An investigation of the thermal stability and sulphur tolerance of Ag/Y-Al2O3 catalysts for the SCR of NOx with hydrocarbons and hydrogen

The sulphur tolerance and thermal stability of a 2 wt% Ag/gamma-Al2O3 catalyst was investigated for the H-2-promoted SCR of NO, with octane and toluene. The aged catalyst was characterised by XRD and EXAFS analysis. It was found that the effect of ageing was a function of the gas mix and temperature of ageing. At high temperatures (800 degrees C) the catalyst deactivated regardless of the reaction mix. EXAFS analysis showed that this was associated with the Ag particles on the surface of the catalyst becoming more ordered. At 600 and 700 degrees C, the deactivating effect of ageing was much less pronounced for the catalyst in the H-2-promoted octane-SCR reaction and ageing at 600 degrees C resulted in an enhancement in activity for the reaction in the absence of H-2. For the toluene + H-2-SCR reaction the catalyst deactivated at each ageing temperature. The effect of addition of low levels of sulphur (1 ppm SO2) to the feed was very much dependent on the reaction temperature. There was little deactivation of the catalyst at low temperatures ( 500 degrees C). The results can be explained by the activity of the catalyst for the oxidation Of SO2 to SO3 and the relative stability of silver and aluminium sulphates. The catalyst could be almost fully regenerated by a combination of heating and the presence of hydrogen in the regeneration mix. The catalyst could not be regenerated in the absence of hydrogen. (c) 2006 Published by Elsevier B.V.

Preparation and evaluation of Fuller's Earth Beads for removal of Cesium from waste streams

This work deals with removal of Cesium (radioactive waste) in dilute aqueous phase by adsorption. Fullers earth was used as an adsorbent. The adsorption capacity of Fullers earth with respect to Cesium was found to be high, 26.3 mg / g of adsorbent.

Quantitative analysis of the reactivity of formate species seen by DRIFTS over a Au/Ce(La)O2 water–gas shift catalyst: First unambiguous evidence of the minority role of formates as reaction intermediates

The reactivity of the species formed at the surface of a Au/Ce(La)O2 catalyst during the water������¢���¯���¿���½���¯���¿���½gas shift (WGS) reaction were investigated by operando diffuse reflectance Fourier transform spectroscopy (DRIFTS) at the chemical steady state during isotopic transient kinetic analyses (SSITKA). The exchanges of the reaction product CO2 and of formate and carbonate surface species were followed during an isotopic exchange of the reactant CO using a DRIFTS cell as a single reactor. The DRIFTS cell was a modified commercial cell that yielded identical reaction rates to that measured over a quartz plug-flow reactor. The DRIFTS signal was used to quantify the relative oncentrations of the surface species and CO2. The analysis of the formate exchange curves between 428 and 493 K showed that at least two levels of reactivity were present. ������¢���¯���¿���½���¯���¿���½Slow formates������¢���¯���¿���½���¯���¿���½ displayed an exchange rate constant 10- to 20-fold slower than that of the reaction product CO2. ������¢���¯���¿���½���¯���¿���½Fast formates������¢���¯���¿���½���¯���¿���½ were exchanged on a time scale similar to that of CO2. Multiple nonreactive readsorption of CO2 took place, accounting for the kinetics of the exchange of CO2(g) and making it impossible to determine the number of active sites through the SSITKA technique. The concentration (in mol g������¢���¯���¿���½���¯���¿���½1) of formates on the catalyst was determined through a calibration curve and allowed calculation of the specific rate of formate decomposition. The rate of CO2 formation was more than an order of magnitude higher than the rate of decomposition of formates (slow + fast species), indicating that all of the formates detected by DRIFTS could not be the main reaction intermediates in the production of CO2. This work stresses the importance of full quantitative analyses (measuring both rate constants and adsorbate concentrations) when investigating the role of adsorbates as potential reaction intermediates, and illustrates how even reactive species seen by DRIFTS may be unimportant in the overall reaction scheme.

