The role of rare earth elements in zeolites and cracking catalysts

This brief review has the objective of showing the role of the rare earth in the context of Fluid Catalytic Cracking (FCC). REHY and RENaY zeolites, two of the most important components of FCC catalysts, were extensively studied in the past years. Their properties were evaluated in different conditions and the discussions of their main characteristics were revisited. It has been shown that RE elements migrate to smaller cages upon calcination and, once located in these cages, they form bridges with framework oxygen atoms, stabilising the zeolite structure. Some hydrolysis reactions take place over RE cations, generating Bronsted acidity and the higher the ionic radius of the RE atom, the higher the degree of hydrolysis. Besides, a correlation between the ionic radius of the RE atom, the Bronsted acidity of the zeolite and the rate of hydrogen transfer reaction was observed. Also, the use of rare earth elements as a vanadium trap has been analysed. Finally, new applications of rate earth containing zeolites in other fields than FCC catalysis indicate that this subject is still a matter of great interest. (C) 2013 Elsevier B.V. All rights reserved.