Ultrastable Y Research Articles

Role of Rare Earth Cations in Y Zeolite for Hydrocarbon Cracking

Reaction kinetics data were collected for isobutane conversion over a series of ultra stable Y (USY) zeolite catalysts with and without rare earth cations and subjected to various extents of dealumination by steaming. We conducted these reaction studies at low temperatures (523-573 K) using isobutane feed streams containing known levels of isobutylene (100-400 ppm) so that the kinetics were controlled by bimolecular hydride transfer and oligomerization/beta-scission processes with little or no participation of monomolecular initiation reactions. These experimental conditions led to stable catalyst performance with the main products of isobutane conversion being propane, n-butane, and isopentane, with smaller amounts of propylene, trans-2-butene, and cis-2-butene. The rates of formation of these products per Brønsted acid site (as counted by pyridine adsorption) depended exponentially on Brønsted acid site density, regardless of whether the catalyst contained rare earth cations. Kinetic modeling showed an exponential dependence of hydride transfer and oligomerization/ beta-scission reaction rates on Brønsted acid site density which translated into composite activation energies for these reactions having a linear relationship with site density. Based on results in the literature from theoretical calculations, we suggest that increasing Brønsted acid site density in zeolite Y leads to larger zeolite elasticity, increased stabilization of cationic transition states, and lower composite activation barriers for hydride transfer and beta-scission steps. The role of rare earth cations, therefore, is to ensure the retention of high Brønsted acid site density under hydrothermal conditions, such as in fluid catalytic cracking (FCC) regenerators, where steam would dealuminate the Y zeolite framework and reduce this site density. It is for this reason that hydride transfer reaction rates are high in the presence of rare earth cations and lead to higher yields of less olefinic gasoline during FCC.

Propane reactions over natural Todorokite

This study reports results of propane transformation over the natural microporous manganese oxide, todorokite, and its hydrogen form (H-Todorokite), at the temperature range of 350°–550 °C. Both materials were fully characterized and their catalytic results were compared with results obtained with commercial Ultra-Stable-Y (USY), and steamed H-ZSM-5 zeolite catalysts. The natural todorokite sample shows appreciable dehydrogenation activity (propylene yield ∼8%, selectivity to propylene >31%), considerably higher compared to H-ZSM-5 zeolite. This is justified by the absence of strong acid sites and the presence of a large amount of ion-exchangeable cations, which induce the dehydrogenation capability of the material. The proton-exchanged form of todorokite, appears to act as a very efficient cracking catalyst (yield to methane and ethylene ∼40%, selectivity to cracking products >85%), due to the formation of a large number of framework Brønsted acid sites. The observed cracking capability of H-todorokite is superior to the activity of the commercial fluid catalytic cracking (FCC) USY catalyst, thus suggesting that the proton form of the mineral is a promising catalyst for the cracking of small alkanes.

シリカ担持Pd，PtおよびPd-Pt触媒の耐硫黄性

Effect of pore structure of silica support on sulfur tolerance and tetralin hydrogenation activity of Pd, Pt and Pd-Pt catalysts was investigated. Pore diameter of SiO2 supports affected the sulfur tolerance of noble metals and resulting hydrogenation activity. High sulfur tolerance and tetralin hydrogenation activity were observed for the Pd-Pt and Pt catalysts supported on SiO2 having the average pore diameter of 3 nm. This sulfur tolerance was comparable to those supported on ultra stable Y (USY) zeolite having the SiO2/Al2O3 ratio of 390.

Acidic property of modified ultra stable Y zeolite: increase in catalytic activity for alkane cracking by treatment with ethylenediaminetetraacetic acid salt

Temperature-programmed desorption (TPD) of ammonia with improved techniques was applied to quantitative determination of the strength and number of acid sites of a series of modified Y zeolites. A weak acid site was generated by the isomorphous substitution of aluminum for silicon, and the strength was independent of the aluminum concentration. This type of acid site showed almost no activity for cracking of octane at 573 K. Multiple types of extra-framework aluminum were formed on the ultra stable Y (USY) zeolite by steaming to create the cracking activity. Strong Brønsted acid sites were increased by the treatment of USY with a sodium salt of ethylenediaminetetraacetic acid (EDTA). The catalytic activity for alkane cracking showed a positive relationship with the number of this type of acid site, suggesting that the active site of USY for the catalytic cracking is this strong Brønsted acid site.

