Gerald S. Koermer

Methylcyclohexane and methylcyclohexene cracking over zeolite Y catalysts

Abstract Naphthenes are an important class of molecules in fluid catalytic cracking. The cracking behavior of the model naphthenes, methylcyclohexane and methylcyclohexene was investigated over rare earth Y and USY zeolite catalysts. Initial products from methylcyclohexane are formed by a combination of protolytic and β-scission cracking plus isomerization, H − transfer, H + transfer and dehydrogenation reactions. Methylcyclohexane is a sensitive probe for characterizing the chemistry occurring on solid acid surfaces. Methylcyclohexene is the key intermediate in the formation of aromatics from methylcyclohexane. Methylcyclohexene cracks at a slower rate than methylcyclohexane but overall conversion is higher because hydride transfer reactions are fast.

Cracking of long-chain alkyl aromatics on USY zeolite catalysts

Abstract Long-chain alkyl aromatics are important precursors for FCC gasoline. It is well known that for short-chain alkyl aromatics like cumene the dominant cracking process is simple alkyl aryl cleavage. In contrast we have found that for long-chain alkyl aromatics like 1-phenylheptane, cracking over in situ USY catalysts is much more complex. Cracking in a long alkyl side chain results in a carbenium ion that isomerizes easily and gives self-alkylation of the aromatic ring. Self-alkylation produces coke precursors and heavy gasoline aromatics. Product selectivities vary with zeolite unit cell size in ways that are rationalized on the basis of decreasing acid site density and zeolite adsorption properties.

A New Palladium-Based Catalyst for Methanol Steam Reforming in a Miniature Fuel Cell Power Source

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Vanadium interactions with treated silica aluminas

Abstract Poisoning of fluid cracking catalysts by vanadium, nickel, iron and copper can decrease the selectivity and overall activity of such catalysts. Silica alumina is often used as a matrix to disperse the active zeolite component, to crack large hydrocarbons at initial stages of reaction and for stability of the fluid cracking catalyst. Vanadium poisons are particularly bothersome due to zeolite destruction by vanadium. This paper explores the interaction of vanadium with various silica aluminas including those with rare earth and magnesia contents. The effects of calcination and steaming were also determined. Spectroscopic techniques such as luminescence, diffuse reflectance, electron paramagnetic resonance, X-ray photoelectron spectroscopy and secondary ion mass spectrometry methods were used to study the oxidation state, chemical composition, and number and type of vanadium species in these materials. The results show that vanadium moves into the particle interior when magnesium or rare earth oxides are present. This is responsible for the decreased mobility of vanadium even during steaming conditions and results in higher catalytic selectivity for catalysts containing these materials.

Luminescent probes of acidity in heterogeneous catalysts

Luminescence experiments have been used to distinguish Bronsted and Lewis sites in alumina and zeolite catalysts.