Identification of a Facile Pathway for Dioxymethylene Conversion to Formate Catalyzed by Surface Hydroxyl on TiO2-Based Catalyst

Simultaneously Promoted Water Resistance and CO2 Selectivity in Methanol Oxidation Over Pd/CoOOH: Synergy of Co-OH and the Pd-Olatt-Co Interface

Catalytic purification of industrial oxygenated volatile organic compounds (OVOCs) is hindered by the presence of water vapor that attacks the active sites of conventional noble metal-based catalysts and the insufficient mineralization that leads to the generation of hazardous intermediates. Developing catalysts simultaneously with excellent water resistance and a high intermediate suppression ability is still a great challenge. Herein, we proposed a simple strategy to synthesize a Pd/CoOOH catalyst that contains abundant hydroxyl groups and lattice oxygen species, over which a negligible effect was observed on CH3OH conversion with 3 vol % water vapor, while a remarkable conversion reduction of 24% was observed over Pd/Co3O4. Moreover, the low-temperature CO2 selectivity over Pd/CoOOH is significantly enhanced in comparison with Pd/Co(OH)2. The high concentration of surface hydroxyl groups on Pd/CoOOH enhances the water resistance owing to the accelerated activation of H2O to generate Co-OH, which replaces the consumed hydroxyl and facilitates the quick dissociation of surface H2O through timely desorption. Additionally, the presence of Pd-Olatt-Co promotes electron transport from Co to Pd, leading to improved metal-support interactions and weakened metal-O bonds. This in turn enhances the catalyst's capacity to efficaciously convert intermediates. This study sheds new insights into designing multifunctional catalytic platforms for efficient industrial OVOC purification as well as other heterogeneous oxidation reactions.

Hierarchical PtCuMnP Nanoalloy for Efficient Hydrogen Evolution and Methanol Oxidation

The higher amount of Pt usage and its poisoning in methanol oxidation reaction in acidic media is a major setback for methanol fuel cells. Herein, a promising dual application high-performance electrocatalyst has been developed for hydrogen evolution and methanol oxidation. A low Pt-content nanoalloy co-doped with Cu, Mn, and P is synthesized using a modified solvothermal process. Initially, ultrasmall ≈2.9 nm PtCuMnP nanoalloy is prepared on N-doped graphene-oxide support and subsequently, it is characterized using several analytical techniques and examined through electrochemical tests. Electrochemical results show that PtCuMnP/N-rGO has a low overpotential of 6.5 mV at 10 mA cm-2 in 0.3 m H2SO4 and high mass activity for the hydrogen evolution reaction. For the methanol oxidation reaction, the PtCuMnP/N-rGO electrocatalyst exhibits robust performance. The mass activity of PtCuMnP/N-rGO is 6.790 mA mg-1 Pt, which is 7.43 times higher than that of commercial Pt/C (20% Pt). Moreover, in the chronoamperometry test, PtCuMnP/N-rGO shows exceptionally good stability and retains 72% of the initial current density even after 20,000 cycles. Furthermore, the PtCuMnP/N-rGO electrocatalyst exhibits outstanding performance for hydrogen evolution and methanol oxidation along with excellent anti-poisoning ability. Hence, the developed bifunctional electrocatalyst can be used efficiently for hydrogen evolution and methanol oxidation.

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.

Low-temperature thermocatalytic removal of formaldehyde in air using copper manganite spinels

