The storage capacity of NOx trap catalysts is affected by the gas composition. The capacity increases when the oxygen content goes from 0% to 3%. Above 3%, no effect is exhibited. The presence of NO2 enhances the storage capacity. Storage is significant even if no oxygen is present in the gas phase and even in the absence of platinum. Two kinds of sites for NO, NO2 and O2 adsorption seem to operate. Platinum sites close to BaO crystallites (sites 1) are responsible for nitrate formation. The other platinum sites allow the catalyst to behave as an oxidation catalyst. A mechanism based on NO, NO2 and O2 adsorption and reaction over type 1 sites is able to qualitatively explain the experimental results. The rate of nitrate formation depends on the gas composition while the rate of nitrate decomposition increases with the amount of nitrate formed. This explains the effect of gas composition on the storage capacity obtained at steady-state, when formation and decomposition rates are the same.

Experimental and mechanistic study of NOx adsorption over NOx trap catalysts

Structural modifications during thermal pretreatment of La(NO{sub 3}){sub 3}, La{sub 2}(CO{sub 3}){sub 3}, and La{sub 2}O{sub 3} is reported. Diffuse reflectance, FTIR, X-ray diffraction, and BET surface area measurements were used in the characterizations. Studies were performed in the presence and absence of O{sub 2}, resulting in different products for the thermal modifications.

Influence of Pretreatment on Lanthanum Nitrate, Carbonate, and Oxide Powders

Thermal decomposition of cobalt nitrato compounds: Preparation of anhydrous cobalt(II)nitrate and its characterisation by Infrared and Raman spectra

In order to obtain copper catalysts with high dispersions at high copper loadings, the gas flow rate and gas composition was varied during calcination of silica gel impregnated with copper nitrate to a loading of 18 wt % of copper. Analysis by X-ray diffraction (XRD), N2O chemisorption, and transmission electron microscopy (TEM) showed that calcination in stagnant air resulted in very large copper crystallites and a low copper surface area (12 m2·gCu–1). A moderate flow of air was sufficient to greatly enhance the copper surface area (∼90 m2·gCu–1) based on a bimodal particle size distribution of few large crystallites and a highly dispersed phase. Changing to an N2 flow resulted in similar copper surface areas compared to samples calcined in air at the same space velocity, while calcination in a 2% NO/N2 flow resulted in a relatively narrow particle size distribution peaking around 8 nm and a slightly lower copper surface area (84 m2·gCu–1). By use of SBA-15 supported samples, in situ XRD and diffuse ref...

/pdf/copper-nitrate-redispersion-to-arrive-at-highly-active-3inpr2xrnb.pdf

Copper nitrate redispersion to arrive at highly active silica-supported copper catalysts

The role of anhydrous zinc nitrate in the thermal decomposition of the zinc hydroxy nitrates Zn5(OH)8(NO3)2·2H2O and ZnOHNO3·H2O

Infrared spectra for the anhydrous nitrates of manganese, copper, zinc, and mercury indicate the presence of covalent metal-nitrate bonds. The anhydrous nitrates of cobalt, silver, cadmium, and lead have spectra characteristic of the nitrate ion. Frequencies for the hydrated nitrates of iron, cobalt, nickel, copper, zinc, and cadmium are given for comparison. Hydrated thorium nitrate exhibits bands characteristic of a co-ordinated nitrato- group. (auth)

B. M. Gatehouse

Papers

125. The infrared spectra of anhydrous transition-metal nitrates