MAS NMR Measurements Research Articles

Temperature‐Induced Modifications in Natural Zeolite Clinoptilolite: Effects on Acidity and Catalytic Acetalization

AbstractThis study delves into the acid modification of natural zeolite clinoptilolite, focusing on the identification of acid site types and their catalytic activity in the Brønsted acid‐catalyzed acetalization of benzaldehyde with 1,3‐butanediol. Following calcination, the samples underwent acidification via ammonium‐ion exchange, resulting in approximately 45 % of the clinoptilolite cations being exchanged with ammonium ions. The investigation evaluates the structural, morphological, and textural alterations induced by this modification using XRD, FTIR, and nitrogen adsorption‐desorption measurements. Ammonia‐temperature‐programmed desorption (NH3‐TPD) analysis confirms the presence of medium to strong acidic protons, highlighting the acidity of the modified samples. Employing 27Al and 29Si magic‐angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy elucidated changes in the state and coordination of aluminum post‐sample activation. Specifically, the 27Al MAS NMR spectra indicate a partial dealumination, evidenced by the emergence of 5 and 6‐fold coordinated aluminum. Moreover, 29Si MAS NMR measurements tracked variations in the Si/Al ratio. The study probes the nature of these sites, their influence on catalytic activity, and the synergistic interplay between Brønsted acid sites and 5‐fold coordinated aluminum. The results showcase that the prepared acidic natural clinoptilolite catalysts augment acidity and porosity, fostering promising implications for catalytic applications.

Electrochemical Sodium Storage in Hard Carbon Powder Electrodes Implemented in an Improved Cell Assembly: Insights from In-Situ and Ex-Situ Solid-State NMR.

In this work, we report on an improved cell assembly of cylindrical electrochemical cells for 23 Na in-situ solid-state NMR (ssNMR) investigations. The cell set-up is suitable for using powder electrode materials. Reproducibility of our cell assembly is analyzed by preparing two cells containing hard carbon (HC) powder as working electrode and sodium metal as reference electrode. Electrochemical storage properties of HC powder electrode derived from carbonization of sustainable cellulose are studied by ssNMR. 23 Na in-situ ssNMR monitors the sodiation/desodiation of a Na|NaPF6 |HC cell (cell 1) over a period of 22 days, showing high cell stability. After the galvanostatic process, the HC powder material is investigated by high resolution 23 Na ex-situ MAS NMR. The formation of ionic sodium species in different chemical environments is obtained. Subsequently, a second Na|NaPF6 |HC cell (cell 2) is sodiated for 11 days achieving a capacity of 220 mAh/g. 23 Na ex-situ MAS NMR measurements of the HC powder material extracted from this cell clearly indicate the presence of quasi-metallic sodium species next to ionic sodium species. This observation of quasi-metallic sodium species is discussed in terms of the achieved capacity of the cell as well as of side reactions of sodium in this electrode material.

Preparation and Characterization of Silica-Based Ionogel Electrolytes and Their Application in Solid-State Lithium Batteries.

In this study, tetraethyl orthosilicate (TEOS) and methyltriethoxysilane (MTES) were used as precursors for silica, combined with the ionic liquid [BMIM-ClO4]. Lithium perchlorate was added as the lithium-ion source, and formic acid was employed as a catalyst to synthesize silica ionogel electrolytes via the sol-gel method. FT-IR and NMR identified the self-prepared ionic liquid [BMIM-ClO4], and its electrochemical window was determined using linear sweep voltammetry (LSV). The properties of the prepared silica ionogel electrolytes were further investigated through FT-IR, DSC, and 29Si MAS NMR measurements, followed by electrochemical property measurements, including conductivity, electrochemical impedance spectroscopy (EIS), LSV, and charge-discharge tests. The experimental results showed that adding methyltriethoxysilane (MTES) enhanced the mechanical strength of the silica ionogel electrolyte, simplifying its preparation process. The prepared silica ionogel electrolyte exhibited a high ionic conductivity of 1.65 × 10-3 S/cm. In the LSV test, the silica ionogel electrolyte demonstrated high electrochemical stability, withstanding over 5 V without oxidative decomposition. Finally, during the discharge-charge test, the second-cycle capacity reached 108.7 mAh/g at a discharge-charge rate of 0.2 C and a temperature of 55 °C.

