Crystal Engineering of TiO2 for Enhanced Catalytic Oxidation of 1,2-Dichloroethane on a Pt/TiO2 Catalyst

Catalytic oxidation of volatile organic compounds over supported noble metal and single atom catalysts: A review

Volatile organic compounds (VOCs) exhausted from industrial processes are the major atmospheric pollutants, which could destroy the ecological environment and make hazards to human health seriously. Catalytic oxidation is regarded as the most competitive strategy for the efficient elimination of low-concentration VOCs. Supported noble metal catalysts are preferred catalysts due to their excellent low-temperature catalytic activity. To further lower the cost of catalysts, single atom catalysts (SAC) have been fabricated and extensively studied for application in VOCs oxidation due to their 100 % atom-utilization efficiency and unique catalytic performance. In this review, we comprehensively summarize the recent advances in supported noble metal (e.g., Pt, Pd, Au, and Ag) catalysts and SAC for VOCs oxidation since 2015. Firstly, this paper focuses on some important influencing factors that affect the activity of supported noble metal catalysts, including particle size, valence state and dispersion of noble metals, properties of the support, metal oxide/ion modification, preparation method, and pretreatment conditions of catalysts. Secondly, we briefly summarize the catalytic performance of SAC for typical VOCs. Finally, we conclude the key influencing factors and provide the prospects and challenges of VOCs oxidation.

Promoting Low-Temperature Toluene Oxidation via Pt-O-Fe Interfacial Sites in a Pt/CuO-Fe3O4 Catalyst

Electronic metal-support interaction (EMSI) has been widely explored in the catalytic degradation of volatile organic compounds (VOCs) owing to the formation of special interfacial sites. Herein, the EMSI effect was engineered by constructing the serial Pt catalysts supported on CuO-Fe3O4 bimetal oxide (Pt/CFO). Among them, the 0.5Pt/CFO catalyst with 0.5 wt % Pt loading exhibited an outstanding catalytic activity, with T90 (the temperature of 90% toluene conversion) lowered to 185 °C, and displayed excellent stability and water resistance. Comprehensive physicochemical characterizations revealed that an evident electron transfer occurred via the interface structure (Pt-O-Fe), producing the positively charged Pt (Ptδ+) and abundant Fe2+ species. Notably, the increased electron density around the Fe species weakened the Fe-O bond and thus activated the surface lattice oxygen (Olatt). Further, temperature-programmed desorption experiments and in situ diffuse reflectance infrared Fourier transform spectroscopy results demonstrated that the electron-deficient Ptδ+ was conducive to the adsorption and activation of toluene at low temperature. Consequently, the deep oxidation of toluene was achieved with the participation of Olatt, benefiting from the Ptδ+-O-Fe2+ interfacial sites with synergistic catalysis for toluene adsorption and oxygen activation. This work provides an interesting idea to explore the relationship between the electron transfer effect and highly efficient VOC abatement.

1,2-Dichloroethane as a Gaseous Acetylene Source for the Rapid Assembly of Isoquinolino[1,2-b]quinazolinone Scaffolds

Reported herein is a novel ruthenium(II)-catalyzed [4 + 2] annulation of quinazolinones with 1,2-dichloroethane (DCE), resulting in a myriad of isoquinolino[1,2-b]quinazolinone scaffolds. In this protocol, DCE serves not only as a solvent but also as an acetylene source. The fused quinazolinones undergo versatile transformations and provide a rapid and convenient way to access several important bioactive molecule analogues such as Rutecarpine, Euxylophoricine B and Euxylophoricine E. The potential reaction pathway was elucidated through detailed mechanistic studies and Density Functional Theory (DFT) calculations.

