Interfacial compatibility critically controls Ru/TiO2 metal-support interaction modes in CO2 hydrogenation

Optically selective catalyst design with minimized thermal emission for facilitating photothermal catalysis

Converting solar energy into fuels is pursued as an attractive route to reduce dependence on fossil fuel. In this context, photothermal catalysis is a very promising approach through converting photons into heat to drive catalytic reactions. There are mainly three key factors that govern the photothermal catalysis performance: maximized solar absorption, minimized thermal emission and excellent catalytic property of catalyst. However, the previous research has focused on improving solar absorption and catalytic performance of catalyst, largely neglected the optimization of thermal emission. Here, we demonstrate an optically selective catalyst based Ti3C2Tx Janus design, that enables minimized thermal emission, maximized solar absorption and good catalytic activity simultaneously, thereby achieving excellent photothermal catalytic performance. When applied to Sabatier reaction and reverse water-gas shift (RWGS) as demonstrations, we obtain an approximately 300% increase in catalytic yield through reducing the thermal emission of catalyst by ~70% under the same irradiation intensity. It is worth noting that the CO2 methanation yield reaches 3317.2 mmol gRu-1 h-1 at light power of 2 W cm-2, setting a performance record among catalysts without active supports. We expect that this design opens up a new pathway for the development of high-performance photothermal catalysts.

Tuning Catalytic Activity of CO2 Hydrogenation to C1 Product via Metal Support Interaction Over Metal/Metal Oxide Supported Catalysts

The metal supported catalysts are emerging catalysts that are receiving a lot of attention in CO2 hydrogenation to C1 products. Numerous experiments have demonstrated that the support (usually an oxide) is crucial for the catalytic performance. The support metal oxides are used to aid in the homogeneous dispersion of metal particles, prevent agglomeration, and control morphology owing to the metal support interaction (MSI). MSI can efficiently optimize the structural and electronic properties of catalysts and tune the conversion of key reaction intermediates involved in CO2 hydrogenation, thereby enhancing the catalytic performance. There is an increasing attention is being paid to the promotion effects in the catalytic CO2 hydrogenation process. However, a systematically understanding about the effects of MSI on CO2 hydrogenation to C1 products catalytic performance has not been fully studied yet due to the diversities in catalysts and reaction conditions. Hence, the characteristics and modes of MSI in CO2 hydrogenation to C1 products are elaborated in detail in our work.

Dynamics of Elementary Steps on Metal Surfaces at High Coverages: The Prevalence and Kinetic Competence of Contiguous Bare-Atom Ensembles

The rate of elementary steps on densely-covered surfaces depends sensitively on repulsive interactions within dense adlayers, situations ubiquitous in practice and with kinetic consequences seldom captured by Langmuirian treatments of surface catalysis. This study develops an ensemble-based method that assesses how such repulsion influences the prevalence and kinetic competence of bare-atom ensembles of different size. Chemisorbed CO (CO*) is used as an example because it forms dense adlayers on metal nanoparticles during CO2 hydrogenation (CO2-H2) and other reactions, leading to significant repulsion that weakens the binding of CO* and kinetically-relevant transition states (TS). This approach is enabled by density functional theory and probability formalisms and describes the prevalence of ensembles of contiguous bare atoms from their formation energy (via CO* desorption); it then determines their competence in stabilizing the TS and mediating the reaction rates. The specific conclusions reflect the extent to which a given TS and CO* desorbed to form bare ensembles "sense" repulsion and the contribution of each ensemble size to each reaction channel mediated by distinct TS structures. These formalisms are illustrated by assessing the relative contributions, kinetic relevance, and ensemble size requirements for two CO2-H2 routes (direct and H-assisted CO2 activation to CO and H2O) on Ru nanoparticles, but they are not restricted to specific bound species or reaction channels. This method is essential to assess the kinetic relevance of elementary steps in a given catalytic sequence and to determine the contributions from parallel reaction channels at the crowded surfaces that prevail in the practice of surface catalysis.

Rationally designed Ru catalysts supported on TiN for highly efficient and stable hydrogen evolution in alkaline conditions

Electrocatalysis holds the key to enhancing the efficiency and cost-effectiveness of water splitting devices, thereby contributing to the advancement of hydrogen as a clean, sustainable energy carrier. This study focuses on the rational design of Ru nanoparticle catalysts supported on TiN (Ru NPs/TiN) for the hydrogen evolution reaction in alkaline conditions. The as designed catalysts exhibit a high mass activity of 20 A mg-1Ru at an overpotential of 63 mV and long-term stability, surpassing the present benchmarks for commercial electrolyzers. Structural analysis highlights the effective modification of the Ru nanoparticle properties by the TiN substrate, while density functional theory calculations indicate strong adhesion of Ru particles to TiN substrates and advantageous modulation of hydrogen adsorption energies via particle-support interactions. Finally, we assemble an anion exchange membrane electrolyzer using the Ru NPs/TiN as the hydrogen evolution reaction catalyst, which operates at 5 A cm-2 for more than 1000 h with negligible degradation, exceeding the performance requirements for commercial electrolyzers. Our findings contribute to the design of efficient catalysts for water splitting by exploiting particle-support interactions.

