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Title: Surface structure of crystalline and amorphous chromia catalysts for the selective catalytic reduction of nitric oxide. 3. Diffuse reflectance FTIR study of ammonia desorption from Broensted and Lewis acid sites

Abstract

Two types of NH{sub 3} molecules bound to Broensted acidic sites on the surface of the chromia catalysts, as well as two species bound to Lewis sites, are identified from the IR spectra. The oxidized surface of {alpha}-Cr{sub 2}O{sub 3} is characterized by a high surface coverage of strongly Lewis-bound ammonia molecules, which desorb at temperatures above 400 K. In contrast, weakly bound NH{sub 3} prevails on the oxidized surface of amorphous chromia. The desorption of the latter species starts at 380 K and is completed around 480 K. A reductive pretreatment of the chromia surfaces by hydrogen (10% in Ar) decreases the number of surface hydroxyl groups and devoids the surface of adsorbed oxygen., As a consequence, the number of Broensted acidic sites is reduced both on the crystalline and the amorphous catalyst. On the reduced surface of {alpha}-Cr{sub 2}O{sub 3}, strongly bound ammonia coordinated to Lewis acidic sites is observed to persist to temperatures beyond 560 K. In contrast, weakly Lewis-bound NH{sub 3} prevails on reduced amorphous chromia, which is quantitatively desorbed at temperatures below 410 K. The formation of NH{sub 3} oxidation products on {alpha}-Cr{sub 2}O{sub 3} is manifested by the observation of two characteristic surface species,more » an N{sub 2}O{sub 2} dimer and an NO{sub 2} chelate surface complex. Corresponding signals are not observed on the surface of amorphous chromia.« less

Authors:
;  [1]; ;  [2]
  1. Univ. of Bayreuth (Germany)
  2. Swiss Federal Inst. of Tech., Zuerich (Switzerland)
Publication Date:
OSTI Identifier:
7160302
Resource Type:
Journal Article
Journal Name:
Journal of Catalysis; (United States)
Additional Journal Information:
Journal Volume: 133:2; Journal ID: ISSN 0021-9517
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 01 COAL, LIGNITE, AND PEAT; 36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CHROMIUM OXIDES; MORPHOLOGY; SURFACE PROPERTIES; NITRIC OXIDE; SELECTIVE CATALYTIC REDUCTION; ABSORPTION SPECTROSCOPY; AMMONIA; AMORPHOUS STATE; BROENSTED ACIDS; CATALYSTS; CATALYTIC EFFECTS; CHEMICAL REACTIONS; CRYSTAL STRUCTURE; DESORPTION; FOURIER TRANSFORMATION; INFRARED RADIATION; LEWIS ACIDS; NITROGEN OXIDES; PH VALUE; REFLECTIVITY; SYNTHESIS; TEMPERATURE CONTROL; CHALCOGENIDES; CHROMIUM COMPOUNDS; CONTROL; DENITRIFICATION; ELECTROMAGNETIC RADIATION; HYDRIDES; HYDROGEN COMPOUNDS; INORGANIC ACIDS; INTEGRAL TRANSFORMATIONS; NITROGEN COMPOUNDS; NITROGEN HYDRIDES; OPTICAL PROPERTIES; OXIDES; OXYGEN COMPOUNDS; PHYSICAL PROPERTIES; RADIATIONS; REDUCTION; SORPTION; SPECTROSCOPY; TRANSFORMATIONS; TRANSITION ELEMENT COMPOUNDS; 540120* - Environment, Atmospheric- Chemicals Monitoring & Transport- (1990-); 010800 - Coal, Lignite, & Peat- Waste Management; 360602 - Other Materials- Structure & Phase Studies; 400201 - Chemical & Physicochemical Properties

Citation Formats

Schraml-Marth, M, Wokaun, A, Curry-Hyde, H E, and Baiker, A. Surface structure of crystalline and amorphous chromia catalysts for the selective catalytic reduction of nitric oxide. 3. Diffuse reflectance FTIR study of ammonia desorption from Broensted and Lewis acid sites. United States: N. p., 1992. Web. doi:10.1016/0021-9517(92)90251-C.
Schraml-Marth, M, Wokaun, A, Curry-Hyde, H E, & Baiker, A. Surface structure of crystalline and amorphous chromia catalysts for the selective catalytic reduction of nitric oxide. 3. Diffuse reflectance FTIR study of ammonia desorption from Broensted and Lewis acid sites. United States. https://doi.org/10.1016/0021-9517(92)90251-C
Schraml-Marth, M, Wokaun, A, Curry-Hyde, H E, and Baiker, A. Sat . "Surface structure of crystalline and amorphous chromia catalysts for the selective catalytic reduction of nitric oxide. 3. Diffuse reflectance FTIR study of ammonia desorption from Broensted and Lewis acid sites". United States. https://doi.org/10.1016/0021-9517(92)90251-C.
@article{osti_7160302,
title = {Surface structure of crystalline and amorphous chromia catalysts for the selective catalytic reduction of nitric oxide. 3. Diffuse reflectance FTIR study of ammonia desorption from Broensted and Lewis acid sites},
author = {Schraml-Marth, M and Wokaun, A and Curry-Hyde, H E and Baiker, A},
abstractNote = {Two types of NH{sub 3} molecules bound to Broensted acidic sites on the surface of the chromia catalysts, as well as two species bound to Lewis sites, are identified from the IR spectra. The oxidized surface of {alpha}-Cr{sub 2}O{sub 3} is characterized by a high surface coverage of strongly Lewis-bound ammonia molecules, which desorb at temperatures above 400 K. In contrast, weakly bound NH{sub 3} prevails on the oxidized surface of amorphous chromia. The desorption of the latter species starts at 380 K and is completed around 480 K. A reductive pretreatment of the chromia surfaces by hydrogen (10% in Ar) decreases the number of surface hydroxyl groups and devoids the surface of adsorbed oxygen., As a consequence, the number of Broensted acidic sites is reduced both on the crystalline and the amorphous catalyst. On the reduced surface of {alpha}-Cr{sub 2}O{sub 3}, strongly bound ammonia coordinated to Lewis acidic sites is observed to persist to temperatures beyond 560 K. In contrast, weakly Lewis-bound NH{sub 3} prevails on reduced amorphous chromia, which is quantitatively desorbed at temperatures below 410 K. The formation of NH{sub 3} oxidation products on {alpha}-Cr{sub 2}O{sub 3} is manifested by the observation of two characteristic surface species, an N{sub 2}O{sub 2} dimer and an NO{sub 2} chelate surface complex. Corresponding signals are not observed on the surface of amorphous chromia.},
doi = {10.1016/0021-9517(92)90251-C},
url = {https://www.osti.gov/biblio/7160302}, journal = {Journal of Catalysis; (United States)},
issn = {0021-9517},
number = ,
volume = 133:2,
place = {United States},
year = {1992},
month = {2}
}