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Luminescence and infrared (IR) spectroscopies of pyridine and ammonia adsorption have been used to measure acidities of [gamma]-alumina. Neither luminescence nor IR spectra of pyridine adsorption show an Bronsted acidity on [gamma]-alumina pretreated to 400[degrees]C. However, luminescence emission data reveal four weak OH bands even when pretreatment is done at 600[degrees]C. Pyridine and subsequent water adsorption yield six luminescence emission bands. A red shift of the pyridine emission band is found when pretreatment or desorption temperature is increased. IR spectra of ammonia on alumina pretreated at 400[degrees]C show three deformation bands at 1452, 1465, and 1485 cm[sup [minus]1]. The first band is also observed together with a band at 1554 cm[sup [minus]1] even for pretreatment at 950[degrees]C, and it corresponds to NH[sup +][sub 4] formed from dissociative adsorption of ammonia, while the other two bands are assigned to ammonia adsorbed on Bronsted acid sites. These two bands disappear along with the appearance of a new band at 1429 cm[sup [minus]1], when deuterated alumina is pretreated at 400[degrees]C and subsequently subjected to ammonia. This new band at 1429 cm[sup [minus]1] is due to NH[sub 3]D[sup +] formed from ammonia adsorbed on acidic OD sites. Consequently, ammonia IR results demonstrate the existencemore » of Bronsted acid sites on alumina pretreated at 400[degrees]C. 38 refs., 9 figs., 2 tabs.« less

Long chain alkyl aromatic compounds crack by a number of competing reaction pathways including dealkylation, side chain cracking, and self-alkylation. Cracking studies of 1-phenylheptane over zeolites Y, beta, mordenite, and ZSM-S, as well as silica-alumina, show that the catalyst can significantly alter the relative importance of these pathways. For example, large pore zeolites give significant amounts of bicyclic reaction products, whereas the medium pore sieve ZSM-S gives almost no bicyclic products. Other catalyst properties such as Si/Al ratio, adsorption characteristics, and geometrical factors also affect cracking catalyst performance.

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.

Long chain alkyl aromatic compounds crack by a number of competing reaction pathways including dealkylation, side chain cracking, and self-alkylation. Cracking studies of 1-phenylheptane over zeolites Y, beta, mordenite, and ZSM-S, as well as silica-alumina, show that the catalyst can significantly alter the relative importance of these pathways. For example, large pore zeolites give significant amounts of bicyclic reaction products, whereas the medium pore sieve ZSM-S gives almost no bicyclic products. Other catalyst properties such as Si/Al ratio, adsorption characteristics, and geometrical factors also affect cracking catalyst performance.

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.

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.

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

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.