Immobilization of Silver(I) Ions on Amino-Functionalized Chromium(III) Terephthalate with Organophosphine and its C-H Carboxylation of a Heteroaromatic Compound.

A newly designed heterogenized catalyst that incorporates silver(I) ions with 2-(dicyclohexylphosphaneyl)acetaldehyde (PCy2 aldehyde) into amino-functionalized chromium(III) terephthalate is developed. Silver(I) ions were robustly immobilized on the amino-functionalized chromium(III) terephthalate, which contains an imine bond formed by the reaction with PCy2 aldehyde. The Ag(I) ion is coordinated with the phosphine in the imine group to create MIL-101-AP(Ag). Characterizations were carefully carried out according to the synthetic steps. The catalytic performance of MIL-101-AP(Ag) was evaluated through the C-H carboxylation of thiophene-2-carbonitrile, achieving a 10 % yield with a turnover number of 1.0. The recyclability of the MIL-101-AP(Ag) catalyst was successfully demonstrated with five cycle, with no loss in activity and selectivity observed. This approach, which involves the formation of an imine bond to facilitate silver loading with phosphine on amino-functionalized MIL-101(Cr), exhibits significant potential for both CO2 fixation and C-H carboxylation, thereby highlighting the modified material's promise as a sustainable catalyst.

Nickel-Tin Nanoalloy Supported ZnO Catalysts from Mixed-Metal Zeolitic Imidazolate Frameworks for Selective Conversion of Glycerol to 1,2-Propanediol.

The successful synthesis of finely tuned Ni1.5 Sn nanoalloy phases containing ZnO catalyst with a small particle size (6.7 nm) from a mixed-metal zeolitic imidazolate framework (MM-ZIF) is investigated. The catalyst was evaluated for the efficient production of 1,2-propanediol (1,2-PDO) from crude glycerol and comprehensively characterized using several analytical techniques. Among the catalysts, 3Ni1Sn/ZnO (Ni/Sn=3/1) showed the best catalytic performance and produced the highest yield (94.2 %) of 1,2-PDO at ~100 % conversion of glycerol; it also showed low apparent activation energy (15.4 kJ/mol) and excellent stability. The results demonstrated that the synergy between Ni-Sn alloy, finely dispersed Ni metallic sites, and the Lewis acidity of SnOx species-loaded ZnO played a pivotal role in the high activity and selectivity of the catalyst. The confirmation of acetol intermediate and theoretical calculations verify the Ni1.5 Sn phases provide the least energetic pathway for the formation of 1,2-PDO selectively. The reusability of solvent for successive ZIF synthesis, along with the excellent recyclability of the ZIF-derived catalyst, enables an overall sustainable process. We believe that the present synthetic protocol that uses MM-ZIF for the conversion of various biomass-derived platform chemicals into valuable products can be applied to various nanoalloy preparations.

Flexible and Extensive Platinum Ion Gel Condensers for Programmable Catalysis.

Catalytic condensers composed of ion gels separating a metal electrode from a platinum-on-carbon active layer were fabricated and characterized to achieve more powerful, high surface area dynamic heterogeneous catalyst surfaces. Ion gels comprised of poly(vinylidene difluoride)/1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide were spin coated as a 3.8 µm film on a Au surface, after which carbon sputtering of a 1.8 nm carbon film and electron-beam evaporation of 2 nm Pt clusters created an active surface exposed to reactant gases. Electronic characterization indicated that most charge condensed within the Pt nanoclusters upon application of a potential bias, with the condenser device achieving a capacitance of ∼20 µF/cm2 at applied frequencies of up to 120 Hz. The maximum charge of ∼1014 |e-| cm-2 was condensed under stable device conditions at 200 °C on catalytic films with ∼1015 sites cm-2. Grazing incidence infrared spectroscopy measured carbon monoxide adsorption isobars, indicating a change in the CO* binding energy of ∼19 kJ mol-1 over an applied potential bias of only 1.25 V. Condensers were also fabricated on flexible, large area Kapton substrates allowing stacked or tubular form factors that facilitate high volumetric active site densities, ultimately enabling a fast and powerful catalytic condenser that can be fabricated for programmable catalysis applications.

Fabrication of Large-Area Metal-on-Carbon Catalytic Condensers for Programmable Catalysis.

