I am preparing Au/Al2O3 catalyst through coprecipitation. I calcined the dried precipitate at 400 degree C for 4 hours, but the XRD of the calcined sample did not showed presence of gamma Alumina. At what temperature should I calcine my sample to obtain gamma Alumina without sintering of Au particles?
Simple examination of the phase diagram for alumina will give the conditions under which gamma-alumina will be produced. For example, take a look at:
Article Control of the γ-alumina to α-alumina phase transformation f...
This thesis is also useful:
'Controlling the Formation and Stability of Alumina Phases'
https://pdfs.semanticscholar.org/d4e1/eeb72ae556ce6ff99b84a68b6fd80366d1a8.pdf
As per our experiments, 650oC is a suitable calcination temperature to get gamma alumina from gibbsite.
In your case, DTA along with XRD will be helpful to specify the suitable calcination temperature.
As mentioned above, 650 C or , for more crystallization, 700 C will be enough for forming gamma phase of alumina. Be careful not to exceed this temperature to avoid the formation of the alpha phase.
You can determine the appropriate calcination temperature by performing DSC and TG analysis of the starting material you use in the precipitation method. Of course, doing this will help you to look at the phase diagram.
Try 600 C for 2 hours. Be careful not to exceed 750 C to avoid alpha phase.
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