Metal-support Interaction Effect Research Articles

Catalytic boosting on AuCu bimetallic nanoparticles by oxygen-induced atomic restructuring

Understanding the structure-activity relationship over silica-supported Au-based bimetallic nanocatalysts in CO oxidation is essential in elucidating active sites and catalytic mechanisms. Here, we uncover that structure-activity relationship over a silica-supported 10 nm sized AuCu bimetallic model nanocatalyst for CO oxidation. Oxygen–induced atomic restructuring of AuCu nanocrystals is comprehensively investigated using combined operando spectroscopic and microscopic techniques, including near-ambient-pressure X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier-transform spectroscopy, and environmental transmission electron microscopy. We show that the formation of CuOx/Au heterostructure gives rise to the enhancement of catalytic activity for CO oxidation. The formation of the reactive heterostructure on catalysis was rationalized by density functional theory calculation. Our results indicate that intermediate heterostructure with a metal-oxide interface leads to strong electronic coupling between catalyst and support (i.e., electronic metal-support interaction effect).

Boosting electrocatalytic performance and durability of Pt nanoparticles by conductive MO2−x (M = Ti, Zr) supports

Metal oxides, especially TiO2, have been studied as an alternative support to replace the carbon in the conventional Pt/C catalysts for their high electrochemical stability at high electrode potentials. The low conductivity of metal oxides has been a big hurdle. In this work, we successfully overcome this issue by forming conductive MO2−x (M = Ti and Zr) through solid state reduction with NaBH4. The temperature of the reaction has turned out to be a crucial parameter to obtain highly conductive MO2−x. Pt/MO2−x catalysts were prepared by depositing Pt nanoparticles (NPs) on MO2−x supports whose analysis data, show that the Pt NPs are uniformly deposited on the surface of MO2−x supports and that there is a strong electronic interaction between Pt NPs and MO2−x supports. The electrocatalysis of Pt/MO2−x catalysts for oxygen reduction reaction (ORR) has been studied. Pt/MO2−x catalysts show significantly enhanced mass activity (MA) and specific activity (SA) from those of Pt/C catalyst. More importantly, Pt/MO2−x catalysts show a superior long-term durability. After 50,000 cycles of durability test, Pt/T370 catalyst retains 75%/84% of initial MA/SA, and Pt/Z438 catalyst retains 81%/88% of initial MA/SA, while Pt/C catalyst keeps only 36%/56% of initial MA/SA after 30,000 cycles. The significantly enhanced ORR performance of Pt/MO2−x catalysts is attributed to the strong metal-support interaction (SMSI) effect between MO2−x and Pt NPs as well as the high conductivity of MO2−x supports. We believe Pt/MO2−x catalysts are a promising form of electrocatalysts that can replace the presently dominating but not quite satisfactory Pt/C in fuel cell applications.

Reduction and Diffusion of Cr-Oxide Layers into P25, BaLa4Ti4O15, and Al:SrTiO3 Particles upon High-Temperature Annealing.

Chromium oxide (Cr2O3) is a beneficial metal oxide used to prevent the backward reaction in photocatalytic water splitting. The present work investigates the stability, oxidation state, and the bulk and surface electronic structure of Cr-oxide photodeposited onto P25, BaLa4Ti4O15, and Al:SrTiO3 particles as a function of the annealing process. The oxidation state of the Cr-oxide layer as deposited is found to be Cr2O3 on the surface of P25 and Al:SrTiO3 particles and Cr(OH)3 on BaLa4Ti4O15. After annealing at 600 °C, for P25 (a mixture of rutile and anatase TiO2), the Cr2O3 layer diffuses into the anatase phase but remains at the surface of the rutile phase. For BaLa4Ti4O15, Cr(OH)3 converts to Cr2O3 upon annealing and diffuses slightly into the particles. However, for Al:SrTiO3, the Cr2O3 remains stable at the surface of the particles. The diffusion here is due to the strong metal-support interaction effect. In addition, some of the Cr2O3 on the P25, BaLa4Ti4O15, and Al:SrTiO3 particles is reduced to metallic Cr after annealing. The effect of Cr2O3 formation and diffusion into the bulk on the surface and bulk band gaps is investigated with electronic spectroscopy, electron diffraction, DRS, and high-resolution imaging. The implications of the stability and diffusion of Cr2O3 for photocatalytic water splitting are discussed.

