Fabrication of highly dispersed Pd-Mn3O4 catalyst for efficient catalytic propane total oxidation

Adjusting the interaction between dual active components for enhancing volatile organic compounds (VOCs) degradation is an effective but still challenging means of air pollution control. Herein, a limited pyrolysis oxidation strategy was adopted to prepare Pd-Mn3O4 spinel catalysts with uniform morphology and active component dispersion. Among these, 1.08Pd-Mn3O4 presented the highest catalytic efficiency with a T90 value of 240 °C, which was 94 °C lower than that of Mn3O4. Characterization and density functional theory (DFT) calculation results revealed that the strong metal-support interaction (SMSI) effect between Pd and Mn3O4 promoted the redistribution of surface charges, thus strengthening the oxidation-reduction ability of the active sites. Moreover, the SMSI effect led to a better migration of surface oxygen species, and boosted the generation of active surface oxygen species. Simultaneously, the Pd catalyst further reduced the energy barrier in the initial stage of the dehydrogenation of propane. Overall, this study provided a novel design strategy for dual active components catalysts with SMSI effect and extended the application of these catalysts in the important field of VOCs elimination.

Investigating the impact of TiO2 crystalline phases on catalytic properties of Ru/TiO2 for hydrogenolysis of polyethylene plastic waste

A series of TiO₂-supported Ru catalysts with different TiO₂ crystalline phases was synthesized and employed for the hydrogenolysis of polyethylene (PE). CO chemisorption, high-angle annular dark-field-scanning transmission electron microscopy, temperature-programmed reduction, and CO-Fourier transform infrared spectroscopy suggested that the degree of strong metal-support interactions (SMSIs) varied depending on the type of the TiO₂ phase and the reduction temperature, eventually influencing the catalysis of PE hydrogenolysis. Among the synthesized catalysts, Ru/TiO₂ with the rutile phase (Ru/TiO₂-R) exhibited the highest catalytic activity after high-temperature reduction at 500 °C, indicating that a certain degree of SMSI is necessary for ensuring high activity in PE hydrogenolysis. Ru/TiO₂-R could be successfully employed for the hydrogenolysis of post-consumer plastic wastes such as LDPE bottles to produce valuable chemicals (liquid fuel and wax) in high yields of 74.7%. This work demonstrates the possibility of harnessing the SMSIs in the design and synthesis of active catalysts for PE hydrogenolysis.

Easily Scalable Shell-Structured Copper Catalyst with High Activity and Durability for Carbon Dioxide Hydrogenation

Inducing strong metal-support interaction (SMSI) has been a useful way to control the structure of surface active sites. The SMSI often causes the encapsulation of metal particles with an oxide layer. Herein, an amorphous ceria shell was formed on Cu nanoparticles under a mild gas condition with high activity and durability for surface reaction. Cu-Ce solid solution promoted the transfer of surface oxygen species, which induced the ceria shell formation on Cu nanoparticles. This catalyst was used for CO2 hydrogenation, selectively producing CO with high low-temperature activity and good durability for operation at high temperature. CO2 activation and H2 spillover could occur at low temperatures, enhancing the activity. The shell prevented the sintering, assuring durability. This catalyst was applied to a bench-scale reactor without loss in performance, resulting in high CO productivity in all temperature ranges.

Pt modified NiMoO4-GO/NF nanorods withstrong metal-support interaction as efficient bifunctional catalysts for overall water splitting

Catalysts for the electrolysis of water are critical in the production of hydrogen for the energy industry. The use of strong metal-support interactions (SMSI) to modulate the dispersion, electron distribution, and geometry of active metals is an effective strategy for improving catalytic performance. However, in currently used catalysts, the supporting effect does not significantly contribute directly to catalytic activity. Consequently, the continued investigation of SMSI, using active metals to stimulate the supporting effect for catalytic activity, remains very challenging. Herein, the atomic layer deposition technique was employed to prepare an efficient catalyst composed of platinum nanoparticles (Pt NPs) deposited on nickel-molybdate (NiMoO₄) nanorods. Nickel-molybdate's oxygen vacancies (V_o) not only help anchor highly-dispersed Pt NPs with low loading but also strengthen the SMSI. The valuable electronic structure modulation between Pt NPs and V_o resulted in a low overpotential of the hydrogen and oxygen evolution reactions, returning results of 190 mV and 296 mV, respectively, at a current density of 100 mA cm^-2 in 1 M KOH. Ultimately, an ultralow potential (1.515 V) for the overall decomposition of water was achieved at 10 mA cm^-2, outperforming state-of-art catalysts based on the Pt/C || IrO₂ couple (1.668 V). This work aims to provide reference and a concept for the design of bifunctional catalysts that apply the SMSI effect to achieve a simultaneous catalytic effect from the metal and its support.

