Release Time:2019-03-09  Hits:

Indexed by: Journal Article

Date of Publication: 2010-11-01

Journal: ENVIRONMENTAL SCIENCE & TECHNOLOGY

Included Journals: Scopus、SCIE、ISTIC、PKU、EI

Volume: 44

Issue: 21

Page Number: 8254-8258

ISSN: 0013-936X

Abstract: The soot combustion with NOx and/or O-2 on potassium-supported Mg-Al hydrotalcite mixed oxides under tight contact condition was studied using temperature-programmed oxidation (TPO), isothermal reaction and in situ FTIR techniques. The presence of NOx in O-2 favors the soot combustion at lower temperatures (<300 degrees C). However, a little suppression was observed at higher temperatures (>300 degrees C), which was accompanied by a substantial NO,reduction. The ketene (C=C=O) and isocyanate (NCO-) species were determined as the reaction intermediates. In NOx + O-2, NO2 directly interacts with the free carbon sites (C=C*) through two parallel reactions: (1) NO2 + C=C* -> C=C=O + NO; (2) NO2 + C=C* -> NCO- + CO2. The two reactions can proceed easily, which accounts for the promotion effect of NOx on soot combustion at lower temperatures. The further oxidation of NCO- by NO2 or O-2 is responsible for the simultaneous reduction of NOx. However, the reactions between NO2 and C=C* are limited by the amount of free carbon sites, which can be provided by the oxidation of soot by O-2 at higher temperatures. The interaction of NOx and catalyst results in the formation of nitrates and nitrites, which poisoned the active K sites.