Construction of Hierarchical PdAgAu Nanorings/MXene–GO Electrocatalysts for Efficient and Ultrastable Hydrogen Evolution Reaction

High overpotential and poor long‐term operation stability of electrocatalysts are two major barriers for the hydrogen evolution reaction (HER). Herein, 2D ultrathin PdAgAu nanorings are synthesized and further self‐assembled on Ti2CTx–graphene oxide (GO) heterostructure for efficiently boosting HER. The best candidate, Pd50Ag31Au19/Ti2CTx–GO electrocatalyst, can initiate hydrogen evolution at an overpotential of 90 mV at 10 mA cm−2 and exhibits the lowest Tafel slope of 75 mV dec−1 as well as the highest mass activity of 284.4 mA mg−1Pd at −100 mV, in comparison with those of Pd50Ag31Au19/Ti2CTx, Pd50Ag31Au19/GO, and commercial Pd/C. Most remarkably, impressive long‐term stability is achieved even after a 112 h chronoamperometric test. The great performance of Pd50Ag31Au19/Ti2CTx–GO electrocatalyst can be attributed to the advantageous synergistic effect among the morphological modulation, composition optimization, and strong metal–support interaction effect between the Pd50Ag31Au19 nanorings and Ti2CTx–GO support.

The metal–support interaction effect in the carbon-free PEMFC cathode catalysts

The metal–support interaction effect in the carbon-free PEMFCs cathode catalysts are summarized in this review.

Strong metal-support interaction of Pt-based electrocatalysts with transition metal oxides/nitrides/carbides for oxygen reduction reaction

The practical application of carbon-supported Pt-based catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) still faces many limitations, including carbon corrosion and their weak interaction with Pt-based nanoparticles (NPs). Harnessing the strong metal-support interaction (SMSI) effects at the interface between Pt-based nanoparticles and alternative corrosion-resistant non-carbon support is an effective strategy to address these issues. The rational design of Pt-based catalysts with favorable SMSI and elucidation of the mechanisms underlying such interactions is indispensable for achieving desirable activity and stability. In this review, first, the basic principles of the ORR are briefly introduced. Next, the formation process of SMSI, construction strategies, and the advantages and drawbacks of representative supports, including transition metal oxides, nitrides, and carbides (TMOs, TMCs, and TMNs, respectively), are fully discussed. Finally, the challenges and prospects in promoting the practical applications of the SMSI effect for ORR are highlighted.

Surface oxygen vacancy defects induced CoTiO3-x perovskite nanostructures for highly efficient catalytic activity from acidic and seawater electrolysis

Efficient electrocatalysts have great demand for improved hydrogen evolution (HE) from natural seawater splitting. In this work, a new type of oxygen (O2) vacancies and Ti3+ defective perovskite nanostructures (DPNSs) of D-CoTiO3-x were prepared by using eco-friendly sonochemical assisted laser irradiation technique (SCA-LIT) for the first time. These DPNSs were thoroughly characterized, and HE activity was evaluated to determine their electrocatalytic potential and efficiency improvement. The existence of abundantly available active sites in the prepared D-CoTiO3-x electrocatalyst composed of defective D-TiO2-x was confirmed through various physicochemical measurements. The designed DPNSs-based working electrode exhibited excellent electrochemical performance due to its low over-potential (0.352 V), reduced Tafel slope (94.7 mV/dec), high double layer capacitance (235.3 µF/cm2), large electrochemically active surface area (6.72 cm2) and exceptional long-term stability. The attained improvement in the HE efficiency was ascribed to the induced synergistic strong metal-support interaction (SMSI) effect of the surface O2 vacancies and Ti3+ defects in DPNSs that yielded high conductivity, high exposure of abundant active sites, wide active surface area, improved kinetics, and fast charge transport. Furthermore, Volmer-Heyrovsky (V-H) reaction mechanism was responsible for the generation of hydrogen (H2) by the proposed DPNSs-based electrode. In addition to the natural seawater, the D-CoTiO3-x DPNSs outperformed in terms of the electrocatalytic hydrogen activity and stability. Thus, our systematic approach for the fabrication of surface O2 vacancy and Ti3+ defect engineering DPNSs-based electrodes to produce H2 from natural seawater splitting may be beneficial for green energy generation, solving future environmental problems and energy demand crises.