Tuning Adsorbate-Mediated Strong Metal-Support Interaction by Oxygen Vacancy: A Case Study in Ru/TiO2

The adsorbate-mediated strong metal-support interaction (A-SMSI) offers a reversible means of altering the selectivity of supported metal catalysts, thereby providing a powerful tool for facile modulation of catalytic performance. However, the fundamental understanding of A-SMSI remains inadequate and methods for tuning A-SMSI are still in their nascent stages, impeding its stabilization under reaction conditions. Here, we report that the initial concentration of oxygen vacancy in oxide supports plays a key role in tuning the A-SMSI between Ru nanoparticles and defected titania (TiO2-x). Based on this new understanding, we demonstrate the in situ formation of A-SMSI under reaction conditions, obviating the typically required CO2-rich pretreatment. The as-formed A-SMSI layer exhibits remarkable stability at various temperatures, enabling excellent activity, selectivity and long-term stability in catalyzing the reverse water gas-shift reaction. This study deepens the understanding of the A-SMSI and the ability to stabilize A-SMSI under reaction conditions represents a key step for practical catalytic applications.

High-Performance TiO2/ZrO2/TiO2 Thin Film Capacitor by Plasma-Assisted Atomic Layer Annealing

Although laminate structures are widely used in electrostatic capacitors, unavoidable heterogeneous interfaces often deteriorate the dielectric properties by impeding film crystallization. In this study, a TiO2/ZrO2/TiO2 (TZT) laminate structure, where upper-TiO2 deposited on the heterogeneous interface was crystallized by plasma-assisted atomic layer annealing (ALA), was investigated. ALA effectively induced the phase transition of the upper-TiO2 from the amorphous or anatase phase to the rutile phase, leading to an increase in the dielectric constant, whereas the ZrO2 blocking interlayer maintained the amorphous phase owing to the extremely localized effect of ALA. Consequently, through the layer-by-layer phase control of ALA, the dielectric constant of the upper-TiO2 was enhanced by 25% by applying ALA, leading to an increase in a capacitance density of 27% of the TZT capacitor, whereas a low leakage current density of ∼10-8 A/cm2 was maintained (at 1 V). In addition, the TZT capacitor on three-dimensional structures (aspect ratio of 5:1) shows a high capacitance density of up to 461 nF/mm2 owing to ALA.

Engineering ZrO2-Ru interface to boost Fischer-Tropsch synthesis to olefins

Understanding the structures and reaction mechanisms of interfacial active sites in the Fisher-Tropsch synthesis reaction is highly desirable but challenging. Herein, we show that the ZrO2-Ru interface could be engineered by loading the ZrO2 promoter onto silica-supported Ru nanoparticles (ZrRu/SiO2), achieving 7.6 times higher intrinsic activity and ~45% reduction in the apparent activation energy compared with the unpromoted Ru/SiO2 catalyst. Various characterizations and theoretical calculations reveal that the highly dispersed ZrO2 promoter strongly binds the Ru nanoparticles to form the Zr-O-Ru interfacial structure, which strengthens the hydrogen spillover effect and serves as a reservoir for active H species by forming Zr-OH* species. In particular, the formation of the Zr-O-Ru interface and presence of the hydroxyl species alter the H-assisted CO dissociation route from the formyl (HCO*) pathway to the hydroxy-methylidyne (COH*) pathway, significantly lowering the energy barrier of rate-limiting CO dissociation step and greatly increasing the reactivity. This investigation deepens our understanding of the metal-promoter interaction, and provides an effective strategy to design efficient industrial Fisher-Tropsch synthesis catalysts.

Strong Interactions between Au Nanoparticles and BiVO4 Photoanode Boosts Hole Extraction for Photoelectrochemical Water Splitting

Strong metal-support interaction (SMSI) is widely proposed as a key factor in tuning catalytic performances. Herein, the classical SMSI between Au nanoparticles (NPs) and BiVO4 (BVO) supports (Au/BVO-SMSI) is discovered and used innovatively for photoelectrochemical (PEC) water splitting. Owing to the SMSI, the electrons transfer from V4+ to Au NPs, leading to the formation of electron-rich Au species (Auδ-) and strong electronic interaction (i.e., Auδ--Ov-V4+), which readily contributes to extract photogenerated holes and promote charge separation. Benefitted from the SMSI effect, the as-prepared Au/BVO-SMSI photoanode exhibits a superior photocurrent density of 6.25 mA cm-2 at 1.23 V versus the reversible hydrogen electrode after the deposition of FeOOH/NiOOH cocatalysts. This work provides a pioneering view for extending SMSI effect to bimetal oxide supports for PEC water splitting, and guides the interfacial electronic and geometric structure modulation of photoanodes consisting of metal NPs and reducible oxides for improved solar energy conversion efficiency.

Insights into the hydrogen generation and catalytic mechanism on Co-based nanocomposites derived from pyrolysis of organic metal precursor

Hydrogen generation from boron hydride is important for the development of hydrogen economy. Cobalt (Co) element has been widely used in the hydrolysis of boron hydride. Pyrolysis is a common method for materials synthesis in catalytic fields. Herein, Co-based nanocomposites derived from the pyrolysis of organic metal precursors and used for hydrolysis of boron hydride are summarized and discussed. The different precursors consisting of MOF, supported, metal, and metal phosphide precursors are summarized. The catalytic mechanism consisting of dissociation mechanism based on oxidative addition-reduction elimination, pre-activation mechanism, SN2 mechanism, four-membered ring mechanism, and acid-base mechanism is intensively discussed. Finally, conclusions and outlooks are conveyed from the design of high-efficiency catalysts, the characterization of catalyst structure, the enhancement of catalytic activities, the investigation of the catalytic mechanism, and the catalytic stability of active structure. This review can provide guidance for designing high-efficiency catalysts and boosting development of hydrogen economy.

