Catalytic reduction of NO by CO over rhodium catalysts. 1. Adsorption and displacement characteristics investigated by in situ FTIR and transient-MS techniques

Journal Article · Fri Mar 10 04:00:00 EST 2000 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1999.2763· OSTI ID:20020870

Chafik, T; Kondarides, D I; Verykios, X E

Adsorption of NO(CO) and displacement by CO(NO) has been investigated at 250 C on Rh catalysts supported on undoped and W{sup 6+}-doped TiO{sub 2}, employing transient mass spectroscopy and FTIR techniques. It is found that, under the experimental conditions employed, four kinds of nitrogen oxide species may coexist in the adsorbed mode, namely, Rh-NO{sup {minus}}(high), Rh-NO{sup {minus}}{angstrom}(low), Rh(NO){sub 2}, and Rh-NO{sup +}, giving rise to IR bands located at 1,770, 1,660, 1,830/1,725, and 1,908 cm{sup {minus}1}, respectively. Both negatively charged species readily dissociate on reduced surface sites, yielding nitride, and are mainly responsible for dinitrogen formation in the gas phase. The dinitrosyl species, the formation of which is favored over partially oxidized surfaces, is related to the production of nitrous oxide. The formation of both N{sub 2} and N{sub 2}O requires the presence of reduced surface sites. In the absence of Rh{sup 0}, dissociative adsorption of NO stops and Rh-NO{sup +} species dominate the catalyst surface. Doping TiO{sub 2} with W{sup 6+} cations alters the electronic properties of supported Rh crystallites and, concomitantly, the chemisorptive behavior of the catalyst toward NO and CO. In particular, doping results in blue shifts in the stretching frequencies of N-O and C-O bonds contained in Rh-NO{sup +}, Rh(NO){sub 2}, Rh-CO, and Rh(CO){sub 2} species, indicating a weaker bonding of the adsorbed molecules with the surface. This is also evidenced by the significantly lower amounts of accumulated species, desorbed in TPD experiments. In contrast, the N-O bond of the Rh-NO{sup {minus}} species is weakened by doping, resulting in higher rates of dissociation and, therefore, in higher transient yields of N{sub 2} production in the gas phase, compared to the undoped catalyst.

• Research Organization: Univ. of Patras (GR)
• OSTI ID: 20020870
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 2 Vol. 190; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

33 ADVANCED PROPULSION SYSTEMS
54 ENVIRONMENTAL SCIENCES
ADSORPTION
CARBON MONOXIDE
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
DESORPTION
NITRIC OXIDE
REACTION INTERMEDIATES
RHODIUM
SELECTIVE CATALYTIC REDUCTION
TUNGSTEN