Low-Loading Sub-3 nm PtCo Nanoparticles Supported on Co-N-C with Dual Effect for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells.

Developing low-loading Pt-based catalysts possessing glorious catalytic performance can accelerate oxygen reduction reaction (ORR) and hence significantly advance the commercialization of proton exchange membrane fuel cells. In this report, we propose a hybrid catalyst that consists of low-loading sub-3 nm PtCo intermetallic nanoparticles carried on Co-N-C (PtCo/Co-N-C) via the microwave-assisted polyol procedure and subsequent heat treatment. Atomically dispersed Co atoms embedded in the Co-N-C carriers diffuse into the lattice of Pt, thus forming ultrasmall PtCo intermetallic nanoparticles. Owing to the dual effect of the enhanced metal-support interaction and alloy effect, as-fabricated PtCo/Co-N-C catalysts deliver an extraordinary performance, achieving a half-wave potential of 0.921 V, a mass activity of 0.700 A mgPt-1@0.9 V, and brilliant durability in the acidic medium. The fuel cell employing PtCo/Co-N-C as the cathode catalyst with an ultralow Pt loading of 0.05 mg cm-2 exhibits an impressive peak power density of 0.700 W cm-2, higher than that of commercial Pt/C under the same condition. Furthermore, the enhanced intrinsic ORR activity and stability are imputed to the downshifted d-band center and the strengthened metal-support interaction, as revealed by density functional theory calculations. This report affords a facile tactic to fabricate Pt-based alloy composite catalysts, which is also applicable to other alloy catalysts.

Recent Progress in Surface and Interface Engineering for Electrocatalytic CO2 Reduction.

The conversion of CO2 through CO2 reduction reaction (CO2 RR) into valuable products has potential to lessen the greenhouse effect caused by uncontrolled CO2 emissions. Challenges of CO2 RR reaction lie in the stabilization of the reaction intermediate and the activation of the inert chemical bond of CO2 , but the application of CO2 RR at large scale is limited by the high cost and structural instability of traditional catalysts. By applying CO2 RR catalyst with delicate structure of stable CO2 intermediate to industrial production, the problems such as high cost of CO2 conversion, low catalytic selectivity and poor catalytic efficiency can be effectively solved, showing better application value and significance than traditional catalysts. This review focuses on the defects, and metal-support interaction (MSI) effect to modify the catalyst and other strategies to enhance the effectiveness of CO2 reduction. The challenges and prospects from the three perspectives are also discussed to provide suggestions for the designing of efficient CO2 RR catalysts in the future. This review offers new insights and research perspectives of reducing CO2 emission through recycling CO2 , and neutralizing the carbon cycle.

NiAl-layered double hydroxides stabilized Pt clusters with enhanced metal-support interaction: Boosting hydrogen isotope separation

Metal-support interaction plays a key role and remains a challenge in exploring highly efficient heterogeneous catalysts, especially for hydrophobic catalysts in Liquid Phase Catalytic Exchange (LPCE) process for water detritiation. In this work, supported Pt catalysts using layered double hydroxides (LDHs) as supports are featured by highly dispersed Pt nanoparticles, water resisting property, and strong interaction of Pt with LDHs, exhibiting excellent anti-aggregation of Pt nanoparticles and catalytic performance over traditional Pt/C at high temperature and humidity conditions. Density Functional Theory calculations show that there is strong interaction between Pt nanoclusters and hydrogen defective LDHs surface, together with significant interfacial charge transfer and metal electronic structure modification, which can restrain the aggregation of Pt on LDHs and enhance catalytic activity. These findings are helpful to deepen understandings of the effects of metal-support interactions in LPCE process, which shed valuable insights for the design and preparation of highly-efficient hydrophobic catalysts on LDHs with prospective applications in water detritiation.

