Synthesis, characterization, and catalytic performance of high-silica Y zeolites with different crystallite size

High-silica NaY (SiO2/Al2O3 > 6.0) was synthesized without organic template in a novel, cheap, and relatively fast way by using as structure directing agent (SDA) a mixture of water glass, sodium aluminate, and sodium hydrate, which had been aged at low temperature. Liquid 27Al NMR characterization showed that the SDA nuclei aged at low temperature contained more silicon and were more stable than SDA prepared with the conventional method, thus inducing the formation of high-silica NaY during crystallization, as determined by XRD, XRF, and 29Si NMR. Particle size had a great effect on the structural stability of zeolite Y and catalytic cracking ability even at a high SiO2/Al2O3 ratio. In the cracking of vacuum gas oil, REY catalysts, made from high-silica NaY with crystallite size 300–500 nm, not only had higher cracking activity, but also higher gasoline and diesel yield and lower coke yield than a conventionally prepared sample. On the other hand, REY catalysts with crystallite size between 100 and 300 nm had a lower activity.

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► Novel structure directing agent with nuclei large, stable and rich in silicon synthesized.
► Nuclei large, stable and rich in silicon enable a quick growth of high-silica NaY.
► REY made from high-silica NaY with 300–500 nm size has higher cracking activity, makes more gasoline and less coke.
► Gasoline product contains more iso-paraffins and aromatics and less olefins.