Abstract
In this study, a series of SnO2 modified zeolite catalysts (Snx-S-1; x is the weight percentage of Sn) were prepared with SnCl2 and a defective Silicalite-1 (S-1) zeolite via facile deposition–precipitation method. It was found that the stannic species modified all-silica zeolite catalysts were active for the intermolecular condensation of ethylenediamine (EDA) to 1, 2-Diazabicyclo [2, 2, 2] octane (TEDA) and piperazine (PIP). The best catalyst Sn6-S-1 (6 wt.% Sn loading) showed 86% EDA conversion and 93% total selectivity to TEDA and PIP. By contrast, the defective S-1 zeolite parent showed only approximately 9% EDA conversion under the same conditions. With the help of catalyst characterization techniques including hydroxyl vibration and pyridine adsorption FT-IR spectroscopy (transmission mode), the enhancement of the catalytic activity of the SnO2 modified zeolite catalysts (Snx-S-1) was mainly attributed to the formation of mild Lewis acid sites in the siliceous zeolite. Both the hydroxyl nests of the defective S-1 zeolite and the dispersed SnO2 clusters should be the important factors for the formation of mild Lewis acid sites on the modified zeolite. Based on the catalytic performance of the modified zeolite in the conversion of EDA to PIP and TEDA, it is inferred that the mildly acidified defective S-1 zeolite by the SnO2 deposition modification might become a very active and durable catalyst for reactions involving strongly alkaline reactants and products.
Highlights
Zeolitic solid acids with strong acidic sites have attracted attention in the past because they are good catalysts for a long list of hydrocarbon transformation reactions in both oil refining and petrochemical industries [1]
One important example of this kind of reaction is the conversion of ethylenediamine (EDA) to heterocyclic amines like 1, 2-Diazabicyclo [2, 2, 2] octane (TEDA) and piperazine (PIP)
Catalyst samples were characterized by scanning electron microscope (SEM), UV−visible spectroscopy nitrogen physisorption, Fourier transform infrared spectroscopy (FT-IR), Catalyst (UV−VIS), samples were characterized by scanning electron microscope (SEM), UV−visible and
Summary
Zeolitic solid acids with strong acidic sites have attracted attention in the past because they are good catalysts for a long list of hydrocarbon transformation reactions in both oil refining and petrochemical industries [1]. In the 1990s, H-ZSM-5 zeolite had been used as catalyst for the conversion of EDA to TEDA and PIP [7,8]. Previous study indicated that the defective S-1 zeolite itself was not very active and selective for the reaction of EDA to TEDA and PIP, giving only 19.5% EDA conversion and 7.5% TEDA selectivity [11]. This implies that the acidity of defective S-1 is too weak to be an efficient catalyst for the conversion of EDA. We think that the Sn-containing S-1 zeolite, as a kind of mild solid acid catalyst, might find many applications in the future, especially in the area of transforming strongly alkaline N-containing organic molecules
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