Aluminas have been used extensively as adsorbenu and active catalysrs and catalyst supponsm the pas. Already in 1197 the aluminadyzed dehydration of ettllnoi was dtscavered by Dutch chermsts: and S;rbatier [3] remewed the use of dumlnas as active cazaiysrs far vanous reacttons UI the second decade of thu century. She that time the applicazions of aluuuas m dycic pmcesses have mcreased tremendously. In tndustrral cualytic pmcesses, alumuus are mostiy used as catalyst suppons [4]. Oxides a d mued oxides ap well as tracuuion mauls and noble meare supported oa alumma. Thuscb. romaa-elumana catalysts are ktng used for the conversion of parafdns to olailnrc hydrocarbons, 10 hydrodealkplation of aromatics. and to a lesser exzm in catalyzic reforming. The larter process LS also caralyzed by molybdena-alumina, a cavlyst system whid is also active for malang toluene and ocher aromatics from satwed hydrocarc bons. It also dyzes the Isomerhation of pm. Great efions are presently be-made to nudy the surface c...

Catalytic Aluminas: Surface Models and Characterization of Surface Sites

Publisher Summary This chapter focuses on organic catalysis over crystalline alumiosilicates. Zeolites are crystalline aluminosilicates composed of SiO4 and AlO4 tetrahedra arranged in various geometric patterns. The chapter discusses reactions over a wide variety of crystalline aluminosilicates and emphasizes on catalysis over X- and Y-type faujasites. Unusual opportunities for organic catalysis were found to exist when these were base exchanged to substantially eliminate their alkali metal content. It is shown that catalytic activity in ion-exchanged faujasites is influenced by cation type, cation location in the lattice, zeolite Si/Al ratio, and the presence of proton donors. The existence of several crystallographically distinct cation locations provides the basis for a potential heterogeneity of sites in catalytic reactions. The Linde workers made calculations for the electrostatic field strengths of surface cations near SII and SIII in an X-type zeolite of Si/Al ratio 1.0 and in a Y-type zeolite of Si/Al ratio 2.0. In both cases, the fields has been significantly larger near SIII than SII at a distance of 2 Ǻ from the center of the cation for the univalent cation-exchanged systems, provided both sites are occupied.

Organic Catalysis over Crystalline Aluminosilicates

The review discusses chemical mechanisms of most important reactions that take place in the course of catalytic cracking of alkenes and alkanes over solid acidic catalysts. The main subject of the review is the mechanism of the principal cracking step, fission of C─C bonds in aliphatic hydrocarbons. The cracking mechanism of alkenes via carbenium ion intermediates (with complications caused by oligomerization reactions) is well established. In contrast, the C─C bond fission mechanism in alkanes is still a controversial subject. The review compares merits and difficulties of different mechanisms proposed in the literature: several carbenium-ion mechanisms, the carbonium-ion mechanism, the chain-reactions mechanism with participation of both carbonium and carbenium ions, and the oxonium-ion mechanism. Reactions accompanying C─C-bond fission in cracking reactions, hydrogen redistribution, formation of cycloalkanes, light aromatic compounds, and coke are also briefly discussed.

Chemical mechanisms of catalytic cracking over solid acidic catalysts: alkanes and alkenes

Quantum chemical study of the electronic structure and geometry of surface alkoxy groups as probable active intermediates of heterogeneous acidic catalysts: What are the adsorbed carbenium ions?

Synthetic inorganic ion exchangers-II Salts of heteropolyacids, insoluble ferrocyanides, synthetic aluminosilicates and miscellaneous exchangers.

Studies of the hydrogen held by solidsIX. The hydroxyl groups of alumina and silica-alumina as sites for the isomerization of butene

Tracer Studies of Acid-Catalyzed Reactions. I. The Isomerization of Cyclopropane over Silica-Alumina

Studies of the hydrogen held by solids: X. Fluorided aluminas as acid catalysts

Tracer studies of acid-catalyzed reactions: IV. Rate constants for n-butene interconversion reactions over alumina, fluorided alumina, and silica-alumina

H.R. Gerberich

Papers

Studies of the hydrogen held by solidsIX. The hydroxyl groups of alumina and silica-alumina as sites for the isomerization of butene

Tracer Studies of Acid-Catalyzed Reactions. I. The Isomerization of Cyclopropane over Silica-Alumina

Studies of the hydrogen held by solids: X. Fluorided aluminas as acid catalysts

Tracer studies of acid-catalyzed reactions: IV. Rate constants for n-butene interconversion reactions over alumina, fluorided alumina, and silica-alumina

Microcatalytic Tracer Studies of the Isomerization of Cyclopropane over Silica-Alumina Catalysts