Construction of a CuO/TiO2@C S-scheme heterojunction for phenol removal by activated peroxymonosulfate

Phenol is a volatile organic compound whose effective degradation using conventional methods is challenging. Rapid charge-carrier recombination and slow Cu(II)/Cu(I) conversion rate in copper-based photocatalysts hinder their activation efficiency of potassium persulfate (PMS). Herein, an S-scheme heterojunction structure comprising TiO2@C and CuO was successfully constructed using an in situ calcination method, enabling the spatial separation of photogenerated charge carriers and thus enhancing the synergistic effect of PMS in the photocatalytic degradation of phenol. The resulting CuO/TiO2@C nanocomposite exhibited notably higher phenol removal efficiency than CuO or TiO2@C alone, removing an 88 % phenol (40 mg/L) and a 48 % total organic carbon within 25 min. The material maintained high degradation efficiency after four cycles. Liquid chromatography-mass spectrometry was employed to identify intermediates generated during phenol degradation, and a potential charge-transfer mechanism was proposed based on the analysis of catalytic active species and energy band structure. Thus, this study provides new insights for enhancing PMS activation for phenol remediation.

Hydrodechlorination under O2 promotes catalytic oxidation of CVOCs over a Pt/TiO2 catalyst at low temperature

A novel strategy to promote elimination of CVOCs at low temperature, specifically involving hydrodechlorination under O2, was proposed. Turnover frequency and HCl yield in oxidation of vinyl chloride increased, respectively, by over 22 and 43 times (225 °C) with the assistance of 1000 ppm H2. A new chemical equation (CH2CHCl + H2 + O2 → CO2 + HCl + H2O) was used to describe the reaction.

Recent Advances of the Effect of H2O on VOC Oxidation over Catalysts: Influencing Factors, Inhibition/Promotion Mechanisms, and Water Resistance Strategies

Water vapor is a significant component in real volatile organic compounds (VOCs) exhaust gas and has a considerable impact on the catalytic performance of catalysts for VOC oxidation. Important progress has been made in the reaction mechanisms of H2O and water resistance strategies for VOC oxidation in recent years. Despite advancements in catalytic technology, most catalysts still exhibit low activity under humid conditions, presenting a challenge in reducing the adverse effects of H2O on VOC oxidation. To develop water-resistant catalysts, understanding the mechanistic role of H2O and implementing effective water-resistance strategies with influencing factors are imperative. This Perspective systematically summarizes related research on the impact of H2O on VOC oxidation, drawing from over 390 papers published between 2013 and 2024. Five main influencing factors are proposed to clarify their effects on the role of H2O. Five inhibition/promotion mechanisms of H2O are introduced, elucidating their role in the catalytic oxidation of various VOCs. Additionally, different kinds of water resistance strategies are discussed, including the fabrication of hydrophobic materials, the design of specific structures and morphologies, and the introduction of additional elements for catalyst modification. Finally, scientific challenges and opportunities for enhancing the design of efficient and water-resistant catalysts for practical applications in VOC purification are highlighted.

Selective Adsorption of Chlorine Species on RuO2 Sites for Efficient Elimination of Vinyl Chloride on the Ru/SnO2 Catalyst

The main bottleneck in the catalytic combustion of chlorinated volatile organic compounds (CVOCs) is deactivation and the production of chlorine-containing byproducts originating from the chlorine species deposited on the catalyst. Herein, Ru supported on SnO2 (Ru/SnO2) was prepared with the lattice matching principle. As RuO2 and SnO2 are both rutile phases, Ru species were present as highly dispersed RuO2 particles on the Ru/SnO2 catalyst. These particles adsorbed chlorine species with greater efficiency during the CVOCs combustion, thereby protecting the oxygen vacancies. Therefore, the double sites, oxygen vacancy to oxidize and RuO2 to adsorb chlorine species, on the Ru/SnO2 catalyst led to a notable enhancement in activity, stability, and byproduct selectivity. In contrast, the high dispersion of Ru species on the CeO2 support, as the typical catalyst for chlorinated hydrocarbon combustion, gave rise to a predominantly Ru-O-Ce structure. This structure did not prevent the adsorption of chlorine species on the oxygen vacancies, resulting in deactivation at low temperatures and an increased polychlorinated byproduct concentration. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) further corroborated the variation in the adsorption sites of chlorine species on the two catalysts. This work provides a new strategy for designing efficient Ru-based catalysts for catalytic CVOCs combustion.

