Correlation Between Reactivity and Oxidation State of Cobalt Oxide Catalysts for CO Preferential Oxidation

Abstract

Catalytic performance is known to be influenced by several factors, with the catalyst surface oxidation state being the most prominent of all. However, in the great majority of industrial heterogeneous catalytic reactions the oxidation state of the active sites is a subject of intense debate. Preferential oxidation of carbon monoxide in hydrogen-rich mixtures (COPrOx) is an important heterogeneous catalytic reaction involved in the purification of hydrogen. In the search for an economically affordable catalyst for this reaction, cobalt appears as one of the most promising materials. Therefore, it is essential to distinguish if a certain surface state of cobalt exists that favors the reaction more than the others. Here we directly compare the activity of CoO and Co3O4 phases by combining ex situ and operando analytical methods with first-principles modeling. CoO is identified as the most favored cobalt surface oxidation state for the COPrOx process, providing a critical element for the rational design of efficient and durable COPrOx catalysts.

Oxidation of Benzyl Alcohol Using Cobalt Oxide Supported Inside and Outside Hollow Carbon Spheres

“…The Co oxidation state therefore played the key role in the reaction, consistent with known studies [31,48,51] . The results reflect differences in the composition of the catalysts with regards to the quantity of Co, Co 2+ and Co 3+ in the initial catalysts.…”

“…The Co oxidation state therefore played the key role in the reaction, consistent with known studies. [31,48,51] The results reflect differences in the composition of the catalysts with regards to the quantity of Co, Co 2 + and Co 3 + in the initial catalysts. Our studies above confirm the importance of the high oxidation state required for Co to be used as a catalyst in the benzyl alcohol reaction.…”

Effect of manganese promotion on the activity and selectivity of cobalt catalysts for CO preferential oxidation

“…The positive effect of manganese is not well understood, but some authors speculated that MnOx contributes to the stabilization of Co 3+ species at the surface by facilitating oxidation of Co 2+ to Co 3+ [32,40]. This hypothesis presumes that Co 3+ sites of Co3O4 are the active sites for COPrOx which opposes recent findings about the negative role of Co3O4 in the activity [48,49]. This evident contradiction was a driving force to investigate in detail the promotional effect of Mn on Co for COPrOx.…”

“…Data treatment, involving energy alignment, background subtraction using an asymmetric least square fitting routine and normalization to the total area under the curves, was performed by using the recently developed THORONDOR code [60]. The relative concentration of each oxidation state was calculated based on linear combination fit (LCF) analysis using as reference NEXAFS spectra of model Co and Mn oxides obtained from previous experiments [48] or from the literature [61]. LCF was carried out using the ATHENA program [62], for the experimental in situ NEXAFS data at Co and Mn L3-edge, pretreated in THORONDOR.…”

Electronic Structure Evolution of Pd@Co Nanocatalysts Under Oxidation and Reduction Conditions and Preferential CO Oxidation

“…As PC11 transform to Pd@Co/CoO x and Pd@Co/Co 3 O 4 in H 2 and O 2 environment, respectively, we have investigated preferential oxidation of CO in H 2 environment and CO oxidation in O 2 environment (known active structure-Co 3 O 4 ). [13,14] It is to be underscored that the interfaces, such as CoÀ CoO, [32] play critical role in the preferential CO oxidation activity. These reactions were evaluated in CO lean (CO : H 2 /O 2 = 1 : 3) and CO-rich reaction stream (CO : H 2 /O 2 = 3 : 1) at total pressure 0.1 mbar and temperature varied from 300 to 575 K. The purpose of CO + H 2 reaction is mainly to explore the surface clean-up of oxide/hydroxide of cobalt on PC11 (which acts as oxygen source), and which reactant is oxidised under milder conditions.…”