The presence of basic centers in some oxides has been recognized for a long time as being important in catalysis [1-4]. Usually both basic and acid sites exist simultaneously. The two centers may work independently or in a concerted way. For instance, in alcohol transformation, dehydration is favored on acidic sites and dehydrogenation on basic centers [3,5]. A large variety of materials are cited as having basic character. They include single-metal oxides (MgO, CaO, ZnO), supported alkali metals (Na/MgO, K/K2CO3), mixed-metal oxides (MgO-A12O3, ZnO-SiO2, MgO-TiO2), zeolites (X and Y saturated with alkaline cations of low electronegativity), hydrotalcite-type anionic clays, asbestoslike materials, carbon-supported basic catalysts, and basic organic resins. ∗ Present address: 16 rue Francois Gillet, 69003 Lyon, France.

Basic zeolites : Characterization and uses in adsorption and catalysis

The recent developments of zeolite chemistry are characterized by the appearance of attempts to explain certain properties of these porous crystalline solids in terms of general chemical properties developed for other solids or even for other states of matter. Transition metal complexes in zeolites sometimes exhibit the same properties as in more conventional solvents [1]. Thus the zeolite behaves as a mono to polydentate macroligand of the transition metal ion [2]. Although numerous observations [2] underline the role of the zeolite as a solid solvent or as a common solid matrix, its unique properties in terms of structure or cage geometry should not be overlooked. Indeed, the appropriate activation of Ru(III) hexammine in faujasite-type zeolites gives a very active water gas-shift catalyst [3]. A cationic Ru-complex seemed to be formed under these conditions, having no homogeneous equivalent, and its stabilization requires the specific geometry of a faujasite supercage.

Acid Zeolites: An Attempt to Develop Unifying Concepts (P. H. Emmett Award Address, 1981)

Science, by its very nature, aspires to the orderly arrangement of knowledge in a way which will allow predictive interpolation and even cautious extrapolation into unstudied regions of performance on the basis of known data. So it is that in the study of kinetics many sophisticated attempts have been made to calculate the rate parameters for some of the simplest gas-phase reactions from basic physical measurements. Most such attempts have so far ended in failure, and kinetics remains basically an experimental science.

The catalytic cracking of cumene

Conversion of alkylbenzenes over zeolite catalysts. I. Dealkylation and disproportionation of ethylbenzene over mordenites

Fossil fuels, amassed over eons of geologic prehistory, are being irreversibly depleted about 106 times more rapidly than they were formed. With this sort of kinetics, there is little question that there exists, in the ultimate sense, an energy crisis [1–3]. That is, there will be fuel deficits for whatever time interval declining volumes of hydrocarbon reserves are not compensated for by increased supply from new energy sources such as nuclear, solar, and geothermal. In the interim period, the petroleum refiner is forced to utilize higher molecular weight, more hydrogen-deficient crudes, and crude fractions which have higher concentrations of impurities. Eventually, substantial quantities of “synthetic crudes” derived from coal, oil shale, tar sands, and bitumens may also become available.

J. A. Rabo

Papers

Structural Aspects of Catalysis With Zeolites; Cracking of Cumene and Hexane