Yani Zhang,Yue Peng,Chizhong Wang,Kezhi Li,Shuai Liu,Xiansheng Li,Jianjun Chen,Junhua Li
Graphical Change for copper : Copper ion exchanged SAPO-47 zeolite catalysts are synthesized and used for the selective catalytic reduction (SCR) of NO x with ammonia, for which they exert high activity. The structure–activity relationship is explored. Copper-exchanged H-SAPO-47 zeolites were synthesized by an aqueous solution ion exchange method and applied in the selective catalytic reduction of NO with NH 3 (SCR). The microporous chabazite (CHA) structure of the catalysts was characterized and confirmed using synchrotron X-ray diffraction and nitrogen adsorption–desorption experiments. The synthesized Cu x -SAPO-47 catalysts exhibited excellent SCR activity and nearly 100 % N 2 selectivity in a wide temperature range. The Cu 0.1 -SAPO-47 sample exhibited higher activity than the other samples below 250 °C. The weak Lewis acid sites originating from the introduction of Cu 2+ were more active than the Brønsted acid sites of the zeolites framework at low temperature. Two types of isolated Cu 2+ species with different coordination surroundings were found, namely, Cu 2+ cations bonded with the six-membered rings and those bonded in the CHA cages. The former species exhibited good stability and activity at high temperature, whereas the latter ones were more active at low temperature. The Cu 0.1 -SAPO-47 catalyst provided a considerable amount of isolated Cu 2+ bonded in the CHA cages. These results indicated that active Lewis acid sites and isolated Cu 2+ species are responsible for their excellent SCR activity.
Bei Liu,Xiaohui Zhao,Wenting Mao,Haijun Chen,Lu Han,Kake Zhu,Xinggui Zhou
Generation of hierarchical zeolites is an effective way to enhance their diffusion-dependent catalytic properties. The fabrication of hierarchical zeolites with enhanced diffusion property, high hydrothermal stability, strong acidity in an inexpensive, facile and efficient way is particularly daunting. Here, a simple synthesis of hierarchical SSZ-13 zeolite in a biphasic water/toluene media under tumbling assisted by organosilane, i.e., trimethoxy[3-(phenylamino)propyl]silane, is proposed. The obtained material with tunable Si/Al from 10 to 30 consists of assembled crystallites of 20–30 nm that construct a hierarchical architecture with mesopores of ca . 7 nm opening to the external facets, and has low defect concentration and preserved strong acidity. Crystallization mechanism is disclosed to obey a non-classic attachment growth of nano building blocks mediated by Pickering emulsion , as organosilane modification changes their surface to be hydrophobic. Such a crystallization pathway has accelerated nucleation process and suppressed the growth of SSZ-13 crystals to micron size. Cu exchanged hierarchical SSZ-13 outperforms the standard sample in typical NH 3 -SCR process in both low and high temperature regimes as a result of enhanced diffusion property, as well as low defect concentrations. The synthesis is a cost-effective method for the generation of hierarchical zeolites mediated by the presence of a liquid/liquid interface, and could inspire more such explorations.
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