Encapsulation of CuO nanoparticles within silicalite-1 as a regenerative catalyst for transfer hydrogenation of furfural

Adaptations of Rhodococcus rhodochrous Biofilms to Oxidative Stress Induced by Copper(II) Oxide Nanoparticles

Copper(II) oxide nanoparticles (CuO NPs) are used in different industries and agriculture, thus leading to their release to the environment, which raises concerns about their ecotoxicity and biosafety. The main toxicity mechanism of nanometals is oxidative stress as a result of the formation of reactive oxygen species caused by metal ions released from nanoparticles. Bacterial biofilms are more resistant to physical and chemical factors than are planktonic cells due to the extracellular polymeric matrix (EPM), which performs a protective function. Hydrocarbon-oxidizing bacteria of the genus Rhodococcus, well-known biodegraders of toxic organic pollutants and bioremediation agents, are capable of producing biofilms, which, as we proposed, are more resistant to metal nanoparticles, while the particular adaptation mechanisms have not yet been clarified. In this study, we study the adaptation mechanisms of Rhodococcus rhodochrous IEGM 1363 biofilms to CuO NPs in a wide range of concentrations (0.001-0.1 g/L), including morphological and ultrastructural cell alterations. The results obtained on the long-term dynamics (≤72 h) and localization of EPM structural components, in particular, lipids, polysaccharides, and proteins, indicated their important role in the complex adaptive response of alkanotrophic Rhodococcus to oxidative stress caused by copper nanooxide. The observed changes in the ultrastructure and element composition included binding of CuO nanoparticles by the cell wall to prevent their penetration inside cells and intracellular accumulation of potassium, magnesium, phosphorus, and sulfur in electron-dense inclusions, which may be associated with a metabolic stress reaction. Understanding the mechanisms of interaction between nanometals and Rhodococcus biofilms will contribute to the development of biocatalysts based on immobilized bacterial cells and bioremediation methods.

Preparation of Metal-Supported Nanostructured Zeolite Catalysts and their Applications in the Upgrading of Biomass-Derived Furans: Advances and Prospects

The development of platform chemicals derived from biomass, in particular, 5-hydroxymethylfurfural (5-HMF) and furfural (FUR), is of crucial importance in biorefinery. Over the past decades, metal-supported nanostructured zeolites, in particular, metal-supported hierarchically porous zeolites or metal-encapsulated zeolites, have been extensively elaborated because of their multiple functionalities and superior properties, for example, shape-selectivity, (hydro)thermal stability, tunable acidity and basicity, redox properties, improved diffusion, and intimacy of multiple active sites. In this review, the effects of such properties of metal-supported nanostructured zeolites on the enhanced catalytic performances in furanic compound upgrading are discussed. In addition, the recent rational design of metal-supported nanostructured zeolites is exemplified. Consequently, the ongoing challenges for further developing metal-supported nanostructured zeolites-based catalysts and their applications in HMF and FUR upgrading are identified.

Elucidation of the Catalytic Pathway for the Direct Conversion of Furfuryl Alcohol into γ-Valerolactone over Al2O3-SiO2 Catalysts

The one-pot conversion of furfuryl alcohol (FA) into GVL was investigated over the sol-gel-synthesized Al2O3-SiO2 (AlSi) catalysts with various Al2O3 loadings (0.2-10 wt %) and commercial zeolites including MFI-1, H-ZSM5, H-beta, and HY-15 in a batch reactor under mild reaction conditions (130 °C, 1 bar N2, and 15-120 min). The reaction pathways depend largely on the acid properties of the catalysts, especially the types of Bronsted (B) and Lewis (L) acid sites. A tandem alcoholysis/hydrogenation/cyclization sequence is dominant on the AlSi catalysts (Al ≥ 4%) and all the zeolites except MFI-1, resulting in complete conversion of FA and GVL with an yield 64-75% with IPL as the major side-product, regardless of the differences in their B/L ratios 0.06-1.35. In the absence of B acid sites (i.e., 0.2% AlSi and MFI-1 catalysts), FA could be straightforwardly converted into GVL on the weak Lewis acid sites from the isolated silanol groups using 2-propanol as a hydrogen source. The AlSi catalysts are promising tunable catalysts for FA conversion with good recyclability.

Emergence of Visible-Light Water Oxidation Upon Hexaniobate-Ligand Entrapment of Quantum-Confined Copper-Oxide Cores

The formation of small 1 to 3 nm organic-ligand free metal-oxide nanocrystals (NCs) is essential to utilization of their attractive size-dependent properties in electronic devices and catalysis. We now report that hexaniobate cluster-anions, [Nb₆ O₁₉ ]^8- , can arrest the growth of metal-oxide NCs and stabilize them as water-soluble complexes. This is exemplified by formation of hexaniobate-complexed 2.4-nm monoclinic-phase CuO NCs (1), whose ca. 350 Cu-atom cores feature quantum-confinement effects that impart an unprecedented ability to catalyze visible-light water oxidation with no added photosensitizers or applied potentials, and at rates exceeding those of hematite NCs. The findings point to polyoxoniobate-ligand entrapment as a potentially general method for harnessing the size-dependent properties of very small semiconductor NCs as the cores of versatile, entirely-inorganic complexes.

In Situ Confined Synthesis of a Copper-Encapsulated Silicalite-1 Zeolite for Highly Efficient Iodine Capture

Effective capture of radioactive iodine is highly desirable for decontamination purposes in spent fuel reprocessing. Cu-based adsorbents with a low cost and high chemical affinity for I2 molecules act as a decent candidate for iodine elimination, but the low utilization and stability remain a significant challenge. Herein, a facile in situ confined synthesis strategy is developed to design and synthesize a copper-encapsulated flaky silicalite-1 (Cu@FSL-1) zeolite with a thickness of ≤300 nm. The maximum iodine uptake capacity of Cu@FSL-1 can reach 625 mg g-1 within 45 min, which is 2 times higher than that of a commercial silver-exchanged zeolite even after nitric acid and NOX treatment. The Cu nanoparticles (NPs) confined within the zeolite exert superior iodine adsorption and immobilization properties as well as high stability and fast adsorption kinetics endowed by the all-silica zeolite matrix. This study provides new insight into the design and controlled synthesis of zeolite-confined metal adsorbents for efficient iodine capture from gaseous radioactive streams.

Continuous conversion of furfural to furfuryl alcohol by transfer hydrogenation catalyzed by copper deposited in a monolith reactor

A polymer monolith catalytic reactor, which is fabricated by anchoring –SO3H groups on the surface of the fibers and by depositing Cu species, exhibits outstanding performance and high stability in continuous transfer hydrogenation of furfural.