Crystalline Phase Engineering to Modulate the Interfacial Interaction of the Ruthenium/Molybdenum Carbide for Acidic Hydrogen Evolution

Ruthenium (Ru) is an ideal substitute to commercial Pt/C for the acidic hydrogen evolution reaction (HER), but it still suffers from undesirable activity due to the strong adsorption free energy of H* (ΔGH*). Herein, we propose crystalline phase engineering by loading Ru clusters on precisely prepared cubic and hexagonal molybdenum carbide (α-MoC/β-Mo2C) supports to modulate the interfacial interactions and achieve high HER activity. Advanced spectroscopies demonstrate that Ru on β-Mo2C shows a lower valence state and withdraws more electrons from the support than that of Ru on α-MoC, indicative of a strong interfacial interaction. Density functional theory reveals that the ΔGH* of Ru/β-Mo2C approaches 0 eV, illuminating an enhancement mechanism at the Ru/β-Mo2C interface. The resultant Ru/β-Mo2C exhibits an encouraging performance in a proton exchange membrane water electrolyzer with a low cell voltage (1.58 V@ 1.0 A cm-2) and long stability (500 h@ 1.0 A cm-2).

Reverse water-gas shift catalyzed by RhnVO3,4- (n = 3-7) cluster anions under variable temperatures

A fundamental understanding of the exact structural characteristics and reaction mechanisms of interface active sites is vital to engineering an energetic metal-support boundary in heterogeneous catalysis. Herein, benefiting from a newly developed high-temperature ion trap reactor, the reverse water-gas shift (RWGS) (CO2 + H2 → CO + H2O) catalyzed by a series of compositionally and structurally well-defined RhnVO3,4- (n = 3-7) clusters were identified under variable temperatures (298-773 K). It is discovered that the Rh5-7VO3,4- clusters can function more effectively to drive RWGS at relatively low temperatures. The experimentally observed size-dependent catalytic behavior was rationalized by quantum-chemical calculations; the framework of RhnVO3,4- is constructed by depositing the Rhn clusters on the VO3,4 "support", and a sandwiched base-acid-base [Rhout--Rhin+-VO3,4-; Rhout and Rhin represent the outer and inner Rh atoms, respectively] feature in Rh5-7VO3,4- governs the adsorption and activation of reactants as well as the facile desorption of the products. In contrast, isolated Rh5-7- clusters without the electronic modification of the VO3,4 "support" can only catalyze RWGS under relatively high-temperature conditions.

Flame Spray Pyrolysis Synthesis of Ultra-Small High-Entropy Alloy-Supported Oxide Nanoparticles for CO2 Hydrogenation Catalysts

The synthesis of high-entropy alloys (HEAs) with ultra-small particle sizes has long been a challenging task. The complex and time-consuming synthesis process hinders their practical application and widespread adoption. This study presents the novel synthesis of TiO2 nanoparticles loaded with a quinary high-entropy alloy through flame spray pyrolysis (FSP) for the first time. The extremely fast heating rate of flame combustion makes the precursor fast pyrolysis gasification, high temperature in the flame field promotes the metal vapor mixing uniformly, and the fast quenching process can reduce the particle aggregation sintering, the ultra-small particle size of HEA firmly attached to the TiO2 surface. The catalysts prepared via this gas-to-particle pathway exhibit excellent performance in CO2 hydrogenation, achieving a conversion rate of 62% at 450 °C, and maintaining their activity for over 220 h without significant particle agglomeration. This finding provides valuable insights for the future design of catalytically active materials with enhanced activity and long-term stability.

Ruthenium-Cobalt Solid-Solution Alloy Nanoparticles for Enhanced Photopromoted Thermocatalytic CO2 Hydrogenation to Methane

Bimetallic alloy nanoparticles have garnered substantial attention for diverse catalytic applications owing to their abundant active sites and tunable electronic structures, whereas the synthesis of ultrafine alloy nanoparticles with atomic-level homogeneity for bulk-state immiscible couples remains a formidable challenge. Herein, we present the synthesis of RuxCo1-x solid-solution alloy nanoparticles (ca. 2 nm) across the entire composition range, for highly efficient, durable, and selective CO2 hydrogenation to CH4 under mild conditions. Notably, Ru0.88Co0.12/TiO2 and Ru0.74Co0.26/TiO2 catalysts, with 12 and 26 atom % of Ru being substituted by Co, exhibit enhanced catalytic activity compared with the monometallic Ru/TiO2 counterparts both in dark and under light irradiation. The comprehensive experimental investigations and density functional theory calculations unveil that the electronic state of Ru is subtly modulated owing to the intimate interaction between Ru and Co in the alloy nanoparticles, and this effect results in the decline in the CO2 conversion energy barrier, thus ultimately culminating in an elevated catalytic performance relative to monometallic Ru and Co catalysts. In the photopromoted thermocatalytic process, the photoinduced charge carriers and localized photothermal effect play a pivotal role in facilitating the chemical reaction process, which accounts for the further boosted CO2 methanation performance.

