Anthony John Silvestri

The conversion of methanol and other O-compounds to hydrocarbons over zeolite catalysts

Abstract The conversion of methanol and other O-compounds to C 2 C 10 hydrocarbons using a new class of shape-selective zeolites is reported. Methanol, dimethyl ether, or an equilibrium mixture thereof appears to be converted in a first reaction sequence to olefins predominantly in the C 2 C 5 range. In the final steps of the reaction path, the C 2 C 5 olefins are converted to paraffins, aromatics, cycloparaffins and C 6 + olefins. The final hydrocarbons are largely in the gasoline (C 4 C 10 ) boiling range. The thermochemistry of the methanol to hydrocarbon reaction is described and possible reaction mechanisms are discussed.

Synthesis gas conversion to aromatic hydrocarbons

Abstract The conversion of synthesis gas to aromatic hydrocarbons over a new class of catalysts comprising a CO reduction function combined with a ZSM-5 class zeolite is reported. The polystep nature of the catalysis is analyzed.

Direct evidence for dual-functional cyclization of paraffins over platinum reforming catalysts

Abstract The reaction of n-heptane containing 100 ppm of sulfur using either a platinum on charcoal catalyst or an alumina catalyst produces relatively few ring hydrocarbons. The large increase in ring production observed when both catalysts are intimately mixed is good evidence that the paraffin cyclization reaction can proceed by a dual-functional mechanism.

Tellurium-loaded zeolites: II. The nature of the dehydrocyclization site

Abstract A study of the elution of tellurium from TeNaX and TeKX by hydrogen at elevated temperature has shown that the reducing atmosphere can prevent complete elution of tellurium from the catalyst. The inferred necessity of hydrogen for the formation of the aromatization site has been combined with the results of a separate crystallographic analysis and leads to a model for the active entity that rationalizes essentially all of our knowledge on these systems. The catalytically active entity is believed to be a tellurium ion, in the supercage of the zeolite base, coordinated to Site II and Site III cations. Support for this model comes from catalytic experiments designed to show the criticality of the presence of Site III cations.

Tellurium-loaded zeolites: I. A novel dehydrocyclization catalyst

Abstract Selective dehydrocyclization catalysts are prepared by the high-temperature treatment of physical mixtures of a tellurium source and support material. An exploratory study of preparation variables—tellurium source, content and method of addition, type of support, and pretreatment conditions—has shown the most effective catalysts are produced from milled mixtures of elemental tellurium and an alkali-metal faujasite of low silica-alumina ratio, heated in a flowing hydrogen atmosphere. The catalyst is interpreted as being a highly dispersed tellurium phase coordinated to the cations of the support under the action of the reducing atmosphere.

Reaction paths for decyclization of methylcyclopentane over PtAl2O3 catalyst

Abstract It is shown that the decyclization of methylcyclopentane on dual-functional Pt Al 2 O 3 catalyst can proceed by an acid-dependent route in addition to an acid-independent platinum catalyzed mechanism. Evidence is based on data obtained using poisoning techniques, in which either the platinum function, or acid function, or both, were de-activated, and also by using the mixed catalyst technique. With only the monofunctional platinum mechanism operative, the distribution of decyclization products is nearly statistical; with only the acid-dependent route, the distribution suggests a carbonium ion mechanism. The observed hydrogen dependency of the acid-catalyzed reaction is consistent with simultaneous monofunctional acid and dual-functional modes of operation.

Tellurium-loaded zeolites: IV. Effect of hydrogen partial pressure on dehydrocyclization activity

Abstract The effect of hydrogen partial pressure on the n -hexane dehydrocyclization activity of Te/NaX catalyst has been determined and compared with that observed for Cr 2 O 3 /Al 2 O 3 . The relative benzene formation rates measured for both catalyst types show an essentially identical dependence on hydrogen pressure. Kinetic analysis of the results is consistent with a stepwise reaction mechanism.