Metal oxide redox chemistry for chemical looping processes

A New Strategy to Regulate the Selectivity of Photo-Mediated Catalytic Reaction

Here we developed a new method for regulating the selectivity of photo-mediated catalytic reaction by manipulating the surface charge of Au/TiO₂ (gold/titanium dioxide) catalysts within chemical reaction timescales. Two kinds of photocatalytic reactions, hydrogenation of acetophenone and benzyl alcohol oxidation, have been applied to investigate the photocatalytic performance over Au/TiO₂ catalysts with tunable surface charges. We found that a suitable timescale of switching surface charge on Au would benefit for the enhanced quantum efficiency and play different roles in the selectivity of desired products in hydrogenation and oxidation reactions. Au/TiO₂ catalyst under 5 μs flashing light irradiation exhibits much higher selectivity of 1-phenylethanol in the hydrogenation of acetophenone than that under continuous light and 5 s flashing light irradiation; by contrast, Au/TiO₂ catalysts under both flashing light and continuous light irradiation exhibit a similar selectivity of benzaldehyde in benzyl alcohol oxidation. Our findings will benefit for a better understanding of electronic structure-mediated reaction mechanism and be helpful for achieving highly efficient photocatalytic systems.

Phase Coexistence and Structural Dynamics of Redox Metal Catalysts Revealed by Operando TEM

Metal catalysts play an important role in industrial redox reactions. Although extensively studied, the state of these catalysts under operating conditions is largely unknown, and assignments of active sites remain speculative. Herein, an operando transmission electron microscopy study is presented, which interrelates the structural dynamics of redox metal catalysts to their activity. Using hydrogen oxidation on copper as an elementary redox reaction, it is revealed how the interaction between metal and the surrounding gas phase induces complex structural transformations and drives the system from a thermodynamic equilibrium toward a state controlled by the chemical dynamics. Direct imaging combined with the simultaneous detection of catalytic activity provides unparalleled structure-activity insights that identify distinct mechanisms for water formation and reveal the means by which the system self-adjusts to changes of the gas-phase chemical potential. Density functional theory calculations show that surface phase transitions are driven by chemical dynamics even when the system is far from a thermodynamic phase boundary. In a bottom-up approach, the dynamic behavior observed here for an elementary reaction is finally extended to more relevant redox reactions and other metal catalysts, which underlines the importance of chemical dynamics for the formation and constant re-generation of transient active sites during catalysis.

Catalytic Dehydrogenation of Ethane: A Mini Review of Recent Advances and Perspective of Chemical Looping Technology

Dehydrogenation processes play an important role in the petrochemical industry. High selectivity towards olefins is usually hindered by numerous side reactions in a conventional cracking/pyrolysis technology. Herein, we show recent studies devoted to selective ethylene production via oxidative and non-oxidative reactions. This review summarizes the progress that has been achieved with ethane conversion in terms of the process effectivity. Briefly, steam cracking, catalytic dehydrogenation, oxidative dehydrogenation (with CO2/O2), membrane technology, and chemical looping are reviewed.

Solid-State Redox Kinetics of CeO2 in Two-Step Solar CH4 Partial Oxidation and Thermochemical CO2 Conversion

The CeO2/CeO2−δ redox system occupies a unique position as an oxygen carrier in chemical looping processes for producing solar fuels, using concentrated solar energy. The two-step thermochemical ceria-based cycle for the production of synthesis gas from methane and solar energy, followed by CO2 splitting, was considered in this work. This topic concerns one of the emerging and most promising processes for the recycling and valorization of anthropogenic greenhouse gas emissions. The development of redox-active catalysts with enhanced efficiency for solar thermochemical fuel production and CO2 conversion is a highly demanding and challenging topic. The determination of redox reaction kinetics is crucial for process design and optimization. In this study, the solid-state redox kinetics of CeO2 in the two-step process with CH4 as the reducing agent and CO2 as the oxidizing agent was investigated in an original prototype solar thermogravimetric reactor equipped with a parabolic dish solar concentrator. In particular, the ceria reduction and re-oxidation reactions were carried out under isothermal conditions. Several solid-state kinetic models based on reaction order, nucleation, shrinking core, and diffusion were utilized for deducing the reaction mechanisms. It was observed that both ceria reduction with CH4 and re-oxidation with CO2 were best represented by a 2D nucleation and nuclei growth model under the applied conditions. The kinetic models exhibiting the best agreement with the experimental reaction data were used to estimate the kinetic parameters. The values of apparent activation energies (~80 kJ·mol−1 for reduction and ~10 kJ·mol−1 for re-oxidation) and pre-exponential factors (~2–9 s−1 for reduction and ~123–253 s−1 for re-oxidation) were obtained from the Arrhenius plots.