The Impact of Intergrain Phases on the Ionic Conductivity of the LAGP Solid Electrolyte Material Prepared by Spark Plasma Sintering.

Li1.5Al0.5Ge1.5(PO4)3 (LAGP) is a promising oxide solid electrolyte for all-solid-state batteries due to its excellent air stability, acceptable electrochemical stability window, and cost-effective precursor materials. However, further improvement in the ionic conductivity performance of oxide solid-state electrolytes is hindered by the presence of grain boundaries and their associated morphologies and composition. These key factors thus represent a major obstacle to the improved design of modern oxide based solid-state electrolytes. This study establishes a correlation between the influence of the grain boundary phases, their 3D morphology, and compositions formed under different sintering conditions on the overall LAGP ionic conductivity. Spark plasma sintering has been employed to sinter oxide solid electrolyte material at different temperatures with high compacity values, whereas a combined potentiostatic electrochemical impedance spectroscopy, 3D FIB-SEM tomography, XRD, and solid-state NMR/materials modeling approach provides an in-depth analysis of the influence of the morphology, structure, and composition of the grain boundary phases that impact the total ionic conductivity. This work establishes the first 3D FIB-SEM tomography analysis of the LAGP morphology and the secondary phases formed in the grain boundaries at the nanoscale level, whereas the associated 31P and 27Al MAS NMR study coupled with materials modeling reveals that the grain boundary material is composed of Li4P2O7 and disordered Li9Al3(P2O7)3(PO4)2 phases. Quantitative 31P MAS NMR measurements demonstrate that optimal ionic conductivity for the LAGP system is achieved for the 680 °C SPS preparation when the disordered Li9Al3(P2O7)3(PO4)2 phase dominates the grain boundary composition with reduced contributions from the highly ordered Li4P2O7 phases, whereas the 27Al MAS NMR data reveal that minimal structural change is experienced by each phase throughout this suite of sintering temperatures.

Effect of particle microstructure and the role of proton on the lithium insertion properties of HTiNbO5 electrode material

Layered oxides showing edge-sharing octahedra are promising negative electrode materials for high-power Li-ion batteries. In this sense, we propose the synthesis of the lamellar HTiNbO5 by solid-state (SS), sol-gel (SG) and exfoliation-restacking (NS) syntheses investigating in the same way the charge storage mechanism of this oxide and the influence of the microstructure on material and electrochemical properties. An arsenal of characterization techniques has been used to investigate these three types of particles using X-Ray Diffraction (XRD), electron microscopy, but also by associating mass spectroscopy to thermogravimetric analyses (TGA). Their ability to intercalate lithium has been compared, showing interesting and very similar specific capacities for solid-state and sol-gel synthesis (> 100 mAh.g − 1 at 0.5 A.g − 1). In addition, it was shown that the synthesis giving rise to nanosheet (NS) led to lower performance due to the presence of organic molecules in the interlayer spacing of the 2D lamellar structure. Lastly, in situ XRD evidenced a solid-solution reaction for HTiNbO5, with an initial and irreversible phase change leading to the formation of Li0.4HTiNbO5. Moreover, ex situ1H MAS NMR measurements highlight the essential role of the proton in the charge storage mechanism of HTiNbO5. Thus, this paper demonstrates the interest of HTiNbO5 as a fast negative electrode material for high-power Li-ion batteries as well as the predominant role that the proton can play in the diffusion of lithium ions inside a confined interlayer space.

Active Buffer Matrix in Nanoparticle‐Based Silicon‐Rich Silicon Nitride Anodes Enables High Stability and Fast Charging of Lithium‐Ion Batteries

