Synergistic effect of V₂O₅-WO₃/TiO₂ and H-ZSM-5 catalysts prepared by physical mixing on the selective catalytic reduction of NO_x with NH₃

There are more application areas where catalysts need a high activity for the selective catalytic reduction (SCR) of either NO or NO₂ with NH₃. V₂O₅-WO₃/TiO₂ is a conventional catalyst with high activity for the SCR of NO, while its catalytic performance is significantly low for the SCR of NO₂. In this work, a physical mixture of V₂O₅-WO₃/TiO₂ catalyst and H-ZSM-5 zeolite (V₂O₅-WO₃/TiO₂ + H-ZSM-5; PM) was prepared for the SCR of NO_x with NH₃. The PM catalyst exhibited similar deNO_x efficiency to the V₂O₅-WO₃/TiO₂ catalyst in the NH₃-SCR of NO. However, in the case of the NH₃-SCR of NO₂, the PM catalyst showed higher catalytic activities than the V₂O₅-WO₃/TiO₂ catalyst, attributed to a higher amount of NO₂ and N₂O₄ adsorption. Also, the PM catalyst produced much less N₂O than the H-ZSM-5 catalyst because of less NH₄NO₃ formed, which is an intermediate of N₂O formation. Moreover, the PM catalyst exhibited higher SO₂ tolerance than the V₂O₅-WO₃/TiO₂ catalyst due to the migration of ammonium bisulfate to the zeolite domain. This study demonstrates the desirable characteristics of PM catalyst, such as high deNO_x efficiency, low N₂O production, and high SO₂ resistance, which are of practical importance to apply for the SCR of either NO or NO₂.