Organic-free synthesis of zincoaluminosilicate zeolites from homogeneous gels prepared by a co-precipitation method

Abstract

Zeolites containing Zn in their frameworks are promising materials for ion-exchange and catalysis because of their unique ion-exchange capabilities and characteristic Lewis acidity. However, expensive organic compounds often required in their synthesis can prevent their practical uses. Here, a facile organic-free synthesis route for new zincoaluminosilicate zeolites having MOR topology, in which both Zn and Al are substituted in the framework, is demonstrated for the first time. The use of homogeneous zincoaluminosilicate gels prepared by a co-precipitation technique as raw materials is vital for the successful incorporation of both Zn and Al into the zeolite frameworks as revealed by several characterization techniques including solid-state NMR and UV-vis spectroscopy, and ion-exchange experiments. The obtained zincoaluminosilicate zeolites had high Zn contents comparable to those in the initial zincoaluminosilicate gels. In contrast, the uses of conventional sources of Si, Al, and Zn resulted in zeolites with very low contents of framework Zn or zeolites with extra-framework zinc oxide-species. FT-IR measurements using probe molecules and ion-exchange experiments suggested that there are two different environments of Zn in the zeolite frameworks. The obtained zincoaluminosilicate zeolites showed a higher ion-exchange efficiency for divalent cations such as nickel compared to the aluminosilicate analog. It is expected that the present co-precipitation technique is efficient for the incorporation of Zn (and other metals) into a variety of zeolite frameworks. To show its extended applicable scope, the synthesis of zincoaluminosilicate *BEA zeolite is also demonstrated.

Synthesis of New Microporous Zincosilicates with CHA Zeolite Topology as Efficient Platforms for Ion‐Exchange of Divalent Cations

“…For the synthesis of zeolite‐like materials with Zn in the frameworks, the formation of the homogeneous mixture of Zn and Si species is crucial to form the zincosilicate structures while preventing the precipitation of zinc oxides/hydroxides during hydrothermal treatment . In procedure (i), Zn species are totally dissolved as [Zn(OH) 4 ] 2− or [Zn(OH) 3 ] − in the clear solution because of the high alkalinity of TMAdaOH solution (pH >14) .…”

“…As reported recently, zincosilicate zeolite‐like materials show strong Lewis acidity . FTIR analysis of Zn‐CHA2, after adsorption of deuterated acetonitrile (CD 3 CN) at 80 °C and then desorption at 80–250 °C, was performed to characterize its Lewis acid sites in comparison with zincoaluminosilicate CHA (Zn,Al‐CHA; Si/Al=10.5, Si/Zn=15.3) (see Figures S8 and S9, and Table S1 in the Supporting Information).…”

“…2284 cm −1 is probably associated with Li‐bearing Zn sites . The bands present at 2308 and 2319 cm −1 are associated with CD 3 CN coordinated to Lewis acid sites . The existence of these two absorption bands suggests that there were two different Lewis acid sites in the zincosilicate CHA product, as the metal‐substituted zeolite‐like materials are known to have different metal sites, the so‐called “closed” and “open” sites (see Scheme ) .…”

“…The existence of these two absorption bands suggests that there were two different Lewis acid sites in the zincosilicate CHA product, as the metal‐substituted zeolite‐like materials are known to have different metal sites, the so‐called “closed” and “open” sites (see Scheme ) . The closed Zn site, (observed at 2308 cm −1 ), creating two negative charges, is suitable for stabilization of bare divalent metal cations, whereas the open Zn site, (observed at 2319 cm −1 ), a monocation ion‐exchangeable site, has been considered as an active Lewis acid . The Zn,Al‐CHA sample also showed similar spectra, however, the band assigned to the Li‐bearing sites at 2284 cm −1 observed in Zn‐CHA2 was shifted to 2277 cm −1 , which is likely associated with Na + present in the Zn,Al‐CHA sample (see Figure S7 b) .…”

Suppressing C–C Bond Dissociation for Efficient Ethane Dehydrogenation over the Isolated Co(II) Sites in SAPO-34

“…Constructing a support–metal–strong-interaction (SMSI) catalyst is a general guide with various top-down and down-top methods. Incorporation of metal ions or oxides into the framework or the matrix of supports can be realized under a one-pot synthesis condition, − where the precursors of the metal and the elements of the support (such as Si and Al) are placed together in a beaker or autoclave. For example, Yang et al reported an Fe-containing MFI siliceous zeolite and Bian synthesized a mesoporous-silica-stabilized Co- m SiO 2 catalyst, and these catalysts have −M δ+ –O δ− – structures that are not easily reduced and have been demonstrated to be active, selective, and stable for alkane dehydrogenation.…”