Surface-modified TS-1 with enhanced activity for cyclohexanone ammoximation in a Pickering emulsion and increased stability in hot aqueous ammonia

Abstract

Functional TS-1, partially hydrophobilized with organosilanes, was found more active and stable in Pickering emulsion system. In this work, TS-1 behaved simultaneously as a catalyst and solid emulsifier favoring cyclohexanone ammoximation reaction in organic solvent-free condition. The composition, structure, formed emulsion morphology, surface morphology were characterized by Fourier-transform infrared (FT-IR) spectroscopy, conductometer, optical microscope with high speed CCD camera, Brunauer-Emmett-Teller (BET)，X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It indicated that hydrophobilization provided TS-1 a moderate wettability, allowing the formation of 2 stable Pickering emulsion, thus promoting the performence in catalyzing cyclohexanone/H 2 O 2 /NH 3 •H 2 O reaction system in the absence of organic solvent.What is more, due to alkyl groups grafted to TS-1, the zeolites were comparatively exclusive to aqueous phase and they are more capable to endure severe environment, ie., 200 ºC, under autogenic pressure. 3 ago, has been widely studied for water/oil and oil/water systems [11] . It has a variety use in functional materials, such as capsules [12,13] , Janus particles [14,15] , composite particles [16,17] , and emulsion assemblies [18,19] . The solid particles used in Pickering emulsion formation are multitudinous, such as SiO 2 [20] , Fe 3 O 4 [21] , Polyoxometalate nanoparticles [22] , and kaolin [23] . Things could also happen to catalyst TS-1.Titanium silicate-1 (TS-1) is the preferred catalyst used in ammoximation of cyclohexanone for its orderly channel and unique shape-selective catalytic function.TS-1, first synthesized by Taramosso et al. [24] in 1983, is a typical environmental friendly catalyst. After 1983, TS-1 is synthesize through many ways [25,26] , derived from the classic method of Taramosso's. It is an important catalyst for selective oxidation of a large number of organic substrates, for instance, alkanes, alkenes, alcohols, aromatics and phenol [27][28][29][30][31][32][33] . TS-1 has the potential to act as solid emulsifier, as well, only if it has a moderate wettability.The stability of zeolite plays an extreme important role in catalyst system, however, according to work of Florian's [34] , the framework structure Si-O-Si could been hydrolyzed by hydroxyl ions, especially in harsh environment, e.g. high temperature and pressure. It has been reported that referentially anchoring hydrophobic functionalities on the external surface can effectively prevent direct contact between bulk liquid water and the zeolite, thus preventing the collapse of the framework in hot water [35] . Xiangyu Wang [36] also a method that after being modified by ethanolamine, TS-1 exhibited excellent catalytic activity and stability in the continuous cyclohexanone ammoximation. 7 Modification with OTSIR spectrum is one of the classical methods for structure determination due to its sensitivity to the chemical composition and architecture of molecules. In t...

Surface-Active Hollow Titanosilicate Particles as a Pickering Interfacial Catalyst for Liquid-Phase Alkene Epoxidation Reactions

“…Zeolites, with shape selectivity, high acidity, and good hydrothermal stability, are extensively used as heterogeneous catalysts in many industrial processes. , The titanium-containing silicate named TS-1, first reported by the company Snamprogetti SpA in 1983, has gained great interest because of its remarkable catalytic properties in the liquid-phase selective oxidations of aromatic hydroxylation, alkene epoxidation, and ketone ammoximation , using hydrogen peroxide as the oxidant under mild conditions. The aforementioned alkene epoxidation reactions are typically liquid–liquid biphasic reactions, that is, at a planar interface.…”