Interfacial Sites Research Articles

Nonclassical Strong Metal-Support Interactions for Enhanced Catalysis.

Strong metal-support interaction (SMSI), which encompasses reversible encapsulation and de-encapsulation and modulation of surface adsorption properties, imposes great impacts on the performance of heterogeneous catalysts. Recent development of SMSI has surpassed the prototypical encapsulated Pt-TiO2 catalyst, affording a series of conceptually novel and practically advantageous catalytic systems. Here we provide our perspective on recent progress in nonclassical SMSIs for enhanced catalysis. Unravelling the structural complexity of SMSI necessitates the combination of multiple characterization techniques at different scales. Synthesis strategies leveraging chemical, photonic, and mechanochemical driving forces further expand the definition and application scope of SMSI. Exquisite structure engineering permits elucidation of the interface, entropy, and size effect on the geometric and electronic characteristics. Materials innovation places the atomically thin two-dimensional materials at the forefront of interfacial active site control. A broader space is awaiting exploration, where exploitation of metal-support interactions brings compelling catalytic activity, selectivity, and stability.

Design of enhanced porous organic cage solubility in Type 2 porous liquids

Decreasing cost of technologies for direct air capture of carbon can be achieved through the design of new materials with high CO2 selectivity that can be incorporated into existing industrial processes. An emerging class of materials for these applications are porous liquids (PLs). PLs are mixtures of porous hosts and solvents with intrinsic porosity due to steric exclusion of solvent from inside the porous host. It is currently unknown how solvent -porous host interactions affect porous host solubility in the bulk solvent. Here, density functional theory simulations were used to investigate interactions between nine solvents and a CC13 porous organic cage (POC). Calculations identified that solvent molecules were the most stable when placed either inside the CC13 POC or in the pore window compared to interfacial binding sites. Structural changes to the CC13 POC correlated with reported experimental solubilities, including expansion of the CC13 POC with solvent molecule infiltration and expansion or contraction of the pore window. Based on these results, new PL design guidelines should include compositions with (1) high concentrations of POCs with flexible cage structures that can expand when solvated and (2) solvent molecule-POC combinations that contract the pore window during solvent molecule-host binding.

Densifying Crystalline-Amorphous Ni3S2/NiOOH Interfacial Sites To Boost Electrocatalytic O2 Production.

The development of an efficient and low-cost electrocatalyst for oxygen evolution reaction (OER) is the key to improving the overall efficiency of water electrolysis. Here, we report the design of a three-dimensional (3-D) heterostructured Ni9S8/Ni3S2 precatalyst composed of unstable Ni9S8 and inert Ni3S2 components, which undergoes in situ electrochemical activation to generate an amorphous-NiOOH/Ni3S2 heterostructured catalyst. In situ Raman spectroscopy combined with ex situ characterizations, such as X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, reveals that during the activation, Ni9S8 loses the sulfur element to form nickel oxides and eventually transforms to amorphous NiOOH at O2-evolving potentials, while the Ni3S2 component is rather inert that its majority in the bulk remains, thus forming a 3-D congee-like NiOOH/Ni3S2 heterostructure with the Ni3S2 crystalline particles randomly dispersed among amorphous NiOOH species. Unlike the sparse heterostructure that consists of a layer of NiOOH on top of Ni3S2, our unique congee-like NiOOH/Ni3S2 heterostructure provides plentiful reactive amorphous-crystalline interfacial sites. Moreover, the partial electron transfer between the NiOOH and remaining Ni3S2, benefiting from their dense interfacial sites, contributes to a higher valence state of the Ni3+ active centers in NiOOH, hence optimizing the adsorption of OER intermediates. Density functional theory calculations further disclose that the electronic structure regulation not only optimizes the Gibbs free energy of intermediate adsorption but also tunes the OH* absorption behavior to be exothermic, elucidating the spontaneous occurrence of OH* absorption and hence improves the OER. Therefore, a low overpotential of only 197 mV at an O2-evolving current density of 10 mA/cm2, a small Tafel slope of 38.8 mV/dec, and good stability are achieved on the amorphous-NiOOH/crystalline-Ni3S2 heterostructured catalyst.

