Catalytic oxidation of CO on metals involving an ionic process in the presence of H₂O: the role of promoting materials

Abstract

A new catalytic oxidation of CO involving an ionic process in the presence of H 2 O is proposed on a Ptcatalyst with specific promoting materials (co-catalysts). Oxidation of CO is very slow at room temperature on ordinary Pt-catalysts such as Pt/SiO 2 , Pt/Al 2 O 3 , Pt/TiO 2 , Pt/Graphite, and Pt/carbon nano-tube (CNT), and H 2 or H 2 O have no effect on the reaction. However, in the presence of specific co-catalysts, the oxidation of CO is markedly enhanced by H 2 or H 2 O, so that highly selective preferential oxidation (PROX) of CO in H 2 is attained. The role that co-catalysts play in the oxidation of The highly selective oxidation of CO in H 2 on the Pt/CNT and Pt/CNF catalysts strongly suggests efficient transport of ionic intermediates from Ni-MgO or FeO x to Pt over the hydrophobic CNT and CNF surface according to the local potential gradient. According to this mechanism, selectivity in the preferential oxidation of CO in H 2 is defined by the turnover number of a H 2 O molecule forming CO 2 during its residence time on the catalyst, which is essentially different from the selectivity based on competitive adsorption and/or reaction. The role of the H 2 O molecule is as a kind of messenger molecule or a molecular catalyst to promote the reaction on the surface expressed by the equation n(CO + 1/2O 2 ) + H 2 O / nCO 2 + H 2 O. In this mechanism, the selectivity is given by n/(n + 1). Curious phenomena previously observed in the PROX reaction of CO in H 2 on various catalysts are well explained by the mechanism including an ionic process proposed in this paper.

Ultralow Doping of Mn Species into Pt Catalyst Enhances the CO Oxidation Performance in the Presence of H2O and SO2

“…92 Reaction temperature is a key factor affecting the water-mediated reaction. 93 As shown in Figure 11a,c O. Hence, it could be speculated that 18 O exchange could also occur between the adsorbed *CO 2 and *OH.…”

“…Hence, the concentrations of C 16 O 18 O and C 18 O 18 O were calculated based on that of C 16 O 16 O and the carbon balance, where the concentrations of C 16 O 18 O and C 18 O 18 O are linear to their signals . Reaction temperature is a key factor affecting the water-mediated reaction . As shown in Figure a,c, when H 2 18 O was introduced into the simulated flue gas at 140 °C, only one 16 O in CO 2 was replaced by the 18 O of H 2 18 O, and a clear signal of C 16 O 18 O was observed.…”

Highly Efficient Removal of CO in Effluent Streams from Real‐Life Propane Oxidation Process over CuO−CeO2−Based Catalysts

“…In contrast, the CO removal rate greatly increased upon the introduction of water over a Pt/FeO x reference catalyst (Figure B), which may be the result of an alternative more favorable lower temperature reaction pathway. Tanaka and co‐workers has found that the dual functionality of catalyst is indispensable for the oxidation of CO on Pt promoted by H 2 O. Accordingly, for Pt/FeO x bi‐functional catalyst, OH − ion formed on the active sites of FeO x surface was easily transported to Pt, on which the CO oxidation barrier could be significantly reduced via the direct reaction of CO (a)+OH − →HCOO − (a), followed by the decomposition of the HCOO − to form CO 2 +H 2 O.…”

Promotional Effect of H2 Pretreatment on the CO PROX Performance of Pt1/Co3O4: A First-Principles-Based Microkinetic Analysis

“…Pt single-atom catalysts (SACs), such as Pt 1 /FeO x , , Pt 1 /CeO 2 , − Pt 1 /Cu x O, Pt 1 /CoO x , Pt 1 / Cr 1.3 Fe 0.7 O 3 , and [Pt 1 – O x −]/SiO 2 (Al 2 O 3 ), have received considerable attention as CO PROX catalyst due to their unique maximal utilization of active sites. − The CO PROX on SAC generally proceeds Mars-van Krevelen (MvK), Eley–Rideal (ER), Langmuir-Hinshelhood (LH), COOH formation, , or OH involving mechanisms, , some of which may work in synergy under reaction conditions. , For instance, Wang et al introduces active surface H atoms that promote CO oxidation on Pt 1 /CeO 2 by activating lattice oxygen via high-temperature steam treatment, which can be considered as the collaborative effect of MvK and OH involving mechanisms. In particular, hydroxyl groups can be formed via H-assisted dissociation , and the formation of surface H 2 O species suppress H 2 oxidation by blocking H ads oxidation sites .…”