Boosted 1,2-Dichloroethane Deep Destruction over CoRu/Al2O3 Bifunctional Catalysts via Surface Oxygen and Water Molecule Synergistic Activation

Developing efficacious catalysts with superior Cl resistance and polychlorinated byproduct inhibition capability is crucial for realizing the environmentally friendly purification of chlorinated volatile organic compounds (CVOCs). Activating CVOC molecules and desorbing Cl species by modulating the metal-oxygen property is a promising strategy to fulfill these. Herein, a bifunctional CoRu/Al2O3 catalyst with synergistic Co and Ru interactions (Ru-O-Co species) was rationally fabricated, which possesses abundant surface Co2+ and Ruδ+ sites and collaboratively facilitates the activation of lattice oxygen (O2-) and molecular oxygen (O2 → O2- → O-), accelerating 1,2-dichloroethane (1,2-DCE) decomposition via the reaction route of enolic species → aldehydes → carboxylate/carbonate. Furthermore, CoRu/Al2O3 stimulates 1,2-DCE oxidation under humid conditions as H2O molecules can be easily activated to active *OH (potential oxidizing agent) over Ru species, accelerating C-Cl dissociation and Cl desorption and promoting the transformation of catecholate-type (C═O) species to easily oxidizable carboxylic acid (COOH) species, remarkably suppressing the formation of hazardous CCl4 and CHCl2CH2Cl. This study provides critical insights into the development of bifunctional catalysts to synergistically activate surface oxygen species and H2O molecules for industrial CVOC stable and efficient elimination.

Pt position determining efficiency and stability for photocatalytic toluene degradation over Pt decorated TiO2

Highly durable photocatalytic degradation of gas toluene pollutants is a great challenge due to the easy deactivation of photocatalysts. Herein, we synthesized the Pt embedded at interface of TiO2 nanocomposites (TiO2/Pt/TiO2) and Pt exposed on the surface of TiO2 nanocomposites (Pt/TiO2/TiO2) to investigate the effect of Pt position on the photocatalytic performance of toluene degradation. It was found that the Pt-exposed samples showed inactivation as the reaction progressed because carbonaceous intermediates such as phenol and benzoic acid were observed to be deposited on the exposed Pt to restrain the role of Pt in electron transfer for the production of reactive oxygen species. Whereas, Pt-embedded nanocomposites had excellent activity and stability for toluene degradation and CO2 production more than 60 h. This was attributed to the protective effect of the TiO2 outerlayer. The embedded Pt was not easily poisoned by the degradation intermediates, resulting in a good electron transfer and the continuous production of reactive oxygen species for photocatalytic reaction. Therefore, this work provides an efficient approach for designing of the stability of metal-decorated photocatalyst for the highly durable photocatalytic performance.

Enhanced performance of photocatalytic oxidation of indoor toluene over Pd/TiO2 catalyst by tuning surface defect concentrations

An effective approach for the elimination of indoor gaseous toluene through photocatalytic oxidation involves the engineering of surface defects on catalysts. In this study, the concentrations of surface oxygen defects in PdTi-xN (x = 10, 30) catalysts were controlled using the sodium borohydride solid-phase reduction method, and their performances in the photocatalytic oxidation of indoor gaseous toluene were evaluated. PdTi-10 N demonstrated high photocatalytic efficiency for toluene oxidation, achieving 84% toluene conversion and approximately 75% CO2 mineralization. Characterization results indicated that surface oxygen defects can enhance the separation of photo-generated electrons and holes, facilitating their interaction with Pd0 species to form Ti3+ species. More reactive oxygen species (·OH-and ·O2-) were generated on PdTi-10 N due to the synergistic effect of surface oxygen defect and Ti3+ species, which played a significant role as the toluene oxidation. This work provides a new insight for the design and development of high-performance Pd/TiO2 catalysts in the field of indoor VOCs treatment.

