Physical properties of coprecipitated chromia-alumina catalysts

Poole, Charles P.

doi:10.1016/0021-9517(62)90091-x

Cited by 45 publications

(5 citation statements)

References 2 publications

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“…At low Zn/Cr ratios (Fig. 5c, d) the peaks are broadened and shifted to higher values and the broad signals are probably due to the Cr 3+ species present in the catalyst [38]. The broad ESR signal of Cr 3+ can be due to CuCr 2 O 4 species [39], which is observed at low Zn/Cr ratios in XRD analysis.…”

Section: Electron Spin Resonance Analyses (Esr)mentioning

confidence: 86%

Cu–Zn–Cr2O3 Catalysts for Dimethyl Ether Synthesis: Structure and Activity Relationship

et al. 2008

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The CuO dispersed on ZnCr 2 O 4 catalysts derived from Cu-Zn-Cr hydrotalcite like layered double hydroxide precursors with varying Zn/Cr ratios have been synthesized, characterized by BET-Surface area, X-ray diffraction (XRD), temperature programmed reduction (TPR), electron spin resonance (ESR), N 2 O titrations and the activities were evaluated for single step dimethyl ether (STD) synthesis from syngas. It is observed that the copper species were in highly dispersed state over Cu-ZnO-Cr 2 O 3 at high Zn/Cr ratios while the copper cluster were present at low Zn/Cr ratios. The ESR analysis revealed signals due to isolated Cu 2+ at high Zn/Cr ratios and clustered Cu 2+ at low Zn/Cr ratio in fresh catalysts and only Cr 3+ species in used catalysts. The TPR results indicated that the reduction peak shifted to high temperatures with an increase in chromium content due to large copper crystallites, which was supported by XRD analysis. The conversion of syngas to DME was well correlated with the copper metal surface areas, indicating that STD synthesis can be controlled by methanol synthesis rate.

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Section: Electron Spin Resonance Analyses (Esr)mentioning

confidence: 86%

Cu–Zn–Cr2O3 Catalysts for Dimethyl Ether Synthesis: Structure and Activity Relationship

et al. 2008

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“…Chromium trioxide may begin to melt and decompose around 200°C and 250°C, respectively, giving rise to mixed valence species Cr 3 O 8 , Cr 2 O 5 , Cr 4+ in the form of CrO 2 , and lastly Cr 2 O 3 . At the final stage, the material would appear to be green . It is important to note that there is some disagreement as to the valence states of Cr 3 O 8 and Cr 2 O 5 , but based on previous work and the available literature, the authors attribute these species to mixed valence Cr 3+ and 6+ species …”

Section: Resultsmentioning

confidence: 99%

Investigation of surface interactions between volatile chromium species and ceramics

Tatar

Gannon

Swain

et al. 2019

Surf Interface Anal

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Stainless steels are often used in high temperature (≥500°C) applications such as solid oxide fuel cells (SOFCs), combustion engine exhaust systems, and in power/chemical plant process equipment. At high temperature and in oxidizing conditions, chromium containing oxides, such as chromia, may form protective surface layers on the underlying alloy. Reactive evaporation of chromium, however, may occur from the protective surface layers given these conditions, resulting in the formation of volatile chromium species such as CrO 2 (OH) 2 . These volatile chromium species may then interact with surrounding materials, potentially resulting in hazardous compound formation, or having detrimental effects on system performance, as in the case of SOFCs. To better understand the interaction of volatile chromium condensation/ deposition on material substrates, volatile chromium species were generated from chromia powder at 500°C to 900°C and flowed past coupons of alumina and mica and quartz wool at temperatures ranging from 150°C to 900°C for 24-and 100-hour exposures. The ceramic surfaces were characterized as a function of these exposures using X-ray photoelectron spectroscopy (XPS). Analysis of Cr 2p 3/2 peak positions revealed the influence of temperature, material, and exposure time on the oxidation states of surface chromium compounds and extent of chromium deposition.Potential mechanisms are proposed to help explain the observed trends.

