Solid catalysts usually consist of multicomponents, within which interfacial interactions have been recognized as a key factor affecting structures and catalytic performance. Metal–support ...interactions (MSI) have been extensively studied in oxide-supported metal catalysts (metal/oxide catalysts), in which the important concepts of strong metal–support interactions (SMSI) and electronic metal–support interactions (EMSI) have been well established and their effects on the metal catalysis have been extensively demonstrated. Recently, metal-supported oxide inverse catalysts (oxide/metal inverse catalysts) have emerged as a new type of efficient catalysts, in which the oxide–metal interactions (OMI) strongly influence the oxide catalysis. Herein we comprehensively review the progresses on the MSI of metal/oxide catalysts and OMI of oxide/metal inverse catalysts with aims to emphasize structure sensitivity of MSI and OMI and to introduce the concepts of electronic oxide–metal interactions (EOMI) and electronic oxide–metal strong interactions (EOMSI) in oxide/metal inverse catalysts, in analogy to the concepts of EMSI and SMSI in metal/oxide catalysts. First, we briefly introduce the background of the topic and the interfacial interactions between metals and oxides with emphasis on the nature of metal–support interfacial interactions depending on the electronic structures. Second, the MSI, with an emphasis on the EMSI and SMSI, in metal/oxide catalysts is reviewed with an emphasis on the recently exported size and facet effects on the electronic structures and MSI. Third, the OMI in oxide/metal inverse catalysts is reviewed with an emphasis on introducing the EOMI and EOMSI. Finally, a summary and outlook is given with emphasis on the local nature and structure sensitivity of MSI and OMI.
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•Conversion of stable CO2 with H2O to valuable chemicals and fuels.•Recent progress in CO2 reduction over developed Ti-oxide-based materials.•Various strategic factors for increasing ...the photocatalytic efficiency.•Non Ti-oxide catalysts and photo-electrocatalytic reduction of CO2.
The conversion of CO2 with H2O to valuable chemicals and fuels is a new solution to current environmental and energy problems, and the high energy barrier of these reactions can be overcome by the input of solar and electrical energy. However, the reduction efficiencies and selectivities of these reactions are insufficient for practical use, and significant effort and strategy are required to overcome the many obstacles preventing the large-scale application of photocatalytic CO2 reduction. This article reviews recent progress in CO2 reduction using titanium oxide-based materials and various strategic factors for increasing photocatalytic efficiency. This article also highlights non-titanium-oxide catalysts, the photoelectrocatalytic reduction of CO2, and other recent review articles concerning the recycling of CO2 to value-added carbon compounds.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Semiconductor photocatalysis has received tremendous attention as a promising way for solving the worldwide energy and environment issues. Many efforts have been devoted to developing distinctive ...morphology and various semiconductor-based composite photocatalysts for enhancing photocatalytic activity in recent years. However, it is still a great challenge and imperative to profoundly understand the transfer mechanisms and to realize complete utilization of photoexcited charge carriers. This perspective for the first time highlights the inner impetus of the photogenerated charge carrier migration (band-band and Z-scheme transfers) over composite photocatalytsts. The notion of relative p-n junction for photocatalysis and the corresponding design principle of Z-scheme photocatalysts are introduced first. Then, simultaneous utilization of photogenerated electrons and holes for photocatalytic selective redox syntheses in one reaction system is recommended. The proposed reaction systems have characteristics of the environmentally friendly, atom economy, synergistic effect and high efficiency. Finally, the challenges and opportunities of photocatalysis are outlined and a perspective is given. We hope that the perspective review could give an inspiration for the fundamental research and guide the research direction of photocatalysis.
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•The notion of relative p-n junction for photocatalysis was proposed.•The Judgment model of direct Z-scheme transfer was established.•The reaction systems of simultaneous utilization of photogenerated carriers were recommended.•The challenges and opportunities in the field of photocatalysis were suggested.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Electrochemical conversion of CO2 to value‐added chemicals using renewable electricity provides a promising way to mitigate both global warming and the energy crisis. Here, a facile ion‐adsorption ...strategy is reported to construct highly active graphene‐based catalysts for CO2 reduction to CO. The isolated transition metal cyclam‐like moieties formed upon ion adsorption are found to contribute to the observed improvements. Free from the conventional harsh pyrolysis and acid‐leaching procedures, this solution‐chemistry strategy is easy to scale up and of general applicability, thus paving a rational avenue for the design of high‐efficiency catalysts for CO2 reduction and beyond.