Thermally stable Ni foam-supported inverse CeAlOx/Ni ensemble as an active structured catalyst for CO2 hydrogenation to methane

Nickel is the most widely used inexpensive active metal center of the heterogeneous catalysts for CO2 hydrogenation to methane. However, Ni-based catalysts suffer from severe deactivation in CO2 methanation reaction due to the irreversible sintering and coke deposition caused by the inevitable localized hotspots generated during the vigorously exothermic reaction. Herein, we demonstrate the inverse CeAlOx/Ni composite constructed on the Ni-foam structure support realizes remarkable CO2 methanation catalytic activity and stability in a wide operation temperature range from 240 to 600 °C. Significantly, CeAlOx/Ni/Ni-foam catalyst maintains its initial activity after seven drastic heating-cooling cycles from RT to 240 to 600 °C. Meanwhile, the structure catalyst also shows water resistance and long-term stability under reaction condition. The promising thermal stability and water-resistance of CeAlOx/Ni/Ni-foam originate from the excellent heat and mass transport efficiency which eliminates local hotspots and the formation of Ni-foam stabilized CeAlOx/Ni inverse composites which effectively anchored the active species and prevents carbon deposition from CH4 decomposition.

Control of metal-support interaction for tunable CO hydrogenation performance over Ru/TiO2 nanocatalysts

The catalytic behavior of CO hydrogenation can be modulated by metal-support interactions, while the role of the support remains elusive. Herein, we demonstrate that the presence of strong metal-support interactions (SMSI) depends strongly on the crystal phase of TiO2 (rutile or anatase) and the treatment conditions for the TiO2 support, which could critically control the activity and selectivity of Ru-based nanocatalysts for CO hydrogenation. High CO conversion and olefin selectivity were observed for Ru/rutile-TiO2 (Ru/r-TiO2), while catalysts supported by anatase (a-TiO2) showed almost no activity. Characterization confirmed that the SMSI effect could be neglected for Ru/r-TiO2, while it is dominant on Ru/a-TiO2 after reduction at 300 °C, resulting in the coverage of Ru nanoparticles by TiOx overlayers. Such SMSI could be suppressed by H2 treatment of the a-TiO2 support and the catalytic activity of the as-obtained Ru/a-TiO2(H2) can be greatly elevated from almost inactive to >50% CO conversion with >60% olefin selectivity. Further results indicated that the surface reducibility of the TiO2 support determines the SMSI state and catalytic performance of Ru/TiO2 in the CO hydrogenation reaction. This work offers an effective strategy to design efficient catalysts for the FTO reaction by regulating the crystal phase of the support.

Significance of Epitaxial Growth of PtO2 on Rutile TiO2 for Pt/TiO2 Catalysts

TiO2-supported Pt species have been widely applied in numerous critical reactions involving photo-, thermo-, and electrochemical-catalysis for decades. Manipulation of the state of the Pt species in Pt/TiO2 catalysts is crucial for fine-tuning their catalytic performance. Here, we report an interesting discovery showing the epitaxial growth of PtO2 atomic layers on rutile TiO2, potentially allowing control of the states of active Pt species in Pt/TiO2 catalysts. The presence of PtO2 atomic layers could modulate the geometric configuration and electronic state of the Pt species under reduction conditions, resulting in a spread of the particle shape and obtaining a Pt/PtO2/TiO2 structure with more positive valence of Pt species. As a result, such a catalyst exhibits exceptional electrocatalytic activity and stability toward hydrogen evolution reaction, while also promoting the thermocatalytic CO oxidation, surpassing the performance of the Pt/TiO2 catalyst with no epitaxial structure. This novel epitaxial growth of the PtO2 structure on rutile TiO2 in Pt/TiO2 catalysts shows its potential in the rational design of highly active and economical catalysts toward diverse catalytic reactions.

Dual-Atom Co/Ni Electrocatalyst Anchored at the Surface-Modified Ti3C2Tx MXene Enables Efficient Hydrogen and Oxygen Evolution Reactions

Dual-atom catalytic sites on conductive substrates offer a promising opportunity for accelerating the kinetics of multistep hydrogen and oxygen evolution reactions (HER and OER, respectively). Using MXenes as substrates is a promising strategy for depositing those dual-atom electrocatalysts, if the efficient surface anchoring strategy ensuring metal-substrate interactions and sufficient mass loading is established. We introduce a surface-modification strategy of MXene substrates by preadsorbing L-tryptophan molecules, which enabled attachment of dual-atom Co/Ni electrocatalyst at the surface of Ti3C2Tx by forming N-Co/Ni-O bonds, with mass loading reaching as high as 5.6 wt %. The electron delocalization resulting from terminated O atoms on MXene substrates, N atoms in L-tryptophan anchoring moieties, and catalytic metal atoms Co and Ni provides an optimal adsorption strength of intermediates and boosts the HER and OER kinetics, thereby notably promoting the intrinsic activity of the electrocatalyst. CoNi-Ti3C2Tx electrocatalyst displayed HER and OER overpotentials of 31 and 241 mV at 10 mA cm-2, respectively. Importantly, the CoNi-Ti3C2Tx electrocatalyst also exhibited high operational stability for both OER and HER over 100 h at an industrially relevant current density of 500 mA cm-2. Our study provided guidance for constructing dual-atom active metal sites on MXene substrates to synergistically enhance the electrochemical efficiency and stability of the energy conversion and storage systems.