Isolated boron in zeolite for oxidative dehydrogenation of propane

Oxidative dehydrogenation of propane (ODHP) is a key technology for producing propene from shale gas, but conventional metal oxide catalysts are prone to overoxidation to form valueless CO _x Boron-based catalysts were recently found to be selective for this reaction, and B-O-B oligomers are generally regarded as active centers. We show here that the isolated boron in a zeolite framework without such oligomers exhibits high activity and selectivity for ODHP, which also hinders full hydrolysis for boron leaching in a humid atmosphere because of the B-O-SiO _x linkage, achieving superior durability in a long-period test. Furthermore, we demonstrate an isolated boron with a -B[OH…O(H)-Si]₂ structure in borosilicate zeolite as the active center, which enables the activation of oxygen and a carbon-hydrogen bond to catalyze the ODHP.

Combined Syngas and Hydrogen Production using Gas Switching Technology

This paper focuses on the experimental demonstration of a three-stage GST (gas switching technology) process (fuel, steam/CO₂, and air stages) for syngas production from methane in the fuel stage and H₂/CO production in the steam/CO₂ stage using a lanthanum-based oxygen carrier (La_0.85Sr_0.15Fe_0.95Al_0.05O₃). Experiments were performed at temperatures between 750–950 °C and pressures up to 5 bar. The results show that the oxygen carrier exhibits high selectivity to oxidizing methane to syngas at the fuel stage with improved process performance with increasing temperature although carbon deposition could not be avoided. Co-feeding CO₂ with CH₄ at the fuel stage reduced carbon deposition significantly, thus reducing the syngas H₂/CO molar ratio from 3.75 to 1 (at CO₂/CH₄ ratio of 1 at 950 °C and 1 bar). The reduced carbon deposition has maximized the purity of the H₂ produced in the consecutive steam stage thus increasing the process attractiveness for the combined production of syngas and pure hydrogen. Interestingly, the cofeeding of CO₂ with CH₄ at the fuel stage showed a stable syngas production over 12 hours continuously and maintained the H₂/CO ratio at almost unity, suggesting that the oxygen carrier was exposed to simultaneous partial oxidation of CH₄ with the lattice oxygen which was restored instantly by the incoming CO₂. Furthermore, the addition of steam to the fuel stage could tune up the H₂/CO ratio beyond 3 without carbon deposition at H₂O/CH₄ ratio of 1 at 950 °C and 1 bar; making the syngas from gas switching partial oxidation suitable for different downstream processes, for example, gas-to-liquid processes. The process was also demonstrated at higher pressures with over 70% fuel conversion achieved at 5 bar and 950 °C.

A tailored multi-functional catalyst for ultra-efficient styrene production under a cyclic redox scheme

Styrene is an important commodity chemical that is highly energy and CO2 intensive to produce. We report a redox oxidative dehydrogenation (redox-ODH) strategy to efficiently produce styrene. Facilitated by a multifunctional (Ca/Mn)1-xO@KFeO2 core-shell redox catalyst which acts as (i) a heterogeneous catalyst, (ii) an oxygen separation agent, and (iii) a selective hydrogen combustion material, redox-ODH auto-thermally converts ethylbenzene to styrene with up to 97% single-pass conversion and >94% selectivity. This represents a 72% yield increase compared to commercial dehydrogenation on a relative basis, leading to 82% energy savings and 79% CO2 emission reduction. The redox catalyst is composed of a catalytically active KFeO2 shell and a (Ca/Mn)1-xO core for reversible lattice oxygen storage and donation. The lattice oxygen donation from (Ca/Mn)1-xO sacrificially stabilizes Fe3+ in the shell to maintain high catalytic activity and coke resistance. From a practical standpoint, the redox catalyst exhibits excellent long-term performance under industrially compatible conditions.

Intensification of Chemical Looping Processes by Catalyst Assistance and Combination

Chemical looping can be considered a technology platform, which refers to one common basic concept that can be used for various applications. Compared with a traditional catalytic process, the chemical looping concept allows fuels’ conversion and products’ separation without extra processes. In addition, the chemical looping technology has another major advantage: combinability, which enables the integration of different reactions into one process, leading to intensification. This review collects various important state-of-the-art examples, such as integration of chemical looping and catalytic processes. Hereby, we demonstrate that chemical looping can in principle be implemented for any catalytic reaction or at least assist in existing processes, provided that the targeted functional group is transferrable by means of suitable carriers.

