Einige strukturelle Ergebnisse an metallischen Phasen (5)

Schubert, K.; Bhan, Suraj; Burkhardt, W.; Gohle, R.; Meissner, H. G.; Potzschke, M.; Stolz, E.

doi:10.1007/bf00600960

Cited by 77 publications

(16 citation statements)

References 1 publication

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“…Since an adlayer on the substrate surface is not a homogeneous system, the coverage/thickness gives a better representation. The ZrO x H y surface coverage is calculated assuming a non-attenuating adlayer on a semi-infinite substrate [20,[23][24][25]. As the maximum ZrO x H y layer thicknesses remained in the sub-monolayer regime in this study, the influence of a potential attenuation effect of the photoelectrons by the overlayer remains negligible even for the highest exposures.…”

Section: Analysis Of the Xps Datamentioning

confidence: 86%

“…Of particular importance in this respect is the question, whether a single Pd-Zr intermetallic phase could be prepared that exhibits beneficial hydroxylation kinetics already at low enough temperatures, eventually enabling to access CO2-selective MSR pathways. Figure 4 shows a comparison of the XRD-derived bulk structures before and after the methanol steam reforming experiment up to 873 K. Before MSR, the XRD pattern can be consistently explained by the presence of a body-centered tetragonal Pd2Zr phase [23] in co-existence with metallic Pd. Pd3Zr [24] is additionally present as a minor component.…”

Section: Methanol Steam Reforming On the Pd-zr Bulk Samplementioning

confidence: 96%

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A Comparative Discussion of the Catalytic Activity and CO2-Selectivity of Cu-Zr and Pd-Zr (Intermetallic) Compounds in Methanol Steam Reforming

et al. 2017

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Abstract:The activation and catalytic performance of two representative Zr-containing intermetallic systems, namely Cu-Zr and Pd-Zr, have been comparatively studied operando using methanol steam reforming (MSR) as test reaction. Using an inverse surface science and bulk model catalyst approach, we monitored the transition of the initial metal/intermetallic compound structures into the eventual active and CO 2 -selective states upon contact to the methanol steam reforming mixture. For Cu-Zr, selected nominal stoichiometries ranging from Cu:Zr = 9:2 over 2:1 to 1:2 have been prepared by mixing the respective amounts of metallic Cu and Zr to yield different Cu-Zr bulk phases as initial catalyst structures. In addition, the methanol steam reforming performance of two Pd-Zr systems, that is, a bulk system with a nominal Pd:Zr = 2:1 stoichiometry and an inverse model system consisting of CVD-grown ZrO x H y layers on a polycrystalline Pd foil, has been comparatively assessed. While the CO 2 -selectivity and the overall catalytic performance of the Cu-Zr system is promising due to operando formation of a catalytically beneficial Cu-ZrO 2 interface, the case for Pd-Zr is different. For both Pd-Zr systems, the low-temperature coking tendency, the high water-activation temperature and the CO 2 -selectivity spoiling inverse WGS reaction limit the use of the Pd-Zr systems for selective MSR applications, although alloying of Pd with Zr opens water activation channels to increase the CO 2 selectivity.

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Section: Analysis Of the Xps Datamentioning

confidence: 86%

Section: Methanol Steam Reforming On the Pd-zr Bulk Samplementioning

confidence: 96%

A Comparative Discussion of the Catalytic Activity and CO2-Selectivity of Cu-Zr and Pd-Zr (Intermetallic) Compounds in Methanol Steam Reforming

et al. 2017

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“…The phase diagram of the binary Pd-Sn system was investigated by Schubert et al [28] and by Knight and Rhys [6] employing X-ray diffraction, metallography, and thermal analysis. On the basis of the results obtained by these authors, Elliott [29] and Massalski et al [8] both present assessed versions of the Pd-Sn phase diagrams.…”

Section: The Binary Systemsmentioning

confidence: 99%

The In–Pd–Sn phase diagram (xPd≤0.6): Isothermal sections

et al. 2005

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“…The third phase can be identified as ab cc structure similar to a-Fe, which is knownt of orm as olid solution with Ga. [29] At 500 8C, the Ga-Fe solids olution undergoes at ransformation into (Fe,Ga)Fe 3 N, which adopts ap erovskite-likes tructure in space group Pm3 m. [23] As the temperature furtheri ncreases, (Fe,Ga)Fe 3 Ni sr educed to Fe 3 Ga that is isotypet oA uricupride (Pm3 m). [30] Precisely in this temperature regime N 2 evolution was observed during the NH 3 -TPD prior and after the temperature programmed NH 3 decomposition over MgFeGaO 4 ( Figure 7). The conversion of the nitride to the intermetallic compound Fe 3 Ga was verifiedb yaRietveld refinement( Figure S4), allowing to quantify the synchronous changes of the amounts of (Fe,Ga)Fe 3 Na nd Fe 3 Ga.…”

Section: Iron Nitride Phasesduring the Catalyticdecomposition Of Ammoniamentioning

confidence: 77%

Ammonia Decomposition and Synthesis over Multinary Magnesioferrites: Promotional Effect of Ga on Fe Catalysts for the Decomposition Reaction

et al. 2017

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Magnesioferrite (MgFe2O4)‐derived Mesoporous spinels of the type MgFeM3+O4 with M3+=Fe, Al, and Ga obtained upon calcination of hydrotalcite‐like compounds were investigated in the ammonia decomposition reaction at 1 bar and the synthesis of ammonia at 90 bar. The corresponding precursors were synthesized by co‐precipitation at 50 °C and constant pH of 10.5. N2 physisorption, PXRD, HR‐TEM, H2‐TPR, and NH3‐TPD were applied in order to obtain information about the textural, (micro‐)structural, solid‐state kinetics in reducing atmosphere, and adsorption properties of the samples. While phase‐pure layered double hydroxides (LDHs) were obtained for Al and Ga, magnesioferrite as the desired oxide phase and a low fraction of magnetite were formed besides the targeted precursor phase during co‐precipitation in the presence of Fe2+ and Fe3+ species. Reduction of the binary and ternary magnesioferrites occurs via two consecutive reactions. Only the second stage is shifted towards higher temperatures after incorporation of Al and Ga. The latter element boosts the catalytic decomposition of ammonia, yielding a 2‐fold and 5‐fold higher conversion at 500 °C compared to the samples containing Fe3+ and Al3+ species, respectively. In situ XRD measurements showed that this unprecedented promotional effect is related to the generation of (Fe, Ga)Fe3N. This phase, however, is detrimental for the synthesis of ammonia at elevated pressures in which the binary system outperforms the ternary spinels, yielding 30 % of the activity obtained with a highly promoted Fe‐based industrial catalyst.

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Einige strukturelle Ergebnisse an metallischen Phasen (5)

Cited by 77 publications

References 1 publication

A Comparative Discussion of the Catalytic Activity and CO2-Selectivity of Cu-Zr and Pd-Zr (Intermetallic) Compounds in Methanol Steam Reforming

A Comparative Discussion of the Catalytic Activity and CO2-Selectivity of Cu-Zr and Pd-Zr (Intermetallic) Compounds in Methanol Steam Reforming

The In–Pd–Sn phase diagram (xPd≤0.6): Isothermal sections

Ammonia Decomposition and Synthesis over Multinary Magnesioferrites: Promotional Effect of Ga on Fe Catalysts for the Decomposition Reaction

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