Theoretical investigation on oxygen source for selective oxidation of glycerol at Au/CeO2−x and Pt/CeO2−x interfaces

Glycerol is considered as a significant green platform chemical, and many efforts have been devoted to design and prepare the efficient catalysts to convert glycerol to glyceric acid; however, the active site as well as reaction mechanism of glycerol oxidation remains rather ambiguous in terms of different oxygen sources. Herein, we studied the oxidation reaction of glycerol to glyceric acid over the catalytic systems of Au/CeO2−x and Pt/CeO2−x on periodic density functional theory (DFT) calculation in detail. By the optimization of catalyst structure models and comparison of substrate adsorption configurations, the interfacial sites of supported catalysts (Au/CeO2−x and Pt/CeO2−x) are regarded as the intrinsic active sites. Potential energy curve confirms that the reaction mechanism of glycerol oxidation includes two main pathways: OH− and O2 as oxygen sources in base and base-free environment, respectively. Mechanism studies indicate that Au/CeO2−x interface facilitates the dehydrogenation of C−H/O−H bond, which further promotes the formation of glyceraldehyde. Moreover, Pt/CeO2−x is favorable for the transfer of intramolecular H, resulting in excellent catalytic performance for the oxidation of glyceraldehyde to glyceric acid. The O2− was involved in oxidative dehydrogenation as active oxygen in base-free condition, and Pt/CeO2−x was more favorable for base-free glycerol oxidation. This work offers detailed insights into interfacial synergy effects of supported catalytic systems and the reaction mechanism of glycerol oxidation, which will pave the way for the selection of solvent conditions toward selective oxidation reaction.

Atomic Structural Origin of the High Methanol Selectivity over In2O3–Metal Interfaces: Metal–Support Interactions and the Formation of a InOx Overlayer in Ru/In2O3 Catalysts during CO2 Hydrogenation

CO2 hydrogenation to methanol is of great environmental and economic interest due to its potential to reduce carbon emissions and produce valuable chemicals in one single reaction. Compared with the unmodified traditional Cu/ZnO/Al2O3 catalyst, an indium oxide (In2O3)-based catalyst can double the methanol selectivity from 30–50 to 60–100%. It is worth noting that over catalysts involving various active metals dispersed on indium oxide (M/In2O3, M = Pd, Ni, Au, etc.), although the methanol yield is boosted, the selectivity remains similar to that of plain In2O3 despite the distinct chemical properties of the added metals. To investigate the phenomena behind this behavior, here we used RuO2/In2O3 as a test catalyst. The results of ambient pressure photoelectron spectroscopy, in situ X-ray absorption fine structure, and time-resolved X-ray diffraction indicate that the structure of the RuO2/In2O3 catalyst is highly dynamic in the presence of a reactive environment. Specifically, under CO2 hydrogenation conditions, Ru clusters facilitate the reduction of In2O3 to generate In2O3–x aggregates, which encapsulate the Ru systems in a migration driven by thermodynamics. In this way, the Ru0 sites for CH4 production are blocked while creating RuOx–In2O3–x interfacial sites with tunable metal–oxide interactions for selective methanol production. In an inverse oxide/metal configuration, indium oxide has properties not seen in its bulk phase that are useful for the binding and conversion of CO2. This work reveals the dynamic nature of In2O3-based catalysts, providing insights for a rational design of materials for the selective synthesis of methanol.

Selective CO2 Photoreduction to Acetate at Asymmetric Ternary Bridging Sites.

