Direct synthesis of copper faujasite

Copper containing faujasite has been successfully prepared for the first time using a direct synthesis method. Faujasite type zeolite can be prepared in the presence of copper species by tuning the synthesis conditions. Ammonium hydroxide was used to form a copper complex that was later mixed with the reacting gel. Sodium is required to obtain copper faujasite. The complete elimination of sodium ions from the starting gel produces amorphous material. Crystallization took place at 358 K for 11 days. Crystallization temperature of 373 K produces ANA type zeolite as an impurity. Increasing by two times the amount of copper complex added to the reacting gel increases the crystallization time of Cu-FAU from 11 to 20 days (the crystallization rate decreases). The copper containing faujasite obtained was characterized by XRD, FESEM, EDX, EPR, FT-IR, TPR, and BET. According to the XRD pattern only FAU type zeolite was obtained. According to TPR experiments, the reduction temperature for Cu²⁺ ions present in Cu-FAU prepared by direct synthesis was 70 K more than for Cu-FAU prepared by ion-exchange. This difference can be due to the different location of the copper ions in the supercages or in the sodalite cages of the faujasite.     

Hydrocracking of phenanthrene over bifunctional Pt catalysts

Hydrocracking of phenanthrene was studied in a fixed bed continuous flow reactor under 60 bar total pressure using a bifunctional catalyst constituted of Pt deposited on silica–alumina. GC–MS analysis was utilised in order to identify the numerous products formed during phenanthrene hydrocracking. Following a kinetic study, a reaction pathway was proposed based on a multi-step mechanism: hydrogenation of aromatic rings, isomerisation and cracking of naphtenic rings, and rearrangements. Reaction temperature showed a great effect in terms of selectivity and catalysts comparison was therefore done at a temperature of 300°C. Three bifunctional catalysts: platinum supported on silica–alumina, on H-Y zeolite and on H-β zeolite were compared in terms of activity and selectivity. A close examination of product distribution indicated that the major contributing factor was the pore structure of the support. Zeolite structures favoured overcracking because of the numerous collisions with acid sites that perhydrophenanthrene could undergo during its diffusion.     

Studies on the catalytic dechlorination and abatement of chlorided VOC: the cases of 2-chloropropane, 1,2-dichloropropane and trichloroethylene

The conversion of monochloropropanes and dichloropropanes over acid catalysts has been investigated in the presence of oxygen. In the temperature range of 450–550 K, dehydrochlorination of monochloropropanes to propene and HCl occurs selectively over silica–alumina, while significant formation of chlorinated by-products is observed over ZSM5 zeolite catalyst even at higher temperatures. Dichloropropanes conversion over silica–alumina catalyst gives rise mainly to chloropropenes in the temperature range 500–700 K. CO_x are predominant products only at the highest reaction temperatures (just above 700 K). Water vapor in the feed only slightly affects conversions and selectivities. Deactivation processes occur upon dichloropropane conversion, mainly due to coke deposition.

The conversion of highly chlorinated compounds, such as trichloroethylene (TCE) has been tested over silica–alumina and over HY zeolite in the presence of water vapor in the so-called “steam reforming” conditions (HVOC:water=1:2). With diluted feed (1200 ppm) on HY, reaction occurs above 800 K and formation of chlorinated by-products is minimized, CO_x being the main reaction products. At higher HVOC concentrations conversion is obtained at even lower temperature (600 K), but no more negligible by-products formation has been detected. In our conditions zeolite catalyst is more effective in TCE total conversion than silica–alumina.     

Activity and stability of alumina zeolite nickel catalysts

The catalytic properties of nickel catalysts (50 wt.% of alumina and 50 wt.% of Ni,H-ZSM-5) were investigated and related to the amount of NiO (0–8 wt.%) and the method of nickel incorporation (8 wt.% NiO). Consideration was also given to the method by which zeolite and alumina were combined. The cracking properties of the catalysts increased when the amount of NiO was raised up to 4 wt.%. To decrease the content of aromatic hydrocarbons in the products it is necessary to raise the amount of NiO to a higher level than 4 wt.%. The catalyst prepared by peptisation of the mixture of zeolite and aluminium hydrogel (with ageing process) displayed reduced activity and stability because of the low susceptibility of NiO to reduction.     

