Regulation of the Copper-OIxide Cluster Structure and DeNOx Activity of Cu-ZSM-5 Catalysts by Variation of OH/Cu2+
Статья (Full article),
, E-ISSN: 1873-4308
||Copper-oxide cluster, Cu-ZSM-5, DeNOx activity, Isolated copper ion, N 2O decomposition, Selective catalytic reduction by propane
Yashnik Svetlana A.
Salnikov Anton V.
Vasenin Nikolai T.
Anufrienko Vladimir F.
Ismagilov Zinfer R.
Boreskov Institute of Catalysis SB RAS, Pr. Akad. Lavrentieva, 5, Novosibirsk 630090, Russia
Institute of Coal Chemistry and Material Science, Pr. Sovetskiy, 18, Kemerovo 650000, Russia
Информация о финансировании (1)
The present work studies a possibility to regulate the size and structure of magnetic associates of copper ions by varying the OH/Cu2+ ratio in a wide range (from 0 to 30) during the hydrolytic polycondensation of copper chloride in the zeolite pores. The redox properties and reactivity in N2O decomposition and NO-SCR by propane of the Cu-modified ZSM-5 catalysts prepared by the hydrolytic polycondensation are examined and compared with the properties of copper-substituted ZSM-5 zeolites having a close copper content (1wt.%) and produced by the ion exchange with water-ammonia solutions of copper chloride at OH/Cu equal to 6-30.
The origin of active copper species, which are formed during hydrolytic polycondensation under variation of ОН/Cu and at subsequent thermal treatment, has been studied by ESR and UV-Vis DR spectroscopy. It was shown that an increase in ОН/Cu from 1-3 to 6-30 leads to the orbital ordering of Cu2+ ions in the weak associates, which shows up as a change of the symmetric signal (g0 = 2.18) from disordered polynuclear copper hydroxocomplexes to the rhombic signals (gz1 = 2.18, gy1 = 2.08, gx1 = 2.03 and gz2 = 2.24, gy2 = 2.08, gx2 = 2.03) corresponding to the ordered polynuclear complexes of copper ammoniate. The 1%Cu(30)ZSM-5-HPC sample prepared at OH/Cu = 30 has a higher amount of isolated tetraammine-copper complex and a lower number of weak associates of Cu2+ ions among samples of this series. Thermal treatment of 1%CuZSM-5-HPC leads to a gradual removal of ammonia from the copper environment. Hence, these samples calcined at 500oC comprise the isolated Cu2+ ions surrounded by the oxygen-containing ligands, similar to the samples prepared at OH/Cu equal to 0-3.
The addition of ammonia solution to the copper-impregnated zeolite for hydrolytic polycondensation and variation of the ammonia to copper ratio (OH/Cu from 1 to 30) have a favorable impact on the Cu-ZSM-5 activity in N2O decomposition and NO-SCR by propane. In the low-temperature region, the ion-exchanged CuZSM-5 catalysts were more active in N2O decomposition, while at high temperatures the ex-polycondensation provided a high N2O conversion. It is suggested that the ordered associated Cu2+ ions of ex-polycondensation catalyst have higher activity and selectivity in both DeNOx processes as compared to the isolated copper ions.