Chromia supported on titania. II. Morphological properties and catalytic behavior in the selective reduction of nitric oxide by ammonia

Journal Article · Sat Jan 01 00:00:00 EST 1994 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1994.1016· OSTI ID:7107397

Engweiler, J; Nickl, J; Baiker, A ^[1]; Koehler, K; Schlaepfer, C W; Zelewsky, A von ^[2]

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1. Swiss Federal Institute of Technology, Zuerich (Switzerland)
2. Univ. of Fribourg (Switzerland)

The chemical and structural properties of chromia on titania have been investigated after different pretreatments and after use for the low temperature selective catalytic reduction (SCR) of NO by NH[sub 3]. A series of catalysts containing 0.5 to 30 wt% chromia was prepared by impregnation with aqueous chromium nitrate solution. The catalysts exhibited high activity for SCR in the low temperature range (T < 470 K). The NO conversion rate was proportional to the chromia loading up to 5 wt%. Higher loadings resulted in less efficient use of the chromia species. Selectivities to N[sub 2] and N[sub 2]O were not influenced by the amount of deposited chromia at higher loadings ([ge]5 wt%), but depended markedly on the pretreatment of the catalysts. Oxidative pretreatment at 573 K for 3 h led to enhanced formation of undesired N[sub 2]O, whereas previous exposure to a H[sub 2]-containing atmosphere at T < 720 K yielded selectivities to N[sub 2] exceeding 90%. The overall conversion of NO was comparatively little influenced by these pretreatments. Thermal analysis (TG, DTA) and temperature-programmed reduction indicated the formation of Cr(III) species upon reduction in the H[sub 2]-containing atmosphere at 720 K. These species were reoxidizable in air at 670 K and probably highly hydroxylated, as indicated by the substantial formation of water during the thermo-analytical run. Exposure to higher temperatures (>720 K) in an inert or a hydrogen-containing atmosphere led to the formation of less active [alpha]-Cr[sub 2]O[sub 3] which was not reoxidizable under similar conditions. Electron paramagnetic resonance (EPR) measurements of catalysts exposed to SCR conditions indicated uniformly sized clusters of Cr(III) together with Cr(V) surface species. 29 refs., 9 figs., 2 tabs.

• OSTI ID: 7107397
• Journal Information: Journal of Catalysis; (United States), Vol. 145:1; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
33 ADVANCED PROPULSION SYSTEMS
CHROMIUM OXIDES
CATALYTIC EFFECTS
NITRIC OXIDE
REDUCTION
TITANIUM OXIDES
STRUCTURAL CHEMICAL ANALYSIS
CHALCOGENIDES
CHEMICAL REACTIONS
CHROMIUM COMPOUNDS
NITROGEN COMPOUNDS
NITROGEN OXIDES
OXIDES
OXYGEN COMPOUNDS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
400201* - Chemical &amp; Physicochemical Properties
330701 - Emission Control- Nitrogen Oxides