A feasible ion‐adsorption strategy is highlighted to bring unprecedentedly efficient and selective CO2 reduction activity to nitrogen‐doped graphene. Free from high‐temperature pyrolysis and acid leaching, this solution‐chemistry route incorporating molecular‐catalyst moieties into a highly conductive carbon matrix provides a practical approach to design high‐efficiency electrocatalysts for CO2 reduction and related catalytic reactions.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Via a comprehensive time-resolved operando-DRIFTS study of the evolutions of various surface species on Au/CeO2 catalysts with Au particle sizes ranging from 1.7 ± 0.6 to 3.7 ± 0.9 nm during CO ...oxidation at room temperature, we have successfully demonstrated size-dependent reaction pathways and their contributions to the catalytic activity. The types and concentrations of chemisorbed CO(a), carbonate, bicarbonate, and formate species formed upon CO adsorption, their intrinsic oxidation/decomposition reactivity, and roles in CO oxidation vary with the size of the supported Au particles. The intrinsic oxidation reactivity of CO(a) does not depend much on the Au particle size, whereas the intrinsic decomposition reactivity of carbonate, bicarbonate, and formate species strongly depend on the Au particle size and are facilitated over Au/CeO2 catalysts with large Au particles. These results greatly advance the fundamental understanding of the size effect of Au/CeO2 catalysts for low-temperature CO oxidation.
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The design of active, selective, and stable CO2 reduction electrocatalysts is still challenging. A series of atomically dispersed Co catalysts with different nitrogen coordination numbers were ...prepared and their CO2 electroreduction catalytic performance was explored. The best catalyst, atomically dispersed Co with two‐coordinate nitrogen atoms, achieves both high selectivity and superior activity with 94 % CO formation Faradaic efficiency and a current density of 18.1 mA cm−2 at an overpotential of 520 mV. The CO formation turnover frequency reaches a record value of 18 200 h−1, surpassing most reported metal‐based catalysts under comparable conditions. Our experimental and theoretical results demonstrate that lower a coordination number facilitates activation of CO2 to the CO2.− intermediate and hence enhances CO2 electroreduction activity.
A remarkable carbon dioxide electroreduction catalytic performance with superior activity and high selectivity was achieved on atomically dispersed Co sites through coordination environment regulating. First step in picture: C–N fragments, 1000 °C; second step: NH3 treatment.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
CeO2 nanocubes (c-CeO2), nanoparticles (p-CeO2), and nanorods calcined at 500 °C (r-CeO2-500) and 700 °C (r-CeO2-700) were used as supports to synthesize a series of Ni/CeO2 catalysts for the propane ...combustion and oxidative dehydrogenation of propane (ODHP) reactions. The Ni-CeO2 interaction greatly promotes the reducibility of CeO2, but CeO2 morphology-dependent Ni-CeO2 interaction was observed to form different speciation of Ni species (Ni2+ dissolved in CeO2, highly dispersive NiO, NiO aggregate) and oxygen species (strongly activated oxygen species, medially activated oxygen species, weakly activated oxygen species) in various Ni/CeO2 catalysts. Ni-CeO2 interaction is stronger in Ni/c-CeO2 catalysts than in other Ni/CeO2 catalysts. Different morphology-dependences of Ni/CeO2 catalysts in propane combustion and ODHP reactions were observed. The Ni/r-CeO2-500 catalyst with the largest strongly activated oxygen species is most catalytic active in the propane combustion reaction while the Ni/c-CeO2 catalyst with the largest amount of weakly activated oxygen species exhibits the best catalytic performance in the ODHP reaction. Thus, the CeO2 morphology engineering strategy is effective in finely tuning the metal-CeO2 interaction and the reactivity of oxygen species to meet the requirements of different types of catalytic oxidation reactions.
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The surface composition and morphology of CH3NH3PbI3 perovskite films stored for several days under ambient conditions were investigated by X-ray photoelectron spectroscopy, scanning electron ...microscopy, and X-ray diffraction techniques. Chemical analysis revealed the loss of CH3NH3 + and I– species from CH3NH3PbI3 and its subsequent decomposition into lead carbonate, lead hydroxide, and lead oxide. After long-term storage under ambient conditions, morphological analysis revealed the transformation of randomly distributed defects and cracks, initially present in the densely packed crystalline structure, into relatively small grains. In contrast to PbI2 powder, CH3NH3PbI3 exhibited a different degradation trend under ambient conditions. Therefore, we propose a plausible CH3NH3PbI3 decomposition pathway that explains the changes in the chemical composition of CH3NH3PbI3 under ambient conditions. In addition, films stored under such conditions were incorporated into photovoltaic cells, and their performances were examined. The chemical changes in the decomposed films were found to cause a significant decrease in the photovoltaic efficiency of CH3NH3PbI3.
