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The lightoff temperatures T50 and T20 were used to compare the activities of the fresh and aged catalysts.

Rh automotive catalysts and its relationship to their activity

Their chemical homogeneity was analyzed by XRF using a semi-quantitative scanning method. The relatively low standard deviations were indicative of a homogeneous catalyst composition as shown previously [14,15].

A stoichiometric factor of 1: Results and discussion The overall chemical composition of catalysts G and V are presented in Table 1.

Any thermal effects hotspots were minimized by diluting the catalyst with silicon carbide at a 1: These catalysts were designed for 1. Therefore, H2 -TPD can be used for comparison of the catalytic activity of these catalysts.

Pt, Pd and Rh are the active metals primarily used in such catalysts because they are less susceptible to poisoning and thermal deactivation [1]. Despite these limitations, the gas chemisorption method is still employed because it can be easily performed using a simple apparatus. The catalysts G and V samples were subjected to two types of thermal aging.

The catalytic evaluation was conducted using a Pyrex U-shape reactor placed in a vertical furnace with PID temperature control. Modern commercial catalysts combine different metal oxides, such as those of cerium, zirconium, barium and lanthanum, that each contributes to a better catalytic performance.

Some compounds used in automotive catalysts, such as ceria and ceria—zirconia mixed oxides, are known to chemisorb H2a process which is favored by hydrogen spillover in the presence of a metallic phase [1,2,22—26].

Next, Ce and Zr hydroxides were precipitated by adding excess ammonium hydroxide.

According to Takeguchi et al. However, for the fresh catalysts, the total amount of adsorbed H2 was greater than the quantity of noble metals determined via chemical analysis, which indicates other processes, such as hydrogen spillover and H2 interactions with the ceria support, can contribute to the hydrogen adsorption.

Catalyst deactivation is usually a complex phenomenon associated with either chemical or thermal effects and may affect different catalyst components that play diverse roles in the entire catalytic system [1—7].

High resolution electron transmission microscopy HRTEM is used to measure the catalyst dispersion but provides little contrast between the small metallic particles and the CeO2 -containing support [21].

The effect of the aging procedure on the catalyst textural properties was previously analyzed [14,15], and the pertinent results are presented in Table 2.

CeO2 —ZrO2 CZ was prepared as a reference support for analysis of the commercial catalysts using the coprecipitation method proposed by Hori et al. Normally, this method leads to a reliable estimation of these parameters. Samples with a controlled particle size 40—60 mesh were used to avoid internal diffusion effects, in accordance with previous experiments [13].

In general, both catalysts had similar compositions, except for certain additives such as barium, hafnium, 64 D. This adsorption-desorption step was performed twice.

These results have now been reviewed, and although they cannot be used to determine the metal dispersion, a correlation between them and the catalytic activities for both propane and CO oxidation and the reduction of NO by CO was found.

The CO and propane oxidation activities were determined using a simulated exhaust gas mixture identical to that used in the aging experiments.

The catalyst samples 1.Journalof CombinatorialTheory,SeriesA () – Contents lists available at SciVerse ScienceDirect JournalofCombinatorialTheory, SeriesA. Chemistry and Physics of Lipids () 59–76 Contents lists available at SciVerse ScienceDirect Chemistry and Physics of Lipids j ournal homepage: ultimedescente.comer.

Contents lists available at SciVerse ScienceDirect Available online4 November Submittedby Keywords: Quasilinearellipticequation Cohomologicalindex Local linking Criticalpoint A three-critical-point theorem related to local linking is obtained and applied to study.

Journal of Molecular Spectroscopy () Contents lists available at SciVerse ScienceDirect Journal of Molecular Spectroscopy journal homepa. CiteSeerX - Document Details (Isaac Councill, Lee Giles, Pradeep Teregowda): (This is a sample cover image for this issue. The actual cover is not yet available at this time.) This article appeared in a journal published by Elsevier.

The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and. The nursing lecturers facilitated the session, being available for assistance when problems were encountered and checked set-ups and answers.

For those students who attended this workshop, this intervention was seen in a very positive light.

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