The removal of formaldehyde (FA) is vital for indoor air quality management in light of its carcinogenic propensity and adverse environmental impact. A series of copper manganite spinel structures (e.g., CuMn2O4) are prepared using the sol-gel combustion method and treated with reduction or oxidation pretreatment at 300 °C condition. Accordingly, CuMn2O4-O ("O" suffix for oxidation pre-treatment in air) is identified as the best performer to achieve 100% conversion (XFA) of FA (50 ppm) at 90 °C; its performance, if assessed in terms of reaction kinetic rate (r) at XFA = 10%, is 5.02E-03 mmol g-1 h-1. The FA removal performance increases systematically with decreases in flow rate, FA concentration, and relative humidity (RH) or with increases in bed mass. The reaction pathways and intermediates of FA catalytic oxidation on CuMn2O4-A are studied with density functional theory simulations, temperature-programmed characterization experiments, and in-situ diffuse reflectance infrared Fourier transform spectroscopy. The synergistic combination of large quantities of adsorbed oxygen (OA) species and oxidized metal species (e.g., Cu2+) contribute to the enhanced catalytic performance of CuMn2O4-O to oxidize FA into CO2 with the reaction intermediates of H2CO2 (DOM), HCOO-, and CO. The present study is expected to provide valuable insights into the thermocatalytic oxidation of FA over spinel CuMn2O4 materials and their catalytic performances in relation to the key process variables.

The practical utility of ternary nickel-cobalt-manganese oxide-supported platinum catalysts for room-temperature oxidative removal of formaldehyde from the air

Formaldehyde (FA), a carcinogenic oxygenated volatile organic compound, is present ubiquitously in indoor air. As such, it is generally regarded as a critical target for air quality management. The oxidative removal of FA under dark and room-temperature (RT) conditions is of practical significance. A series of ternary nickel-cobalt-manganese oxide-supported platinum catalysts (Pt/NiCoMnO4) have been synthesized for FA oxidative removal at RT in the dark. Their RT conversion values for 50 ppm FA (XFA) at 5,964 h-1 gas hourly space velocity (GHSV) decrease in the following order: 1 wt% Pt/NiCoMnO4 (100 %) > 0.5 wt% Pt/NiCoMnO4 (25 %) > 0.05 wt% Pt/NiCoMnO4 (14 %) > NiCoMnO4 (6 %). The catalytic performance of 1 wt% Pt/NiCoMnO4 has been examined further under the control of various process variables (e.g., catalyst mass, flow rate, relative humidity, FA concentration, time on stream, and molecular oxygen content). The catalytic oxidation of FA at low temperatures (e.g., RT and 60 °C) is accounted for by Langmuir-Hinshelwood mechanism (single-site competitive-adsorption), while Mars van Krevelen kinetics is prevalent at higher temperatures. In situ diffuse-reflectance infrared Fourier-transform spectroscopy reveals that FA oxidation proceeds through a series of reaction intermediates such as DOM, HCOO-, and CO32-. Based on the density functional theory simulations, the unique electronic structures of the nearest surface atoms (platinum and nickel) are suggested to be responsible for the superior catalytic activity of Pt/NiCoMnO4.

Efficient and Durable Oxidation Removal of Formaldehyde over Layered Double Hydroxide Catalysts at Room Temperature

Room temperature catalytic oxidation (RTCO) using non-noble metals has emerged as a highly promising technique for removal of formaldehyde (HCHO) under ambient conditions; however, non-noble catalysts still face the challenges related to poor water resistance and low stability under harsh conditions. In this study, we synthesized a series of layered double hydroxides (LDHs) incorporating various dual metals (MgAl, ZnAl, NiAl, NiFe, and NiTi) for formaldehyde oxidation at ambient temperature. Among the synthesized catalysts, the NiTi-LDH catalyst showed an HCHO removal efficiency and CO2 yield close to 100.0%, and exceptional water resistance and chemical stability on running 1300 min. The abundant hydroxyl groups in LDHs directly bonded with HCHO, leading to the production of CO2 and H2O, thus inhibiting the formation of CO, even in the absence of O2 and H2O. The coexistence of O2 effectively reduced the reaction barrier for H2O molecule dissociation, facilitating the formation of hydroxyl groups and their subsequent backfill on the catalyst surface. The mechanisms underlying the involvement and regeneration of hydroxyl groups in room temperature oxidation of formaldehyde were elucidated with the combined in situ DRIFTS, HCHO-TPD-MS, and DFT calculations. This work not only demonstrates the potential of LDH catalysts in environmental applications but also advances the understanding of the fundamental processes involved in room temperature oxidation of formaldehyde.