Renaissance of Strong Metal-Support Interactions

Strong metal-support interactions (SMSIs) have emerged as a significant and cutting-edge area of research in heterogeneous catalysis. They play crucial roles in modifying the chemisorption properties, interfacial structure, and electronic characteristics of supported metals, thereby exerting a profound influence on the catalytic properties. This Perspective aims to provide a comprehensive summary of the latest advancements and insights into SMSIs, with a focus on state-of-the-art in situ/operando characterization techniques. This overview also identifies innovative designs and applications of new types of SMSI systems in catalytic chemistry and highlights their pivotal role in enhancing catalytic performance, selectivity, and stability in specific cases. Particularly notable is the discovery of SMSI between active metals and metal carbides, which opens up a new era in the field of SMSI. Additionally, the strong interactions between atomically dispersed metals and supports are discussed, with an emphasis on the electronic effects of the support. The chemical nature of SMSI and its underlying catalytic mechanisms are also elaborated upon. It is evident that SMSI modification has become a powerful tool for enhancing catalytic performance in various catalytic applications.

Pd Decoration with Synergistic High Oxygen Mobility Boosts Hydrogen Sensing Performance at Low Working Temperature on WO3 Nanosheet

Pd-based materials have received remarkable attention and exhibit excellent H2 sensing performance due to their superior hydrogen storage and catalysis behavior. However, the synergistic effects originated from the decoration of Pd on a metal oxide support to boost the sensing performance are ambiguous, and the deep investigation of metal support interaction (MSI) on the H2 sensing mechanism is still unclear. Here, the model material of Pd nanoparticle-decorated WO3 nanosheet is synthesized, and individual fine structures can be achieved by treating it at different temperatures. Notably, the Pd-WO3-300 materials display superior H2 sensing performance at a low working temperature (110 °C), with a superior sensing response (Ra/Rg = 40.63 to 10 ppm), high sensing selectivity, and anti-interference ability. DFT calculations and detailed structural investigations confirm that the moderate MSI facilitates the generation of high mobility surface O2- (ad) species and a proper ratio of surface Pd0-Pd2+ species, which can significantly boost the desorption of intermediate PdHx species at low temperatures and contribute to enhanced sensing performance. Our work illustrates the effect of MSI on sensing performance and provides insight into the design of advanced sensing materials.

Enhanced Hydrosaturation Selectivity and Electron Transfer for Electrocatalytic Chlorophenols Hydrogenation on Ru Sites

Electrocatalytic hydrogenation is acknowledged as a promising strategy for chlorophenol dechlorination. However, the widely used Pd catalysts exhibit drawbacks, such as high costs and low selectivity for phenol hydrosaturation. Herein, we demonstrate the potential and mechanism of Ru in serving as a Pd substitute using 2,4,6-trichlorophenol (TCP) as a model pollutant. Up to 99.8% TCP removal efficiency and 99% selectivity to cyclohexanol, a value-added compound with an extremely low toxicity, were achieved on the Ru electrode. In contrast, only 66% of TCP was removed on the Pd electrode, with almost no hydrosaturation selectivity. The superiority of Ru over Pd was especially noteworthy in alkaline conditions or the presence of interfering species such as S2-. The theoretical simulation demonstrates that Ru possesses a hydrodechlorination energy barrier of 0.72 eV, which is comparable to that on Pd. Meanwhile, hydrosaturation requires an activation energy of 0.69 eV on Ru, which is much lower than that on Pd (0.92 eV). The main reaction mechanism on Ru is direct electron transfer, which is distinct from that on Pd (indirect pathway via atomic hydrogen, H*). This work thereby provides new insights into designing cost-effective electrocatalysts for halogenated phenol detoxification and resource recovery.

Light-Reinforced Key Intermediate for Anticoking To Boost Highly Durable Methane Dry Reforming over Single Atom Ni Active Sites on CeO2

Dry reforming of methane (DRM) has been investigated for more than a century; the paramount stumbling block in its industrial application is the inevitable sintering of catalysts and excessive carbon emissions at high temperatures. However, the low-temperature DRM process still suffered from poor reactivity and severe catalyst deactivation from coking. Herein, we proposed a concept that highly durable DRM could be achieved at low temperatures via fabricating the active site integration with light irradiation. The active sites with Ni-O coordination (NiSA/CeO2) and Ni-Ni coordination (NiNP/CeO2) on CeO2, respectively, were successfully constructed to obtain two targeted reaction paths that produced the key intermediate (CH3O*) for anticoking during DRM. In particular, the operando diffuse reflectance infrared Fourier transform spectroscopy coupling with steady-state isotopic transient kinetic analysis (operando DRIFTS-SSITKA) was utilized and successfully tracked the anticoking paths during the DRM process. It was found that the path from CH3* to CH3O* over NiSA/CeO2 was the key path for anticoking. Furthermore, the targeted reaction path from CH3* to CH3O* was reinforced by light irradiation during the DRM process. Hence, the NiSA/CeO2 catalyst exhibits excellent stability with negligible carbon deposition for 230 h under thermo-photo catalytic DRM at a low temperature of 472 °C, while NiNP/CeO2 shows apparent coke deposition behavior after 0.5 h in solely thermal-driven DRM. The findings are vital as they provide critical insights into the simultaneous achievement of low-temperature and anticoking DRM process through distinguishing and directionally regulating the key intermediate species.