Effect of vanadium on USY zeolite destruction in the presence of sodium ions and steam—studies by solid-state NMR

The effect of deposited vanadium on the thermal destruction of ultra stable Y (USY) zeolite in the presence of sodium ions and steam was investigated by solid-state NMR. When USY zeolite containing few sodium ions was heated in a dry atmosphere, SiOH groups, which corresponded to defect sites, and strong adsorption sites were formed by the dealumination. The former mainly caused an increase in the mean void volume per supercage and the latter originated from cationic extra framework Al in the supercages. Furthermore, in the dry atmosphere, the sodium ions inhibited the dealumination; the effect of the deposited vanadium on the structural change was not large. After the heat treatment in 100% steam, in case of USY zeolite containing few sodium ions, the crystallinity and the supercage structure hardly changed although the dealumination occurred remarkably. This process did not depend on the deposited vanadium. Data suggested that the heat treatment in 100% steam causes the framework stabilization. In case of USY zeolite containing a number of sodium ions, the synergistic effect between a few deposited vanadium ions and the sodium ions on the framework destruction in 100% steam was tremendous. We propose that the deposited vanadium functions as vanadic acid and catalyzes the conversion of the sodium ions into NaOH. Thus, an increase in the NaOH content promotes the ‘dissolution’ of the zeolite crystal, i.e. the framework destruction. In addition, when the sample containing both a few vanadium ions and a number of sodium ions was heated in 100% steam, the supercage was plugged partially. We believe that the blockage compounds in the supercage are sodium vanadates.

Study of Interactions between Ion-Exchanged Chromium and Impregnated Vanadium in USY Zeolite Material

The steam treatment effect on the structure stability and acidity of ultrastable Y (USY) and Cr(III)-exchanged USY zeolites is investigated in the presence and absence of impregnated vanadium at 1000 up to 4000 ppm concentrations. Under steam-treatment conditions and in the presence of vanadium, the obtained results give evidence of the complete structure breakdown of an USY zeolite sample, which is nearly proportional to the percent dealumination; however, the structure breakdown of a Cr(III)-exchanged USY zeolite sample is limited even though the percent dealumination is still high. In addition, it is proved that the impregnated vanadium attacks selectively the strong acid sites, i.e., removes isolated framework Al atoms; however, although this action comes to completeness, the zeolite structure of the Cr(III)-exchanged USY sample is strong enough to keep its crystallinity at a high percentage. Finally, the acidity measurements give evidence that the Cr(III)-exchanged USY zeolite possesses medium streng...

Ultra-deep Hydrodesulfurization and Aromatics Hydrogenation of Diesel Fuel over a Pd-Pt Catalyst Supported on Yttrium-modified USY

Bimetallic palladium-platinum catalyst supported on yttrium-modified ultrastable Y (USY) zeolite, Pd-Pt/Y-USY, showed high activity and stability for deep hydrodesulfurization (HDS) and hydrodearomatization (HDA) of diesel fuel. In model reactions, the HDS activity based on rate constant increased as much as 5.3 times and HDA activity increased as much as 1.9 times after yttrium modification. The deeper hydrogenation of 4,6-dimethyldibenzothiophene (4,6-DMDBT) allowed the following HDS reactions to be promoted over the Pd-Pt/Y-USY catalyst. The adsorptive interaction between Pd-Pt/Y-USY and basic tetralin was weaker than that between Pd-Pt/USY and tetralin. Under reaction conditions of P = 4.9 MPa, WHSV= 4 h -1 and T = 280°C for hydrotreating desulfurized gas oil feedstock, Pd-Pt/Y-USY successfully removed a large part of 4,6-DMDBT and also almost all refractory alkyl-substituted sulfur compounds, which are supposed to be more difficult to hydrodesulfurize. The hydrotreated product after 216 h on stream contained 28 wtppm sulfur and 8 wt% aromatics. NH 3 adsorption analyses showed that yttrium modification decreased the number of strong acidic sites with little change in the total acidic sites. This modification in acidity could help to minimize the excessive hydrocracking which causes carbonaceous deposits, and to increase the nitrogen tolerance. Scanning transmission electron microscopy (STEM) analyses clearly showed that yttrium modification suppressed the agglomeration of Pd-Pt phases, which might be linked to the high stability of the Pd-Pt/Y-USY catalyst. Therefore, Pd-Pt/Y-USY catalyst is quite promising as a second stage catalyst for the integrated two-stage reformulation of gas oils.