Photoreduction of CO2 is a promising strategy to synthesize value-added fuels or chemicals and realize carbon neutralization. Noncopper catalysts are seldom reported to generate C2 products, and the selectivity over these catalysts is low. Here, we design rich-interface, heterostructured In2O3/InP (r-In2O3/InP) for highly competitive photocatalytic CO2-to-CH3COOH conversion with a productivity of 96.7 μmol g-1 and selectivity > 96% along with water oxidation to O2 in pure water (no sacrificial agent) under visible light irradiation. The hard X-ray absorption near-edge structure (XANES) shows that the formation of r-In2O3/InP with the isogenesis cation adjusts the coordination environment via interface engineering and forms O-In-P polarized sites at the interface. In situ FT-IR and Raman spectra identify the key intermediates of OCCO* for acetate production with high selectivity. Density functional theory (DFT) calculations reveal that r-In2O3/InP with rich O-In-P polarized sites promotes C-C coupling to form C2 products because of the imbalanced adsorption energies of two carbon atoms. This work reports an interesting indium-based photocatalyst for selective CO2 photoreduction to acetate under strict solution and irradiation conditions and provides significant insights into fabricating interfacial polarization sites to promote the process.

Direct Active Site at the Van der Waals Heterostructure Interface with Synthetic Drug Analogue N-Methylphenethylimine Ultrasensitivity.

CNT/organic probe-based chemiresistive sensors suffer from the problem of low sensitivity and poor stability due to the unstable and unfavorable CNT/organic probe interface. A new designing strategy of a one-dimensional van der Waals heterostructure was developed for ultrasensitive vapor sensing. By modifying the perylene diimide molecule at the bay region with phenoxyl and further Boc-NH- phenoxy side chains, a highly stable 1D VDW heterostructure SWCNT-probe molecule system was formed with ultrasensitivity and specificity. Interfacial recognition sites consisting of SWCNT and the probe molecule are responsible for the synergistical and excellent sensing response to MPEA molecules, which was proved by Raman, XPS, and FTIR characterizations together with dynamic simulation. Based on such a sensitive and stable VDW heterostructure system, the measured detection limit reached as low as 3.6 ppt for the synthetic drug analogue N-methylphenethylimine (MPEA) in the vapor phase, and the sensor showed almost no performance degradation even after 10 days. Furthermore, a miniaturized detector was developed for real-time monitoring of drug vapor detection.

Sustained-Compensated Interfacial Zincophilic Sites to Assist High-Capacity Aqueous Zn Metal Batteries.

Aqueous Zn metal batteries have attracted extensive attention due to their intrinsic advantages. However, zinc ions tend to deposit irregularly, seriously depleting the capacity and stability of the battery. The construction of zincophilic sites can effectively regulate the nucleation and growth of Zn, but there is a defect that these sites will be covered with gradual failure after long-term cycling. Here, in combination with the sustained-compensated strategy, interfacial zincophilic sites are continuously constructed, thus effectively avoiding the threat of dendrites and improving the electrochemical performance. Impressively, at 10 mA cm-2 and 5 mAh cm-2, the protected Zn metal exhibits excellent cycling stability over 2000 cycles in the Zn//Zn battery. Moreover, even the cathode mass loading is considerably high (35 mg cm-2), and the Zn//NVO full cell significantly outperforms with high areal capacity (up to 4 mAh cm-2). This novel strategy provides a direction for the development of high-capacity aqueous batteries.

Inducing electronic asymmetricity on Ru clusters to boost key reaction steps in basic hydrogen evolution

Modulating electronic asymmetricity of catalysts is a novel option to regulate the electrocatalytic performance. Nevertheless, the efficient regulation of asymmetric degree of heterostructured catalysts at the atomic level still remains challenging. Herein, Ru nanoclusters (NCs, average particle size of ∼ 1.3 nm) were anchored on carbon materials doped by controllable N functional groups to optimize the electronic asymmetricity toward efficient hydrogen evolution reaction (HER). The electronic interaction between Ru and N species, and hence, the asymmetric electronic distribution of Ru NCs is subjectively manipulated by precisely tailoring the type of N dopants, especially pyrrolic-N, of carbon substrates. As a result, the pyrrolic-N dominated Ru-based heterostructures exhibit excellent HER activity compared to most of the current Ru-based electrocatalysts in basic media. Multiple spectroscopy experiments and density functional theory simulations demonstrate that the asymmetric distribution of surface electron of Ru-based heterostructures not only accelerates H2O adsorption and dissociation at interfacial Ru sites with positive charge but also facilitates the adsorption behavior of hydrogen on surface Ru sites with negative charge, thereby simultaneously optimizing the elementary steps in basic HER process. The present findings would provide some crucial understanding in manipulating the local electronic asymmetricity toward reasonable design and fabrication of advanced catalysts and beyond.