Zeolite Beta nanosized assemblies

Nanosized zeolite Beta assemblies are prepared by a steam assisted conversion (SAC) method from micron-sized porous amorphous silica grains soaked in clear solutions containing the alumina source and organic template. The zeolite Beta assemblies are built of closely packed uniform nanocrystals (100 nm) and retain the size and morphological features of the primary silica grains. The crystallinity and the phase purity depend strongly on the temperature and time of SAC treatment as well as on the initial aluminum content. For comparison, colloidal zeolite Beta samples with similar Si/Al ratio were prepared by a hydrothermal treatment (HT). The Raman and NMR spectroscopic data reveal that the method of preparation (SAC or HT) does not affect the local structure of Al-rich samples, while for high-silica samples the degree of disorder is higher in the ones obtained via the SAC approach. The adsorption/desorption isotherms of zeolite Beta assemblies and colloidal Beta powders indicate the presence of both micro- and mesoporosity. The catalytic behavior of the zeolite Beta assemblies and colloidal Beta powders in pentane hydroisomerization reaction is studied.     

Preparation and Properties of Fluid Cracking Catalysts for Residual Oil Conversion

Catalytic cracking of petroleum to produce gasoline began in about 1912. The early pioneering work was carried out by Eugene Houdry [1]. Modern fluid catalytic cracking (FCC) was conceived at Exxon and commercially developed in about 1940 [2] using amorphous catalysts. Fluid catalysts are small spherical particles ranging from 40 to 150 um in diameter with acid sites capable of cracking large petroleum molecules to products boiling in the gasoline range. One advantage of the FCC process is the absence of the diffusion limitations present in conventional gas oil cracking due to the small size of the catalyst particle. Since 1964 virtually all catalysts contain faujasite, a stable, large pore, Y-type zeolite dispersed in a silica/alumina matrix [3]. The catalytic aspects of contemporary FCC processes have been reviewed by Venuto and Habib [4], Gates, Katzer, and Schuit [5], Magee and Blazek [6], and Magee [7]. A more recent update of refinery trends has been made available by Blazek [8].     

Preparation and Properties of Fluid Cracking Catalysts for Residual Oil Conversion

Catalytic cracking of petroleum to produce gasoline began in about 1912. The early pioneering work was carried out by Eugene Houdry [1]. Modern fluid catalytic cracking (FCC) was conceived at Exxon and commercially developed in about 1940 [2] using amorphous catalysts. Fluid catalysts are small spherical particles ranging from 40 to 150 um in diameter with acid sites capable of cracking large petroleum molecules to products boiling in the gasoline range. One advantage of the FCC process is the absence of the diffusion limitations present in conventional gas oil cracking due to the small size of the catalyst particle. Since 1964 virtually all catalysts contain faujasite, a stable, large pore, Y-type zeolite dispersed in a silica/alumina matrix [3]. The catalytic aspects of contemporary FCC processes have been reviewed by Venuto and Habib [4], Gates, Katzer, and Schuit [5], Magee and Blazek [6], and Magee [7]. A more recent update of refinery trends has been made available by Blazek [8].     

水热固相法将稀土引入Y型分子筛的研究

用XRD和静态低温氮吸附容量法考察了不同水蒸汽焙烧条件对FCC催化剂的晶胞、相对结晶保留度、比表面积和孔结构等物化性能的影响。通过高级裂化评价装置(ACE)和NH3-TPD酸性测试考察了水蒸汽焙烧条件对FCC催化剂催化性能和酸性的影响，发现含稀土FCC催化剂在合适水蒸汽条件下焙烧后，其物化性能和催化性能明显改善，这是因为其中的稀土化合物和Y型分子筛发生了固相离子交换反应并迁移至分子筛晶内的结果。     

Sulfided Mo and CoMo supported on zeolite as hydrodesulfurization catalysts: transformation of dibenzothiophene and 4,6-dimethyldibenzothiophene