Propane dehydrogenation: catalyst development, new chemistry, and emerging technologies

This review describes recent advances in the propane dehydrogenation process in terms of emerging technologies, catalyst development and new chemistry.

Enhanced methane conversion using Ni-doped calcium ferrite oxygen carriers in chemical looping partial oxidation systems with CO2 utilization

Enhanced methane and CO2 conversion by utilizing Ni-doped calcium ferrite oxygen carriers for the chemical looping partial oxidation technology.

Hierarchical Structural Changes During Redox Cycling of Fe-Based Lamellar Foams Containing YSZ, CeO2, or ZrO2

Several high-temperature energy conversion and storage technologies rely on redox cycling of Fe-based materials, including storage materials in solid-oxide Fe-air batteries and oxygen carriers in chemical-looping combustion. The materials' macroporosity necessary for gas flow is, however, irreversibly diminished during redox cycling due to (i) large volume changes during the redox transformations, (ii) foam sintering at elevated operating temperature (550-900 °C), and (iii) formation and growth of Kirkendall microporosity. To address these challenges, we use directional freeze-casting to create highly porous, lamellar, Fe-composite foams containing uniformly distributed sintering inhibitor (SI) particles-either Y₂O₃-stabilized ZrO₂ (YSZ), CeO₂, or ZrO₂-at 0, 5, 10, or 15% of the solid volume. We characterize these foams before, during, and after redox cycling (Fe/FeO/Fe₃O₄, via H₂O and H₂) at 800 °C using operando synchrotron X-ray microtomography, metallography, and scanning electron microscopy. Shrinkage of the foam volume and formation of a gas-blocking shell surrounding the foam are reduced as the SI fraction increases. Volumetric shrinkage after the first five redox cycles is decreased from 66% (for pure-Fe foams) to 45% (for all Fe-composites containing 5 vol % SI). Foams containing 15 vol % YSZ show no volumetric shrinkage after five cycles, although, after 20 cycles, they have shrunk 53%. Post-cycling analysis reveals segregation of the SI particles to the cores of individual lamellae, surrounded by thick layers of sintered Fe on the lamellae surfaces. This segregation occurs due to Fe diffusion through FeO to the lamellae surfaces during oxidation, leaving behind the SI particles, which are then pushed into clusters by FeO/Fe₃O₄ contraction during reduction. The SI is thus rendered ineffective, which explains why foam densification is delayed (compared with pure-Fe foams), rather than fully prevented, after repeated cycling.

Facile CO2 separation and subsequent H2 production via chemical-looping combustion over ceria-zirconia solid solutions

A novel chemical-looping combustion scheme is proposed, where facile gas separation via steam condensation enables the production of sequestrable CO2 from alkanes, such as CH4, and pure H2 from H2O. This cycle consists of two steps, namely, (1) the endothermic reduction of a ceria-based solid solution via the complete oxidation of CH4, followed by (2) the exothermic oxidation of the reduced metal oxide via H2O splitting. Relative to iron oxide-based materials and undoped ceria, ceria-zirconia solid solutions possess favorable partial molar enthalpic and entropic properties; this promotes selective production of complete combustion products, H2O and CO2, during the reforming reaction. Thermodynamic predictions suggest that the complete oxidation of CH4 is possible by increasing the Zr content to 20 mol%, operating below 600 °C, increasing total pressure, or reducing the amount of delivered reactant. Furthermore, any H2, CO, or unreacted CH4 that may persist is thermodynamically favored to oxidize if exposed to unreacted oxide downstream, as is typical for a packed-bed or downer reactor configuration. Experiments were performed to validate the thermodynamic trends using isothermal thermogravimetry coupled with residual gas analysis, which confirmed that high selectivity towards H2O and CO2 is attainable for methane-driven reduction of Ce0.9Zr0.1O2; selectivities greater than 0.70 were observed at initial reaction extents. Importantly, metal oxide oxidation via H2O splitting and selective production of H2 (or CO if CO2 is the delivered oxidant) is also thermodynamically favored at the operating conditions considered for the first step. This work ultimately presents a viable avenue for the carbon-neutral conversion of CH4 (or other alkanes) to H2 if a renewable energy resource, such as solar energy, is leveraged to supply process heat.

