fac-Re(2,2’-bipyridine)(CO)sub.3Cl (denoted as ReCC) is an efficient molecule-catalyst with high selectivity in the photoreduction of COsub.2 to CO in a homogeneous system. However, the two major ...drawbacks of Re(I) complexes in the homogeneous system, easy degradation and difficult separation, seriously hinder its development in the field of industrial applications. In this paper, we designed and prepared two different Re-complex fixation systems (denoted as ReCC@TiOsub.2-5 wt% and ReCC-TiOsub.2-5 wt%) based on TiOsub.2 gel via the sensitization method and sol–gel method, respectively. Compared with a pure ReCC complex, both of them exhibited excellent photocatalytic reduction activity. In particular, the sol–gel hybrid system (ReCC-TiOsub.2-5 wt%) displayed outstanding positive synergistic effects on the photocatalytic activity and the long durability of the photocatalytic process. A series of characterizations were carried out to explore the probable photocatalytic reduction process mechanism, which provides the theoretical basis and technical support for the Re complex fixation method.
COsub.2 is the most abundant greenhouse gas, and for this reason, it is the main target for finding solutions to climatic change. A strategy of environmental remediation is the transformation of ...COsub.2 to an aggregated value product to generate a carbon-neutral cycle. COsub.2 reduction is a great challenge because of the large C=O dissociation energy, ~179 kcal/mol. Heterogeneous photocatalysis is a strategy to address this issue, where the adsorption process is the fundamental step. The focus of this work is the role of adsorption in COsub.2 reduction by means of modeling the COsub.2 adsorption in rutile metallic oxides (TiOsub.2, GeOsub.2, SnOsub.2, IrOsub.2 and PbOsub.2) using Density Functional Theory (DFT) and periodic DFT methods. The comparison of adsorption on different metal oxides forming the same type of crystal structure allowed us to observe the influence of the metal in the adsorption process. In the same way, we performed a comparison of the adsorption capability between two different surface planes, (001) and (110). Two COsub.2 configurations were observed, linear and folded: the folded conformations were observed in TiOsub.2, GeOsub.2 and SnOsub.2, while the linear conformations were present in IrOsub.2 and PbOsub.2. The largest adsorption efficiency was displayed by the (001) surface planes. The COsub.2 linear and folded configurations were related to the interaction of the oxygen on the metallic surface with the adsorbate carbon, and the linear conformations were associated with the physisorption and folded configurations with chemisorption. TiOsub.2 was the material with the best performance for COsub.2 interactions during the adsorption.
In heterogeneous catalysis, supports play a crucial role in modulating the geometric and electronic structure of the active metal phase for optimizing the catalytic performance. A γ-Al2O3 nanosheet ...that contains 27% pentacoordinate Al(3+) sites can nicely disperse and stabilize raft-like Pt-Sn clusters as a result of strong interactions between metal and support. Consequently, there are strong electronic interactions between the Pt and Sn atoms, resulting in an increase in the electron density of the Pt sites. When used in the propane dehydrogenation reaction, this catalyst displayed an excellent specific activity for propylene formation with >99% selectivity, and superior anti-coking and anti-sintering properties. Its exceptional ability to maintain the high activity and stability at ultrahigh space velocities further showed that the sheet construction of the catalyst facilitated the kinetic transfer process.
It is well documented that different surface structures of catalytically active metals may exhibit different catalytic properties. This is typically examined by comparing the catalytic activities ...and/or selectivities of various well-defined smooth and stepped/kinked single crystal surfaces. Here we report the direct observation of the heterogeneity of active polycrystalline surfaces under reaction conditions, which is manifested by multifrequential oscillations during hydrogen oxidation over rhodium, imaged in situ by photoemission electron microscopy. Each specific surface structure, i.e. the crystallographically different µm-sized domains of rhodium, exhibits an individual spiral pattern and oscillation frequency, despite the global diffusional coupling of the surface reaction. This reaction behavior is attributed to the ability of stepped surfaces of high-Miller-index domains to facilitate the formation of subsurface oxygen, serving as feedback mechanism of the observed oscillations. The current experimental findings, backed by microkinetic modeling, may open an alternative approach towards addressing the structure-sensitivity of heterogeneous surfaces.
The electrocatalytic carbon dioxide reduction reaction is an effective means of combating the greenhouse effect caused by massive carbon dioxide emissions. Carbon nitride in the graphitic phase ...(g-Csub.3Nsub.4) has excellent chemical stability and unique structural properties that allow it to be widely used in energy and materials fields. However, due to its relatively low electrical conductivity, to date, little effort has been made to summarize the application of g-Csub.3Nsub.4 in the electrocatalytic reduction of COsub.2. This review focuses on the synthesis and functionalization of g-Csub.3Nsub.4 and the recent advances of its application as a catalyst and a catalyst support in the electrocatalytic reduction of COsub.2. The modification of g-Csub.3Nsub.4-based catalysts for enhanced COsub.2 reduction is critically reviewed. In addition, opportunities for future research on g-Csub.3Nsub.4-based catalysts for electrocatalytic COsub.2 reduction are discussed.
