Low Temperature PROX Reaction of CO Catalyzed by Dual Functional Catalysis of the Pt Supported on CNT, CNF, Graphite, and Amorphous-C with Ni−MgO, Fe, and Fe-Al₂O₃: Oxidation of CO via HCOO Intermediate

Preferential oxidation (PROX) reaction of CO in H 2 proceeded rapidly on Pt supported on carbon nanotube (CNT) at room temperature, whereas the oxidation of CO was very slow in the absence of H 2 . On the other hand, no low temperature PROX reaction proceeded on Pt supported on the CNT purified Ni−MgO (CNT -p ). Similarly, Pt supported on carbon nanofiber (Pt/CNF) was extremely active for the PROX reaction of CO at room temperature, but the activity of Pt supported on purified CNF (CNF -p ) was very low. Pt particles are on the wall of CNT and CNF, whereas Ni−MgO and Fe are at the end of CNT and CNF. When Ni−MgO or Fe−Al 2 O 3 was doped to inactive Pt/CNT -p, Pt/CNF -p, Pt/graphite, and Pt/amorphous-C (a-C), the activity for the oxidation of CO in H 2 was markedly improved but no effect on the oxidation of CO in the absence of H 2 . The kinetic feature of the oxidation of CO on Pt/CNT in the presence of H 2 or H 2 O was very similar to that on the FeOx/Pt/TiO 2, where the oxidation of CO in the presence of H 2 /D 2 had an isotope effect. A dual functional mechanism catalyzing CO(a) + OH − → HCOO − and HCOO + OH → CO 2 + H 2 O was proposed, and the contribution of OH − anion was deduced by an experiment neutralizing OH − anion on the Pt/CNT with H + diffused from the anode of polymer electrolyte hydrogen fuel cell (PEFC). The proposed mechanism is entirely different from the H-assisted dissociation of O 2 proposed by Alayoglu et al. on a Pt-shell/Ru-core catalyst.