TY - JOUR
T1 - Determination of active palladium species in ZSM-5 zeolite for selective reduction of nitric oxide with methane
AU - Ogura, Masaru
AU - Hayashi, Masayoshi
AU - Kage, Susumu
AU - Matsukata, Masahiko
AU - Kikuchi, Eiichi
PY - 1999/12/6
Y1 - 1999/12/6
N2 - The active site in ZSM-5 zeolite-supported palladium, which shows the catalytic activity for NO reduction with methane as a reducing agent, has been investigated qualitatively and quantitatively by means of NO chemisorption and NaCl titration, comparing with PdO supported on silica. Palladium species in 0.4 wt.% Pd loaded H-ZSM-5 can adsorb NO equimolarly after calcination at 773 K, and almost all the NO was desorbed at around 673 K, while the palladium species on PdO/SiO2 hardly adsorbed NO. The palladium species in Pd(0.4)/H-ZSM-5 are ion-exchangeable with Na+ in NaCl solution, indicating that they exist in a cationic state of an isolated Pd2+. This method for quantitative analysis of the isolated Pd2+ cations is named as 'NaCl titration'. The amount of the isolated Pd2+ cationic species increased with increasing palladium content on Pd/H-ZSM-5, and PdO co-existed above 1 wt.%. The amount of the isolated Pd2+ cation was unchanged after the reaction of NO2-CH4, NO2-CH4-O2, or CH4-O2 at 673 K, while the adsorbed amount of NO per the Pd2+ as determined by NO-TPD decreased after the NO2-CH4-O2 reaction. It was found by NaCl titration that the catalytic activity of Pd/H-ZSM-5 for NO2-CH4-O2 reaction increased with increasing amount of the isolated Pd2+ cationic species up to 0.7 wt.%, while the increase in the amount of PdO led to decrease in selectivity towards NO2 reduction. The palladium species that are active and selective for NO reduction with CH4 will be proposed.
AB - The active site in ZSM-5 zeolite-supported palladium, which shows the catalytic activity for NO reduction with methane as a reducing agent, has been investigated qualitatively and quantitatively by means of NO chemisorption and NaCl titration, comparing with PdO supported on silica. Palladium species in 0.4 wt.% Pd loaded H-ZSM-5 can adsorb NO equimolarly after calcination at 773 K, and almost all the NO was desorbed at around 673 K, while the palladium species on PdO/SiO2 hardly adsorbed NO. The palladium species in Pd(0.4)/H-ZSM-5 are ion-exchangeable with Na+ in NaCl solution, indicating that they exist in a cationic state of an isolated Pd2+. This method for quantitative analysis of the isolated Pd2+ cations is named as 'NaCl titration'. The amount of the isolated Pd2+ cationic species increased with increasing palladium content on Pd/H-ZSM-5, and PdO co-existed above 1 wt.%. The amount of the isolated Pd2+ cation was unchanged after the reaction of NO2-CH4, NO2-CH4-O2, or CH4-O2 at 673 K, while the adsorbed amount of NO per the Pd2+ as determined by NO-TPD decreased after the NO2-CH4-O2 reaction. It was found by NaCl titration that the catalytic activity of Pd/H-ZSM-5 for NO2-CH4-O2 reaction increased with increasing amount of the isolated Pd2+ cationic species up to 0.7 wt.%, while the increase in the amount of PdO led to decrease in selectivity towards NO2 reduction. The palladium species that are active and selective for NO reduction with CH4 will be proposed.
KW - Methane
KW - NO reduction
KW - NO-TPD
KW - NaCl titration
KW - Palladium
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U2 - 10.1016/S0926-3373(99)00082-X
DO - 10.1016/S0926-3373(99)00082-X
M3 - Article
AN - SCOPUS:0033530889
SN - 0926-3373
VL - 23
SP - 247
EP - 257
JO - Applied Catalysis B: Environmental
JF - Applied Catalysis B: Environmental
IS - 4
ER -