EPR investigation of paramagnetic species on palladium-promoted yttria and lanthana

Filimonov, Igor N.; Ikonnikov, I. A.; Loginov, A. Yu.

doi:10.1039/ft9949000219

Cited by 5 publications

(2 citation statements)

References 33 publications

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“…According to Angevine et al for a monatomically dispersed and uniformly distributed metal, the XPS I metal / I support ratio should be proportional to the nominal surface density of metal, calculated from the number of metal atoms ( N M ) and the total surface area of the support ( S BET ). Values of I metal / I support higher than those predicted by the nominal surface density indicate metal migration to the outer surface, such as it was found by Fillimonov et al for Pd/lanthana and Pd/yttria and for Rh on small carbon pores . On the other hand, values below those predicted suggest either metal particle growth or preferential deposition of metal inside the small pores, as was shown for supported Pt 26 and Pd 27 catalysts.…”

Section: Resultssupporting

confidence: 58%

Hydrodechlorination of Carbon Tetrachloride to Chloroform in the Liquid Phase with Metal-Supported Catalysts. Effect of the Catalyst Components

Gómez-Sainero

Cortés

Seoane

et al. 2000

Ind. Eng. Chem. Res.

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The effect of the nature of catalyst components has been analyzed in the hydrodechlorination of carbon tetrachloride to chloroform. Active carbon, alumina, silica, and sepiolite were used as supports and Ru, Rh, Pd, Pt, and Ni as the metallic phase. The catalysts were characterized by CO chemisorption, TPR, and XPS. Reaction was carried out at 373 and 413 K in a slurry semibatch reactor. Dispersion of the catalysts containing different metals are very similar, while the values corresponding to Pd supported on different carriers follow the trend Pd/Al2O3 > Pd/carbon > Pd/SiO2 ≈ Pd/sepiolite. The XPS analysis showed that Pd, Ru, and Rh are homogeneously distributed on the carbon, Pt is preferentially deposited on the external surface, and Ni is inside the pores. On the other hand, Pd on silica or alumina is mainly located on the external surface of the support. Pd/C is highly active and selective to chloroform, but Pd supported on the other carriers is less active and leads the reaction toward hexachloroethane. Hydrodechlorination activity of carbon-supported catalysts are in the order Pd/C ≫ Pt/C > Rh/C > Ru/C > Ni/C, all of them being very selective toward chloroform. The results of the reaction are interpreted in terms of the spillover of hydrogen on carbon, the distribution of the metal on the support, and the density of states of the metals.

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Section: Resultssupporting

confidence: 58%

Hydrodechlorination of Carbon Tetrachloride to Chloroform in the Liquid Phase with Metal-Supported Catalysts. Effect of the Catalyst Components

Gómez-Sainero

Cortés

Seoane

et al. 2000

Ind. Eng. Chem. Res.

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“…Sulfated zirconia, being an acidic support, is likely to stabilize palladium in its active phase for reduction of NOx. Pd 2+ cations, however, are diamagnetic in nature and cannot be observed using EPR; but, Pd + and Pd 3+ cations being paramagnetic species, are detectable by EPR [53,54]. Furthermore, we can also gain additional understanding about the sulfated zirconia support since only the paramagnetic Zr 3+ can be observed using EPR while the Zr 4+ species being diamagnetic cannot be detected.…”

Section: Electron Paramagnetic Resonance (Epr)mentioning

confidence: 98%

In-situ incorporation of binder during sol-gel preparation of Pd-based sulfated zirconia for reduction of nitrogen oxides under lean-burn conditions: Effect on activity and wash-coating characteristics

Majumdar

Çelik

Alexander

et al. 2017

Applied Catalysis B: Environmental

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We have developed a dual-catalyst aftertreatment system for reducing nitrogen oxides (NOx) in the exhaust stream of natural-gas fired lean-burn engines by utilizing the unburned hydrocarbons present in the engine exhaust. The dual-catalyst bed consists of a physical mixture of a reduction catalyst (Pd/SZ) and an oxidation catalyst (Co/CeO2). In order to make this dualcatalyst system viable for practical use in the real aftertreatment units, it is necessary to develop a catalytically active washcoat for loading it onto cordierite monolith cores. To be able to handle large throughputs of gases typical of aftertreatment units, irreversible loss of activity due to separation of the wash-coat from the monolith walls can be reduced by adding binders to improve the adhesive properties of the wash-coat. However, addition of such binders may affect the catalytic activity of the resulting dual-catalyst bed. In our study, we have incorporated binders such as alumina, boehmite, bentonite or silica to the Pd/SZ catalyst using a novel technique in which the binders were added in situ during the sol-gel synthesis rather than the conventional method of adding binders (ex-situ) in catalyst slurry. Surface area analysis, X-ray diffraction (XRD) and diffuse reflectance Fourier transform spectroscopy (DRIFTS) with pyridine show that in-situ addition of binder affects the textural properties, crystal phase of zirconia and the acidic properties of the resulting Pd/SZ catalyst respectively. Electron Paramagnetic Resonance (EPR) indicated the presence of Pd + , Pd 3+ and Zr 3+ species in the binder-free and in situ alumina-incorporated Pd/SZ catalysts. Furthermore, steady-state activity tests on the modified dual-catalyst bed with the alumina-incorporated Pd/SZ exhibit the best performance amongst the other binder-incorporated catalysts in the dual-catalyst bed. In-situ incorporation of binder during sol-gel synthesis yielded catalysts with far superior catalytic activity for NOx reduction than conventional ex-situ binder addition to the catalyst slurry for wash-coating. Time-on-stream experiments show that the alumina-incorporated Pd/SZ catalyst maintains the hydrothermal stability of the binder-free Pd/SZ in the mixed bed. Several parameters such as pH of the binder-incorporated catalyst slurry and calcination temperature of the wash-coat have also been optimized to develop a catalytically active wash-coat and its adhesivity and uniformity were tested using ultrasonication, cyclic thermal shock and SEM imaging.

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Flame-synthesized LaCoO3-supported Pd1. Structure, thermal stability and reducibility

Chiarello

Grunwaldt

Ferri

et al. 2007

Journal of Catalysis

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EPR investigation of paramagnetic species on palladium-promoted yttria and lanthana

Cited by 5 publications

References 33 publications

Hydrodechlorination of Carbon Tetrachloride to Chloroform in the Liquid Phase with Metal-Supported Catalysts. Effect of the Catalyst Components

Hydrodechlorination of Carbon Tetrachloride to Chloroform in the Liquid Phase with Metal-Supported Catalysts. Effect of the Catalyst Components

In-situ incorporation of binder during sol-gel preparation of Pd-based sulfated zirconia for reduction of nitrogen oxides under lean-burn conditions: Effect on activity and wash-coating characteristics

Flame-synthesized LaCoO3-supported Pd1. Structure, thermal stability and reducibility

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