rinsing, pickling and surface treatment procedures of industrial processes, such as hydrometallurgy, plating and photography. As a result we are living in an environment with a multitude of potentially harmful toxic metal ions. In contrast, the demand for metals increases significantly with the development and growth of industry. Even though research on the photocatalytic recovery of waste and noble metals has escalated in the past 10 years, the practical implementation of these processes is not yet justified. The successful implementation of large scale reactors, for industrial application, has to consider several reactor design parameters that must be optimised, such as reactor geometry and the utilization of radiated energy. In this study the effect of various parameters such as initial platinum(IV)chloride concentrations, initial sacrificial reducing agent (ethanol) concentrations, catalyst (TiO2) concentration, pH, temperature and light intensity has been investigated as a first step towards optimising a photocatalytic batch and photocatalytic flow reactor. Langmuir–Hinshelwood kinetics has been applied to calculate the photocatalytic rate constant kr as well as the adsorption equilibrium constant Ke for both the initial platinum(IV) dependency as well as the initial ethanol concentration dependency. The results in this study may be used in future work for the optimisation and comparison of both batch and flow reactors towards the industrial implementation of these processes. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

L'objectif général du travail de recherche était l'amélioration de la compréhension de la réaction de dégradation photocatalytique de l’acide salicylique choisi comme polluant modèle. Un réacteur ouvert ayant un canal parallélépipédique, de largeur et de profondeur de l'ordre du millimètre, imprégné de catalyseur TiO₂ , a permis de caractériser la dégradation de l’acide salicylique en fonction des dimensions du canal, du débit, de la concentration en polluant et de l’intensité d'irradiation UV. La fraction dégradée d’acide salicylique diminue avec le débit, la concentration d’entrée et augmente avec l’intensité d’irradiation UV. Pour un temps de passage donné, la réduction de la profondeur et la largeur du microcanal, améliore l’efficacité de la dégradation. En effet, d'une manière générale, la vitesse de la réaction de dégradation est proportionnelle à la surface catalytique sur le volume réactionnel. Le rapport de la surface imprégnée sur le volume du microcanal est augmenté par la miniaturisation du canal ce qui entraine une meilleure dégradation. Un modèle basé sur le modèle de Langmuir-Hinshelwood et tenant compte du transfert de matière permet de rendre compte des résultats expérimentaux. Ce modèle met en évidence que la limitation de la réaction de dégradation par le transfert de matière est plus importante aux plus faibles débits (< 10 ml/h) et quand le canal devient plus profond. La simulation prédit des taux de conversion de l’ordre de 90 %, soit en agissant sur la géométrie (réacteur multicanaux, longueur totale des canaux de l’ordre du mètre), soit sur le procédé (réacteur à recyclage fermé) / The overall objective of the research work was to improve the understanding of the photocatalytic reaction of salicylic acid degradation chosen as model pollutant. An open reactor having a parallelepiped channel, of width and depth near millimetre size, coated with TiO₂ catalyst, was used to characterize the salicylic acid degradation in function of channel dimensions, flow rates, inlet pollutant concentrations and UV irradiation intensities. The degraded fraction of salicylic acid decreases with the flow rate, inlet concentration while it increases with UV irradiation intensity. For a given residence time, the reduction of the microchannel depth and width improve the degradation efficiency. Indeed, the reaction rate of degradation generally increases with the ratio of catalyst area on reaction volume. The ratio of coated area on microchannel volume is increased by miniaturization of the channel which leads to a larger degradation. A model based on the Langmuir-Hinshelwood approach which takes into account the mass-transfer account very well for the experimental results. This model highlights that reaction limitation by mass-transfer is larger at the lowest flows (< 10 mL/h) and when the channel becomes deeper. The simulation allows us to predict that conversion ratio of about 90%, can be reach by both acting on the geometry (multichannel reactor, total length of channels of the order of meter) or on the process (batch recirculation reactor)

