Nickel-based zeolite catalysts

Although nickel is not the most active metal, for reasons of cost and stability, commercial catalysts are based on this metal. These catalysts are in general supported on alumina and contain relatively high metal loadings. There is, however, interest in the development of more thermally stable, sulfur resistant, and possibly even regenerable catalysts in the future. It may be for these reasons that zeolite-based methanation catalysts have recently attracted more interest. 

The performance of several of the nickel and cobalt zeolite catalysts for steam reforming of n-hexane at 400°-500°C has been evaluated by short test runs with the reactor and the procedures described above (Table II). A Girdler reforming catalyst (G56) was tested under the same conditions as a comparative standard. All tests were conducted at a total pressure of 1 atm. Plateaus of sustained reforming activity were established within 1 hour. The cobalt catalysts lost essentially all reforming activity within 3 hours, presumably because of oxidation by steam. The space velocities reported are calculated in terms of theoretical hydrogen production based on the n-hexane injection rate and extent of conversion (Equation 2, Table II). The equation for the steam reforming of n-hexane with complete conversion to carbon dioxide is... 

Other metal oxide catalysts studied for the SCR-NH3 reaction include iron, copper, chromium and manganese oxides supported on various oxides, introduced into zeolite cavities or added to pillared-type clays. Copper catalysts and copper-nickel catalysts, in particular, show some advantages when NO—N02 mixtures are present in the feed and S02 is absent [31b], such as in the case of nitric acid plant tail emissions. The mechanism of NO reduction over copper- and manganese-based catalysts is different from that over vanadia—titania based catalysts. Scheme 1.1 reports the proposed mechanism of SCR-NH3 over Cu-alumina catalysts [31b],... 

Catalyst Preparation. For most of the experiments conducted in this study, nickel or vanadium impregnated non-zeolitic particles were blended with metals-free high activity cracking component. This allowed us to examine the effects of the metals on the non-zeolitic component. The high activity zeolitic particles were prepared by in-situ zeolite synthesis on kaolin-based microspheres... 

Cobalt, copper and nickel metal ions were deposited by two different methods, ionic exchange and impregnation, on an amorphous silica-alumina and a ZSM-5 zeolite. The adsorption properties towards NH3 and NO were determined at 353 and 313 K, respectively, by coupled calorimetric-volumetric measurements. The average acid strength of the catalysts supported on silica-alumina was stronger than that of the parent support, while the zeolite-based catalysts had (with the exception of the nickel sample) weaker acid sites than the parent ZSM-5. The oxide materials used as supports adsorbed NO in very small amounts only, and the presence of metal cations improved the NO adsorption [70]. 

Figure 5.12 Identification of the chemical state of nickel involved from the poisoning of two model catalysts based on (A) zeolite with a high Si/AI ratio and (B) alumina.

Catalyst Composition. Chemical compositions of typical nickel and cobalt zeolites are summarized in Table 1. Based on the total CEC derived from the initial sodium composition, 23 to 37% of the Zeolon and 8.4% of the Linde SK400 exchange sites are occupied by nickel cations. In Zeolon, 55% of the exchange sites are occupied by cobalt cations. A ratio of 1.41 1 for cobalt to nickel on the Zeolon exchange sites resulted where nickel and cobalt were exchanged under comparable conditions. 

Table I shows the results of catalytic activity in the WG5 reaction, expressed as the reaction rate constants, for the series of nickel-free and nickel enriched molybdenum loaded Y-zeolites. The data concerning alumina based Co-Mo industrial catalysts are presented only for comparison reasons.

This process carries out the vapor phase oxychlorination of ethane, in the presence of oxygen or air enriched with oxygen, between 350 and 450°C, and between Oil and 10.10 Pa absolute. It employs a catalyst system based on silver doped by derivatives of manganese, cobalt or nickel, and possibly of rare earths (such as lanthanum), and which is employed in mass form or supported on a Y-type zeolite (offretite). 

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