Operando Investigation of Toluene Oxidation over 1D Pt@CeO2 Derived from Pt Cluster-Containing MOF

Lattice atom-bridged chemical bond interface facilitates charge transfer for boosted photoelectric response

The construction of chemical bonds at heterojunction interfaces currently presents a promising avenue for enhancing photogenerated carrier interfacial transfer. However, the deliberate modulation of these interfacial chemical bonds remains a significant challenge. In this study, we successfully established a p-n junction composed of atomic-level Pt-doped CeO2 and 2D metalloporphyrins metal-organic framework nanosheets (Pt-CeO2/CuTCPP(Fe)), which enables the realization of photoelectric enhancement by regulating the interfacial Fe-O bond and optimizing the built-in electric field. Atomic-level Pt doping in CeO2 leads to an increased density of oxygen vacancies and lattice mutation, which induces a transition in interfacial Fe-O bonds from adsorbed oxygen (Fe-OA) to lattice oxygen (Fe-OL). This transition changes the interfacial charge flow pathway from Fe-OA-Ce to Fe-OL, effectively reducing the carrier transport distance along the atomic-level charge transport highway. This results in a 2.5-fold enhancement in photoelectric performance compared with the CeO2/CuTCPP(Fe). Furthermore, leveraging the peroxidase-like activity of the p-n junction, we employed this functional heterojunction interface to develop a photoelectrochemical immunoassay for the sensitive detection of prostate-specific antigens.

Regulation of electron density in Pt nanoparticles via bimetallic metal-organic frameworks for enhancing photothermal catalysis of toluene decomposition

Volatile Organic Compounds (VOCs) are omnipresent in the sphere of human industrial, harboring latent adverse consequences for health and the ecological system. The photothermal catalytic oxidation of VOCs is an advanced integrated technology that harnesses the combined effects of light and heat energy to enhance the efficiency of VOCs degradation. Herein, a bimetallic Metal-Organic Framework (MOF) was synthesized with the incorporation of Ce into the UiO-66-NH2(Zr) (i.e., UNH(Zr)), UiO-66-NH2(Zr2Ce) (i.e., UNH(Z2C)), which was achieved with Ce atom substituting for a portion of Zr atom within the Zr-oxo clusters. Pt nanoparticles (NPs) are integrated with MOFs to form composites using the dual-solvent method. Ce-oxo fulfills a bifunctional role: it not only facilitates the enhancement of the ligand-to-metal charge transfer (LMCT), but also establishes interaction with Pt NPs. Ce-oxo mediates an enhancement of electron density on Pt NPs. This phenomenon enhances the adsorption and activation of oxygen, significantly boosting the photocatalytic performance for toluene degradation, as demonstrated by a reduction of 30 ℃ for complete mineralization of toluene as compared to that of Pt@UiO-66-NH2(Zr) (i.e., PUNH(Zr)). This study potentially offers new insights into the relationship between electron transfer effects in bimetallic MOF-based catalysts and their efficient catalytic performance for VOCs degradation.

Constructing Bridge Hydroxyl Groups on the Ru/MOx/HZSM-5 (M = W, Mo) Catalysts to Promote the Hydrolysis Oxidation of Multicomponent VOCs

Chlorinated and oxygenated volatile organic compounds (CVOCs and OVOCs) pose a significant threat to human health. Catalytic oxidation effectively removes these pollutants, but catalyst deactivation is a challenge. Our study focused on the hydrolysis oxidation of chlorobenzene (CB) and ethyl acetate (EA) over Ru/MOx/HZSM-5 (M = W, Mo). It was found that doping MoOx to the catalyst increased the structural hydroxyl amount and balanced surface acidity, thus significantly improving the catalytic stability, with Ru/MoOx/HZSM-5 exhibiting a better activity for CB and EA oxidation (T90% = 438 and 276 °C at space velocity = 20,000 mL g-1 h-1, respectively). Water vapor introduction considerably promoted hydrolysis oxidation and protected the active sites from being poisoned by cumulative chlorine. The synergistic interaction of the Mo-O(H)-Al structure in Ru/MoOx/HZSM-5 with the Si-OH-Al structure promotes the activation of H2O to form bridging hydroxyl groups, which provide a proton-rich environment for hydrolysis oxidation. It was also found that dissociated H2O reacted with adsorbed oxygen species to form highly active *OOH, accelerating the deep oxidation of intermediates. We believe that the present study can provide a unique strategy for the effective elimination of multicomponent VOCs under complex conditions.

A catalytic perspective to nanomaterials reactivity-based toxicity; implications for single- and multiple-component nanomaterials (nanocomposites)

The extended use of a given product normally precedes concerns about it. The reactivity-based nanotoxicity is a major concern that must be tackled from its fundamental understanding to its regulatory management. Moreover, concepts and ideas must seamlessly flow between relevant performers. Functional nanomaterials have been used in many fields; among these, catalysis is probably the earliest more extended application of nanomaterials, these are engineered to afford specific properties, and are typically known as Engineered Nanomaterials (ENMs). Heterogenous catalysis shares its basic features with reactivity-based toxicity. In both cases, we are dealing with phenomena triggered by reactions occurring at the surface of the nanomaterial. Therefore, the extensive knowledge in heterogeneous catalysis is key to understanding reactivity-based nanotoxicology. In this regard, determining surface exposure is fundamental to mechanistically comprehend dose-response, similar to how catalysis shifted from mass-based to surface-centered metrics. Catalysis science made a further refinement iteration: reactions occur at surfaces, though not all surfaces are necessarily reactive, making it crucial to normalize per reactive site. This perspective focuses on two key aspects that link heterogeneous catalysis and reactivity-based nanotoxicity: the reactive sites on the surface of nanomaterials and how different combinations of nanomaterials appear and perform. A comment is also made regarding the somewhat vague term 'multicomponent nanomaterial,' which is contrasted with the well-defined, established, and widely accepted term 'nanocomposite' within the chemical community. Clear and precise terminology and concepts are essential for effective research and regulation.