AbstractA very promising way to improve the stability of silicon in lithium‐ion battery (LIB) anodes is the use of nanostructured silicon‐rich silicon nitride (SiNx), known as a conversion‐type anode material. To investigate the conversion mechanism in this material in detail, SiN0.5 nanoparticles are synthesized and examined as LIB anodes using a combination of ex situ X‐ray photoelectron spectroscopy and solid‐state 7Li MAS NMR measurements. During the initial cycle, the conversion of SiN0.5 nanoparticles results in the formation of lithium silicides and a buffer matrix consisting of different lithium nitridosilicates and lithium nitride. These phases can be reversibly lithiated and contribute to the total reversible capacity of the silicon nitride active material. The structure of the material after conversion is best described by an amorphous solid solution. Further, it is shown that silicon‐rich silicon nitrides possess improved rate capability because of the higher ionic conductivity of the buffer matrix compared to pure silicon, and very fine dispersion of silicon clusters throughout the buffer matrix. Thus, unlike most conversion materials, the silicon‐rich silicon nitride exhibits an additional intrinsic active functionality of the buffer matrix that goes far beyond the mere reduction of electrolyte contact area and volume expansion.

Spectroscopic Characterizations of Porous Mixed Metal Oxides Derived from Metal–Organic Framework MIL-53(Ga, Al) for Propane Dehydrogenation

The structure and properties of porous mixed metal oxide catalysts (GaxAl2–xO3 and Pt/GaxAl2–xO3) derived from calcination treatment of bimetallic MIL-53(Ga, Al) precursors were comprehensively characterized using XRD, N2 adsorption–desorption isotherms, TEM, and solid-state NMR. Both Ga and Pt species are highly dispersed in Pt/Ga0.1Al1.9O3 and Pt/Ga0.5Al1.5O3 catalysts with low Ga content, whereas Ga2O3 particles are present in Ga1.0Al1.0O3 and Ga1.5Al0.5O3 catalysts with high Ga content. Well-mixed Al and Ga species in the calcined Ga0.1Al1.9O3 and Ga0.5Al1.5O3 samples are identified from 1H–71Ga S-RESPDOR and 1H–27Al TRAPDOR NMR experiments. The coordination states and relative amounts of Al and Ga species in the MIL-53(Ga, Al) derivatives are determined by 27Al and 71Ga MAS NMR measurements. It is found that Pt species are readily anchored with pentacoordinate Al, favoring the formation of tetrahedral GaIV species, and the synergy between highly dispersed Pt and tetrahedral GaIV active species in Pt/Ga0.1Al1.9O3 and Pt/Ga0.5Al1.5O3 catalysts renders their superior catalytic performance with high conversion and good recyclability toward the propane dehydrogenation reaction.

Enhanced catalytic activity of phosphorus-modified SSZ-13 zeolite in the ethylene-to-propylene reaction by controlling acidity and intracrystalline diffusivity

A highly selective means of producing propylene via the ethylene-to-propylene (ETP) reaction is required to manage the supply-demand balance of light olefins. To improve the catalytic activity of the ETP reaction, a phosphorus-modified SSZ-13 zeolite (P-SSZ-13) was prepared by introducing phosphorus to the SSZ-13 zeolite via a simple impregnation method. The P-SSZ-13 catalyst exhibited increased propylene selectivity and yield compared to the pristine catalyst. According to solid-state NMR spectroscopy and STEM-EDS observation, the phosphorus species were mainly located on the outer part of the crystal as a form of polyphosphate. To reveal the effect of the phosphorus loading on the enhancement of ETP reactivity, a series of surface-modified SSZ-13 catalysts were prepared and investigated. It was found that the polyphosphate species in the P-SSZ-13 catalyst not only weakened the acidity of the zeolite by bonding with the framework aluminum species but also reduced the diffusion out of the relatively large-sized hydrocarbon species by partially blocking the pore mouths. The change in the diffusivity of the hydrocarbons over the SSZ-13 catalysts also affected the ETP reactivity. The relationship between the amount of phosphorus and the ETP reactivity of the P-SSZ-13 catalysts could also be clearly demonstrated in terms of the change in both acidity and intracrystalline diffusivity. Moreover, 13C MAS NMR measurement with isotopic switch experiment confirmed the alkyl naphthalene-based hydrocarbon pool mechanism over the P-SSZ-13 for the ETP reaction.