Thermocatalytic oxidation of a binary mixture of formaldehyde and toluene at ambient levels by a titanium dioxide supported platinum catalyst

The thermocatalytic oxidative potential of various supported noble metal catalysts (SNMCs) is well-known for hazardous volatile organic compounds (VOCs), e.g., formaldehyde (FA) and toluene. However, little is known about SNMC performance against ambient VOC pollution with low concentration (subppm levels) relative to industrial effuluents with high concentrations (several hundred ppm). Here, the thermocatalytic oxidation performance of a titanium dioxide (TiO2)-supported platinum catalyst (Pt/TiO2) has been evaluated for a low-concentration binary mixture of FA and toluene at low temperatures and in the dark. A sample of TiO2 containing 1 wt% Pt with thermal reduction pre-treatment under hydrogen achieved 100 % conversion of FA (500 ppb) and toluene (100 ppb) at 130 °C and a gas hourly velocity of 59,701 h-1. Its catalytic activity was lowered by either a decrease in catalyst mass or an increase in VOC concentration, relative humidity, or flow rate. In situ diffuse reflectance infrared Fourier transform spectroscopy, density functional theory simulations, and molecular oxygen (O2) temperature-programmed desorption experiments were used to identify possible VOC oxidation pathways, reaction mechanisms, and associated surface phenomena. The present work is expected to offer insights into the utility of metal oxide-supported Pt catalysts for the low-temperature oxidative removal of gaseous VOCs in the dark, primarily for indoor air quality management.

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.

Dark-Light Tandem Catalytic Oxidation of Formaldehyde over SrBi2Ta2O9 Nanosheets

Formaldehyde (HCHO), as one of the main indoor toxic pollutions, presents a great threat to human health. Hence, it is imperative to efficiently remove HCHO and create a good indoor living environment for people. Herein, a layered perovskite material SrBi2Ta2O9 (SBT), was studied for the first time and exhibited superior photocatalytic efficiency and stability compared to commercial TiO2 (P25). Furthermore, a unique dark-light tandem catalytic mechanism was constructed. In the dark reaction stage, HCHO (Lewis base) site was adsorbed on the terminal (Bi2O2)2+ layer (Lewis acid) site of SBT in the form of Lewis acid-base complexation and was gradually oxidized to CO32- intermediate (HCHO → DOM (dioxymethylene) → HCOO- → CO32-). Then, in the light reaction stage, CO32- was completely converted into CO2 and H2O (CO32- → CO2). Our study contributes to a thorough comprehension of the photocatalytic oxidation of HCHO and points out its potential for day-night continuous work applications in a natural environment.

Tunable Interfacial Electronic Pd-Si Interaction Boosts Catalysis via Accelerating O2 and H2O Activation

Engineering the interfacial structure between noble metals and oxides, particularly on the surface of non-reducible oxides, is a challenging yet promising approach to enhancing the performance of heterogeneous catalysts. The interface site can alter the electronic and d-band structure of the metal sites, facilitating the transition of energy levels between the reacting molecules and promoting the reaction to proceed in a favorable direction. Herein, we created an active Pd-Si interface with tunable electronic metal-support interaction (EMSI) by growing a thin permeable silica layer on a non-reducible oxide ZSM-5 surface (termed Pd@SiO₂/ZSM-5). Our experimental results, combined with density functional theory calculations, revealed that the Pd-Si active interface enhanced the charge transfer from deposited Si to Pd, generating an electron-enriched Pd surface, which significantly lowered the activation barriers for O₂ and H₂O. The resulting reactive oxygen species, including O₂ ^-, O₂ ^2-, and -OH, synergistically facilitated formaldehyde oxidation. Additionally, moderate electronic metal-support interaction can promote the catalytic cycle of Pd⁰ ⇆ Pd²⁺, which is favorable for the adsorption and activation of reactants. This study provides a promising strategy for the design of high-performance noble metal catalysts for practical applications.

