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The catalytic properties of ultrastable Y (USY) are directly influenced by the zeolite destruction which occurs during formation of USY and during subsequent hydrothermal treatment. A new picture of the formation and evolution of mesopores during hydrothermal treatment has emerged from recent electron microscopy studies on hydrothermally dealuminated USY materials. Laboratory steam treatments give rise to an inhomogeneous distribution of mesopores, which occurs concomitantly with further zeolite dealumination. Such inhomogeneities are observed among different USY grains as well as within single grains. In regions with high defect concentration, mesopores “coalesce” to form channels and cracks which, upon extended hydrothermal treatment, ultimately define the boundaries of fractured crystallite fragments. The predominant fate of aluminum ejected from lattice sites appears to be closely associated with dark bands which often decorate these newly formed fracture boundaries. High-silica Y materials, having little or no nonframework Al, exhibit poor catalytic activity. The results of recent studies provide compelling evidence that the critical nonframework Al species are (1) highly dispersed, and (2) quite possibly exist as cationic species in the small cages of dealuminated H-Y. Investigations of Lewis acidity in mildly dealuminated zeolites indicate that the origin of the high catalytic activity is a synergistic interaction between Bronsted (framework) and highly dispersed Lewis (nonframework) acid sites. The enhanced cracking, isomerization activity associated with the presence of highly dispersed nonframework Al species is not reflected in direct measures of solid acidity, as, for example, by calorimetry, or by NMR spectroscopy. The enhanced activity of mildly steamed protonated zeolites is not due to an increase in acidity of the bridging hydroxyl or Bronsted sites.

Combined high resolution electron microscope (HREM) and analytical electron microscope (AEM) investigations have been used to study the formation and evolution of mesopores in hydrothermally dealuminated ultrastable Y (USY) materials. The HREM results give clear evidencc for an inhomogeneous formation and distribution of the 5- to 50- nm defect regions attributed to mesopores. Such features are characteristic of extended hydrothermal treatment. In regions with high defect concentration, mesopores coalesce to form channels and cracks, which ultimately define the boundaries of fractured crystallite fragments. At these boundaries, a dark band is often observed which is highly enriched in aluminum, while within the mesopore itself, aluminum appears to be deficient. These dark bands are observed both in a neat USY material subjected to several cycles of steam acid treatment and in a high-temperature steam-deactivated USY fluid catalytic cracking (FCC) catalyst. Individual grains of both the neat USY and the dealuminated USY catalyst exhibit extreme fracturing into small crystallites of dimensions 20 to 50 nm. The fracturing is attributed to the nonequilibrium nature of the high-temperature steam treatments which characterizes accelerated deactivation procedures in the laboratory.

Gallosilicate molecular sieves with an MFI structure are very promising catalysts for upgrading light olefins and paraffins to aromatics. Gallosilicate catalysts are quite stable at low reaction temperature, however, when subjected to high temperature, gallosilicate catalysts deactivate rapidly. The activity and selectivity of these catalysts are greatly influenced by both framework and non-framework gallium. Although the framework gallium imparts acidity to the sieve, the nature of the non-framework gallium is unclear. In the present study, combined techniques of analytical electron microscopy (AEM), high resolution transmission electron microscopy (HREM) and X-ray diffraction (XRD) have been applied to study the fate of framework and non-framework gallium in progressively deactivated gallosilicate molecular sieve catalysts. To study this progressive process, fresh gallosilicate molecular sieve and the gallosilicate catalysts (with 40% Cab-O-Sil matrix) subjected to steaming treatments at different temperatures and durations were characterized.The microstructure of fresh gallosilicate catalysts consists of highly crystalline molecular sieve which is uniformly distributed in the amorphous supporting matrix (Fig. 1).

Recently we have introduced the use of choline / fatty acid derived compounds, in particular lauroylcholine chloride (LCC), to probe selectively Photosystem II (PS II) structure and function (Wydrzynski, T. and Huggins, B.J. (1983) in The Oxygen-Evolving System of Photosynthesis (Inoue, Y., Crofts, A.R., Govindjee, Murata, N., Renger, G. and Satoh, K., eds.), pp. 265–272, Academic Press Tokyo, Japan). In this paper we report an unusual condition in thylakoid membrane samples at relatively low amounts of LCC in which detectable O 2 evolution cannot be measured, yet electron flow through PS II is near normal without added electron donors. LCC does not appear to interfere with the O 2 yield measurements directly nor act as an electron donor itself after the Tris block. Under this condition, steady state and flash O 2 yield measurements show no O 2 release or uptake, while steady-state ferricyanide photoreduction and the variable component of the chlorophyll a fluorescence transient remains at more than 50% of the control. The photoreduction of the primary quinone acceptor, Q A , measured by microsecond range chlorophyll a fluorescence continues for a minimum of 200 single turnover excitation light flashes. Most importantly, the yield of the 35 |gms component of the chlorophyll a delayed fluorescence remains at approx. 65% of the control and oscillates with a normal period four over two cycles, indicating the normal cycling of the S-state transitions in PS II. Thus, it appears that PS II can operate normally without detectable O 2 evolution. The question remains as to whether water is still being photooxidized under this condition without the release of the dioxygen product, or whether there is another source of electrons. The results are interpreted in terms of the possible existence of an additional water binding component (termed ‘H’) in PS II and a concerted oxidation reaction mechanism for photosynthetic water splitting.

Publisher Summary This chapter discusses the use of lauroyl choline chloride (LCC) to probe photosystem II (PS II) function. LCC treatment is extremely mild, causing the loss of only a few percent of the chlorophyll from the membrane while removing a number of protein components. LCC treatment of photosynthetic membrane samples specifically perturbs PS II function inhibiting electron flow from water splitting site to Q reduction. LCC has some effect on Photosystem I (PS I) but does not inhibit electron flow through the intersystem chain and the PS I reaction center. LCC treatment does not disrupt membrane structure to a large degree and under certain conditions its effects can be reversed using polyethylene glycol. As LCC extracts out a number of protein components, LCC offers a useful approach to probe the structure function relationships in water splitting activity and PS II photochemistry. The absorption spectra of LCC treated thylakoid pellets show the same features as control thylakoids absorption spectra except for a 2nm blue shift in the red band.