On the acid-dealumination of USY zeolite: a solid state NMR investigation

The dealumination of USY (ultrastable Y) zeolites by nitric acid and oxalic acid treatment was systematically investigated by multinuclear solid-state NMR and MQ MAS NMR experiments. The results show that both acids are very effective in removing non-framework Al as well as framework Al but that aluminum is extracted from the lattice at a higher rate by oxalic acid even at low concentrations. The presence of different species (e.g. silanol nest, Al–OH, four-coordinated framework Al, six-coordinated framework Al, six-coordinated non-framework Al and five-coordinated non-framework Al) was detected, and their changes were followed during the dealumination. The investigation gives evidence that the breakdown of the parent USY zeolite mainly depends on the degree of dealumination and that non-framework Al exerts a great effect on the acidity of the USY zeolite. Leaching-induced increase in the Brønsted acidity of the USY zeolite was also observed by 1H MAS NMR spectroscopy. The different distribution of Al species in these samples accounted for the different catalytic performance of n-dodecane cracking.

Molecular Competition of C 7 and C 9n-Alkanes in Vapor- and Liquid-Phase Hydroconversion over Bifunctional Pt–USY Zeolite Catalysts

Molecular competition effects in the hydroconversion of an equimolar heptane/nonane mixture were studied in liquid-phase reaction conditions in a fixed-bed reactor filled with a Pt–ultrastable-Y (USY) catalyst. Liquid-phase conditions were attained by feeding the hydrocarbon mixture with hydrogen dissolved in it at 100 bar and 230°C. Comparative vapor-phase experiments were run at 230°C, a pressure of 4.5 bar, and a hydrogen-to-hydrocarbon ratio of 13. Whereas catalytic experiments in the vapor-phase showed a marked referential conversion of nonane over heptane, in liquid-phase the differences in conversion rate between nonane and heptane were much less pronounced. Adsorption-reaction models were used to explain the difference. For this purpose, intrinsic kinetic constants for heptane and nonane were derived from experimental data from vapor-phase conversions of the n-alkanes individually, using an adsorption-reaction model with independently determined adsorption equilibria, and assuming the classic bifunctional reaction scheme. The liquid-phase conversion of the heptane/nonane mixture was predicted very well using these intrinsic reaction kinetics derived from the vapor-phase experiments and assuming no adsorption preference between heptane and nonane. In contrast to this, the conversion of the heptane/nonane mixture in the vapor phase could only be appropriately described by a model involving adsorption according to a Langmuir-with-interaction model, favoring adsorption of the heaviest compound. In liquid-phase reaction conditions and at saturation of the Pt–USY zeolite pores with n-alkanes, there is no such selective adsorption of the heaviest compound. In liquid-phase, the conversion of the mixture reflects the intrinsic reaction kinetics of the individual compounds.

Control of hydrodesulfurization and hydrodearomatization properties over bimetallic Pd–Pt catalysts supported on Yb-modifed USY zeolite

Increasingly stringent regulations on the removal of aromatic and sulfur compounds in diesel fuel require the development of new catalysts and processes. Here, control of hydrodesulfurization (HDS) and hydrodearomatization (HDA) properties was studied by preparing bimetallic Pd–Pt catalysts supported on ytterbium-modified ultrastable Y (USY) zeolite by impregnation and subsequent calcination under different temperatures. Catalytic performances of the prepared catalysts, such as HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and HDA of tetralin, were investigated in a high-pressure continuous-flow reactor. With changing calcination temperature, the HDS activity is only slightly affected, although the maximum HDS conversion was obtained at 300°C. In contrast, the HDA activity decreased significantly, with hydrogenation selectivity remaining relatively constant as confirmed by the weak variation of the trans-decalin to cis-decalin ratio. A low calcination temperature of 200°C simultaneously favored both deep HDS and deep HDA, whereas a high calcination temperature of 500°C favored selective HDS reactions with minimal HDA reactions (i.e. saving of expensive hydrogen). These results clearly indicate that the selectivity of HDS to HDA can be controlled by simply changing the calcination temperature of Pd–Pt/Yb/USY zeolite catalysts.

