N. Takeda et al., EFFECT OF INERT SUPPORTS FOR TITANIUM-DIOXIDE LOADING ON ENHANCEMENT OF PHOTODECOMPOSITION RATE OF GASEOUS PROPIONALDEHYDE, Journal of physical chemistry, 99(24), 1995, pp. 9986-9991
Effects of the use of inert supports for TiO2 loading on photocatalyze
d decomposition of propionaldehyde in the gas phase was investigated f
or mordenite support with various amounts of TiO2 loading and for seve
ral kinds of supports such as other zeolites, alumina, silica, and act
ivated carbon. The adsorption constant and the amount of adsorption of
propionaldehyde were evaluated for TiO2-loaded supports by obtaining
Langmuir adsorption isotherms. By correlating these parameters to the
photodecomposition rates of propionaldehyde, the involvement of the su
pport in the photodecomposition reaction is clarified. The photocataly
tic activity of TiO2 on mordenite having various amounts of TiO2 loadi
ng increases with increase in the amount of loaded TiO2 up to an optim
um value (ca. 50 wt %), beyond which a decreasing tendency of the acti
vity appeared. In the region of ascending activity, plenty of adsorbed
substrate is available and the activity is controlled by the content
of TiO2, while in the region of descending activity, the decrease in t
he amount of adsorbed substrate due to a decrease in the occupancy of
the support by the TiO2 loading is responsible for the activity decrea
se. The photocatalytic activities are greatly influenced by the kind o
f inert supports used and show a volcano type dependence on the adsorp
tion constant of the TiO2-loaded supports. In cases where the adsorpti
on constant is low, the decomposition rate is determined by the amount
of adsorbed substrate, while if the adsorption constant is very high,
plenty of adsorbed substrate is available on the support, but it is n
ot mobile to the loaded TiO2. We conclude that the use of an inert sup
port having a medium adsorption constant is necessary to obtain the hi
ghest activity, where a high amount of adsorbed substrate that can be
supplied to TiO2 particles is available.