Rhenium Suppresses Iridium (IV) Oxide Crystallization and Enables Efficient, Stable Electrochemical Water Oxidation.

IrO2 as benchmark electrocatalyst for acidic oxygen evolution reaction (OER) suffers from its low activity and poor stability. Modulating the coordination environment of IrO2 by chemical doping is a methodology to suppress Ir dissolution and tailor adsorption behavior of active oxygen intermediates on interfacial Ir sites. Herein, the Re-doped IrO2 with low crystallinity is rationally designed as highly active and robust electrocatalysts for acidic OER. Theoretical calculations suggest that the similar ionic sizes of Ir and Re impart large spontaneous substitution energy and successfully incorporate Re into the IrO2 lattice. Re-doped IrO2 exhibits a much larger migration energy from IrO2 surface (0.96eV) than other dopants (Ni, Cu, and Zn), indicating strong confinement of Re within the IrO2 lattice for suppressing Ir dissolution. The optimal catalysts (Re: 10 at%) exhibit a low overpotential of 255mV at 10mA cm-2 and a high stability of 170h for acidic OER. The comprehensive mechanism investigations demonstrate that the unique structural arrangement of the Ir active sites with Re-dopant imparts high performance of catalysts by minimizing Ir dissolution, facilitating *OH adsorption and *OOH deprotonation, and lowering kinetic barrier during OER. This study provides a methodology for designing highly-performed catalysts for energy conversion.

Surface-modified liquid metal nanocapsules derived multiple triboelectric composites for efficient energy harvesting and wearable self-powered sensing

Liquid metal (LM) has been widely used as flexible electrodes for triboelectric nanogenerators (TENGs). However, the development of high-performance triboelectric composites based on LM droplets is still challenging due to the mismatched surface tension. Here, copolymer surface-modified LM nanocapsules (CPLM NCs) with core–shell structure are successfully synthesized via two-step method containing chelation reaction and in situ free-radical polymerization. The as-synthesized NCs can be incorporated into various polymers to fabricate diverse flexible polymer/NCs nanocomposites. Based on surface engineering, CPLM will not leak and drop off from nanocomposites when they suffer severe deformations, exhibiting good interfacial compatibility and robust mechanical properties. The introduction of NCs can improve the charge storage capability and electric outputs of various nanocomposites owing to more interfacial polarization sites, showing a versatile strategy for manufacturing high-powered triboelectric composites. The optimized polydimethylsiloxane/NCs-based TENG (PDMS/NCs-TENG) delivers a significant enhancement of power density by 28.3-fold and can availably power wearable electronics. PDMS/NCs-TENG can be also developed as a wearable self-powered sensor to detect physiological signals and joint-related motions in a real-time, rapid, and noninvasive way. This work not only renders a versatile strategy for the development of high-performance triboelectric materials but also provides a sustainable energy solution for wearable electronics.

Weak CO binding sites induced by Cu–Ag interfaces promote CO electroreduction to multi-carbon liquid products

Electrochemical reduction of carbon monoxide to high-value multi-carbon (C2+) products offers an appealing route to store sustainable energy and make use of the chief greenhouse gas leading to climate change, i.e., CO2. Among potential products, C2+ liquid products such as ethanol are of particular interest owing to their high energy density and industrial relevance. In this work, we demonstrate that Ag-modified oxide-derive Cu catalysts prepared via high-energy ball milling exhibit near 80% Faradaic efficiencies for C2+ liquid products at commercially relevant current densities (>100 mA cm−2) in the CO electroreduction in a microfluidic flow cell. Such performance is retained in an over 100-hour electrolysis in a 100 cm2 membrane electrode assembly (MEA) electrolyzer. A method based on surface-enhanced infrared absorption spectroscopy is developed to characterize the CO binding strength on the catalyst surface. The lower C and O affinities of the Cu–Ag interfacial sites in the prepared catalysts are proposed to be responsible for the enhanced selectivity for C2+ oxygenates, which is the experimental verification of recent computational predictions.