Dry Reforming of Ethane over FeNi/Al–Ce–O Catalysts: Composition-Induced Strong Metal–Support Interactions

Dry reforming of ethane (DRE) has received significant attention because of its potential to produce chemical raw materials and reduce carbon emissions. Herein, a composition-induced strong metal-support interaction (SMSI) effect over FeNi/Al–Ce–O catalysts is revealed via X-ray photoelectron spectroscopy (XPS), H 2 -temperature programmed reduction (TPR), and energy dispersive X-ray spectroscopy (EDS) elemental mapping. The introduction of Al into Al–Ce–O supports significantly influences the dispersion of surface active components and improves the catalytic performance for DRE over supported FeNi catalysts due to enhancement of the SMSI effect. The catalytic properties, for example, C 2 H 6 and CO 2 conversion, CO selectivity and yield, and turnover frequencies (TOFs), of supported FeNi catalysts first increase and then decrease with increasing Al content, following the same trend as the theoretical effective surface area (TESA) of the corresponding catalysts. The FeNi/Ce–Al 0.5 catalyst, with 50% Al content, exhibits the best DRE performance under steady-state conditions at 873 K. As observed by with in situ Fourier transform infrared spectroscopy (FTIR) analysis, the introduction of Al not only increases the content of surface Ce 3+ and oxygen vacancies but also promotes the dispersion of surface active components, which further alters the catalytic properties for DRE over supported FeNi catalysts.

Pd supported on defective TiO2 polymorphic mixtures: Effect of metal-support interactions upon glycerol selective oxidation

Palladium catalysts supported on defective mixes of anatase, TiO2 (II) and rutile crystalline phases, previously obtained by high-energy ball milling, were synthesized and tested for glycerol selective oxidation. A deep characterization of these unusual materials was carried out to elucidate catalytic and physicochemical features. Electron density transfer from support to metal or vice versa, depending on the polymorphs present, could not only alter palladium particle sizes and its surface oxidation state but also reducibility and oxygen mobility of catalysts. Furthermore, acid-base properties achieved also influenced catalytic activity under mild conditions of liquid-phase glycerol oxidation. A conversion of 94% and a selectivity to glyceric and lactic acids of 48% and 22% respectively were obtained for the Pd catalyst supported on mechanochemically activated anatase. The presence of several polymorphs in a metal oxide support could therefore benefit or handicap catalytic cycle for a particular reaction. Metal-support interactions play a key role in heterogenous catalysts and thus the rational design of supports comes on the scene.

Impact of Different Supports on the Performance of Ir Oxide Based Catalysts Synthesized Using Incipient Wetness Method

