Zeolite cracking catalysts, rare

The Use of Rare Earth Elements in Zeolite Cracking Catalysts... 

Following their introduction to the refining industry in 1962, zeolite cracking catalysts, have virtually replaced the amorphous silica alumina cracking catalysts that had previously dominated the marketplace. To the rare earth industry the development of zeolite catalysts represented a new end use without precedent. Nearly all zeolite cracking... 

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. 

The revolutionary zeolite cracking catalyst (synthetic Linde X and Y) was introduced commercially over 28 years ago, but considerable effort is still being expended on the improvement of its stability and catalytic properties. Decreasing the aluminum content of the zeolite framework and the replacing the rare-earth with the hydrogen form have greatly increased activity at the expense of stability. The thermal stability of the faujasites is fairly well understood, while the reasons for the increased catalytic activitity are still not fully known. 

We launched an Intensive effort to develop these highly ordered crystalline zeolites for commercial use, and by the early 1960s we commercialized the first synthetic zeolite cracking catalyst (Refs. 2,3). This catalyst was derived from a synthetic faujasite, first made by Union Carbide. Converting the faujasite into a useful cracking catalyst was a rather involved procedure, incluoing the removal of sodium, the introduction of rare earth, and severe steam treatment. 

Different procedures can be used in practice to activate the zeolite, and the choice of a particular method will depend on the catalytic characteristics desired. If the main objective is to prepare a very active cracking catalyst, then a considerable percentage of the sodium is exchanged by rare earth cations. On the other hand, if the main purpose is to obtain gasoline with a high RON, ultrastable Y zeolites (USY) with very low Na content are prepared. Then a small amount of rare earth cations is exchanged, but a controlled steam deactivation step has to be introduced in the activation procedure to obtain a controlled dealumination of the zeolite. This procedure achieves a high thermal and hydrothermal stability of the zeolite, provided that silicon is inserted in the vacancies left by extraction of A1 from the framework (1). The commercial catalysts so obtained have framework Si/Al ratios in the... 

Rare Earths and Alumina. A much easier and cheaper way of getting the SO2 removal enhancement from rare earths that was observed with the well-exchanged rare earth Y zeolite was to add rare earths, especially cerium, by direct impregnation to high alumina cracking catalyst (24). 

Faced with the need of obtaining more transportation fuels from a barrel of crude, Ashland developed the Reduced Crude Conversion Process (RCC ). To support this development, a residuum or reduced crude cracking catalyst was developed and over 1,000 tons were produced and employed in commercial operation. The catalyst possessed a large pore volume, dual pore structure, an Ultrastable Y zeolite with an acidic matrix equal in acidity to the acidity of the zeolite, and was partially treated with rare earth to enhance cracking activity and to resist vanadium poisoning. 

Chemical prqperties are also used in the largest field of application for the rare earth elements as catalysts. Most important are the cracking catalysts for the petroleum industry. The rare earth elements are combined into molecular sieves (Y-Zeolite) and serve in fluid bed or fixed bed reactors to increase the yield of gasoline. In addition thereto, there are the combustion catalysts for automobiles and for air pollution control. 

What about the future Like many other industries, catalyst manufacturers are dependent on refinery requirements and crude oil availability. Although crude oil supplies may become limited and catalyst usage reduced, rare earth usage in cracking catalyst may be unaffected. This is because crudes that are likely to be processed are expected to be more difficult to crack requiring higher stability and activity and thus more rare earth exchanged zeolite pef unit of catalyst. 

Simultaneously scientists at Esso Research and Engineering and Mobil Oil were working with X based catalysts [33-35]. Mobil Oil introduced the first zeolite based catalysts for cracking gas oils in 1962 using rare earth exchanged X in a silica-alumina matrix. This replaced the older silica-alumina catalysts. When we made Y available, the Y based catalysts largely replaced the X based catalysts in this application. 

Components of fluidized cracking catalysts (FCC), such as an aluminosilicate gel and a rare-earth (RE) exchanged zeolite Y, have been contaminated with vanadyl naphthenate and the V thus deposited passivated with organotin complexes. Luminescence, electron paramagnetic resonance (EPR) and Mossbauer spectroscopy have been used to monitor V-support interactions. Luminescence results have indicated that the naphthenate decomposes during calcination in air with generation of (V 0)+i ions. After steam-aging, V Og and REVO- formation occurred. In the presence of Sn, Tormation Of vanadium-tin oxide species enhance the zeolite stability in the presence of V-contaminants. 

According to this concept, Masuda et al. [75] studied the catalytic cracking of the oil coming from a previous thermal pyrolysis step of polyethylene at 450°C in the bench-scale fixed-bed reactor shown in Figure 3.11. The catalysts employed were different zeolite types REY (rare earth exchanged zeolite Y), Ni-REY (nickel and rare earth... 

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