The hydrodesulfurization (HDS) of dibenzothiophene (DBT) and of 4,6-dimethyldibenzothiophene (4,6-DMDBT) was carried out on sulfided Mo and CoMo on HY catalysts, and also on sulfided Mo and CoMo on alumina catalysts (fixed bed reactor, 330°C, 3 MPa hydrogen pressure). On all the catalysts, the two reactants transformed through the same parallel pathways: direct desulfurization (DDS) leading to biphenyl-type compounds, and desulfurization after hydrogenation (HYD) leading first to tetrahydrogenated intermediates, then to cyclohexylbenzene-type products. However, additional reactions were observed with the zeolite-supported catalysts, namely methylation of the reactants, cracking of the desulfurized products, and, in the case of 4,6-DMDBT, displacement of the methyl groups and transalkylation. The global activity of Mo/zeolite in DBT or 4,6-DMDBT transformation as well as its activity for the production of desulfurized products (HDS) were much higher than those of Mo/alumina. On the other hand, cobalt exerted a promoting effect on the activity in the transformation of DBT or 4,6-DMDBT of all the molybdenum catalysts. However, this effect was much less significant with the zeolite support than with the alumina support, which indicated that the promoter was not well associated to molybdenum on the zeolite support. Therefore, the activity of CoMo/zeolite in the HDS of DBT was much lower than that of CoMo/alumina. On the contrary, in the case of 4,6-DMDBT CoMo/zeolite was more active in HDS than CoMo/alumina. This increase in HDS activity was attributed to the transformation of 4,6-DMDBT into more reactive isomers through an acid-catalyzed methyl migration. The consequence was that on the zeolite-supported catalyst 4,6-DMDBT was more reactive than DBT.     

Stability of Pt-Co bimetallic particles: effect of the support induced morphology on reactivity in CO hydrogenation

The structure and the stability of bimetallic particles are controlled by their interaction with surface oxide species on support or by support geometry. Location and size of the bimetallic particles estimated by XRD and XPS, depends on the environment and treatment. Thus, the Pt-Co bimetallic particles entrapped in NaY zeolite cages become unstable upon mild oxidation by O₂ and/or reaction with surface protons causing the Co²⁺ ions formed to migrate irreversibly from the supercages into the sodalite cages as determined by TPR and TPD. Differences in the selectivity pattern observed for the CO hydrogenation over alumina and NaY zeolite supported Pt-Co catalysts, can be interpreted by the interaction between bimetallic particles with surface cobalt oxide species and the zeolite cage wall, respectively.On leave from Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, Shanxi 030001, PR China.     

Fractal Extra-Framework Species in De-aluminated LaY Zeolites and Their Catalytic Activity

Lanthanum-containing Y (LaY) zeolites were prepared by ionic exchange from NaY parent zeolite. The LaY zeolites were de-aluminated by steaming. De-aluminated zeolites presented different Si/Al ratio. The physicochemical properties of these catalysts were characterized by X-ray diffraction, pyridine and xenon adsorption, infrared spectroscopy and ²⁹Si, ²⁷Al, ¹²⁹Xe, ¹³⁹La solid-state nuclear magnetic resonance spectroscopy. Furthermore, a fractal geometry approach was adopted to describe the evolution in the texture as a consequence of de-alumination. The catalytic properties of materials were evaluated in the n-hexane cracking reaction. The catalyst with the highest catalytic activity was the zeolite highest de-aluminated (Si/Al ratio of 3.7). Such performance was attributed on the one hand, to active extra-framework aluminum species hosted in the large cavities of zeolites and, on the other hand to redistribution of lanthanum species into the zeolite as a consequence of de-alumination.     

Heavy crude oil hydroprocessing: A zeolite-based CoMo catalyst and its spent catalyst characterization

This study presents an effect of zeolite with alumina as a support for heavy oil hydroprocessing. The high surface area, moderately acidic meso- and macro-porous support was prepared with the mixing of alumina and ultra-stable Y zeolite (US-Y). The micro-structure and the composition of the zeolite crystals formed in the bulk of the alumina were examined by scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), and there were two main crystal phases homogeneously distributed in it. A CoMo sulfide supported catalyst is evaluated for hydroconversion of Maya heavy crude oil at moderate pressure conditions. The combination of ultra-stable zeolite and alumina is able to produce bi-modal type of pores in the catalyst which may contribute to a better combination of hydrodesulfurization (HDS), hydrodemetallization (HDM) and the selective cracking of asphaltene over the acidic catalysts. The characterization of spent catalysts can help as an assistance for the selection of optimum catalyst properties along with the reactor bed length and type of catalyst pore in each bed. The strapping reaction condition indicated that the acidic catalyst for heavy oil can be used more effectively at lower temperature. An increase in temperature showed that the HDM and hydrogenation of asphaltenes (HDAs) conversions are more affected than HDS and HDN. These results indicate occurrence of a thermal cracking of complex molecules like asphaltene and metal porphyrins, which is confirmed by the gaseous selectivity of the hydrocarbons.     