Tuning the crystallinity of the MnOx catalysts to promote toluene catalytic oxidation

In this paper, the MnOx catalysts with excellent toluene oxidation performance were prepared by a simple precipitation method. The physicochemical properties of the prepared MnOx catalysts were investigated by XRD, BET, H2-TPR, O2-TPD and XPS. The obtained results revealed that the crystallinity of the prepared MnOx catalysts could be effectively regulated by changing the (NH4)2CO3/Mn(NO3)2 molar ratio, and thus affecting the oxygen vacancy concentration of the prepared MnOx catalysts. The prepared MnOx-4 catalyst with the (NH4)2CO3/Mn(NO3)2 molar ratio of 4.0 had the poor crystallinity and small grain size, which effectively promoted the oxygen defects in the MnOx catalyst to be formed. At the same time, the MnOx-4 catalyst had a large specific surface area, the highest low temperature reducibility and the largest number of oxygen vacancies and surface adsorbed oxygen species, which allowed more surface oxygen species to participate in the redox reaction, and promoted the toluene deep oxidation. Therefore, when the (NH4)2CO3/Mn(NO3)2 molar ratio was 4.0, the prepared MnOx-4 catalyst exhibited an excellent toluene catalytic oxidation performance and robust catalytic stability. What's more, the toluene oxidation conversion on the MnOx-4 catalyst reached 99% at 230°C, and the MnOx-4 catalyst showed excellent resistance to water vapour.

Upcycling of Polyethylene Wastes to Valuable Chemicals over Group VIII Metal-decorated WO3 Nanosheets

Catalytic cracking of polyolefin wastes into valuable chemicals at mild conditions using non-noble metal catalysts is highly attractive yet challenging. Herein it is reported that 2D tungsten trioxide (2D WO3) nanosheets, after decorating with group VIII metal promoters (i.e., Fe, Co, or Ni), convert high-density polyethylene (HDPE) into alkylaromatics and olefins at low temperature and ambient pressure without using any solvent or hydrogen: 2D Ni/WO3 with abundant Brønsted acidic sites initiates HDPE cracking at a low temperature of 240 °C; 2D Fe/WO3 with low energy barrier of cyclization achieves a high HDPE conversion to 84.2% liquid hydrocarbons with a selectivity of 30.9% to aromatics at 300 °C. In-situ spectroscopic investigations and supplementary theoretical calculations illustrate that these aromatics are formed through the cyclization of alkene intermediates. These 2D catalysts also display high efficiency in the low-temperature cracking of single-use commercial polyethylene wastes such as packaging bags and bottles. This work has demonstrated the high potential of 2D non-noble metal catalysts in the efficient upcycling of waste polyolefin at mild conditions.

Enhancement of Selective Catalytic Oxidation of Lignin β-O-4 Bond via Orbital Modulation and Surface Lattice Reconstruction

The orbital modulation and surface lattice reconstruction represent an effective strategy to regulate the interaction between catalyst interface sites and intermediates, thereby enhancing catalytic activity and selectivity. In this study, the crystal surface of Au-K/CeO2 catalyst can undergo reversible transformation by tuning the coordination environment of Ce, which enables the activation of the Cβ-H bond and the oxidative cleavage of the Cβ-O and Cα-Cβ bonds, leading to the cleavage of 2-phenoxy-1-phenylethanol. The t2g orbitals of Au 5d hybridize with the 2p orbitals of lattice oxygen in CeO2 via π-coordination, modulating the coordination environment of Ce 4 f and reconstructing the lattice oxygen in the CeO2 framework, as well as increasing the oxygen vacancies. The interface sites formed by the synergy between Au clusters in the reconstructed Ce-OL1-Au structure and doped K play dual roles. On the one hand, it activates the Cβ-H bond, facilitating the enolization of the pre-oxidized 2-phenoxy-1-phenylethanone. On the other hand, through single-electron transfer involving Ce3+ 4f1 and the adsorption by oxygen vacancies, it enhances the oxidative cleavage of the Cβ-O and Cα-Cβ bonds. This study elucidates the complex mechanistic roles of the structure and properties of Au-K/CeO2 catalyst in the selective catalytic oxidation of lignin β-O-4 bond.

In chemico methodology for engineered nanomaterial categorization according to number, nature and oxidative potential of reactive surface sites

Methanol probe chemisorption quantifies the number of reactive sites at the surface of engineered nanomaterials, enabling normalization per reactive site in reactivity and toxicity tests, rather than per mass or physical surface area. Subsequent temperature-programmed surface reaction (TPSR) of chemisorbed methanol identifies the reactive nature of surface sites (acidic, basic, redox or combination thereof) and their reactivity. Complementary to the methanol assay, a dithiothreitol (DTT) probe oxidation reaction is used to evaluate the oxidation capacity. These acellular approaches to quantify the number, nature, and reactivity of surface sites constitute a new approach methodology (NAM) for site-specific classification of nanomaterials. As a proof of concept, CuO, CeO2, ZnO, Fe3O4, CuFe2O4, Co3O4 and two TiO2 nanomaterials were probed. A harmonized reactive descriptor for ENMs was obtained: the DTT oxidation rate per reactive surface site, or oxidative turnover frequency (OxTOF). CuO and CuFe2O4 ENMs exhibit the largest reactive site surface density and possess the highest oxidizing ability in the series, as estimated by the DTT probe reaction, followed by CeO2 NM-211 and then titania nanomaterials (DT-51 and NM-101) and Fe3O4. DTT depletion for ZnO NM-110 was associated with dissolved zinc ions rather than the ZnO particles; however, the basic characteristics of the ZnO NM-110 particles were evidenced by methanol TPSR. These acellular assays allow ranking the eight nanomaterials into three categories with statistically different oxidative potentials: CuO, CuFe2O4 and Co3O4 are the most reactive; ceria exhibits a moderate reactivity; and iron oxide and the titanias possess a low oxidative potential.

4d-2p-4f Gradient Orbital Coupling Enables Tandem Catalysis for Simultaneous Abatement of N2O and CO on Atomically Dispersed Rh/CeO2 Catalyst

N2O and CO coexist in various industrial and mobile sources. The synergistic reaction of N2O and CO to generate N2 and CO2 has garnered significant research interest, but it remains extremely challenging. Herein, we constructed an atomically dispersed Rh-supported CeO2 catalyst with asymmetric Rh-O-Ce sites through gradient Rh 4d-O 2p-Ce 4f orbital coupling. This design effectively regulates the 4f electron states of Ce and promotes the electron filling of the O 3π* antibonding orbital to facilitate N-O bond cleavage. Near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) reveals that CO reacts with the surface-adsorbed O* generated by N2O decomposition through self-tandem catalysis, accelerating the rate-limiting step in N2O decomposition and activating the synergistic reaction of N2O and CO at temperatures as low as 115 °C. This work can guide the development of high-performance catalysts using the strategy of high-order orbital hybridization combined with the tandem concept to achieve versatile catalytic applications.

