Lucia G. Appel

The CO2–CeO2 interaction and its role in the CeO2 reactivity

The interaction between CO2 and CeO2 and its role in the surface reactivity of alumina-supported cerium oxide has been studied by programmed thermodesorption (TPD) of CO2 and FTIR spectroscopy. The performance of Ce/Al2O3 systems was then analyzed for the propane oxidation in presence of CO2. The results have shown that the catalytic activity decreased when carbonate species are formed at the surface of CeO2. This behavior was attributed to the presence of CO2 from three different sources: contamination before use, during the handling of the samples, contamination proceeding from the reactants and from CO2 produced by the reaction itself.

Active sites for ethanol oxidation over SnO2-supported molybdenum oxides

Abstract SnO2-supported molybdenum oxides with varying coverage were synthesized and used for the catalytic oxidation of ethanol. The catalysts were obtained from precipitation of SnCl4 by ammonia in the presence of (NH4)2Mo7O24 (A). Some catalysts were also prepared by impregnation of (NH4)2Mo7O24 on SnO2 (B) for comparison. It was verified that molybdenum oxides inhibited the sintering of SnO2 crystals during calcination for preparation A, resulting in homogeneous systems with high specific areas. The solids were characterized by FTIR, temperature programmed reduction (TPR), DRS-UV, XPS and X-ray diffraction (XRD). The molybdenum coverage was determined by oxygen pulses after reduction at 400°C under hydrogen. The results indicated two structurally different superficial sites. Four-coordinated molybdates were preferentially formed on the surface of co-precipitated catalysts at low molybdenum loading, while six-coordinated polymolybdates were obtained in other cases. Bulk MoO3 oxide was also observed at very high loading. The turnover numbers (TONs) measured for ethanol oxidative dehydrogenation suggested that dispersed, four-coordinated molybdates were the active phase. These species also gave higher selectivity to acetic acid.

A poluição gerada por máquinas de combustão interna movidas à diesel - a questão dos particulados. Estratégias atuais para a redução e controle das emissões e tendências futuras

The exhaust emissions of vehicles greatly contribute to environmental pollution. Diesel engines are extremely fuel-efficient. However, the exhaust compounds emitted by diesel engines are both a health hazard and a nuisance to the public. This paper gives an overview of the emission control of particulates from diesel exhaust compounds. The worldwide emission standards are summarized. Possible devices for reducing diesel pollutants are discussed. It is clear that after-treatment devices are necessary. Catalytic converters that collect particulates from diesel exhaust and promote the catalytic burn-off are examined. Finally, recent trends in diesel particulate emission control by novel catalysts are presented.

The role of water in ethanol oxidation over SnO2-supported molybdenum oxides

The role of water in the oxidation of ethanol to acetic acid on Sn–Mo–O catalysts was studied by catalytic test and FTIR spectroscopy of adsorbed species. The reaction showed a typical behavior of series reactions involving oxidation of ethanol to acetaldehyde and of the latter to acetic acid and CO2. Addition of water to the feed gas decreased the oxidation rate and significantly increased the selectivity to acetic acid, strongly contributing to decreasing the number of secondary products. FTIR analyses showed that water promotes desorption of ethanol and carboxylates, present as bridging and monodentate species. Decreasing catalytic rate values and increasing selectivity to acetic acid in the presence of water follow from site blocking by hydroxyl groups.

Effect of the nature of the support on molybdenum catalytic behavior in diesel particulate combustion

Abstract Mo/SiO 2 and Mo/TiO 2 catalysts with three different molybdenum contents were prepared using non-porous supports and the thermal spreading method for the combustion of a particulate material (PM). The results of scanning electron microscopy (SEM) and N 2 adsorption/desorption techniques showed that the thermal spreading preparation method does not induce relevant textural changes on the supports. X-ray diffraction (XRD) results showed the occurrence of thermal spreading of MoO 3 onto silica and titania supports. Diffuse reflection spectroscopy (DRS) results provided clear evidence of different Mo species on these systems: highly dispersed species on the silica catalysts and polymolybdates on the titania catalysts. It may be inferred that when prepared by the thermal spreading method the nature of the support determines the kind of molybdenum species formed in these catalysts, irrespective of the Mo content. The reactive data were evaluated by differential scanning calorimetry (DSC), using a physical mixture of PM and the catalysts. The silica-supported catalysts showed higher reactivity for PM combustion than the titania-supported ones, being the most active the systems with the Mo monolayer. The results suggested that the dispersed species are far more active than the polymolybdates or MoO 3 itself.