Development of an active and durable catalyst for oxygen evolution reaction (OER) is a pivotal part of designing an efficient PEM water electrolyser. Iridium is one of the best available catalysts because of its corrosion resistance and activity [1]. Use of Ir is however, limited by its scarcity, limited durability and high cost. Its deposition on a support is a popular way to improve the available surface area, activity and stability [2]. For applications in acidic water electrolysis, supports with the highest chemical resistance and conductivity are preferred. While different methods have been studied to impregnate a support with catalyst nanoparticles, such as Adams’s fusion method and polyol method, their scalability remains questionable due to intensive resource requirements. In this work, Ir oxide based supported catalysts have been synthesized using the incipient wetness method (IWM), one of the most commonly used method of catalyst synthesis in the industry due to its ease of scalability, limited resource requirement and the opportunity to explore the effect of strong metal support interactions. This method however has not been discussed in literature. In this study, Ir oxide (IrOx) (Ir loading on support = 20 wt. percent) was dispersed on commercial supports (ZrO2, Nb2O5, Ta2O5, ATO) using H2IrCl6.xH2O precursor (99.9% trace metal basis, Sigma Aldrich). The catalysts were calcined at 400oC for 2 h in a muffle furnace to produce Ir oxide based catalysts.Electrochemical measurements were carried out on a standard rotating-disk electrode (RDE) system (PINE Research MSR Rotator), and a three-electrode electrochemical cell in 1.0 M sulfuric acid electrolyte (H2SO4 optima grade, Fisher Scientific). The performance of the aforementioned supported Ir oxide catalyst was compared among themselves, and to benchmark commercial catalysts (Umicore Ir Black and IrOx TKK) using metrics such as mass normalized activity (A/g-1 Ir), ECSA normalized activity (mA/cm2 Ir ECSA), Tafel slope (mV/dec) and charge transfer resistance (Rct) measured during the electrochemical test. It was observed that the activity of IrOx/ZrO2 (415 A/gIr, 5.2 mA/cm2 Ir ECSA) was the best among all the 4 impregnated catalysts, and was in fact, more than an order of magnitude greater than that of IrOx/ATO (30 A/gIr, 0.3 mA/cm2 Ir ECSA) at a potential of 1.53 VRHE. A significant drop in the Tafel slope measured in the potential range of 1.45-1.55 VRHE was observed upon changing the support from ATO (80 mV/dec) to ZrO2 (60 mV/dec) hinting towards a change in the reaction mechanism. IrOx/ATO was used as a baseline due to prevalent recognition of ATO as an excellent support for OER catalysts in the literature.Upon comparison with commercial benchmark catalysts it was observed that the Ir ECSA normalized activity of IrOx/Nb2O5, IrOx/Ta2O5, IrOx/ZrO2 surpasses both Umicore Ir black ( 2.23 mA/cm2 Ir ECSA) and IrOx TKK (1.23 mA/cm2 Ir ECSA) with IrOx/ZrO2 providing the highest activity. While Yttria-stabilized zirconia (YSZ) has been a popular choice as an electrolyte and anode for high temperature SOFC due to its non-reducing nature, high thermal stability and mechanical strength, and acceptable oxygen ion conductivity [3], its application in PEM water electrolysis as catalyst support has not been discussed. In this work, we focus on finding the causes for superior performance of ZrO2 as a support for Ir oxide based OER reaction in acidic conditions through the lens of electrocatalysis.

Selective oxidation of methane to CO on Ni@BOx via reaction-induced vapor migration of boron-containing species onto Ni

Dynamic migration of support-derived species and subsequent encapsulation of supported metal nanoparticles (NPs) are the well-known features of the Strong Metal-Support Interaction (SMSI) effect. Here, we report occurrence of the classical SMSI state in physical mixture of Ni NPs and porous hexagonal boron nitride powder (Ni|pBN) during methane oxidation reaction at 600 ℃, in which Ni NPs are encapsulated by BOx overlayers derived from the pBN component. The SMSI state can switch the methane oxidation selectivity from CO2 on the fresh Ni|pBN catalyst to CO on the used catalyst. The encapsulation of Ni NPs by BOx overlayers has also been observed in Ni/Al2O3 catalyst which is physically mixed with pBN. Comprehensive characterizations confirm that the SMSI state is induced by vapor migration of boron-containing species e.g. BOxHy from pBN to metal surfaces, in which both high reaction temperature and water product play an important role.

Construction of a single-atom palladium catalyst by electronic metal-support interaction and interface confinement effect with remarkable performance in Suzuki coupling reaction

Atomically distributed metal catalysts with maximal atom utilization and distinctive catalytic properties have drawn attention in a variety of reactions. However, accessing excellent catalytic efficiency while preserving high stability is critical but challenging. Here we report a straightforward strategy by synergizing electronic metal-support interaction and interface confinement effect, which enables the precise construction of atomic palladium atoms supported over UiO-66-NH2. For the Suzuki coupling of bromobenzene with phenylboronic acid, this palladium catalyst demonstrates extraordinary catalytic performance in terms of activity (turnover frequency of 13043 h−1), selectivity (>99 %), and yield (>99 %). Additionally, it shows excellent recyclability, storage stability, and wide substrate scope. The experimental characterizations and DFT calculations demonstrate the high catalytic activity is attributed to the optimized electronic metal-support interactions and positive valence state of palladium atoms over the support. This study provides fundamental insights into the precise synthesis of single atom catalysts and their application in organic transformations.

