Immobilization of Aspergillus sp. laccase on hierarchical silica MFI zeolite with embedded macropores

Laccase from Aspergillus sp. (LC) was immobilized on functionalized silica hierarchical (microporous-macroporous) MFI zeolite (ZMFI). The obtained immobilized biocatalyst (LC#ZMFI) was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (ATR-FTIR), N2 adsorption/desorption isotherms, solid-state NMR spectroscopy and thermogravimetric analysis (TGA) confirming the chemical anchoring of the enzyme to the zeolitic support. The optimal pH, kinetic parameters (KM and Vmax), specific activity, as well as both storage and operational stability of LC#ZMFI were determined. The LC#ZMFI KM and Vmax values amount to 10.3 µM and 0.74 µmol·mg-1 min-1, respectively. The dependence of specific activity on the pH for free and immobilized LC was investigated in the pH range of 2-7, The highest specific activity was obtained at pH = 3 for both free LC and LC#ZMFI. LC#ZMFI retained up to 50 % and 30 % of its original activity after storage of 21 and 30 days, respectively. Immobilization of laccase on hierarchical silica MFI zeolite allows to carry out the reaction under acidic pH values without affecting the support structure

129Xe NMR on Porous Materials: Basic Principles and Recent Applications

A large number of functional and catalytic materials exhibit porosity, often on different length scales and with a hierarchical structure. The assessment of pore sizes, pore geometry, and pore interconnectivity is complex and usually not feasible by classical spectroscopic and diffraction techniques. One of the most powerful methods to probe these parameters is nuclear magnetic resonance (NMR) spectroscopy of xenon, which is introduced into the pore system. Adsorbed to the pore walls, it acts as probe nucleus. In this tutorial review, an introduction into the basic principles of 129Xe NMR spectroscopy and the models developed to determine pore sizes in different materials are given. The possibilities and limitations of this method for obtaining insights into hierarchical structures of functional materials are highlighted and a review of recent works is presented

Continuous Gas-Phase Synthesis of Oxymethylene Dimethyl Ethers Using Supported Ionic Liquid Phase Catalysts

Acidic Supported Ionic Liquid Phase (SILP) catalysts were investigated for the synthesis ofoxymethylene dimethyl ethers (OME). The application of OME1 and trioxane for the gas-phasesynthesis of higher OMEs and in particular the generation of OMEn with n higher than 3 wassuccessfully demonstrated. Raising the pressure led to an increase in the conversion of OME1 andto higher selectivity for higher molecular weight OMEs. Furthermore, a correlation between theionic liquid’s acidity and the catalytic activity was shown with higher acidity leading to higher conversion of trioxane and OME1. Moreover, successful long-term operation for more than 200 h time-on-stream has been demonstrated with good catalyst system stability

Biological Chitin-MOF composites with hierarchical pore systems for air-filtration applications

Metal-organic frameworks (MOFs) are promising materials for gas-separation and air-filtration applications. However, for these applications, MOF crystallites need to be incorporated in robust and manageable support materials. We used chitin-based networks from a marine sponge as a non-toxic, biodegradable, and low-weight support material for MOF deposition. The structural properties of the material favor predominant nucleation of the MOF crystallites at the inside of the hollow fibers. This composite has a hierarchical pore system with surface areas up to 800 m2g-1 and pore volumes of 3.6 cm3g-1, allowing good transport kinetics and a very high loading of the active material. Ammonia break-through experiments highlight the accessibility of the MOF crystallites and the adsorption potential of the composite indicating their high potential for filtration applications for toxic industrial gases

Tailoring Pore Structure and Properties of Functionalized Porous Polymers by Cyclotrimerization

Porous polymers were prepared by cyclotrimerization reaction in molten <i>p</i>-toluenesulfonic acid. Their properties could be tailored by functionalization of the aromatic diacetyl monomers. Thus, a range of homo- and copolymers based on hydrogen-, amine-, or nitro-functionalized 4,4′-diacetylbiphenyl derivatives and 1,4-diacetylbenzene was synthesized. The pores size could be tuned from mainly microporous to hierarchical micro- and mesoporous or even hierarchical micro- and macroporous. BET surface areas up to 720 m²/g and total pore volumes up to 1.76 cm³/g were achieved. The formation of different pore types was related to the solvent–monomer/polymer interactions, which is shown by ¹⁵N solid state MAS NMR spectroscopy and SEM. Other physical properties such as surface polarity and thermal stability were influenced by the different monomers as well

Solid‐State NMR Spectroscopic Investigation of TiO2 Grown on Silica Nanoparticles by Solution Atomic Layer Deposition

