Zeolites stabilization

Silica-magnesia matrices have not yet been properly evaluated as an RCC catalyst matrix. However, such a matrix in conjunction with stabilized zeolite might provide an attractive matrix with a Kaolin-enhanced dual pore structure. Silica-magnesia matrices are notorious for their poor regeneration characteristics. When prepared by the dual pore Kaolin-enhanced method, they might be easier to regenerate and, thereby, open up a new family of residuum catalysts. Such catalysts have not yet been explored. 

Since 1962 rare earths have been used to stabilize zeolite cracking catalysts for the petroleum industry (1, 2. Until recently this application to catalysis has been the only commercially significant one. Currently, however, a number of new applications of potential commercial significance are appearing. One of the most important of these is the use of cerium in catalysts for automobile exhaust emission control. We will emphasize this application in our review without neglecting other applications. 

When the cracking activity of SAPO-37 is compared with that of an USY with unit cell size of 2.447 nm (Fig. 5), which would be equivalent to the stabilized zeolite compared in the patent literature (13,14), the activity of the SAPO 37-2 is higher. 

Stabilized zeolite-Y is the principal acidic constituent of the catalyst, responsible for most of the cracking activity. The metal catalyst is a supported Pt, added in small amounts, and which functions as a CO oxidation catalyst, allowing cleaner gaseous emissions from the regenerator. 

W. Schmidt, F. Schuth, H. Reichert, K. Unger, and B. Zibrowius, VPI-5 and Related Aluminophosphates Preparation and Thermal Stability. Zeolites, 1992, 12, 2-8. 

Catalyst preparations. Y zeolites with overall Si/Al ratio equal to 2.7, 15 and 45 were used as supports. The Y2>7 sample was a stabilized zeolite available from Union Carbide (LZY 82). This material when submitted to selfsteaming and acid leaching yielded HY4g. The HY15 sample derived from a commercial NaY (Union Carbide LZY 52) the transformation involved successive ammonium exchange, self-steaming and acid washing. 

Therapy, adjuvants Thermal activation, clinoptilolite Thermal analysis, ETS-4 Thermal behavior, clinoptilolite Thermal desorption Thermal stability, FAU Thermal stability, MOR Thermal stability, zeolites Thermal treatment, MFl... 

Reasons for use abrasion resistance, cost reduction, electric conductivity (metal fibers, carbon fibers, carbon black), EMI shielding (metal and carbon fibers), electric resistivity (mica), flame retarding properties (aluminum hydroxide, antimony trioxide, magnesium hydroxide), impact resistance improvement (small particle size calcium carbonate), improvement of radiation stability (zeolite), increase of density, increase of flexural modulus, impact strength, and stiffness (talc), nucleating agent for bubble formation, permeability (mica), smoke suppression (magnesium hydroxide), thermal stabilization (calcium carbonate), wear resistance (aluminum oxide, silica carbide, wollastonite)... 

Indeed the FCC process as early as the late fifties started to use catalyst formulations based on the incorporation of thermally-stabilized zeolites in a suitable matrix. The advantages were increased rates, increased liquid products, increased tolerance to poisons and larger operating flexibility as compared to former silica-alumina based catalysts. 

In a great number of cases, zeolites are used as auxiliary elements. They may act either as a framework to stabilize the sensor material, as filter layers (either catalytic or size restrictive) to enhance selectivity of a sensitive film, or as a preconcentrator of specific analytes from diluted solutions. For example, due to excellent chemical and thermal stability, zeolites can be used as a substrate to prepare compounds and devices with desirable fundamental physical and chemical properties (Xu et al. 2006). For example, inorganic or organic compounds, metal and metal-organic compounds, and their clusters can be assembled into the pores and cages in zeohtes. Some nanosized metal or metal oxide particles have been successfully inserted into the caves and the pores or highly dispersed on the external surface of zeohtes. 

Rare earth compounds are also used in numerous catalytic reactions in petrochemical industry. One example is the use of rare earth salts to stabilize zeolites used for the catalytic cracking of crude oils to gasoline. Rare earth doping increases the activity of these zeolites with the consequence of higher gasoline yields. In addition, these rare earth-modified catalysts have found expanded application as a consequence of the refineries use of residual or heavy crude oils which contain high levels of nickel, vanadium, and sulfur which attack zeolites and reduce their activity rare earths are more resistant to these catalytic poisons. ... 

The aluminum defects (III) in the above scheme created by dealumination may be eliminated by silicon species from the zeolite structure of amorphous silica contained in the material. The dealumination can be achieved also by the reaction with silicon tetrachloride. In this case, no vacancies are formed since aluminum in the structure is directly substituted by silicon. Since the thermal stability of zeolites increases with increasing Si/Al ratio, zeolites become thermally more stable after dealumination. In the case of Y-zeolites, the stabilized zeolites are called ultra-stable zeolites. 

Polyaniline (PANI) nanocomposite membranes are also prepared by a sol-gel process, embedding silica in the hydrophilic clusters (Nafion) followed by its deposition by redox polymerization [51]. PANI modified the membrane structure and reduced the methanol crossover, while silica Incorporation improved the conductivity and stability. Zeolite has been incorporated as potential filler for PEMs, either by blending or by infiltration in swelled membrane, to reduce the methanol permeability and enhance the thermal stabihty [52,53]. Although the fuel cell performance of these membranes was Inferior compared with pristine Nafion membrane, incorporation of semipermeable particles is an effective method to engineer the transport properties of composite membranes. Chen et al [54] reported nanocomposite membranes by in situ hydrothermal crystallization method, with similar proton conductivity, but low methanol permeability (40% less) in comparison with Nafion membrane. These membranes showed higher OCV (3%) and power density (21%) than Nafion. 

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