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

Exploring highly efficient and robust non-noble metal catalysts for VOC abatement is crucial but challenging. Mn-based perovskites are a class of redox catalysts with good thermal stability, but their activity in the catalytic combustion of light alkanes is insufficient. In this work, we modulated the Mn-O bond strength in a Mn-based perovskite via defect engineering, over which the catalytic activity of propane combustion was significantly enhanced. It demonstrates that the oxygen vacancy concentration and the Mn-O bond strength can be efficiently modulated by finely tuning the Ni content in SmNixMn1-xO3 perovskite catalysts (SNxM1-x), which in turn can enhance the redox ability and generate more active oxygen species. The SN0.10M0.90 catalyst with the lowest Mn-O bond strength exhibits the lowest apparent activation energy, over which the propane conversion rate increases by 3.6 times compared to that on the SmMnO3 perovskite catalyst (SM). In addition, a SN0.10M0.90/cordierite monolithic catalyst can also exhibit a remarkable catalytic performance and deliver excellent long-term durability (1000 h), indicating broad prospects in industrial applications. Moreover, the promotional effect of Ni substitution was further unveiled by density functional theory (DFT) calculations. This work brings a favorable guidance for the exploration of highly efficient perovskite catalysts for light alkane elimination.

In-Depth Understanding of the Oxidative Compatibility of Volatile Organic Compounds with Mn2O3 and Pt-Loaded Catalysts

Designing suitable catalysts for efficiently degrading volatile organic compounds (VOCs) is a great challenge due to the distinct variety and nature of VOCs. Herein, the suitability of different typical VOCs (toluene and acetone) over Pt-based catalysts and Mn2O3 was investigated carefully. The activity of Mn2O3 was inferior to Pt-loaded catalysts in toluene oxidation but showed superior ability for destroying acetone, while Pt loading could boost the catalytic activity of Mn2O3 for both acetone and toluene. This suitability could be determined by the physicochemical properties of the catalysts and the structure of the VOC since toluene destruction activity is highly reliant on Pt0 in the metallic state and linearly correlated with the amount of surface reactive oxygen species (Oads), while the crucial factor that affects acetone oxidation is the mobility of lattice oxygen (Olat). The Pt/Mn2O3 catalyst shows highly active Pt-O-Mn interfacial sites, favoring the generation of Oads and promoting Mn-Olat mobility, leading to its excellent performance. Therefore, the design of abundant active sites is an effective means of developing highly adaptive catalysts for the oxidation of different VOCs.

Efficient Catalytic Elimination of Chlorobenzene Based on the Water Vapor-Promoting Effect within Mn-Based Catalysts: Activity Enhancement and Polychlorinated Byproduct Inhibition

Achieving no or low polychlorinated byproduct selectivity is essential for the chlorinated volatile organic compounds (CVOCs) degradation, and the positive roles of water vapor may contribute to this goal. Herein, the oxidation behaviors of chlorobenzene over typical Mn-based catalysts (MnO2 and acid-modified MnO2) under dry and humid conditions were fully explored. The results showed that the presence of water vapor significantly facilitates the deep mineralization of chlorobenzene and restrains the formation of Cl2 and dichlorobenzene. This remarkable water vapor-promoting effect was conferred by the MnO2 substrate, which could suitably synergize with the postconstructed acidic sites, leading to good activity, stability, and desirable product distribution of acid-modified MnO2 catalysts under humid conditions. A series of experiments including isotope-traced (D2O and H218O) CB-TPO provided complete insights into the direct involvement of water molecules in chlorobenzene oxidation reaction and attributed the root cause of the water vapor-promoting effect to the proton-rich environment and highly reactive water-source oxygen species rather than to the commonly assumed cleaning effect or hydrogen proton transfer processes (generation of active OOH). This work demonstrates the application potential of Mn-based catalysts in CVOCs elimination under practical application conditions (containing water vapor) and provides the guidance for the development of superior industrial catalysts.