O presente trabalho apresenta um estudo sistemático sobre a adsorção e a eletrooxidação do CO sobre eletrodos monocristalinos de platina. A partir da análise das intensidades das bandas integradas e das freqüências do Pt(111)-CO, apresenta-se uma interpretação dos efeitos de acoplamento dipolo-dipolo e de interconversão do COads.. Assim, sobre a Pt(111) os espectros de FTIR in situ mostram que o aumento na razão da intensidade das bandas integradas ACOB/ACOL e nas freqüências do &nu;COB quando &theta;CO,total diminue é devido à redução do acoplamento dipolo-dipolo entre as moléculas do CO em diferentes sítios e, adicionalmente, à interconversão das formas inclinadas dos COL e COB para a forma do COB. No sentido de explicar esta interconversão, propomos um mechanism baseado nas interações dos orbitais de fronteiras do CO e do metal, associado com a retrodoação de elétrons. Nesse modelo, os deslocamentos das formas inclinadas do COL e do COB em direção à forma do COB são favoráveis provavelmente porque a retrodoação de elétrons, Ptd &rarr; CO2&pi;* (LUMO), aumenta quando &theta;CO,total diminui. Experimentos potenciostáticos sugerem que a cinética de nucleação e crescimento é o melhor modelo para descrever a eletrooxidação do CO. Propomos que no potencial de oxidação, ECO oxi. pode existir uma via muito rápida de formação do precursores oxigenados e que este pode lateralmente colidir com as ilhas de CO, impedindo que ocorra a dissipação das ilhas do COads. no potencial de oxidação, ECO oxi.. Apresentamos a evolução do crescimento e da oxidação de sub-monocamada de CO sobre monocristais de platina facetados. Em baixo grau de recobrimento do CO foi observado que a adsorção dessa molécula ocorre sem ocupação preferencial de sítios quinas ou terraças. Assim, sugerimos que a adsorção é um processo randômico e que depois que as moléculas do CO são adsorvidas estas não apresentam apreciáveis deslocamentos a partir de CO-(111) em direção aos sítios CO-(110). Isto significa que depois da adsorção, as moléculas do CO têm um longo tempo de residência ou que apresentam um coeficiente de difusão muito baixo. Mas, para alto grau de recobrimento por CO, os resultados mostram que é possível que laterais interações desempanham importantes papéis na distribuição de ocupação dos sítios e observamos que durante a eletrooxidação, são liberados simultaneamente sítios quinas e sítios terraços. Quanto à pré-oxidação, foi observado que quatro condições experimentais precisam ser satisfeitas para que ela ocorra sobre os monocristais de platina: (i) alto grau de recobrimento por CO; (ii) que a superfície onde oncorre a oxidação do CO tenha defeitos, como sítios quinas (110); (iii) que a camada do CO seja formada sob potenciais mais negativos do que o potencial de carga total zero do metal; (iv) e que exista pequena quantidade de CO dissolvido. As condições (i) e (ii) precisam ser satisfeitas simultaneamente para promover a pré-oxidação do CO; as condições (iii) e (iv) essencialmente contribuem correspondendo à condição (i). Observamos que a magnitude do pre-pico aumenta com o aumento do grau de recobrimento por CO. Então, isto pode ser indicativo que a pré-oxidação não tem relação com a difusão do CO em superfície porque o aumento do grau de recobrimento reduz a probabilidade de difusão em superfície. O modelo de ilhas comprimidas parece ser mais apropriado para descrever a pré-oxidação do CO. / This work presents a systematic study on the CO adsorption and its oxidation at platinum single crystal electrodes. From analysis of integrated band intensity and band frequency position of the Pt(111)-CO interface in acid, it is presented an interpretation of the dipole-dipole coupling effect and surface site inter-conversions of COads.. Thus, on Pt(111), in situ FTIR data show that the increase in both ratio integrated band intensity ACOB/ACOL and frequency of &nu;COB when &theta;CO,total reduces it is indicative of reduce in dipole-dipole coupling interactions between CO molecules in different surface active sites and a mechanism where the tilted COL and COB in CO pressed adlayer displace or inter-convert in favor of increase of COB concentration. In order to explain that CO interconversion, we propose a mechanism based in frontier molecular orbitals of CO and the orbitals of the metal associated with the electron back bond donation. Thus, the displacement of tilted COL and COB on the surface towards COB is more stable because probably the back bond