Maria do Carmo Rangel

An environmental friendly dopant for the high-temperature shift catalysts

Abstract The high-temperature shift (HTS) reaction is an important step in industrial processes and gas purification. Although the catalyst shows a stable performance, the search for non-toxic systems is much needed, especially due to environmental restrictions related to chromium compounds. In this work, the performance of aluminum-doped catalysts with low amounts of copper was investigated, because of the role of copper on decreasing the surface area of the catalysts based on iron oxides. Samples were prepared by precipitation methods, characterized by several techniques and evaluated under different conditions, in order to find operational conditions more effective in the use of energy. The addition of small amounts of copper to aluminum-doped hematite leads to better catalytic properties. Likely, copper behaves as a structural promoter while aluminum is a textural one. The catalyst can work at more severe conditions than the industrial condition, that is, lower steam to gas molar ratio (S/G=0.4) and at a lower temperature (350°C). In addition, it can be easily handled and discarded without any damage to the environment or human beings.

A thorium-doped catalyst for the high temperature shift reaction

The reforming of natural gas feedstock in the presence of steam is the main industrial route to produce high purity hydrogen. However, this process also produces carbon oxides which can poison most hydrogenation catalysts as well as ammonia catalysts. In industrial processes, these compounds are often removed from the gaseous stream by the water gas shift reaction (WGSR), which is performed in two steps due to thermodynamics and kinetics considerations. A chromium and copper-doped hematite has been recently proposed as an industrial catalyst in the high temperature shift (HTS). This solid shows a stable performance but the search for non-toxic systems is much needed due to environmental restrictions related to chromium compounds. In this work, the use of thorium instead of chromium in iron- and copper-based catalysts for the HTS reaction was investigated. Catalysts were prepared in the active form (magnetite) in order to save energy, characterized by several techniques and then evaluated in operational conditions close to the industrial ones. It was found that thorium can replace chromium in these catalysts leading to better catalytic properties as compared to chromium. The catalyst has the advantage of being less toxic and can be prepared in the active phase.

Processos avançados de oxidação de compostos fenólicos em efluentes industriais

In an effort to minimize the impact on the environment, removal of pollutants, such as phenolic compounds, from the industrial wastewater has great importance nowadays because of the high toxicity and low biodegradability of these compounds. This work discusses the different methods to remove these compounds from industrial wastewater, showing their advantages and disadvantages. Advanced Oxidation Process (AOPs) are presented as a promising technology for the treatment of wastewater containing phenolic compounds. Among the AOPs, photolysis, photocatalysis and the processes based on hydrogen peroxide and on ozone are discussed with emphasis on the combined processes and the oxidation mechanisms.

Chromium and Copper-Doped Magnetite Catalysts for the High Temperature Shift Reaction

Copper and chromium-doped magnetite was prepared to be used as catalysts, in the active phase, in the high temperature shift (HTS) reaction. Samples were produced by heating a mixed hydrate ferric oxyhydroxide (IHA) in the range of 150-400 °C and characterized by means of chemical analysis, X-ray diffraction, thermal analysis (DSC and TG), infrared spectroscopy, surface area measurements, scanning electron microscopy and X-ray microanalysis. It was found that copper favors magnetite formation but does not affect significantly the crystallinity of the solids. Both chromium and copper improve the performance of the catalysts towards the HTS reaction: chromium acts as a stabilizer whereas copper increases the intrinsic activity. However, copper favors sinterization leading to solids with low surface areas. The increase in the catalytic activity and in the surface area of the solids reflects the synergy of these dopants.

