SCR of NO by NH3 catalyzed by Mo- and V-exchanged zeolite: Effect of Mo precursor salt

• V–Mo/ZSM-5 solids (V = 2 wt.%, Mo = 3 wt.%) were tested in SCR of NO by NH3.
• 27Al NMR analyses enlightened the suitable conditions for Al2(MoO4)3 detection.
• Mo acetylacetonate and MoO3 salts enhance the formation of inactive Al2(MoO4)3.
• Inefficient species could be avoided using MoCl3 and NH4VO3 precursors.

V and Mo exchanged H+–ZSM-5 (Si/Al = 15) zeolite catalysts, prepared by solid-state ion exchange of ammonium metavanadate (2 wt.%) and different molybdenum salt precursors (acetylacetonate, oxide, carbonyl and chloride, molar ratio V/V + Mo = 2/3), were tested in the SCR of NO by NH3. Using [CH3COCHC(O–)CH3]2MoO2 like-precursor, acetylacetonate ligands extracted Al atoms from the zeolite framework and the formation of Al2(MoO4)3 was therefore extended. In the SCR of NO, such an undesired phase as well as crystalline MoO3 inhibited the diffusion of reactants. Starting from MoO3 and Mo(CO)6 precursors, the formation of small amounts of Al2(MoO4)3 is considered. However, the sublimation of Mo(CO)6 during the solid-state exchange avoided the agglomeration of Al2(MoO4)3 and the catalytic performance was therefore improved. The catalyst issued from MoCl3 is highly active in the studied reaction. V2O5 and Mo–V–O species are plausible active sites, while Al2(MoO4)3 and MoO3 oxide could be avoided during the exchange of MoCl3 into H+–ZSM-5.

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