a typical correlation between framework alumina content and ucs is shown in fig1 note that the y type zeolite used in fcc catalysts typically can have a ucs of 24 65 24 70 angstroms as synthesized it can be reduced down to 24 50 24 60 angstroms in the manufacturing process i e as the zeolite is transformed into ultrastable y zeolite using prior art processes this is called ultstrastabilization usy and is done by controlled hydrothermal calcination of the zeolite to carefully dealuminate it carefully bringing the ucs down in a controlled manner to ca 24 55 angstroms results in a more stable zeolite as it heads off to the harsh uncontrolled hydrothermal environment in the fluid cracking catalyst unit u201c fccu u201d fig1 equilibrium catalysts ecat the circulating inventory in an fccu have a range of ucs 39 s dependent upon the catalyst properties and the severity of the fccu environment about 90 of the world 39 s fccus operate at an ecat ucs of 24 24 24 32a fig1 there are trade offs as ucs decreases while activity is lessened less active alumina sites depending upon the objectives of the fccu selectivity can be improved for example customers who desire maximum gasoline octane and maximum olefins look to equilibrate.