Surface structure of crystalline and amorphous chromia catalysts for the selective catalytic reduction of nitric oxide

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

DOI:https://doi.org/10.1016/0021-9517(92)90025-D· OSTI ID:5517467

Schraml-Marth, M; Wokaun, A ^[1]; Baiker, A ^[2]

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1. Univ. of Bayreuth (Germany)
2. ETH Zentrum, Zuerich (Switzerland)

Adsorption of NO onto the oxidized surfaces of both crystalline and amorphous chromia results in the formation of nitrato complexes, by the reaction of NO with surface oxygen. Up to six differently bound species exhibiting different thermal stabilities have been identified. As the catalyst surfaces are saturated with adsorbed oxygen, the bound NO molecules are not decomposed: Upon heating, NO is molecularly desorbed, and neither formation of N[sub 2]O nor of N[sub 2] is observed. Reduced chromia surfaces, which are partially depleted in surface oxygen, are more reactive towards NO. Decomposition of NO, to form N[sub 2]O and N[sub 2], is taking place already at room temperature and is accompanied by a partial reoxidation of the catalyst surface. Nitrato complexes are the most abundant surface species also on the reduced chromia: signals of adsorbed mono- and dinitrosyl complexes are comparatively weak. This observation shows that NO preferentially binds to the Lewis basic surface oxygen ions. As a consequence of the decreased surface oxygen concentration, the coverage of bridging surface nitrate species (requiring two adjacent surface oxygens) is smaller than on the oxidized catalysts. The reaction of NO with surface hydroxyl groups, producing N[sub 2] and NO[sub 2][sup [minus]], results in a minor concentration of Cr-NO[sub 2] surface nitro complexes. On the reduced amorphous catalyst, extensive reoxidation of the surface accompanied by N[sub 2]O formation is observed between 311 and 411 K in temperature-programmed reaction and desorption (TPRD) experiments, while this process is observed to a much smaller extent on reduced crystalline chromia. Above 473 K, bridging and bidentate surface nitrates are the most abundant species on both morphologies. Further heating results in the decomposition of these nitrates yielding N[sub 2], N[sub 2]O (on crystalline chromia only), and surface oxygen. 20 refs., 10 figs., 1 tab.

• OSTI ID: 5517467
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 138:1; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ABSORPTION SPECTROSCOPY
ADSORPTION
AMORPHOUS STATE
BASES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
CHROMIUM COMPOUNDS
CHROMIUM OXIDES
CRYSTALS
DENITRIFICATION
DESORPTION
EVEN-EVEN NUCLEI
HETEROGENEOUS CATALYSIS
ISOTOPES
LEWIS BASES
LIGHT NUCLEI
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN OXIDES
NUCLEI
OXIDES
OXYGEN 20
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
RADIOISOTOPES
REDUCTION
SECONDS LIVING RADIOISOTOPES
SELECTIVE CATALYTIC REDUCTION
SORPTION
SORPTIVE PROPERTIES
SPECTROSCOPY
SURFACE PROPERTIES
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K
TRANSITION ELEMENT COMPOUNDS