Ruthenium and Platinum-Modified Titanium Dioxide Support for NaBH4 Hydrolysis

Highly stable platinum (Pt) and ruthenium (Ru)-based catalysts on titanium oxide (TiO2) nanoparticle support were prepared. The productivity of hydrogen generation from sodium borohydride (NaBH4) hydrolysis was observed to be as high as 95%. The activation energies for the hydrolysis reaction in the presence of Ru/TiO2 in aqueous and alkaline solutions were 62.00 and 64.65 kJ mol-1, respectively. On the other hand, the activation energy value of the hydrolysis reaction with the Pt/TiO2 catalyst decreased from 60.5 to 53.2 kJ mol-1, and the solution was changed from an aqueous to an alkaline medium. The experimental results have indicated that NaOH concentration (ranging from 0.5 to 2 M) affected the hydrogen generation rate (HGR) differently for both metals on the TiO2 support. Consequently, the HGR of the hydrolysis reaction in the presence of the Ru/TiO2 catalyst decreased with increasing NaOH concentration, whereas the Pt/TiO2 catalyst efficiency increased with increasing NaOH concentration.

Boosting the ammonia synthesis activity of ceria-supported Ru catalysts achieved through trace Pr addition

The amount of dopant used in conventional cases for improving catalytic performance is higher than 5%. In this work, a strategy to enhance the ammonia synthesis performance of a Ru/CeO2 catalyst by using trace Pr (0.1 mol%) is reported. Owing to the improvement of oxygen defects, Ce3+ concentration and interfaced Ru species, the hydrogen adsorption was enhanced, and the desorption of hydrogen species would be promoted. As a result, Ru/CeO2 with 0.1 mol% Pr shows 1.4 times higher ammonia synthesis rate and excellent stability compared to Ru/CeO2 or the sample with high Pr loading (50 mol% Pr). This study provides a new idea for the design of high-efficiency ammonia synthesis catalysts.

Photocatalytic Synthesis of Ultrafine Pt Electrocatalysts with High Stability Using TiO2 -Decorated N-Doped Carbon as Composite Support

Commercial Pt/C (Com. Pt/C) electrocatalysts are considered optimal for oxygen reduction and hydrogen evolution reactions (ORR and HER). However, their high Pt content and poor stability restrict their large-scale application. In this study, photocatalytic synthesis was used to reduce ultrafine Pt nanoparticles in-situ on a composite support of TiO2 -decorated nitrogen-doped carbon (TiO2 -NC). The nitrogen-doped carbon had a large surface area and electronic effects that ensured the uniform dispersion of TiO2 nanoparticles to form a highly photoactive and stable support. TiO2 -NC served as a composite support that enhanced the dispersibility and stability of ultrafine Pt electrocatalyst, owing to the presence of N sites and the strong metal-support interaction. Relative to Com. Pt/C, the as-obtained Pt/TiO2 -NC had positive shifts of 44 and 10 mV in the ORR half-wave potential and HER overpotential at -10 mA cm-2 , respectively. After an accelerated durability test, Pt/TiO2 -NC had lower losses in electrochemical specific area (0.7 %) and electrocatalytic activity (0 mV shift) than Com. Pt/C (25.6 %, 22 mV shift). These results indicate that the developed strategy enabled the facile synthesis and stabilization of ultrafine Pt nanoparticles, which improved the utilization efficiency and long-term stability of Pt-based electrocatalysts.

Highly active Ru/TiO2 nanostructures for total catalytic oxidation of propane

Ruthenium is a robust catalyst for a variety of applications in environmental heterogeneous catalysis. The catalytic performance of Ru/TiO2 materials, synthesized by using the deposition precipitation with urea method, was assessed in the catalytic oxidation of C3H8, varying the ruthenium loading. The highest catalytic reactivity was obtained for a Ru loading of 2 wt. % in comparison with the 1, 1.5, 3, and 4 wt. % Ru catalysts. The physicochemical properties of the synthesized materials were investigated by XRD, N2 adsorption, TEM, FT-IR pyridine, H2-TPR, and XPS. The size of ruthenium particles was found to be greatly dependent on the pretreatment gas (air or hydrogen) and the catalytic activity was enhanced by the small-size ruthenium metal nanoparticles, leading to changes in the reduction degree of ruthenium, which also increased the Brönsted and Lewis acidity. Metal to support charge transfer enhanced the reactant adsorption sites while oxygen vacancies on the interface enabled the dissociation of O2 molecules as revealed through DFT calculations. The outstanding catalytic activity of the 2Ru/TiO2 catalysts allowed to convert C3H8 into CO2 at reaction temperatures of about 100 °C. This high activity may be attributed to the metal/support interaction between Ru and TiO2, which promoted the reducibility of Ti4+/Ti3+ and Ru4+/Ru0 species, and to the fast migration of TiO2 lattice oxygen in the catalyst. Furthermore, the Ru/TiO2 catalyst exhibited high stability and reusability for 30 h under reaction conditions, using a GHSV of 45,000 h-1. The underlying alkane-metal interactions were explored theoretically in order to explain the C-H bond activation in propane by the catalyst.

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.

