Abstract
In this study, titanium silicalite (TS-1) crystals containing Al were synthesized using aluminosilicate MFI zeolites as seeds in a tetrapropylammonium bromide (TPAB)–ethanolamine (EA) system. The TS-1 containing Al possessed large size, large Lb value and higher catalytic activity in cyclohexanone ammoximation. Larger Lb value would endow the TS-1 crystals with better mechanical strength and erosion resistance. The introduction of an Al atom into the TS-1 crystals resulted in the production of more acid sites and a bit strong Brönsted acid sites; these acid sites were more favorable to the catalytic performances in cyclohexanone ammoximation.
Highlights
TS-1 molecular sieves with an MFI topology structure have received signi cant attention due to their active and selective catalytic performances in many selective oxidation reactions[1] such as hydroxylation of aromatics,[2,3] epoxidation of alkenes,[4,5] ammoximation of ketone,[6,7] and oxidation of bulky molecules.[8]
The rst effective strategy was to enlarge the size of the b-axis micropores; hierarchical TS-1 materials were synthesized using the mesopore template,[12,13,14] and hierarchical porous structures were constructed by treating the TS-1 zeolite with organic bases.[15,16,17]
For TS-1 prepared with the same type of seeds, higher cyclohexanone conversion was obtained over the catalysts with a smaller size, and the catalytic activity was TS-1-4 > TS-1-1 > TS1-4 > TS-1-2, which should be attributed to the incorporation of Al atoms and thinner size of TS-1.48 TS-1-2, synthesized by micro S-1 (m-S-1) seed with a size of 2.32 mm, provided worse catalytic performances than TS-1-1 in cyclohexanone ammoximation due to its high Si/Ti ratio
Summary
Bifunctional zeolite catalysts have been employed in various processes in the petroleum re ning and petrochemical industries because of their metallic and acid sites.[28] Some metals, such as precious metals,[29,30,31] Cd2+,32 and Fe2+,33 incorporated into the TS-1 skeletons have improved the catalytic activity of TS-1. The hierarchical porous structure was much more effective in improving the catalytic properties of TS-1 zeolite for ketone ammoximation[38,39] because the ori ces on the surface of the catalysts could alleviate the diffusion limitations. Aluminosilicate and pure silicon zeolites were used as seeds to prepare the TS-1 crystals and TS-1 containing Al. The resources of the Ti and Si template used in this study were costeffective and suitable for industrialization production. The TS-1 using nano ZSM-5 seed exhibited big size, excellent catalytic activity and stability in cyclohexanone ammoximation
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