An FTIR Study of the Surface Acidity of USY Zeolites: Comparison of CO, CD3CN, and C5H5N Probe Molecules

A comparison of three basic probe molecules of varying strength, namely pyridine, acetonitrile, and carbon monoxide, was made, and their suitability toward the characterization of surface acidity in zeolitic materials was assessed. Two test samples were employed: both ultrastable Y (USY) zeolites but with differing silica:alumina ratios and degree of extraframework material. Carbon monoxide proved to be the most selective probe, not only being able to differentiate Bronsted (BAS) from Lewis acid sites (LAS), but BAS with varying acid strength as well. However, its weak basicity did not allow interaction with OH groups situated within the sodalite cages, this only being achieved with the two more basic probes. OH groups interacting with extraframework material also failed to form H-bonds with CO. Both pyridine and acetonitrile interacted with all OH groups, and pyridine was protonated by the most acidic bridged species. Although LAS could be told apart from BAS, differentiation of different types of LAS a...

Optimization of nanopores and acidity of USY zeolite by citric modification

To meet the challenges of the crude oil becoming heavier and poorer quality, and the tendency of the increasing liquefied petroleum gas (LPG) and diesel in fluid catalytic cracking (FCC) process, the ultrastable Y (USY) zeolites were further modified by citric acid to optimize their nanopores and acid sites. The nanopores and acid sites of modified zeolites were extensively investigated by N 2 adsorption, XRD and in situ IR methods. The micro-activities of modified samples were also evaluated. The results showed that the nanopore volume of the modified samples is rather more developed than that of the parent zeolite. It indicated that micropores and mesopores might be generated by skeletal reconstruction. The dealumination process might be occurred gradually from the upmost surface to subsurface, then to bulk sites of the USY framework because of the larger volume of citric acid molecules. It resulted in the gradient distribution of nanopores and acid sites in modified zeolites. The hydroxyls with IR bands of 3610 and 3575 cm −1 in the micropores or small cages bears the stronger acidity and much more sites than those in mesopores or larger cavities. This gradient acid distribution was rather preferable to produce preferably LPG and diesel in FCC process. MAT evaluations indicated that the LPG and diesel yields of citric modified samples were effectively improved. Optimization of nanopores and acid sites of ultrastabilized USY zeolites modified with citric acid in unbuffered system might result in an industrial process to design novel FCC catalysts.

Sulfur-tolerant Pd-Pt/Yb-USY zeolite catalysts used to reformulate diesel oils

Bimetallic Pd-Pt catalysts supported on ytterbium-modified ultrastable Y (USY) zeolite showed excellent hydrodesulfurization (HDS) and hydrodearomatization (HDA) activity as well as high stability when used to reformulate hydrotreated diesel oils; sulfur decreased from 263 to <20 ppm, and aromatics decreased from 26 to <5% after a time on stream of 192 h at a hydrogen pressure of 3.9 MPa at 553 K and WHSV=4 h −1. Modification of USY zeolite with ytterbium by impregnation decreased the number of strong acidic sites, while it increased the dispersion of the Pd-Pt phases, thus, possibly contributing to the increase in the nitrogen- and sulfur-tolerance and stability of Pd-Pt/Yb-USY zeolite catalysts.

Reaction of Positronium with Proton in Ultra-stable Y Zeolite Studied by Positrons

The positron annihilation lifetime spectra were measured as a function of the heating temperature for the ultrastable Y (USY) zeolites. The lifetime spectra were well resolved into five lifetime components, and the longer lifetimes τ3, τ4 and τ5 are assigned to ortho-positronium annihilating in the β-cage, super-cage and the second pore in USY zeolite, respectively. The interesting observation is that the annihilation rate λ5 (the reciprocal of the τ5) of the fifth component increases and its intensity I5 decreases with the increasing heating temperature. The result is interpreted in terms of the increase in proton and the reaction between the positronium and proton in USY zeolite after heated.