Synergistic effects of WO3 and NiCu bimetals for the One-Pot conversion of cellulose into ethylene glycol

One-pot catalytic conversion of cellulose to ethylene glycol (EG) provides an efficient way toward the production of high value-added chemicals from the abundant biomass resource. However, control of product selectivity is a challenge due to the thermal instabilities of cellulose derived sugars. Here, a series of multifunctional NiCu/WO3 catalysts were prepared and applied to this process. By tuning the metal ratio and WO3 content, a high EG selectivity of 58.9% was obtained. The selectivity of total diols even reached 83.9%. Besides, the catalyst revealed excellent performance in the conversion of raw biomass. Characterization results showed that the special catalyst structure of WO3-wrapped metal particles enabled the reaction to proceed in a well-defined sequence and also facilitated the formation of NiCu-WOx-1-O(H) interfacial sites. These interfacial sites offered high activity for the CC bond cleavage to produce glycolaldehyde from glucose. An appropriate amount of each active site ensured a well-synergistic effect of CC cleavage and hydrogenation capabilities, thus resulting in the highly selective formation of EG.

Contribution of surface carboxyl of cellulose in the formation mechanism and interfacial catalysis activity of ZnO/cellulose nanocomposites

The morphology, structure, and dispersion of photocatalysts play important roles in tailoring the surface active sites, photocatalytic productivity, and light utilization efficiency. Cellulose has been widely used in supporting and dispersing ZnO catalysts. However, surface groups of cellulose were ignored as a factor governing ZnO morphology. This work aims to explore the effects of cellulose surface groups on the formation and properties of ZnO catalysts. The reactivity, electronegativity, ion adsorption, and dispersion of the cellulose are improved after the introduction of carboxyl groups, which is beneficial to observe the induction of cellulose surface charge on the growth of ZnO. The results indicate that the diameter, sheet number, and thickness of flower-like ZnO in porous ZnO/cellulose nanocomposites are increased with the enhancement of cellulose surface electronegativity. The ZnO/cellulose nanocomposites with surface carboxyl content of 1.63 mmol*g−1 and zeta potential of –52.6 mV (ZnO/TOCNF3) have the highest photocatalytic activities and recycling for MO degradation due to the exposure of the interfacial active sites and strong electrostatic adsorption between carboxyl and ZnO. These findings provide a green method to regulate the formation and properties of catalysts by adjusting the surface electronegativity of cellulose nanofibers.

Mitigating Coke Formations for Dry Reforming of Methane on Dual-Site Catalysts: A Microkinetic Modeling Study

Dry reforming of methane (DRM) utilizes carbon dioxide (CO2) and methane (CH4) for syngas production. However, carbon accumulation leads to quick catalyst deactivation. In this study, we developed microkinetic models to describe dual-site catalyst systems to promote catalytic reactivity and suppress coke formation. These dual-site systems serve as idealized bifunctional catalyst models with well-defined active sites targeting different types of chemistries in one reaction network. According to density functional theory (DFT) calculations, the Co and Co–Mo2N interfacial sites in the Co–Mo ternary nitride (i.e., Co3Mo3N) show distinct reactivities toward CH4 decomposition and CHx oxidation, respectively. DFT calculations suggested that DRM intermediates (e.g., OH, CHO) do not always follow unified linear scaling relationships. Hence, a breakthrough was achieved from the limitations of the intrinsic linear correlations embedded in species adsorptions and activations. We employed microkinetic modeling to quantify the enhancement in syngas productions related to bifunctionality. Moreover, we confirmed that Co3Mo3N is the most effective in mitigating coke formation by facilitating the oxidation and transportation of carbonaceous species (e.g., C, CH) from the initial active sites to sustain a high reactivity. This work has shed light on rational catalyst designs to achieve high reactivity and long-term stability, especially for reactions such as DRM.

