Allotropes Anatase and Brookite

Support Effects from Structural Differences of the T1O2 Allotropes (Anatase and Brookite) 

Curves (a) and (b) in Fig. 5.3 compare the light-off curves for the gold catalysts supported on anatase and brookite after being treated with O2 at 300°C. Interestingly, the catalytic activity of the brookite-supported gold catalyst remained highly active, with the onset for 100% CO conversion occurring around —20°C. In contrast, the onset 

FIGURE 5.1. Left Powder XRD patterns of (a) anatase simulated, (b) anatase as-synthesized, (c) as-synthesized Au-anatase, (d) Au-anatase treated at 300°C in O2, (e) Au-anatase treated at 500°C in O2, and (f) Au simulated. Right Powder XRD patterns of (a) brookite simulated, (b) brookite as-synthesized, (c) as-synthesized Au-brookite, (d) Au-brookite treated at 300°C in O2, (e) Au-brookite treated 500°C in O2, and (f) Au simulated. 

The light-off curves of CO oxidation over Au-anatase and Au-brookite catalysts after treatment at 500°C in O2 are shown in curves (c) and (d), respectively, in Fig. 5.3. Both catalysts were deactivated by this heat treatment however, the Au-brookite remains significantly more active than the Au-anatase. The onset of 100% CO conversion for the Au-brookite occurs at approximately 60°C, while the corresponding onset for the Au-anatase occurs at temperatures as high as 160°C. The corresponding XRD patterns of these two samples are shown in Fig. 5.1 [curves (e)]. A very weak gold XRD peak at 20 44.5° can be seen in the XRD pattern of Au-brookite treated at 500°C in 

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