Luis M. Madeira

Catalytic oxidative dehydrogenation of n-butane

This review deals with the catalytic conversion of n-butane by oxidative dehydrogenation as an alternative process to direct dehydrogenation, making special reference to the catalytic systems used, kinetic studies performed and reaction mechanisms proposed. Particular attention is also focused on the hydrocarbon activation process and on the main factors governing catalytic efficiency. Finally, after some general conclusions, future trends are analyzed.

Treatment of textile effluent by chemical (Fenton's Reagent) and biological (sequencing batch reactor) oxidation.

The removal of organic compounds and colour from a synthetic effluent simulating a cotton dyeing wastewater was evaluated by using a combined process of Fentons Reagent oxidation and biological degradation in a sequencing batch reactor (SBR). The experimental design methodology was first applied to the chemical oxidation process in order to determine the values of temperature, ferrous ion concentration and hydrogen peroxide concentration that maximize dissolved organic carbon (DOC) and colour removals and increase the effluents biodegradability. Additional studies on the biological oxidation (SBR) of the raw and previously submitted to Fentons oxidation effluent had been performed during 15 cycles (i.e., up to steady-state conditions), each one with the duration of 11.5h; Fentons oxidation was performed either in conditions that maximize the colour removal or the increase in the biodegradability. The obtained results allowed concluding that the combination of the two treatment processes provides much better removals of DOC, BOD(5) and colour than the biological or chemical treatment alone. Moreover, the removal of organic matter in the integrated process is particularly effective when Fentons pre-oxidation is carried out under conditions that promote the maximum increase in wastewater biodegradability.

An overview of photocatalysis phenomena applied to NOx abatement.

This review provides a short introduction to photocatalysis technology in terms of the present environmental remediation paradigm and, in particular, NOx photoabatement. The fundamentals of photoelectrochemical devices and the photocatalysis phenomena are reviewed, highlighting the main reaction mechanisms. The critical historical developments on heterogeneous photocatalysis are briefly discussed, giving particular emphasis to the pioneer works in this field. The third part of this work focus mainly on NOx removal technology considering topics such as: TiO2 photochemistry; effect of the operating conditions on the photocatalysis process; Langmuir-Hinshelwood modeling; TiO2 photocatalytic immobilization approaches; and their applications. The last section of the paper presents the main conclusions and perspectives on the opportunities related to this technology.

Optimization of the azo dye Procion Red H-EXL degradation by Fenton's reagent using experimental design.

Chemical oxidation by Fentons reagent of a reactive azo dye (Procion Deep Red H-EXL gran) solution has been optimized making use of the experimental design methodology. The variables considered for the oxidative process optimization were the temperature and the initial concentrations of hydrogen peroxide and ferrous ion, for a dye concentration of 100mg/L at pH 3.5, the latter being fixed after some preliminary runs. Experiments were carried out according to a central composite design approach. The methodology employed allowed to evaluate and identify the effects and interactions of the considered variables with statistical meaning in the process response, i.e., in the total organic carbon (TOC) reduction after 120 min of reaction. A quadratic model with good adherence to the experimental data in the domain analysed was developed, which was used to plot the response surface curves and to perform process optimization. It was concluded that temperature and ferrous ion concentration are the only variables that affect TOC removal, and due to the cross-interactions, the effect of each variable depends on the value of the other one, thus affecting positively or negatively the process response.

Effect of alkali metal promoters on nickel molybdate catalysts and its relevance to the selective oxidation of butane

Abstract The role of alkali metal promoters (Li, Na, K, Cs) in the α and β phases of NiMoO4 for butane oxidative dehydrogenation (ODH) was studied. The catalysts were characterized by BET, ICP, X-ray fluorescence, AA, XRD, TG, DSC, IR, and XPS techniques. It was evidenced that the added alkali metals are deposited only on the catalyst surface and practically do not affect the bulk. An influence of the concentration and basicity of the promoters on the decrease of the catalyst surface area was observed. Reaction studies show that addition of promoters generally reduces the catalytic activity but the promoters induce a high selectivity to butenes and butadiene. The greater the basicity and the amount of promoter ion, the higher is the selectivity and this improvement arises largely by suppression of total oxidation. The combination of activity and selectivity effects leads to improvement of yields of C4 hydrocarbons by addition of small amounts of alkali promoters up to an optimum loading. Overdoping deteriorates yields, specially for β phases. The observed changes are understood by considering the physical and chemical effects related with the interaction of the alkali promoters with the catalyst. Basicity is shown to be fundamental to promote the selective ODH of butane in the NiO MoO3 system.

Nickel molybdate catalysts and their use in the selective oxidation of hydrocarbons

Abstract This paper reviews the preparation techniques, characterization, and use of nickel molybdate catalysts in the selective oxidation of hydrocarbons, particularly of light alkanes. Catalysts with different Ni:Mo ratios, unsupported and supported, undoped and doped, were considered. Particular attention is given to the thermal activation process for the transition of the low temperature α‐phase into the metastable β‐phase, which was shown to be more selective in some cases. Special reference is also made to the results of kinetic studies performed, to the mechanisms proposed for some important reactions, and to the nature of the active sites. Finally, after some general conclusions, future trends are analyzed.

