The role of Bi-doping in promoting electron transfer and catalytic performance of Pt/3DOM-Ce1−Bi O2−δ

Strong metal-support interaction (SMSI) in environmental catalysis: Mechanisms, application, regulation strategies, and breakthroughs

The strong metal-support interaction (SMSI) in supported catalysts plays a dominant role in catalytic degradation, upgrading, and remanufacturing of environmental pollutants. Previous studies have shown that SMSI is crucial in supported catalysts' activity and stability. However, for redox reactions catalyzed in environmental catalysis, the enhancement mechanism of SMSI-induced oxygen vacancy and electron transfer needs to be clarified. Additionally, the precise control of SMSI interface sites remains to be fully understood. Here we provide a systematic review of SMSI's catalytic mechanisms and control strategies in purifying gaseous pollutants, treating organic wastewater, and valorizing biomass solid waste. We explore the adsorption and activation mechanisms of SMSI in redox reactions by examining interfacial electron transfer, interfacial oxygen vacancy, and interfacial acidic sites. Furthermore, we develop a precise regulation strategy of SMSI from systematical perspectives of interface effect, crystal facet effect, size effect, guest ion doping, and modification effect. Importantly, we point out the drawbacks and breakthrough directions for SMSI regulation in environmental catalysis, including partial encapsulation strategy, size optimization strategy, interface oxygen vacancy strategy, and multi-component strategy. This review article provides the potential applications of SMSI and offers guidance for its controlled regulation in environmental catalysis.

Hollow CoFe Oxide Prisms for Cross-Dehydrogenative Coupling Reactions of 1,2,3,4-Tetrahydroisoquinolines under Mild Conditions

A three-dimensional hollow CoFe oxide prism catalyst was successfully prepared via a self-template strategy. This bimetallic oxide catalyst demonstrated excellent catalytic activity in cross-dehydrogenative coupling reactions of 1,2,3,4-tetrahydroisoquinolines under mild conditions compared to its monometallic oxide counterparts. A preliminary mechanistic investigation showed the involvement of reactive oxygen species, produced from molecular O2 by the active bimetallic oxide catalyst in the catalytic cycle.

From bench to industry, the application of all-inorganic solid base materials in traditional heterogeneous catalysis: a mini review

Acids and bases generally occur in pairs as concepts, and a large number of catalytic reactions can be considered as interactions between acids and bases. Many chemical reactions are a combination of acid-catalyzed processes and base-catalyzed processes, and thus it is particularly important to study and explain the mechanisms of acid-base synergy or acid-base interactions. However, compared to the in-depth research on acid catalysts, there is a lack of research on solid bases. In addition to the application of basic materials to non-petroleum processes, recent studies have also applied basic materials to the catalytic cracking reaction process of heavy oils, providing new ideas for the processing of heavy oils. The formation of carbanions with the contribution of basicity is a critical stage in many fine chemical reactions, as well as in the hydrocarbon cracking reactions promoted by a base. Thus, herein, we summarize the research progress on the main types of all-inorganic solid base catalysts, including the types of catalysts used in non-petroleum processes and petroleum processes, their preparation, the properties of their basic sites, and their structure-performance correlation in the reactions. Also, we provide an outlook on the future research directions of all-inorganic solid base materials.

Insight into modified CeMn based catalysts for efficient degradation of toluene by in situ infrared