Gas sensors based on Pd-decorated and Sb-doped SnO2 for hydrogen detection

Pd-modified Sb-doped SnO2 nanomaterials were prepared by a simple hydrothermal reaction and reduction method. The as-obtained samples were characterized by X-ray diffraction, scanning electron microscopy, X-ray phosphorescence, and elemental mapping analysis. The extracted results demonstrated even doping of Sb within the SnO2 lattice, and Pd was successfully incorporated on the surface of samples. Compared with the pristine SnO2, 3 mol% Sb doping with 7 wt% Pd decorating exhibited the highest response of 9.7 to 100 ppm H2 at 320 °C and revealed excellent selectivity and cycling stability to hydrogen. The mechanism of the enhanced sensing performance of Pd@Sb-SnO2 can be attributed to the change in the energy band structure by Sb doping, the energy-band bending, and depletion layer generated with the Pd loading. The increased oxygen vacancy caused by the lattice distortion generated by the Sb doping, and the strong metal-support interaction effect between the Pd and SnO2 also plays an important role.

Hydrogen Production of Clean Energy by Partial Oxidation of Methane over M(1)-Ni(5)/SBA-15 (M = Tb, Pr, Eu, and Dy) Catalysts

Objectives : In order to solve the environmental problem that is the cause of the global greenhouse effect, We want to evaluate the effects of 1wt% of lanthanum (Tb, Pr, Eu, and Dy) as a promoter added to Ni(5)/SBA-15 catalyst by performing the partial oxidation of methane, the main component of natural gas, to hydrogen over M(1)-Ni(5)/SBA-15 (M = Tb, Pr, Eu and Dy) catalyst and to identify the active site of the catalyst by means of instrumentation such as XPS, FETEM, and EDS.Methods : The catalytic activities of the partial oxidation of methane (POM) to hydrogen as a clean energy over M(1)-Ni(5)/SBA-15 (M = Tb, Pr, Eu, and Dy) catalysts are investigated using a fixed bed flow reactor under atmospheric pressure. The active sites of the catalyst are verified through instrumental analysis with XPS, FETEM, and EDS.Results and Discussion : The XPS results show that when 1wt% of Eu is added to the Ni(5)/SBA-15 catalyst, the atomic percent of Ni2p3/2 is increased from 0.12% to 0.15%, and the oxygen atomic number including lattice oxygen and oxygen vacancies is increased 1.32 times compared to that of the Ni(5)/SBA-15 catalyst. Further, the O1s characteristic peak is chemically shifted toward the lower binding energy. The FETEM images show that the nanoparticles of Ni and Eu are uniformly distributed on the surface of a reduced Eu(1)-Ni(5)/SBA-15 catalyst. The EDS mappings of Eu, Ni, O, and Si are confirmed. It is believed that the activity of the catalyst was improved by increasing the dispersion of nanoparticles of Ni0 on the surface of the catalyst due to the increased mobility of oxygen by creating oxygen vacancies. Methane conversion of Ni(5)/SBA-15 catalyst was deactivated rapidly after the reaction time of 12h whereas M(1)-Ni(5)/SBA-15 (M = Tb, Pr, Eu, and Dy) catalyst showed constant and stable catalyst activity until 12h ~ 50h. It is also considered to be the case that the sintering of Ni particles is prevented by the strong metal support interaction (SMSI) effect between Eu3+, Ni2+, and the SBA-15 carrier, and the stability of the catalyst is thereby maintained. The hydrogen yield of catalyst was in the order of Eu(1)-Ni(5)/SBA-15(57.2%, 25h) >> Dy(1)-Ni(5)/SBA-15 (49%, 14h) > Pr(1)-Ni(5)/SBA-15 (43.1%, 29h) > Tb(1)-Ni(5)/SBA-15 (42.8%, 25h).Conclusion : The Ni(5)/SBA-15 catalyst was showed that the conversion of methane was rapidly reduced after a reaction time of 12h, while when 1wt% of lanthanum (Tb, Pr, Eu and Dy) as a promoter was added to the Ni(5)/SBA-15 catalyst, the conversion of methane and yields of hydrogen were showed constant and stable catalytic activity in the reaction time of 12h to 50h. It is believed that the conversion of methane was improved by increasing the dispersion of nanoparticles of Ni0 on the surface of the catalyst due to the increased mobility of oxygen by creating oxygen vacancies. Moreover, sintering of Ni0 nanoparticles on the surface of M(1)-Ni(5)/SBA-15 (M = Tb, Pr, Eu, Dy) catalyst is prevented by strong metal support interaction (SMSI) effect.