The preparation of ultrastable Al3+ doped CeO2 supported Au catalysts: Strong metal-support interaction for superior catalytic activity towards CO oxidation

The classical strong metal-support interaction (SMSI) plays a key role in improving thermal stability for supported Au catalysts. However, it always decreases the catalytic activity because of the encapsulation of Au species by support. Herein, we demonstrate that Al³⁺ is a functional additive which could effectively improve both catalytic activity and sintering resistant property for H₂ pretreated Al³⁺ doped CeO₂ supported Au (AuCeAl) catalyst at high temperature. The physical characterization and in-situ DRIFTS results provide insight that more oxygen vacancies generated by Al³⁺ doping could be as preferential adsorption sites for CO molecules when the encapsulation of Au species occurred, which is certificated by an accelerated formation of bicarbonate species. In the meantime, smaller Au nanoparticles with higher dispersion (2.8 nm, 85.63%) is achieved in AuCeAl catalysts, compared with that in CeO₂ supported Au (AuCe) catalysts (5.1 nm, 36.17%). Additionally, the as-prepared AuCeAl catalysts also have superior catalytic performance even after calcination at 800 °C in air.

Pt/MnOx for toluene mineralization via ozonation catalysis at low temperature: SMSI optimization of surface oxygen species

The problem of deep oxidation of low concentrations of VOCs in industrial tail gas is exceptionally urgent. The preparation of VOCs ozonation catalyst with a high mineralization rate is still a challenge. In this paper, manganese oxide carriers with different morphologies were synthesized by simple methods and used to catalyze ozone mineralization of toluene after loading Pt nanoparticles efficiently. The conversion of toluene over Pt/MnO_x-T catalyst was more than 98 % at ambient temperature, and the mineralization rate of toluene was close to 100 % at 70 °C. Through a variety of characterization methods, the strong metal-support interaction (SMSI) between Pt nanoparticles and carriers was successfully constructed. It was found that SMSI successfully optimized the surface oxygen species and oxygen migration ability of the catalyst, and then realized the high degree of mineralization of toluene at low temperature. This paper guides the subsequent development of Pt-Mn catalysts for catalytic organic pollutants ozonation with high activity.

Enhanced hydrogen evolution reaction in alkaline solution by constructing strong metal-support interaction on Pd-CeO2-x-NC hybrids

Diminishing the size of metal nanostructures can significantly improve the performance of catalysts. However, the self-aggregation of small particles is still an insurmountable obstacle, resulting in the unfavorable stability and recyclability. Herein, we designed and fabricated the Pd-CeO_2-x-NC catalyst though an accurate deposition strategy to downsize the Pd particle to sub-nanometer level and enhance its running stability. The CeO_2-x nanoclusters were firstly dispersed on the nitrogen-doped carbon nanosheets. Further, the active Pd sub-nanoclusters were accurately scattered on the surface of CeO_2-x ascribing to the strong metal-support interaction (SMSI) between Pd and CeO_2-x, which was beneficial to promote the catalytic activity. Subsequently, the high oxidation state Pdⁿ⁺ species were formed due to the electron transfer from Pd to CeO_2-x caused by the SMSI effect. Strikingly, the HER performance of Pd-CeO_2-x-NC was surprisingly correlated with the ratio of Pdⁿ⁺, suggesting Pdⁿ⁺ acted as the dominant active species. Besides, the SMSI effect stabilized the valence state of active Pdⁿ⁺ species and prevented the sub-nanometer Pd clusters from aggregation, which played a vital role for the enhanced stability of the hybrid catalyst. This synthetic process described here is contributed to prepare various nanostructured catalysts with satisfactory stability through the direct targeting strategy.