Treatment of azo dye-containing wastewater by a Fenton-like process in a continuous packed-bed reactor filled with activated carbon

In this work, oxidation with a Fenton-like process of a dye solution was carried out in a packed-bed reactor. Activated carbon Norit RX 3 Extra was impregnated with ferrous sulfate and used as catalyst (7 wt.% of iron). The effect of the main operating conditions in the Chicago Sky Blue (CSB) degradation was analyzed. It was found that the increase in temperature leads to a higher removal of the dye and an increased mineralization. However, it also increases the iron leaching, but the values observed were below 0.4 ppm (thus, far below European Union limits). It was possible to reach, at steady-state, a dye conversion of 88%, with a total organic carbon (TOC) removal of ca. 47%, being the reactor operated at 50°C, pH 3, W(cat)/Q=4.1 g min mL(-1) (W(cat) is the mass of catalyst and Q the total feed flow rate) and a H(2)O(2) feed concentration of 2.25 mM (for a CSB feed concentration of 0.012 mM). The same performance was reached in three consecutive cycles.

Treatment of textile dye wastewaters using ferrous sulphate in a chemical coagulation/flocculation process

The coagulation/flocculation treatment using FeSO4·7H2O as a coagulant is evaluated in this work for the removal of organic compounds and colour from synthetic effluents simulating the cotton, acrylic and polyester dyeing wastewaters. The coagulant dose, temperature, pH, stirring speed and stirring time that maximized the removal of dissolved organic carbon (DOC) and colour for each effluent are determined for the coagulation process. The effect of the stirring speed, stirring time and the dose of flocculant (Magnafloc 155 or Superfloc C-573) on the flocculation stage is also evaluated for effluents pretreated by coagulation at the optimal conditions previously determined. The obtained results showed that the optimal operating conditions are different for each effluent, and the process (coagulation/flocculation) as a whole was efficient in terms of colour removal (∼91% for cotton, ∼94% for acrylic effluents; polyester effluent is practically colourless). However, the DOC removal observed is not significant (∼33% for polyester, ∼45% for cotton and ∼28% for acrylic effluents). On the other hand, the remaining dissolved iron content is appropriate for further integrating the treatment with an iron-catalysed Fenton process, thus reducing the consumption of chemicals in the overall treatment.

Photo-oxidation of NO using an exterior paint — Screening of various commercial titania in powder pressed and paint films

The present work aims to evaluate the photocatalytic activity of photo-TiO(2) from various producers (Evonik, Kemira, Kronos, Millennium, Sachtleben and Tayca), in the form of powder pressed films and upon incorporation in a water-based paint, for outdoor NO abatement. The photocatalytic activity of the different samples was evaluated in terms of NO conversion and selectivity towards nitrite and nitrate ions following approximately the ISO 22197-1:2007(E) standard. The highest yields obtained for powder pressed films were achieved with VLP7000 (0.70), followed by VLP7101 (0.55) and UVLP7500 (0.55), all from Kronos. On the other hand, when incorporated in paint films, the highest yields were obtained with PC500 and PC105 from Millennium and UV100 from Sachtleben (ca. 0.15). The paint matrix plays an important role on the photocatalytic activity. In particular, the time for steady state is one or two orders of magnitude higher when the photocatalysts are incorporated in paint films in relation to the powder pressed films. The paint films were activated following the procedure recommended by the above-mentioned standard. However, the photocatalytic activity of films incorporating P25 (Evonik) was displayed only when higher power radiation and higher humidity conditions were used. This allowed for similar levels of photocatalytic activity as the other paint films.

Reducibility of undoped and Cs-doped α-NiMoO4 catalysts : Kinetic effects in the oxidative dehydrogenation of n-butane

Abstract Temperature-programmed reduction (TPR) was used to study the reduction of undoped and doped α-NiMoO 4 with several Cs loads. The results contributed to clarify the mechanism of the nickel molybdate reduction by hydrogen. It was found that the reducibility of the catalysts, as inferred from the temperature of reduction onset, decreases with Cs load. The catalysts were tested for the oxidative dehydrogenation of n -butane and the activity followed the same trend recorded in the TPR experiments. It was possible to conclude that the catalytic activity is related to the reducibility of the sample while the selectivity is determined by the basicity of the surface. Kinetic studies over unpromoted and 3% Cs-promoted α-NiMoO 4 evidenced that Cs doping only affects the partial order with respect to butane, which increases for dehydrogenation products and decreases for CO and CO 2 . The partial order with respect to oxygen is almost unaffected. The kinetic results were discussed based on the basicity and reducibility of the catalysts.