New insights regarding the calcination as a critical parameter in the synthesis of sol–gel made titania powders

The number of studies regarding sol–gel made titania powders is quite high, and nearly all of them use the calcination as the crystallization process. However, several papers are not providing crucial information regarding the calcination parameters, such as, heat treatment atmosphere, heating rate or heat treatment time. Furthermore, nearly no investigations were done regarding short calcination times and fast heating rates. The present paper points out the missing or under-evaluated aspects in the literature and demonstrates their importance throughout simple experiments. First of all, the influence of the calcination atmosphere and the applied flow rate (in tubular furnaces) was proven by demonstrating the inhomogeneity of the obtained samples. Secondly, the major influence of the chosen calcination time and rate was proven by obtaining fast heat treated titania powders. Their activity varied significantly with the applied calcination time, achieving two activity maxima. Also, the obtained activity trend shows that by varying the calcination time highly active titanias can be obtained (more active than Evonik Aeroxide P25).