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Electrochemical CO2reduction to produce value-added chemicals and fuels is one of the research hotspots in the field of energy conversion. The development of efficient catalysts with high conductivity and readily accessible active sites for CO2electroreduction remains challenging yet indispensable. In this work, a reliable poly(ethyleneimine) (PEI)-assisted strategy is developed to prepare a hollow carbon nanocomposite comprising a single-site Ni-modified carbon shell and confined Ni nanoparticles (NPs) (denoted as Ni@NHCS), where PEI not only functions as a mediator to induce the highly dispersed growth of Ni NPs within hollow carbon spheres, but also as a nitrogen precursor to construct highly active atomically-dispersed Ni-Nxsites. Benefiting from the unique structural properties of Ni@NHCS, the aggregation and exposure of Ni NPs can be effectively prevented, while the accessibility of abundant catalytically active Ni-Nxsites can be ensured. As a result, Ni@NHCS exhibits a high CO partial current density of 26.9 mA cm–2and a Faradaic efficiency of 93.0% at −1.0 V vs.RHE, outperforming those of its PEI-free analog. Apart from the excellent activity and selectivity, the shell confinement effect of the hollow carbon sphere endows this catalyst with long-term stability. The findings here are anticipated to help understand the structure-activity relationship in Ni-based carbon catalyst systems for electrocatalytic CO2reduction. Furthermore, the PEI-assisted synthetic concept is potentially applicable to the preparation of high-performance metal-based nanoconfined materials tailored for diverse energy conversion applications and beyond.

Among insulating transition-metal oxides, ZrO2has the potential to be a photocatalyst; however, its wide bandgap (∼5 eV) interferes with its ability to absorb sufficient light. Defect engineering—that is, the creation of oxygen vacancies (VOs) and/or Zr3+ions, is a promising strategy for adjusting the bandgap of ZrO2for photocatalytic applications. This study demonstrates that the included VOs play an important role in boosting photocatalytic activity. In addition, the crystal phase of ZrO2(e.g., monoclinic or tetragonal) strongly influences both VOformation and photocatalytic activity. After a Pt cocatalyst was deposited onto ZrO2with a single crystal phase (i.e., monoclinic (m-) or tetragonal (t-)), the specimens were reduced at 200, 400, and 600 °C to obtain photocatalysts with different amounts of VOs. As-synthesized m-ZrO2possessed Zr3+ions in the absence of VOs, and the reduction treatment promoted VOformation accompanied by the disappearance of Zr3+. The as-synthesized t-ZrO2originally included VOs, and their amount in Pt/t-ZrO2−xincreased with increasing reduction temperature. Pt/t-ZrO2−xpossessed a greater amount of VOs than Pt/m-ZrO2−xreduced at the same temperature, suggesting that VOformation occurs more easily in t-ZrO2than in m-ZrO2. Photocatalytic activity increased with increasing reduction temperature, which is the same tendency observed for the VOamount. In a comparison of the crystal phases, Pt/m-ZrO2−xexhibited relatively higher activity than Pt/t-ZrO2−xdespite its fewer VOs, suggesting that the VOformed in the monoclinic ZrO2contributes to the enhancement of the photocatalytic activity more efficiently than in the tetragonal one.

Hydrogenation of carbon dioxide (CO2) using CO2-free hydrogen (H2) to produce methanol (CH3OH) is a promising reaction that can alleviate both carbon emissions and the dependence on fossil fuels. Nonstoichiometric molybdenum suboxide coupled with Pt nanoparticles (NPs) acts as a promising catalyst for this reaction, in which surface oxygen vacancies (VO) and the redox ability of Mo in molybdenum suboxide are the keys to transforming CO2into the CO intermediate and further to afford CH3OH. In this study, a series of molybdenum oxides with different morphologies, including bulk, nanosheet, nanobelt, and rod morphologies, are used as catalysts, and the effects of particle morphologies on the catalytic performance toward CO2hydrogenation are examined. A Pt-loaded molybdenum suboxide nanosheet (Pt/HxMoO3–y(Sheet)) with a high specific surface area affords 1.35 times greater CO2conversion and CH3OH yield in liquid-phase CO2hydrogenation compared with the corresponding bulk analog under relatively mild reaction conditions (total 4.0 MPa, 200 °C). Experiments and comprehensive analyses, including X-ray diffraction and in situ X-ray absorption fine structure studies, reveal that the enhanced activity of Pt/HxMoO3–y(Sheet) is attributable to a high concentration of surface-exposed VOsites, which are introduced in the (010) plane during the H2reduction due to the high surface-to-volume ratio of the nanosheet-structured MoO3. In addition, the nanosheet-structured catalyst exhibits better reusability because of its antiaggregation behavior for Pt NPs compared with the conventional bulk analog.

Fenton reaction has important implications in biology- and environment-related remediation. Hydroxyl radicals (•OH) and hydroxide (OH–) were formed by a reaction between Fe(II) and hydrogen peroxide (H2O2). The acidic H2O2/Fe(II/III) redox-induced low H2O2utilization efficiency is the bottleneck of Fenton reaction. Electron paramagnetic resonance, surface-enhanced Raman scattering, and density functional theory calculation indicate that the unpaired electrons in the defects of carbon quantum dots (CQDs) and the carboxylic groups at the edge have a synergistic effect on CQDs Fenton-like catalysis. This leads to a 33-fold higher H2O2utilization efficiency in comparison with Fe(II)/H2O2Fenton reaction, and the pseudo-first-order reaction rate constant (kobs) increases 38-fold that of Fe(III)/H2O2under equivalent conditions. The replacement of acidic H2O2/Fe(II/III) redox with CQD-mediated Fe(II/III) redox improves the sluggish Fe(II) generation. Highly effective production of •OH in CQDs-Fe(III)/H2O2dramatically decreases the selectivity of toxic intermediate benzoquinone. The inorganic ions and dissolved organic matter (DOM) in real groundwater show negligible effects on the CQDs Fenton-like catalysis process. This work presents a process with a higher efficiency of utilization of H2O2in situchemical oxidation (ISCO) to remove persistent organic pollutants.

