In Situ Construction of Manganese Oxide Photothermocatalysts for the Deep Removal of Toluene by Highly Utilizing Sunlight Energy

Unveiling mechanistic insight into boosting oxygen species activation over CeO2/Mn2O3 p-n heterojunction for efficient photothermal mineralization of toluene

The activation mechanism of oxygen species activation (including lattice oxygen and gaseous oxygen) in the photothermal catalytic reaction process is important for boosting the efficient removal of VOCs. Herein, we have successfully synthesized a p-n heterojunction photothermal catalyst CeO2/Mn2O3 for exploring the activation of molecular oxygen and lattice oxygen in toluene catalytic reaction under full spectrum conditions. Various characterization tests and theoretical calculations showed that the formed composite has enhanced light absorption ability, oxygen species migration and transformation ability as well as nice redox cycles, which is conducive to the fast replenishment of surface lattice oxygen and continuous capture and activation of molecular oxygen. Meanwhile, the results of in-situ DRIFTS tests not only confirmed the enhanced activation process of surface lattice oxygen and molecular oxygen under the synergistic effect of light and heat, but also revealed the pathway and mechanism of photothermal catalytic toluene over CeO2/Mn2O3.

Unveiling the critical role of surface adsorbed oxygen species for efficiently photothermocatalytic oxidation of VOCs: Replenishing the active surface lattice oxygen sites

Surface oxygen species play a crucial role in the photothermocatalytic oxidation of volatile organic compounds (VOCs), but their exact functions and evolutionary processes remain unclear. Herein, a series of spinel CoxMn3-xO4 catalysts are synthesized and employed for photothermocatalytic oxidation of toluene. Co1.5Mn1.5O4 catalysts achieve 91.6 % toluene degradation and 81.2 % CO2 yield in a continuous flow reaction under 400 mW/cm2 light intensity, as well as remarked stability and water resistance. During the reaction, surface lattice oxygen on CoxMn3-xO4 serves as the active sites, directly participating in the oxidation of VOCs. The replenishment pathway of surface lattice oxygen is investigated through a series of designed in situ experiments, revealing O2 molecules adsorbed on the catalyst surface to be O2- species, which are then activated to O- species via increase in temperature. The active O- species effectively replenish the consumed surface lattice oxygen species, facilitating subsequent oxidation reactions. This study provides valuable insight into the replenishment mechanism of surface lattice oxygen during oxidation of VOCs.

Photothermal Catalytic Degradation of VOCs: Mode, System and Application

Human production and living processes emit excessive VOCs into the atmosphere, posing significant threats to both human health and the environment. The photothermal catalytic oxidation process is an organic combination of photocatalysis and thermocatalysis. Utilizing photothermal catalytic degradation of VOCs can achieve better catalytic activity at lower temperatures, resulting in more rapid and thorough degradation of these compounds. Photothermal catalysis has been increasingly applied in the treatment of atmospheric VOCs due to its many advantages. A brief introduction on the three modes of photothermal catalysis is presented. Depending on the main driving force of the reactions, they can be categorized into thermal-assisted photocatalysis (TAPC), photo-assisted thermal catalysis (PATC) and photo-driven thermal catalysis (PDTC). The commonly used catalyst design methods and reactor types for photothermal catalysis are also briefly introduced. This paper then focuses on recent developments in specific applications for photothermal catalytic oxidation of different types of VOCs and their corresponding principles. Finally, the problems and challenges facing VOC degradation through this method are summarized, along with prospects for future research.

Insights into the roles of superficial lattice oxygen in formaldehyde oxidation on birnessite

K+-modified birnessite materials were constructed to remove formaldehyde (HCHO) in this work. The introduction of K+ led to weakening of the Mn-O bonds and enhanced the migration of superficial lattice oxygen, resulting in improved redox properties and catalytic activity. MnO2-3K with the largest specific surface area and greatest abundance of superficial lattice oxygen showed the best catalytic performance at 30-130 °C. The operando analyses reveal that HCHO is primarily activated to dioxymethylene (DOM) and subsequently converted to formate species (*COOH). The accumulation of formate species caused a decline in catalytic performance during extended testing at 30 °C, a challenge that could be mitigated by raising the temperature. Theoretical studies disclose that the *COOH → *H2CO3 step with the largest energy barrier is the rate limiting step for HCHO deep decomposition. Molecular oxygen could be activated at oxygen vacancies to replenish the depleted lattice oxygen after decomposition of carbonate species (*H2CO3) and CO2 and H2O desorption. The adsorbed oxygen and water did not limit the deep oxidation of HCHO. This research presents a promising approach for designing highly efficient, non-noble metal catalysts for formaldehyde degradation.