The pozzolanic activity of a calcined waste FCC catalyst and its effect on the compressive strength of cementitious materials

Equilibrium catalyst (Ecat), one of the spent fluid catalytic cracking (FCC) catalysts from oil companies, shows pozzolanic activity. In this study, the effects on the pozzolanic activity of calcination of Ecat and on the compressive strength of the resulting cementitious materials were examined. The pozzolanic activity of this mineral additive was indicated from DSC measurements. The results show that the pozzolanic activity of Ecat increases with calcined temperature initially, reaches a maximum, and then decreases afterwards. Ecat calcined at about 650 °C becomes the most active. Mortars with 10% calcined catalyst at 3-28 curing days exhibit strength 8-18% greater than that with the untreated. Concrete with a 10% calcined Ecat at 3-28 curing days exhibits strength 7-11% greater than that with the untreated. If the calcined catalyst is further ground, its pozzolanic activity is enhanced, and the compressive strength of the resulting mortars or concrete becomes higher.     

Technological Applications of Zeolites in Catalysis

Zeolites have been used as catalysts in industry since the early 1960s. The great majority of commercial applications employ one of three zeolite types: zeolite Y (faujasite); mordenite; ZSM-5. By far the largest use of zeolites is in catalytic cracking, and to a lesser extent in hydrocracking. Table 1 presents some data showing the commercial importance of this field [1]. The data are for United States refineries only and must be multiplied by a factor to arrive at worldwide use. Better than 90% of free-world cracking units now use zeolite catalysts. For many years it had been assumed that crystalline aluminosilicates with their uniform pore structure would make inferior catalysts to amorphous silica-slumina with a rather wide pore size distribution. The tremendous acid activity of hydrogen zeolites also was not recognized. Rabo and co-workers [2] showed at the 2nd International Congress on Catalysis that hydrogen exchanged faujasites possessed good isomerization ability, but commercial application in catalytic cracking became feasible only after Plank and Rosinsky at Socony-Mobil Oil Co. succeeded in stabilizing zeolite Y against steam and heat sintering by exchange with rare earth ions and by separating zeolite crystallites by incorporating them into a silica-alumina matrix which provided a heat reservoir along with some synergistic cracking effects. Modern cracking catalysts comprise 10-40% rare earth exchanged H-Y zeolite dispersed in a matrix of silica-alumina, semisynthetic clay, or natural clay.     

Crystal growth of faujasite observed by atomic force microscopy

Atomic force microscopy (AFM) was employed to reveal the crystal growth mechanism of faujasite. The seeded growth of faujasite in dilute aluminosilicate solutions was observed. Two solutions were prepared: one was near equilibrium with the seed and the other was in growth mode for the seed. Morphological changes during the seeded growth were observed along with the growth period at the same position on the seed (ex situ observation). These observations showed the rough surface of the seed changing into a well-ordered (1 1 1) face in the solution that was near equilibrium with the seed. This surface ordering proceeded by thermodynamic stabilization of the top-surface structure via the mutual transfer of aluminosilicate species between the solution and solid phases, and/or by the dissolution of the amorphous matter on the seed. In growth mode, most of the top surfaces of the seeded crystals were terminated by double six-membered rings (D6Rs), while some were by complete or incomplete sodalite cage. These results showed that aluminosilicate species equal to or smaller than 6R contributed to the crystal growth.     

Effect of cation location on the hydrothermal stability of rare earth-exchanged Y zeolites

NaY zeolites ion-exchanged with rare earth (RE) cations (La^3 +, Ce^3 +, Pr^3 +, Nd^3 +) were prepared by a double-exchange double-calcination method. The position, occupation and coordination of the zeolite extra-framework RE cations were identified by powder X-ray diffraction with the Rietveld refinement. The results indicate that Ce species were insusceptible to migration into the sodalite cages compared with others under the same circumstances, which may be attributed to the facile formation of CeO₂(IV) based on Ce(OH)^2 + and oxygen as well as the retarded migration of tetravalent cerium. Furthermore, the stability and activity of REY zeolites increased with decreasing ionic radii of RE elements.     

