The specific behavior of HY in some steps that possibly occurred in the selective catalytic reduction of No by hydrocarbon (HC-SCR) was investigated. Experimental results indicated that the activity of HY for NO oxidation to NO2 Was much lower than those of the pentasil zeoiites (HZSM-5. HFER and HMOR). In addition, FTIR measurements showed that both nitrosonium ions (NO+) and nitrate species were remarkably produced at 300 C over the pentasil zeolites and they were highly active towards hydrocarbons at the temperature. On the contrary, no NO+ Species Could be detected over HY and the nitrate species produced over the zeolite were almost inactive towards reduction at the same reaction condition. It is proposed that the low amount of strong Bronsted acids of HY accounts for the above inferior functions of the zeolite required by HC-SCR, leading to the low NO reduction activity. (C) 2009 Elsevier B.V. All rights reserved.