Alumina silicate crystalline

Zeolites are crystalline alumina-silicates having a regular pore structure. Their basic building blocks are silica and alumina tetrahedra. Each tetrahedron consists of silicon or aluminum atoms at the center of the tetrahedron with oxygen atoms at the comers. Because silicon and aluminum are in a +4 and +3 oxidation state, respectively, a net charge of -1 must be balanced by a cation to maintain electrical neutrality. 

Faujasite is a naturally occurring mineral, having a specific crystalline, alumina-silicate structure, used in the manufacturing of the FCC catalyst. Zeolite faujasite is a synthetic form of the mineral. 

Zeolite is a synthetic crystalline alumina-silicate material used in the manufacturing of FCC catalyst. 

Alkylation of Benzene with Propylene over a Crystalline Alumina Silicate... 

There are many examples of the alkylation of aromatics with olefins to produce alkylbenzene In textbooks, the open literature, and In numerous patents. This reaction Is catalyzed by both proton and Lewis acids In a homogeneous phase and In heterogeneous phases. The latter systems are characterized by both proton (H FO ) and Lewis acids (BF ) on supports and the amorphous and crystalline alumina silicates. And, the reaction has been studied extensively. However, up until the start of this Investigation (1969) there had not been a systematic investigation of the kinetic parameters nor an adequate catalyst aging study on the alkylation of benzene with propylene over a crystalline alumina silicate. 

Zeolites, crystalline alumina silicates with open regular structure, oiFer unusual opportunities for carrying out catal3rtic studies. Their well-defined crystalline structure and their regular pore distribution permit a better description of the surface than that offered by alumina-silica gel catalysts. Consequently, in recent years they have been the object of many scientific investigations. In addition, zeolites of a variety of types have shown highly desirable properties in industrial catalysis (1.2). This chapter is a review of the work on zeolites carried out at Princeton University and is not intended to be an exhaustive review of the topic. 

Platinum (metal)- and acid (oxide)-catalyzed processes were developed to convert petroleum to high-octane fuels. Hydrodesulfurization catalysis removed sulfur from the crude to prevent catalyst deactivation. The discovery of microporous crystalline alumina silicates (zeolites) provided more selective and active catalysts for many reactions, including cracking, hydrocracking, alkylation, isomerization, and oligomerization. Catalysts that polymerize ethylene, propylene, and other molecules were discovered. A new generation of bimetallic catalysts that were dispersed on high-surface-area (100-400 m /g) oxides was synthesized. 

Acid-base catalysis produces mostly carbenium ions by electron or by proton transfer. Among the solid acids, microporous, crystalline alumina silicates (zeolites) are utilized most frequently. 

Microporous, crystalline oxides (alumina, silicates, phosphates, etc.) are used as catalyst is in the petroleum and in the chemical technologies in large volume to carry out cracking, isomerization, alkylation, and many other important hydrocarbon conversion reactions [198, 199, 203]. Discuss the structure of these so-called zeolites that have one-dimensional and two-dimensional micropores. How can the acidity of the catalysts be altered How do their acid strengths compare with concentration H2SO4 and HF ... 

Low coefficient of thermal expansion and the consequent resistance to thermal shock arises when the thermal expansion of the crystalline phase is very low. In the lithium-alumina silicate system described in Table 6.16, the crystals are either )8-quartz or /3-spodumene solid solutions that have very low, or even negative, volume thermal expansion. [Expansion is positive along one crystal axis (c) and negative along the other two a and >).] These properties led to applications as varied as cookware, stovetops and stove windows, and giant (8-meter-diameter) earth-based telescope mirror substrates. 

Zeolites form a special class of oxides, which are catalytically active owing to the presence of acid sites. Zeolites are crystalline alumina-silicates with micropores defined by the crystallographic structure of the solid (Figure 3.8). Micropore dimensions may vary and can be of the order of the size of an organic molecule. 

NaY zeolite is produced by digesting a mixture of silica, alumina, and caustic for several hours at a prescribed temperature until crystallization occurs (Figure 3-8). Typical sources of silica and alumina are sodium silicate and sodium aluminate. Crystallization of Y-zeolite typically takes 10 hours at about 210°F (100°C). Production of a quality zeolite requires proper control of temperature, time, and pH of the crystallization solution. NaY zeolite is separated after filtering and water-washing of the crystalline solution. 

Common (dry) cement consists of anhydrous crystalline calcium silicates (the major ones being tricalcium silicate, CasSiOs, and (3-dicalcium silicate, Ca2Si04), lime (CaO, 60%), and alumina (a complex aluminum silicate, 5%). While cement is widely used and has been studied in good detail, its structure and the process whereby it is formed are not completely known. This is due to at least two factors. First, its three-dimensional arrangement of various... 

Iron(III) oxide or alumina is refined from bauxite. Approximately 175 million tons of bauxite are mined annually worldwide, with virtually all of this processed into alumina. Alumina is a white crystalline substance that resembles salt. Approximately 90% of all alumina is used for making aluminum, with the remainder used for abrasives and ceramics. Alumina is produced from bauxite using the Bayer process patented in 1887 by Austrian Karl Josef Bayer (1847-1904). The Bayer process begins by grinding the bauxite and mixing it with sodium hydroxide in a digester. The sodium hydroxide dissolves aluminum oxide components to produce aluminum hydroxide compounds. For gibbsite, the reaction is Al(OH)3 + NaOH —> Al(OH)4 + Na+. Insoluble impurities such as silicates, titanium oxides, and iron oxides are removed from the solution while sodium hydroxide is recovered and recycled. Reaction conditions are then... 

The crystallites in alumina ceramics are mainly oc-A1203, mineralogically known as corundum (a synonym for sapphire). Corundum is 9 on the Mohs scale of hardness, i.e. it is next hardest to diamond, at 10. Examples of the micro structures of a high-purity alumina and a debased alumina are shown in Figs 5.20(a) and 5.20(b) respectively. The latter consists of a-Al203 crystallites embedded in a glass-crystalline matrix usually composed of calcium and magnesium silicates. 

---