Development of Highly Durable Zeolites as Hydrocarbon Trap Materials for Automotive Catalysts

Paper #:
  • 2018-01-0947

Published:
  • 2018-04-03
Abstract:
Low temperature activity has been highly required for automotive catalysts. In particular, the most part of tailpipe emissions occur right after the engine starting (Cold Emissions). To reduce these emissions, trap material such a zeolite for hydrocarbon (HC) adsorption would be one of the most powerful tools for automotive catalysts. However, the range of application is quite narrow due to its low durability under hydrothermal aging condition. And that is the reason why zeolites can be often used for diesel engines to keep away from thermal loading and take advantages of their adsorption abilities. Generally, thermal endurance of close-coupled catalysts for gasoline powered vehicles proceeds at about 1000˚C in the presence of water in which condition zeolite structures would be decomposed by dissociation of aluminum from zeolite frameworks. In this paper, we describe that hydrothermal durability of zeolite can be dramatically improved by the reaction with zirconium phosphate and this modified zeolite shows much higher SSA and the amount of HC adsorption than the corresponding unmodified zeolites after aging. Specially, this improvement strategy works well for β-type zeolites (BEAs) with low SiO2/Al2O3 ratio, which can be easily decomposed at around 1000 ˚C. We also found that this modified BEA worked well as HC trap material and showed a strong effect on the reduction of cold HC emissions with Pd/Rh three-way catalyst (TWC). In an engine test evaluations with aged catalysts, this effect on cold emissions carried out decreasing up to 43% of HC emissions from the corresponding TWC without zeolite. And also, the detailed analysis of this effect showed that this improvement was given by the adsorption-desorption process by zeolite and the purification process by TWCs. Details of fundamental properties of modified zeolite and these corporative catalytic effects will be discussed in oral presentation.
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