Reduction of α-MoO3via“hydrogen spillover” process mediated by noble metal nanoparticles leads to a formation of hydrogen molybdenum bronze with plasmon-induced optical features. We herein report that Pd-loaded hydrogen molybdenum bronze effectively promotes the hydrodeoxygenation of aromatic ketones to the corresponding alkyl aromatics at room temperature and under atmospheric pressure of H2. The catalyst shows a further enhanced catalytic activity under the irradiation of visible light due to the plasmonic effect.Reduction of α-MoO3via “hydrogen spillover” process leads to a formation of hydrogen molybdenum bronze with plasmon-induced optical features. We herein report that Pd-loaded hydrogen molybdenum bronze effectively promotes the hydrodeoxygenation of aromatic ketones to alkyl aromatics under mild conditions. The catalyst shows a further enhanced catalytic activity under the irradiation of visible light due to the plasmonic effect.

Hydrogen spillover can assist the introduction of defects such as Ti3+and concomitant oxygen vacancies (VO) in a TiO2crystal, thereby inducing a new level below the conduction band to improve the conductivity of photogenerated electrons and the visible light absorption property of TiO2. Meanwhile, crystal facet engineering offers a promising approach to achieve improved activity by influencing the recombination step of the photogenerated electrons and holes. In this study, with the aim of achieving enhanced visible light-driven photocatalytic activity, rutile TiO2nanorods with different aspect ratios were synthesized by crystal facet engineering, and Pt-deposited TiO2–xnanorods (Pt/TNR) were then obtained via reduction treatment assisted by hydrogen spillover. The reduction treatment at 200 °C induced the formation of surface Ti3+exclusively, whereas surface Ti3+and VOwere formed by performing the reduction at 600 °C. The Pt/TNR with a higher aspect ratio reduced at 200 °C exhibited the highest activity in photocatalytic H2production under visible light irradiation owing to the synergistic effect of the introduction of Ti3+defects and the spatial charge carrier separation induced by crystal facet engineering.

Electrocatalytic conversion of nitrate (NO3−) to ammonia (NH3) holds significant potential in the control of nitrogen oxide (NOx) from stationary sources. However, previous studies on reaction intermediates remain unclear. Here we report that PdCu/Cu2O hybrids with mesoporous hollow sphere structure show high selectivity (96.70%) and Faradaic efficiency (94.32%) for NH3synthesis from NO3−. Detailed characterizations demonstrate that (1) Pd enables electron transfer (Pd 3d → Cu 3d) and causes the polarization of Cu 3d orbitals by forming partial PdCu alloys, which makes Pd electron deficient but offers empty orbits to adsorb NO3−, and (2) electron-rich Cu is more conducive to the occurrence of NO3−reduction. The mutual confirmation of online differential electrochemical mass spectrometry and density functional theory calculations demonstrates that PdCu alloys block the generation of ∗NOH intermediate and facilitate the formation of ∗N, providing a new mechanism for NH3synthesis from NO3−reduction reactions.

Defect engineering of metal oxides is a facile and promising strategy to improve their photocatalytic activity. In the present study, Pt/TiO2–xwas prepared by a reduction treatment assisted by hydrogen spillover to pure rutile, anatase, and brookite and was subsequently used for hydrogen production from an aqueous methanol solution. With increasing reduction temperature, the photocatalytic activity of the rutile Pt/TiO2–xincreased substantially, whereas the activity of anatase Pt/TiO2–xdecreased and that of brookite Pt/TiO2–xwas independent of the treatment temperature. Electron-spin resonance analysis revealed that rutile and brookite possess similar defect sites (Ti3+and concomitant oxygen vacancy) after the reduction at 600 °C, whereas different resonance signals were observed for anatase after the reduction at 600 °C. During the reduction process, electrons donated from spillover hydrogen migrate between the conduction band and the inherent midgap states. This research demonstrates that the depth of the inherent midgap states, depending on the crystal phases, influences the generation of defects, which play a key role in the photocatalytic performance of Pt/TiO2–x.

Molybdenum sulfide has attracted intense attention owing to unique heteromorphism. A natural molybdenum sulfide shows a semiconductive 2H crystal structure, while another metallic 1T-MoS2exhibits a higher catalytic activity. However, the strict synthetic condition and the metastable property of 1T-MoS2have limited its application. Hybrid-phase 1T/2H-MoS2possesses both higher catalytic activity than 2H-MoS2and better thermal/chemical stability than 1T-MoS2, which is a more promising candidate in the catalytic field. As for photocatalytic field, 2H-MoS2has been only used as a cocatalyst but not as an individual photocatalyst due to its fast electron–hole recombination level and nonideal surface active site nature. Hybrid-phase MoS2would provide a proper solution for individual MoS2as a photocatalyst because 1T sites can collect photoelectrons and provide active sites for various reactions. In this work, we report a hybrid-phase MoS2synthesized by a simple hydrothermal method, which is applied to the photocatalytic conversion of a series of nitroaromatics to aminoaromatics. The reactions are not favorable with natural 2H-MoS2, which reveals new potential of MoS2as a noble metal-free photocatalyst.

Porous silica with a unique nanostructure and interesting properties has a versatile range of applications. Hierarchically ordered macroporous silica (MacroS) can trap incident light inside the pores through a multiple scattering process, which is attractive for light harvesting. Mesoporous silica (MesoS) with a high specific surface area has been widely employed as a support material. Macro-/mesoporous silica (MMS) that combines both characteristics can provide multi-functionality, such as light scattering properties, high surface area, and efficient mass transfer. In this study, MMS, MacroS, MesoS, and bulk silica without pores were utilized as supports for plasmonic Ag catalysts, and the structural effect of silica supports on plasmonic Ag catalysis was investigated. Macropores with a diameter of ca.300 nm and mesopores with diameters of ca.2–3 nm were fabricated by a template method with a hybrid of polymethylmethacrylate colloidal crystals and octadecyltrimethylammonium chloride. Under dark conditions, Ag/MMS exhibited the highest activity for 4-nitrophenol reduction due to effective mass transfer through the mesopores that connected neighboring macropores, which provided accessibility of the reactants to the Ag nanoparticles (NPs). Ag/MMS exhibited the largest enhancement of activity under visible light irradiation not only because of its effective mass transfer and multiple scattering process but also because of the formation of moderate-sized plasmonic Ag NPs.