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Model catalysts with uniform and well-defined surface structures have been extensively employed to explore structure–property relationships of powder catalysts. Traditional oxide model catalysts are ...based on oxide single crystals and single crystal thin films, and the surface chemistry and catalysis are studied under ultrahigh-vacuum conditions. However, the acquired fundamental understandings often suffer from the “materials gap” and “pressure gap” when they are extended to the real world of powder catalysts working at atmospheric or higher pressures. Recent advances in colloidal synthesis have realized controlled synthesis of catalytic oxide nanocrystals with uniform and well-defined morphologies. These oxide nanocrystals consist of a novel type of oxide model catalyst whose surface chemistry and catalysis can be studied under the same conditions as working oxide catalysts. In this Account, the emerging concept of oxide nanocrystal model catalysts is demonstrated using our investigations of surface chemistry and catalysis of uniform and well-defined cuprous oxide nanocrystals and ceria nanocrystals. Cu2O cubes enclosed with the {100} crystal planes, Cu2O octahedra enclosed with the {111} crystal planes, and Cu2O rhombic dodecahedra enclosed with the {110} crystal planes exhibit distinct morphology-dependent surface reactivities and catalytic properties that can be well correlated with the surface compositions and structures of exposed crystal planes. Among these types of Cu2O nanocrystals, the octahedra are most reactive and catalytically active due to the presence of coordination-unsaturated (1-fold-coordinated) Cu on the exposed {111} crystal planes. The crystal-plane-controlled surface restructuring and catalytic activity of Cu2O nanocrystals were observed in CO oxidation with excess oxygen. In the propylene oxidation reaction with O2, 1-fold-coordinated Cu on Cu2O(111), 3-fold-coordinated O on Cu2O(110), and 2-fold-coordinated O on Cu2O(100) were identified as the active sites, respectively, to produce acrolein, propylene oxide, and CO2. Ceria rods enclosed with the {110} and {100} crystal planes, ceria cubes enclosed with the {100} crystal planes, and ceria octahedra enclosed with the {111} crystal planes exhibit distinct morphology-dependent oxygen vacancy concentrations and structures that can be well correlated with the surface compositions and structures of exposed crystal planes. Consequently, the metal–ceria interactions, structures, and catalytic performances of ceria-supported catalysts depend on the CeO2 morphology. Our results comprehensively reveal the morphology-dependent surface chemistry and catalysis of oxide nanocrystals that not only greatly deepen the fundamental understanding of oxide catalysis but also demonstrate a morphology-engineering strategy to optimize the catalytic performance of oxide catalysts. These results adequately exemplify the concept of oxide nanocrystal model catalysts for the fundamental investigations of oxide catalysis without the “materials gap” and “pressure gap”. With the structure–catalytic property relationships learned from oxide nanocrystal model catalyst studies and the advancement of controlled-synthesis methods, it is promising to realize the structural design and controlled synthesis of novel efficient oxide catalysts in the future.
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Following the remarkable success of the application of CH3NH3PbI3 perovskites in photovoltaics, a great focus has been placed on their stability to improve their optoelectronic properties and seek ...commercial production. To gain a better understanding of their thermal stability, we investigated the chemical, morphological, and photovoltaic transformations of CH3NH3PbI3 perovskites under elevated temperatures and various controlled atmospheric conditions (vacuum, 1 mbar O2, and 1 mbar H2O). A temperature-dependent study showed that CH3NH3PbI3 decomposed to PbI2 with the release of CH3NH2 and HI under low-temperature annealing (25–150 °C). Further annealing resulted in the formation of metallic lead (Pb0) under vacuum and Pb oxides and hydroxides under an O2 or H2O pressure. Moreover, the sublimation of Pb-based compounds occurred at temperatures above 150 °C, causing structural changes, which resulted in a decrease in the power conversion efficiency of the solar cell. A time-dependent study showed that, compared with vacuum conditions, the addition of O2 or H2O accelerated the degradation of the perovskite films.
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