electron donation, Ptd &rarr; CO2&pi;* (LUMO), increase when &theta;CO,total diminishes. Potentiostatic experiments suggest that the nucleation and growth is the better model to describe the CO oxidation. It is proposed here that close to ECO oxi. might there is a fast pathway toward formation of oxygenated species and it might reach the CO islands by side and this hinder the dissipation of COads. islands at ECO oxi.. We report also time evolution studies of low CO adsorption coverage and oxidative stripping on stepped platinum surfaces. In low CO coverage, it was observed that there is no preferential site occupancy for CO adsorption on step or terrace. It is proposed that CO adsorption onto these surfaces is a random process, and after CO adsorption there is no appreciable shift from CO-(111) to CO-(110) sites. This implies that after adsorption, CO molecules either have a very long residence time, or that the diffusion coefficient is much lower than previously thought. But, in high CO coverage, the results show that it is possible that the lateral interaction might play important role in CO site occupancy and it was observed that during the CO electrooxidation the sites released included both terrace (111) and step (110) orientations. Among the CO oxidation a clear CO preoxidation process also occurs. It was observed four experimental conditions which were verified to be fulfilled to promote CO pre-oxidation on platinum single crystal: (i) the CO coverage is should be higher than minimum threshold; (ii) the surface where CO oxidation take place should have defects, such as (110) steps; (ii) the CO monolayer should be formed at potentials below the potential of zero total charge; (iv) and in a small amount of dissolved CO should be present in the electrolyte solution. In both conditions (i) and (ii) are necessary to take place simultaneously to promote CO pre-oxidation, (iii) and (iv) essentially contribute in fulfilling condition (i). It was verified that the magnitude of pre-peak increases with the amount of CO coverage. Thus, this might indicate that the CO pre-oxidation is not having relationship with the CO diffusion on the surface, because the increase of CO coverage diminishes surface diffusion. A picture model of compressed CO islands seems the most to describe CO pre-oxidation.

O presente trabalho apresenta um estudo sistemático sobre a adsorção e a eletrooxidação do CO sobre eletrodos monocristalinos de platina. A partir da análise das intensidades das bandas integradas e das freqüências do Pt(111)-CO, apresenta-se uma interpretação dos efeitos de acoplamento dipolo-dipolo e de interconversão do COads.. Assim, sobre a Pt(111) os espectros de FTIR in situ mostram que o aumento na razão da intensidade das bandas integradas ACOB/ACOL e nas freqüências do &nu;COB quando &theta;CO,total diminue é devido à redução do acoplamento dipolo-dipolo entre as moléculas do CO em diferentes sítios e, adicionalmente, à interconversão das formas inclinadas dos COL e COB para a forma do COB. No sentido de explicar esta interconversão, propomos um mechanism baseado nas interações dos orbitais de fronteiras do CO e do metal, associado com a retrodoação de elétrons. Nesse modelo, os deslocamentos das formas inclinadas do COL e do COB em direção à forma do COB são favoráveis provavelmente porque a retrodoação de elétrons, Ptd &rarr; CO2&pi;* (LUMO), aumenta quando &theta;CO,total diminui. Experimentos potenciostáticos sugerem que a cinética de nucleação e crescimento é o melhor modelo para descrever a eletrooxidação do CO. Propomos que no potencial de oxidação, ECO oxi. pode existir uma via muito rápida de formação do precursores oxigenados e que este pode lateralmente colidir com as ilhas de CO, impedindo que ocorra a dissipação das ilhas do COads. no potencial de oxidação, ECO oxi.. Apresentamos a evolução do crescimento e da oxidação de sub-monocamada de CO sobre monocristais de platina facetados. Em baixo grau de recobrimento do CO foi observado que a adsorção dessa molécula ocorre sem ocupação preferencial de sítios quinas ou terraças. Assim, sugerimos que a adsorção é um processo randômico e que depois que as moléculas do CO são adsorvidas estas não apresentam apreciáveis deslocamentos a partir de CO-(111) em direção aos sítios CO-(110). Isto significa que depois da adsorção, as moléculas do CO têm um longo tempo de residência ou que apresentam um coeficiente de difusão muito baixo. Mas, para alto grau de recobrimento por CO, os resultados mostram que é possível que laterais interações desempanham