Trace activated carbon (AC) and diatomaceous earth (DE) were used as structural promoters to be incorporated into Ce-Mn-based solid-solution catalysts by the redox precipitation method. The modified catalysts exhibit superior reducibility, with abundant Ce3+, Mn3+and reactive oxygen species, which are facilitated to the migration of oxygen and the generation of oxygen vacancies. In particular, the catalytic combustion temperatures of 90 % toluene (3000 ppm) on Ce1Mn3Ox-AC/DE were 84 °C (dry) and 123 °C (10 vol% H2O), respectively. The role of lattice oxygen and adsorbed oxygen was revealed by in situ DRIFTS. Additionally, in situ DRIFTS was employed to verify that the degradation of toluene by Ce1Mn3Ox-AC/DE satisfied the Langmuir-Hinshelwood (L-H) mechanism and the Mars-Van Krevelen (MvK) mechanism. The possible reaction pathway was elucidated (toluene → benzyl alcohol → benzoic acid → maleic anhydride → CO2 + H2O). Furthermore, final products attributed to toluene oxidation were detected by in situ DRIFTS at 50 °C in the absence of oxygen, confirming that the catalyst possessed outstanding performance at low temperatures beyond mere adsorption.

Symmetry or asymmetry: which one is the platform of nitrogen vacancies for alkaline hydrogen evolution

Conventional nitrogen vacancies with a symmetric coordination of metal cations (i.e., M1-Nv-M1) play a crucial role in tuning the local environment of the metal sites in metal nitrides and improving their electrochemical activity in the hydrogen evolution reaction (HER). However, the symmetric Nv sites, which feature a uniform charge distribution on adjacent metal sites, suffer from sluggish water dissociation kinetics and a poor capability for hydrogen desorption. Here, we fabricated Cr-doped and Nv-rich Co4N nanorods grown on a Ni foam (Cr-Co4N-Nv/NF) with asymmetric Cr-Nv-Co sites to effectively catalyze hydrogen evolution under alkaline conditions, with a low overpotential of 33 mV at a current density of 10 mA cm-2 and a small Tafel slope of 37 mV dec-1. The experimental characterizations and theoretical simulations collectively reveal that the construction of asymmetric Cr-Nv-Co sites gives rise to the upshift of the d-band center, thus promoting water adsorption and activation. Moreover, asymmetric Nv sites allow a balance between hydrogen adsorption and desorption, which avoids the limited desorption process over the symmetric Co-Nv-Co sites.

Oxygen Vacancy-Induced Metal-Support Interactions in AuPd/ZrO2 Catalysts for Boosting 5-Hydroxymethylfurfural Oxidation

The construction of strong metal-support interactions in oxide-supported noble metal nanocatalysts has been considered an emerging and efficient way in improving catalytic performance in biomass-upgrading reactions. Herein, a citric acid (CA)-assisted synthesized ZrO2 layer with improved oxygen vacancy (Ov) concentrations on a natural clay mineral of halloysite nanotubes (HNTs) was designed. Moreover, AuxPdy/ZrO2@HNTs-zCA catalysts were prepared by loading AuPd bimetal and employed for aerobic oxidation of the lignocellulosic biomass-derived 5-hydroxymethylfurfural (HMF) platform to the bioplastic monomer 2,5-furandicarboxylic acid (FDCA) with water as the solvent. The results of catalytic experiments revealed that the Au3Pd1/ZrO2@HNTs-1.0CA catalyst exhibited excellent catalytic activity at 0.5 MPa O2, with a satisfactory FDCA yield of 99.5% and outstanding FDCA formation rate of 1057.9 mmol·g-1·h-1. The improved Ov concentration in the ZrO2 support enhanced the adsorption and activation ability of the catalyst for O2, and a higher Lewis acid concentration provided a stronger adsorption ability of the catalyst for reaction substrates. Besides, the synergistic effect of AuPd bimetallic nanoparticles steered the tandem oxidation of aldehyde and alcohol groups in HMF and accelerated the rate-determining step. More importantly, the relationship between the Ov concentration and catalytic performance also demonstrated that the enhanced catalytic activity for HMF oxidation was mainly attributed to the active interface of AuPd-ZrOx. This work offers fresh insights into rationally designing oxygen vacancy-driven strong interactions between the oxide support and noble nanoparticles for the catalytic upgrade of biomass platform chemicals.