Crystal-Phase Engineering in Heterogeneous Catalysis

The performance of a chemical reaction is critically dependent on the electronic and/or geometric structures of a material in heterogeneous catalysis. Over the past century, the Sabatier principle has already provided a conceptual framework for optimal catalyst design by adjusting the electronic structure of the catalytic material via a change in composition. Beyond composition, it is essential to recognize that the geometric atomic structures of a catalyst, encompassing terraces, edges, steps, kinks, and corners, have a substantial impact on the activity and selectivity of a chemical reaction. Crystal-phase engineering has the capacity to bring about substantial alterations in the electronic and geometric configurations of a catalyst, enabling control over coordination numbers, morphological features, and the arrangement of surface atoms. Modulating the crystallographic phase is therefore an important strategy for improving the stability, activity, and selectivity of catalytic materials. Nonetheless, a complete understanding of how the performance depends on the crystal phase of a catalyst remains elusive, primarily due to the absence of a molecular-level view of active sites across various crystal phases. In this review, we primarily focus on assessing the dependence of catalytic performance on crystal phases to elucidate the challenges and complexities inherent in heterogeneous catalysis, ultimately aiming for improved catalyst design.

Binary and nanostructured NiMn perovskite fluorides as efficient electrocatalysts for urea oxidation reaction

Urea electrolysis holds tremendous promise to provide green and sustainable energy and environmental solutions, because it can simultaneously remedy urea-containing wastewater and provide energy-saving hydrogen. However, the development of this emerging technology remains challenging mainly due to a dearth of high-performance electrocatalysts for efficient urea oxidation reaction (UOR). Perovskite fluorides have the advantages of intrinsic 3D diffusion pathways, robust architecture, and tunable chemical composition, thus receiving increasing attention in many applications. In this work, the UOR performances of a series of ABF3 samples (A = K; B = Ni/Mn, Ni/Co, Co/Mn) with various compositions are investigated in a systematic fashion for the first time. Among the binary samples, KNMF41 (Ni/Mn atomic ratio = 4:1) is the optimal sample with reduced overpotential (reaching 100 mA cm-2 at 1.43 V), low Tafel slope (40 mV dec-1), enhanced reaction rate constant (6.3 × 105 cm3 mol-1 s-1), and high turnover frequency (TOF, 0.19 s-1 at 1.60 V) toward urea oxidation. By comparing with NiCo and CoMn samples, the binary NiMn design is confirmed to endow the perovskite fluoride with higher electrocatalytic activity, thanks to the directed adsorption of urea molecules on the adjacent NiMn active sites. This work presents a targeted synthetic strategy for obtaining efficient electrocatalysts.

Co-Fe3C pair sites catalyst with heterometallic dual active sites for efficient oxygen reduction reaction

Newly emerging metal-based pair sites catalysts show great potential because they can provide more metal active centers with synergistic effect for green catalysis, compared with single site catalysts. However, both the synthesis and catalytic mechanisms of the pair sites catalyst with new structural features need to be developed vigorously to promote the desired chemical reactions, especially carbon-based metal catalysts for green energy storage and conversion devices. Herein, we constructed highly active Co-Fe3C pair sites on N-doped graphite catalyst (CNCo-Fe3C) by a two-step strategy, which have electron interactions of heterometallic atoms and can play better synergistic effect. X-ray absorption spectra and density functional theory (DFT) calculation further identify the presence of heterometallic active sites in the pair sites catalyst, resulting in electron redistribution and positive d-band center due to the electron interactions. The more positive d-band center model predicts the optimization of the adsorption energy of oxygen-containing intermediates, and reduces the energy barrier of the determining step. This further results in superior oxygen reduction reaction (ORR) performance with a half-wave potential of 0.90 V versus reversible hydrogen electrode (vs.RHE) and superior long-term stability for about 20 h with only 2.3 % decrease at 0.75 V vs.RHE in 0.1 M KOH solution. Additionally, it also shows significant peak power density of 124 mW cm-2 and prominent cycling stability performance exceeding 400 h at 5 mA cm-2 in the Zn-air battery (ZAB) test, which is higher than that of Pt/C catalyst. This work provides a new idea for the regulation of intrinsic activity of non-noble metal ORR catalysts through the synergistic effect of the pair sites.

