Insight into the Role of Unsaturated Coordination O2c-Ti5c-O2c Sites on Selective Glycerol Oxidation over AuPt/TiO2 Catalysts

Atomic Scale Responses of High Entropy Oxides to Redox Environments

The potential of high entropy oxides (HEOs) as high-performance energy storage materials and catalysts has been mainly understood through their bulk structures. However, the importance of their surfaces, which may play an even more critical role, remains largely unknown. In this study, we employed advanced scanning transmission electron microscopy to investigate the atomic-scale structural and chemical responses of CeYLaHfTiZrOx HEOs to high-temperature redox environments. Our observations reveal dynamic elemental and structural reconstructions in the surface of HEOs under different gas environments, contrasting with the high stability of the bulk structure. Notably, the surfaces of HEO particles consistently exhibit abundant oxygen vacancies, regardless of the redox environment. These findings indicate that HEOs offer distinct advantages in facilitating chemical and electrochemical reactions, relying on oxygen vacancies. Our results also suggest that the exceptional performance of HEOs in energy storage applications arises from surface structural and chemical adaptability.

Stable and Active Au Catalyst Supported on CeMnO3 Perovskite for Selective Oxidation of Glycerol

The selective oxidation of glycerol holds promise to transform glycerol into value-added chemicals. However, it remains a big challenge to achieve satisfactory selectivity toward the specific product at high conversion due to the multiple reaction pathways. Here, we prepare a hybrid catalyst via supporting Au nanoparticles on CeMnO₃ perovskite with a modest surface area, achieving promoted conversion of glycerol (90.1%) and selectivity of glyceric acid (78.5%), which are much higher than those of CeMnO_x solid-solution-supported Au catalysts with larger surface area and other Ce-based or Mn-based Au catalysts. The strong interaction between Au and CeMnO₃ perovskite facilitates the electron transfer from the B-site metal (Mn) in the CeMnO₃ perovskite to Au and stabilizes Au nanoparticles, which results in the enhanced catalytic activity and stability for glycerol oxidation. Valence band photoemission spectral analysis reveals that the uplifted d-band center of Au/CeMnO₃ promotes the adsorption of the glyceraldehyde intermediate on the catalyst surface, which benefits further oxidation of glyceraldehyde into glyceric acid. The flexibility of the perovskite support provides a promising strategy for the rational design of high-performance glycerol oxidation catalysts.

Tailored Cl- Ligation on Supported Pt Catalysts for Selective Primary C-H Bond Oxidation

It is challenging to achieve high selectivity over Pt-metal-oxide catalysts widely used in many selective oxidation reactions because Pt is prone to over-oxidize substrates. Herein, our sound strategy for enhancing the selectivity is to saturate the under-coordinated single Pt atoms with Cl^- ligands. In this system, the weak electronic metal-support interactions between Pt atoms and reduced TiO₂ cause electron extraction from Pt to Cl^- ligands, resulting in strong Pt-Cl bonds. Therefore, the two-coordinate single Pt atoms adopt a four-coordinate configuration and thus inactivated, thereby inhibiting the over-oxidation of toluene over Pt sites. The selectivity for the primary C-H bond oxidation products of toluene was increased from 50.1 to 100%. Meanwhile, the abundant active Ti³⁺ sites were stabilized in reduced TiO₂ by Pt atoms, leading to a rising yield of the primary C-H oxidation products of 249.8 mmol g_cat^-1. The reported strategy holds great promise for selective oxidation with enhanced selectivity.

Semi-quantitative design of synergetic surficial/interfacial sites for the semi-continuous oxidation of glycerol

Qualitatively identifying the dominant catalytic site for each step of a semi-continuous reaction and semi-quantitatively correlating such different sites to the catalytic performance is of great significance toward the integration of multiple well-optimized sites on a heterogeneous catalyst. Herein, a series of structurally defined TiOx-based catalysts were synthesized to provide a feasible approach to investigate the aforementioned issues using the semi-continuous oxidation of glycerol as a model reaction. Detailed investigations have verified the simultaneous presence of two kinds of Pt active sites: 1) Negatively charged Pt bound to the oxygen vacancies of modified TiOx in the form of Ptδ--Ov-Ti3+ sites and 2) metallic Pt (Pt0 site) located away from the interface. Meanwhile, the proportion of surficial and interfacial sites varies over this series of catalysts. Combined in situ FTIR experiments revealed that the reaction network was well-tuned via a site cooperation mechanism: The surficial Pt0 sites dissociatively adsorb the OH group of glycerol with a monodentate bonding geometry and the Ptδ--Ov-Ti3+ sites dissociate the C=O bond of the aldehyde group in a bidentate form. Furthermore, CO-FTIR spectroscopy confirmed a correlation between the reaction rate/product selectivity and the fraction of surficial/interfacial sites. A rational proportion of surficial and interfacial sites is key to enabling a high yield of glyceric acid. The most active catalyst with 32% surface sites and 68% interfacial sites exhibited 90.0% glycerol conversion and 68.5% GLYA selectivity. These findings provide a deeper understanding of the structure-activity relationships using qualitative identification and semi-quantitative analysis.