Electron donation of Fe-Mn biochar for chromium(VI) immobilization: Key roles of embedded zero-valent iron clusters within iron-manganese oxide

The dense surface passivation layer on zero-valent iron (ZVI) restricts its efficiency for water decontamination, causing a poor economy and waste of resources. Herein, we found that the ZVI on Fe-Mn biochar could afford a high electron-donating efficiency for the Cr(VI) reduction and immobilization. Over 78.0% of Fe in the Fe-Mn biochar was used for the Cr(VI) reduction and immobilization, i.e., 56.2 - 161.7 times higher than the commercial ZVI (0.5%) and modified ZVI (0.9 -1.3%), indicating that the unique ZVI species in Fe-Mn biochar offered an outstanding Fe utilization efficiency. We proposed that oxygen atoms in the FeO in the FeMnO₂ precursor were removed during pyrolysis with biochar while the MnO skeleton was preserved, forming the embedded ZVI clusters within Fe-Mn oxide. The unique structure inhibited the formation of the Fe-Cr complex on Fe(0), which would facilitate the electron transfer between core Fe(0) and Cr(VI). Moreover, the surface FeMnO₂ inhibited the diffusion of Fe and facilitated its affinity with pollutants, thus supporting higher efficiency for pollutant immobilization. The preserved performance of Fe-Mn biochar was proved in industrial wastewater and after long-term oxidation process, and the economic benefit was evaluated. This work provides a new approach for developing active ZVI-based materials with high Fe utilization efficiency and economics for water pollution control.

Selective adsorption of cysteamine molecules on Au/TiO2 boosts visible light-driven photocatalytic hydrogen evolution

Photocatalytic evolution of hydrogen is becoming a research hotspot because it can help to produce clean energy and reduce environmental pollution. Titanium dioxide (TiO₂) and its composites are photocatalysts that are widely used in hydrogen evolution because of their high abundance in nature, low price, and high photo/chemical stability. However, their catalytic performances still need to be further improved, particularly in the visible light spectrum. Herein, visible light-driven photocatalytic evolution of hydrogen on Au/TiO₂ nanocomposite is enhanced ∼ 10 folds by selectively functionalizing the nanocomposite with cysteamine molecules. It is revealed that the amine group (-NH₂) in cysteamine favors the transfer and separation of photo-generated hot carriers. The rate of hydrogen produced can be further tuned by varying the ionization of the functionalized molecules at different pH values. This work provides a simple, convenient, and effective method that can be used to improve the photocatalytic evolution of hydrogen. This method can also be used for many other nanocatalysts (e.g., Au-MoS₂, Au-BiVO₄) and catalytic reactions (e.g., carbon dioxide reduction, nitrogen reduction).

Directional Migration and Rapid Coalescence of Au Nanoparticles on Anisotropic ReS2

Interfacial atomic configuration and its evolution play critical roles in the structural stability and functionality of mixed zero-dimensional (0D) metal nanoparticles (NPs) and two-dimensional (2D) semiconductors. In situ observation of the interface evolution at atomic resolution is a vital method. Herein, the directional migration and structural evolution of Au NPs on anisotropic ReS₂ were investigated in situ by aberration-corrected transmission electron microscopy. Statistically, the migration of Au NPs with diameters below 3 nm on ReS₂ takes priority with greater probability along the b-axis direction. Density functional theory calculations suggest that the lower diffusion energy barrier enables the directional migration. The coalescence kinetics of Au NPs is quantitatively described by the relation of neck radius (r) and time (t), expressed as r2=Kt. Our work provides an atomic-resolved dynamic analysis method to study the interfacial structural evolution of metal/2D materials, which is essential to the study of the stability of nanodevices based on mixed-dimensional nanomaterials.

Carbon Dioxide Conversion on Supported Metal Nanoparticles: A Brief Review

The increasing concentration of anthropogenic CO2 in the air is one of the main causes of global warming. The Paris Agreement at COP 21 aims to reach the global peak of greenhouse gas emissions in the second half of this century, with CO2 conversion towards valuable added compounds being one of the main strategies, especially in the field of heterogeneous catalysis. In the current search for new catalysts, the deposition of metallic nanoparticles (NPs) supported on metal oxides and metal carbide surfaces paves the way to new catalytic solutions. This review provides a comprehensive description and analysis of the relevant literature on the utilization of metal-supported NPs as catalysts for CO2 conversion to useful chemicals and propose that the next catalysts generation can be led by single-metal-atom deposition, since in general, small metal particles enhance the catalytic activity. Among the range of potential indicators of catalytic activity and selectivity, the relevance of NPs’ size, the strong metal–support interactions, and the formation of vacancies on the support are exhaustively discussed from experimental and computational perspective.

Enhancing bioactivity and stability of polymer-based material-tissue interface through coupling multiscale interfacial interactions with atomic-thin TiO2 nanosheets

Stable and bioactive material-tissue interface (MTF) basically determines the clinical applications of biomaterials in wound healing, sustained drug release, and tissue engineering. Although many inorganic nanomaterials have been widely explored to enhance the stability and bioactivity of polymer-based biomaterials, most are still restricted by their stability and biocompatibility. Here we demonstrate the enhanced bioactivity and stability of polymer-matrix bio-composite through coupling multiscale material-tissue interfacial interactions with atomically thin TiO2 nanosheets. Resin modified with TiO2 nanosheets displays improved mechanical properties, hydrophilicity, and stability. Also, we confirm that this resin can effectively stimulate the adhesion, proliferation, and differentiation into osteogenic and odontogenic lineages of human dental pulp stem cells using in vitro cell-resin interface model. TiO2 nanosheets can also enhance the interaction between demineralized dentinal collagen and resin. Our results suggest an approach to effectively up-regulate the stability and bioactivity of MTFs by designing biocompatible materials at the sub-nanoscale.

