Search

New materials based on electric arc furnace (EAF) dust have been produced via temperature-programmed reduction using hydrogen gas at different temperatures. Scanning electron microscopy, thermal analysis, X-ray diffraction, and Mössbauer spectroscopy suggested that the EAF dust is reduced by hydrogen at 600 and 700 °C producing reduced iron, e.g., iron (II) and iron metallic, magnetics and more active catalytic phases. The new materials show magnetic behavior as well as EAF starting material. Electron paramagnetic resonance studies using N-t-butyl-α-phenylnitrone as a trapped radical agent were performed showing characteristic signals related to paramagnetic species produced exclusively by the interaction of catalysts with hydrogen peroxide (H2O2). The new magnetic materials were successfully used for pollutant removal by adsorption followed by oxidation of model dyes such as methylene blue and indigo carmine. In addition, the great advantage of these materials is that they may be easily recovered magnetically and reused. [ABSTRACT FROM AUTHOR]

Tin and titanium dioxides and their compositions were studied as catalysts for the reaction of complete oxidation of methane. The catalytic activity of the test samples was compared in terms of first-order reaction rate constants with reference to the unit surface area of a catalyst. The crystal structures and specific surface areas of the obtained compositions were characterized. The thermal stability of SnO was investigated. Data on the temperature-programmed reduction of SnO and the composition SnTiO in hydrogen were given. [ABSTRACT FROM AUTHOR]

In NO/CO reaction, there is a competition between NO reduction by CO and Mo2C oxidation by oxygen generated during NO dissociation. A complete equality of NO conversion and NO reduction degree can be achieved after increasing CO concentration in the system, which makes establishing a catalytic cycle on Mo2C catalyst possible. [ABSTRACT FROM AUTHOR]

Redox reactions catalyzed by cobalt nitrides should be carried out below the critical temperature at which bulk oxidation of the nitrides occurs. Then, a catalytic redox cycle could be established by introducing a reducing agent into the system below this temperature so that the oxygen could be removed prior to the occurrence of bulk oxidation. [ABSTRACT FROM AUTHOR]

Ag/SBA-15 catalysts have been prepared by means of in situ reduction methods using hexamethylenetetramine and formaldehyde as reducing agents, respectively, and characterized by N2 adsorption/desorption, XRD, TEM and XPS. Presence of nanoparticles of silver in SBA-15 were confirmed by high angle X-ray diffraction data (peaks between 2 θ = 35–80º) and XPS, and transmission electron microscopy confirmed the diameter of the nanoparticles. When hexamethylenetetramine was used as reducing agent, uniform Ag nanoparticles inside the channels were formed, and diameter of nanoparticles is found to be ~6.0 nm which is coincident with channel diameter of SBA-15. The catalysts were subjected to CO oxidation in a flow reactor at atmospheric pressure and temperatures up to 300 °C. Studies revealed that catalysts prepared with different reducing agents strongly influence their catalytic performance in the CO oxidation, what prepared with hexamethylenetetramine as mild reducing reagent shows a certain low temperature catalytic activity. [ABSTRACT FROM AUTHOR]

Composites of polyaniline (PANI) or polypyrrole (PPy) doped with chloride ions and Pt or Rh particles were prepared by chemical reduction of metal ions conducted in the presence of the polymers. Based on X-ray diffraction studies it was established that the composites contained metal nanoparticles (5–9 in size). However, according to SEM investigations metal particles were agglomerated (40 nm–1.1 μm in size). Redox activity of the composites in the catalytic isopropyl alcohol conversion was ca. ten times higher than the acid–base one. Pt dispersed in polymer matrices showed higher catalytic activity than Rh. PPy doped with chloride ions had a promoting effect on the activity of Pt catalysts. [ABSTRACT FROM AUTHOR]

Vanadium-containing H6+xP2Mo18-xVxO62 (x = 0–3) Wells–Dawson heteropolyacid (HPA) catalysts were prepared. The successful formation of the Wells–Dawson HPAs was confirmed by FT-IR and ICP–AES analyses. The reduction potential of the H6+xP2Mo18–xVxO62 (x = 0–3) catalysts was determined by temperature-programmed reduction measurements. The Wells–Dawson HPA catalysts were applied to the vapor-phase oxidation of methacrolein and benzyl alcohol. The reduction potential, conversion of methacrolein, and conversion of benzyl alcohol showed volcano-shaped curves with respect to vanadium substitution, and decreased in the order of H8P2Mo16V2O62 > H7P2Mo17V1O62 > H9P2Mo15V3O62 > H6P2Mo18O62. A correlation between reduction potential and catalytic activity clearly showed that the conversion was monotonically increased with increasing reduction potential of the HPA catalyst in both oxidation reactions. [ABSTRACT FROM AUTHOR]

A Pd catalyst is particularly effective for the oxidation of CO and C3H6 at low temperatures, while the Pt/Rh/Ce catalyst is active for NO reduction. The TWC activity of both catalysts generally decreased as the catalyst mileage increased. However, the NO reduction activity was less affected by catalyst aging compared to the oxidation reactions. The selectivity of the catalysts in favor of the CO–O2 reaction (vs. C3H6–O2 reaction) in the O2 partitioning experiments became less pronounced as the catalyst aged. The NO partitioning experiments reveal the superior capability of H2 in NO reduction to the other reductants (CO and C3H6) examined in the present study. The reactivities of NO with both H2 and CO were found to decrease upon catalyst aging, resulting in decreased overall NO removal activity. [ABSTRACT FROM AUTHOR]

NO x -storage catalysts (NSC) with varied washcoat compositions have been investigated experimentally under lean and rich conditions. Besides the fact that Ba and Rh are essential for NO x -storage and -reduction, it was observed that Ba accelerates the NO-reduction and decreases NO-oxidation kinetics. It also turned out to be the promoting species regarding water gas shift reaction. The results revealed kinetic inhibition effects by CO, C3H6 and NO, being less pronounced with Ba in the washcoat. It is further shown that the cyclic NOx-conversion of the NSC is mainly determined by the processes in the regeneration phase. [ABSTRACT FROM AUTHOR]

A model of a Pt/Rh/Ce/Ba/Al2O3–NOx-storage catalyst has been developed. It considers the influence of typical exhaust components on the NO-oxidation and NOx-reduction reactions under realistic flow conditions over a wide temperature range. The NOx-storage dynamics are limited by the diffusion of the reactants into the Ba-particle through an increasingly thick, dense nitrate layer. The regeneration reaction instead is fast since the nitrate shell breaks up. By calculation of the nitrate front position and the nitrate fraction in the Ba-particle, it is possible to describe the complex dynamic behaviour of the NSC. [ABSTRACT FROM AUTHOR]

We used pulsed reduction and temperature programmed oxidation to study the interaction of methane and oxygen with the surface of manganese oxide-containing catalysts. We hypothesized that during oxidative dimerization of methane, the phase supplying strongly bound oxygen for selective methane coupling is an acceptor for weakly bound oxygen of the phase catalyzing exhaustive oxidation. [ABSTRACT FROM AUTHOR]