Accelerating Toluene Oxidation over Boron-Titanium-Oxygen Interface: Steric Hindrance of the Methyl Group Induced by the Plane-Adsorption Configuration

Elimination of dilute gaseous toluene is one of the critical concerns within the field of indoor air remediation. The typical degradation route on titanium-based catalysts, "toluene-benzaldehyde-carbon dioxide", necessitates the oxidation of the methyl group as a prerequisite for photocatalytic toluene oxidation. However, the inherent planar adsorption configuration of toluene molecules, dominated by the benzene rings, leads to significant steric hindrance for the methyl group. This steric hindrance prevents the methyl group from contacting the active species on the catalyst surface, thereby limiting the removal of toluene under indoor conditions. To date, no effective strategy to control the steric hindrance of the methyl group has been identified. Herein, we showed a B-Ti-O interface that exhibits significantly enhanced toluene removal efficiency under indoor conditions. In-depth investigations revealed that, compared to typical Ti-based photocatalysts, the steric hindrance between the methyl group and the catalyst surface decreased from 3.42 to 3.03 Å on the designed interface. This reduction originates from the matching of orbital energy levels between Ti 3dz2 and C 2pz of the benzene ring. The decreased steric hindrance improved the efficiency of toluene being attacked by surface active species, allowing for rapid conversion into benzaldehyde and benzoic acid species for subsequent reactions. Our work provides novel insights into the steric hindrance effect in the elimination of aromatic volatile organic compounds.

In Situ Symbiosis of Cerium Oxide Nanophase for Enhancing the Oxygen Electrocatalysis Performance of Single-Atom Fe─N─C Catalyst with Prolonged Stability for Zinc-Air Batteries

The Fenton reaction, induced by the H2O2 formed during the oxygen reduction reaction (ORR) process leads to significant dissolution of Fe, resulting in unsatisfactory stability of the iron-nitrogen-doped carbon catalysts (Fe-NC). In this study, a strategy is proposed to improve the ORR catalytic activity while eliminating the effect of H2O2 by introducing CeO2 nanoparticles. Transmission electron microscopy and subsequent characterizations reveal that CeO2 nanoparticles are uniformly distributed on the carbon substrate, with atomically dispersed Fe single-atom catalysts (SACs) adjacent to them. CeO2@Fe-NC achieves a half-wave potential of 0.89 V and a limiting current density of 6.2 mA cm-2, which significantly outperforms Fe-NC and commercial Pt/C. CeO2@Fe-NC also shows a half-wave potential loss of only 1% after 10 000 CV cycles, which is better than that of Fe-NC (7%). Further, H2O2 elimination experiments show that the introduction of CeO2 significantly accelerate the decomposition of H2O2. In situ Raman spectroscopy results suggest that CeO2@Fe-NC significantly facilitates the formation of ORR intermediates compared with Fe-NC. The Zn-air batteries utilizing CeO2@Fe-NC cathodes exhibit satisfactory peak power density and open-circuit voltage. Furthermore, theoretical calculations show that the introduction of CeO2 enhances the ORR activity of Fe-NC SAC. This study provides insights for optimizing SAC-based electrocatalysts with high activity and stability.

Enhancing Oxygen Activation Ability by Composite Interface Construction over a 2D Co3O4-Based Monolithic Catalyst for Toluene Oxidation

Developing robust metal-based monolithic catalysts with efficient oxygen activation capacity is crucial for thermal catalytic treatment of volatile organic compound (VOC) pollution. Two-dimensional (2D) metal oxides are alternative thermal catalysts, but their traditional loading strategies on carriers still face challenges in practical applications. Herein, we propose a novel in situ molten salt-loading strategy that synchronously enables the construction of 2D Co3O4 and its growth on Fe foam for the first time to yield a unique monolithic catalyst named Co3O4/Fe-S. Compared to the Co3O4 nanocube-loaded Fe foam, Co3O4/Fe-S exhibits a significantly improved catalytic performance with a temperature reduction of 44 °C at 90% toluene conversion. Aberration-corrected scanning transmission electron microscopy and theoretical calculation suggest that Co3O4/Fe-S possesses abundant 2D Co3O4/Fe3O4 composite interfaces, which promote the construction of active sites (oxygen vacancy and Co3+) to boost oxygen activation and toluene chemisorption, thereby accelerating the transformation of reaction intermediates through Langmuir-Hinshelwood (L-H) and Mars-van Krevelen (MvK) mechanisms. Moreover, the growth mechanism reveals that 2D Co3O4/Fe3O4 composite interfaces are generated in situ in molten salt, inducing the growth of 2D Co3O4 onto the surface lattice of 2D Fe3O4. This study provides new insights into enhancing oxygen activation and opens an unprecedented avenue in preparing efficient monolithic catalysts for VOC oxidation.

Efficacious destruction of typical aromatic hydrocarbons over CoMn/Ni foam monolithic catalysts with boosted activity and water resistance

Developing cost-effective monolith catalyst with superior low-temperature activity is critical for oxidative efficacious removal of industrial volatile organic compounds (VOCs). However, the complexity of the industrial flue gas conditions demands the need for high moisture tolerance, which is challenging. Herein, CoMn-Metal Organic Framework (CoMn-MOF) was in situ grown on Ni foam (NiF) at room temperature to synthesize the cost-effective monolith catalyst. The optimized catalyst, Co1Mn1/NiF, exhibited excellent performance in toluene oxidation (T90 = 239 °C) due to the substitution of manganese into the cobalt lattice. This substitution weakened the Co-O bond strength, creating more oxygen vacancies and increasing the active oxygen species content. Additionally, experimentally and computationally evidence revealed that the mutual inhibiting effect of three typical aromatic hydrocarbons (benzene, toluene and m-xylene) over the Co1Mn1/NiF catalyst was attributed to the competitive adsorption occurring on the active site. Furthermore, the Co1Mn1/NiF catalyst also presents outstanding water resistance, particularly at a concentration of 3 vol%, where the activity is even enhanced. This was attributed to the lower water adsorption and dissociation energy derived from the interaction between the bimetals. Results demonstrate that the dissociation of water vapor enables more reactive oxygen species to participate in the reaction which reduces the formation of intermediates and facilitates the reaction. This investigation provides new insights into the preparation of oxygen vacancy-rich monolith catalysts with high water resistance for practical applications.

Catalytic Oxidation of Toluene over Pt/CeO2 Catalysts: A Double-Edged Sword Effect of Strong Metal-Support Interaction

Strong metal-support interaction (SMSI), which has drawn widespread attention in heterogeneous catalysis, is thought to significantly affect the catalytic performance for volatile organic chemical (VOC) abatement. In the present study, strong interactions between platinum and ceria are constructed by modulating the oxygen vacancy concentration of CeO2 through a NaBH4 reduction method. For a catalyst with higher content of oxygen vacancy, more electrons would transfer from ceria to Pt, which is attributed to the stronger effect of SMSI. The obtained electron-richer Pt sites exhibit higher ability for toluene activation, contributing to better performance for toluene oxidation. On the other hand, the stronger metal-support interaction would facilitate CeOx species migrating to the Pt nanoparticle surface and forming an encapsulated structure. Smaller Pt dispersion leads to fewer sites for toluene adsorption and activation, which is to the disadvantage of the reaction. Therefore, taking the negative and positive effects together, the Pt/CeO2-0.5 catalyst has the highest catalytic performance for toluene abatement. Our study provides new insights into strong metal-support interaction on toluene oxidation and contributes to designing noble metal catalysts for VOC abatement.