Influence of different additives on the rheology and microstructural development of MgO–SiO2 mixes

Development of alternative binder systems to be used in additive and automated manufacturing technologies is crucial for increasing the sustainability and productivity of the construction process . Advancements in this area facilitate shorter construction durations, enhanced resource efficiency and reduced construction waste; enabling complex, high-quality and functional designs that would not be possible with traditional methods. The novelty of this work involves the demonstration of the properties of a promising alternative binder, reactive MgO–SiO 2 (RMS) binder, that can highlight its feasibility to be used in large-scale applications and the identification of the effects of different phosphate additives during this process. RMS mixes containing three different phosphate additives (sodium hexametaphosphate, trimetaphosphate and orthophosphate (OP)) were analyzed for their pH, reaction kinetics, workability, mechanical performance and rheological properties to reveal the influence of these additives on the properties of RMS mixes. These findings were supported by FTIR, 29 Si MAS NMR and XRD measurements. The inclusion of OP in RMS binder systems increased the pH of solution, thereby improving the dissolution of silica and its reaction with Mg-phases and resulting in enhanced magnesium-silicate-hydrate (M-S-H) formation. These improvements in hydration mechanisms translated into better mechanical performance and rheological properties, which can correlate to desirable properties for 3D printing applications.

Effect of water on the organofunctionalization of SAPO-5 to form an efficient oleic acid esterification catalyst

In this study, SAPO-5 having a high silicon content was synthesized and further modified by functionalization with sulfonic acid groups using 3-mercaptopropyltrimethoxysilane (MTPS) as a precursor. In particular, we focused on the effect of water on the organofunctionalization process using SAPO-5 either dehydrated under vacuum (S5–SO3H/Vac) or without any thermal pretreatment (S5–SO3H). Using X-ray diffractometry, inductively coupled plasma–optical emission spectroscopy, elemental analysis of carbon, nitrogen, hydrogen and sulfur, thermogravimetric analysis, Fourier transform infrared spectroscopy, and 29Si, 27Al, 31P, and 13C NMR spectroscopy, it was possible to identify important structural differences in the obtained hybrid materials. The results showed that S5–SO3H has a Si:S molar ratio five times larger than that of S5–SO3H/Vac. The presence of Tm sites (organic-modified silica sites, Si–C bonds), as revealed by 29Si MAS-NMR measurements, suggests that the organic pending groups are bonded covalently to the Si–OH groups in the SAPO-5 network during silanization. Further differences between the material obtained under dry conditions and that prepared from hydrated SAPO-5 were revealed by measuring the acidity via potentiometric titration: S5–SO3H was 40% more acidic than S5–SO3H/Vac. Both materials were also tested for their catalytic oleic acid esterification ability. Although the turnover frequency of S5–SO3H/Vac was four times higher than that of S5–SO3H, its conversion after five sequential cycles dropped from 97.4 to 28.3%. In contrast, S5–SO3H yielded a conversion of 84.4%, starting from 99.4%, after the same number of cycles; thus, microporous SAPO-5 is a promising catalyst support for reactions involving bulky molecules such as oleic acid.

A study of zircon crystallization, structure, and chemical resistance relationships in ZrO2 containing ceramic glazes

This study aims to investigate zircon (ZrSiO4) formation during thermal treatment and its influence on the structure and properties of the ceramic glazes. Four raw ceramic glazes with the addition of 5, 9, 13, and 17wt% of ZrO2 (<5μm) at the expense of SiO2 were prepared by the ceramic traditional route. To obtain homogeneous melting and consequently a high-quality surface, 5wt% of colemanite (2CaO·3B2O3·5H2O) was added to the ceramic glazes formulation. XRD, NMR, Raman spectroscopy and FTIR measurements revealed the formation of ZrSiO4. An increase of ZrSiO4 from 35 to 86wt% with an increase of ZrO2 content in the composition of ceramic glazes was observed. 29Si solid-state MAS NMR measurements also showed that with successive increases of ZrO2 concentration the relative intensity of zircon resonance increases. The evaluation of the chemical resistance revealed the beneficial effect of ZrSiO4 on this property.

