465376 Control of Al Sites in the CON-Type Aluminosilicate Zeolite

Monday, November 14, 2016: 12:48 PM
Golden Gate 4 (Hilton San Francisco Union Square)
Masato Yoshioka and Toshiyuki Yokoi, Chemical Resources Laboratory, Tokyo Institute of Technology, Yokohama, Japan

Al-containing CON-type zeolites has been synthesized by the post-synthesis method using the CON-type borosilicate zeolite ([B]-CON). Very recently, a method for directly synthesizing Al-containing CON-type borosilicate zeolites ([Al,B]-CON) has been developed. We have first found that the directly synthesized [Al,B]-CON exhibited a higher catalytic performance in the MTO reaction in terms of duration and the propene selectivity than the MFI and *BEA-type aluminosilicate zeolites. Based on the high-resolution 27Al MAS NMR, the Al distribution in the framework would be dependent on the preparation method, i.e., direct or post-synthesis ones. The purpose of this study is to synthesize Al-containing CON-type zeolites with different Al distributions and to investigate their MTO activity.

[Al,B]-CONs were directly synthesized from the mother gel containing N,N,N-trimeth-yl-(-)-cis-myrtanylammonium hydroxide (TMMAOH) as OSDA. Additionally, CON-type borosilicates ([B]-CON) and Zn-containing CON-type borosilicates ([Zn,B]-CON were also prepared. Al-containing CON-type zeolites were synthesized by post synthesis method using [B]-CON and [Zn,B]-CON zeolites.

The Al state was investigated by 27Al MAS NMR technique in detail. The directly-synthesized [Al,B]-CON gave two peaks assigned to tetrahedrally-coordinated Al species at 58 and 54 ppm. the post-synthesized [Al]-CON using [B]-CON as parent (denoted as “[Al]-CON-P_[Zn]-CON”) had only one peak at 58 ppm. Interestingly, the post-synthesized [Al]-CON using [Zn,B]-CON as parent (denoted as “[Al]-CON-P_[Zn,B]-CON”) had peaks assigned to tetrahedrally-coordinated Al species at 60 and 54 ppm. These results imply that the Al distributions in the framework is strongly dependent on the preparation method. In general, Zn and B species are easily removed from the zeolite framework under acidic conditions. Considering that the 27Al MAS NMR spectrum of [Al]-CON-P_[Zn,B]-CON was clearly different from that of [Al]-CON-P_[B]-CON, Al atoms would be inserted into the Zn site, not B site.

Furthermore, we found that the Al distributions in the framework is varied with the B content of the [B]-CON as parent; [Al]-CON-P_[B]-CON was also prepared using [B]-CON (Si/B = 5). Its 27Al MAS NMR spectrum was different from [Al]-CON-P_[B]-CON (Si/B = 25) and [Al]-CON-P_[Zn,B]-CON.

11B MAS NMR spectrum of [B]-CON (Si/B = 25) showed one peak ascribed to tetrahedral B species, while [B]-CON (Si/B = 5) showed two peaks ascribed to trigonal B species in addition to tetrahedral B ones. Thus, we assumed that Al was inserted into the trigonal B site for [Al]-CON-P_[B]-CON (Si/B = 5) .

The directly prepared [Al,B]-CON catalyst showed a short life under W/F of 1.7 g h mol-1; the conversion of methanol was kept at >99 % until only 3 h. [Al]-CON-P_[B]-CON (Si/B = 25) also showed a short life under W/F of 3.3 g h mol-1, the conversion was drastically decreased at 1 h.

On the other hand, [Al]-CON-P_[Zn,B]-CON showed a much longer catalytic life but the trend of the products’ selectivities was almost the same. These facts imply that the Al distribution of the CON-type aluminosilicate strongly affects catalytic life in the MTO reaction.

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