题目

英语翻译
Fig.3 shows the DR UV–vis spectra of the (Co,H)-Y,the (Co,H)-Beta and as an example of the (Co,H)-Beta/Y (II).The spectra of other composites are similar to that of this sample.By deconvoluting the spectra with origin 6.1,six bands at about 645,618,560,522,506 and 472 nm could be observed for the (Co,H)-Beta sample.According to Děděcek et al's suggestion ,the quartet bands at 645,618,565 and 474 nm are attributed to β-type Co2+ ions (located at the position close to the plane of the deformed six-membered ring (MR) of the hexagonal cage present in polymorphs A and B) (see Scheme 1),whereas the doublet bands at 510 and 522 nm characterize for γ-type Co2+ ions (inside the hexagonal cage of polymorphs A and B).As for α-type Co2+ ions,the representative band should be near685 nm,which is absent in the prepared sample.This indicates that H+ ions in the α-type positions were difficult to be exchanged with Co2+ ions or the absence of α-type cationic sites in the prepared sample.It was suggested that this type of sites was formed by an elongated 6-MR composed of two-fold-connected 5-MRs in the polymorph C of zeolite Beta (Scheme 1) .As we know,Al-Beta synthesized in a common system free of Ge is usually composed of polymorph A and B,while polymorph C was hard to form in such a synthesis system.Therefore,it is not surprising of the absence of α-type Co2+ ions in the prepared sample.This also holds true for the (Co,H)-Y sample except that the positions of six bands were slightly different (645,617,568,529,500 and 474 nm) owing to the small difference in the local structure of various zeolites.The absence of α-type Co2+ species in the (Co,H)-Y could not be well understood yet for the moment since the similar ascription of cationic Co2+ sites has not been reported yet for Co-Y.Possibly this is due to the framework of zeolite Y free of 5-MRs.The probability for occupying the cationic sites by Co2+ ions depends on the coordination and local structure of these cationic sites as well as the Co loading and the co-cations present in the sample.As a consequence,the so-ascribed γ-type Co2+ species predominated the spectrum of the prepared (Co,H)-Beta catalyst probably as a result of the different local structure caused by the different preparation methods since zeolite Beta topology has three types of polymorphs.In contrast,in the case of the (Co,H)-Beta/Y (II) composite,although the band corresponding to α-type Co2+ ions could not be detected,either,by DR UV–vis spectroscopy,the quartet bands around 474,569,600 and 640 nm drastically increased in intensity.The area ratio of the quartet bands to the doublet bands was 1.37 in contrast to 0.39 and 1.07 for the (Co,H)-Beta and the (Co,H)-Y,respectively (Fig.3).This is in line with Děděcek's ascription that Co2+ ions in the β-type sites predominate the spectra regardless of Co loading and polymorphs of zeolite Beta .
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提问时间：2020-11-06

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