The modification of surface basicity and its role in naphthalene oxidation: The effect of the basic sites introduced by Ce

A series of V-xCe/Ti catalysts was prepared by a step impregnation method with gradual increased Ce amount. Compared to the commercial V-W/Ti catalysts, the V-xCe/Ti catalysts exhibited considerably higher COx selectivity during the oxidation of naphthalene (Nap), and less intermediates or by-products were detected both in gas phase and on the surface of the catalysts. Through a series of characterizations, it was found that abundance of weak basic sites in the form of OH was introduced by Ce, as well as the oxygen vacancies caused by the redox cycle of V4++Ce4+↔V5++Ce3+. The weak basic sites introduced by Ce could greatly enhance the Nap adsorption, and the Nap adsorbed was quickly converted to naphthol on Ce-OH. Furthermore, V existed at a high valence with the interaction of V and Ce, and the oxygen vacancies also increased the Oads and OOH. It improved the redox ability and the regeneration of Ce-OH on V-xCe/Ti catalysts. The intermediates could be further oxidized, and the Ce-OH consumed in the reaction could recover quickly. Therefore, almost 100% Nap conversion and a high COx selectivity was observed in the V-xCe/Ti catalysts system.

Modulating the Electronic Structures of Pt on Pt/TiO2 Catalyst for Boosting Toluene Oxidation

Surface hydroxyl groups commonly exist on the catalyst and present a significant role in the catalytic reaction. Considering the lack of systematical researches on the effect of the surface hydroxyl group on reactant molecule activation, the PtOx/TiO2 and PtOx-y(OH)y/TiO2 catalysts were constructed and studied for a comprehensive understanding of the roles of the surface hydroxyl group in the oxidation of volatiles organic compounds. The PtOx/TiO2 formed by a simple treatment with nitric acid presented greatly enhanced activity for toluene oxidation in which the turnover frequency of toluene oxidation on PtOx/TiO2 was around 14 times as high as that on PtOx-y(OH)y/TiO2. Experimental and theoretical results indicated that adsorption/activation of toluene and reactivity of oxygen atom on the catalyst determined the toluene oxidation on the catalyst. The removal of surface hydroxyl groups on PtOx promoted strong electronic coupling of the Pt 5d orbital in PtOx and C 2p orbital in toluene, facilitating the electron transfers from toluene to PtOx and subsequently the adsorption/activation of toluene. Additionally, the weak Pt-O bond promoted the activation of surface lattice oxygen, accelerating the deep oxidation of activated toluene. This study clarifies the inhibiting effect of surface hydroxyl groups on PtOx in toluene oxidation, providing a further understanding of hydrocarbon oxidation.

Modulating the Electronic States of Pt Nanoparticles on Reducible Metal-Organic Frameworks for Boosting the Oxidation of Volatile Organic Compounds

The adsorption and activation of pollutant molecules and oxygen play a critical role in the oxidation reaction of volatile organic compounds (VOCs). In this study, superior adsorption and activation ability was achieved by modulating the interaction between Pt nanoparticles (NPs) and UiO-66 (U6) through the spatial position effect. Pt@U6 exhibits excellent activity in toluene, acetone, propane, and aldehyde oxidation reactions. Spectroscopic studies, 16O2/18O2 kinetic isotopic experiments, and density functional theory (DFT) results jointly reveal that the encapsulated Pt NPs of Pt@U6 possess higher electron density and d-band center, which is conducive for the adsorption and dissociation of oxygen. The toluene oxidation reaction and DFT results indicate that Pt@U6 is more favorable to activate the C-H of toluene and the C═C of maleic anhydride, while Pt/U6 with lower electron density and d-band center exhibits a higher oxygen dissociation temperature and higher reactant activation energy barriers. This study provides a deep insight into the architecture-performance relation of Pt-based catalysts for the catalytic oxidation of VOCs.

The removal of toluene by thermoscatalytic oxidation using CeO2-based catalysts:a review

Volatile organic compounds (VOCs) pose a serious threat to human health and the ecological environment. Thermal catalytic oxidation based on cerium dioxide based (CeO2-based) catalysts is widely used in the degradation of toluene. However, new problems and challenges such as how to reduce the energy consumption during catalytic oxidation, improve the anti-poisoning performance of catalysts, and enhance the multi-species synergistic catalytic ability of catalysts continue to emerge. On this basis, we systematically summarize the current status of research progress on the thermocatalytic oxidation of toluene based on CeO2-based catalysts. Firstly, we summarized the rules on how to improve the catalytic performance and anti-poisoning performance of CeO2-based catalysts; Secondly, we discussed the effect of light reaction conditions on the thermal coupled catalytic oxidation of toluene; In addition to this, we explored the current status of synergistic multi-pollutant degradation, mainly of toluene; Finally, we summarized the mechanism of catalytic oxidation of toluene by combining theoretical simulation calculations, in-situ infrared analyses, and other means. We present the promising applications of CeO2-based catalysts in the catalytic oxidation of toluene, and hope that these summaries will provide an important reference for the catalytic treatment of VOCs.

Formaldehyde Ambient-Temperature Decomposition over Pd/Mn3O4-MnO Driven by Active Sites' Self-Tandem Catalysis

The widespread presence of formaldehyde (HCHO) pollutant has aroused significant environmental and health concerns. The catalytic oxidation of HCHO into CO2 and H2O at ambient temperature is regarded as one of the most efficacious and environmentally friendly approaches; to achieve this, however, accelerating the intermediate formate species formation and decomposition remains an ongoing obstacle. Herein, a unique tandem catalytic system with outstanding performance in low-temperature HCHO oxidation is proposed on well-structured Pd/Mn3O4-MnO catalysts possessing bifunctional catalytic centers. Notably, the optimized tandem catalyst achieves complete oxidation of 100 ppm of HCHO at just 18 °C, much better than the Pd/Mn3O4 (30%) and Pd/MnO (27%) counterparts as well as other physical tandem catalysts. The operando analyses and physical tandem investigations reveal that HCHO is primarily activated to gaseous HCOOH on the surface of Pd/Mn3O4 and subsequently converted to H2CO3 on the Pd/MnO component for deep decomposition. Theoretical studies disclose that Pd/Mn3O4 exhibits a favorable reaction energy barrier for the HCHO → HCOOH step compared to Pd/MnO; while conversely, the HCOOH → H2CO3 step is more facilely accomplished over Pd/MnO. Furthermore, the nanoscale intimacy between two components enhances the mobility of lattice oxygen, thereby facilitating interfacial reconstruction and promoting interaction between active sites of Pd/Mn3O4 and Pd/MnO in local vicinity, which further benefits sustained HCHO tandem catalytic oxidation. The tandem catalysis demonstrated in this work provides a generalizable platform for the future design of well-defined functional catalysts for oxidation reactions.

