The effect of Si environments on NH3 selective catalytic reduction performance and moisture stability of Cu-SAPO-34 catalysts

SAPO-34s with varying Si content templated by bulky tetraethylammonium hydroxide (TEAOH) were prepared to investigate the effect of Si environments on the selective catalytic reduction (SCR) of NOx and the moisture stability of Cu-SAPO-34 catalysts. These Cu-SAPO-34s have similar Cu loadings, isolated Cu2+ content, and Brønsted acid sites (BAS). Both the ratio of Si islands and the acid strength of Cu-SAPO-34s increase with increasing Si content. In situ diffused reflection infrared Fourier transform spectroscopy (DRIFTS) studies reveal that the NH3 adsorbed on mild BAS (associated with Si(4Al) species) is more active for NOx conversion than NH3 adsorbed on strong ones (associated with Si islands). This agrees well with the high turnover frequency (TOF) and the low activation energy on Cu-SAPO-34 with low Si content and abundant Si(4Al) species (sample Si-7.7). Upon hydration treatment, the textural properties, strong acid sites, and reducibility of isolated Cu2+ ions show a decrease. This deterioration intensifies with the increasing Si islands in the catalysts due to the easier occurrence of Si migration and the formation of larger Si islands. Sample Si-7.7 exhibits the best moisture stability and thus well-preserved denitration performance. These results imply that a practical Cu-SAPO-34 catalyst with superior activity and moisture stability may be achieved by controlling the Si environments of SAPO-34 templated by bulky amines.