gas-phase photocatalytic oxidation of volatile organic ... - Doria

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To improve the contact surface, the catalyst loading could be increased. Normally, the
PCO rate increases with increasing photocatalyst amount due to an increase in the surface
area of the porous catalyst available for adsorption and degradation. However, for
immobilized TiO2 there is an optimum thickness of the catalyst film, since not only the
contact surface, but also the internal mass transfer resistance for both organic species and
photogenerated electrons/holes will increase with increasing thickness. This improves the
electron-hole recombination possibility and, as a consequence, the degradation
performance is reduced (Carp at al., 2004).
2.2.2 Photocatalyst deactivation
Photocatalyst deactivation is a crucial issue in practical applications. The analysis of
published material reveals that photocatalyst deactivation is generally found in
continuous-flow photocatalytic reactors with a surface attached catalyst (Sauer and Ollis,
1996). Depending on the character of the organic compounds, either reversible or
irreversible deactivation was evidenced (Piera et al., 2002; Peral and Ollis, 1997). The
catalyst may be deactivated either by formation of surface intermediates with higher
adsorption ability than the target pollutant (reversible deactivation) or by sticky “heavy”
products that are difficult to decompose or desorb (irreversible deactivation).
An extensive review of the reactivation of the photocatalyst has been published by Carp
et al., (2004). They propose the following regeneration schemes:
- thermal regeneration at high temperatures. Lower temperatures result in the conversion
of reaction intermediates to lesser volatile ones, accelerating the formation of
carbonaceous deposits (Piera et al., 2002);
- photocatalytic regeneration using simultaneous UV illumination and exposure to
humidified air. Photocatalytic regeneration may be more practical than thermal
regeneration, particularly in indoor air treatment systems because it can be carried out at