Dual function of H2O on interfacial intermediate conversion and surface poisoning regulation in simultaneous photodegradation of NO and toluene

Co-existing air pollutants, especially NOx and VOCs, will generate secondary photochemical pollution under light irradiation. However, simultaneous elimination of multi-pollutants has long been a challenge. Photocatalysis could turn the reaction pathway between pollutants to convert them into harmless products, which is a promising technology for multi-pollutant control. Here we achieved synergistic photocatalytic degradation of NO and C7H8 on InOOH photocatalyst, and the performance can be adjusted by H2O through affecting the interaction between surface species and catalyst. In situ DRIFTS and GC-MS revealed that the improved efficiency originated from the fast conversion of C-N coupling intermediates led by additional H2O. Surface characterizations and DFT simulation determined that accumulated nitrates will compete with the adsorption of NO and C7H8, resulting in a decline in efficiency in the later stage. Although improved efficiency would bring more nitrates, as H2O has comparable adsorption to nitrate at the same site, high humidity can mitigate the deactivation. The photocatalyst can be also simply regenerated by water washing. This work reveals the complex interaction in the multi-pollutant system and provides guidelines for precisely regulating the synergistic removal of NOx and VOCs.

Electronic Interactions on Platinum/(Metal-Oxide)-Based Photocatalysts Boost Selective Photoreduction of CO2 to CH4

By supporting platinum (Pt) and cadmium sulfide (CdS) nanoparticles on indium oxide (In2 O3 ), we fabricated a CdS/Pt/In2 O3 photocatalyst. Selective photoreduction of carbon dioxide (CO2 ) to methane (CH4 ) was achieved on CdS/Pt/In2 O3 with electronic Pt-In2 O3 interactions, with CH4 selectivity reaching to 100 %, which is higher than that on CdS/Pt/In2 O3 without electronic Pt-In2 O3 interactions (71.7 %). Moreover, the enhancement effect of electronic Pt-(metal-oxide) interactions on selective photoreduction of CO2 to CH4 also occurs by using other common metal oxides, such as photocatalyst supports, including titanium oxide, gallium oxide, zinc oxide, and tungsten oxide. The electronic Pt-(metal-oxide) interactions separate photogenerated electron-hole pairs and convert CO2 into CO2 δ- , which can be easily hydrogenated into CH4 via a CO2 δ- →HCOO*→HCO*→CH*→CH4 path, thus boosting selective photoreduction of CO2 to CH4 . This offers a new way to achieve selective photoreduction of CO2 .

Gel transformation as a general strategy for fabrication of highly porous multiscale MOF architectures

The structure and chemistry of metal-organic frameworks or MOFs dictate their properties and functionalities. However, their architecture and form are essential for facilitating the transport of molecules, the flow of electrons, the conduction of heat, the transmission of light, and the propagation of force, which are vital in many applications. This work explores the transformation of inorganic gels into MOFs as a general strategy to construct complex porous MOF architectures at nano, micro, and millimeter length scales. MOFs can be induced to form along three different pathways governed by gel dissolution, MOF nucleation, and crystallization kinetics. Slow gel dissolution, rapid nucleation, and moderate crystal growth result in a pseudomorphic transformation (pathway 1) that preserves the original network structure and pores, while a comparably faster crystallization displays significant localized structural changes but still preserves network interconnectivity (pathway 2). MOF exfoliates from the gel surface during rapid dissolution, thus inducing nucleation in the pore liquid leading to a dense assembly of percolated MOF particles (pathway 3). Thus, the prepared MOF 3D objects and architectures can be fabricated with superb mechanical strength (>98.7 MPa), excellent permeability (>3.4 × 10^-10 m²), and large surface area (1100 m² g^-1) and mesopore volumes (1.1 cm³ g^-1).

Constructing Highly Active Metal Oxides for Toluene Degradation by Fenton Iron Mud Modulation

Fenton iron mud (IM) is a hazardous solid waste produced by Fenton oxidation technology after treating industrial wastewater. Thus, it is necessary and challenging to develop a recycling technology to back-convert dangerous materials into useful products. Herein, we develop a sustainable approach to prepare highly active metal oxides via a solid-state grinding method. IM, as an amorphous material, can disperse and interact well with these supported metal oxides, boosting toluene degradation significantly. Among these IM-based catalysts, the catalyst 8% MnO_x/IM-0.2VC exhibits the best performance (T₁₀₀ = 290 °C), originating from the oxide-support interaction and optimal balance between low-temperature reducibility and oxygen vacancy concentration. In addition, in situ diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) results expound that ring breakage is prone to occur on MnO_x, and oxygen vacancies are beneficial to adsorb oxygen and activate oxygen species to boost toluene oxidation following the Mars-van Krevelen mechanism. This work advances a complete industrial hazardous waste recycling route to develop extremely active catalysts.

Combined effects of Pt nanoparticles and oxygen vacancies to promote photothermal catalytic degradation of toluene

Pt/Mn-TiO₂ photothermal catalysts with abundant oxygen vacancies are prepared by loading Pt onto a composite of MnO_x and TiO₂ using MIL-125 as precursor (abbreviated as Mn-TiO₂) and subsequent hydrogen reduction treatment. Under light irradiation with intensity of 625 mW/cm², the optimal 0.65Pt/Mn-TiO₂ catalyst can achieve toluene conversion of 90.4 % and CO₂ yield of 85.6 %, respectively, and maintain stable activity for at least 30 h in the presence of coke and water. The introduction of Pt nanoparticles improves the utilization of solar spectrum and facilitates the generation of more oxygen vacancies. The comparative experiments of photothermal catalysis and thermal catalysis further verify that light not only acts as a heat source but also enhances catalytic reaction through photocatalysis and photoactivation of lattice oxygen. In the follow-up work, catalytic oxidation under natural sunlight is performed on 0.65Pt/Mn-TiO₂ to reach 75.0 % of toluene conversion, displaying a good practical application potential.

