990 resultados para Cu-ZnO-ZrO2 : HZSM-5
Resumo:
A kinetic model presented for the selective reduction of NO with CH4 over an InFe2O3/HZSM-5 catalyst by considering the process as a combination of two simultaneous reactions: NO+O2CH4 (reaction 1) and O-2+CH4 (reaction 2). Linear regression calculation was employed to find the kinetic parameters. It was found that although the activation energies of the two reactions were almost identical, the reaction rate constants were dramatically different, namely, k(1)much greater than k(2), indicating that the NO+O-2+CH4 reaction was more preferable to take place on the In-Fe2O3/HZSM-5 catalyst as compared with the O-2+CH4 reaction.
Resumo:
Variations in the structure and acidity properties of HZSM-5 zeolites with reduction in crystal sizes down to nanoscale (less than 100 nm) have been investigated by XRD, TEM and solid-state NMR with a system capable of in situ sample pretreatment. As evidenced by a combination of Al-27 MAS NMR, Si-29 MAS, CP/MAS NMR and H-1 MAS NMR techniques, the downsize of the zeolite crystal leads to an obvious line broadening of the Al-27, Si-29 MAS NMR spectrum, an increasing of the silanol concentration on the external surface, and a pronounced alteration of the acidity distribution between the external and internal surfaces of the zeolite. In a HZSM-5 zeolite with an average size at about 70 nm, the nonacidic hydroxyl groups (silanols) are about 14% with respect to the total amount of Si, while only 4% of such hydroxyl groups exist in the same kind of zeolite at 1000 nm crystal size. The result of H-1 MAS NMR obtained using Fluorinert(R) FC-43 (perfluorotributyl amine) as a probe molecule demonstrates that most of the silanols are located on the external surface of the zeolite. Moreover, the concentration of Bronsted acid sites on the external surface of the nano-structured zeolite appears to be distinctly higher than that of the microsized zeolite.
