It should be noted that during the manufacturing of USY zeolites via steaming process,occurs a partial amorphization of the faujasite framework due to the dealumination process with steam, forming amorphous material rich in EFAL species (extraframework Aluminum) that deposit on USY zeolite crystal surfaces, thus decreasing the relative crystallinity values determined from XRD patterns. Such amorphization process is favored by the temperature, the operational time and the partial pressure of water.

At moderate temperatures, it's reached a stability value in the Si/Al ratios of the obtained USY zeolite due to the increased hydrothermal stability of the remaining faujasite crystals, but if the temperature is too high, the dealumination rate of Y zeolite is too high, can this becoming totally in amorphus material.

What were the operational conditions of temperature, water vapor pressure and time at which you carried out the steaming process?.

I recommend you that you review the work done by the researcher Wolfgang Lutz starting with the review article "Zeolite Y: Synthesis, Modification, and Properties-A Case Revisited". He and his collaborators have deeply studied the effect of operational conditions in the steaming process on the crystalline and surface properties of the USY zeolite obtained.

If you want to get  a highly crystalline USY zeolite, one of the most common ways is to submit  the steaming process product to mild acid leaching treatments in order to remove the amorphous material rich in EFAl species, one of the most used acid agent is EDTA due to its great effectiveness and selectivity , although in theory any acidic agent can work. You should be particularly careful with the treatment conditions (temperature, time and acid agent concentration),since this procedure can also remove aluminum from USY zeolite framework.

I hope I have been able to help you. Greetings.

Hi Amin.

The temperature or/and time of your Steaming is too high.