Effect of MnO2 Crystal Type on the Oxidation of Furfural to Furoic Acid

The base-free oxidation of furfural by non-noble metal systems has been challenging. Although MnO2 emerges as a potential catalyst application in base-free conditions, its catalytic efficiency still needs to be improved. The crystalline form of MnO2 is an important factor affecting the oxidation ability of furfural. For this reason, four crystalline forms of MnO2 (α, β, γ, and δ-MnO2) were selected. Their oxidation performance and surface functional groups were analyzed and compared in detail. Only δ-MnO2 exhibited excellent activity, achieving 99.04% furfural conversion and 100% Propo.FA (Only furoic acid was detected by HPLC in the product) under base-free conditions, while the furfural conversion of α, β, and γ-MnO2 was below 10%. Characterization by XPS, IR, O2-TPD and other means revealed that δ-MnO2 has the most abundant active oxygen species and surface hydroxyl groups, which are responsible for the best performance of δ-MnO2. This work achieves the green and efficient oxidation of furfural to furoic acid over non-noble metal catalysts.

Plasmonic Cu Nanoparticles for the Low-temperature Photo-driven Water-gas Shift Reaction

The activation of water molecules in thermal catalysis typically requires high temperatures, representing an obstacle to catalyst development for the low-temperature water-gas shift reaction (WGSR). Plasmonic photocatalysis allows activation of water at low temperatures through the generation of light-induced hot electrons. Herein, we report a layered double hydroxide-derived copper catalyst (LD-Cu) with outstanding performance for the low-temperature photo-driven WGSR. LD-Cu offered a lower activation energy for WGSR to H₂ under UV/Vis irradiation (1.4 W cm^-2 ) compared to under dark conditions. Detailed experimental studies revealed that highly dispersed Cu nanoparticles created an abundance of hot electrons during light absorption, which promoted *H₂ O dissociation and *H combination via a carboxyl pathway, leading to the efficient production of H₂ . Results demonstrate the benefits of exploiting plasmonic phenomena in the development of photo-driven low-temperature WGSR catalysts.

Formaldehyde oxidation on Pd/USY catalysts at room temperature: The effect of acid pretreatment on supports

The complete catalytic oxidation of formaldehyde (HCHO) to CO₂ and H₂O at room temperature is a green route for indoor HCHO removal. Zeolite is an excellent carrier material for HCHO oxidation due to its large surface area, intricate pores and high adsorption capacity. However, the zeolite-supported noble metal catalysts have currently shown relatively low activity especially at room temperature. In this work, we present a facile acid treatment strategy for zeolite catalysts to improve the hydroxyl concentration and further enhance their catalytic activity for HCHO oxidation. Activity tests illustrated that HCHO could be completely oxidized to CO₂ and H₂O at a nearly 100% conversion rate with a weight hourly space velocity (WHSV) of 150,000 mL/(g∙hr) at 25°C, when the support of Pd/USY catalysts was pretreated by hydrochloric acid with a concentration of 0.20 mol/L. The characterization results revealed that the active hydroxyl groups originated from the dealumination in the acid treatment play a key role in the HCHO oxidation reaction. The deduced reaction mechanism suggests that bridging hydroxyl groups may oxidize HCHO to dioxymethylene (DOM) species and terminal hydroxyl groups are responsible for the transformation of DOM groups to formate (HCOO) species.