Rare Earth Doping Engineering Tailoring Advanced Oxygen-Vacancy Co3 O4 with Tunable Structures for High-Efficiency Energy Storage

Co₃ O₄  with high theoretical capacitance is a promising electrode material for high-end energy applications, yet the unexcited bulk electrochemical activity, low conductivity, and poor kinetics of Co₃ O₄  lead to unsatisfactory charge storage capacity. For boosting its energy storage capability, rare earth (RE)-doped Co₃ O₄  nanostructures with abundant oxygen vacancies are constructed by simple, economical, and universal chemical precipitation. By changing different types of RE (RE = La, Yb, Y, Ce, Er, Ho, Nd, Eu) as dopants, the RE-doped Co₃ O₄  nanostructures can be well transformed from large nanosheets to coiled tiny nanosheets and finally to ultrafine nanoparticles, meanwhile, their specific surface area, pore distribution, the ratio of Co²⁺ /Co³⁺ , oxygen vacancy content, crystalline phase, microstrain parameter, and the capacitance performance are regularly affected. Notably, Eu-doped Co₃ O₄  nanoparticles with good cycle stability show a maximum specific capacitance of 1021.3 F g^-1 (90.78 mAh g^-1 ) at 2 A g^-1 , higher than 388 F g^-1 (34.49 mAh g^-1 ) of pristine Co₃ O₄  nanosheets. The assembling asymmetric supercapacitor delivers a high energy density of 48.23 Wh kg^-1  at high power density of 1.2 kW kg^-1 . These findings denote the significance and great potential of RE-doped Co₃ O₄  in the development of high-efficiency energy storage.

Cerium-Bismuth Oxides/Oxynitrates with Low Toxicity for the Removal and Degradation of Organophosphates and Bisphenols

Nanoscale cerium-bismuth oxides/oxynitrates were prepared by a scalable low-temperature method at ambient pressure using water as the sole solvent. Solid solutions were formed up to a 1:1 Ce/Bi molar ratio, while at higher doping levels, bismuth oxynitrate photocatalysts with a pronounced layered structure were formed. Bismuth caused significant changes in the structure and surface properties of nanoceria, such as the formation of defects, oxygen-containing surface groups, and Lewis and Brønsted acid sites. The prepared bifunctional adsorbents/photocatalysts were efficient in the removal of toxic organophosphate (methyl paraoxon) from water by reactive adsorption followed by photocatalytic decomposition of the parent compound and its degradation product (p-nitrophenol). Bi-doped ceria also effectively adsorbed and photodegraded the endocrine disruptors bisphenols A and S and outperformed pure ceria and the P25 photocatalyst in terms of efficiency, durability, and long-term stability. The very low toxicity of Bi-nanoceria to mammalian cells, aquatic organisms, and bacteria has been demonstrated by comprehensive in vivo/in vitro testing, which, in addition to its simple "green" synthesis, high activity, and durability, makes Bi-doped ceria promising for safe use in abatement of toxic chemicals.

Leveraging Pt/Ce1-xLaxO2-δ To Elucidate Interfacial Oxygen Vacancy Active Sites for Aerobic Oxidation of 5-Hydroxymethylfurfural

The interfacial oxygen-defective sites of oxide-supported metal catalysts are generally regarded as active centers in diverse redox reactions. Identification of their structure-property relationship at the atomic scale is of great importance but challenging. Herein, a series of La³⁺-doped three-dimensionally ordered macroporous CeO₂ (3D-Ce_1-xLa_xO_2-δ) were synthesized and applied as supports for Pt nanoparticles. The pieces of evidence from a suite of in-situ/ex-situ characterizations and theoretical calculations revealed that the La³⁺-mono-substituted La-□(-Ce)₂ sites (where □ represents an oxygen vacancy) exhibited superior charge transfer ability, behaving as trapping centers for Pt nanoparticles. The resulting interfacial Pt^δ+/La-□(-Ce)₂ sites served as the reversible active species in the aerobic oxidation of 5-hydroxymethylfurfural to boost catalytic performance by simultaneously promoting oxygen activated capacity and the cleavage of O-H/C-H bonds of adsorbed hydroxymethyl groups. Consequently, the Pt/3D-Ce_0.9La_0.1O_2-δ catalyst possessing the highest number of Pt^δ+/La-□(-Ce)₂ sites showed the best catalytic performance with 99.6% yield to 2,5-furandicarboxylic acid in 10 h. These results offer more insights into the promoting mechanism of interfacial oxygen-defective sites for the liquid-phase aerobic oxidation of aldehydes and alcohols.