n‐octane reforming over alumina‐supported Pt, Pt–Sn and Pt–W catalysts

Pt, Pt–Sn and Pt–W supported on γ‐Al2O3 were prepared and characterized by H2 chemisorption, TEM, TPR, test reactions of n‐C8 reforming (500°C), cyclohexane dehydrogenation (315°C) and n‐C5 isomerization (500°C), and TPO of the used catalysts. Pt is completely reduced to Pt0, but only a small fraction of Sn and of W oxides are reduced to metal. The second element decreases the metallic properties of Pt (H2 chemisorption and dehydrogenation activity) but increases dehydrocyclization and stability. In spite of the large decrease in dehydrogenation activity of Pt in the bimetallics, the metallic function is not the controlling function of the bifunctional mechanisms of dehydrocyclization. Pt–Sn/Al2O3 is the best catalyst with the highest acid to metallic functions ratio (due to its lower metallic activity) presenting a xylenes distribution different from the other catalysts. The acid function of Pt–Sn/Al2O3 is tuned in order to increase isomerization and cyclization and to decrease cracking, as compared to Pt and Pt–W.

Effect of chromium on magnetite formation

Chromium-doped magnetite is the traditional catalyst used in the high temperature shift reaction in industrial processes. This work reports a method for preparing this solid, by heating chromium-doped iron(III)hydroxoacetates (IHA), prepared both by coprecipitation and by impregnation. This method provides the production of the catalyst in its active form avoiding the step of activation in industrial processes. It was noted that the presence of chromium affects magnetite formation as well as its characteristics. IHA containing chromium produces magnetite at higher temperature than does the pure IHA. Chromium-doped magnetites have higher surface areas, are less crystalline, have lower Fe(II)/Fe(III) ratios and are catalysts more active than those obtained from plain IHA. These effects depend on the preparation method of the precursor. It was also found that the impregnated sample is made of aggregates of a few crystals whereas the coprecipitate is made of smaller polycrystalline particles. In addition, the coprecipitation method leads to a more even distribution of chromium in solids. These observations are consistent with the best performance shown by the catalyst prepared by coprecipitation.

Effect of cobalt on the activity of iron-based catalysts in water gas shift reaction

The water gas shift reaction (WGSR) is an important step in the commercial prodution of high pure hydrogen for several applications. In order to find alternative catalysts to this reaction, the effect of cobalt on the activity of iron-based catalysts was studied in this work. It was found that cobalt changed the properties of iron oxide depending on its content. In small amounts (Co/Fe(molar)= 0.05), it did not affect significantly the specific surface area but decreased the catalytic activity, a fact which can be assigned to the production of a cobalt and iron phase, less active in WGSR than magnetite. In higher amounts (Co/Fe= 1.0), cobalt led to an increase of specific surface area and to the production of cobalt ferrite and Co 3 Fe 7 alloy, which was more active and more resistant against reduction than magnetite. This catalyst can probably work under low steam conditions, decreasing the operational costs.

Nanotecnologia: aspectos gerais e potencial de aplicação em catálise

In recent years nanomaterials, such as metallic nanoparticles, nanowires, nanotapes, nanotubes and nanocomposites, have attracted increasing interest for several technological applications. In catalysis, the great potential of nanomaterials is related to the high catalytic activity exhibited by these materials as a function of the high surface/volume ratio when the particles acquire diameter below 5 nm. In this work, a review about concepts and background of nanoscience and nanotechnology is presented with emphasis in catalysis. Special attention is given to gold nanoparticles and carbon nanotubes, focusing the properties and characteristics of these materials in several catalytic reactions.

Catalytic activity of aluminium and copper-doped magnetite in the high temperature shift reaction

Aluminium and copper-doped magnetite was evaluated as high temperature shift catalyst and compared with a hematite-based sample. The first one is less active but can save energy in industrial processes.Aluminium and copper-doped magnetite was evaluated as high temperature shift catalyst and compared with a hematite-based sample. The first one is less active but can save energy in industrial processes.

The influence of the preparation method on the catalytic properties of lanthanum-doped hematite in the ethylbenzene dehydrogenation

The influence of the preparation method on the catalytic properties of lanthanum-doped hematite was studied in this work. It was found that the preparation method strongly affects the properties of the catalysts. The samples showed different particle sizes and specific surface areas as well as different resistance against reduction. The most active catalyst in the ethylbenzene dehydrogenation was obtained by adding the iron and lanthanum nitrate solutions to an ammonium hydroxide solution This solid is also able to produce a low amount of coke and has the advantage of being non-active.