Stability of Chromium Oxides

Mosesman, M.

doi:10.1021/ja01630a092

Cited by 7 publications

(4 citation statements)

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“…This observation can be further substantiated by the evolution of isotopic peaks of mass 50, 53, 54 along with 52 the mass of elemental chromium. It is also known that the melting point of bulk chromia is 474 K. Consequently, it begins to decompose into Cr 2 O 3 and O 2 at 533 K [22]. The DSC study carried out in our laboratory for bulk CrO 3 shows an exothermic peak at 474 K corresponding to the melting point of CrO 3 and is in accordance with the literature [2].…”

Section: Evolved Gas Analysissupporting

confidence: 87%

“…Supported chromia systems find their applications in polymerisation reactions and many catalysed reactions such as dehydrogenation of alkanes, dehydrocyclisation, catalytic reforming, hydrodesulphurisation and partial oxidation of hydrocarbons [1]. Despite the extensive physico-chemical studies carried out over these systems for the past three decades, the comprehension of the surface structures of chromium oxide species (CrO x ) stabilised on various supports and of the true nature of these species in various catalytic processes is still a matter of debate [1][2][3][4][5][6][7][8][9][10][11][12][13]. Recently we have made an attempt to investigate the supported chromia systems in our laboratory and are reported elsewhere [14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

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Structural Properties and Catalytic Behaviour of CrOx/TiO2 Systems

Wilson¹,

Rao

Viswanath

2017

Eurasian Chem. Tech. J.

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The present investigation comprises of an attempt to investigate the titania supported chromia catalysts using X-ray diffraction measurements (XRD), evolved gas analysis (EGA), FT infrared spectroscopy (FTIR) and FT-Raman spectroscopic techniques with catalytic evaluation by dehydrogenation of cyclohexane. Evolved Gas Analysis shows a modified decomposition pattern than that of bulk chromia and presence of surface heterogeneity owing to the modified surface anchored chromia species formed as a result of interaction between chromia and titania. Above 773 K, Cr 6+ is not stable over TiO 2 surface and the reduction of the Cr 6+ to intermediate chemical states take place. XRD investigations illustrate the significance of X-ray source in examining supported chromia catalysts to study the morphological modifications of the active phase when crystalline supports are employed. FT Raman spectra reveals that on calcining the sample at 573 K, for 2 hours, the chromia phase assumes a monomerically anchored molecular state. Longer calcination time (6 hours) at the same temperature, leads to the diffusion of insitu formed Cr 3+ ions into the anatase lattice. On calcination at 973 K for 6 hours, amorphous chromia phase is no more stable on TiO 2 support resulting in agglomeration leading to the germination of microcrystalline α-Cr 2 O 3 . Evaluation of catalytic performance of above catalysts by dehydrogenation of cyclohexane confirms the fact that diffusion of part of Cr 3+ species into the bulk of anatase phase occurs under reaction conditions.

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Section: Evolved Gas Analysissupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Structural Properties and Catalytic Behaviour of CrOx/TiO2 Systems

Wilson¹,

Rao

Viswanath

2017

Eurasian Chem. Tech. J.

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“…It should be recalled that the utilization of chromium-based catalysts have been often avoided since Cr 2 O 3 can be oxidized to CrO 3 , which is potentially carcinogenic . However, it has been shown that CrO 3 is thermally unstable above 250 °C, liberating oxygen and eventually transforming to Cr 2 O 3 . So, the utilization of Cr 2 O 3 support for CH 4 oxidation does not generate hazardous CrO 3 during CH 4 oxidation because the catalytic reaction occurs at high temperatures (above 300 °C).…”

Section: Resultsmentioning

confidence: 99%

“…54 However, it has been shown that CrO 3 is thermally unstable above 250 °C, liberating oxygen and eventually transforming to Cr 2 O 3 . 55 So, the utilization of Cr 2 O 3 support for CH 4 oxidation does not generate hazardous CrO 3 during CH 4 oxidation because the catalytic reaction occurs at high temperatures (above 300 °C).…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Performance of Pt/Cr₂O₃, Pt/ZrO₂, and, Pt/γ-Al₂O₃ Catalysts in Total Oxidation of Methane: Effect of Metal–Support Interaction

Corro

Cruz-Mérida

Montalvo

et al. 2021

Ind. Eng. Chem. Res.

