Tetrapropylammonium hydroxide TPAOH

Taramasso et al. (5) had originally reported two methods for the hydrothermal synthesis of TS-1. The first method (mixed alkoxide method) involves the preparation of a solution of mixed alkoxides of titanium and silica (preferably ethoxides) followed by hydrolysis with alkali-free solution of tetrapropylammonium hydroxide (TPAOH), distillation of the alcohol and crystallization of the resulting gel at 448 K. In the second method (dissolved or hydrolyzed titanium method) a soluble tetrapropylammonium peroxo-titanate species was prepared initially and then colloidal SiC>2 (Ludox AS-40) was added. This entire operation had to be carried out at 278 K. The TS-1 samples obtained by these two synthesis routes differed, particularly because of the presence of impurities such as Al3+ usually present in colloidal silica (33). 

Scholle et al. (220) used 27A1 MAS NMR at 130.3 MHz to study the intermediates of zeolite ZSM-5 containing tetrapropylammonium hydroxide (TPAOH) as template as a function of crystallization time. For the samples... 

The isomorphous substitution of T atoms by other elements produces novel hybrid atom molecular sieves with interesting properties. In the early 1980s, the synthesis of a zeolite material where titanium was included in the MFI framework of silicalite, that is, in the aluminum-free form of ZSM-5, was reported. The name given to the obtained material was titanium silicalite (TS-1) [27], This material was synthesized in a tetrapropylammonium hydroxide (TPAOH) system substantially free of metal cations. A material containing low levels (up to about 2.5 atom %) of titanium substituted into the tetrahedral positions of the MFI framework of silicalite was obtained [28], TS-1 has been shown to be a very good oxidation catalyst, mainly in combination with a peroxide, and is currently in commercial use. It is used in epoxidations and related reactions. TS-1, additionally an active and selective catalyst, is the first genuine Ti-containing microporous crystalline material. 

Basic silicate solutions were prepared by using silicic acid (ex Baker, dried at 350 °C) and a solution of the organic bases [25 wt % tetramethylammonium hydroxide (TMAOH), 40 wt % tetra-ethylammonium hydroxide (TEAOH), 20 wt % tetrapropylammonium hydroxide (TPAOH) ex Fluka] and, optionally, dimethyl sulfoxide (DMSO). A solution of hexamethonium hydroxide [ (MejNCgH NM ) (OH) 2] was prepared from the bromide salt (ex Sigma) and A O. 

Mixed alkoxide method. Hydrothermal synthesis using tetraethylorthosilicate (TEOS) as the source of Si, tetraethyltitanate (TEOT) as the source of Ti, tetrapropylammonium hydroxide (TPAOH) as structure directing agent (template), base and distilled water... 

SZl synthesis. A transparent sol is formed by adding 66.0 g of Zr(OC3H7)4 (70 wt % in n-PrOH) and 10.0 g of tetrapropylammonium hydroxide (TPAOH, 40 wt % in water) to 364.0 g of n-PrOH. After 2 hours of ageing under stirring, the sol is added with 50 g of aqueous solution of 0.44 M H2SO4. The dense slurry obtained is stirred for 4 hours at room temperature, followed by 4 hours at 60 °C. The sample is dried for 8 hours at 100 °C under vacuum and calcined at 550 °C for 5 hours. 

Mesoporous ZSM-5 named Z41(X), with X = Si/Al ratio used in the synthesis gel, were prepared by impregnation of the dried carbon cast with aqueous tetrapropylammonium hydroxide (TPAOH 1 mol/L) until incipient wetness. Subsequently a calculated amount of aluminum sulfate and TEOS were added to achieve a molar composition of 1 Si02 x AI2O3 0.36 TPAOH 8 H2O with x=0.005 for Z41(100) and =0.01 for Z41(50). The crystallization was carried out in a saturated water atmosphere at 180 °C for 72 h and the carbon cast and the occluded template cations were burned off at 550 °C for 6 h. 

Samples were prepared via sol-gel in alkali-free medium using Si(OC2H5)4 (Dynasil-A, Nobel), Al(sec-OC4H9)3 (Fluka), tetrapropylammonium hydroxide (TPAOH, Sachem),... 

The first method uses the controlled concurrent hydrolysis of tetraethoxytitanium (IV) and tetraethoxysilane. This procedure has been labeled the mixed alkoxide method. Frequently, the acronyms TET (tetraethyltitanate) and TEOS (tetraethyl orthosilicate or tetraethoxysilane) are used for the respective reactants these are derived from the alternative names tetraethyl titanate and tetraethylorthosilicate. In examples described in patents, the synthesis involves adding TET to TEOS and then combining the alkoxide mixture with an aqueous solution of a SDA, which is typically tetrapropylammonium hydroxide (TPAOH). The resulting precursor mixture is then heated to a temperature of 175 °C to initiate crystallization. Subsequent washing of the crystallized solid with water, drying, and air calcination produces framework titanium-containing silicalite. 

The preparation method, firstly reported by Taramasso et al. [10] in 1983, is based on the controlled hydrolysis of an aqueous solution containing tetraethyl-orthosilicate (TEOS), tetraethylorthotitanate (TEOT) and tetrapropylammonium hydroxide (TPAOH) as template. This procedure is known as the mixed alkoxide method. Another procedure has been proposed, known as the dissolved titanium method, which makes use of colloidal siUca instead of TEOS [11]. The mixed alkoxide method allows the best control of the synthesis parameters, assuring the crystallization of high quaUty products. 

Mordenite Framework Inverted (MFI) zeolite membranes were synthesized on the inner surface of a-alumina tubes (Pall Corp.) from an aluminum-free precursor solution containing Si02, NaOH, H2O, and template tetrapropylammonium hydroxide (TPAOH) by in situ hydrothermal crystallization at 453 K for 20 h (Tang et al. 2009). The resultant zeolite membrane had a thickness of 2-3 xm. The membrane surface was modified by the in situ catalytic cracking deposition of methyl-diethoxysilane (MDBS) molecules at the sites of [(tSi-0")H ] whereas MDBS vapor was carried by an equimolar H2/CO2 mixture flowing over the membrane surface at a pressure of 1.5 bar and a temperature of 723 K. 

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