Designing of 3D MnO2-graphene catalyst on sponge for abatement temperature removal of formaldehyde

The Mn-based catalysts, with low cost and high activity, are believed to be the effective composites for eliminating in-door formaldehyde (HCHO), while the powdered form nanosized catalysts are hardly to apply for practical application. Herein, hetero-structure of nanosheets manganese oxide (MnO₂) encapsulating N-doping graphene sphere (GS) were deposited in network-like sponge for constructing 3D catalyst. The prepared MnO₂-GS-Sponge composite catalyst exhibited excellent performance for removing HCHO at room temperature compared with GS and commercial MnO₂. The MnO₂-GS with larger specific surface area (209.1 m²·g^-1) was dispersed evenly in 3D network of sponge, which facilitated exposing more activate sites and achieving fast transport kinetics accelerating catalytic reaction for converting 97.1 % of 100 ppm of HCHO continuously to CO₂ for 120 h. Moreover, rely on the chemisorption of amino groups on N-doping GS surface, HCHO could be enriched even at low concentrations and efficient elimination (from 1000 ppb to12 ppb, at 35 ℃ in 48 h). The average oxidation state and infrared spectra analysis suggested that abundant oxygen vacancies on MnO₂-GS-Sponge could be identified as surface-active sites of converting HCHO into the intermediates of dioxymethylene and formate. This work might inspire the designing 3D composite material for potential application in other fields of environmental engineering or energy industrial.

Enhanced Formaldehyde Oxidation Performance of the Mesoporous TiO2(B)-Supported Pt Catalyst: The Role of Hydroxyls

As one of the crystal phases of titania, TiO2(B) was first utilized as a catalyst carrier for the oxidation of formaldehyde (HCHO). The mesoporous TiO2(B) loaded with Pt nanoparticles enhanced the HCHO oxidation reaction whose reaction rate was 4.5-8.4 times those of other crystalline TiO2-supported Pt catalysts. Simultaneously, Pt/TiO2(B) exhibited long-term stable HCHO oxidation performance. The structural characterization results showed that in comparison with Pt/anatase, Pt/TiO2(B) had more abundant hydroxyls, facilitating increasing the content of oxygen species. Studies on the role of hydroxyls in HCHO oxidation of Pt/TiO2(B) illustrated that synergistic involvement of terminally bound hydroxyls and bridging hydroxyls in HCHO oxidation accelerated the transformation from HCHO to formate via dioxymethylene. Moreover, hydroxyls could avoid the accumulation of excessive formate on Pt/TiO2(B) and promote the rapid oxidation of CO. Accordingly, the hydroxyl groups could accelerate each substep of formaldehyde oxidation, which enabled Pt/TiO2(B) to exhibit excellent formaldehyde oxidation performance.

Distinct Role of Surface Hydroxyls in Single-Atom Pt1/CeO2 Catalyst for Room-Temperature Formaldehyde Oxidation: Acid-Base Versus Redox

The development of highly efficient catalysts for room-temperature formaldehyde (HCHO) oxidation is of great interest for indoor air purification. In this work, it was found that the single-atom Pt₁/CeO₂ catalyst exhibits a remarkable activity with complete removal of HCHO even at 288 K. Combining density functional theory calculations and in situ DRIFTS experiments, it was revealed that the active O_latticeH site generated on CeO₂ in the vicinity of Pt²⁺ via steam treatment plays a key role in the oxidation of HCHO to formate and its further oxidation to CO₂. Such involvement of hydroxyls is fundamentally different from that of cofeeding water which dissociates on metal oxide and catalyzes the acid-base-related chemistry. This study provides an important implication for the design and synthesis of supported Pt catalysts with atom efficiency for a very important practical application-room-temperature HCHO oxidation.

Low-temperature oxidative removal of gaseous formaldehyde by an eggshell waste supported silver-manganese dioxide bimetallic catalyst with ultralow noble metal content