Competitive physisorption effects in hydroisomerisation of n-alkane mixtures on Pt/Y and Pt/USY zeolite catalysts

Physisorption isotherms and separation factors of n-C6–n-C12 alkanes on zeolite Y with Si/Al of 2.7 and on ultrastable Y (USY) zeolites with Si/Al ratios of 13 and 30 were determined using perturbation chromatography, at 506 K and for the hydrocarbon pressure range relevant to hydroisomerisation catalysis with platinum loaded versions of these zeolites. For the n-alkane pressure range from 0.3 to 0.9 bar, a refined Langmuir model with an interaction factor accounting for adsorbate–adsorbate interactions and surface heterogeneity gave the best agreement with the experimental single component adsorption data. Expressions for multicomponent adsorption equilibria among the n-alkanes, their isomers and cracked products, and expressions with interaction factors for the single components into multicomponent expressions were obtained. Separation factors among the n-alkanes and their variation with adsorbent loading derived from these multicomponent expressions are in agreement with experimental separation factors. The expressions for the adsorption equilibria were used to extract intrinsic kinetic constants of individual n-alkanes from experimental catalytic conversion data of pure compounds. It is demonstrated that the conversion of the individual components of a four component n-alkane mixture can be accurately predicted by a model combining intrinsic reaction constants for the individual components with the multicomponent adsorption isotherms. The approach was equally successful with the H-Y zeolite as with the strongly dealuminated USY zeolites exhibiting strongly different acidity, catalytic activity and adsorption behaviour.

Characterization of the acidity of ultrastable Y, mordenite, and ZSM-12 via NH 3-stepwise temperature programmed desorption and Fourier transform infrared spectroscopy

The acidity of ultrastable Y (USY), mordenite, and ZSM-12 of variable Si/Al ratios has been characterized by coupling NH 3-stepwise temperature programmed desorption (STPD) and FT-IR. The former technique allows us to quantify accurately the ammonia chemisorbed on acid sites of different strengths. In contrast to other acidic oxide catalysts, it was found that protonated zeolites possess distinct limits of acid strength and that chemisorbed ammonia desorbs from each type of site only within particular temperature ranges. It was observed that for zeolites with Si/Al ratios smaller than about 20 the number of ammonia molecules chemisorbed on both Lewis and Brønsted sites is smaller than the total number of Al atoms present in the zeolite. However, an increase in the Si/Al ratio above this threshold results in a 1:1 relation between the total number of acid sites and the amount of ammonia adsorbed. It was found that for mordenite and ZSM-12 an increase of the dealumination severity results in a decrease of the acid site strength. For USY the acid strength decreased with steam treatment, but then increased with acid leaching. The FT-IR studies revealed that for the protonated USY, Lewis-bound ammonia is evolved within each temperature stage. For mordenite, the Lewis sites are associated with desorption up to 250°C. The non-dealuminated ZSM-12 (Si/Al=35) sample possesses a relatively small number of Lewis sites, whereas the ZSM-12 samples with higher Si/Al ratios had only Brønsted acid sites. A peak deconvolution procedure was performed in order to decompose accurately the complex hydroxyl region of USY and mordenite and was used to separate the Lewis peak from structural vibrations for ZSM-12. As a result, important information concerning the nature of the aluminum species present in these zeolites (extraframework species, framework species present within the side pockets of mordenite, framework species present within the β cages of USY, etc.) was obtained.

Activity and Structure of Hydrotreating Ni, Mo, and Ni–Mo Sulfide Catalysts Supported on γ-Al2O3–USY Zeolite