Efficient Photothermal Catalytic Oxidation Enabled by Three-Dimensional Nanochannel Substrates

Photothermal catalysis exhibits promising prospects to overcome the shortcomings of high-energy consumption of traditional thermal catalysis and the low efficiency of photocatalysis. However, there is still a challenge to develop catalysts with outstanding light absorption capability and photothermal conversion efficiency for the degradation of atmospheric pollutants. Herein, we introduced the Co3O4 layer and Pt nanoclusters into the three-dimensional (3D) porous membrane through the atomic layer deposition (ALD) technique, leading to a Pt/Co3O4/AAO monolithic catalyst. The 3D ordered nanochannel structure can significantly enhance the solar absorption capacity through the light-trapping effect. Therefore, the embedded Pt/Co3O4 catalyst can be rapidly heated and the O2 adsorbed on the Pt clusters can be activated to generate sufficient O2- species, exhibiting outstanding activity for the diverse VOCs (toluene, acetone, and formaldehyde) degradation. Optical characterization and simulation calculation confirmed that Pt/Co3O4/AAO exhibited state-of-the-art light absorption and a notable localized surface plasmon resonance (LSPR) effect. In situ diffuse reflectance infrared Fourier transform spectrometry (in situ DRIFTS) studies demonstrated that light irradiation can accelerate the conversion of intermediates during toluene and acetone oxidation, thereby inhibiting byproduct accumulation. Our finding extends the application of AAO's optical properties in photothermal catalytic degradation of air pollutants.

Monolithic Catalyst of Ni Foam-Supported MnOx for Boosting Magnetocaloric Oxidation of Toluene

Catalytic oxidation has been considered an effective technique for volatile organic compound degradation. Development of metal foam-based monolithic catalysts coupling electromagnetic induction heating (EMIH) with efficiency and low energy is critical yet challenging in industrial applications. Herein, a Mn18.2-NF monolithic catalyst prepared by electrodeposition exhibited superior toluene catalytic activity under EMIH conditions, and the temperature of 90% toluene conversion decreased by 89 °C compared to that in resistance furnace heating. Relevant characterizations proved that the skin effect induced by EMIH encouraged activation of gaseous oxygen, leading to superior low-temperature redox properties of Mn18.2-NF under the EMIH condition. In situ Fourier transform infrared spectroscopy results showed that skin effect-induced activation of oxidizing species further accelerated the conversion of intermediates. As a result, the Mn18.2-NF monolithic catalyst under EMIH demonstrated remarkable performance for the toluene oxidation, surpassing the conventional nonprecious metal catalyst and other reported monolithic catalysts.

Efficient Solar-Driven CO2 Methanation and Hydrogen Storage Over Nickel Catalyst Derived from Metal-Organic Frameworks with Rich Oxygen Vacancies

Solar-driven photothermal conversion of carbon dioxide (CO2 ) to methane (CH4 ) is a promising approach to remedy energy shortage and climate changes, where highly efficient photothermal catalysts for CO2 methanation urgently need to be designed. Herein, nickel-based catalysts (Ni/ZrO2 ) derived from metal-organic frameworks (MOFs) are fabricated and studied for photothermal CO2 methanation. The optimized catalyst 50Ni/ZrO2 achieves a stable CH4 production rate of 583.3 mmol g-1  h-1 in a continuous stability test, which is almost tenfold higher than that of 50Ni/C-ZrO2 synthesized via commercial ZrO2 . Physicochemical properties indicate that 50Ni/ZrO2 generates more tetragonal ZrO2 and possesses more oxygen vacancies (OVs) as well as enhanced nickel-ZrO2 interaction. As a result, 50Ni/ZrO2 exhibits the strong abilities of light absorption and light-to-heat conversion, superior adsorption capacities of reactants (H2 , CO2 ), and an intermediate product (CO), which finally boosts CH4 formation. This work provides an efficient strategy to design a photothermocatalyst of CO2 methanation through utilizing MOFs-derived support.