Rare-earth-exchanged catalysts, effect

Alkaline earth and rare earth metal cocation effects are reported in this paper for copper ion-exchanged ZSM-5 zeolites used for the catalytic decomposition of nitric oxide in 02- free, 02- rich, and wet streams. Severe steaming (20% H2O) of Na-ZSM-5 at temperatures above 6(X)°C leads to partial vitreous glass formation and dealumination. Unpromoted Cu-ZSM-5 catalysts suffer drastic loss of NO decomposition activity in wet gas streams at 500°C. Activity is partially recovered in dry gas. Copper migration out of the zeolite channels leading to CuO formation has been identified by STEM DX. In Ce/Cu-ZSM-5 catalysts the wet gas activity is greatly improved. CuO particle formation is less extensive and the dry gas activity is largely recovered upon removal of the water vapor. 

The most widely used conventional chemical methods are pyrolysis [21-25] and catalytic cracking [13, 26-30], The latter yields products with a smaller range of carbon numbers and of a higher quality than products generated by the former method. Several types of solid acid catalysts, which are known to be effective for catalytic cracking (e.g. HZSM-5, HY and rare earth metal-exchanged Y-type (REY) zeolite and silica-alumina (SA)) were evaluated by catalyst screening tests and are listed in Table 6.1. The acidic... 

A rare earth metal-exchanged Y-type (REY) zeolite catalyst was found to be an effective catalyst for the catalytic cracking of heavy oil. The influence of the reaction conditions and the catalytic properties of REY zeolite on the product yield and on gasoline quality have been described above. In this section, a reaction pathway is proposed for the catalytic cracking reaction of heavy oil, and a kinetic model for the cracking reaction is developed [14,33]. 

Mori et al. (1993) studied the liquid reaction of acetaldehyde over various ZSM-5 zeolites. Although cfr-paraldehyde and trans-paraldehyde were the main reaction products, rare-earth (La, Ce,Nd,Y) exchanged H-ZSM-5 or Na-ZSM-5 zeolites exhibited high activities for the formation of trans-paraldehyde while neither cis-paraldehyde nor trans-paraldehyde were formed over alkaline-exchanged zeolite. As for other reactions it is not surprising that the catalytic behaviour depends on the zeolite used. Thus, catalysts prepared from H-ZSM-5 exhibited a higher activity than those prepared from Na-ZSM-5. This particular effect has been explained on the basis of the presence of Bronsted acid sites in the neighbourhood of a Mn+ site in the ZSM-5 zeolite pore. 

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