Abstract Atomic layer deposition in solution (sALD) is just emerging as a technology for the preparation of thin films. Unlike ALD from the gas phase, it allows for mild reaction conditions in a solvent phase and at room temperature, thus decreasing the energy requirements of the process and widening the range of accessible precursor molecules. In this work, the deposition of thin films of titania on silica is investigated using titanium(IV) isopropoxide (TTIP) and water as precursors, which are alternatingly brought into contact with the support in a home‐built plug flow reactor. The mechanism of covalent grafting of the precursor to the surface, subsequent hydrolysis, and reaction to a layer of titania are investigated in detail using magic angle spinning (MAS) solid‐state nuclear magnetic resonance (NMR) spectroscopy. TTIP preferentially reacts with Q2 groups of condensed silica. 2D solid‐state NMR spectra allow to clearly show the successful grafting of this compound to the support by the appearance of a characteristic signal at −107 ppm, which is tentatively attributed to silicon nuclei in a SiOTi bond, and to reveal the presence of titanol groups on the emerging TiO2 film

Structural Characterization of Phosphate Species Adsorbed on γ-Alumina by Combining DNP Surface Enhanced NMR Spectroscopy and DFT Calculations

International audienceObtaining an atomic-scale description of the chemical interactions of phosphates with an oxide support, such as γ-Al2O3, is essential to get a rational understanding of the role of phosphate additives for a great number of heterogeneous catalysts, as well as to improve the use of this element. Combining cutting-edge Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy (DNP SENS) techniques with Density Functional Theory (DFT) calculations, we provide an accurate molecular description of phosphate speciation on γ-Al2O3 surfaces for various P surface coverages after drying at 120 °C. Thanks to 31P double- and triple-quantum filtered NMR experiments as well as to 27Al–31P dipolar- and scalar-based correlation spectra, we demonstrate the presence of polyphosphates and of Al–O–P connectivities at the exposed facets of γ-Al2O3. DFT-based thermodynamics shows that phosphates (mono- or di-) are preferentially covalently bonded on the (1 1 0) γ-Al2O3 facet with high-dentation modes. These high-dentation modes are favored by entropy gain due to water desorption. We used the gauge-including projector-augmented wave (GIPAW) DFT method for 31P NMR chemical shifts calculations and propose a systematic identification of the various types of phosphates covalently or noncovalently bonded to the alumina surface. The calculations confirm the existence of polyphosphates as observed experimentally. Since the surface condensation into polyphosphates is endergonic, the presence of polyphosphates on the surface is likely to result from their direct adsorption in impregnation solution. The observed increasing concentration of polyphosphates with the coverage could be related to a less likely hydrolysis due to the reduced availability of sites to stabilize the fragmented oligomers. This understanding opens the way to a better control over the speciation of phosphate species that are known to be key in the preparation of supported catalysts over alumina

How do zeolite-templated carbons grow?

International audienceMajor insights into the formation mechanism of zeolite-templated carbons (ZTCs) were achieved via a thorough ex situ kinetic study of the hybrid (carbon/zeolite) and carbon materials. In depth characterization of the chemical, electrical, textural and morphological properties of the materials allowed us to draw a precise picture of the key steps of the ZTC formation. An in situ time resolved GC study enabled us to achieve complementary insights on the ethylene consumption and hydrogen production during ZTC synthesis. Three stages could be disclosed: nucleation, growth and condensation. During nucleation, individual polyaromatic hydrocarbons (PAHs) develop through the aromatization of ethylene. These PAHs present high spin concentration and react upon zeolite dissolution, leading to unstructured carbon particles of undefined morphology. These carbons feature persistent radicals. During growth the PAHs evolve to form more complex rylene-type molecules. Typical structural, textural and morphological features of ZTCs start to emerge during this second stage. The evolution of electrical conductivity of hybrid materials indicates partial condensation of PAHs throughout the zeolite crystals leading to their connection. The carbon materials achieved during the second stage can be described as composites of ZTCs and randomly reacted PAHs. Condensation, which is importantly induced by heat treatment, triggers full connection of the ZTC network. Textural, morphological, structural, and electrical features develop, which result directly from zeolite templating. Final ZTCs feature carbonyl functionalization, which is inherent to the zeolite dissolution step and probably results from radical quenching with water

Unravelling the molecular structure and confinement of an or-ganometallic catalyst heterogenized within amorphous porous polymers

The catalytic activity of multifunctional microporous materials is directly linked to the spatial arrangement of their struc-tural building blocks. Despite great achievements in the design and use of isolated catalytic sites within such materials, the precise determination of their atomic-level structure and their local environment still remains a fundamental chal-lenge, especially when they are hosted in non-crystalline solids. Here, we show that by combining NMR measurements with pair distribution function (PDF) analysis and computational chemistry, a very accurate picture of the organometallic Cp*Rh catalytic sites inside the cavity of porous organic polymers can be determined. Two microporous supports based on bipyridine and biphenyl motifs functionalized with NH2 or NO2 groups were considered. Making use of differential PDF, Dynamic Nuclear Polarization (DNP) enhanced solid-state NMR spectroscopy on 15N labelled–NH2 and –NO2 materi-als, and 129Xe NMR, the detailed structure of the heterogenized organometallic complex and its confinement within the amorphous porous organic polymers is revealed with a precision of 0.1 Å, fully matched by the computed models. While the same well-defined molecular structure is observed for the organometallic catalyst independently of the functionalisa-tion of the porous organic polymer, subtle changes are detected in the average ligand-pore wall distance and interactions in the two materials