Gamma alumina (γ-Alsub.2Osub.3) is widely used as a catalyst and catalytic support due to its high specific surface area and porosity. However, synthesis of γ-Alsub.2Osub.3 nanocrystals is often a ...complicated process requiring high temperatures or additional post-synthetic steps. Here, we report a single-step synthesis of size-controlled and monodisperse, facetted γ-Alsub.2Osub.3 nanocrystals in an inductively coupled nonthermal plasma reactor using trimethylaluminum and oxygen as precursors. Under optimized conditions, we observed phase-pure, cuboctahedral γ-Alsub.2Osub.3 nanocrystals with defined surface facets. Nuclear magnetic resonance studies revealed that nanocrystal surfaces are populated with AlOsub.6, AlOsub.5 and AlOsub.4 units with clusters of hydroxyl groups. Nanocrystal size tuning was achieved by varying the total reactor pressure yielding particles as small as 3.5 nm, below the predicted thermodynamic stability limit for γ-Alsub.2Osub.3.
With the recent emphasis on green chemistry in the chemical industries, there is the need for environmentally friendly large-scale syntheses. This book lays out an important catalytic reaction class ...for these green/sustainable reactions, covering catalyst characterization and performance as well as paying special attention to catalyst stability and recyclability. An international team of authors guides readers in the selection, preparation, and use of catalysts for industrial organic synthesis in the pharmaceutical, fragrance, fine chemical, and petrochemical industries.
Decarbonization has become an urgent affair to restrain global warming. COsub.2 hydrogenation coupled with Hsub.2 derived from water electrolysis is considered a promising route to mitigate the ...negative impact of carbon emission and also promote the application of hydrogen. It is of great significance to develop catalysts with excellent performance and large-scale implementation. In the past decades, metal-organic frameworks (MOFs) have been widely involved in the rational design of catalysts for COsub.2 hydrogenation due to their high surface areas, tunable porosities, well-ordered pore structures, and diversities in metals and functional groups. Confinement effects in MOFs or MOF-derived materials have been reported to promote the stability of COsub.2 hydrogenation catalysts, such as molecular complexes of immobilization effect, active sites in size effect, stabilization in the encapsulation effect, and electron transfer and interfacial catalysis in the synergistic effect. This review attempts to summarize the progress of MOF-based COsub.2 hydrogenation catalysts up to now, and demonstrate the synthetic strategies, unique features, and enhancement mechanisms compared with traditionally supported catalysts. Great emphasis will be placed on various confinement effects in COsub.2 hydrogenation. The challenges and opportunities in precise design, synthesis, and applications of MOF-confined catalysis for COsub.2 hydrogenation are also summarized.
A new metal-organic framework (MOF), Cosub.2(L)sub.2(azpy)sub.n (compound 1, Hsub.2L = 5-(pyridin-4-ylmethoxy)-isophthalic acid, azpy = 4,4′-azopyridine), was synthesized by a solvothermal method and ...further characterized by elemental analysis, IR spectra, thermogravimetric analysis, single-crystal and powder X-ray diffraction. The X-ray single-crystal diffraction analysis for compound 1 indicated that two cis L2sup.2− ligands connected to two cobalt atoms resulted in a macrocycle structure. Through a series of adsorption tests, we found that compound 1 exhibited a high capacity of COsub.2, and the adsorption capacity could reach 30.04 cmsup.3/g. More interestingly, under 273 K conditions, the adsorption of COsub.2 was 41.33 cmsup.3/g. In addition, when the Co-MOF was irradiated by a 730 nm laser, rapid temperature increases for compound 1 were observed (temperature variation in 169 s: 26.6 °C), showing an obvious photothermal conversion performance. The photothermal conversion efficiency reached 20.3%, which might be due to the fact that the parallel arrangement of azo units inhibited non-radiative transition and promoted photothermal conversion. The study provides an efficient strategy for designing MOFs for the adsorption of COsub.2 and with good photothermal conversion performance.
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•The influencing factors on photocatalytic uranium extraction was evaluated.•The design strategy of photocatalysts for uranium extraction was summarized.•The rational design was ...provided from band structure and surface coordination.•The technical methods for identificating uranium reduction species were summarized.•The challenges and prospects of photocatalytic uranium reduction were pointed out.
Nuclear energy has been regarded as one of the promising energy sources to replace traditional fossil fuels due to its advantages of high energy density and carbon-free emission. Unfortunately, the limited storage of uranium ore restricted the sustainable development of nuclear energy, together with the generation of uranium-containing wastewater resulting in the problems of environmental pollution. Therefore, extracting and recycling uranium from seawater and radioactive uranium-containing wastewater is necessary for the sustainable development of nuclear energy and environmental protection. The light-driven heterogeneous photocatalytic technology is an appealing strategy to significantly promote the kinetics, capacity, and selectivity during uranium extraction. However, the recovery of uranium from radioactive wastewater/seawater is restricted by various factors, such as abundant competing ions, low uranium concentration, coexisting organic matter, and strong acidity or alkalinity in special environmental in the process of practical application. In this review, we described the general background of uranium extraction, followed by a brief discussion of the several possible reduction paths for photocatalytic reduction of uranium. Then, the effects of experimental conditions, photocatalyst stability and environmental adaptability on the performance of photocatalytic uranium reduction were systematically discussed. After having some fundamental understanding on photocatalytic uranium reduction, we summarized the design guidelines of photocatalysts for uranium reduction, and further discussed the corresponding advantages and disadvantages in photocatalytic uranium reduction. In addition, we concluded the current available characterization techniques for identifying uranium species after reduction, which is critical to the mechanistic study. Finally, we end this review with an outlook into the remaining challenges and future perspectives of photocatalytic uranium reduction.
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