Mario L. Occelli

New routes to the preparation of pillared montmorillonite catalysts

Abstract Clay catalysts have been prepared using reagents different from the aluminum chlorhydrate solution usually employed to pillar smectite minerals. Colloidal alumina, alumina-coated silica and solutions containing chlorhydrated complexes of zirconium and aluminum produced pillared bentonites which, upon calcination at 400 °C, formed microporous two-dimensional structures with 200 – 500 m 2 g −1 Langmuir surface area and basal spacing between 17 and 18 A. These pillared clays contain both Bronsted and Lewis acid sites; above 300 °C, pyridine is retained predominantly on Lewis centers. The presence of zirconia seems to enhance Bronsted acidity, whereas pillaring with colloidal alumina particles increases the catalyst Lewis acidity. Cracking activity for gas oil conversion depends mainly on the surface area generated by pillaring. Pillared bentonites are more active but less selective than similarly prepared pillared hectorite catalysts.

Advances in Fischer-Tropsch Synthesis, Catalysts, and Catalysis

Advances in Fischer-Tropsch synthesis, catalysts, and catalysis , Advances in Fischer-Tropsch synthesis, catalysts, and catalysis , کتابخانه دیجیتال جندی شاپور اهواز

Diffusion of n-paraffins in offretite-erionite type zeolites

Abstract Intracrystalline diffusivities are reported for a series of n -paraffins (C 6 to C 20 ) in four different offretite-erionite intergrowths with constraint indices (Cl) varying from 2.1 to 115 (a low value of Cl corresponds to nearly pure offretite, whereas a high value corresponds to erionite). The intracrystalline diffusivities for each sample show a monotonic decrease with carbon number, except for one of the intermediate samples (HZSM-34), which has the highest proportion of extraframework Al. For the sorbates studied, the diffusivities decrease with the Cl. Activation energies show different trends with carbon number, depending on the erionite/offretite character of the sample. The experimental evidence does not support the existence of a window effect, as suggested by Gorring (Gorring, R.L. J. Catal. 1973, 31 , 13) on the basis of measurements with a zeolite of similar structure.

Metal contaminant effects on the properties of a silica-rich fluid cracking catalyst

A fluid cracking catalyst (FCC) was prepared by spray drying a solid slurry obtained by first titrating diluted sodium silicate with an acid alum solution to pH = 3.0 and then by adding to the hydrogel a partially dealuminated kaolin mineral, together with calcined rare earth exchanged zeolite Y (CREY). Catalyst contamination by surface vanadium and nickel species is correlated with observed luminescence quenching of the zeolite. Steaming causes Ni migration from luminescence centers and restoration of band intensity. In contrast, vanadium irreversibly quenches REY emission bands. XPS data indicate that steaming causes nickel (and vanadium) migration to the cracking catalyst surface where nickel sinters and nickel crystallites 50 to 70 μm in size are observed by TEM. The SiO2-rich matrix prevents good Ni distribution on the surface; large Ni crystallites and inert NiSiO3 formation are believed responsible for the catalysts low carbon and hydrogen generation during gas oil cracking.

Chapter 2: Physico Chemical Properties of Pillaredclay Catalysts

Publisher Summary This chapter discusses the physicochemical properties of pillared clay catalysts. Pillared clays represents a versatile new class of heterogeneous catalysts with zeolite-like properties capable of upgrading high molecular weight hydrocarbons like the ones found in synthetic and heavy oils. These materials are thermally stable for most hydrotreating applications such as hydrocracking. However, under hydrothermal conditions, structural stability is significantly reduced and the commercial use of these materials in fluidized cracking applications must be questioned. Spectroscopic studies of chemisorbed pyridine have revealed that pillared clays contain both Bronsted and Lewis acid sites and that at cracking conditions; acidity is mostly of the Lewis type. The nature of the acid sites and the ease with which n-paraffins and branched aromatics can be sorbed and diffuse are believed to be responsible for the high cracking activity and product selectivity of pillared clays. After a mild hydrothermal pretreatment, pillared clays are as active as several commercial catalysts containing zeolites in converting gas oil. At conversion levels in the range of 60–80%, pillared clays exhibit higher selectivity with respect to light cycle oil formation than any of the reference catalysts tested. Carbon makes and hydrothermal stability will have to be improved before these materials can compete with existing commercially available fluid cracking catalysts (FCC).

Spectroscopic characterization of some iron-containing pillared clays

Abstract Bentonites, when pillared with Al2O3-oxide clusters, can generate materials with BET surface area in the 290–310 m2 g−1 range having high cracking activity for gas oil conversion. The high coke make tendency of these catalysts has been attributed to their strong Lewis type acidity. Mossbauer and X-ray photoelectron spectroscopy have shown that iron in pillared clays can be found on the clay platelets, between the clay silicate layers or in the clay octahedral layer in substitution for Al. On heating, iron migration occurs. When iron is found near the pillars it can easily catalyze secondary cracking reactions and greatly enhances the already high coke make generation observed during gas oil conversion.

