Preferential Oxidation of CO in H₂ on Pure Co₃O_4−x and Pt/Co₃O_4−x

Abstract

Driven by the development of a catalyst made of earth‐abundant elements for on‐board purification of H2 of this energy conversion technology, preferential oxidation (PROX) on pure Co3O4 nanorods and Co3O4 nanorods with supported Pt nanoparticles was explored with the aid of in situ studies. This catalyst remains its 100 % conversion of CO in H2 at a gas hourly space velocity of 42 857 mL h−1 g−1 at 120 °C for at least 96 h. In situ studies showed that the active surface phase during PROX is nonstoichiometric Co3O4−x. A correlation between density of surface oxygen vacancies and conversion of CO to CO2 suggest that oxygen vacancy is a necessary component of a catalytic site for PROX on Co3O4−x. Compared to pure Co3O4 nanorods, anchoring Pt nanoparticles on Co3O4 nanorods unfortunately increases selectivity for oxidation of H2 owing to the low dissociation barrier of molecular H2 on Pt. Co3O4−x exhibits much higher selectivity for CO oxidation in PROX than Pt/Co3O4−x at a temperature lower than 140 °C.

Effect of Hydrazine Pretreatment on the Activity, Stability and Active Sites of Cobalt Species for Preferential Oxidation (PROX) of CO in H2-Rich Stream

“…These XPS data ( Figure 4B) suggest that a transformation from Co 2+ to Co 3+ species has occurred, which supports the XRD data (Figure 1f). These findings are supported by the data recorded by Nguyen et al [10], who noted the presence of a Co3O4 spinel structure during PROX. This structural change was also suggested elsewhere under CO oxidation [18].…”

“…The O 1s spectra of CoO(H) ( Figure 4B) shows one sharp peak at 529.5 eV and two weak shoulder peaks at 531.2 and 533.3 eV. The high binding energy shoulders are assigned to nonstoichiometric oxygen atoms [41,42] and were defined to be oxygen atoms around oxygen vacancies in the surface lattice [10]. The main peak at 529.5 eV is due to the stoichiometric oxygen atoms of the catalyst surface [10].…”

“…The high binding energy shoulders are assigned to nonstoichiometric oxygen atoms [41,42] and were defined to be oxygen atoms around oxygen vacancies in the surface lattice [10]. The main peak at 529.5 eV is due to the stoichiometric oxygen atoms of the catalyst surface [10]. Upon exposure to PROX gases, the two shoulder peaks become more visible and remain the same even at higher temperatures.…”

“…However, some of these catalysts are mainly active at a higher temperature range (150-300 • C) with a lower selectivity to CO 2 and are not cost-effective as compared to a variety of metal oxides. Furthermore, previous studies have shown that platinum group metals (PGMs) decrease the activity of the metal oxide catalysts on CO PROX [5,[10][11][12]. For example, Nguyen et al [10] reported higher selectivity of H 2 oxidation at a low temperature on a Pt surface than on Co 3 O 4 , due to a lower dissociation barrier of H 2 on the Pt surface.…”

“…Furthermore, previous studies have shown that platinum group metals (PGMs) decrease the activity of the metal oxide catalysts on CO PROX [5,[10][11][12]. For example, Nguyen et al [10] reported higher selectivity of H 2 oxidation at a low temperature on a Pt surface than on Co 3 O 4 , due to a lower dissociation barrier of H 2 on the Pt surface. Other researchers have shown that supported Pd species suppress CO PROX activity due to the formation of β-hydrides (which promotes moisture formation and lower CO conversion) [11,13].…”