Bulk O2 formation and Mg displacement explain O-redox in Na0.67Mn0.72Mg0.28O2

Summary O-redox in compounds with Li on the transition-metal layers (TML) has recently been attributed to the formation of molecular O2 on charge, trapped in the lattice. Here, we show that a similar process occurs for P2-Na0.67[Mn0.72Mg0.28]O2, which contains Mg2+ on the TML. The molecular O2 is identified by high-resolution RIXS and quantified by magnetometry, showing that it equates to the charge passed. This O2 is trapped in voids that are formed by Mg2+ out-of-plane displacement and Mn4+ in-plane disordering and is then reduced on discharge associated with a large voltage hysteresis. In contrast to compounds containing Li+ in the TML, in which the honeycomb ordering and the high-voltage plateau are irreversibly lost after the first cycle, in P2-Na0.67[Mn0.72Mg0.28]O2, the plateau reappears partially on the second charge due to the partial reversibility of Mn in-plane and Mg out-of-plane migration and the local reformation of the honeycomb ordering.

Silanization of siliceous materials, part 3: Modification of surface energy and acid-base properties of silica nanoparticles determined by inverse gas chromatography (IGC)

Surface modified silica nanoparticles are well-established composite materials. To improve their embedding and application behavior, surface energy analysis has been performed before and after silanization with mercaptopropyltrimethoxysilane (MPTMS) using inverse gas chromatography technique (IGC). Experiments with two silica materials have been conducted at infinite dilution to determine the dispersive component of the surface energy (γsd) as well as the specific component (γssp) using the van Oss theory and a least-squares procedure evaluating the IGC data of 8 polar probe molecules collectively (instead of evaluating only the data of a pair of monopolar probes as is often the case in IGC studies). After surface silylation, the total surface energy (γst) of pyrogenic silica nanoparticles decreased from 225 mJ/m2 to 149 mJ/m2 referring to both a reduced wettability and an increased hydrophobicity of the MPTMS-modified sample. Moreover, the acidity/basicity parameters according to the van Oss and the Gutmann approach indicated that the acidity of the silica surface decreases by MPTMS grafting. In addition, IGC at finite concentration (using isopropanol as probe molecule) was applied to obtain the energetic heterogeneity of the silica surface. The results showed a bimodal energy distribution with maxima at about 18 and 25 kJ/mol and a reduction of the higher energetic sites from 65% to only 35% after MPTMS treatment. Overall, it can be seen that the dominance of specific interactions on silica surfaces is maintained even after extensive silanization. These findings are in agreement with the results of 29Si CP MAS NMR measurements which confirm the assignment of higher energetic sites to silanol groups. For the interpretation of the IGC results, quantum chemical calculations proved the preferred interaction of isopropanol onto silica surfaces via hydrogen bridging.

Hydration Characteristics of Tricalcium Aluminate in the Presence of Nano-Silica.

Tricalcium aluminate (C3A) is the most reactive component of the Portland cement and its hydration has an important impact on the workability and early strength of concrete. Recently, nanomaterials such as nano-silica (nano-SiO2) have attracted much attention in cement-based materials because of its pozzolanic reactivity and the pore-filling effect. However, its influence on the hydration of C3A needs to be well understood. In this study, the hydration kinetics of C3A mixed with different percentages of nano-SiO2 were studied and compared with pure C3A. The hydration products were examined by different characterization techniques including XRD, XPS, and NMR spectroscopy and isothermal calorimetry analyses. The XRD results showed that the addition of nano-SiO2 promoted the conversion of the intermediate product C4AH13. The isothermal calorimetry results showed that the addition of nano-SiO2 significantly reduced the hydration exotherm rate of C3A from 0.34 to less than 0.1 mW/g. With the presence of nano-SiO2, the peaks for Q1 were observed in 29Si MAS-NMR measurements, and the content of Q1 increased from 6.74% to 30.6% when the nano-SiO2 content increased from 2 wt.% to 8 wt.%, whereas the proportion of Q4 gradually decreased from 89.1% to 63.6%. These results indicated a pozzolanic reaction provoked by the nano-SiO2 combined with aluminate structures generating C-A-S-H gel.