Recent advances in single-atom catalysts for advanced oxidation processes in water purification

Single-atom catalysts (SACs) have attracted considerable attention from researchers because of their distinct structures and characteristics, especially in maximizing atomic utilization and elevating the intrinsic catalytic activity. More recently, SACs have been becoming a burgeoning area of the environmental field and are extensively applied to remove various refractory organic pollutants. This review summarizes the emerging synthetic and characterization strategies of SACs and analyzes their development tendency. Besides, the application of SACs in advanced oxidation processes (AOPs, e.g., catalysis of H₂O₂, activation of persulfates and photocatalysis) is discussed. The excellent removal of pollutants depends on the fast generation of reactive oxygen species (SO₄^•-, ^•OH, ¹O₂, and O₂^•-). The advantages of SACs in AOPs are summarized, and constructive opinions are put forward for the stability and activity of the catalyst. Finally, the opportunities and challenges faced by SACs and its future development direction in the AOPs catalytic field are proposed.

Pt-support interaction and nanoparticle size effect in Pt/CeO2-TiO2 catalysts for low temperature VOCs removal

A series of Pt/CeO₂-TiO₂ catalysts (0.5 wt% Pt) with size-controllable Pt nanoparticles were prepared by a modified ethylene glycol reduction method and the Pt particle size effect of Pt/CeO₂-TiO₂ catalysts on benzene and 1,2-dichloroethane (DCE) degradation was investigated. It reveals that the metal-support interaction of PtO_x species and CeO₂-TiO₂ mixed oxides is enhanced by the reduced Pt particle sizes. The formation of more Pt²⁺ species and stronger redox properties at low-temperature resulted by the enhanced metal-support interaction of Pt/CeO₂-TiO₂ catalysts both greatly promotes the deep oxidation for benzene and C₂H₃Cl byproduct during DCE degradation at low temperature. Pt/CeTi-11 with the smallest average Pt particle size (1.53 nm) exhibits the highest activity among all the catalysts for benzene degradation, with T_90% of only 152 °C (1000 ppm, GHSV = 15,000 h^-1). However, more acidic sites (especially the strong acid) were formed on the Pt/CeO₂-TiO₂ catalysts with bigger Pt nanoparticle (>2.95 nm), contributing to activate and convert DCE to C₂H₃Cl. More importantly, Pt/CeO₂-TiO₂ catalysts are extremely stable in DCE degradation reaction, and have been scarcely influenced by the presence of benzene and water in the feed gases.

Enhancement of catalytic toluene combustion over Pt-Co3O4 catalyst through in-situ metal-organic template conversion

A Pt-Co₃O₄ catalyst named Pt-Co(OH)₂-O was prepared by metal-organic templates (MOTs) conversion and used for catalytic oxidation of toluene. Through the conversion, the morphology of catalysts transformed from rhombic dodecahedron to nanosheet and the coated Pt nanoparticles (NPs) were more exposed. The Binding energy shift in XPS test indicates that the strong metal-support strong interaction (SMSI) has enhanced, and the physicochemical changes caused by it are characterized by other techniques. At the same time, Pt-Co(OH)₂-O showed the best catalytic performance (T₅₀ = 157 °C, T₉₀ = 167 °C, E_a = 40.85 kJ mol^-1, TOF_Pt = 2.68 × 10^-3 s^-1) and good stability. In addition, the in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) studies have shown that because SMSI weakened the Co-O bond, the introduction of Pt NPs can make the migration of oxygen in the catalyst easier. The change of binding energy change and the content of various species in the quasi in situ XPS experiment further confirmed that the Pt-Co(OH)₂-O catalyst has stronger SMSI, resulting in its stronger electron transfer ability and oxygen migration ability, which is conducive to catalytic reactions. This work provides new ideas for the development of supported catalysts and provides a theoretical reference for the relevant verification of SMSI.

In situ electrochemical redox tuning of Pd-Co hybrid electrocatalysts for high-performance methanol oxidation: Strong metal-support interaction

Construction of strong metal-support interaction (SMSI) is of fundamental interest in the preparation of supported metal nanoparticle catalysts with enhanced catalytic activity. Herein, we report a facile in situ electrochemical redox tuning approach to build strong interactions between metals and supports. As for a typical example, a composite electrocatalyst of Pd-Co hybrid nanoparticles directly developed on Ni substrate is found to follow a distinct surface self-reconstruction process in alkaline media via an in situ electrochemical redox procedure, which results in structural transition from the original nanoparticles (NPs) to nanosheets (NSs) coupled with a phase transformation of the Co component, Co → CoO/Co(OH)₂. The SMSI is observed in the electrochemically tuned Pd-Co hybrid system and leads to significantly enhanced catalytic activity for methanol oxidation reaction (MOR) due to the modified atomic/electronic structure, increased surface area, and more exposed electroactive sites. Compared with commercial Pd/C catalyst, the electrochemically tuned Pd-Co hybrid catalyst with SMSI exhibits superior catalytic activity (2330 mA∙mg_Pd^-1) and much better stability (remains 503 mA∙mg_Pd^-1 after 1000 cycles and 172 mA∙mg_Pd^-1 after 5000 s), and therefore has great potential in practical applications.