Optical observations of 23 distant Jupiter Family Comets, including 36P/Whipple at multiple phase angles

We present photometry on 23 Jupiter Family Comets (JFCs) observed at large heliocentric distance, primarily using the 2.5-m Isaac Newton Telescope (INT). Snapshot images were taken of 17 comets, of which five were not detected, three were active and nine were unresolved and apparently inactive. These include 103P/Hartley 2, the target of the NASA Deep Impact extended mission, EPOXI. For six comets we obtained time-series photometry and use this to constrain the shape and rotation period of these nuclei. The data are not of sufficient quantity or quality to measure precise rotation periods, but the time-series do allow us to measure accurate effective radii and surface colours. Of the comets observed over an extended period, 40P/Väisälä 1, 47P/Ashbrook-Jackson and P/2004 H2 (Larsen) showed faint activity which limited the study of the nucleus. Light curves for 94P/Russell 4 and 121P/Shoemaker-Holt 2 reveal rotation periods of around 33 and 10h, respectively, although in both cases these are not unique solutions. 94P was observed to have a large range in magnitudes implying that it is one of the most elongated nuclei known, with an axial ratio a/b >= 3. 36P/Whipple was observed at five different epochs, with the INT and ESO's 3.6-m NTT, primarily in an attempt to confirm the preliminary short rotation period apparent in the first data set. The combined data set shows that the rotation period is actually longer than 24h. A measurement of the phase function of 36P's nucleus gives a relatively steep ß = 0.060 +/- 0.019. Finally, we discuss the distribution of surface colours observed in JFC nuclei, and show that it is possible to trace the evolution of colours from the Kuiper Belt Object (KBO) population to the JFC population by applying a `dereddening' function to the KBO colour distribution.

An investigation of possible mechanisms of the water-gas shift reaction over a ZrO2-supported Pt catalyst

The present work investigates the reactivity of the surface species observable by in situ DRIFTS formed over a Pt/ZrO2 during the water-gas shift (WGS) reaction. A DRIFTS cell/mass spectrometer system was operated at the chemical steady state during isotopic transients to yield information about the true nature (i.e., main reaction intermediate or spectators) of adsorbates. Only carbonyl and formate species were observed by DRIFTS under reaction conditions; the surface coverage of carbonate species was negligible. Isotopic transient kinetic analyses revealed that formates exchanged uniformly according to a first-order law, suggesting that most formates observed by DRIFTS were of the same reactivity. In addition, the time scale of the exchange of the reaction product CO2 was significantly shorter than that of the surface formates. Therefore, a formate route based on the formates as detected by DRIFTS can be ruled out as the main reaction pathway in the present case. The number of precursors of the reaction product CO2 was smaller than the number of surface Pt atoms, suggesting that carbonyl species or some \

Insight into the key aspects of the regeneration process in the NOx storage reduction (NSR) reaction probed using fast transient kinetics coupled with isotopically labelled (NO)-N-15 over Pt and Rh-containing Ba/Al2O3 catalysts

For the first time, the coupling of fast transient kinetic switching and the use of an isotopically labelled reactant (15NO) has allowed detailed analysis of the evolution of all the products and reactants involved in the regeneration of a NOx storage reduction (NSR) material. Using realistic regeneration times (ca. 1 s) for Pt, Rh and Pt/Rh-containing Ba/Al2O3 catalysts we have revealed an unexpected double peak in the evolution of nitrogen. The first peak occurred immediately on switching from lean to rich conditions, while the second peak started at the point at which the gases switched from rich to lean. The first evolution of nitrogen occurs as a result of the fast reaction between H2 and/or CO and NO on reduced Rh and/or Pt sites. The second N2 peak which occurs upon removal of the rich phase can be explained by reaction of stored ammonia with stored NOx, gas phase NOx or O2. The ammonia can be formed either by hydrolysis of isocyanates or by direct reaction of NO and H2.

The study highlights the importance of the relative rates of regeneration and storage in determining the overall performance of the catalysts. The performance of the monometallic 1.1%Rh/Ba/Al2O3 catalyst at 250 and 350 °C was found to be dependent on the rate of NOx storage, since the rate of regeneration was sufficient to remove the NOx stored in the lean phase. In contrast, for the monometallic 1.6%Pt/Ba/Al2O3 catalyst at 250 °C, the rate of regeneration was the determining factor with the result that the amount of NOx stored on the catalyst deteriorated from cycle to cycle until the amount of NOx stored in the lean phase matched the NOx reduced in the rich phase. On the basis of the ratio of exposed metal surface atoms to total Ba content, the monometallic 1.6%Pt/Ba/Al2O3 catalyst outperformed the Rh-containing catalysts at 250 and 350 °C even when CO was used as a reductant.