Role of NH3 as an intermediate in reduction of NO with CH4 over sol–gel Pd catalysts on TiO2

✍ Scribed by Junko M. Watson; Umit S. Ozkan

• Book ID: 104421995
• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 424 KB
• Volume: 192
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/s1381-1169(02)00217-0

✦ Synopsis

Our previous studies [Catal. Commun., in press; J. Catal., in press] on sol-gel-prepared Pd catalysts for reduction of NO with CH 4 suggested that one of the key surface species for the NO-CH 4 -O 2 reaction involved NH x species. In this study, the use of NH 3 as the reducing agent for NO reduction on the Gd-Pd/TiO 2 catalyst was investigated under steady-state conditions. Also, temperature-programmed desorption using mass spectrometry and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were used to study the adsorption/desorption characteristics of NH 3 on Gd-Pd/TiO 2 . It was found that NH 3 was effective in reduction of NO on the reduced catalyst in the absence of O 2 at 300 • C (100% NO conversion). This result was consistent with our earlier suggestion that NH x species formed through the interaction of methane and NO adspecies could act as a reducing agent for Pd-NO species. In the presence of O 2 , however, NH 3 oxidation takes place faster than NO reduction and NO conversion decreased. Our NH 3 -TPD experiments indicated that the reversible NH 3 adsorption capacity was higher on the reduced catalyst compared to the oxidized catalyst. Also, there was a strong evidence obtained by DRIFTS that adsorbed NH 3 is transformed into monodentate nitrate species on the oxidized catalyst.