DFT study the water-gas shift reaction over Cu/α-MoC surface

Cu-based catalysts have been widely used for water-gas shift reaction (WGS, CO + H₂O → CO₂ + H₂), and α-MoC support also shows the good performance for the reaction. Therefore, WGS reaction is systematically studied over Cu/α-MoC by using density functional theory (DFT). DFT result shows the strong metal-support interaction between Cu and α-MoC(111) support. As a result, an extensive tensile strain is introduced in the Cu lattice due to α-MoC support, and Cu 3d band center shifts to Fermi level. However, the strong metal-support interaction does not lead to significant polarization of the Cu/α-MoC surface due to the less charge transfer from Mo to Cu. For the WGS reaction, small Cu particles on α-MoC(111) are likely to facilitate the reaction. At the interface of Cu-α-MoC(111), oxygen stabilizes the dissociated *H, which is benefit of H₂O scission. Then, the activity increases compared with Cu(111) surface. In general, small Cu particles on α-MoC support also have good activity for WGS reaction compared with Au deposition on α-MoC. Graphical abstract.

Promotion effect of strong metal-support interaction to thermocatalytic, photocatalytic, and photothermocatalytic oxidation of toluene on Pt/SrTiO3

The importance of strong metal-support interaction (SMSI) in reducible oxide supported noble metal nanoparticles (NP) has been recognized in many thermocatalytic systems but rarely explored in photocatalytic and photothermocatalytic systems. Herein, the promotion effect of SMSI in strontium titanate (STO) supported Pt NP for thermocatalytic, photocatalytic, and photothermocatalytic oxidation (TCO, PCO and PTO) of toluene is reported. SMSI in Pt/STO is achieved through calcination in air (Air-Pt/STO), reduction in H₂ atmosphere (H₂-Pt/STO), wet reduction in HCHO solution (HCHO-Pt/STO) or NaBH₄ solutions (NaBH₄-Pt/STO), resulting in the formation of chemisorbed oxygen and negatively charged Pt NP and promoting oxygen activation in TCO and surface plasmon resonance effects of Pt NP in visible-light-induced PCO and PTO. Both TCO and PCO activities go along with the degree of SMSI as Air-Pt/STO > H₂-Pt/STO > HCHO-Pt/STO > NaBH₄-Pt/STO. Under both visible-light illuminating and thermal environment at 150 °C, the PTO toluene degradation efficiency of Air-Pt/STO is further improved with a factor of 32 times or 9 times than the single PCO or TCO process. The unique synergistic photothermocatalytic oxidation performance of Air-Pt/STO is ascribed to the function of Pt NP and the effect of SMSI. Our findings provide a facile way to design multifunctional supported noble metal catalysts for efficient VOCs degradation process.

In-situ green assembly of spherical Mn-based metal-organic composites by ion exchange for efficient electrochemical oxidation of organic pollutant

In this study, we develop a facile ion exchange strategy for in-situ assembly of novel spherical metal-organic composites on a large scale. The functional groups (-NH₂, -COOH and -SO₃H) on chelating and exchange resins had significant effects on improving uniform distribution of metallic sites and metal-support interaction. Without any addition of H₂O₂, Mn-based metal-organic composites realized the recovery of waste metallic ions and exhibited high activity for methylene blue (MB) electro-Fenton degradation (97.8% decoloration and 54.7% TOC removal) within 150 min under low current density (7.53 mA·cm^-2) and 3.0 g·L^-1 catalyst dosage. Analyses of performance on different active sites (Fe^II, Mn^II, Co^II, Ce^III and Cu^II) and supports clearly indicated that synergetic effect of Mn^II and organic supports played crucial roles in electrochemical oxidation. Kinetic rate constant of 0.037 min^-1 and turn over frequency of 0.23 h^-1 were much better than those of inorganic supported catalysts, which were attributed to intramolecular electron transfer greatly accelerating Mn^II/Mn^III autocatalytic cycle. Meanwhile, possible degradation pathway of MB was proposed by analysis of oxidative intermediate products. Benefiting from excellent properties and millimeter-level size structure, metal-organic composites can be applied in wide pH range of 2.0-9.0 and easily separated in the industrial application.