Under dark/low temperature (DLT) conditions, the oxidative removal of gaseous formaldehyde (FA) was studied using eggshell waste supported silver (Ag)-manganese dioxide (MnO₂) bimetallic catalysts. To assess the synergistic effects between the two different metals, 0.03%-Ag-(0.5-5%)-MnO₂/Eggshell catalysts were prepared and employed for DLT-oxidation of FA. The steady-state FA oxidation reaction rate (mmol g^-1 h^-1), when measured using 100 ppm FA at 80 °C (gas hourly space velocity (GHSV) of 5308 h^-1), varied as follows: Ag-1.5%-MnO₂/Eggshell-R (9.4) > Ag-3%-MnO₂/Eggshell-R (8.1) > Ag-1.5%-MnO₂/Eggshell (7.5) > Ag-5%-MnO₂/Eggshell-R (7.2) > Ag-1.5%-MnO₂/CaCO₃-R (6.8) > MnO₂-R (6) > Ag-0.5%-MnO₂/Eggshell-R (3.2) > Ag/Eggshell-R (2.6). (Here, 'R' denotes hydrogen-based thermochemical reduction pretreatment.) The temperature required for 90% FA conversion (T₉₀) at the same GHSV exhibited a contrary ordering: Ag/Eggshell-R (175 °C) > Ag-0.5%-MnO₂/Eggshell-R (123 °C) > Ag-5%-MnO₂/Eggshell-R (113 °C) > MnO₂-R (99 °C) > Ag-1.5%-MnO₂/Eggshell (96 °C) > Ag-3%-MnO₂/Eggshell-R (93 °C) > Ag-1.5%-MnO₂/Eggshell-R (77 °C). The eggshell catalyst outperformed the ones made of commercial calcium carbonate due to the presence of defects in the former. The MnO₂ co-catalyst enhances the catalytic activities through the capture and activation of atmospheric oxygen (O₂) with rapid catalytic regeneration. Also, MnO₂ favorably captures the hydrogen of the adsorbed FA molecules to make the oxidation pathway thermodynamically more favorable.

Acid pretreatment of support promotes Pd/SiO2 activity for formaldehyde oxidation at room temperature

Hydroxyl groups on SiO2 produced by acid pretreatment favored the anchoring of Pd particles and increased their dispersion, which induced more oxygen vacancies on the surface of catalysts and further enhanced H2O activation.

One-step fabrication of electrospun flexible and hierarchically porous Pt/γ-Al2O3 nanofiber membranes for HCHO and particulate removal

A flexible Pt/γ-Al2O3 nanofiber membrane with optimal 2 wt% Pt content can effectively decompose HCHO into CO2 at room temperature.

N-Coordinated Ir single atoms anchored on carbon octahedrons for catalytic oxidation of formaldehyde under ambient conditions

N-Coordinated Ir single atoms using N-doped carbon as a non-oxide support for formaldehyde removal under ambient conditions for the first time.

A simple method to regulate surface hydroxy groups on Al2O3 for improving catalytic oxidation performance for HCHO on Pt/Al2O3

For supported noble metal catalysts, the properties of the support had great influence on the state of noble metals. Herein, we chose Al2O3 as model to find a simple method...

Tuning Metal-Support Interaction of Pt-CeO2 Catalysts for Enhanced Oxidation Reactivity

Metal-support interaction (MSI) has been widely recognized to be playing a pivotal role in regulating the catalytic activity of various reactions. In this work, the degree of MSI between Pt and CeO₂ support was finely tuned by adjusting the activation condition, and the obtained catalysts were tested for the oxidative abatement of CO and HCHO under ambient conditions. The characterization of catalysts shows that activation of strongly interacting Pt-CeO₂ at higher temperatures by H₂ leads to a weaker MSI with increased electron density of Pt, and this modification of local electronic properties is demonstrated to result in enhanced O₂ adsorption/activation to prevent the CO self-poisoning effect, while it abates the activity of CO adsorption/activation and oxidation of adsorbed CO. The Pt-CeO₂ catalyst with a moderate MSI, which is able to balance each step in the catalytic cycle over Pt and Pt-CeO₂ interface domains, displays the highest activity for CO/HCHO oxidation under ambient conditions.