Crystal Faces-Tailored Oxygen Vacancy in Au/CeO2 Catalysts for Efficient Oxidation of HMF to FDCA

Developing an efficient catalyst to upgrade 5-hydroxymethylfurfural (HMF) to high-value-added downstream chemicals is of great significance in biomass conversion. Nanorod (110)-, nanocube (100)-, and nanooctaheron (111)-CeO₂ -supported Au nanoparticles were prepared to investigate the intrinsic effect of CeO₂ crystal faces on the oxidation of HMF to 2,5-furandicarboxylic acid (FDCA). The experimental results and density functional theory calculation revealed that the concentration of oxygen vacancy (V_O ) for exposed specific crystal faces was crucial to the oxygen adsorption ability, and Au/nanorod-CeO₂ with the highest V_O concentration promoted the formation of more oxygen active species (superoxide radical) on CeO₂ (110) crystal face than (100) and (111) crystal faces. Besides, the higher V_O concentration could provide a strong adsorption ability of HMF, greatly boosting the activation of HMF. Thus, these results led to a superior catalytic activity for HMF oxidation over Au/nanorod-CeO₂ (FDCA yield of 96.5 %). In-situ Fourier-transform (FT)IR spectroscopy uncovered the HMF oxidation pathway, and the possible catalytic mechanism was proposed. The deep insight into the role of regulation for crystal faces provides a basis for the rational design of highly active facets for the oxidation of HMF and related reactions.

Au-Pd separation enhances bimetallic catalysis of alcohol oxidation

In oxidation reactions catalysed by supported metal nanoparticles with oxygen as the terminal oxidant, the rate of the oxygen reduction can be a limiting factor. This is exemplified by the oxidative dehydrogenation of alcohols, an important class of reactions with modern commercial applications^1-3. Supported gold nanoparticles are highly active for the dehydrogenation of the alcohol to an aldehyde⁴ but are less effective for oxygen reduction^5,6. By contrast, supported palladium nanoparticles offer high efficacy for oxygen reduction^5,6. This imbalance can be overcome by alloying gold with palladium, which gives enhanced activity to both reactions^7,8,9; however, the electrochemical potential of the alloy is a compromise between that of the two metals, meaning that although the oxygen reduction can be improved in the alloy, the dehydrogenation activity is often limited. Here we show that by separating the gold and palladium components in bimetallic carbon-supported catalysts, we can almost double the reaction rate compared with that achieved with the corresponding alloy catalyst. We demonstrate this using physical mixtures of carbon-supported monometallic gold and palladium catalysts and a bimetallic catalyst comprising separated gold and palladium regions. Furthermore, we demonstrate electrochemically that this enhancement is attributable to the coupling of separate redox processes occurring at isolated gold and palladium sites. The discovery of this catalytic effect-a cooperative redox enhancement-offers an approach to the design of multicomponent heterogeneous catalysts.