A Perspective on Heterogeneous Catalysts for the Selective Oxidation of Alcohols

Selective oxidation of higher alcohols using heterogeneous catalysts is an important reaction in the synthesis of fine chemicals with added value. Though the process for primary alcohol oxidation is industrially established, there is still a lack of fundamental understanding considering the complexity of the catalysts and their dynamics under reaction conditions, especially when higher alcohols and liquid-phase reaction media are involved. Additionally, new materials should be developed offering higher activity, selectivity, and stability. This can be achieved by unraveling the structure-performance correlations of these catalysts under reaction conditions. In this regard, researchers are encouraged to develop more advanced characterization techniques to address the complex interplay between the solid surface, the dissolved reactants, and the solvent. In this mini-review, we report some of the most important approaches taken in the field and give a perspective on how to tackle the complex challenges for different approaches in alcohol oxidation while providing insight into the remaining challenges.

Substoichiometric titanium oxide Ti2O3 exhibits greater efficiency in enhancing hydrolysis of 1,1,2,2-tetrachloroethane than TiO2 nanomaterials

Oxygen-deficient substoichiometric titanium oxides, or "titanium suboxides," are produced incidentally from coal combustion and are environmentally abundant. Additionally, titanium suboxide nanomaterials are promising new materials with likely future environmental release. How these materials may affect contaminant fate differently than stoichiometric TiO₂ (nano)materials is largely unknown. Here, we show that Ti₂O₃ (selected as a model titanium suboxide) exhibits significantly greater efficiency in enhancing the hydrolysis of 1,1,2,2-tetrachloroethane (TeCA), a common groundwater contaminant, than the stoichiometric anatase and rutile TiO₂. At environmentally relevant pH (6.5-7.5), the surface area-normalized pseudo-first-order hydrolysis rate constant in the presence of Ti₂O₃ is approximately an order of magnitude higher than those associated with TiO₂. The superior catalytic efficiency of Ti₂O₃ can be attributed to both its higher surface hydrophobicity, which renders higher adsorption affinity for TeCA, and its higher concentration of Lewis acid sites (mainly the Ti³⁺ and the five-coordinated Ti⁴⁺). Particularly, the deprotonated hydroxyl groups attached to Ti³⁺ (a weaker Lewis acid than Ti⁴⁺) exhibit higher basicity and thus, are more effective in catalyzing the base-promoted hydrolysis reaction. The findings call for further understanding of the environmental implications of titanium suboxide (nano)materials, which may not be readily predictable based on the knowledge acquired for TiO₂.

The selective oxidation of glycerol over metal-free photocatalysts: insights into the solvent effect on catalytic efficiency and product distribution

Solvent effect in selective aerobic oxidation of glycerol over O-doped g-C₃N₄ was studied combining with control experiments and DFT theory calculation. Notably, a novel oxidative esterification of glycerol to yield esters was discovered in CH₃CN.

Coordinately unsaturated O2c–Ti5c–O2c sites promote the reactivity of Pt/TiO2 catalysts in the solvent-free oxidation of n-octanol

Coordination unsaturated O_2c–Ti_5c–O_2c of TiO₂ (001) facets promote the formation of low-coordinate Pt metal clusters, which enhances catalytic performance in aerobic 1-octanol oxidation.

Cu2O-mediated assembly of electrodeposition of Au nanoparticles onto 2D metal-organic framework nanosheets for real-time monitoring of hydrogen peroxide released from living cells

The development of metal nanoparticles (MNP) combined with a metal-organic framework (MOF) has received more and more attention due to its excellent synergistic catalytic ability, which can effectively broaden the scope of catalytic reactions and enhance the catalytic ability. In this work, we developed a novel ternary nanocomposite named Cu₂O-mediated Au nanoparticle (Au NP) grown on MIL-53(Fe) for real-time monitoring of hydrogen peroxide (H₂O₂) released from living cells. First, Cu₂O-MIL-53(Fe) was prepared by redox assembly technology, which provided the growth template, and active sites for AuCl^4-. Au@Cu₂O-MIL-53(Fe)/GCE biosensor was prepared by further loading nano-Au uniformly on the surface of Cu₂O by electrochemical deposition. Compared to individual components, the hybrid nanocomposite showed superior electrochemical properties as electrode materials due to the synergistic effect between AuNPs, Cu₂O, and MIL-53(Fe). Electrochemical measurement showed that the Au@Cu₂O-MIL-53(Fe)/GCE biosensor presented a satisfactory catalytic activity towards H₂O₂ with a low detection limit of 1.01 μM and sensitivity of 351.57 μA mM^-1 cm^-2 in the linear range of 10-1520 μM. Furthermore, this biosensor was successfully used for the real-time monitoring of dynamic H₂O₂ activated by PMA released from living cells. And the great results of confocal fluorescence microscopy of the co-culture cells with PMA and Au@Cu₂O-MIL-53(Fe) verified the reliability of the biosensor, suggesting its potential application to the monitoring of critical pathological processes at the cellular level.