Insights into CO Oxidation in Cu/CeO2 Catalysts: O2 Activation at the Dual‐Interfacial Sites

AbstractCu clusters supported on CeO2 have been reported as a promising and active catalyst for CO oxidation. However, the identification of interfacial interactions and active sites is still a great challenge. In this work, we demonstrated that interfacial chemistry can be understood and predicted by using a simple descriptor of adsorbate‐surface interactions that uncovers structure‐activity relationships. The catalytic activity of CeO2 supported Cu clusters for CO oxidation was studied by density functional theory. The Cu−Ce dual site mechanism enables the Cu/CeO2 catalyst to have a much lower reaction energy barrier than the Mars‐van Krevelen (M‐vK) mechanism and the Cu‐only mechanism. The reaction energy barriers of Cu/CeO2‐x with an oxygen vacancy on the CeO2 surface were 0.10, 0.37 and 0.77 eV, respectively. The excellent performance of Cu/CeO2 catalysts is related to the interfacial interaction between Cu and CeO2 and their synergistic redox behaviors, and oxygen vacancies facilitate the generation and stabilization of active Cu+ species through the interaction with Cu clusters. And we have identified the binding energy of O2* can describe the CO oxidation activity of Cu/CeO2. Our study provides insight into the nature of active sites for Cu/CeO2 catalysts and guidance for high‐performance.

A Heterostructure Photoelectrode Based on Two-Dimensional Covalent Organic Framework Film Decorated TiO2 Nanotube Arrays for Enhanced Photoelectrochemical Hydrogen Generation.

The well-defined heterostructure of the photocathode is desirable for photoelectrochemically producing hydrogen from aqueous solutions. Herein, enhanced heterostructures were fabricated based on typical stable covalent organic framework (TpPa-1) films and TiO2 nanotube arrays (NTAs) as a proof-of-concept model to tune the photoelectrochemical (PEC) hydrogen generation by tailoring the photoelectrode microstructure and interfacial charge transport. Ultrathin TpPa-1 films were uniformly grown on the surface of TiO2 NTAs via a solvothermal condensation of building blocks by tuning the monomer concentration. The Pt1@TpPa-1/TiO2-NTAs photoelectrode with single-atom Pt1 as a co-catalyst demonstrated improved visible-light response, enhanced photoconductance, lower onset potential, and decreased Tafel slope value for hydrogen evolution. The hydrogen evolution rate of the Pt1@TpPa-1/TiO2-NTAs photoelectrode was five times that of Pt1@TpPa-1 under AM 1.5 simulated sunlight irradiation and the bias voltage of 0 V. A lower overpotential was recorded as 77 mV@10 mA cm-2 and a higher photocurrent density as 1.63 mA cm-2. The hydrogen evolution performance of Pt1@TpPa-1/TiO2-NTAs photoelectrodes may benefit from the well-matched band structures, effective charge separation, lower interfacial resistance, abundant interfacial microstructural sites, and surficial hydrophilicity. This work may raise a promising way to design an efficient PEC system for hydrogen evolution by tuning well-defined heterojunctions and interfacial microstructures.

Heterostructured Core-Shell Ni-Co@Fe-Co Nanoboxes of Prussian Blue Analogues for Efficient Electrocatalytic Hydrogen Evolution from Alkaline Seawater.

The rational construction of efficient and low-cost electrocatalysts for the hydrogen evolution reaction (HER) is critical to seawater electrolysis. Herein, trimetallic heterostructured core-shell nanoboxes based on Prussian blue analogues (Ni-Co@Fe-Co PBA) were synthesized using an iterative coprecipitation strategy. The same coprecipitation procedure was used for the preparation of the PBA core and shell, with the synthesis of the shell involving chemical etching during the introduction of ferrous ions. Due to its unique structure and composition, the optimized trimetallic Ni-Co@Fe-Co PBA possesses more active interfacial sites and a high specific surface area. As a result, the developed Ni-Co@Fe-Co PBA electrocatalyst exhibits remarkable electrocatalytic HER performance with small overpotentials of 43 and 183 mV to drive a current density of 10 mA cm-2 in alkaline freshwater and simulated seawater, respectively. Operando Raman spectroscopy demonstrates the evolution of Co2+ from Co3+ in the catalyst during HER. Density functional theory simulations reveal that the H*-N adsorption sites lower the barrier energy of the rate-limiting step, and the introduced Fe species improve the electron mobility of Ni-Co@Fe-Co PBA. The charge transfer at the core-shell interface leads to the generation of H* intermediates, thereby enhancing the HER activity. By pairing this HER catalyst (Ni-Co@Fe-Co PBA) with another core-shell PBA OER catalyst (NiCo@A-NiCo-PBA-AA) reported by our group, the fabricated two-electrode electrolyzer was found to achieve high output current densities of 44 and 30 mA cm-2 at a low voltage of 1.6 V in alkaline freshwater and simulated seawater, respectively, exhibiting remarkable durability over a 100 h test.