Praseodymia–titania mixed oxide supported gold as efficient water gas shift catalyst: modulated by the mixing ratio of oxides

Modulating the active sites for controllable tuning of the catalytic activity has been the goal of much research, however, this remains challenging. The O vacancy is well known as an active site in reducible oxides. To modify the activity of O vacancies in praseodymia, we synthesized a series of praseodymia–titania mixed oxides. Varying the Pr : Ti mole ratio (2 : 1, 1 : 2, 1 : 1, 1 : 4) allows us to control the electronic interactions between Au, Pr and Ti cations and the local chemical environment of the O vacancies. These effects have been studied study by X-ray photoelectron spectroscopy (XPS), CO diffuse reflectance Fourier transform infrared spectroscopy (CO-DRIFTS) and temperature-programmed reduction (CO-TPR, H₂-TPR). The water gas shift reaction (WGSR) was used as a benchmark reaction to test the catalytic performance of different praseodymia–titania supported Au. Among them, Au/Pr₁Ti₂O_x was identified to exhibit the highest activity, with a CO conversion of 75% at 300 °C, which is about 3.7 times that of Au/TiO₂ and Au/PrO_x. The Au/Pr₁Ti₂O_x also exhibited excellent stability, with the conversion after 40 h time-on-stream at 300 °C still being 67%. An optimal ratio of Pr content (Pr : Ti 1 : 2) is necessary for improving the surface oxygen mobility and oxygen exchange capability, a higher Pr content leads to more O vacancies, however with lower activity. This study presents a new route for modulating the active defect sites in mixed oxides which could also be extended to other heterogeneous catalysis systems.

Schematic illustration of H₂O activation on the Pr-TiO_x support and the following reaction with CO in the Au–oxide interface.

Activation of molecular oxygen over Mn-doped La2CuO4 perovskite for direct epoxidation of propylene

The synergetic interaction between manganese and copper in LaMn0.5Cu0.5O3 significantly promoted the epoxidation of propylene at lower temperature by converting the active sites from oxygen vacancies to Cu active sites of Cu–O–Mn.

A strategy of asymmetric local structure based on mesoporous MoO2 toward efficient electrocatalysis

Combined with density functional theory (DFT) calculations, a substitutional heteroatom-doping approach is employed to design asymmetric local structures based on highly ordered mesoporous MoO2 nanostructures. Such synergistic strategies on increasing both the number and intrinsic activity of active sites jointly lead to a significant water oxidation performance boost.

Boosting Interfacial Electron Transfer between Pd and ZnTi-LDH via Defect Induction for Enhanced Metal-Support Interaction in CO Direct Esterification Reaction

Strong metal-support interaction is crucial to the stability of catalysts in heterogeneous catalysis. However, reports on boosting interfacial electron transfer between metal and support via defect induction for enhanced metal-support interaction are limited. In this work, ultrathin reducible ZnTi-layered double hydroxide (LDH) nanosheets with rich oxygen defects were synthesized to stabilize Pd clusters, and the rich oxygen defects promoted Pd cluster bonding with Zn and Ti atoms in supports, thereby forming a metal-metal bond. Electron spin resonance (ESR), X-ray absorption fine spectra (XAFS), and density functional theory (DFT) calculations demonstrate remarkable interfacial electron transfer (0.62 e). The Pd/ZnTi-LDH catalyst shows superior catalytic stability for CO direct esterification to dimethyl oxalate. By contrast, the nonreducible Pd/ZnAl-LDH catalyst with a few oxygen defects shows minimal interfacial electron transfer (0.08 e), which leads to relatively poor catalytic stability. This work provides a deep insight into promoting the stability of catalysts by boosting interfacial electron transfer via defect induction.

Fabrication of stable high-performance urchin-like CeO2/ZnO@Au hierarchical heterojunction photocatalyst for water remediation

In this paper, the urchin-like CeO₂/ZnO@Au photocatalyst was rationally designed and prepared through hydrothermal method, chemical precipitation and photo reduction deposition. The optimal photocatalyst (CZA8) degraded Rhodamine B (RhB), 4-nitrophenol (4-NP) and Naproxen (NPX) about 100% within 20 min, 91.4% within 60 min and 88.9% within 30 min under Xe lamp illumination, respectively. Besides, the CZA8 possesses outstanding photo corrosion resistance capacity which has been verified with the cycle degradation experiments. The photocatalyst displays excellent light response and efficient separation of photo-induced carriers due to the fabrication of type-II heterojunction, the presence of surface plasmon resonance (SPR) effect and as well as the oxygen vacancy. The oxygen vacancy was systematically characterized by XPS, PL and Raman. Moreover, the photocatalytic degradation pathways are proposed based on the LC-MS results. Finally, a novel photocatalytic mechanism for photocatalytic oxidation of RhB, 4-NP and NPX is discussed and schematically illuminated.