Fast Lithium Ionic Conductors Li14SiP6, Li14GeP6, and Li14SnP6 – Structure-Property-Relationships in the Newly Discovered Family of Lithium Phosphidotetrelates

A broad repertoire of potential solid-state electrolytes (SSEs) is a prerequisite for the development and optimization of high-energy-density all-solid-state batteries (ASSBs). In this context, the key challenge in solid state chemistry and material science is to get access to new materials with improved properties which allow for detailed investigation of structure-property relationships.[1]Recently, a new class of promising lithium ion conductors has been studied intensively. The so-called lithium phosphidotetrelates consisting of lithium phosphidosilicates, phosphidogermanates, and phosphidostannates as well as the closely related lithium phosphidoaluminates are suitable candidates for the systematic investigation of structure-property-relationships of next generation lithium ion conductors.[1-5] As the name implies, the materials are structurally related to (oxo-)silicates, thiosilicates and thiophosphates. In contrast to the latter, which are well-known for some of the most prominent sulfide-based lithium super ionic conductors, lithium phosphidotetrelates are basically built up by tetrahedrally coordinated [SiP4]8−, [GeP4]8−, and [SnP4]8− units. The substitution of sulfur by phosphorus allows for much higher charge carrier concentration within the structure and thus higher ionic conductivities (Figure 1: a) Structure of Li14SiP6. b) Arrhenius and Nyquist plot (inset) of Li14SiP6.).[4] Hence, lithium phosphidotetrelates and phosphidoaluminates offer a large structural variety combined with low activation energies and fast lithium ion conductivity up to 3 mS cm−1 at room temperature.[5]Here, the preparation and characterization of new lithium-rich phosphidotetrelates is reported. Characterization of the materials applying X-ray diffraction (powder and single crystal) and solid-state MAS NMR measurements as well as elastic coherent neutron scattering experiments enabled the thorough investigation of the structural and thermal behavior of the compounds. Activation energies, ionic and electronic conductivities have been determined using solid-state 7Li NMR measurements and electrochemical impedance spectroscopy. Furthermore, diffusion pathways were analyzed by temperature-dependent powder neutron diffraction measurements in combination with MEM and DFT calculations to extend the knowledge about the material properties. Finally, the structural differences and the consequential material properties are analyzed with respect to the resulting structure-property-relationship which is crucial for further development of high-performance lithium ion conductors.

WITHDRAWN: New frontiers in sustainable binders: Development of 3D printable MgO-SiO2 mixes

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal .

Improved Understanding of Atomic Ordering in Y4SixAl2–xO9–xNx Materials Using a Combined Solid-State NMR and Computational Approach

Ceramics based around silicon aluminum oxynitrides are of both fundamental structural chemistry and technological interest. Certain oxynitride crystal structures allow very significant compositional variation through extensive Si/N exchange for Al/O, which implies a degree of atomic ordering. In this study, solid-state 29Si MAS NMR and variable field 1D and 2D 27Al MAS NMR measurements are combined with density functional theory calculations of both the structural and NMR interaction parameters for various points across the Y4Si2O7N2-Y4Al2O9 compositional range. This series provides numerous possibilities for significant variation of atomic ordering in the local ditetrahedral (Si,Al)2O7-xNx units. The two slightly structurally inequivalent aluminum sites in Y4Al2O9 are unambiguously assigned to the observed resonances. Computational findings on Y4Si2O7N2 demonstrate that the single observed 29Si NMR resonance covers a range of local inequivalent silicon environments. For the first time, the MAS NMR and neutron diffraction data from the Y4SiAlO8N structure have been directly reconciled, thus establishing aspects of atomic order and disorder that characterize this system. This comparison suggests that, although the diffraction data indicates long-range structural order supporting a highly crystalline character, the short-range information afforded by the solid-state NMR measurements indicates significant atomic disorder throughout the (Si,Al)2O7-xNx units.

Highly efficient synthesis of high-silica SSZ-13 zeolite by interzeolite transformation of L zeolite at higher temperature

High-silica SSZ-13 zeolites were synthesized rapidly and efficiently by interzeolite transformation of low-silica L zeolite at higher temperature in the presence of organic SDAs, additional SiO2 and SSZ-13 seeds. The obtained samples were characterized by XRD, SEM, N2-adsorption, FTIR, TG-DTG, 27Al MAS NMR and NH3-TPD measurements. The effects of temperature and SDA content on the crystallization process were investigated in detail. It was found that the crystallization time can be notably reduced at elevated temperature, and the SDA content in the starting gel can modulate flexibly the crystallization rate, solid yield, crystal size and acidity of samples. Additionally, the role of seed crystals during the interzeolite transformation process was also discussed. As a result, the pure SSZ-13 zeolites with high crystallinity were prepared in only 6h at 180 ​°C at SDA/SiO2 ratio of 0.2. Intriguingly, the solid yield of the samples under SDA/SiO2 ratio of 0.1–0.15 can reach ~96%. In addition, the samples exhibited good catalytic performance in methanol-to-olefins reaction.

