Yttrium-modified Co3O4 as efficient catalysts for toluene and propane combustion: Effect of yttrium content.

A series of Y-modified cobalt oxides with various Y/(Co+Y) molar ratios (0.25 %, 0.5 %, 1 %, 3 % and 5 %) were prepared to study the effect of Y content on toluene and propane combustion. The characterization of the catalysts revealed that proper Y incorporation resulted in smaller crystallite sizes, larger specific surface areas, more oxygen vacancies and weaker Co-O bonds. As such, the Y-modified Co3O4 showed enhanced low-temperature reducibility, boosted oxygen mobility and better catalytic activity. However, excess Y (> 1 %) aggregates on the surface of Co3O4 and forms yttrium carbonate species, hindering the catalyst activity. A volcano-type relationship between the Y content and the catalytic activity was established. The optimal catalyst 1 % Y-Co (with Y/(Co+Y) molar ratio of 1 %) exhibited toluene oxidation rate of 24 nmol g-1 s-1 at 220 °C and propane oxidation rate of 69 nmol g-1 s-1 at 180 °C. Besides, 1 % Y-Co presented perfect cycling stability and long-term durability in propane oxidation. Regarding its low cost, high efficiency and good stability, 1 % Y-Co is a promising catalyst for the practical elimination of hydrocarbon emissions.

Static and dynamic adsorption studies of PolyChloroBiphenyls (PCBs) over activated carbons.

Since PolyChloroBiphenyls (PCBs) have been extensively used in the past century, they are frequently detected in surface water and ground water. Due to their poor solubility, extremely low concentrations are observed in water. However, PCBs were demonstrated more recently to be highly toxic and need to be eliminated. The adsorption rapidly appeared as a key technology for their efficient and economical removal from water. In this study, activated carbons were shown to be highly efficient in the adsorption of 2-PCB under static conditions, i.e. at long contact time (several hours) when the adsorption-desorption equilibrium was reached. Under such conditions, the main key parameter was shown to be the activated carbon texture (specific surface area, porosity). Moreover, the main driving force was identified to be the combination between the very limited solubility of 2-PCB in pure water and the hydrophobic nature of the activated carbon. In turn, under dynamic conditions, i.e. at short contact time (less than 5 s), the overall adsorption process was shown to be quite inefficient and unambiguously controlled by internal surface diffusion limitations. In this later case, the operating parameters, especially the activated carbon bed morphology, played a major role.

Catalytic wet air oxidation of 2-chlorophenol over sewage sludge-derived carbon-based catalysts.

A sewage sludge derived carbon-supported iron oxide catalyst (FeSC) was prepared and used in the Catalytic Wet Air Oxidation (CWAO) of 2-chlorophenol (2-CP). The catalysts were characterized in terms of elemental composition, surface area, pHPZC, XRD and SEM. The performances of the FeSC catalyst in the CWAO of 2-CP was assessed in a batch reactor operated at 120°C under 0.9MPa oxygen partial pressure. Complete decomposition of 2-CP was achieved within 5h and 90% Total Organic Carbon (TOC) was removed after 24h of reaction. Quite a straight correlation was observed between the 2-CP conversion, the amount of iron leached in solution and the pH of the reaction mixture at a given reaction time, indicating a strong predominance of the homogeneous catalysis contribution. The iron leaching could be efficiently prevented when the pH of the solution was maintained at values higher than 4.5, while the catalytic activity was only slightly reduced. Upon four successive batch CWAO experiments, using the same FeSC catalyst recovered by filtration after pH adjustment, only a very minor catalyst deactivation was observed. Finally, based on all the identified intermediates, a simplified reaction pathway was proposed for the CWAO of 2-CP over the FeSC catalyst.

Catalytic wet air oxidation of chlorophenols over supported ruthenium catalysts.

A series of noble metal (Pt, Pd, Ru) loaded zirconia catalysts were evaluated in the catalytic wet air oxidation (CWAO) of mono-chlorophenols (2-CP, 3-CP, 4-CP) under relatively mild reaction conditions. Among the investigated noble metals, Ru appeared to be the best to promote the CWAO of CPs as far as incipient-wetness impregnation was used to prepare all the catalysts. The position of the chlorine substitution on the aromatic ring was also shown to have a significant effect on the CP reactivity in the CWAO over 3wt.% Ru/ZrO(2). 2-CP was relatively easier to degradate compared to 3-CP and 4-CP. One reason could be the higher adsorption of 2-CP on the catalyst surface. Further investigations suggested that 3wt.% Ru/ZrO(2) is a very efficient catalyst in the CWAO of 2-CP as far as high 2-CP conversion and TOC abatement could still be reached at even lower temperature (393K) and lower total pressure (3MPa). Additionally, the conversion of 2-CP was demonstrated to increase with the initial pH of the 2-CP solution. The dechlorination reaction is promoted at higher pH. In all cases, the adsorption of the reactants and the reaction intermediates was shown to play a major role. All parameters that would control the molecule speciation in solution or the catalyst surface properties would have a key effect.