importantes papéis na distribuição de ocupação dos sítios e observamos que durante a eletrooxidação, são liberados simultaneamente sítios quinas e sítios terraços. Quanto à pré-oxidação, foi observado que quatro condições experimentais precisam ser satisfeitas para que ela ocorra sobre os monocristais de platina: (i) alto grau de recobrimento por CO; (ii) que a superfície onde oncorre a oxidação do CO tenha defeitos, como sítios quinas (110); (iii) que a camada do CO seja formada sob potenciais mais negativos do que o potencial de carga total zero do metal; (iv) e que exista pequena quantidade de CO dissolvido. As condições (i) e (ii) precisam ser satisfeitas simultaneamente para promover a pré-oxidação do CO; as condições (iii) e (iv) essencialmente contribuem correspondendo à condição (i). Observamos que a magnitude do pre-pico aumenta com o aumento do grau de recobrimento por CO. Então, isto pode ser indicativo que a pré-oxidação não tem relação com a difusão do CO em superfície porque o aumento do grau de recobrimento reduz a probabilidade de difusão em superfície. O modelo de ilhas comprimidas parece ser mais apropriado para descrever a pré-oxidação do CO. / This work presents a systematic study on the CO adsorption and its oxidation at platinum single crystal electrodes. From analysis of integrated band intensity and band frequency position of the Pt(111)-CO interface in acid, it is presented an interpretation of the dipole-dipole coupling effect and surface site inter-conversions of COads.. Thus, on Pt(111), in situ FTIR data show that the increase in both ratio integrated band intensity ACOB/ACOL and frequency of &nu;COB when &theta;CO,total reduces it is indicative of reduce in dipole-dipole coupling interactions between CO molecules in different surface active sites and a mechanism where the tilted COL and COB in CO pressed adlayer displace or inter-convert in favor of increase of COB concentration. In order to explain that CO interconversion, we propose a mechanism based in frontier molecular orbitals of CO and the orbitals of the metal associated with the electron back bond donation. Thus, the displacement of tilted COL and COB on the surface towards COB is more stable because probably the back bond electron donation, Ptd &rarr; CO2&pi;* (LUMO), increase when &theta;CO,total diminishes. Potentiostatic experiments suggest that the nucleation and growth is the better model to describe the CO oxidation. It is proposed here that close to ECO oxi. might there is a fast pathway toward formation of oxygenated species and it might reach the CO islands by side and this hinder the dissipation of COads. islands at ECO oxi.. We report also time evolution studies of low CO adsorption coverage and oxidative stripping on stepped platinum surfaces. In low CO coverage, it was observed that there is no preferential site occupancy for CO adsorption on step or terrace. It is proposed that CO adsorption onto these surfaces is a random process, and after CO adsorption there is no appreciable shift from CO-(111) to CO-(110) sites. This implies that after adsorption, CO molecules either have a very long residence time, or that the diffusion coefficient is much lower than previously thought. But, in high CO coverage, the results show that it is possible that the lateral interaction might play important role in CO site occupancy and it was observed that during the CO electrooxidation the sites released included both terrace (111) and step (110) orientations. Among the CO oxidation a clear CO preoxidation process also occurs. It was observed four experimental conditions which were verified to be fulfilled to promote CO pre-oxidation on platinum single crystal: (i) the CO coverage is should be higher than minimum threshold; (ii) the surface where CO oxidation take place should have defects, such as (110) steps; (ii) the CO monolayer should be formed at potentials below the potential of zero total charge; (iv) and in a small amount of dissolved CO should be present in the electrolyte solution. In both conditions (i) and (ii) are necessary to take place simultaneously to promote CO pre-oxidation, (iii) and (iv) essentially contribute in fulfilling condition (i). It was verified that the magnitude of pre-peak increases with the amount of CO coverage. Thus, this might indicate that the CO pre-oxidation is not having relationship with the CO diffusion on the surface, because the increase of CO coverage diminishes surface diffusion. A picture model of compressed CO islands seems the most to describe CO pre-oxidation.