Dual-Function Reaction Center for Simultaneous Activation of CH4 and O2 via Oxygen Vacancies during Direct Selective Oxidation of CH4 into CH3OH

The direct oxidation of methane (CH₄) to methanol (CH₃OH) has been a focus of global concern and is quite challenging due to the thermodynamically stable CH₄ and uncontrolled overoxidation of the products. Here, we provided a new viewpoint on the role of oxygen vacancies that induce a dual-function center in enhancing the adsorption and activation of both CH₄ and O₂ reactants for the subsequent selective formation of a CH₃OH liquid fuel on two-dimensional BiOCl photocatalysts at atmospheric pressure. The key for the favorable activity lies in the simultaneous ability of the electron-trapped Bi atom in activating CH₄ and the formation of ^•O₂^- radicals due to the activation of O₂ at the adjacent oxygen vacancy site, which immediately attack the activated CH₄ to directly produce CH₃OH, in initiating the oxidation reaction. What is more, the relatively low reaction barriers and the easy desorption of CH₃OH concertedly facilitate the highly selective conversion of CH₄ up to 85 μmol of CH₃OH, with a small amount of CO₂ and CO as the byproducts over the BiOCl nanosheets with an oxygen vacancy concentration of 2.4%. This work could broaden the avenue toward the application of oxygen-defective metal oxides in the photocatalytic selective conversion of CH₄ to CH₃OH and offer a disparate perspective on the role of oxygen vacancy acting as the surface electron transfer channel in enhancing the photocatalytic performance.

Insoluble matrix proteins from shell waste for synthesis of visible-light response photocatalyst to mineralize indoor gaseous formaldehyde

HCHO is the most concerned indoor air pollutant that photocatalytic degradation is a feasible approach. To achieve efficient and complete degradation of HCHO under visible light irradiation, heteroatoms are usually doped in TiO₂. But using natural materials as a dopant instead of expensive and toxic chemicals to fertilize TiO₂ remains challenging. This paper proposes a sustainable and green approach to synthesize an efficient N, Ca co-doped TiO₂ photocatalyst (TIMP) by using the insoluble matrix proteins (IMPs) extracted from abalone shell. TIMP-0.8 achieves near completely degradation HCHO within 45 min under visible light at ambient temperature and exhibits superior stability after 7 cycles. TIMP-0.8 has monodispersity with smaller diameter, high porosity, abundant defects and high adsorption affinity for surface hydroxyls compared with pure TiO₂. With the assistance of IMPs, the rate-determining step of HCHO degradation changes from -COOH oxidation to spontaneous decomposition of HCO₃^-, significantly facilitating the elimination and mineralization of HCHO. Overall, IMPs from abalone shell are natural surfactant, bio-templet, and dopant for TiO₂ modification, contributing to desirable visible-light photocatalytic performance for HCHO degradation. This paper provides new insight for high-value utilization of waste shell and photocatalytic indoor purification.

Site Sensitivity of Interfacial Charge Transfer and Photocatalytic Efficiency in Photocatalysis: Methanol Oxidation on Anatase TiO2 Nanocrystals

Photocatalytic oxidation of methanol on various anatase TiO₂ nanocrystals was studied by in situ and time-resolved characterizations and DFT calculations. Surface site and resulting surface adsorbates affect the surface band bending/bulk-to-surface charge migration processes and interfacial electronic structure/interfacial charge transfer processes. TiO₂ nanocrystals predominantly enclosed by the {001} facets expose a high density of reactive fourfold-coordinated Ti sites (Ti_4c ) at which CH₃ OH molecules dissociate to form the CH₃ O adsorbate (CH₃ O(a)_Ti4c ). CH₃ O(a)_Ti4c localized density of states are almost at the valence band maximum of TiO₂ surface, facilitating the interfacial hole transfer process; CH₃ O(a)_Ti4c with a high coverage promotes upward surface band bending, facilitating bulk-to-surface hole migration. CH₃ O(a)_Ti4c exhibits the highest photocatalytic oxidation rate constant. TiO₂ nanocrystals enclosed by the {001} facets are most active in photocatalytic methanol oxidation.