Pseudo-boehmite

The mechanism of sealing has been shown to involve an initial dissolution and reprecipitation of hydrated aluminium oxide on the pore walls, pseudo-boehmite gel formation within the pores, and conversion of this to crystalline boehmite at the film surface. The presence of an intermediate layer close to the film surface, in which the identity of the original pores has been lost, has also been recognised . 

A number of reagents containing oxide components are used in zeolite manufacture [19]. Silica is provided by addihon of sodium or other alkali silicate solutions, precipitated, colloidal, or fumed silica, or tetraalkylorthosihcate (alkyl = methyl, ethyl) and certain mineral silicates such as clays and kaolin. Alumina is provided as sodium aluminate, aluminum sulfate soluhon, hydrous aluminum oxides such as pseudo boehmite, aluminum nitrate, or aluminum alkoxides. Additional alkali is added as hydroxide or as halide salts, while organic amines and/or... 

The effect of anions needs special consideration. For example, if aqueous dispersions of purified aluminum hydrous oxide particles (i.e., freed of sulfate ions) are reheated, crystallization into boehmite takes place with simultaneous change in the morphology (Figure 1.1.11 A) (39). On the other hand, heating aluminum chloride or perchlorate solutions at higher temperatures results directly in uniform (pseudo)-boehmite particles of unique shapes, as illustrated in Figure 1.1.1 IB (40). 

Vanadium and Pseudo-Boehmite Alumina. The 79 MHz wideline NMR spectra of these steam aged samples containing only 0.5 to 5.0% V (loaded using VO -Naphthenate) are shown in Figure 1. Two... 

The catalyst used in this study is a model FCC catalyst with composition zeolite US-Y (30%), silica hinder (25%), kaolin (25%) and pseudo boehmite alumina matrix (20%)-Hexadecane was used as feedstock and in the catalyst poisoning studies 10% by volume quinoline or phenanthrene were added to the hexadecane. Reactivity and coking were determined using a standard MAT reactor test (6). 

Reactants include pseudo-boehmite alumina and magnesium acetate). 

The procedure for the preparation of alumina spheres is as follows. Pseudo-boehmite powder (AIOOH.2H2O) is dispersed in an aqueous solution of urea and a monovalent inorganic acid, e.g. HNO3. The type of powder or powder mixture may exert considerable influence on the properties of the sol and the end product [12]. The type of acid which is used for the peptization of the pseudoboehmite powder is not very important [12], so nitric acid is used, being the most suitable one. 

FIGURE 121 Pseudo-boehmite gel produced by precipitation of alumina by acid-base neutralization. Versal a Kaiser Aluminum Corp. product. Photo courteay Ron Rigge. 

II M Tijburg, J W Geus, and H W Zandbergen, Application of lanthanum to pseudo-boehmite and y AI2O3, J Mater Sci 26 6479 (1991)... 

Al-sol can be prepared using various aluminum precursors, such as pseudo-boehmite, A10(0H) xH20, and aluminum alkoxide [48-50,55,60]. Xu et al. [55] described several possibilities. Additives, e.g., urea, or organic amines, e.g., hexamethylenetetramine (HMT), can be added to the sol in order to improve the quality of alumina obtained. The decomposition of these additives in heat treatment (calcination) may lead to a better porosity of the alumina. The reaction for urea decornposition is as follows ... 

Using a different gel composition, with pseudo-boehmite instead of AIP, the effects of gel metal concentration and crystallization temperature on MAP0-34 synthesis with TEAOH can be illustrated (Figures 4 and 5). Reaction mixtures were prepared differing only in Mg concentration (x) ... 

A number of FCC catalysts was used in the present study. For comparison of the effects of quinoline and phenanthrene additions to the n-hexadecane feedstock a model catalyst of composition, zeolite US-Y (30%), silica binder (25%), Kaolin (25%) and pseudo Boehmite matrix (20%) was used. Quinoline and phenanthrene additions to the n-hexadecane amounted to 1% and 10%. The catalysts used to assess the effect of composition on product yields varied from a basic matrix material through a variety of zeolitic catalysts containing 20% zeolite and 15% silica binder, the remainder being clay, to a pure zeolite catalyst. Data for all the catalysts used are presented in Table 1. In addition for the C NMR analysis a sample of coked refinery catalyst obtained from a unit processing heavy feedstock was obtained. The coke level on this catalyst was 0.9% and 30g. of this catalyst was demineralised by standard HF treatment to produce a 250 mg sample of coke concentrate containing 65% carbon. 

Sodium aluminate NaA102 Boehmite (pseudo-boehmite) AlOOH, A1203 70%, H20 30% aluminum hydroxide (Gibbsite), Al(OH)3 aluminum isopropoxide A1(0- C3H7)3 aluminum nitrate A1(N03)3 9 H20 metallic aluminum. 

Commonly used aluminum sources in the synthesis of zeolites include sodium aluminate (NaA102, Na20 54%), pseudo-boehmite, home-made aluminum hydroxide, and aluminum isopropoxide, which is the mostly used in the synthesis of microporous aluminophosphates. The structures of the two most important aluminum sources are shown in Figure 5.11 and Figure 5.12, respectively. 

Figure 5.11 Structure of pseudo-boehmite. Reprinted from [ 19], Copyright (1999) john Wiley Sons, Inc.

Properties Amorphous (XRD) with traces of pseudo-boehmite and bayer-ite[1199], BET specihc surface area 182 mVg [1199,1201,1202]. 

Similar experiments were carried out with pseudo-boehmite. The conversion was higher, as pseudo boehmite was more active than gibbsite (Table 1). The final product was indistinguishable from that produced from gibbsite as a starting material for the preparation of high surface area alumina. 

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