Effects of morphology and exposed crystal planes of NiOx-decorated CeO2(NiCeO2) nanostructured catalysts on activity during CO2methanation were examined, using nanorod (NR), nanocube (NC), and nanooctahedron (NO) structures. The NiCeO2nanorods (NiCeO2-NR) showed superior activity to NiCeO2-NC and NiCeO2-NO along with excellent selectivity for CH4. This material also demonstrated exceptional durability, with no significant loss of catalytic activity or structural change after use. Comprehensive physicochemical characterization as well as density functional theory calculations determined that the high performance of the NiCeO2-NR was closely related to the large quantity of surface oxygen vacancies and the high degree of reversibility associated with the Ce4+↔ Ce3+redox cycle of the support. These effects originate from the enhanced reactivity of oxygen atoms on the (110) surfaces of the oxide compared with the (100) and (111) surfaces. This information is expected to assist in the rational design of practical catalysts for the activation of CO2molecules and other important transformations.

Palladium nanoparticles (Pd NPs) were synthesized by the reduction-by-solvent method using polyvinylpirrolidone (PVP) as capping agent. The nonstatic interaction between PVP and the metallic surface may change the properties of the NPs due to the different possible interactions, through either the O or N atoms of the PVP. In order to analyze these effects and their repercussions in their catalytic performance, Pd NPs with various PVP/Pd molar ratios (1, 10, and 20) were prepared, deposited on silica, and tested in the formic acid decomposition reaction. The catalytic tests were conducted using catalysts prepared by loading NPs with three different time lapses between their purification and their deposition on the silica support (1 day, 1 month, and 6 months). CO adsorption, FTIR spectroscopy, XPS, and TEM characterization were used to determine the accessibility of the Pd NPs surface sites, the electronic state of Pd, and the average NPs size, respectively. The H2production from the formic acid decomposition reaction has a strong dependence on the Pd surface features, which in turn are related to the NPs aging time due to the progressive removal of the PVP.

Au–CeO2catalysts are prepared from amorphous Ce–Al alloys by the dealloying method, and their catalytic performances are examined in the oxidation of benzyl alcohol to benzaldehyde using O2as an oxidant. The catalytic activity of the Au–CeO2catalysts is improved using an amorphous alloy as a precursor, and further improved activity is attained by directly alloying Au with Ce–Al rather than by depositing Au on preformed CeO2. Consequently, Au–CeO2prepared directly from an amorphous Au–Ce–Al alloy exhibits the highest activity among the prepared samples, despite its low surface area. Detailed characterization by means of XPS analysis indicates that most of the Au species in Au–CeO2prepared from the amorphous Au–Ce–Al alloy exist in a +1 oxidation state (Au+). The presence of Au+facilitates the migration of oxygen atoms through the lattice, which likely contributes to the high catalytic activity of the Au–CeO2catalyst.

It is intriguing yet challenging to synthesize high-performance heterogeneous catalysts for carbon dioxide (CO2) hydrogenation reactions. The excellent catalytic performance of heterogeneous catalysts has attracted widespread attention recently. Herein, a series of Pd–Cu alloy nanoparticles confined within mesoporous hollow carbon spheres (MHCS) were prepared and tested as catalysts for CO2hydrogenation to formate. The optimized Pd2Cu14–N@MHCS catalyst, which was obtained with about 1 wt % Pd loading and a Pd/Cu molar ratio of 2:14 by the coreduction method, exhibited high activity for CO2hydrogenation to formate, showing a high turnover number (TON) of 1432 at 100 °C after 24 h. Scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure spectroscopy (XAFS) analyses revealed that when the Pd/Cu molar ratio was 2:14, the Pd atoms were well isolated by the Cu atoms via a Pd–Cu alloy. Density functional theory (DFT) calculations demonstrated that the PdCu2(111) surface enhanced not only the dissociation of H2but also the attack of the C atoms of the adsorbed HCO3–on Cu atoms by the dissociated H atoms on Pd atoms. This was attributed to an electron transfer from Cu to Pd in the alloy.

Amorphous alloys are still attracting great attention in the field of catalysis despite the fact that they have been investigated since the 1950s. One of the reasons why amorphous alloys have been in the spotlight until now, are their physical and chemical properties, which would make them suitable materials to be used as catalysts at industrial scale. This review deals with the recent research on applications of amorphous alloys for catalysis. These investigations were addressed to elucidate the relationship between the structural changes (morphology, surface-exposed metal sites, etc.) and the catalytic activity for representative reactions such as hydrogenations, oxidations and hydrogen production from hydrogen carrier molecules. Furthermore, the impact of the combination of an amorphous alloy with another kind of material (MOF and CeO2) and the introduction of a third metal was also discussed.Amorphous alloys attract great attention in the field of catalysis because their physical and chemical properties make them suitable materials to be used as catalysts at industrial scale. In this review we report some representative examples of amorphous alloys applied to hydrogenation, dehydrogenation, and oxidation reactions.

Phase engineering has been recognized as a promising method for boosting the catalytic activity of molybdenum sulfide (MoS2) in the field of electrocatalysts and photocatalysts. The metallic 1T-MoS2exhibits much higher catalytic activity than natural semiconducting 2H-MoS2but suffers from harsh synthetic conditions and metastable physical/chemical properties. The hybrid 1T/2H phase MoS2shows higher catalytic activity than the 2H-MoS2and exhibits better stability than the 1T-MoS2, which is more favorable than the 2H-MoS2in the photocatalytic reactions. In this study, we report a hydrothermal synthesis of the hybrid 1T/2H-MoS2phase coupled with SiC as a heterojunction photocatalyst for 4-nitrophenol (4-NP) degradation. SiC acts as a counterpart of the heterojunction structure and a morphology modifier, which dramatically promotes the reaction rate and visible light responsibility, providing new candidates and strategies in photocatalysis.