Instant exactness synthesis and n-heptane hydroisomerization of high performance Ni/SAPO-11 catalyst

A new method called Instant Exactness Synthesis (IES), which was applied to prepare SAPO-11 molecular sieve, was introduced innovatively. The metal–acid bifunctional Ni/SAPO-11-IES catalyst with a Ni content of 4% was prepared by the impregnation method. Ni/SAPO-11-H catalyst was prepared as a comparative sample through the traditional hydrothermal method. In addition, the growth mechanism was used to explain the excellent performance of catalyst prepared by IES method in detail. The structure of Ni/SAPO-11-IES was confirmed via XRD and TEM characterization. The pore structure of the molecular sieve was determined by nitrogen adsorption and desorption. 29Si MAS NMR measurement was used to illustrate multiple silicon environment which supported the excellent acidity in NH3-TPD measurement. Furthermore, the favourable dispersibility of Ni species was proved by the mapping of the elements and EDS. Benefiting from the superior performance of materials, Ni/SAPO-11-IES catalyst exhibited a higher catalytic performance for n-heptane hydroisomerization with n-heptane conversion of 82% and isoheptane selectivity of 86%, respectively, compared with other catalysts in the same system. The study also provides new ideas for the preparation of molecular sieve materials.

Peptides from diatoms and grasses harness phosphate ion binding to silica to help regulate biomaterial structure

Many life forms generate intricate submicron biosilica structures with various important biological functions. The formation of such structures, from the silicic acid in the waters and in the soil, is thought to be regulated by unique proteins with high repeats of specific amino acids and unusual sidechain modifications.Some silicifying proteins are characterized by high prevalence of basic amino acids in their primary structures. Lysine-rich domains are found, for instance, in diatom silaffin proteins and in the sorghum grass siliplant1 protein. These domains exhibit catalytic activity in silica chain condensation, owing to molecular interactions of the lysine amine groups with the forming mineral. The use of amine chemistry by two very remote organisms has motivated us to seek other molecular biosilicification processes that may be common to the two life forms.In diatom silaffins, domains rich in phosphoserine residues are thought to assist the assembly of silaffin molecules into an organic supra-structure which serves as a template for the silica to precipitate on. This mold, held by salt bridges between serine phosphates and lysine amines, dictates the shape of the silica particles formed. Yet, silica synthesized with the dephosphorylated silaffin in phosphate buffer showed similar morphology to the one prepared with the native protein, suggesting that a defined spatial arrangement of serine phosphates is not required to generate silica with the desired shape. Concurrently, free phosphates enhanced the activity of siliplant1 in silica formation.It is therefore beneficial to characterize the involvement of these anions as co-factors in regulated silicification by functional peptides from the two proteins and to understand whether they play similar molecular role in the mechanism of mineralization.Here we analyze the molecular interactions of free phosphate ions with silica and the silaffin peptide PL12 and separately with silica and siliplant1 peptide SLP1 in the two biomimetic silica products generated by the two peptides. MAS NMR measurements show that the phosphate ions interact with the peptides and at the same time may be forming bonds with the silica mineral. This bridging capability may add another avenue by which the structure of the silica material is influenced. A model for the molecular/ionic interactions at the bio-inorganic interface is described, which may have bearings for the role of phosphorylated residues beyond the function as intermolecular cross linkers or free phosphate ions as co-factors in regulation of silicification. Statement of SignificanceThe manuscript addresses the question how proteins in diatoms and plants regulate the biosilica materials that are produced for various purposes in organisms. It uses preparation of silica in vitro with functional peptide derivatives from a sorghum grass protein and from a diatom silaffin protein separately to show that phosphate ions are important for the control that is achieved by these proteins on the final shape of the silica material produced. It portrays via magnetic resonance spectroscopic measurements, in atomic detail, the interface between atoms in the peptide, atoms on the surface of the silica formed and the phosphate ions that form chemical bonds with atoms on the silica as part of the mechanism of action of these peptides.