Ce travail a pour objet d’améliorer les performances d’un réacteur photocatalytique tubulaire de traitement des COVs, en le garnissant avec des supports structurés et imprégnés de TiO2. Grâce à un montage adapté, l’efficacité du réacteur est suivie en mesurant le taux de conversion du méthanol, choisi comme polluant modèle. Différentes géométries de support catalytique ont été fabriquées par stéréolithographie. Parmi toutes les géométries testées, la structure alvéolaire, constituée de canaux verticaux pour le passage du fluide et de canaux horizontaux pour le passage de la lumière, permet une efficacité optimale du réacteur. La modélisation du réacteur, tenant compte de la distribution de la lumière dans le support, montre que le transfert de matière est limitant lorsque le diamètre des canaux est plus petit que 4 mm. En revanche, lorsque le diamètre des canaux est supérieur à 5 mm, le manque d'efficacité est dû à une diminution de l'absorption de la lumière incidente. / The aim of the work is to improve the efficiency of a photocatalytic tubular reactor for VOCs abatement, while loading it with structured catalytic supports impregnated of TiO2.Thanks to a photocatalytic set-up , the efficiency of the reactor is followed by measuring the conversion rate of a model pollutant: methanol. Different geometries of support have been made by stereolithography. Among all tested geometries, the alveolar structure, composed of vertical channels for light penetration, and horizontal channels for the circulation of the gas flow, leads to an optimal degradation of the pollutant. The modelling of the reactor, taking into account the light distribution, shows that the mass transfer is limiting when the diameter of the channels is smaller than 4 mm. On the other hand, when the diameter of the channels is bigger than 5 mm, the lack of efficiency is due to a reduction of the absorption of the incident light by the catalytic surface.

La formation de H2 dans le milieu interstellaire, à partir de deux atomes H, est une question essentielle en astrophysique. Cette réaction exothermique qui a lieu à la surface d'un grain de poussière interstellaire est la première étape d'une suite de réactions primordiales pour la physico-chimie. Dans les nuages diffus et les régions de photodissociation, on invoque pour mécanisme de formation une réaction de catalyse hétérogène Eley Rideal, un des atomes étant chimisorbé. Les grains sont principalement carbonés et constitués notamment de graphite. Les travaux théoriques antérieurs effectués en géométrie réduite n'ont pas permis d'expliquer la formation de H2 dans les états rovibrationnels observés (v<5). Pour prendre en compte les degrés de liberté de tous les atomes, nous avons conçu à partir du potentiel de Brenner, un nouveau potentiel pour modéliser le système graphène-H-H avec lequel nous avons réalisé une étude de dynamique moléculaire classique de la formation de H2. Cette étude a été effectuée pour des énergies de collision d'atomes H incidents de 0.015eV à 0.2eV et pour des surfaces à 0, 10 et 30K. Un des résultats principaux est que la section efficace de réaction est directement reliée à l'allure du potentiel que voit l'atome H incident. De plus, il a été mis en évidence que la distribution rovibrationnelle obtenue en autorisant la relaxation de la surface correspond mieux à celle observée par les astrophysiciens (v < 6), la surface absorbant ~25% de l'énergie disponible. Des travaux étudiant l'influence de la présence d'un atome H supplémentaire sur la surface ou d'une possible structure poreuse des grains, sur la formation de H2, sont présentés en annexe.

