Calcined rare-earth-exchanged zeolite

In the early 70 s, FCC formulations containing 10-40% CREY (calcined rare-earth exchanged Y zeolites) were widely employed because these catalysts offered improved chemical as well as thermal and hydrothermal stability over FCC compositions containing equivalent amounts of (low sodium) HY crystals (23-25). The... 

In REHY and in calcined rare earths exchanged Y-zeolites (CREY) containing about 7.6% CeA, 4.0% La203, 2.8% Nd203 and 0.9 Pr203 crystals, it is believed that Ce+4 ions, present as an oxycerium complex, undergo a redox reaction with oxyvanadyl cations (VO+2) and form a stable orthovanadate (74) ... 

In a new, environmentally acceptable NCL process developed by Rajappa and collaborates (Deshmukh et al., 1990a,b,c,d Reddy et al., 1993), nitro-methane (10) is condensed with A -methylcarbonimidodithioic ester (11) in the presence of rare-earth-exchanged NaY zeolite to give (12) which then is easily converted to (13). The yields are good, and the catalyst can be recycled after calcination. A plausible mechanism for reaction 6.7 has been proposed (Bhawal et al., 1994). It is expected that this new ecofriendly process will soon be taken up by industry. 

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. 

Materials Used. The NaY zeolite and an ion-exchanged form of it, SK-500, were supplied by Union Carbide Corp., Linde Division, in the form of uncalcined powder. The SK-500 (Lot Number 12506-39) is a rare earth-ammonium exchanged type Y zeolite and had not been activated previously or calcined in its preparation. The calculated unit cell formula was... 

The first generation of zeolite FCC catalyst involved the use of zeolite Y exchanged with trivalent rare earth ions and was activated by calcination according to Eq. 3. 

The zeolite is synthesized in its Na-form, which is a nonactive material, since acidic sites (Broensted acid sites) responsible for the formation of carbocations and hence cracking reactions are not present. Thus, the NaY zeoUte must undergo ion exchange with ammonium (or rare earth ions) to prepare the ammonium/RE form of the zeolite which will generate the acidic form HY upon calcination. 

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