Engineering the strong metal support interaction of titanium nitride and ruthenium nanorods for effective hydrogen evolution reaction

Designing low-cost, high-efficiency hydrogen evolution reaction (HER) catalysts to break the bottleneck of current electrocatalytic water splitting processes remains a formidable challenge. Here, we report a strong metal-support interaction (SMSI) effect constructed with ruthenium nanorods (Ru NRs) loaded in porous titanium nitride (TiN) nanosheet assembled hollow tube (labeled as Ru NRs/TiN). Ru NRs/TiN exhibits outstanding HER performance in 1.0 M KOH solution, requiring an overpotential of only 25 mV to achieve a current density of 10 mA cm−2, and demonstrates ultra-high mass activity (20 times than that of Pt/C) and superior turnover frequency values with respect to most Ru-based catalysts. Density functional theory calculations show that the SMSI can induce a notable charge redistribution at the Ru-TiN interface and enhance the HER activity of the catalyst. Moreover, the catalyst exhibits excellent stability (10,000 cycles without decay) due to the SMSI effect between the Ru species and the TiN support. Our work has broadened the range of support options for Ru-based catalysts for HER, and provided new insights into the SMSI engineering.

Solvent-free multi-alkylation of urea with alcohols catalyzed by titania-supported iridium catalyst with a strong metal-support interaction

One of the primary responsibilities of chemists is the development of environmentally friendly and economically efficient catalytic systems to minimize pollution and reduce energy and raw material consumption. Here we report the titania-supported iridium-catalyzed multi-alkylation of urea by various alcohols under solvent-free conditions, where strong metal-support interaction plays a dominant role in catalyst activity. Experiments revealed that titania supports significantly affect the catalysis. Compared with the iridium catalyst supported on rutile, anatase-supported ones were more active in N-alkylation, resulting in higher yields of the desired products. By increasing the loading of iridium on titania support, the activity of the catalyst was effectively promoted. The hydrogen temperature-programmed reduction and X-ray photoelectron spectra showed that the amount of iridium loading significantly affected the reduction behavior and valence state of iridium, indicating the significant effects of the strong metal-support interaction on the activity of the catalyst. The catalyst could be used at least five times without significant inactivation.

Single Atom Catalysts for Selective Methane Oxidation to Oxygenates

Direct conversion of methane (CH4) to C1-2 liquid oxygenates is a captivating approach to lock carbons in transportable value-added chemicals, while reducing global warming. Existing approaches utilizing the transformation of CH4 to liquid fuel via tandemized steam methane reforming and the Fischer-Tropsch synthesis are energy and capital intensive. Chemocatalytic partial oxidation of methane remains challenging due to the negligible electron affinity, poor C-H bond polarizability, and high activation energy barrier. Transition-metal and stoichiometric catalysts utilizing harsh oxidants and reaction conditions perform poorly with randomized product distribution. Paradoxically, the catalysts which are active enough to break C-H also promote overoxidation, resulting in CO2 generation and reduced carbon balance. Developing catalysts which can break C-H bonds of methane to selectively make useful chemicals at mild conditions is vital to commercialization. Single atom catalysts (SACs) with specifically coordinated metal centers on active support have displayed intrigued reactivity and selectivity for methane oxidation. SACs can significantly reduce the activation energy due to induced electrostatic polarization of the C-H bond to facilitate the accelerated reaction rate at the low reaction temperature. The distinct metal-support interaction can stabilize the intermediate and prevent the overoxidation of the reaction products. The present review accounts for recent progress in the field of SACs for the selective oxidation of CH4 to C1-2 oxygenates. The chemical nature of catalytic sites, effects of metal-support interaction, and stabilization of intermediate species on catalysts to minimize overoxidation are thoroughly discussed with a forward-looking perspective to improve the catalytic performance.