Mechanism Study of Organic Sulfur Hydrogenation over Pt- and Pd-Loaded Alumina-Based Catalysts

The hydrogenation of organic sulfur (CS2) present in industrial off-gases to produce sulfur-free hydrocarbons and H2S can be achieved by using noble-metal catalysts. However, there has been a lack of comprehensive investigation into the underlying reaction mechanisms associated with this process. In this study, we have conducted an in-depth examination of the activity and selectivity of Pt- and Pd-loaded alumina-based catalysts, revealing significant disparities between them. Notably, Pd/Al2O3 catalysts exhibit an enhanced performance at low temperatures. Furthermore, we have observed that CS2 displays a higher propensity for conversion to methane when employing Pt/Al2O3 catalysts, while Pd/Al2O3 catalysts demonstrate a greater tendency for coke deposition. By combining experimental observations with theoretical calculations, we revealed that the capability of H2 spillover along with the adsorption capacity of CS2, play pivotal roles in determining the observed differences. Moreover, the key intermediate species involved in the methanation and coke pathways were identified. The intermediate CH2S* is found to be crucial in the methanation pathway, while the intermediate CSH* is identified as significant in the coke pathway.

Sn-based materials in photocatalysis: A review

Development and the application of Sn-based materials have become more prevalent in recent years due to concerns regarding the energy crisis, environmental pollution, and the urgent need of constructing inexpensive and highly effective photocatalysis. The recent advancement in Sn-based materials for efficient photocatalysts, such as Sn alloys, Sn oxides, Sn sulfides, Sn selenides, Sn niobates, Sn tantalites, and Sn tungstates, is summarized in this study. Several design ideas for increasing the photoactivity of Sn-based materials in various photocatalytic applications are emphasized. In addition, we considered their present applications in energy generation (H2 evolution, CO2 reduction, and N2 fixation) and environmental remediation (air purification and wastewater treatment). As a result, the current review will deepen the reader's understanding of the properties and potential uses of Sn-based materials in photocatalysis. Hence, this paper will serve as a guide in promoting the domain of Sn-based materials for future photocatalytic technologies.

Microbial synthesis of titanium dioxide nanoparticles and their importance in wastewater treatment and antimicrobial activities: a review

Nanotechnology (NT) and nanoparticles (NPs) have left a huge impact on every field of science today, but they have shown tremendous importance in the fields of cosmetics and environmental cleanup. NPs with photocatalytic effects have shown positive responses in wastewater treatment, cosmetics, and the biomedical field. The chemically synthesized TiO2 nanoparticles (TiO2 NPs) utilize hazardous chemicals to obtain the desired-shaped TiO2. So, microbial-based synthesis of TiO2 NPs has gained popularity due to its eco-friendly nature, biocompatibility, etc. Being NPs, TiO2 NPs have a high surface area-to-volume ratio in addition to their photocatalytic degradation nature. In the present review, the authors have emphasized the microbial (algae, bacterial, fungi, and virus-mediated) synthesis of TiO2 NPs. Furthermore, authors have exhibited the importance of TiO2 NPs in the food sector, automobile, aerospace, medical, and environmental cleanup.

Constructing an oxygen vacancy- and hydroxyl-rich TiO2-supported Pd catalyst with improved Pd dispersion and catalytic stability

Surface property modification of catalyst support is a straightforward approach to optimize the performance of supported noble metal catalysts. In particular, oxygen vacancies and hydroxyl groups play significant roles in promoting noble metal dispersion on catalysts as well as catalytic stability. In this study, we developed a nanoflower-like TiO2-supported Pd catalyst that has a higher concentration of oxygen vacancies and surface hydroxyl groups compared to that of commercial anatase and P25 support. Notably, due to the distinctive structure of the nanoflower-like TiO2, our catalyst exhibited improved dispersion and stabilization of Pd species and the formation of abundant reactive oxygen species, thereby facilitating the activation of CO and O2 molecules. As a result, the catalyst showed remarkable efficiency in catalyzing the low-temperature CO oxidation reaction with a complete CO conversion at 80 °C and stability for over 100 h.