The catalytic hydrocracking (HC) of diphenylmethane (DPM) and hydrodesulfurization (HDS) of dibenzothiophene (DBT) over Ni, Mo, and Ni–Mo sulfide catalysts supported on a mixed ultrastable Y (USY) zeolite and γ-Al2O3 were studied. The catalysts were characterized using NH3 temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), UV–Vis–NIR diffuse reflectance spectroscopy (DRS), high-resolution transmission electron microscopy (HRTEM), and chemical composition analysis. Because addition of zeolite to a conventional alumina support improves acidity, Ni, Mo, and Ni–Mo catalysts supported on the combined supports had much higher HC activity. Ni was found to be uniformly distributed throughout the catalysts; however, Mo preferentially entered the structure of γ-Al2O3 or was accommodated as oxide aggregates on γ-Al2O3, rather than associating with zeolite. Ni and Mo catalysts supported on γ-Al2O3–USY zeolite were good HDS catalysts and showed a shallow maximum in catalytic activity at a NiO and MoO3 content of 5 mol%. The higher activity at this content occurred because Ni or Mo species had higher surface concentrations, higher dispersion, and were more easily sulfided. Ni–Mo catalysts supported on γ-Al2O3–USY zeolite had high HDS activity, which showed a prominent maximum at a NiO/(NiO+MoO3) ratio of about 0.4, because at this ratio the surface species of Ni and Mo were well dispersed and more easily sulfided to form a Ni–Mo–S phase responsible for the high HDS activity. The Ni–Mo catalysts supported on γ-Al2O3–USY zeolite have slightly higher HDS activity than γ-Al2O3-supported Ni–Mo catalysts.

Catalytic Conversion of Palm Oil to Hydrocarbons: Performance of Various Zeolite Catalysts

The catalytic cracking of palm oil to fuels was studied in a fixed bed microreactor operated at atmospheric pressure, a reaction temperature of 350−450 °C and weight hourly space velocities (WHSVs) of 1−4 h-1. HZSM-5, zeolite β, and ultrastable Y (USY) zeolites with different pore sizes were used to study the effects of reaction temperature and WHSV on the conversion of palm oil and yields of gasoline. The performances of HZSM-5−USY and HZSM-5−zeolite β hybrid catalysts containing 10, 20, and 30 wt % HZSM-5 were investegated. Potassium-impregnated K−HZSM-5 catalysts with different potassium loadings were used to study the effect of acidity on the selectivity for gasoline formation. The major products obtained were organic liquid product (OLP), hydrocarbon gases, and water. HZSM-5 catalyst gave conversion of 99 wt % and a gasoline yield of 28 wt % at a reaction temperature of 350 °C and WHSV of 1 h-1 and was the best among the three zeolites tested. The HZSM-5−USY hybrid catalyst performed better than USY ...

Investigation of the Benzene Molecule Adsorbed on Faujasite Zeolite Using Double Quantum Filtered NMR Spectral Analysis

Deuteron NMR relaxation studies including double quantum filtered (DQF) spectral analyses, T1, and line widths are used to probe the dynamics and exchange process of various-loading benzene molecules adsorbed into NaY and dealuminated Y (DAY) including ultrastable Y (USY) zeolite. DQF NMR is a very sensitive method to determine the residual quadrupolar interaction resulting from the local order. In this work, we modified the cone model to describe the in-plane rotation around the hexad axis and the restricted wobbling motion of the benzene ring on the surface of the interaction site. The in-plane rotation and wobbling motion of adsorbed benzene molecules reflects a host−guest effect on the isolated adsorption site and also the mobility in the cage. In addition, the effect of a site-to-site hopping process results in a small net residual quadrupolar interaction. With increased loading, the in-plane rotation of benzene is significantly hindered in all faujasites but the population of adsorbed benzene dramat...

Oligomerization of Hex-1-ene over Acidic Aluminosilicate Zeolites, MCM-41, and Silica-Alumina Co-gel Catalysts: A Comparative Study

Hex-1-ene in octane solvent was oligomerized in a down-flow tubular reactor holding a fixed catalyst bed at temperatures of 80–300°C and a pressure of 5 MPa. Ultrastable Y (US-Y), hydrogen beta, and MCM-22 zeolites, MCM-41, silica–alumina and silica–magnesia co-gels, and γ-alumina were evaluated as catalysts. The reaction products obtained are composed of hexene dimers and trimers, cracked products, C6alkanes, and isohexenes. The catalytic activity of the mesoporous silica–alumina co-gels and MCM-41 is very similar to that of beta, MCM-22, and US-Y zeolites. The oligomerization process occurs in the mesopores and on the exterior surfaces of the zeolite crystals. In the micropores of zeolite beta and US-Y, the hexenes undergo dimerization-cracking reactions generating isohexenes and cracked products. In MCM-22, having narrower micropores, these cracking reactions are suppressed. MCM-22, MCM-41, and silica–alumina co-gels lacking microporosity are the most selective hexene dimerization catalysts.