In semiconductor nanocrystals (NCs), a new regime has been opened in the plasmonic field since the discovery of localized surface plasmon resonances (LSPRs). LSPRs that lead to near-field enhancement, scattering, and resonant absorption around the NC can be tuned in the range from the visible to the near-infrared (NIR) region across a wide optical spectrum by synthetically varying the doping level, and post synthetically viaelectrochemical control, photochemical control, and chemical oxidation and reduction. In this review, we will focus on the three widely explored and interrelated examples and their manipulation methods of LSPR of (1) hydrogen molybdenum bronze (HxMoO3−y) NCs, (2) hydrogen tungsten bronze (HxWO3−y) NCs, and (3) oxygen vacancy doped molybdenum tungsten oxide (MoxW1−xO3−y) NCs. Finally, a brief outlook on the applications of these plasmonic NCs is presented.

In this work, a water splitting photoanode composed of hematite (α-Fe2O3) nanorods was modified with a Co(salen)-based cocatalyst, which was proven to exhibit special photoelectrochemical (PEC) oxygen evolution activity. Co(salen) was deposited on the surface of the α-Fe2O3photoanode as a precursor of the cocatalyst and then heat-treated at different temperatures. When the annealing temperature is 250 °C, Co(salen) transforms into Co3+species stabilized with C–N ligands, which act as active sites and decrease the OER energy barrier for the photoelectrochemical process of the α-Fe2O3photoanode. Meanwhile, the interaction between Co–C–N and Fe (Co–C–NFe) viavan der Waals force can provide a photocarrier transfer pathway to achieve a 1.7 fold higher photocurrent at 1.23 V vs.RHE and 180 mV onset potential negative shift compared to those of the pure α-Fe2O3photoanode. This work demonstrates a unique surface structure of a cocatalyst created by a post synthetic strategy using a metal complex precursor containing organic ligands.

A new type of pyrene–thiol derivative-modified Pd nanoparticle (NP) catalyst on a carbon black support for the efficient semihydrogenation of alkynes to alkenes is reported herein. Colloidal Pd NPs surrounded by pyrene–thiol modifiers were prepared using the two-phase Brust method followed by impregnation of carbon black materials. Based on the structural characterization of the prepared catalyst (PyC12S-Pd/VC) by NMR, UV–vis, FT-IR, TEM, HAADF-STEM, Pd K-edge XAFS, XRD, N2adsorption, and XPS, we show that highly dispersed Pd NPs are immobilized on the catalysts via π–π interaction between pyrene groups bound to the Pd NPs and carbon black supports. PyC12S-Pd/VC efficiently catalyzes the alkyne semihydrogenation reaction while maintaining high alkene selectivity; an alkene selectivity of 94% is attained at 98% conversion after 5 h of reaction, and the selectivity was retained around 80% in 10 h of reaction. This performance is superior to that of a catalyst without pyrene groups and that of a commercial Lindlar catalyst. The steric hindrance of pyrene groups restricts access of the substrates to Pd NP surfaces, suppressing the unfavorable overhydrogenation of alkenes to alkanes, which is revealed by the solvent and substrate dependency on the catalytic performance and a DFT calculation study. Furthermore, the high selectivity and stability of PyC12S-Pd/VC are caused by the strong interaction between pyrene groups and carbon supports, which prevents the separation of pyrene modifiers and the leaching or sintering of Pd NPs during the catalytic reaction. It is demonstrated that the combination of Pd NPs, pyrene–thiol modifiers, and carbon supports offers high activity, alkene selectivity, and stability in the semihydrogenation reaction.

Visible-light boosting chemical reactions by surface plasmon resonance (SPR) have recently received much attention in photocatalysis. Although multiple types of plasmonic catalysts have been developed, the efficient utilization of SPR-induced hot-electrons remains to be a challenging task due to their ultrafast decay. In this study, structure-controlled Pd-graphene-Au nanorod nanocomposite catalysts are fabricated for maximizing hot-electron utilization in SPR-enhanced reactions. The characterization confirmed that highly dispersed Pd clusters were deposited on a homogeneous reduced graphene oxide (rGO) layer-coated Au nanorods. The catalytic activity in the Suzuki–Miyaura coupling reaction was highly enhanced under visible-light irradiation due to the SPR of the Au nanorods, whose performance was superior to that without an rGO layer. Further experimental and calculation study demonstrated that the electro-conductive rGO layer plays a crucial role as an electron mediator for promoting hot-electron transportation from Au to Pd, which resulted in the reaction acceleration.

Especially in the context of current greenhouse effect and energy shortage, the development of various catalysts to catalyze CO2resource utilization is an attractive field. Recently, the yolk-shell catalyst solves the problems of coking and sintering and further provides confinement effects as well as improved stability. In this mini-review, the development status of carbon, silicon-based yolk-shell structured catalysts for hydrogenation of CO2to formate/formic acid, and CO2dry reforming of methane are introduced. The latest research progress of catalysts and active metals commonly used in these reactions is reviewed, as well as how to provide superior performance in these reactions. In addition, the properties of customized yolk-shell structure and the effect of pore size change on CO2hydrogenation and dry reforming reaction will be briefly described. Furthermore, the effect of space restriction and how to enhance the performance of the yolk-shell structure nanoreactor are also discussed. We firmly believe that this mini-review will stimulate more research in the catalysis community, especially to advance the design of yolk-shell catalytic materials, and ultimately achieve sustainable development of the carbon cycle.

The well-defined cavities of metal–organic frameworks (MOFs) offer interesting opportunities for the encapsulation of various nanoparticles, organic dyes and metal complexes. In particular, [Ru(bpy)3]2+-incorporated MOFs (bpy = 2,2′-bipyridine) have been studied because of the high photocatalytic activity of the Ru complex. However, the successful application of this composite in photocatalysis is rarely reported. We herein report the facile encapsulation of [Ru(bpy)3]2+in MIL-125-NH2, an MOF composed of 2-aminoterephthalic acid linkers and Ti8O8(OH)4clusters. The Ru complex-incorporated MOF showed significantly enhanced activity in the photocatalytic aerobic oxidation of benzylalcohol to benzaldehyde as compared to its complex-free and amine-free counterparts. The high activity of the metal complex-incorporated MOF was attributed to the combined visible light absorption by both MIL-125-NH2and the [Ru(bpy)3]2+complex.

