Metal content and temperature effects on the photocatalytic isotopic exchange cyclopentane-deuterium over Pt or NiTiO2 catalysts in the “normal” or “strong metal-support” “interaction” state
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AbstractA cyclopentane-deuterium isotopic exchange (CDIE) was carried out in gas phase, in the temperature range 228–273 K, using a static reactor with a fixed-bed layer of illuminated (300–410 nm) catalyst. Over PtTiO2, an optimal temperature of about 260 K was found; at lower temperatures CDIE was limited by the hydrogen desorption from the metal crystallites; above 260 K the rate became dependent on the cyclopentane adsorption on TiO2. At 260 K, an optimal content of about 0.5 wt% Pt, corresponding to ca. 1 Pt particle (homodispersed; ~2 nm diam, regardless of the content) per TiO2 grain, was found for catalysts pretreated at 473 K in D2 and containing 0.1 to 10 wt% Pt; beyond 0.5 wt% Pt, the detrimental recombination of the photoproduced charges at the Pt particles became apparent. PtTiO2 samples pretreated at 773 K in D2 showed the inhibition of CDIE by the so-called “strong metal-support interaction” (SMSI) effect as expected since reversible hydrogen chemisorption is required. Finally, CDIE also took place over NiTiO2 samples where the metal was deposited as much larger particles (~15–18 nm diam); however, its rate was markedly reduced most likely because of the poorer interaction between the two catalyst components. These results are interpreted in terms of electronic exchanges and hydrogen spillover and substantiate the mechanism we proposed previously.

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