21.  The process of claim  20  wherein said conventional  cracking catalyst is zeolite  Y.  20.  In a process for catalytic cracking of a petroleum  faction under cracking conditions in the presence of a  conventional cracking catalyst and an additive catalyst com› prising ZSM-5, the improvement wherein said additive  catalyst is formed by the process of claim  1.  6.  The process of claim  5  wherein said elevated tempera- ture is 150---200°  C. and said time of reaction is from about  10-25 hours.  5.  The process of claim  1  wherein said elevated tempera› ture is 130-240°  C. and said time for reaction is from about  5-30 hours.  4.  The process of claim  1  wherein the pH of said reaction  mixture is at a range of 10.5 to less than 14.  3.  The process of claim  1  wherein said calcined kaolin  microspheres are agitated during said reacting.  2.  The process of claim  1  wherein the mole ratio of silica  to reactive alumina in said reaction mixture is at least 30.  19.  The process of claim  16  where said calcined kaolin  microspheres contain less than 5 wt  %  metakaolin.  18.  The process of claim  1  wherein said calcined kaolin  microspheres have a BET surface area of less than 200 g/m 2 .  17.  The process of claim  1  wherein said solution of seed  includes zeolite  Y  crystals.  16.  The process of claim  1  wherein said solution of seeds  does not exhibit detectable crystallinity by x-ray diffraction.  15.  The process of claim  1  wherein said calcined kaolin  microspheres have an average particle size of from about 40  to about 100 microns.  14.  The process of claim  1  wherein said calcined kaolin  microspheres have an average particle size of from about 20  to about 150 microns.  13.  The process of claim  1  wherein said calcined kaolin  microspheres comprise silica-rich components and/or  metakaolin which has been leached with an acid to extract  at least a portion of the aluminum oxide content of said  metakaolin.  1. A  process for making ZSM-5 comprising forming an  aqueous reaction mixture containing calcined kaolin  microspheres, a solution of seeds characterized as promoting  growth of zeolite  Y  crystals, and silicate, said reaction 50  mixture having a mole ratio of silica to reactive alumina of  at least 20 and a pH of less than 14, reacting said mixture at  elevated temperature and for a time to form in-situ ZSM-5  crystals on said microspheres, said aqueous reaction mixture  being free of organic templates and free of ZSM-5 seed- 55  crystals.  What is claimed is:  12.  The process of claim  9  wherein said calcined kaolin  microspheres contain less than 5 wt.  %  metakaolin.  11.  The process of claim  9  wherein said calcined kaolin  microspheres contain less than 10 wt.  %  metakaolin.  10.  The process of claim  9  wherein said calcined kaolin  microspheres comprise spinel, mullite, or mixture thereof.  9.  The process of claim  8  wherein said calcined kaolin  microspheres are formed with a silica or silicate binder.  8.  The process of claim  1  wherein said calcined kaolin  microspheres are formed from hydrous kaolin, metakaolin,  kaolin calcined at a temperature of greater than 1400°  F., or  mixtures thereof.  As  can be seen from Table 8, the additive catalyst of the  present invention was substantially more active than the  baseline catalyst and even more active than the incorporated  ~!~Jedcf~a!:~u:~;~/~~~!~ v!h;f :~:t~}i~~e  ~~~~;~r;:~  additive. The addition of ZSM-5 additive to the baseline is  expected to increase activity for gasoline cracking as is  characterized by the reduced gasoline yield of both compo› sitions containing the additive ZSM-5 catalysts. What is  surprising is that the in-situ additive at a 2.5% level (0.625%  ZSM-5) is more active than the incorporated ZSM-5 addi› tive at a 10% level (1.5% ZSM-5) (gasoline 44.8 versus  47.54). Importantly, the propylene yield of the in-situ addi› tive was increased relative to the ZSM-5 incorporated  additive, again even though the in-situ additive was present  in smaller amounts (propylene 7.9 versus 6.8).  $^{1}$2.5% Example 3, 90% FCC catalyst, balance 7.5% inert microsphere.  $^{2}$10% ZSM-5 additive and 90% FCC catalyst.  $^{3}$Incorporated additive contains 15% ZSM-5  $^{4}$Activity is defined as x/(1 - x), where x is the gas oil conversion.  7. The process of claim  1  wherein said reaction mixture  includes an acid to provide said  pH.  wt. % FCC zeolite Y, the stated amount of in-situ ZSM-5,  and the balance inert particles.  US 6,908,603 B2  12  11  $^{2}$10.00%  Percent  $^{1}$2.50%  $^{2}$10.00%  incorporated  Additive  Baseline  Example 3  Example 3  additive 3  Conversion  74.49  75.147  75.358  76.502  76.439  Activity 4  2.92  3.024  3.058  3.256  3.244  Product  Yield, wt%  Hydrogen  0.07  0.071  0.074  0.096  0.101  Methane  0.57  0.563  0.576  0.692  0.707  Ethylene  0.62  2.125  2.048  3.173  3.067  Ethane  0.49  0.595  0.593  0.953  0.953  Propane  1.30  2.779  2.651  6.034  5.934  Propylene  4.68  7.991  7.829  7.491  7.552  nButane  1.11  1.3  1.278  1.989  1.996  iButane  4.94  5.935  6.092  7.115  7.076  1 Butene  1.22  1.206  1.2  0.969  0.969  t2Butene  1.67  1.725  1.731  1.518  1.566  c2Butene  1.27  1.307  1.311  1.128  1.16  iButylene  1.30  1.807  1.753  1.963  1.97  Gasoline  52.26  44.801  45.253  40.047  39.985  LCO  16.27  14.935  15.802  14.939  15.165  Bottoms  9.24  9.917  8.84  8.559  8.397  Coke  2.99  2.94  2.97  3.354  3.403  75.54  3.09  0.06  0.62  0.88  0.53  1.86  6.83  1.19  6.35  1.23  1.88  1.4  1.68  47.54  15.74  8.71  3.5  TABLE  8 