Combining Exsolution and Infiltration for Redox, Low Temperature CH4 Conversion to Syngas

Exsolution of surface and bulk nanoparticles in perovskites has been recently employed in chemical looping methane partial oxidation because of the emergent materials’ properties such as oxygen capacity, redox stability, durability, coke resistance and enhanced activity. Here we attempt to further lower the temperature of methane conversion by complementing exsolution with infiltration. We prepare an endo/exo-particle system using exsolution and infiltrate it with minimal amount of Rh (0.1 wt%) in order to functionalize the surface and induce low temperature activity. We achieve a temperature decrease by almost 220 °C and an increase of the activity up to 40%. We also show that the initial microstructure of the perovskite plays a key role in controlling nanoparticle anchorage and carbon deposition. Our results demonstrate that microstructure tuning and surface functionalization are important aspects to consider when designing materials for redox cycling applications.

A molten carbonate shell modified perovskite redox catalyst for anaerobic oxidative dehydrogenation of ethane

Acceptor-doped, redox-active perovskite oxides such as La0.8Sr0.2FeO3 (LSF) are active for ethane oxidation to CO x but show poor selectivity to ethylene. This article reports molten Li2CO3 as an effective "promoter" to modify LSF for chemical looping-oxidative dehydrogenation (CL-ODH) of ethane. Under the working state, the redox catalyst is composed of a molten Li2CO3 layer covering the solid LSF substrate. The molten layer facilitates the transport of active peroxide (O2 2-) species formed on LSF while blocking the nonselective sites. Spectroscopy measurements and density functional theory calculations indicate that Fe4+→Fe3+ transition is responsible for the peroxide formation, which results in both exothermic ODH and air reoxidation steps. With >90% ethylene selectivity, up to 59% ethylene yield, and favorable heat of reactions, the core-shell redox catalyst has an excellent potential to be effective for intensified ethane conversion. The mechanistic findings also provide a generalized approach for designing CL-ODH redox catalysts.

Approaches for Selective Oxidation of Methane to Methanol

Methane activation chemistry, despite being widely reported in literature, remains to date a subject of debate. The challenges in this reaction are not limited to methane activation but extend to stabilization of the intermediate species. The low C-H dissociation energy of intermediates vs. reactants leads to CO2 formation. For selective oxidation, nature presents methane monooxygenase as a benchmark. This enzyme selectively consumes methane by breaking it down into methanol. To assemble an active site similar to monooxygenase, the literature reports Cu-ZSM-5, Fe-ZSM-5, and Cu-MOR, using zeolites and systems like CeO2/Cu2O/Cu. However, the trade-off between methane activation and methanol selectivity remains a challenge. Density functional theory (DFT) calculations and spectroscopic studies indicate catalyst reducibility, oxygen mobility, and water as co-feed as primary factors that can assist in enabling higher selectivity. The use of chemical looping can further improve selectivity. However, in all systems, improvements in productivity per cycle are required in order to meet the economical/industrial standards.

Lower olefins from methane: recent advances

Modern methods for methane conversion to lower olefins having from 2 to 4 carbon atoms per molecule are generalized. Multistage processing of methane into ethylene and propylene via syngas or methyl chloride and methods for direct conversion of CH4 to ethylene are described. Direct conversion of syngas to olefins as well as indirect routes of the process via methanol or dimethyl ether are considered. Particular attention is paid to innovative methods of olefin synthesis. Recent achievements in the design of catalysts and development of new techniques for efficient implementation of oxidative coupling of methane and methanol conversion to olefins are analyzed and systematized. Advances in commercializing these processes are pointed out. Novel catalysts for Fischer – Tropsch synthesis of lower olefins from syngas and for innovative technique using oxide – zeolite hybrid catalytic systems are described. The promise of a new route to lower olefins by methane conversion via dimethyl ether is shown. Prospects for the synthesis of lower olefins via methyl chloride and using non-oxidative coupling of methane are discussed. The most efficient processes used for processing of methane to lower olefins are compared on the basis of degree of conversion of carbonaceous feed, possibility to integrate with available full-scale production, number of reaction stages and thermal load distribution.

The bibliography includes 346 references.

