An XPS study of the Phillips Cr/silica polymerization catalyst

Merryfield, R. N.; McDaniel, Max P.; Parks, George D.

doi:10.1016/0021-9517(82)90178-6

Cited by 194 publications

(93 citation statements)

References 21 publications

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“…36,45 Concerning the hexavalent chromium content in Figure 5, a likely prominent hexavalent compound is the anhydrous form of the incident chromium species CrO 2 (OH) 2 -CrO 3 . Evidence supporting this conclusion includes similar binding energies reported in literature for CrO 3 , 30,38,39,42 in addition to the color of pure CrO 3 being a dark brown. The presence of CrO 3 has also been observed in literature for temperatures less than and greater than the estimated temperature range in this study (100-230 • C).…”

Section: Resultssupporting

confidence: 89%

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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: Resultssupporting

confidence: 89%

“…The observed range is well supported in literature for chromia. 25,41,42 Determining 37 and as tetrahedral Cr 6+ and octahedral Cr 3+ linkages. 33,36 Claims have also been made that Cr 2 O 5 is a single valence Cr 5+ species.…”

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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“…The growth of polyethylene seems to be associated with the presence of bivalent chromium compounds at the model catalyst surface. These findings agree with the previously proposed mechanisms [1,[31][32][33][34]. Moreover, it is known that aldehyde could by formed during ethylene polymeration [1].…”

Section: Mechanism Of Ethylene Polymerizationsupporting

confidence: 92%

Activation processes and polyethylene formation on a phillips model catalyst studied by laser ablation, laser desorption, and static secondary ion mass spectrometry

Aubriet

Müller²,

Poleunis

et al. 2006

J. Am. Soc. Mass Spectrom.

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Since the discovery of the Phillips catalysts, there still is much uncertainty concerning their activation, their molecular structure, the nature of the active chromium sites, and the polymerization mechanisms. Surface techniques are not easy to be used for such study according to the nonconductive behavior of the support. Therefore, model Phillips catalyst is elaborated by spin coating a trivalent chromium precursor on a silicon wafer. The surface characterization of this model catalyst is conducted by laser ablation mass spectrometry (LA-MS), laser desorption/ionization mass spectrometry (LDI-MS), and static secondary ion mass spectrometry (s-SIMS), at different steps of its preparation. To validate our approach, a comparison is also made between the model and the real Philips catalyst. Moreover, the model catalyst efficiency for polyethylene synthesis is evaluated and allows us to discuss the validity of the mechanisms previously proposed to explain the catalytic process. The characterization of Phillips model catalyst by mass spectrometry allows us to better understand the activation processes of such catalyst. Depending on the activation temperature, chromium oxide species are formed and anchored at the support surface. They consist mainly in mono-chromium sites at high temperature. The chromium valence is hexavalent. This model catalyst is active for the polymerization of ethylene. A pseudo-oligomer molecular weight distribution is observed by LA-MS, whereas s-SIMS allows us to elucidate the anchorage of the polymer at activate chromium surface sites. (J Am Soc Mass Spectrom 2006, 17, 406 -414)

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“…41 After 1270 s sputtering, metallic Cr begins to show up with peak at 574.5 eV binding energy. 42 After 3970 s sputtering, no Cr(OH) 3 can be detected and nearly all the Cr species is ascribed to the metallic Cr. Above all, the initial deposits of the Cr species during electrodeposition are metallic Cr, but change into Cr(OH) 3 with time.…”

Section: Electrodeposition Of the As-preparedmentioning

confidence: 99%

Preparation of La-Cr Perovskite Coating Using Electrodeposition Method

Zhang

You

Luo

et al. 2016

J. Electrochem. Soc.

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An adhesive LaCrO 3 perovskite coating has been prepared on stainless steel substrate by cathodic electrodeposition from aqueous solution 0.03 M La(CH 3 COO) 3 + 0.03 M CrCl 3 + 0.03 M Na 3 C 6 H 5 O 7 , followed by heat-treatment at 800 • C in air. The electrodeposition of La-Cr coatings has been examined in the solution with pH of 2∼3 at the current density of 1∼5 mA cm −2 . It is shown that the change of pH by even 0.1 can affect obviously the deposition of La-Cr coatings, and increasing the current density will lead to the generation of more cracks in the coatings. A more uniform and compact La-Cr coating can be obtained in the solution with the optimized pH value of 2.7 at the optimized current density of 1 mA cm −2 . The La and Cr deposits change from their metallic states to the hydroxides during electrodeposition, corresponding to the increase in the pH with time. The as-prepared La-Cr coating is rich in La, due to the strong coordination of trivalent chromium with complex agent in the bath. The outward diffusion of Cr from the stainless steel substrate supplies the as-prepared La-rich coating to form LaCrO 3 during heat-treatment. which are capital intensive and difficult for scale production. Electrodeposition of Ln-M coatings from aqueous solutions followed by heat-treatment is an advantageous method for preparing perovskite coatings. [11][12][13][14][15] This method offers a more economical and efficient technique for the fabrication of perovskite coatings. Nevertheless, although the Ln-M coatings have been successful prepared using both anodic and cathodic electrodeposition methods, relevant research is still limited and challenging.Matsumoto et al [11][12][13] conducted a series of research on the anodic electrodeposition of Ln-M (M = Co, Mn) coatings. Their studies indicated that Ln ions did not participate in any oxidation reactions. The incorporation of Ln ions into the M hydroxide/oxide coatings was achieved by enriching the bath with Ln ions and their consequent adsorption. This gives poor control over the Ln contents in the coatings and requires a high concentration of Ln ions for deposition. 15By comparison, cathodic electrodeposition is an inherently superior technique as both Ln and M ions participate in the reactions, leading to facile deposition of Ln and M elements. 14 However, the cathodic electrodeposition of Ln-M coatings still faces some problems. The main obstacle stems from the low equilibrium potentials of Ln ions. Since the equilibrium potentials of Ln ions (Ln 3+ + 3e -→Ln; E 0 = -2.52 ∼-2.25 V SHE ) are much more negative than that of water (2H 2 O + 4e -→2OH -+ H 2 ; E 0 = -0.828 V SHE ), electrolytic decomposition of water appears preferentially.16,17 Fortunately, electrodeposition of Ln elements can be achieved by adding some complex agents to shift their evolution potentials to more positive values. 18,19 Lokhande et al 20 investigated the electrodeposition of La from aqueous solutions on different substrates and found that sodium citrate was a suitable complex agent for L...

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An XPS study of the Phillips Cr/silica polymerization catalyst

Cited by 194 publications

References 21 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

Activation processes and polyethylene formation on a phillips model catalyst studied by laser ablation, laser desorption, and static secondary ion mass spectrometry

Preparation of La-Cr Perovskite Coating Using Electrodeposition Method

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