Silica-alumina, recrystallization

A new class of hi alumina silica-aluminas has been prepared with hi pore volume and with controllable pore size. For 20 wt % Si02 content materials steam treatment at 760°C serves to substantially increase the gas oil cracking activity. Steam stability at 870°C has also been demonstrated for these unique materials. These samples are prepared by recrystallization of co-gels of aluminum and silicon alkoj compounds losing a two-step procedure. AmorjAious alumina shows similar physical properties to those of the silica-alumina co-gels vhen re-crystallized in an analogous manner. 

We will next consider the case of a lew silica content co-gel. A 5% silica-content silica-alumina was prepared by precipitation of aluminum isdsutoxide and tetraethoxv-silane as described for the silica-free gel. After gelation water was added just sufficient to fill the pore voids of the gel. The added water led to formation of a boehmite-rich hase during recrystallization. After drying at 120 and calcination at 500 0 for 16 hours, a transitional alumina hase is formed with a surface area of 410 m /g and a pore volume of 1.9 oc/g. This silica-alumina had an average pore diameter of 18 nm, similar to the silica-free material discussed previously. Steam treatment of this 18 nm pore diameter silica-alumina at 870°C (1600 ) in 90% H20-10% N2 for 16 hours resulted in a material with surface area of 196 m /g. This surface area is much hi er than expected for an amori ous gel and is consistent with silica enrichment of the outer surface during the recrystallization step vhere water was added to the pores of the amoridious gel. Silica stabilization of bodunite alumina by formation of a surface Aiase complex has been reported in recent work (9). ESCA analysis also indicates silica surface enrichment vhen compared to the amori ous gel. 

If ten times the amount of water is added to the undried 5% Si02 content gel than required to fill the pore voids a much more dense silica-alumina jAiase is formed than in the previous example. After drying at 120 and calcination at 500 a material of 283 m2/g surface area and a pore volume of 0.9 oc/g is formed. The average pore diameter of this material is 8 nm. There is an unmistakable parallel in the recrystallization of the silica-free gel to the 5% silica-content silica described here. Addition of limited water to the amorphous gel produces large pores and a hi pore volume. Addition of water so that a slurry is formed with the amorphous gel results in smaller pores and a relatively dense phase i n recrystallization. 

If water was added to the 15% Si02 co-gel to fill the pore voids a partially recrystallized boehmite was formed with a surface area of 464 m /g and with a pore volume of 1.8 oc/g. If water was added to the 15% Si02 co-gel to form a slurry and then dried and calcined at 500 a partially recrystallized bodunite was formed with a surface area of 334 m /g. steam treatment at 760 of this second, small pore, bodunite-like silica-alumina resulted in no change in the surface area. The gas oil cracking activity of the steamed sample was definitely hi er than that for the amorphoias co-gel, i.e., a Micro Activity Test (MAT) Activity Number of 38 (see Table 1.). 

The increased solubility of substituted phthalocyanines (vide infra) enables more common purifications as used for other organic compounds. Usually the purification is done by chromatography either on alumina or silica gel, but recrystallization and extraction procedures can also be used. In some cases, the methods used for unsubstituted phthalocyanines can also be practiced, although the increased molecular weight accompanied by a reduced thermal stability makes sublimation more difficult.97 98 However, for substituted phthalocyanines, the stability towards acid may be reduced97 and, therefore, purification by treatment with sulfuric acid cannot generally be recommended. 

Piperonal lc (5 mmol), hydroxylamine hydrochloride (6 mmol), and n-dibutyltin oxide (0.5 mmol) were admixed with alumina (1 g) and exposed to microwave irradiation at 450 W (BPL, BMO-700T) for an appropriate time. After complete conversion, as indicated by TLC, the reaction mixture was filtered and the residue washed with dichloromethane (2x15 mL) which was then concentrated in vacuo. The resulting solid was recrystallized in ethanol to give 3,4-methylene-dioxybenzonitrile 2c in 92% yield as a white solid, mp 68-70 °C. The liquid products were purified by column chromatography on silica gel (Merck, 100-200 mesh, ethyl acetate-hexane, 1 9) to afford the corresponding nitriles in pure form. 

A solution of N-(4-pyridinyl)-lH-indol-l-amine (6 g) in 25 ml of dimethylformamide was slowly added to an ice-cooled suspension of NaH (1.3 g of 60% NaH dispersion in mineral oil was washed with hexanes, the liquid was decanted and the residual solid was dispersed in 5 ml of dimethylformamide). After anion formation, a solution of 1-bromopropane (4 g) in 5 ml of dimethylformamide was added. After one hour of stirring at ambient temperature, the reaction mixture was stirred with ice-water and extracted with dichloromethane. The organic extract was washed with water and saturated sodium chloride solution, was dried over anhydrous magnesium sulfate, filtered and concentrated to 8 g of oil. This oil was purified by HPLC (silica, ethyl acetate) and thereafter by column chromatography (alumina, ether) to give 6.4 g oil. This oil was converted to the maleate salt and recrystallized from methanol/ether to give 6.8 g of crystals, m.p. 115-116°C. 

Unwanted a lomeration during storage mostly by recrystallization of dissolved materials. (See also bag set.) A powder of alumina, silica, lime, iron oxide, and magnesium oxide burned together in a kiln, finely pulverized, and used as an ingredient of mortar and concrete. Also any mixture used for a similar purpose. (See also pozzolan.)... 

Activated alumina is a porous high-area form of aluminum oxide, prepared either directly from bauxite (AI2O3 3H2O) or from the monohydrate by dehydration and recrystallization at elevated temperature. The surface is more strongly polar than that of silica gel and has both acidic and basic character, reflecting the amphoteric nature of the metal. 

The piehydiolysis of the TEOS can also improve the resistance to crystallization. A sample of chemical composition 50 Si02- 50 AIPO crystallizes at a higher temperature if the TEOS is hydrolysed during two hours at 60 C under acid catalysis than if no hydrolysis is made before the coprecipitation step (fig 6). Moreover, without the hydrolysis step, the precipitation of TEOS is not quantitative and the silica precipitation partly occurs after the precipitation of alumina or aluminophosphale. This causes inhomogeneity in the amorphous phase which eases the thomal recrystallization and decreases the useful temperature range. 

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