Recent years have marked substantial research interest in the design and development of photocatalyst materials for the conversion of solar to chemical energy. In this brief account, we present some of the recent research on silver-based plasmonic nanocatalysts supported on silica for their preparative techniques, characterization and efficient catalysis under visible light irradiation conditions. Ag nanoparticles (NPs) which can be prepared with different color and morphology, are explored for possible enhancement effects in catalytic performance activities under visible light irradiation. A number of combinations of Ag with other catalytically active metal NPs is studied for exploring the plasmonic enhancement activities. Ag NPs combined with single site Ti-oxide moiety is studied for the enhanced hydrogen production activity attributing to the Ag plasmonic effect under UV-vis light irradiation. The account is further elaborated by citing some recently reported works, plausible mechanism of enhancements, conclusions and outlook. We expect that the present account will provide insights into the design and investigation of catalytic performances in the visible light driven plasmon-mediated chemical reactions.The ability of plasmonic nanostructures to concentrate light in small volumes has been widely researched for their application in solar energy production. In this review, we have presented the design of silver-based plasmonic nanostructures confined within the mesoporous channels of silica material. These nanocatalysts are explored in the variety of chemical reactions for their efficient catalysis under visible light irradiation.

Carbon materials have been extensively studied for several decades as catalytic supports because of their high surface area and porous structures. However, carbon black supports, such as Ketjen black or Vulcan XC-72, have rarely been utilized for organic syntheses, though they have recently been widely studied in electrocatalysts. In this study, we examined Ketjen black with high surface area and high pore volume as a support for Ru nanoparticles (NPs) in the catalytic transfer hydrogenation (CTH) reaction. The performance of the Ru NP catalyst supported on Ketjen black was superior to that on other carbon supports. The catalysts were structurally characterized using X-ray diffraction, X-ray absorption fine structure, transmission electron microscopy, CO chemisorption, and N2adsorption/desorption measurements. A clear correlation was observed among the micro- and mesopore volume, the adsorption capacity of reactant, and the catalytic activity, and therefore, micro- and mesopores in Ketjen black were found to adsorb the reactant, acetophenone, and thus play a crucial role in achieving high catalytic performance in the CTH reaction.

Harvesting solar light to boost commercially important organic synthesis still remains a challenge. Coupling of conventional noble metal catalysts with plasmonic oxide materials which exhibit intense plasmon absorption in the visible light region is a promising option for efficient solar energy utilization in catalysis. Herein, we for the first time demonstrate that plasmonic hydrogen molybdenum bronze coupled with Pt nanoparticles (Pt/HxMoO3–y) shows a high catalytic performance in the deoxygenation of sulfoxides with 1 atm of H2at room temperature, with dramatic activity enhancement under visible light irradiation relative to dark conditions. The plasmonic molybdenum oxide hybrids with strong plasmon resonance peaks pinning at around 556 nm are obtained via a facile H-spillover process. Pt/HxMoO3–yhybrid provides excellent selectivity for the deoxygenation of various sulfoxides as well as pyridine N-oxides, in which drastically improved catalytic efficiencies are obtained under the irradiation of visible light. Comprehensive analyses reveal that oxygen vacancies massively introduced via a H-spillover process are the main active sites, and the reversible redox property of Mo atoms and strong plasmonic absorption play key roles in this reaction. The catalytic system works under extremely mild conditions and can boost the reaction by the assistance of visible light, offering an ultimately greener protocol to produce sulfides from sulfoxides. Our findings may open up a new strategy for designing plasmon-based catalytic systems that can harness visible light efficiently.

There is an evident urgent need to find a renewable and clean energy vector to ensure the worldwide energy supply while minimizing environmental impacts, and hydrogen stands out as a promising alternative energy carrier. The social concern around its safe storage is constantly fostering the search for alternative options to conventional storage methods and, in this context, chemical hydrogen storage materials have produced abundant investigations with particular attention to the design of heterogeneous catalysts that can boost the generation of molecular hydrogen. Among the chemical hydrogen storage materials, formic acid and ammonia–borane hold tremendous promise, and some of the recent strategies considered for the preparation of high-performance carbon-supported catalysts are summarized in this review. The outstanding features of carbon materials and their versatility combined with the tunability of the metal active phase properties (e.g., morphology, composition, and electronic features) provide numerous options for the design of promising catalysts. Precise control over the size and composition of metal nanoparticles is critical to the safe production of hydrogen from chemical storage systems. Kohsuke Mori and Hiromi Yamashita from Osaka University in Japan and colleagues review recent progress in producing hydrogen gas for fuel cell technology from the energy-rich molecules formic acid and ammonia borane. By immobilizing nanosized metal catalysts onto carbon-based supports with shapes including ultrasmall spheres, nanotubes, and graphene oxide sheets, researchers can tune hydrogen generation rates to record-high levels while still ensuring easy recovery and reuse. Catalytic reactions with formic acid can be improved by using noble metal-based palladium catalysts. While ruthenium nanocatalysts are favored for ammonia borane reactions, less expensive metal nickel and cobalt nanoparticles are gaining attention. This review recapitulates some of the most representative studies recently reported on carbon-supported catalysts for the hydrogen production from formic acid and ammonia borane by considering both active phase features and support properties. Several synthetic strategies are herein summarized to highlight the versatility of carbon materials in affording highly-performing catalysts for the hydrogen production from hydrogen carrier molecules.