Electronic Supplementary Material

Supplementary material (further details of fabrication and characterization of TiO2 NSs and TiO2-ARCs, the bioactivity evaluation of TiO2-ARCs on hDPSCs, and the measurement of interaction with demineralized dentin collagen) is available in the online version of this article at 10.1007/s12274-022-5153-1.

Direct production of olefins from syngas with ultrahigh carbon efficiency

Syngas conversion serves as a competitive strategy to produce olefins chemicals from nonpetroleum resources. However, the goal to achieve desirable olefins selectivity with limited undesired C1 by-products remains a grand challenge. Herein, we present a non-classical Fischer-Tropsch to olefins process featuring high carbon efficiency that realizes 80.1% olefins selectivity with ultralow total selectivity of CH₄ and CO₂ (<5%) at CO conversion of 45.8%. This is enabled by sodium-promoted metallic ruthenium (Ru) nanoparticles with negligible water-gas-shift reactivity. Change in the local electronic structure and the decreased reactivity of chemisorbed H species on Ru surfaces tailor the reaction pathway to favor olefins production. No obvious deactivation is observed within 550 hours and the pellet catalyst also exhibits excellent catalytic performance in a pilot-scale reactor, suggesting promising practical applications.

CO-tolerant RuNi/TiO2 catalyst for the storage and purification of crude hydrogen

Hydrogen storage by means of catalytic hydrogenation of suitable organic substrates helps to elevate the volumetric density of hydrogen energy. In this regard, utilizing cheaper industrial crude hydrogen to fulfill the goal of hydrogen storage would show economic attraction. However, because CO impurities in crude hydrogen can easily deactivate metal active sites even in trace amounts such a process has not yet been realized. Here, we develop a robust RuNi/TiO₂ catalyst that enables the efficient hydrogenation of toluene to methyl-cyclohexane under simulated crude hydrogen feeds with 1000-5000 ppm CO impurity at around 180 °C under atmospheric pressure. We show that the co-localization of Ru and Ni species during reduction facilitated the formation of tightly coupled metallic Ru-Ni clusters. During the catalytic hydrogenation process, due to the distinct bonding properties, Ru and Ni served as the active sites for CO methanation and toluene hydrogenation respectively. Our work provides fresh insight into the effective utilization and purification of crude hydrogen for the future hydrogen economy.

Synergy in Au-CuO Janus Structure for Catalytic Isopropanol Oxidative Dehydrogenation to Acetone

The controlled oxidation of alcohols to the corresponding ketones or aldehydes via selective cleavage of the β-C-H bond of alcohols under mild conditions still remains a significant challenge. Although the metal/oxide interface is highly active and selective, the interfacial sites fall far behind the demand, due to the large and thick support. Herein, we successfully develop a unique Au-CuO Janus structure (average particle size=3.8 nm) with an ultrathin CuO layer (0.5 nm thickness) via a bimetal in situ activation and separation strategy. The resulting Au-CuO interfacial sites prominently enhance isopropanol adsorption and decrease the energy barrier of β-C-H bond scission from 1.44 to 0.01 eV due to the strong affinity between the O atom of CuO and the H atom of isopropanol, compared with Au sites alone, thereby achieving ultrahigh acetone selectivity (99.3 %) over 1.1 wt % AuCu_0.75 /Al₂ O₃ at 100 °C and atmospheric pressure with 97.5 % isopropanol conversion. Furthermore, Au-CuO Janus structures supported on SiO₂ , TiO₂ or CeO₂ exhibit remarkable catalytic performance, and great promotion in activity and acetone selectivity is achieved as well for other reducible oxides derived from Fe, Co, Ni and Mn. This study should help to develop strategies for maximized interfacial site construction and structure optimization for efficient β-C-H bond activation.

Effect of nanostructuring on the interaction of CO2 with molybdenum carbide nanoparticles

Transition metal carbides are increasingly used as catalysts for the transformation of CO₂ into useful chemicals. Recently, the effect of nanostructuring of such carbides has started to gain relevance in tailoring their catalytic capabilities. Catalytic materials based on molybdenum carbide nanoparticles (MoC_y) have shown a remarkable ability to bind CO₂ at room temperature and to hydrogenate it into oxygenates or light alkanes. However, the involved chemistry is largely unknown. In the present work, a systematic computational study is presented aiming to elucidate the chemistry behind the bonding of CO₂ with a representative set of MoC_y nanoparticles of increasing size, including stoichiometric and non-stoichiometric cases. The obtained results provide clear trends to tune the catalytic activity of these systems and to move towards more efficient CO₂ transformation processes.

Controlling CO2 hydrogenation selectivity by Rh-based catalysts with different crystalline phases of TiO2

A series of Rh-based catalysts with various crystalline phases (p25, anatase, and rutile) were prepared via the incipient-wetness impregnation method. It was found that these catalysts had different metal-support interactions. Hence, 1%Rh/p, 1%Rh/r, and 1%Rh/a exhibited methane, CO, and methanol selectivity, respectively.