Promotional removal of oxygenated VOC over manganese-based multi oxides from spent lithium-ions manganate batteries: Modification with Fe, Bi and Ce dopants

In this work, cathode materials of spent lithium-ions manganate batteries are recovered as the precursor of manganese-based oxides catalysts and furthermore, different amount of Fe, Bi, Ce are introduced to modify their properties. A series of MnOx(MS)-X Fe, MnOx(MS)-X Bi and MnOx(MS)-X Ce samples with crystal phase of Mn₅O₈ are synthesized using combustion method and then the catalytic behavior and physicochemical properties of prepared catalysts are investigated. Compared to binary MnOx-5% Fe, MnOx-15% Bi and MnOx-10% Ce samples, multi MnOx(MS)-5% Fe, MnOx(MS)-15 Bi and MnOx(MS)-10% Ce catalysts display enhanced catalytic performance significantly in the removal of oxygenated VOC, which could be attributed to larger specific surface area, higher concentration of surface active oxygen species and Mn⁴⁺ ions and better reducibility at low temperature. In-situ DRIFTS results imply that main oxygen-containing functional groups such as carbonyl (-C=O), carboxyl (-COO), hydroxyl (-OH) can be observed during VOC oxidation and by comparison, it can be found that gas-phase O₂ plays a crucial role in facilitating the further oxidation of by-products into CO₂. In addition, TD/GC-MS results point out that the main by-products are formaldehyde; 2-propanol, 1-methoxy-; ethanol, 2-methoxy-, acetate; 2-ethoxyethyl acetate; acetic acid during VOC oxidation.

Oxidation of lignocellulosic platform molecules to value-added chemicals using heterogeneous catalytic technologies

This minireview gives an overview about heterogeneous catalytic technologies for the oxidation of key platform molecules (glucose, 5-hydroxymethylfurfural, furfural and levulinic acid) into valuable chemicals.

Asymmetric Oxygen Vacancies: the Intrinsic Redox Active Sites in Metal Oxide Catalysts

To identify the intrinsic active sites in oxides or oxide supported catalysts is a research frontier in the fields of heterogeneous catalysis and material science. In particular, the role of oxygen vacancies on the redox properties of oxide catalysts is still not fully understood. Herein, some relevant research dealing with M1-O-M2 or M1-□-M2 linkages as active sites in mixed oxides, in oxide supported single-atom catalysts, and at metal/oxide interfaces of oxide supported nanometal catalysts for various reaction systems is reviewed. It is found that the catalytic activity of these oxides not only depends on the amounts of oxygen vacancies and metastable cations but also shows a significant influence from the local environment of the active sites, in particular, the symmetry of the oxygen vacancies. Based on the recent progress in the relevant fields, an "asymmetric oxygen vacancy site" is introduced, which indicates an oxygen vacancy with an asymmetric coordination of cations, making oxygen "easy come, easy go," i.e., more reactive in redox reactions. The establishment of this new mechanism would shed light on the future investigation of the intrinsic active sites in oxide and oxide supported catalysts.

Selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over Au/CeO2 catalysts: the morphology effect of CeO2

A morphological effect of Au/CeO₂ catalysts in 5-hydroxymethylfurfural (HMF) oxidation.

Effect of the oxygen coordination environment of Ca–Mn oxides on the catalytic performance of Pd supported catalysts for aerobic oxidation of 5-hydroxymethyl-2-furfural

Pd/CaMn₂O₄ provides ideal active sites for oxygen adsorption and desorption, resulting in the promoted charge transfer ability and catalytic activity.