Fe-Doped manganese oxide catalysts were prepared by the citrate method and their catalytic activities in soot combustion were examined in air under tight contact mode. Among the catalysts tested, 12 mol% of Fe-doped α-Mn2O3exhibited the highest activity, giving a soot combustion temperature (T50) of 328 °C, which is comparable to that previously reported for rare-earth-based catalysts, while pure α-Mn2O3gave a T50value of 339 °C. Comprehensive analyses by means of X-ray diffraction (XRD), specific surface area measurement, oxygen release rate measurement, X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) measurements revealed that the improved activity was due to i) an increased specific surface area and ii) an improved oxygen release rate involving reactive surface-adsorbed oxygen species. In situXAFS measurements suggested that the interaction between Mn and Fe facilitated the activation of the Mn–O–Fe bond and increased the proportion of reactive oxygen species, thereby improving the redox properties of the catalysts. Furthermore, simultaneous doping of Ag and Fe into Mn2O3was examined to further enhance the catalytic activity, which gave a drastically improved catalytic activity with T50= 290 °C. Based on temperature programmed reduction (TPR) and in situXAFS measurements, the direct oxidation mechanism of soot by the activated lattice oxygen species viathe redox of Ag0/Ag2O species was proposed.

A well-crystallized plasmonic MoxW1–xO3–yhybrid was obtained by a nonaqueous method. Detailed characterization by means of XRD, TEM, Raman, UV–vis, N2physisorption, and XPS measurements revealed that the synthesized plasmonic MoxW1–xO3–yhybrid showed strong localized surface plasmon resonance (LSPRs). It was demonstrated that such strong LSPRs was generated from crystal vacancies, mainly including mutual doping vacancies of molybdenum ions and tungsten ions and oxygen vacancies. More importantly, the LSPR absorption intensity of MoxW1–xO3–ywas almost 20, 16, and 8 times larger than that of as-synthesized MoO3–x, WO3–x, and our previously reported MoO3–xnanosheets (NS), respectively. To the best of our knowledge, such materials exhibiting strong LSPR absorption intensity have never been reported elsewhere. We also demonstrated that such plasmonic MoxW1–xO3–ycould be used as a highly efficient catalyst that dramatically enhanced the dehydrogenation activity from ammonia borane (NH3BH3; AB) under visible light irradiation.

A series of MnOx-decorated CeO2(MnCeO) catalysts with different morphologies have been prepared by the shape-controlled synthesis of single-crystalline CeO2, such as nanorod, nanoparticle, and nanocube, by a hydrothermal method followed by the deposition of MnOxphase by a simple impregnation method. Their shape-dependent physicochemical properties were investigated by means of XRD, BET, UV–vis, HRTEM, XPS, TPR and oxygen storage/release properties measurements. The MnOx/CeO2nanorod (MnCeO-NR) showed prominent carbon soot combustion activity at lower temperature under tight contact mode with a T50temperature of 317 °C, which is attributed to larger surface area and higher oxygen release rate, as compared with particle and cubic catalysts. MnCeO-NR also exhibited higher catalytic activity (a shift of T50by 127 °C) in NO-assisted soot combustion under a loose contact mode. Not only the higher surface area but also the superior NO conversion ability at low temperature as well as greater NO absorption contributes to the improved catalytic activities. The MnCeO-NR further displayed high stability and satisfactory recyclability without significant loss of catalytic activity. The use of cheaper combinations without noble metals makes the MnOx/CeO2catalyst a promising candidate to satisfy future requirements in industry.The MnOx/CeO2nanorod (MnCeO-NR) exhibited higher catalytic activity in NO-assisted soot combustion under a loose contact mode. Not only the higher surface area but also the superior NO conversion ability at low temperature as well as greater NO absorption contributes to the improved catalytic activities. The MnCeO-NR further displayed high durability and good recyclability.

Localized surface plasmon resonances (LSPR) in near-infrared (NIR) region have been extensively studied for copper chalcogenide nanostructures, not only for the absorption enhancement but also tunable LSPR characteristics with their free carrier concentrations or defects. In the present work, one-step cation exchange method has been used to synthesize Cu2−xS nanowires with x varied between 0 and 1, including Cu2S, Cu7S4and CuS and so forth. The plasmonic band of Cu2−xS nanowires shifts to a shorter wavelength with the increase in x, as observed in vis-NIR spectra, which is attributed to the increase in density of copper vacancies. The Cu2−xS nanowires have been used as catalysts towards the photocatalytic generation of H2from ammonia borane (AB). Among samples with different Cu-S compositions, Cu7S4samples exhibited the highest activity in terms of H2evolution rate (25.54mmol/gh). Moreover, a marked enhancement of the H2evolution rate (157.04mmol/gh) could be achieved after decorating the Cu2−xS nanowires with Pd nanoparticles to form the hybrid structures. The results of the present investigation may lead to an effective strategy for the design and development of LSPR materials for photocatalytic applications.

A series of bimetallic M/Ag (where M represents Pd, Ru, Ni and Co metallic species) nanorod (NR)-based plasmonic photocatalysts with 0.5 wt% loading of M on Ag (1.0 wt%) are prepared within the mesoporous channels of SBA-15. The chemical structure, morphology and optical properties of M/Ag/SBA-15 are well characterized by UV-vis spectroscopy, TEM, FT-EXAFS, XPS and N2adsorption–desorption measurement studies. Subsequently, the photocatalytic activity is assessed by hydrogen production from ammonia borane (AB) and chemical reduction of 4-nitrophenol (NP) to 4-aminophenol (AP) under visible light irradiation. The enhanced catalytic activities under light irradiation in comparison with dark conditions are explained by a plausible photocatalytic and charge separation mechanism to envisage the tentative reaction pathway. Finally, the reusability of the catalyst is evaluated viafour consecutive catalytic runs.

Solar energy is one of the most rapidly growing energy technologies and is directly involved in transitioning toward a more sustainable society. Solar to hydrogen fuel generation via photocatalysis is ideal for addressing the energy crisis worldwide. It requires the discovery of new materials or a new combination of materials to efficiently harvest sunlight with maximum solar-to-photon conversion efficiency. Plasmonic catalysts have recently emerged as a new class of materials and are promising candidates for confining light in the nanoscale regimes via localized surface plasmon resonance effect. In this review, we have collated state-of-the-art photocatalysts for hydrogen generation utilizing the combination of supports, including metal–organic framework (MOF), metal–organic matrix (MOM), g-C3N4, TiO2, MoS2, and WO3. The synthesis, characterization, and catalytic performance, along with the technical and novelty aspect, have been discussed. Finally, the future perspective section includes key directions to further improve the photocatalytic route of hydrogen generation by plasmonic catalysts.

