Effects of water vapor and sulfur dioxide on the performance of Ce-Ag-ZSM-5 for the SCR of NO with CH4

Citation
Zj. Li et M. Flytzani-stephanopoulos, Effects of water vapor and sulfur dioxide on the performance of Ce-Ag-ZSM-5 for the SCR of NO with CH4, APP CATAL B, 22(1), 1999, pp. 35-47
Citations number
33
Categorie Soggetti
Physical Chemistry/Chemical Physics","Environmental Engineering & Energy
Journal title
APPLIED CATALYSIS B-ENVIRONMENTAL
ISSN journal
09263373 → ACNP
Volume
22
Issue
1
Year of publication
1999
Pages
35 - 47
Database
ISI
SICI code
0926-3373(19990823)22:1<35:EOWVAS>2.0.ZU;2-Q
Abstract
The activity and stability of Ce-Ag-ZSM-5 catalysts for the selective catal ysts reduction (SCR) of NO with CH4 in the presence of water vapor and SO2 was studied in this work. Pre-steaming or wet aging of the catalyst in the reaction gas mixture caused a drop in activity. The loss of catalytic activ ity was partially irreversible and with an increase of water content and/or temperature the irreversible loss became predominant. However, at all test ed conditions, including at a temperature of 600 degrees C and in the prese nce of 8% water, the catalyst was capable of retaining a stable NO conversi on to N-2 during a 100 h-long test. In the presence of SO2. the activity of Ce-Ag-ZSM-5 decreased significantly at 500 degrees C, but it was recovered by increasing the temperature to above 550 degrees C. NO uptake measuremen ts and characterization of steamed, sulfated and reaction-aged catalyst sam ples by XRD, HRTEM, STEM/EDS and XPS were carried out to study the deactiva tion. The NO uptake capacity of pre-steamed samples decreased as steaming t emperature was raised from 400 degrees C to 600 degrees C, but that of pre- sulfated catalysts increased with temperature reaching 80% of the fresh mat erial-uptake capacity after the 600 degrees C-sulfation. Water induced sint ering of silver. This, in turn, caused the lower NO uptake and the irrevers ible loss of the SCR activity observed after severe steaming. In the case o f SO2, inhibition of the SCR reaction at low temperatures is caused by SO2 adsorption on active sites. However, this is fully reversible with temperat ure. No permanent loss of activity due to structural modification took plac e in SO2-containing reaction gases. (C) 1999 Elsevier Science B.V. All righ ts reserved.