Influence of the Precursor on Cerium Distribution over Alumina

The Ce/Al 2 O 3 catalysts were prepared with Ce(NO 3 ) 3 , (NH 4 ) 2 Ce(NO 3 ) 6 and with cerium acethylacetonate precursors over alumina, by impregnation and grafting, respectively. Results have shown that the CeO2 surface area of the catalysts with the nitrate precursors is very similar but much higher on the catalysts with the acethylacetonate after grafting. The reducibility of this catalyst is better than of the catalysts with the nitrate precursor. TPR results indicate a reduction of CeO2, the formation of CeAlO 3 and Ce 2 O 3 . The experimental condition employed here allows to attain saturation over alumina which is probably due to steric effects of the Ce(Acet)3 molecules.

Characterization of Mo-Sn-O system by means of Raman spectroscopy and electrical conductivity measurements

Abstract Mo–Sn–O systems were characterized by Raman spectroscopy and electrical conductivity measurements. The catalysts were obtained from precipitation of SnCl 4 by ammonia in the presence of (NH 4 ) 2 Mo 7 O 24 using four different levels of Mo concentration. The electrical conductivity measurements showed that particles are formed by agglomeration of SnO 2 crystals aggregated by polymolybdate. Raman spectroscopy suggested that four-coordinated species are dispersed at the external surface while six-coordinated species are inside the particles. For high Mo concentration (Mo >10%), octahedral coordinated species are also on the surface. Bulk MoO 3 oxide was not observed. These results confirm the model previously proposed.

Catalysis involved in dimethylether production and as an intermediate in the generation of hydrocarbons via Fischer-Tropsch synthesis and MTG process

Dimethyl ether (DME) is the simplest of all ethers. It has been employed since 1966 as propellant in aerosols, painting areas, cosmetics and agriculture, replacing chlorine and fluorine-based compounds, which are noxious to the environment. The vast application of DME is associated with its characte...

Chemicals from ethanol: the acetone synthesis from ethanol employing Ce0.75Zr0.25O2, ZrO2 and Cu/ZnO/Al2O3

Acetone is an important solvent and widely used in the synthesis of drugs and polymers. Currently, acetone is mainly generated by the Cumene Process, which employs benzene and propylene as fossil raw materials. Phenol is a co-product of this synthesis. However, this ketone can be generated from ethanol (a renewable feedstock) in one-step. The aim of this work is to describe the influence of physical–chemical properties of three different catalysts on each step of this reaction. Furthermore, contribute to improve the description of the mechanism of this synthesis. The acetone synthesis from ethanol was studied employing Cu/ZnO/Al2O3, Ce0.75Zr0.25O2 and ZrO2. It was verified that the acidity of the catalysts needs fine-tuning in order to promote the oxygenate species adsorption and avoid the dehydration of ethanol. The higher the reducibility and the H2O dissociation activity of the catalysts are, the higher the selectivity to acetone is. In relation to the oxides, these properties are associated with the presence of O vacancies. The H2 generation, which occurs during the TPSR, indicates the redox character of this synthesis. The main steps of the acetone synthesis from ethanol are the generation of acetaldehyde, the oxidation of this aldehyde to acetate species (which reduces the catalyst), the H2O dissociation, the oxidation of the catalyst producing H2, and, finally, the ketonization reaction. These pieces of information will support the development of active catalysts for not only the acetone synthesis from ethanol, but also the isobutene and propylene syntheses in which this ketone is an intermediate.Graphical abstractAcetone from ethanol.

Acetic Acid Synthesis from Ethanol: Describing the Synergy Between PdO and m-ZrO2

The PdO and m-ZrO2 oxides show different catalytic properties which are not only complementary but also relevant for the ethanol selective oxidation. Due to the spillover of the oxygenated intermediates from PdO to m-ZrO2 and vice versa these compounds are able to generate a promising system for ethanol oxidation to acetic acid.Graphical Abstract