An alternative approach to fabricate thin layers of metal organic frameworks (MOFs) on metal substrates without any needs of specific apparatuses was developed. Cu substrates were immersed into acid solution containing 1,3,5-benzenetricarboxylic acid (H3BTC) organic linker for the MOFs synthesis, where in-situ dissolved Cu2+ions were assembled to form [Cu3(BTC)2] (HKUST-1; BTC: 1,3,5-benzenetricarboxylate) crystals on the Cu substrates. The optimization of the choice of acids, solvents and preparation conditions were carried out to fabricate densely packed MOFs thin layers on Cu substrates. Use of a low-polarity solvent, benzyl alcohol (ε= 13), afforded a best balance between a dissolution rate of Cu and a coordination rate of the ligands, which led to the formation of a homogeneous thin layer composed of densely deposited small HKUST-1 crystals with a thickness of up to ca. 5 µm on the Cu substrates. The thus synthesized MOFs thin layers exhibited a gas-adsorption property for H2and CO2with an excellent mechanical stability, making this method a promising approach to functionalize metal substrates.A facile method to fabricate densely packed HKUST-1 layers onto Cu substrates without any specific apparatuses was developed. The combination of benzyl alcohol and HNO3acid was the best choice for the fabrication of dense coatings of HKUST-1 on Cu.

In this work, we propose a straightforward method to enhance the catalytic activity of AB dehydrogenation by using non-noble-metal nanoparticle supported on chromium-based metal–organic framework (MIL-101). It was demonstrated to be effective for hydrogen generation from ammonia borane under assistance of visible light irradiation as a noble-metal-free catalyst. The catalytic activity of metal nanoparticles supported on MIL-101 under visible light irradiation is remarkably higher than that without light irradiation. The TOFs of Cu/MIL-101, Co/MIL-101, and Ni/MIL-101 are 1693, 1571, and 3238 h–1, respectively. The enhanced activity of catalysts can be primarily attributed to the cooperative promoting effects from both non-noble-metal nanoparticles and photoactive metal–organic framework in activating the ammonia borane molecule and strong ability in the photocatalytic production of hydroxyl radicals, superoxide anions, and electron-rich non-noble-metal nanoparticle. This work sheds light on the exploration of active non-noble metals supported on photoactive porous materials for achieving high catalytic activity of various redox reactions under visible light irradiation.

The shape and composition effects of platinum–palladium (Pt–Pd) alloy nanoparticle cocatalysts on visible-light photocatalytic hydrogen evolution from an aqueous ammonium sulphite solution have been reported and discussed. The activity of Pt–Pd nanoparticles loaded Pt–Pd/CdS photocatalysts are affected based on both the Pt–Pd alloy nanoparticles’ shape and their compositions. In this research, two shapes of Pt–Pd nanoparticles have been studied. One is Pt–Pd nanocubes enclosed by {100} crystal planes and the other is nano-octahedra covered with {111} crystal facets. Results show that the photocatalytic turnover frequency (TOF), defined as moles of hydrogen produced per surface mole of Pt–Pd metal atom per second, for Pt–Pd nanocubes/CdS (Pt–Pd NCs/CdS) photocatalyst can be 3.4 times more effective than Pt–Pd nano-octahedra/CdS (Pt–Pd NOTa/CdS) nanocomposite photocatalyst. Along with the shape effect, the atomic ratio of Pt to Pd can also impact the efficiency of Pt–Pd/CdS photocatalysts. When the Pt to Pd atomic ratio changes from 1:0 to about 2:1, the rate of hydrogen production increases from 900 μmol/h for Pt NCs/CdS catalyst to 1837 μmol/h for Pt–Pd (2:1) NCs/CdS photocatalysta 104% rate increase. This result suggests that the 33 mol % of more expensive Pt can be replaced with less costly Pd, resulting in a more than 100% hydrogen production rate increase. The finding of this research will lead to the research and development of highly effective catalysts for photocatalytic hydrogen production using solar photonic energy.

A layered double hydroxide (LDH) type adsorbent for phosphate removal from aqueous solution was prepared from blast furnace slag (BFS) which is vastly discharged by the iron manufacturing industry. The phosphate adsorption performances of the prepared adsorbent and its calcined derivatives were examined using simulated wastewater solutions containing 124 P-mg L−1which is close to the effluent produced by the sewage sludge dewatering process, and factors such as pH, nature, and amount of adsorbent were studied to establish the optimum adsorption conditions. The adsorbent exhibited a great ability to efficiently remove phosphate in a variety of environments, especially even from 15 ppm phosphorus aqueous solutions, owing to a strong affinity of Ca(OH)xspecies and an ion-exchange ability of Cl−anions accommodated in the layers. The maximum phosphorus adsorption uptake reached 91.9 P-mg g−1after 24 h of adsorption at an initial pH of 7.0 and at 25 °C, which was 126-fold higher than that of raw BFS (0.73 P-mg g−1). The adsorption process followed a pseudo-second-order kinetic model and Freundlich adsorption isotherms. The results suggest that the slag-made LDH is a promising low-cost adsorbent for efficient phosphate removal from wastewater streams and phosphorus recovery processes.

The liquid-phase oxidation of alkylaromatics with molecular O2over manganese hydroxide catalysts supported on various oxides was examined. The reaction kinetics in ethylbenzene oxidation with O2indicated some configurational/electronic alterations of Mn species during the induction period of the reaction due to their interaction with benzoic acid. Characterization by means of FT-IR and XAFS revealed that the Mn(OH)xspecies was easily transformed into a monomeric Mn(iii) species coordinated with the PhCOO−ligand and anchored on the oxide support surface during the initial induction period of the reaction, which was the real active species. Among the catalysts examined, the in situ-created Mn species supported on γ-Al2O3particularly exhibited superior catalytic activity with good ketone selectivity compared to the other supported Mn catalysts. Moreover, leaching and agglomeration of the active Mn(iii) species were scarcely observed, and the recovered catalyst could be reused without significant loss of activity in the presence of the benzoic acid ligand. Such an in situ-created Mn(iii) species offers a simple, reusable and efficient oxidation system for alkylaromatics, such as ethylbenzene and diphenylmethane, with activity greater than that of its unsupported counterpart.