A- and B-site Codoped SrFeO3 Oxygen Sorbents for Enhanced Chemical Looping Air Separation

Chemical-looping air separation has numerous potential benefits in terms of energy saving and emission reductions. The current study details a combination of density functional theory calculation and experimental efforts to design A- and B-site codoped SrFeO₃ perovskites as "low-temperature" oxygen sorbents for chemical-looping air separation. Substitution of the SrFeO₃ host structure with Ca and Co lowers oxygen vacancy formation energy by 0.24-0.46 eV and decreases the oxygen release temperature. As a result, Sr_1-x Ca_x Fe_1-y Co_y O₃ (SCFC; x=0.2, 0.0<y<1.0) spontaneously releases oxygen at 400-500 °C even under a relatively high oxygen partial pressure (e.g. P O 2 =0.05 atm). Sr_0.8 Ca_0.2 Fe_0.4 Co_0.6 O₃ exhibits a significantly higher oxygen capacity of 1.2 wt % at 400 °C and under a P O 2 swing between 0.05 and 0.2 atm, when compared to the <0.2 wt % capacity for undoped a SrFeO₃ (SF) and Ca-doped Sr_0.8 Ca_0.2 FeO₃ (SCF). Electrical conductivity relaxation (ECR) study demonstrates that codoping of Ca and Co lowers the activation energy of oxygen diffusion and surface oxygen exchange by 26.6 or 137.9 kJ mol^-1 , respectively, resulting in faster redox kinetics for SCFC than for SCF perovskite. The SCFC oxygen sorbent also exhibits excellent stability for 2000 redox cycles for air separation.

Endogenous Nanoparticles Strain Perovskite Host Lattice Providing Oxygen Capacity and Driving Oxygen Exchange and CH4 Conversion to Syngas

Particles dispersed on the surface of oxide supports have enabled a wealth of applications in electrocatalysis, photocatalysis, and heterogeneous catalysis. Dispersing nanoparticles within the bulk of oxides is, however, synthetically much more challenging and therefore less explored, but could open new dimensions to control material properties analogous to substitutional doping of ions in crystal lattices. Here we demonstrate such a concept allowing extensive, controlled growth of metallic nanoparticles, at nanoscale proximity, within a perovskite oxide lattice as well as on its surface. By employing operando techniques, we show that in the emergent nanostructure, the endogenous nanoparticles and the perovskite lattice become reciprocally strained and seamlessly connected, enabling enhanced oxygen exchange. Additionally, even deeply embedded nanoparticles can reversibly exchange oxygen with a methane stream, driving its redox conversion to syngas with remarkable selectivity and long term cyclability while surface particles are present. These results not only exemplify the means to create extensive, self-strained nanoarchitectures with enhanced oxygen transport and storage capabilities, but also demonstrate that deeply submerged, redox-active nanoparticles could be entirely accessible to reaction environments, driving redox transformations and thus offering intriguing new alternatives to design materials underpinning several energy conversion technologies.

TiO2-Supported catalysts with ZnO and ZrO2 for non-oxidative dehydrogenation of propane: mechanistic analysis and application potential

Non-oxidative dehydrogenation of propane is one of the most promising technologies for propene production in terms of environmental impact and sustainability.

Cyclic redox scheme towards shale gas reforming: a review and perspectives

Alkanes are potential precursors to many value-added chemicals such as olefins and other petrochemicals.

Near 100% CO selectivity in nanoscaled iron-based oxygen carriers for chemical looping methane partial oxidation

Chemical looping methane partial oxidation provides an energy and cost effective route for methane utilization. However, there is considerable CO₂ co-production in current chemical looping systems, rendering a decreased productivity in value-added fuels or chemicals. In this work, we demonstrate that the co-production of CO₂ can be dramatically suppressed in methane partial oxidation reactions using iron oxide nanoparticles embedded in mesoporous silica matrix. We experimentally obtain near 100% CO selectivity in a cyclic redox system at 750–935 °C, which is a significantly lower temperature range than in conventional oxygen carrier systems. Density functional theory calculations elucidate the origins for such selectivity and show that low-coordinated lattice oxygen atoms on the surface of nanoparticles significantly promote Fe–O bond cleavage and CO formation. We envision that embedded nanostructured oxygen carriers have the potential to serve as a general materials platform for redox reactions with nanomaterials at high temperatures.

Chemical looping methane partial oxidation is an effective technology to produce syngas with a minimal energy penalty. Here, the authors design and develop a mesoporous silica supported nanoparticle oxygen carrier that enables a near 100% CO generation with high recyclability and substantially lower operating temperature.