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“…(Figures 4b, 6, and 10). 52 Decomposition of CrO 3 to Cr 2 O 3 would likely leave remaining surface chromate species as the primary contributor to the hexavalent peak in Figure 6. Chromium(II) oxide has also been observed, but only under reducing conditions 35,50 which are not present in this study, so its presence is not considered plausible.…”

Section: Resultsmentioning

confidence: 99%

“…While the studies from Liu et al and Okamoto et al are the only XPS studies the authors could find claiming Cr 5+ , other studies using different characterization techniques also report the presence of Cr 5+ . 50,52 Additional work is necessary not only to resolve the possible presence of Cr 5+ , but also to support the inferred conclusions based on XPS evidence and scrutiny of relevant literature. 27 used extended X-ray absorption fine structure and X-ray absorption nearedge structure spectra to examine chromium compounds on silica and did report a mixed valence Cr 3+/6+ oxide in the form of Cr 5 O 12 , but called for additional careful studies using these techniques.…”

Section: Resultsmentioning

confidence: 99%

XPS Characterization of Aluminosilicate Fibers Post Interaction with Chromium Oxyhydroxide at 100–230°C

Tatar¹,

Gannon²,

Swain³

et al. 2018

J. Electrochem. Soc.

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Chromium containing materials, e.g. stainless steels, are commonly used in high temperature (>500 • C) applications such as solid oxide fuel cell (SOFC) stacks, combustion exhaust systems, and in various chemical process equipment. At these temperatures and in oxidizing atmospheres, chromium oxide (chromia) surface layers form and grow, effectively protecting the underlying alloy. Also known to form under these conditions, however, are volatile chromium species such as CrO 2 (OH) 2 and CrO 3 . Formation of these volatile species may have detrimental effects not only on the source material, but also on surrounding materials in the system which may interact with these species. To better understand how volatile chromium species interact with materials, volatile chromium species were generated from ferritic stainless steel (FSS) T409 at 700 • C and directed into aluminosilicate fibers at 100-230 • C for 150 hours. Post exposure fibers were noted to possess yellow, brown, and/or green stained regions which were isolated and characterized using X-ray photoelectron spectroscopy (XPS). Examination of Cr 2p 3/2 peaks revealed varied Cr(VI) content and Cr(III) multiplet-split components for different discolored regions. Possible explanations for differences in chromium content by discoloration color are discussed. The volatilization of chromium species from chromium containing materials is a well-documented phenomenon which holds consequences for SOFCs, human health, and the environment. Using chromia as an example for a source, in the presence of oxygen and absence of water vapor, the dominant volatilization pathway proceeds according to Reaction 1.If, however, water vapor is present in addition to oxygen, then the dominant volatilization pathway proceeds according to Reaction 2. 1-7The generation of these gas/vapor species is well understood, but the same cannot be said of how they interact with (e.g. condense onto) other materials. This is of great importance for human health and the environment considering that chromium species may take toxic forms (hexavalent) or non-toxic forms (trivalent). This relative dearth of understanding also holds negative implications for SOFCs, and so many investigative efforts have been undertaken to understand how CrO 2 (OH) 2 interacts with ceramic components in SOFCs. Electrochemical reduction of CrO 2 (OH) 2 has often been observed to occur at the triple phase boundary (TPB), where cathode, electrolyte, and gas phase meet. [8][9][10] This electrochemical reaction is not limited to the TPB, however, and can occur away from the TPB given: the formation of a continuous chromia layer for hole transport, a mixed conducting electrolyte, or a mixed conducting cathode. 8 While there is evidence for preferential electrochemical reduction of CrO 2 (OH) 2 , 11,12 open circuit chemical reactions have also been observed with cathodes containing Mn or Sr. 13 It should be noted that Cr transport to lanthanum strontium manganite (LSM) was observed via solid state diffusion, whereas vapor deposition o...

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Physical properties of coprecipitated chromia-alumina catalysts

Cited by 45 publications

References 2 publications

Cu–Zn–Cr2O3 Catalysts for Dimethyl Ether Synthesis: Structure and Activity Relationship

Cu–Zn–Cr2O3 Catalysts for Dimethyl Ether Synthesis: Structure and Activity Relationship

Investigation of surface interactions between volatile chromium species and ceramics

XPS Characterization of Aluminosilicate Fibers Post Interaction with Chromium Oxyhydroxide at 100–230°C

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