Distribution of Al atoms in zeolite framework has been recognized as an important factor for catalytic activity and selectivity, and its control and evaluation have been extensively tackled by many research groups. The CHA-type zeolite has one unique nonequivalent tetrahedral site (T site) in double 6-membered ring (D6R) building unit that connects to form a three-dimensional pore system with the large cha cages. Hence, the Al distribution in the CHA-type zeolite has been discussed in terms of the distance between Al atoms, so-called “isolated” or “pairing” Al spices. The influence of the starting materials, i.e., Si and Al sources, has been investigated in terms of the component in the final CHA framework, while its impact on the Al distribution has not fully been clarified to date. We have considered the proportion of “Q4(1Al)”, Si(OSi)3(OAl)1, “Q4(2Al)”, Si(OSi)2(OAl)2 and “Q4(3Al)”, Si(OSi)1(OAl)3 in the total framework Al species, which can be estimated by solid state 29Si MAS NMR technique as an index for Al distribution. Here, the CHA-type aluminosilicate zeolites were synthesized from the different starting materials including fumed silica, aluminum hydroxide, and the FAU-type zeolite, with their proportions varied. When the proportions of FAU in the raw material were 10 and 100 %, the products were designated as “CHA-F-0.10” and “CHA-F-1.0”, respectively. By the 29Si MAS NMR spectra of CHA-F-0.10 and CHA-F-1.0, CHA-F-0.10 had a higher Q4(1Al) peak, but lower Q4(1Al) peak than CHA -F-1.0. Thus observed differences imply that the Al distribution of the products would be influenced by the proportion of FAU (Si / Al = 2.8) in the raw material gel. The catalytic properties of the CHA-F-0.10 and CHA-F-1.0 samples synthesized for the MTO reaction at 623 K were representatively evaluated. There was no marked difference in the products distributions, while CHA-F-0.10 exhibited a much longer catalytic life than CHA-F-1.0. This would be caused by the difference in the Si(1Al)/Si(2Al) ratio, i.e., Al distribution in the framework. Thus, we have successfully found that the proportion of FAU in the raw material strongly affect the distribution of Al in the CHA framework, leading to the difference in the catalytic properties.

Impact of starting materials on the Al distribution of the CHA-type aluminosilicate zeolites

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.