Influence Of Preparation Conditions Of Mixed-valence Con+/zsm-5 Zeolites On Their Adsorption
INFLUENCE OF PREPARATION CONDITIONS OF MIXED-VALENCE Con+/ZSM-5 ZEOLITES ON THEIR ADSORPTION
AND CATALYTIC PROPERTIES IN CO OXIDATION
L.P. Oleksenko, V.K. Yatsimirsky, L.V. Lutsenko
Kiev Shevchenko National University, Kiev, Ukraine
Search of efficient catalysts for purification of exhaust gases is actually of a great importance. Because Co-containing zeolites are active redox catalysts we consider it interesting to investigate Co/ZSM-5 zeolites with cobalt species in different oxidation states in catalytic reaction of CO oxidation.
The Co-containing ZSM-5 zeolites have been prepared by ion exchange and impregnation methods using Co(NO3)2 and [Co(NH3)6]Cl3 solutions. In catalysis and the other experiments Co2+/, Co3+/ and Co2+-Co3+/ZSM-5 were used as initial system and as one after reduction treatment in hydrogen flow at 300 – 500 0C during 2 – 5 hours.
The catalytic activity of Co-loaded zeolites was measured in CO oxidation in reaction gas mixture enriched with oxygen. It was found that treatment in H2 causes the activity increasing for all Co2+ and Co2+-Co3+ systems, but the activity of the Co3+/ZSM-5 remains uniform pointing at very low reducibility of cobalt hexaaminocomplex ion embedded into zeolite framework. Catalytic activity changes in the order Co3+/ZSM-5
The acidic property investigation by TPD of ammonia displays a presence of two types of acid sites. The NH3 desorption from weak and strong sites was fixed at temperature 100 – 380° C and 400 – 700° C relatively. The strong adsorption has a predominant contribution in ammonia adsorption process for all samples used. The acidity decrease because of proton elimination during cation introduction and reduction treatment is seen to correspond to increase of the catalytic activity.
Related articles::