Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides

Weckhuysen, Bert M.; Wachs, Israel E.; Schoonheydt, Robert A.

doi:10.1021/cr940044o

Cited by 764 publications

(748 citation statements)

References 172 publications

(512 reference statements)

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“…Discoloration arose on aluminosilicate fibers after 150 hours of exposure to CrO 2 (OH) 2 over a temperature range of 100-230 • C. Examination of Cr 2p 3/2 peaks in Figures 5-7 revealed varied Cr(VI) content and Cr(III) multiplet-split components for different discolored regions. While differences in color may be generally associated with oxidation state, 24 it may be more precise to attribute colors to specific chromium compounds. Hexavalent chromium, for example, may appear as yellow, orange, red, or brown.…”

Section: Resultsmentioning

confidence: 99%

“…Hexavalent chromium, for example, may appear as yellow, orange, red, or brown. 1,23,24 Given that the human eye is inadequate for discerning subtle mixtures of color, for example "pure" brown from "mixed" brown, it is reasonable to expect mixed compounds in each stain.…”

Section: Resultsmentioning

confidence: 99%

“…27,31,44 The stability of CrO 3 is temperature dependent, however, and can give rise to other compounds beginning at temperatures as low as 200 • C. 31 Theories regarding the formation of these compounds are also available from literature. Formation of chromate (M-CrO 4 ) is believed to be caused by an esterification reaction between CrO 3 and surface hydroxyl groups which may occur near 200 • C, and subsequently stabilize the hexavalent form for temperatures exceeding 1000 • C. 24,31,46,47 Dichromate (M-Cr 2 O 7 ) is believed to form from anchored chromate as chromium loading increases on the sample surface. 27,28,48 Thermal decomposition of CrO 3 may begin at temperatures as low as 200 • C, which may cause melting and effervescing, resulting in a loss of oxygen.…”

Section: Resultsmentioning

confidence: 99%

“…[29][30][31] Regarding speciation, chromium compounds with oxidation states 2-6 have been claimed in literature on alumina and silica surfaces. 24,25,29,[31][32][33][34][35] …”

mentioning

confidence: 99%

“…[29][30][31] Regarding speciation, chromium compounds with oxidation states 2-6 have been claimed in literature on alumina and silica surfaces. 24,25,29,[31][32][33][34][35] Some of these claims appear to be contradictory. For example, some contend that compounds such as Cr 2 O 5 and Cr 3 O 8 are of mixed valences, consisting of 3+ and 6+, 33,36 while others claim 4+ and 6+, 37 whereas others claim the Cr within Cr 2 O 5 to be pentavalent.…”

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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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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…[29][30][31] Regarding speciation, chromium compounds with oxidation states 2-6 have been claimed in literature on alumina and silica surfaces. 24,25,29,[31][32][33][34][35] …”

mentioning

confidence: 99%

mentioning

confidence: 99%

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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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Transition Metal Ions in Microporous Crystalline Aluminophosphates: Isomorphous Substitution

Weckhuysen¹,

Rao

Martens

et al. 1999

Eur. J. Inorg. Chem.

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122

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Microporous crystalline metalloaluminophosphates (MeAPO‐n) represent an important group of molecular sieves because of their potential catalytic and adsorptive properties. Many transition metal ions are claimed to incorporate in the framework of these molecular sieves. Here, the concept of isomorphous substitution, and the different indirect and direct tools available to verify this substitution process for Co, Cr, V, Fe and Mn are reviewed taking the AlPO4‐5 structure as an example. In addition, it will be shown that transition metal ions can be used as a probe to follow the hydrothermal synthesis process of microporous aluminophosphates.

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Catalyst Characterization—Heterogeneous

Stavitski

Beale

Weckhuysen

2010

Encyclopedia of Catalysis

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The study of catalysts under in‐situ conditions enables the catalyst scientist to identify and understand the important steps, e.g., the formation of important reaction intermediates and active sites, and stages in a catalyst?s lifetime, such as activation/deactivation. The development of characterization methods as well as the design and construction of appropriate in‐situ cells and reactor probes are inevitable in order to obtain such insight. Both spectroscopic and scattering techniques have been used in attempt to understand quantitative structure/composition‐activity/selectivity relationships in catalysis. Armed with such detailed knowledge about the catalyst, it is then possible for scientists to design, in a more rational way, new and efficient catalysts for sustainable production of bulk and fine chemicals as well as for the removal of harmful compounds in industrial catalytic processes. This chapter provides an overview of the in‐situ characterization techniques available for investigation of catalytic materials. The possibilities and limitations of the methods are discussed and illustrated with numerous case studies.

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Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides

Cited by 764 publications

References 172 publications

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

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

Transition Metal Ions in Microporous Crystalline Aluminophosphates: Isomorphous Substitution

Catalyst Characterization—Heterogeneous

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