Quenching-Induced Defect-Rich Platinum/Metal Oxide Catalysts Promote Catalytic Oxidation

Enhancing oxygen activation through defect engineering is an effective strategy for boosting catalytic oxidation performance. Herein, we demonstrate that quenching is an effective strategy for preparing defect-rich Pt/metal oxide catalysts with superior catalytic oxidation activity. As a proof of concept, quenching of α-Fe₂O₃ in aqueous Pt(NO₃)₂ solution yielded a catalyst containing Pt single atoms and clusters over defect-rich α-Fe₂O₃ (Pt/Fe₂O₃-Q), which possessed state-of-the-art activity for toluene oxidation. Structural and spectroscopic analyses established that the quenching process created abundant lattice defects and lattice dislocations in the α-Fe₂O₃ support, and stronger electronic interactions between Pt species and Fe₂O₃ promote the generation of higher oxidation Pt species to modulate the adsorption/desorption behavior of reactants. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) characterization studies and density functional theory (DFT) calculations determined that molecular oxygen and Fe₂O₃ lattice oxygen were both activated on the Pt/Fe₂O₃-Q catalyst. Pt/CoMn₂O₄, Pt/MnO₂, and Pt/LaFeO₃ catalysts synthesized by the quenching method also offered superior catalytic activity for toluene oxidation. Results encourage the wider use of quenching for the preparation of highly active oxidation catalysts.

Catalytic removal of toluene using MnO2-based catalysts: A review

Volatile organic compounds (VOCs) have serious hazard to human health and ecological environment. Due to its low cost and high activity, the catalytic oxidation technology considered to be the most effective method to remove VOCs. Toluene is one of the typical VOCs, hence its catalytic elimination is crucial for the regulation of VOCs. Manganese dioxide (MnO₂) has been extensively studied for its excellent redox performance and low-temperature operation conditions. In this review, we summarize the research progresses in the toluene catalytic oxidation of MnO₂-based catalysts, which contain single MnO₂, metal-doped MnO₂ and supported MnO₂ catalyst. In particular, we pay much attention on the relationship between the chemical properties and toluene oxidation performance over MnO₂ catalyst, as well as the catalytic reaction mechanisms. Moreover, the effects of different crystal forms and morphologies on the catalytic toluene reaction were discussed. And the perspective on MnO₂ catalysts for the catalytic oxidation of toluene has been proposed. We expect that the summary of these important findings can serve as an important reference for the catalytic treatment of VOCs.

Simultaneously Constructing Active Sites and Regulating Mn-O Strength of Ru-Substituted Perovskite for Efficient Oxidation and Hydrolysis Oxidation of Chlorobenzene

Chlorinated volatile organic compounds (CVOCs) are a class of hazardous pollutants that severely threaten environmental safety and human health. Although the catalytic oxidation technique for CVOCs elimination is effective, enhancing the catalytic efficiency and simultaneously inhibiting the production of organic byproducts is still of great challenge. Herein, Ru-substituted LaMn(Ru)O_{3+ δ} perovskite with Ru-O-Mn structure and weakened Mn-O bond strength has been developed for catalytic oxidation of chlorobenzene (CB). The formed Ru-O-Mn structure serves as favorable sites for CB adsorption and activation, while the weakening of Mn-O bond strength facilitates the formation of active oxygen species and improves oxygen mobility and catalyst reducibility. Therefore, LaMn(Ru)O_{3+ δ} exhibits superior low-temperature activity with the temperature of 90% CB conversion decreasing by over 90 °C compared with pristine perovskite, and the deep oxidation of chlorinated byproducts produced in low temperature is also accelerated. Furthermore, the introduction of water vapor into reaction system triggers the process of hydrolysis oxidation that promotes CB destruction and inhibits the generation of chlorinated byproducts, due to the higher-activity *OOH species generated from the dissociated H₂ O reacting with adsorbed oxygen. This work can provide a unique, high-efficiency, and facile strategy for CVOCs degradation and environmental improvement.

Thermal-Driven Optimization of the Strong Metal-Support Interaction of a Platinum-Manganese Oxide Octahedral Molecular Sieve to Promote Toluene Oxidation: Effect of the Interface Pt2+-Ov-Mnδ. ACS APPLIED MATERIALS & INTERFACES 2022;14:56790-56800. [PMID: 36524882 DOI: 10.1021/acsami.2c16923] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Strong metal-support interactions (SMSIs) have a significant effect on the performance of supported noble-metal catalysts for volatile organic compound (VOC) elimination. Herein, the strength of the SMSI of Pt/OMS-2 between Pt and the OMS-2 support is regulated by simply changing calcination temperatures, and the catalyst calcined at 300 °C (Pt/OMS-2-300) performs the best in the catalytic combustion of toluene. Through systematic structural characterizations, it is revealed that much more Pt²⁺-O_v-Mn^δ+ species are formed in Pt/OMS-2-300, which can help facilitate the generation of more reactive oxygen species and promote lattice oxygen mobility. Moreover, the results of in situ DRIFTS experiments further confirm that abundant Pt²⁺-O_v-Mn^δ+ species at the Pt-MnO₂ interface on Pt/OMS-2-300 can better enhance the adsorption and activation of toluene, thus boosting the catalytic performance in toluene combustion. This newly developed strategy of thermal-driven regulation of the SMSI provides a novel perspective for constructing highly efficient catalysts for VOC emission control.

In Situ Fabrication of Highly Dispersed Co-Fe-Doped-δ-MnO2 Catalyst by a Facile Redox-Driving MOFs-Derived Method for Low-Temperature Oxidation of Toluene

Cost-efficient and durable manganese-based catalysts are in great demand for the catalytic elimination of volatile organic compounds (VOCs), which are dominated not only by the nanostructures but also by the oxygen vacancies and Mn-O bond in the catalysts. Herein, a series of nanostructured Co-Fe-doped-δ-MnO₂ catalysts (Co-Fe-δ-MnO₂) with high dispersion were in situ fabricated by employing metal-organic-frameworks (MOFs) as reducing agents, dopants, and templates all at the same time. The as-obtained Co-Fe-δ-MnO₂-20% catalyst exhibited robust durability and high catalytic activity (225 °C) for toluene combustion even in the presence of 5 vol % water vapor, which is 50 °C lower than that of pristine δ-MnO₂. Various characterizations revealed that the homogeneously dispersed codoping of Co and Fe ions into δ-MnO₂ promotes the generation of oxygen vacancies and weakens the strength of the Mn-O bond, thus increasing the amount of adsorbed oxygen (O_ads) and improving the mobility of lattice oxygen (O_latt). Meanwhile, due to successfully inheriting the framework structures of MOFs, the obtained catalyst exhibited a high surface area and three-dimensional mesoporous structure, which contributes to diffusion and increases the number of active sites. Moreover, in situ DRIFTS results confirmed that the toluene degradation mechanism on the Co-Fe-δ-MnO₂-20% follows the MVK mechanism and revealed that more O_ads and high-mobility O_latt induced by this novel method contribute to accumulating and mineralizing key intermediates (benzoate) and thus promote toluene oxidation. In conclusion, this work stimulates the opportunities to develop Co-Fe-δ-MnO₂ as a class of nonprecious-metal-based catalysts for controlling VOC emissions.