Catalytic condensers stabilize charge on either side of a high-k dielectric film to modulate the electronic states of a catalytic layer for the electronic control of surface reactions. Here, carbon sputtering provided for fast, large-scale fabrication of metal-carbon catalytic condensers required for industrial application. Carbon films were sputtered on HfO2 dielectric/p-type Si with different thicknesses (1, 3, 6, and 10 nm), and the enhancement of conductance and capacitance of carbon films was observed upon increasing the carbon thickness following thermal treatment at 400 °C. After Pt deposition on the carbon films, the Pt catalytic condenser exhibited a high capacitance of ∼210 nF/cm2 that was maintained at a frequency ∼1000 Hz, satisfying the requirement for a dynamic catalyst to implement catalytic resonance. Temperature-programmed desorption of carbon monoxide yielded CO desorption peaks that shifted in temperature with the varying potential applied to the condenser (-6 or +6 V), indicating a shift in the binding energy of carbon monoxide on the Pt condenser surface. A substantial increase in capacitance (∼2000 nF/cm2) of the Pt-on-carbon devices was observed at elevated temperatures of 400 °C that can modulate ∼10% of charge per metal atom when 10 V potential was applied. A large catalytic condenser of 42 cm2 area Pt/C/HfO2/Si exhibited a high capacitance of 9393 nF with a low leakage current/capacitive current ratio (<0.1), demonstrating the practicality and versatility of the facile, large-scale fabrication method for metal-carbon catalytic condensers.

Fabrication of Hierarchical, Porous, Bimetallic, Zeolitic Imidazolate Frameworks with the Incorporation of Square Planar Pd and Its Catalytic Application.

Bimetallic zeolitic imidazolate frameworks (ZIFs) containing two different metal ions can exhibit superior performances when applied in heterogeneous catalysis. Herein, we present a facile one-pot synthesis method for PdCo-ZIFs with various Pd/Co ratios, where Pd(II) ions are successfully incorporated into the Co node sites of the ZIF structure. The local structure of the bimetallic ZIFs was comprehensively investigated by pore-structure, X-ray absorption fine structure, and in situ CO adsorption Fourier transform infrared analyses. The results demonstrated that the framework comprises different coordination geometries of Co (tetrahedral) and Pd (square planar) ions connected by the benzimidazolate ligand. Notably, the inherently nonporous, 2D Co-ZIF structure was transformed into a hierarchical porous structure, and the PdCo-ZIFs exhibited a significantly increased concentration of defects and distorted Co sites. Based on these results, the catalytic performances of the synthesized ZIFs in the cycloaddition of CO2 to epoxides were evaluated under a cocatalyst and solvent-free conditions. The PdCo-ZIFs exhibited significantly higher catalytic activity (maximum turnover frequency, TOF = 2501 h-1) than Co-ZIF (TOF = 65 h-1) and Pd-ZIF (no activity), which revealed that the undercoordinated Co sites with distorted structure are the active sites rather than the incorporated Pd ions. This study provides a facile one-pot method for synthesizing bimetallic ZIFs with mixed-coordination modes, hierarchical porous structures, and modified defect concentrations, which would expand the library of structurally diverse bimetallic ZIFs toward various applications.

Immobilization of a trimeric ruthenium cluster in mesoporous chromium terephthalate and its catalytic application.

Molecular trimeric ruthenium carboxylate clusters (Ru3 clusters) have been introduced into the pore channels of mesoporous metal-organic framework chromium terephthalate [MIL-101(Cr)] by employing a facile two-step post-synthetic strategy in which diamine hooks anchored on the framework metal nodes of the MOF are used to covalently immobilize the Ru3 clusters. The catalytic activity of the isolated Ru3 clusters in the pore channels of the MOF was significantly improved compared to the bulk counterpart.

Ag-exchanged mesoporous chromium terephthalate with sulfonate for removing radioactive methyl iodide at extremely low concentrations in humid environments.

The development of efficient adsorbents to remove radioactive methyl iodide (CH3I) in humid environments is crucial for air purification after pollution by nuclear power plant waste. In this work, we successfully prepared a post-synthetic covalent modified MIL-101 with a sulfonate group followed by the ion-exchange of Ag (I), which is well characterized by diffuse reflectance FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and the hydrophobic index (HI). After modification of the MOFs, we applied functionalized MIL-101 obtained by either one-pot synthesis (MIL-101-SO3Ag) or a post-synthetic modification process (MIL-101-RSO3Ag, R = NH(CH2)3) to remove the CH3I at an extremely low concentration (0.31 ppm) in an environment with very high relative humidity (RH 95%). Enhanced hydrophobicity of the surface-modified MIL-101 was evaluated by examining the HI with the competitive adsorption of water and cyclohexane vapor, with a high surface area maintained, as confirmed by Ar physisorption. Interestingly, the post-synthetically modified MIL-101-RSO3Ag showed exceptional adsorption performance as determined by its decontamination factor (DF = 195,350) at 303 K and RH 95%. This performance was in comparison to Ag (I)-exchanged 13X zeolite and MIL-101-SO3Ag, which include much higher amounts of Ag. Furthermore, MIL-101-RSO3Ag retained ~94-100% of its fresh adsorbent performance during five cycle repetitions.