Thermal Stability, Acidity and Cracking Properties of Pillared Rectorite Catalysts

Abstract X-ray diffraction (XRD), pyridine chemisorption, and microactivity test (MAT) results have been used to characterize a sample of natural rectorite pillared with alumina clusters. After reaction with chlorhydrol, a pillared product was obtained that after drying at 100°C/10h had d(001) spacing of 28.7 A. The pillared rectorite retained its structure even after calcining in air at 800°C/5h or after steam aging at 760°C/5h with steam at 1 atm. Thus, pillared rectorites have thermal and hydrothermal stability comparable to that of zeolites with the Faujasite structure. Steam-aged pillared rectorites, at MAT conditions, have cracking activity similar to that of a commercial fluidized cracking catalyst (FCC) and can be regenerated with ease. However, their coke and light gas (H2, CH4) selectivity will have to be drastically improved before these clays can compete with zeolites in cracking catalyst preparation.

Luminescence probes of vanadium-contaminated fluid cracking catalysts

Vanadium deactivation and tin passivation of vanadium impurities in a model fluid cracking catalyst system consisting of an europium-exchanged Y zeolite and an amorphous aluminosilicate gel have been studied by luminescence techniques. Vanadium is found to be preferentially adsorbed by the gel and does not migrate after deposition and calcination but does migrate between the zeolite and the matrix during steaming. After heating in air at 575 °C, vanadium is in the form of VO2+ cations on the zeolite and primarily in the form of V2O5 on the gel. The environment of Eu3+ cations is found to be very sensitive to heat treatment but not to the order of tin and vanadium deposition. Upon steaming, EuVO4 is formed on the zeolite and this formation is promoted by the presence of excess Sn.

Tin passivation of vanadium in metal-contaminated fluid-cracking catalysts: Electron paramagnetic resonance studies

Abstract Vanadium interactions with model fluid cracking catalysts and vanadium passivation with tin have been monitored by electron paramagnetic resonance (EPR). Model systems such as EuY, amorphous aluminosilicate gels, and EuY-gel mixtures have been investigated. Vanadium, introduced in the form of vanadyl naphthenate, is stabilized on the zeolite primarily as octahedrally coordinated VO 2+ cations. In contrast, the gel preferentially sorbs vanadium where it is stabilized mainly in the form of V 2 O 5 . The presence of tin on the zeolite favors oxidation of VO 2+ to V 5+ and the generation of Sn 4+ OV 5+ species during steaming. Formation of europium orthovanadate (EuVO 4 ) is promoted by the presence of excess tin. Removal of Eu 3+ ions from the zeolite lattice in the form of vanadates contributes to zeolite destabilization; thus excess tin is to be avoided.

Vanadium resistant fluid cracking catalysts

Abstract 29 Si and 27 Al MAS NMR spectroscopy has shown that on calcination cracking components such asHY, Si-enriched HY, REHY, and CREY undergo dealumination and that steam-aging increases the presence of extra-framework Al in these zeolites. Dealumination is more severe in HY-type materials. The zeolite V resistance seems to decrease when RE ions are present and to increase with increasing extra-framework Al (generated during steam-aging). At the high temperatures used for FCC regeneration, oxycations of vanadium (VO 2 + or VO 2+ could attack the Al−O−Si bond in HY and cause lattice collapse. In REHY and CREY crystals, it is believed that Ce 4+ ions, present as an oxycerium complex, undergo a redox reaction with oxyvanadyl cations (VO 2+ ), and form a stable orthovanadate. Removal of other charge-compensating cations (such as Na + ions) in the form of vanadates further destabilizes the crystal lattice, thus promoting zeolite destruction. Atomic Force Microscopy (AFM) can provide details of the surface topography of an FCC with unprecedented resolution, and can be used to rationalize the deleterious effects that metals such as Ni and V have on the properties of FCC. The deleterious effects of V deposits on zeolite-containing FCC can be greatly reduced by addition of certain materials (metal scavengers) capable of minimizing direct V-FCC interactions by selectively (and irreversibly) sorbing migrating V compounds such as H 4 V 2 O 7 . Dual-function cracking catalyst (DFCC) mixtures have been prepared that can retain most of their useful cracking activity (at MAT condition), even in the presence of 1.0% to 1.5% V. Thus, DFCC systems appear to have the necessary metal tolerance to crack residual oil as well as heavily V-contaminated crudes and may offer cost (as well as coke selectivity) advantages over conventional FCC.