The study combined photoelectrocatalytic technology (PEC) with electrical glassfiber filter (EGF) to decompose volatile organic compounds (VOCs). External electrical voltage was applied to retard the recombination of electron-electron hole pairs and increase the surface temperature of the photocatalysts coated on the electrical glassfiber filter, which could further decompose VOCs more effectively via photoelectrocatalytic technology. Acetone was selected as the gasous pollutant for this particular study. A commercial TiO2 photocatalyst (AG-160) was coated on GFF via impregnation to decompose acetone in a batch PEC reactor. Operation parameters investigated in this study included acetone concentration (50~400 ppm), electrical voltage (0~6,500V), water content (0~20,000 ppm), reaction temperature (40¢J~80¢J).The incident UV light of 365 nm wavelength was irradiated by three 15-wat low pressure mercury lamps (£f=365 nm) placing above the batch PEC reactor. The TiO2-coated EGF was placed at the center of the batch PEC reactor. Acetone was injected into the reactor by a gasket syringe to conduct the PEC decomposition test. Acetone was analyzed quantitatively by a gas chromatography with a flame ionization detector (GC/FID). Finally, a Langmuir-Hinshelwood kinetic (L-H) model was proposed to simulate the PEC reaction rate of acetone. Experimental results showed that the size range of the self-produced nano-sized photocatalyst prepared by sol-gel was 35~50 nm. Three duplicate tests of PC and PEC degradation of acetone indicated that TiO2 was not deactivated during the PC and PCE reactions, hence TiO2 can be reused in the experiments. Results obtained from the PC and PEC degradation experiments indicated that the PEC reaction rate was higher than the PC reaction rate.The PEC reaction rate increased with applied electrical voltage, and the highest decomposition efficiency occurred at 6,500 V. Electrical field generated by the differences of electrical voltage can effectively enhance the oxidation capability of TiO2 since electron (e-) can be conducted to retard the recombination of electron and electron hole pairs. Both PC and PEC technologies could be used to decompose acetone. Among them, PEC had highter decomposition efficiency of acetone than PC up to 34%. Rsults obtained from the operation parameter tests reaveled that raising electrical voltage could enhance the decomposition efficiency of acetone only for electrical voltages above 2,000 V. However, the decomposition efficiency of acetone tended to level off as electrical voltage became higher. Zero-order reaction rate of the PEC reaction was observed for initial acetone concentration of 100~400 ppm, while the PEC reaction decreased gradually for initial acetone concentration reaction below 100 ppm. It revealed that the PEC reaction was pseudo ozero-order for initial acetone concentration of 100~400 ppm, and pseudo first-order reaction for acetone concentration below 100 ppm. Additionally, the PC reaction rate increased with temperature at 45-80¢J. However the PEC reaction rate increased with temperature at 45-60¢J, and decreased with temperature at 60-80¢J. An adsorptive competition between acetone and water molecules at the active sites over TiO2 surface caused either promotion or inhibition of TiO2 decomposition depending on moisture content . For the PC and PEC reactions, the optimum operating condition of water vapor concentration was 10,000 ppm, but inhibition occurred when the water vapor concentration increased up to 20,000 ppm. Finally, the Langmuir-Hinshelwood kinetic model was applied to investiage the influences of reaction temperature, initial concentration of acetone, and water content on the photoelectrocatalytic reaction rate of acetone. Model simulation results showed that photoelectrocatalytic reaction rate constant of acetone(kLH) and adsorptive equilibrium constant(KA) increased with electrical voltage and acetone initial concentration. This study sevealed that experimental and simulated results were in good agreement. Thus, PEC reaction rate of acetone on the surface of TiO2 can be also succesfully simulated by the L-H kinetic model.