Dual-heterophase MoS2-MoC@rGO cocatalyst with rapid electron transfer and interfacial H2-evolution reaction toward efficient photocatalytic activity of TiO2

Cubic molybdenum carbide (MoC) as a non-noble cocatalyst has been extensively reported in the area of photocatalytic H2 generation because of its comparable H+-adsorption ability to noble-metal Pt. However, its relatively low conductivity and insufficient content of hydrogen-evolution active sites lead to a limited H2-generation activity of MoC-based photocatalysts. Considering that the introduction of graphene nanosheets and MoS2 is beneficial to promoting electron transfer and increasing interfacial H2-evolution active sites, in this article, MoS2-MoC (inner heterophase) was grown on reduced graphene (rGO) as an outer-heterophase support to construct dual-heterophase MoS2-MoC@rGO cocatalyst for the enhanced hydrogen-production performance of TiO2. Herein, MoS2-MoC@rGO cocatalysts were first synthesized by controlling a ratio between the materials (GO, (NH4)6Mo7O24 and thiourea) during one-step calcination, and further coupled with the TiO2 to prepare the MoS2-MoC@rGO/TiO2 via a simple sonication method. The hydrogen-production test indicated that the highest H2-production rate of MoS2-MoC@rGO/TiO2 reached 575 μmol h−1 g−1 (AQE = 1.73%), which was 58, 3.6 and 2.1 times of that for the TiO2, MoC@rGO/TiO2, and MoS2@rGO/TiO2, respectively. The enhanced performance of MoS2-MoC@rGO/TiO2 can be ascribed to the dual-heterophase MoS2-MoC@rGO, where the rGO nanosheets accelerate the photoelectron transfer and the MoS2 increases the number of interfacial hydrogen-evolution active sites. This work provides a viable strategy for exploring effective MoC-modified photocatalysts in the area of photocatalytic hydrogen production.

Construction of CuO/CeO2 Catalysts via the Ceria Shape Effect for Selective Catalytic Oxidation of Ammonia

Tuning the interaction between the loaded metal oxide and the support material is an efficient strategy to boost catalytic purification of ammonia (NH3) as an important factor in the formation of haze. Herein, CuO/CeO2 catalysts based on the ceria shape effect (Ce-NR and Ce-NC) are prepared and tested for the selective catalytic oxidation of ammonia (NH3-SCO). The interaction between CuO and CeO2 with different shapes is crucial to regulate the interface structure and the content of oxygen vacancies. The Cu/Ce-NR possesses more Cu+-Ov-Ce3+ interfacial sites and more oxygen vacancies and achieves a higher catalytic activity (T100 = 240 °C) and a lower apparent activation energy (37.18 kJ mol–1) for NH3-SCO compared with Cu/Ce-NC (T100 = 270 °C, 86.57 kJ mol–1). In situ diffuse reflectance infrared Fourier transform spectra and density functional theory calculation results prove that the Cu+-Ov-Ce3+ interfacial site is the main adsorption site for NH3. The further reaction of in situ generated nitrate with NH3 is the rate-determining step over the CuO/CeO2 catalysts, and it is revealed that NH3 much more easily reacts with the monodentate nitrate species formed on the Cu/Ce-NR catalyst than the bidentate nitrate formed on the Cu/Ce-NC catalyst at 240 °C. This study enriches the understanding of designing efficient catalysts by support shape to modulate their interfacial structure and thus improve the activity of NH3-SCO.