Regis Joseph Pellet

Catalytic cracking studies and characterization of steamed Y and LZ-210 zeolites

Abstract Catalytic cracking catalysts prepared using Y zeolite crystals which have been silicon enriched by treatment with ammonium fluorosilicate solution show substantially superior crystal retention upon exposure to severe hydrothermal treatments, relative to similarly treated Y-zeolite-based catalysts. The silicon-enriched Y-based catalysts, following hydrothermal pretreatment, also show superior activity retention and higher gasoline selectivity relative to Y-zeolite-based catalysts. The study of steamed Y and the silicon-enriched Y product by solid-state MAS NMR shows that upon steaming the silicon-enriched zeolite displays superior retention of the framework structure relative to Y, and that the Y product shows not only aluminum loss but also significant silicon loss from the crystal framework, contributing to deterioration of the crystal. Thermometric titrations of Y zeolites, following exposure to steam treatments of increasing severity, indicates that upon severe steam treatment the strong acid character typical of stabilized Y is greatly reduced while a substantial concentration of milder acid sites is formed, similar in acid strength to amorphous silica-alumina gel. These data are interpreted on the basis that upon steaming amorphous alumina and silica-alumina phases are formed, occluded in the zeolite crystal, and that the occluded amorphous, acidic debris adversely affects cracking selectivity to produce gasoline.

Skeletal Rearrangement Reactions of Olefins, Paraffins and Aromatics Over Aluminophosphate Based Molecular Sieve Catalysts

Medium pore aluminophosphate based molecular sieves with the -11, -31 and -41 crystal structures are active and selective catalysts for 1-hexene isomerization, hexane dehydrocyclization and C8 aromatic reactions. With olefin feeds, they promote isomerization with little loss to competing hydride transfer and cracking reactions. With C8 aromatics, they effectively catalyze xylene isomerization and ethylbenzene disproportionation at very low xylene loss. As acid components in bifunctional catalysts, they are selective for paraffin and cycloparaffin isomerization with low cracking activity. In these reactions the medium pore aluminophosphate based sieves are generally less active but significantly more selective than the medium pore zeolites. Similarity with medium pore zeolites is displayed by an outstanding resistance to coke induced deactivation and by a variety of shape selective actions in catalysis. The excellent selectivities observed with medium pore aluminophosphate based sieves is attributed to a unique combination of mild acidity and shape selectivity. Selectivity is also enhanced by the presence of transition metal framework constituents such as cobalt and manganese which may exert a chemical influence on reaction intermediates.

Molecular Sieve Effects in Carboniogenic Reactions Catalyzed by Silicoaluminophosphate Molecular Sieves

Several novel silicoaluminophosphate (SAPO) molecular sieves representing a broad variety of crystal structures and pore sizes ranging from small to large were evaluated for catalytic activity in the reactions of propylene oligomerization and toluene methylation. The medium pore SAPOs −11, −31, −40 and −41, combining features of unique pore structure and mild acidity were outstanding catalysts with high selectivity to gasoline range olefinic products in propylene reactions and high para xylene yields in toluene methylation.