Modulating Lattice Oxygen in Dual-Functional Mo-V-O Mixed Oxides for Chemical Looping Oxidative Dehydrogenation

Oxygen chemistry plays a pivotal role in numerous chemical reactions. In particular, selective cleavage of C-H bonds by metal oxo species is highly desirable in dehydrogenation of light alkanes. However, high selectivity of alkene is usually hampered through consecutive oxygenation reactions in a conventional oxidative dehydrogenation (ODH) scheme. Herein, we show that dual-functional Mo-V-O mixed oxides selectively convert propane to propylene via an alternative chemical looping oxidative dehydrogenation (CL-ODH) approach. At 500 °C, we obtain 89% propylene selectivity at 36% propane conversion over 100 dehydrogenation-regeneration cycles. We attribute such high propylene yield-which exceeds that of previously reported ODH catalysts-to the involvement and precise modulation of bulk lattice oxygen via atomic-scale doping of Mo and show that increasing the binding energy of V-O bonds is critical to enhance the selectivity of propylene. This work provides the fundamental understanding of metal-oxygen chemistry and a promising strategy for alkane dehydrogenation.

Structure, electrical conductivity and oxygen transport properties of perovskite-type oxides CaMn1-x-yTixFeyO3-δ

Calcium manganite-based perovskite-type oxides hold promise for application in chemical looping combustion processes and oxygen transport membranes. In this study, we have investigated the structure, electrical conductivity and oxygen transport properties of perovskite-type oxides CaMn1-x-yTixFeyO3-δ. Distinct from previous work, data of high-temperature X-ray diffraction (HT-XRD) in the temperature range 600-1000 °C (with intervals of 25 °C) demonstrates that CaMnO3-δ (CM) transforms from orthorhombic to a mixture of orthorhombic and tetragonal phases between 875 °C and 900 °C. Rietveld refinements show the formation of a pure tetragonal phase at 975 °C and of a pure cubic phase at 1000 °C. Partial substitution of manganese by iron and/or titanium to yield CaMn0.875Ti0.125O3-δ (CMT), CaMn0.85Fe0.15O3-δ (CMF) or CaMn0.725Ti0.125Fe0.15O3-δ (CMTF) leads to different phase behaviours. While CMT remains orthorhombic up to the highest temperature covered by the HT-XRD experiments, CMF and CMTF undergo an orthorhombic → tetragonal → cubic sequence of phase transitions. Electrical conductivity relaxation measurements are conducted to determine the chemical diffusion coefficient (Dchem) and the surface exchange coefficient (kchem) of the materials. The results demonstrate that oxygen transport is hindered in the tetragonal phase, when occurring, which is attributed to a possible ordering of oxygen vacancies. The small polaron electrical conductivity of CM in the cited temperature range is lowered upon partial manganese substitution, by about 10% for CMF and up to half an order of magnitude for CMT and CMTF.

Fast Semiconductor-Metal Bidirectional Transition by Flame Chemical Vapor Deposition

A simple yet powerful flame chemical vapor deposition technique is proposed that allows free control of the surface morphology, microstructure, and composition of existing materials with regard to various functionalities within a short process time (in seconds) at room temperature and atmospheric pressure as per the requirement. Since the heat energy is directly transferred to the material surface, the redox periodically converges to the energy dynamic equilibrium depending on the energy injection time; therefore, bidirectional transition between the semiconductor/metal is optionally available. To demonstrate this, a variety of Sn-based particles were created on preformed SnO2 nanowires, and this has been interpreted as a new mechanism for the response and response times of gas-sensing, which are representative indicators of the most surface-sensitive applications and show one-to-one correspondence between theoretical and experimental results. The detailed technologies derived herein are clearly influential in both research and industry.

Defect engineering of metal-oxide interface for proximity of photooxidation and photoreduction

Close proximity between different catalytic sites is crucial for accelerating or even enabling many important catalytic reactions. Photooxidation and photoreduction in photocatalysis are generally separated from each other, which arises from the hole-electron separation on photocatalyst surface. Here, we show with widely studied photocatalyst Pt/[Formula: see text] as a model, that concentrating abundant oxygen vacancies only at the metal-oxide interface can locate hole-driven oxidation sites in proximity to electron-driven reduction sites for triggering unusual reactions. Solar hydrogen production from aqueous-phase alcohols, whose hydrogen yield per photon is theoretically limited below 0.5 through conventional reactions, achieves an ultrahigh hydrogen yield per photon of 1.28 through the unusual reactions. We demonstrated that such defect engineering enables hole-driven CO oxidation at the Pt-[Formula: see text] interface to occur, which opens up room-temperature alcohol decomposition on Pt nanoparticles to [Formula: see text] and adsorbed CO, accompanying with electron-driven proton reduction on Pt to [Formula: see text].