Chlorine-Coordinated Pd Single Atom Enhanced the Chlorine Resistance for Volatile Organic Compound Degradation: Mechanism Study

The development of catalysts with high chlorine resistance for volatile organic compound (VOC) degradation is of great significance to achieve air purification. Herein, Pd@ZrO₂ catalysts with monodispersed Pd atoms coordinated with Cl were prepared using an in situ grown Zr-based metal-organic framework (MOF) as the sacrifice templates to enhance the chlorine resistance for VOC elimination. The residual Cl species from the Zr-MOF coordinated with Pd, forming Pd₁-Cl species during the pyrolysis. Meanwhile, abundant oxygen vacancies (V_O) were generated, which enhanced the adsorption and activation of gaseous oxygen molecules, accelerating the degradation of VOCs. In addition, the Pd@ZrO₂ catalysts exhibited satisfactory water resistance, long-term stability, and great resistance to CO and dichloromethane (DCM) for VOC elimination. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results elucidated that the generation of Pd₁-Cl species in Pd@ZrO₂ suppressed the absorption of DCM, releasing more active sites for toluene and its intermediate adsorption. Simultaneously, the monodispersed Pd atoms and V_O improved the reactivity of gaseous oxygen molecule adsorption and dissociation, boosting the deep decomposition of toluene and its intermediates. This work may provide a new strategy for rationally designing high-chlorine resistance catalysts for VOC elimination to improve the atmospheric environment.

Symmetry-breaking synthesis of Janus Au/CeO2 nanostructures for visible-light nitrogen photofixation

Precise manipulation of the reactive site spatial distribution in plasmonic metal/semiconductor photocatalysts is crucial to their photocatalytic performance, but the construction of Janus nanostructures through symmetry-breaking synthesis remains a significant challenge. Here we demonstrate a synthetic strategy for the selective growth of a CeO2 semi-shell on Au nanospheres (NSs) to fabricate Janus Au NS/CeO2 nanostructures with the assistance of a SiO2 hard template and autoredox reaction between Ag+ ions and a ceria precursor. The obtained Janus nanostructures possess a spatially separated architecture and exhibit excellent photocatalytic performance toward N2 photofixation under visible-light illumination. In this scenario, N2 molecules are reduced by hot electrons on the CeO2 semi-shell, while hole scavengers are consumed by hot holes on the exposed Au NS surface, greatly promoting the charge carrier separation. Moreover, the exposed Au NS surface in the Janus structures offers an additional opportunity for the fabrication of ternary Janus noble metal/Au NS/CeO2 nanostructures. This work highlights the genuine superiority of the spatially separated nanoarchitectures in the photocatalytic reaction, offering instructive guidance for the design and construction of novel plasmonic photocatalysts.

Synergistic Catalytic Performance of Toluene Degradation Based on Non-Thermal Plasma and Mn/Ce-Based Bimetal-Organic Frameworks

A series of Mn/Ce-based bimetal-organic frameworks, recorded as MCDx (x = 1, 2, 4, 6), were prepared by a solvothermal synthesis method to explore their effects and performance in the synergistic catalysis of toluene under the irradiation of non-thermal plasma. The catalytic properties of different manganese loadings in MCDx for degradation of toluene were investigated. The microphysical structures of the material were analyzed by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The results showed that a MCDx coupling with non-thermal plasma can greatly improve the degradation efficiency, the energy efficiency and the CO2 selectivity, and could also significantly reduce the generation of O3 in the by-products. Among the test samples, MCD6 with Mn:Ce = 6:1 (molar ratio) showed the best catalytic performance and stability, exhibited toluene catalytic efficiency 95.2%, CO2 selectivity 84.2% and energy efficiency 5.99 g/kWh, and reduced O3 emission concentration 81.6%. This research provides a reference for the development and application of synergistic catalysis based on bimetal-organic frameworks and non-thermal plasma in the reduction of industrial volatile organic compounds.

Boosting catalytic stability for VOCs removal by constructing PtCu alloy structure with superior oxygen activation behavior

The elimination of volatile organic compounds (VOCs) emitted from the process of industry production is of great significance to improve the atmospheric environment. Herein the catalytic oxidation of the toluene and iso-hexane mixture, as the typical components from furniture paint industry, and the enhancement in the catalytic stability for toluene oxidation were investigated in detail. The formation rate of active oxygen species was very important for the development of the catalyst with high catalytic stability. Compared with the Pt/M catalyst, the Pt-Cu/M catalyst owned stronger ability of VOCs adsorption and gaseous oxygen activation by introducing additional sites for activating O₂. The Langmuir-Hinshelwood (adsorbed oxygen) and Mars-van Krevelen (lattice oxygen) mechanism existed in toluene oxidation over the present Pt/M and Pt-Cu/M catalysts, respectively. The change in the involved active oxygen species during toluene oxidation was resulted from the Pt-Cu alloy structure. In addition to the adsorption of O₂, a part of active lattice oxygen species can also be replenished by the migration of bulk lattice oxygen over Pt-Cu/M. With a rise in the reaction temperature, weakly adsorbed iso-hexane could be timely reacted with the more active lattice oxygen species to keep the catalytic stability over the Pt/M and Pt-Cu/M catalysts. Generally, we not only prepared a promising material for the catalytic removal of VOCs from the furniture paint industry, but also provided a new strategy for the generation of active oxygen species, making the catalyst exhibit high catalytic oxidation stability.

Substitution of B-site in BaSb2O6 perovskite for surface lattice oxygen activation and boosted photocatalytic toluene mineralization

Perovskite oxides possess significant prospects in environment application because of their compositional versatility and controllable band structure for redox reactions. Nevertheless, low charge separation and limited reactants activation restrict their performance for practical applications. In this work, we reveal that the electronic structure of BaSb₂O₆ can be modulated effectively by substituting B-site cations, leading to broadened light response range and promoted carrier separation. The Ga atoms substitute the Sb atoms to form GaO bonds and enable octahedral distortion, resulting in the electron transfer from Ga atom to O atoms and realizing lattice oxygen activation. The unique electronic localization in the BaSb₂O₆ surface facilitates the adsorption and activation of O₂, H₂O, toluene and reaction intermediates, thus enhancing ROS generation for toluene mineralization. Compared with the performance of pure BaSb₂O₆, the photocatalytic toluene degradation and mineralization of 5 wt% Ga-BaSb₂O₆ are increased by 4.5 times and 4.8 times without obvious deactivation. The reported facile and valid strategy for in situ controlling of B-site in perovskite and their unique effects on the electronic structure would benefit the development of high-performance perovskites for environmental applications.

