The effects of Na ions on the properties of calcined rare-earths Y (CREY) zeolites

FTIR spectroscopy of pyridine thermal desorption, nitrogen sorption, powder X-ray diffraction (XRD), together with elemental analysis have been used to study the physicochemical properties of a family of rare earth (RE) containing faujasite (REY) crystals having different composition, unit cell dimension, acidity and hydrothermal stability (at 760 degrees C with 100% steam, 1 atm). The calcined REY (CREY) was prepared by ion-exchanging Na ions in NH4Y with a mixture of RE chlorides prepared by acid-leaching bastneasite. At 70 degrees C, a 2M NH4NO3 solution can reduce the GREY Na2O level from 3.3% to 0.41% in only Ih and after an intermediate calcination step at 500 degrees C/h, a second ion-exchange reaction can further reduce the Na2O level to 0.06% without severely affecting crystals properties. De-alumination after the intermediate calcination step, is believed responsible for minor losses of La and for unit cell contraction. The selective removal of framework of Na ions, change the distribution of Bronsted (B) and Lewis (L) acid sites as well as acid site strength. In GREY with 3.3% Na2O, acidity is mainly of the B-type and at 200 degrees C the B/L ratio is 21.1. The B/L ratio monotonically decreases to 4.36 from 21.1 when the %Na2O decreases to 0.06% from 3.30% and the crystals's Si/Al molar ratio increases to 2.83 from 2.38. Acidity, hydrothermal stability and resistance to vanadium deactivation in GREY crystals having Si/Al=2.83 and containing trace amounts of Na, are similar to those observed for silicon-enriched HY with Si/Al in the 5.0-10.0 range. (C) 1999 Elsevier Science B.V. All rights reserved.