Technological Applications of Zeolites in Catalysis

Abstract

Zeolites have been used as catalysts in industry since the early 1960s. The great majority of commercial applications employ one of three zeolite types: zeolite Y (faujasite); mordenite; ZSM-5. By far the largest use of zeolites is in catalytic cracking, and to a lesser extent in hydrocracking. Table 1 presents some data showing the commercial importance of this field [1]. The data are for United States refineries only and must be multiplied by a factor to arrive at worldwide use. Better than 90% of free-world cracking units now use zeolite catalysts. For many years it had been assumed that crystalline aluminosilicates with their uniform pore structure would make inferior catalysts to amorphous silica-slumina with a rather wide pore size distribution. The tremendous acid activity of hydrogen zeolites also was not recognized. Rabo and co-workers [2] showed at the 2nd International Congress on Catalysis that hydrogen exchanged faujasites possessed good isomerization ability, but commercial application in catalytic cracking became feasible only after Plank and Rosinsky at Socony-Mobil Oil Co. succeeded in stabilizing zeolite Y against steam and heat sintering by exchange with rare earth ions and by separating zeolite crystallites by incorporating them into a silica-alumina matrix which provided a heat reservoir along with some synergistic cracking effects. Modern cracking catalysts comprise 10–40% rare earth exchanged H-Y zeolite dispersed in a matrix of silica-alumina, semisynthetic clay, or natural clay.     

Structure of sulfur complexes in zeolite Na<Emphasis Type="Italic">X</Emphasis>(S)

The distribution of sulfur atoms embedded in single crystals of zeolite NaX is investigated using the single-crystal X-ray diffraction analysis. It is shown that, in the unit cell of the NaX(S) zeolite, 67 sulfur atoms are located in the form of S₈ or S₆ rings and S₂ molecules in large cavities and in the form of Na₄S₄ complexes in the sodalite cages.     

Conversion of naphthenes to a high value steamcracker feedstock using H-ZSM-5 based catalysts in the second step of the ARINO-process

Future regulations for the limitation of sulfur and aromatics in fuels driven by the European Auto Oil Program (AOP II) stimulate the need for an alternative utilization of the resulting surplus of pyrolysis gasoline (pygas). The conversion of heavy pyrolysis gasoline into valuable steam cracker feedstock with a maximum yield of C₂–C₄ n-alkanes is achieved via the ARINO^® two-step process, jointly developed by Linde, VEBA Oil and Süd-Chemie. The first step involves a hydrogenation of aromatics to naphthenes followed by the subsequent ring opening and cracking in the second step.

Süd-Chemie developed a new commercial cracking catalyst for the second step of the ARINO^® process with the aim to maximize the yield of C₂–C₄ n-alkanes at low formation of methane and aromatics. The ring opening and cracking reaction of naphthenes was studied in a bench scale tubular reactor over extruded H-ZSM-5 based zeolite catalysts.

In a series of screening tests using a commercial, hydrogenated and desulphurized heavy pyrolysis gasoline, the influence of the preparation parameters such as zeolite acidity, palladium content as well as the type of binder were investigated. Furthermore, the influence of the process conditions space velocity and temperature was studied.

High yields of C₂–C₄ n-alkanes at low formation of undesired methane and aromatics were achieved over an alumina bound zeolite with medium Brønsted acidity loaded with palladium.

The reduction of the space velocity resulted in an increase in the C₂–C₄ n-alkane yield and lower formation of aromatics, but a simultaneous increase in the methane make. Raising the temperature from 280 to 370 °C significantly increased the catalyst activity.     

Simultaneous isomerization of n-heptane and saturation of benzene over Pt/Beta catalysts: The influence of zeolite crystal size on product selectivity and sulfur resistance

In this work we show that decreasing the zeolite crystal size has a clear benefit on product selectivity and sulfur resistance of Pt/Beta catalysts during the simultaneous hydroisomerization of n-heptane and hydrogenation of benzene. The higher isomerization selectivity of the catalyst prepared from a nanocrystalline Beta zeolite can be ascribed to a faster diffusion of the iso-C₇ products through the small crystallites preventing cracking reactions to occur, while the improved sulfur resistance can be related to a better dispersion of Pt owing to its higher surface area and mesoporosity.