Accelerated Dual Activation of Lattice Oxygen and Molecule Oxygen over CoMn₂O₄ Catalysts for VOC Oxidation: Promoting the Role of Oxygen Vacancies

Abstract

The in-depth activation mechanism of oxygen species (including lattice oxygen and gaseous oxygen) for catalytic oxidation reactions has not been elucidated and still remains a question on the experimental level. In this work, the dual activation of lattice oxygen and molecule oxygen for highly efficient volatile organic compound oxidation was observed on spinel catalysts through the construction of oxygen vacancy engineering (urea modification). The active surface lattice oxygen species were generated via weakening the metal−oxygen bond strength, which could be easily activated to participate in the catalytic oxidation of toluene to form CO 2 . Simultaneously, the activation ability of gaseous molecular oxygen was also enhanced to promote the replenishment of lattice oxygen species. Moreover, the formation and consumption rates of intermediates could be significantly accelerated due to the dual activation of oxygen species. Hence, the U400 catalyst (T 90 = 217 °C) exhibited significantly enhanced catalytic performance for toluene oxidation compared with the pristine catalyst (T 90 = 250 °C). This work provided a credible comprehension of the dual activation process of lattice oxygen and molecule oxygen in the heterogeneous catalytic oxidation reaction, which was efficient for developing a pathway to boost the catalytic oxidation activity.

Weakening Mn–O Bond Strength in Mn-Based Perovskite Catalysts to Enhance Propane Catalytic Combustion

“…At present, the bond force constant ( k ) calculated from Hooke’s law (eq ) has been widely used for the evaluation of the metal–oxygen bond ( e.g. , Mn–O) strength, in which ω, c , and μ represent the Raman shift (cm –1 ), light velocity (3.0 × 10 8 m s –1 ), and effective mass, respectively. − ω = 1 2 π c k μ As displayed in Figure b, the Mn–O bond force constants are calculated, which reduce in the order SM > SN 0.05 M 0.95 > SN 0.20 M 0.80 > SN 0.15 M 0.85 > SN 0.10 M 0.90 , demonstrating that the doping of Ni could reduce the Mn–O bond force constants, i.e., weaken the Mn–O strength of catalysts. This will increase the mobility and reactivity of lattice oxygen and enhance the reducibility of catalysts.…”

Efficient activation of the Co/SBA-15 catalyst by high-frequency AC-DBD plasma thermal effects for toluene removal

“…The reason for this can be attributed to the increase in the space velocity, which led to an increase in the temperature of the catalyst zone. An increase in temperature can enhance lattice oxygen activation [47] while, simultaneously, the catalyst provides more active sites to participate in the reaction, thus improving the degradation efficiency of toluene. However, when the space velocity is further increased, although the temperature of the catalyst zone increases, the number of active sites provided by the catalyst is limited.…”

“…The MvK mechanism, widely accepted in transition metal oxides, is generally considered to dominate the reaction pathway in this step [56,57]. According to the different positions on the catalyst, whole lattice oxygen can be divided into surface lattice oxygen and lattice oxygen (O latt ) [47]. Since the reaction occurs on the catalyst surface, surface lattice oxygen directly participates in the reaction, while gaseous oxygen can be replenished through surface oxygen vacancies to compensate for consumed oxygen species [58].…”

The Surface/Interface Modulation of Platinum Group Metal (PGM)-Free Catalysts for VOCs and CO Catalytic Oxidation

“…However, the oxygen molecule exhibits high chemical stability due to its high activation barrier. Oxygen vacancies were widely reported to serve as crucial sites for the adsorption and activation of O 2 molecules by facilitating electron donation, thereby enhancing their activation . Recent studies have shed light on the significance of oxygen vacancies in activation of surface chemisorbed oxygen (O 2 – , O 2 2– , O – ) and surface lattice oxygen (O 2 – ). , Chen et al demonstrated that the oxygen vacancy on CeO 2 -TiO 2 mixed oxide catalyst trigger the O 2 molecule interaction with the Ce 3+ site, which acts as an electron donor center to achieve the Ce 4+ -O 2 – structure .…”