Surface structure of crystalline and amorphous chromia catalysts for the selective catalytic reduction of nitric oxide. 1. Characterization by temperature-programmed reaction and desorption

Journal Article · Sat Feb 01 04:00:00 EST 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90249-H· OSTI ID:7200490

Curry-Hyde, H E; Musch, H; Baiker, A ^[1]; Schraml-Marth, M; Wokaun, A ^[2]

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1. Swiss Federal Inst. of Tech., Zuerich (Switzerland)
2. Univ. of Bayreuth (Germany)

Amorphous and crystalline chromia catalysts used for the selective catalytic reduction (SCR) of NO by NH{sub 3} have been characterized using temperature-programmed reaction and desorption of preadsorbed NO and NH{sub 3}. The acidity of the Lewis acid sites and the associated labile oxygen species are investigated using NH{sub 3} as a probe molecule. The degree of coordinative unsaturation of these sites is inferred from the reactions of NO. The effects of reduction, oxidation, and SCR treatment on the state of the Lewis acid sites and the labile oxygen are discussed. Lewis acid sites on crystalline chromia are more acidic than those on amorphous chromia. Different labile oxygen species are discernible based on their oxidizing strengths and the products formed. All labile oxygen is readily removed by reduction; SCR treatment leads to the partial removal of labile oxygen from both morphologies of chromia. The degree of lability of the different oxygen species is related to the morphology of the chromia. The proportions of one- and twofold coordinatively unsaturated sites (1 and 2 c.u.s.) depends strongly on the morphology of the chromia and its pretreatment. Both types of sites show distinct differences in the acidity dependent on the morphology of the chromia. The most significant difference between the two morphologies is seen after SCR treatment. Crystalline chromia shows a very high density of 1 c.u.s. compared to amorphous chromia. These sites are generated from 2 c.u.s. by abstraction of oxygen from NO. Implications of these results on the SCR reaction are discussed.

• OSTI ID: 7200490
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 133:2; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

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Atmospheric-- Chemicals Monitoring & Transport-- (1990-)
AMMONIA
AMORPHOUS STATE
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
CHROMIUM COMPOUNDS
CHROMIUM OXIDES
CONTROL
CRYSTAL STRUCTURE
DENITRIFICATION
DESORPTION
ELEMENTS
HYDRIDES
HYDROGEN COMPOUNDS
MORPHOLOGY
NITRIC OXIDE
NITROGEN
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NITROGEN OXIDES
NITROUS OXIDE
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PH VALUE
REDUCTION
SELECTIVE CATALYTIC REDUCTION
SORPTION
SURFACE PROPERTIES
SYNTHESIS
TEMPERATURE CONTROL
TRANSITION ELEMENT COMPOUNDS