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We present the catalytic performance of Pt-supported Cr2O3, and ZrO2 (semiconductors), and γ-Al2O3 (insulator) in CH4 oxidation under lean conditions. XPS analysis of the catalysts showed only Pt2+ at the Pt/γ-Al2O3 surface, and stable Pt x –Pt y dipolar catalytic sites at the surface of Pt/Cr2O3 and Pt/ZrO2. The presence of such dipolar moieties increases the polarization probability of methane molecules, resulting in an increment of the molecule’s kinetic energy and in an increase of the strength of its impact with the catalyst surface, weakening the C–H bond energy and enhancing hydrogen detachment from CH4 adsorbed molecules. The detachment of this hydrogen is the rate-determining step of the reaction. The formation and stability of the Pt x –Pt y dipolar moieties have been related to the electronic effects associated with platinum and metal oxide semiconductor support interactions. Results reported in this investigation demonstrate the possibility of tuning the catalytic activity of Pt supported on metal oxides for methane oxidation by controlling the nature of the Pt x –Pt y dipolar moieties at the surface of metal oxide supports by selecting the semiconducting supports of suitable work functions.

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Oberflächenverbindungen von Übergangsmetallen. XVIII. Der Einfluß der Cr‐Konzentration auf Oxydationszahl und „Qualität”︁ von Cr‐Oberflächenverbindungen auf Silicagel

Westphal

1977

Zeitschrift anorg allge chemie

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Mittlere Oxydationszahl (OZ) und mittlerer ungesättigter Charakter (q) von Cr‐reduzierten Oberflächenverbindungen auf Silicagel sind von der Cr‐Konzentration des Produkts abhängig. Verantwortlich für den erstgenannten Effekt ist der im aktivierten Produkt mit steigender Cr‐Konzentration sinkende Anteil von thermisch stabilem O′fl. CrVI, da nur dieses (mit konstanter Ausbeute von ∼90%) zu O′fl. CrII reduziert werden kann; dementsprechend führt Konzentrationserhöhung zu ansteigender OZred. — Die beobachtete Abnahme von q mit steigender Cr‐Konzentration ist nicht — wie bei der Beeinflußung dieses Wertes durch Ta‐t und Tred — mit einer koordinativen Absättigung durch benachbarte SiOH‐Gruppen korrelierbar; andere Möglichkeiten für eine Deutung werden vorgeschlagen. Insgesamt unterstützen die Befunde das für die untersuchten Produkte postulierte Modell eines Ensembles topologisch differenzierter individueller Oberflächenspezies von unterschiedlicher Reaktivität.

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Stability of Chromium Oxides

Cited by 7 publications

References 0 publications

Structural Properties and Catalytic Behaviour of CrOx/TiO2 Systems

Structural Properties and Catalytic Behaviour of CrOx/TiO2 Systems

Performance of Pt/Cr₂O₃, Pt/ZrO₂, and, Pt/γ-Al₂O₃ Catalysts in Total Oxidation of Methane: Effect of Metal–Support Interaction

Oberflächenverbindungen von Übergangsmetallen. XVIII. Der Einfluß der Cr‐Konzentration auf Oxydationszahl und „Qualität”︁ von Cr‐Oberflächenverbindungen auf Silicagel

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Stability of Chromium Oxides

Cited by 7 publications

References 0 publications

Structural Properties and Catalytic Behaviour of CrOx/TiO2 Systems

Structural Properties and Catalytic Behaviour of CrOx/TiO2 Systems

Performance of Pt/Cr2O3, Pt/ZrO2, and, Pt/γ-Al2O3 Catalysts in Total Oxidation of Methane: Effect of Metal–Support Interaction

Oberflächenverbindungen von Übergangsmetallen. XVIII. Der Einfluß der Cr‐Konzentration auf Oxydationszahl und „Qualität”︁ von Cr‐Oberflächenverbindungen auf Silicagel

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Performance of Pt/Cr₂O₃, Pt/ZrO₂, and, Pt/γ-Al₂O₃ Catalysts in Total Oxidation of Methane: Effect of Metal–Support Interaction