CO2 absorption and desorption characteristics of MgO-based absorbent promoted by triple eutectic alkali carbonate.

Carbon capture and sequestration is emerging as a promising technology to mitigate the greenhouse effect by reducing CO2 emissions. Of a number of metal oxides applied as CO2 absorbents, MgO is a potential material that can operate in a relatively low elevated temperature range (200-500 °C), namely, intermediate-temperatures. In the present research, we investigated the characteristics of CO2 absorption and desorption on MgO-based absorbents promoted by molten alkali metal carbonate that has a melting point of 397 °C (eutectic molar ratio of Li2CO3 : Na2CO3 : K2CO3 = 0.435 : 0.315 : 0.250). These absorbents absorb CO2 in two steps with the first step being very fast and large in capacity in comparison with other related absorbents in the literature and the second step being much slower than the first one. The overall capacity can be as large as 77% MgO conversion, much larger than other carbonate-promoted MgO absorbents in the literature. The fast first step of CO2 absorption is associated with the reaction of highly basic sites on the MgO surface formed through the interaction between the carbonates and MgO upon pre-treatment. Detailed analyses via in situ XRD revealed that MgCO3 and a new phase, probably a double carbonate between Mg and alkali ions, are formed as the carbonation products. A detailed mechanism is proposed based on the experimental data, which highlights the unique properties of the molten alkali carbonate as a dissolution medium for CO2 and MgO and even the product MgCO3.

Characteristics of NaNO3-Promoted CdO as a Midtemperature CO2 Absorbent.

In this study, we explored the reaction system CdO(s) + CO2(g) ⇄ CdCO3(s) as a model system for CO2 capture agent in the intermediate temperature range of 300-400 °C. While pure CdO does not react with CO2 at all up to 500 °C, CdO mixed with an appropriate amount of NaNO3 (optimal molar ratio NaNO3/CdO = 0.14) greatly enhances the conversion of CdO into CdCO3 up to ∼80% (5.68 mmol/g). These NaNO3-promoted CdO absorbents can undergo many cycles of absorption and desorption by temperature swing between 300 and 370 °C under a 100% CO2 condition. Details of how NaNO3 promotes the CO2 absorption of CdO have been delineated through various techniques using thermogravimetry, coupled with X-ray diffraction and electron microscopy. On the basis of the observed data, we propose a mechanism of CO2 absorption and desorption of NaNO3-promoted CdO. The absorption proceeds through a sequence of events of CO2 adsorption on the CdO surface covered by NaNO3, dissolution of so-formed CdCO3, and precipitation of CdCO3 particles in the NaNO3 medium. The desorption occurs through the decomposition of CdCO3 in the dissolved state in the NaNO3 medium where CdO nanoparticles are formed dispersed in the NaNO3 medium. The CdO nanoparticles are aggregated into micrometer-large particles with smooth surfaces and regular shapes.

Mechanisms of absorption and desorption of CO2 by molten NaNO3-promoted MgO.

In order to realize carbon capture and sequestration (CCS), a technology proposed to circumvent the global warming problem while maintaining the present level of economic activity, the development of efficient carbon-capturing agents is of prime importance. In addition to the prevailing amine-based agents that operate at temperatures lower than 200 °C, agents that can operate at higher temperatures are being considered to reduce the cost of CCS. For the mid-temperature (200-500 °C) operation, alkali nitrate-promoted MgO is a promising candidate; whose detailed reaction mechanisms are not yet fully understood, however. In the present study, we have performed a comprehensive investigation on the mechanisms of CO2 absorption and desorption of NaNO3-promoted MgO. Highly efficient CO2 absorbents were obtained by decomposing Mg5(CO3)4(OH)2·4H2O with NaNO3 intimately mixed with it. Our collective data, including isothermal CO2 uptake curves, MgO solubility in molten NaNO3, and observations on the reaction of MgO wafers with CO2, indicate that the absorption takes place in the molten NaNO3 medium in which both CO2 and MgO are dissolved. MgCO3 is formed inside the molten promoter through the nucleation and growth steps. The decomposition of MgCO3 back to MgO, that is desorption of CO2, is also facilitated by molten NaNO3, which we attribute to the decreased relative stability of MgCO3 with respect to MgO when in contact with molten NaNO3. The relative affinity of molten nitrate to MgO and MgCO3 was estimated by measuring the 'contact angles' of nitrate on them. Implications of our findings for the real applications of alkali nitrate-promoted MgO absorbents with numerous repeated cycles of absorption and desorption of CO2 are discussed.