A high effective adsorbent of NOx: Preparation, characterization and performance of Ca-beta zeolites

A NOx adsorbent of H-beta zeolites modified with calcium oxide (Ca-beta) was prepared by an incipient wetness impregnation method, and characterized by XRD, N2 adsorption/desorption, CO2-TPD, NO-TPD and in situ FT-IR spectroscopy. The results show that the CaO loading amount affects obviously the textural structure properties and adsorption capacity of Ca-beta for NOx, and the presence of O2 in the feed gas is in favor of oxidizing NO to NO2 and promoting NO adsorption on Ca-beta. The presence of water vapor in feed gas can partly destroy the selective adsorption sites and block the micropore, resulting in lowering the adsorption property of Ca-beta. There are two kinds of adsorption sites for adsorbing NOx on Ca-beta, which are weak base sites on H-beta zeolites and strong sites from supported CaO, respectively. The in situ   FT-IR spectra show that the NOx species absorbed on Ca-beta are mainly the NO3-, NO2- and NO+ species, among which the concentration of NO3- species is the highest and the second is NO2-. The NO3- species adsorbed on Ca-beta can be decomposed and desorbed at 500–550 °C.

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► H-beta zeolite modified with CaO is a high effective NOx adsorbent.
► CaO amount affects obviously the textural structure and NOx adsorptivity of Ca-beta.
► O2 in feed gas promotes NO adsorption on Ca-beta and vapor lowers NOx adsorption on it.
► NOx absorbed species on Ca-beta are mainly NO3-, secondly NO2- and a little NO+.