A coaxial arc plasma deposition (CAPD) source was developed to generate metallic nanoparticles (NPs) with sizes from sub-nanometer to several nanometers. Pt NPs were deposited on a carbon support by CAPD for use as a polymer electrolyte membrane fuel cell (PEMFC) electrode catalyst. The principle of catalyst formation and the mechanism for control of the particle size by CAPD were investigated. Transmission electron microscopy observations were performed for Pt/C catalysts with various Pt contents. Single PEMFCs were fabricated using 1, 5, and 10 wt% Pt/C catalysts, of which the best cell performance was obtained with the 10 wt% Pt/C catalyst.

The structure–activity relationship of carbon-supported Co catalysts was investigated in solvent-free aerobic oxidation of ethylbenzene under microwave irradiation. A single-site Co species show specifically high catalytic activity under microwave irradiation compared to conventional heating, while the oxidation is not accelerated by microwave when Co nanoparticle catalysts are used.The single-site Co species show specifically high catalytic activity in the solvent-free aerobic oxidation under microwave irradiation compared to the conventional heating, while the oxidation is not accelerated by microwave when Co(salen) or Co nanoparticle catalysts are used.

Blast furnace slag, a high volume byproduct resulting from iron and steel making industry, was used as an inexpensive and abundant precursor for the preparation of layered double hydroxide (LDH) compound. The synthesized LDH worked as an efficient heterogeneous base catalyst for the cycloaddition reaction of epoxides with 1atm CO2to provide five-membered cyclic carbonates.

Titanium dioxide (TiO2) is ideally most promising photocatalyst for degradation of organic compounds under environmentally benign conditions. For further exploitation of its catalytic properties, some strategies to improve adsorption of organic substrates by hybridization with various support materials have become important. This article reviews recent developments in designing TiO2 photocatalyst with the objective of fabricating efficient photodegradation systems toward organic compounds diluted in water and air. We highlight that the hydrophobic support materials can offer significant enhancement in photodegradation, where adsorption properties of organics onto TiO2 surface play much more dominant role than other structural and compositional factors in photocatalysis of TiO2.

Layers of metal organic framework (MOF) crystals on skeletal Cu were prepared. The use of DMF as a solvent led to the deposition of densely packed MOF crystals on skeletal Cu and to high catalytic activity in the gas-phase hydrogenation reaction of ethylene.Layers of metal organic frameworks (MOFs) crystals on skeletal Cu was prepared. The use of DMF as a solvent led to the deposition of densely packed MOFs crystals on skeletal Cu and a high catalytic activity in the gas-phase hydrogenation reaction of ethylene due to the densely packed arrangement of MOFs crystals.

Hexagonal mesoporous silica (HMS) material, which is commonly used in catalysis and the nanostructural design field as an adsorbent or host material, was hydrophobically modified via a simple silylation process using a fluorine-containing silylation agent, triethoxyfluorosilane [TEFS or SiF(OEt)3]. Structural analyses performed by XRD and N2adsorption−desorption suggested that the mesoporous structure and large surface area of the HMS were retained even after the modification. Surface chemical information obtained from XPS indicated that the TEFS reagent was covalently anchored to the surface hydroxyl sites and fluorine atoms existed in a Si−F bonding state. From the H2O adsorption isotherm on the modified HMS, it was clearly shown that the modified HMS was more hydrophobic compared with the unmodified HMS. Moreover, the hydrophobically modified HMS was used as support for the TiO2photocatalyst. From EXAFS analysis, as well as UV−vis spectroscopy and XRD, it was confirmed that the highly crystallized TiO2particles were formed in the hydrophobic HMS pores, whereas the titanium species on the original HMS showed physicochemical features similar to those of isolated titanium oxide. With the aim of evaluating its availability as an efficient support, photocatalytic degradation of 2-propanol and phenol diluted in water was performed. Both the adsorption property and the TiO2photocatalytic activity toward these organic compounds were dramatically improved by increasing the content of the TEFS reagent because the hydrophobically modified HMS worked as an efficient adsorbent to condense organic molecules instead of H2O molecules. By evaluating the obtained physicochemical parameters and degradation rate constant of organic molecules, we clarified the advantages of surface modification by TEFS and the participation of the hydrophobic support in the photocatalytic reactions.

A new photoassisted deposition (PAD) method using fullerene C60is developed. Photoexcited fullerene C60introduced within the mesopore of SBA-15 acts as an anchor to reduce Ru3+ions to the highly dispersed Ru metal with a narrow size distribution. Such uniform Ru nanoparticles (NPs) show high catalytic activity for dehydrogenation of ammonia borane than the sample prepared by conventional impregnation method.

Particle size dependence in the H2production from formic acid was investigated over Pd/C catalysts with nanoparticle sizes ranging from 2.7 to 5.5 nm. A volcano type relationship between catalytic activity and nanoparticle size was obtained and the average size of 3.9 nm exhibited the highest activity under mild reaction conditions.

The fluorine-modified mesoporous silica HMS(F20) was synthesized by using the mixture of TEFS(SiF(OC2H5)3) and TEOS(Si(OC2H5)4) as the silica source. The specific surface and pore size distribution were characterized by N2 adsorption and the hydrophilic-hydrophobic property was measured by water adsorption. The photocatalytic activities of TiO2 nanoparticles loaded on HMF(F20) and HMS were investigated for the degradation of iso-butanol diluted in water. The results show that the fluorine-modified mesoporous silica HMS(F20) has higher hydrophobic property than HMS and the TiO2/HMS(F20) exhibits the higher photocatalytic activity than TiO2/HMS. The hydrophobic mesopores benefit the condensation of hydrophobic organic compounds diluted in water, which results in higher photocatalytic degradation efficiency.

Levulinic acid and its esters, important intermediate chemicals produced from biomass resources, were converted to γ-valerolactone via a catalytic transfer hydrogenation process over silica-supported zirconia catalysts. Silica support with a higher surface area provided highly dispersed active zirconium oxide species, which exhibited superior catalytic activity to the conventional ZrO2catalyst.