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Abstract
Temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR) and stop flow-TPD techniques as well as FT-IR spectroscopy of pre-adsorbed NH3 and NO are applied to characterize active sites present in Co-containing BEA zeolites. Cobalt is introduced into BEA zeolite by different methods: (i) two-step postsynthesis – PS, (ii) conventional wet impregnation – Imp and (iii) ion-exchange – IE. The obtained catalysts are labelled as Co(PS)SiBEA (postsynthesis), Co(IMP)AlBEA (wet impregnation) and Co(IE)AlBEA (ion exchange). All the obtained catalysts are found to be active in the process of selective catalytic reduction (SCR) of NO with ammonia. The catalytic activity depends on the method used for cobalt introduction and thus on cobalt centres speciation. The reactivity of NH3 and NO adsorbed on Co(IMP)AlBEA and Co(IE)AlBEA is higher than that measured for the Co(PS)SiBEA catalysts. The temperature-programmed studies and FT-IR with NO and/or NH3 adsorption for the Co-containing samples show that during SCR reaction NO and NH3 molecules compete for the same adsorption sites. The main reaction pathways of the DeNOx process performed in the presence of Co(IMP)AlBEA and Co(IE)AlBEA involves the reaction between chemisorbed ammonia and NO from gas phase, according to the Eley-Riedel mechanism.
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