Low-Temperature Combustion of Toluene over Cu-Doped SmMn2O5 Mullite Catalysts via Creating Highly Active Cu2+-O-Mn4+ Sites

Catalytic combustion of volatile organic compounds (VOCs) at low temperatures is still an urgent issue to be solved. Herein, low-temperature combustion of toluene over Cu-doped SmMn₂O₅ mullite catalysts via creating highly active Cu²⁺-O-Mn⁴⁺ sites has been originally demonstrated. Cu-doped SmMn₂O₅ mullite catalysts exhibited 90% conversion of toluene at 206 °C and displayed robust stability even in the presence of water. It has been demonstrated that Cu doping created Cu²⁺-O-Mn⁴⁺ active composite sites that were more exposed after removing surface Sm species via acid-etching. Benefiting from this, the redox and oxygen activation ability of catalysts was significantly enhanced. The consumption of benzaldehyde and benzoic acid as intermediate species and the CO₂ generation ability were apparently promoted, which were the direct reasons for the enhanced low-temperature combustion of toluene. This work provides novel ideas for the development of high-performance catalysts for low-temperature VOC combustion, which has great industrial application prospects.

Excellent Catalytic Performance of Ce–MOF with Abundant Oxygen Vacancies Supported Noble Metal Pt in the Oxidation of Toluene

Metal organic framework (MOF) is a type of porous organic material. In this work, three catalysts loaded with noble metal Pt were prepared by NaBH4 reduction method with three different morphologies of Ce–MOF as carriers. Their physicochemical properties were characterized by XRD, Raman, FTIR, N2 adsorption, SEM, XPS, and TGA. The catalytic performances of different catalysts were evaluated via toluene oxidation and CO2 selectivity. Rod–shaped Pt/MOF–BTC exhibited best catalytic performance compared to Pt/MOF–808 and Pt/UiO–66, its T50 and T90 were 140 °C and 149 °C, respectively. After deducting the effect of specific surface, Pt/MOF–BTC still had the lowest apparent activation energy (62.8 kJ·mol−1), which is due to the abundant atomic Pt and oxygen vacancy content on its surface. After the reaction, the structure of Pt/MOF–BTC may become amorphous according to XRD results. Furthermore, the presence of amorphous structure had no effect on the catalytic activity of the catalyst. In the stability test of Pt/MOF–BTC to toluene oxidation, both toluene conversion and CO2 selectivity remained at 100%, and remained stable for 11 h. Moreover, Pt/MOF–BTC also had better resistance to high weight hourly space velocity (WHSV) or water resistance. The catalyst maintained high catalytic activity for 3 times reusability. This study provides valuable experience for the future work of MOF in the field of VOC catalytic oxidation.

Modulating the Electronic Metal-Support Interactions in Single-Atom Pt1 -CuO Catalyst for Boosting Acetone Oxidation

The development of highly active single-atom catalysts (SACs) and identifying their intrinsic active sites in oxidizing industrial hazardous hydrocarbons are challenging prospects. Tuning the electronic metal-support interactions (EMSIs) is valid for modulating the catalytic performance of SACs. We propose that the modulation of the EMSIs in a Pt₁ -CuO SAC significantly promotes the activity of the catalyst in acetone oxidation. The EMSIs promote charge redistribution through the unified Pt-O-Cu moieties, which modulates the d-band structure of atomic Pt sites, and strengthens the adsorption and activation of reactants. The positively charged Pt atoms are superior for activating acetone at low temperatures, and the stretched Cu-O bonds facilitate the activation of lattice oxygen atoms to participate in subsequent oxidation. We believe that this work will guide researchers to engineer efficient SACs for application in hydrocarbon oxidation reactions.

NOx Reduction over Smart Catalysts with Self-Created Targeted Antipoisoning Sites

Selective catalytic reduction of NO_x in the presence of alkali (earth) metals and heavy metals is still a challenge due to the easy deactivation of catalysts. Herein, NO_x reduction over smart catalysts with self-created targeted antipoisoning sites is originally demonstrated. The smart catalyst consisted of TiO₂ pillared montmorillonite with abundant cation exchange sites to anchor poisoning substances and active components to catalyze NO_x into N₂. It was not deactivated during the NO_x reduction process in the presence of alkali (earth) metals and heavy metals. The enhanced surface acidity, reducible active species, and active chemisorbed oxygen species of the smart catalyst accounted for the remarkable NO_x reduction efficiency. More importantly, the self-created targeted antipoisoning sites expressed specific anchoring effects on poisoning substances and protected the active components from poisoning. It was demonstrated that the tetrahedrally coordinated aluminum species of the smart catalyst mainly acted as self-created targeted antipoisoning sites to stabilize the poisoning substances into the interlayers of montmorillonite. This work paves a new way for efficient reduction of NO_x from the complex flue gas in practical applications.

Interaction Mechanism for Simultaneous Elimination of Nitrogen Oxides and Toluene over the Bifunctional CeO2-TiO2 Mixed Oxide Catalyst

Simultaneous catalytic elimination of nitrogen oxides (NO_x, x = 1 and 2) and volatile organic compounds (VOCs) is of great importance for environmental preservation in China. In this work, the interactions of simultaneous removal of NO_x and methylbenzene (PhCH₃) were investigated on a CeO₂-TiO₂ mixed oxide catalyst, which demonstrated excellent bifunctional removal efficiencies for the two pollutants. The results indicated that NO_x positively promotes PhCH₃ oxidation, while NH₃ negatively inhibits through competitive adsorption with PhCH₃. The underlying mechanism is that a pseudo PhCH₃-SCR reaction happened in this process is parallel to NH₃-SCR. Combined with in situ diffuse reflectance infrared Fourier transform spectroscopy and quasi in situ X-ray photoelectron spectroscopy, the interaction mechanism between NO_x and PhCH₃ is proposed. Specifically, NO_x is adsorbed on the catalyst surface to produce nitrate species, which reacts with the carboxylate generated during PhCH₃ oxidation to form organic nitrogen intermediates that create N₂ and CO₂ in the following reactions. In the reaction process, the superoxide (O₂^-) generated by O₂ activation on the catalyst surface is an important species for the propelling of oxidation reaction. This work could provide guidelines for the design of state-of-the-art catalysts for simultaneous catalytic removal of NO_x and VOCs.