Number Of Si Research Articles

Temperature-dependent water corrosion mechanism of silicon carbide: Atomic insights from reactive molecular dynamics simulation

Silicon carbide (SiC) is an ideal material for both aeronautics and space industries, but SiC is highly susceptible to water corrosion at high temperature. A clear understanding of water corrosion mechanism of SiC is still lacking because the complex interaction dynamics are extremely difficult to be investigated experimentally. In this study, the temperature-dependent of water corrosion mechanism of SiC was investigated by reactive molecular dynamics simulation, and three different corrosion regimes were observed with the increase of the ambient temperature. In regime I (below 1000 K), only Si–H and Si–OH terminations were formed on SiC surface and almost no corrosion occurred; in regime II (1000–1500 K), the same number of carbon and silicon atoms were corroded in the form of gaseous molecules, and the relation between the number of atoms lost and temperature was in good agreement with the Arrhenius expectation; lastly, in regime III (above 1500 K), the number of Si–O–Si groups formed exceeded the volatilized number, leading to the obvious retention of the Si–O–Si network structures. These results can guide the design and preparation of SiC materials for aerospace applications by providing an atomic insight into the mechanisms of water corrosion on SiC.

FORMATION OF CRYSTALLINE SiC IN NEAR-SURFACE SILICON LAYERS BY METHOD OF COORDINATED SUBSTITUTION OF ATOMS

In this work, monocrystalline films of silicon carbide were synthesized on the surface of a Si(100) silicon wafer using the method of coordinated substitution of atoms. The films were synthesized at temperatures of 1200 °C and 1300 °C for 20 minutes in a CO gas flow at a pressure of 0.8 Pa. The effect of 1200–1300 °C temperatures on the formation of single- and polycrystalline layers, as well as nanostructured SiC phases in the near-surface region of silicon by the method of atom substitution, is analyzed. The formation of a high-quality crystalline silicon carbide film and the influence of synthesis conditions on the total volume of SiC structural phases, microstructure and nanostructure of the surface are shown. It was found that an increase in temperature from 1200 °C to 1300 °C led to a more intensive formation of silicon carbide and an increase in the number of Si–C bonds by 1.9 times due to an increase in the thickness of the synthesized silicon carbide layer. There is an increase in the proportion of the crystalline phase due to a more intense transformation of the nuclei of nanocrystals into micro- and nanocrystals. Intense processes of penetration of carbon atoms deep into silicon at a temperature of 1300 °C with amorphization of its structure and the formation of Si-C, which can transform into crystalline phases at temperatures above 1300 °C, are assumed. The proportion of the SiC crystalline phase increases to 50.2% of the film volume due to the intensive transformation of nanocrystal nuclei into micro- and nanocrystals. It has been experimentally shown that the formation of various SiC structures on Si (100) occurs in full accordance with the main principles of the method of coordinated substitution of atoms.

Preparation and Properties of a Lightweight, High-Strength, and Heat-Resistant Rigid Cross-Linked PVC Foam.

A rigid poly(vinyl chloride) foam with a cross-linked network structure was prepared by adding 3-glycidoxypropyltriethoxysilane (KH-561) into the universal formulation. The resulting foam had excellent heat resistance because of the increasing degree of cross-linking and number of Si-O bonds with a high heat resistance. The as-prepared foam was verified using Fourier-transform infrared spectroscopy (FTIR), energy-dispersive spectrometry (EDS) and foam residue (gel) analysis, which demonstrated that KH-561 was successfully grafted and cross-linked on the PVC chains. Finally, the effects of different KH-561 and NaHSO3 additions on the mechanical properties and heat resistance of the foams were studied. The results showed that the mechanical properties of the rigid cross-linked PVC foam were raised after adding a certain amount of KH-561 and NaHSO3. The residue (gel), decomposition temperature, and chemical stability of the foam significantly improved compared to the universal rigid cross-linked PVC foam (Tg = 72.2 °C). The Tg of the foam could reach 78.1 °C without any mechanical degradation. The results have important engineering application value regarding the preparation of lightweight, high-strength, heat-resistant, and rigid cross-linked PVC foam materials.

Ring compaction as a mechanism of densification in amorphous silica

The structure of permanently densified silica glass is investigated by neutron and x-ray diffraction, and by the production of atomistic models that reproduce the diffraction results. The focus is on the nature of the ordering on an intermediate length scale that originates from the formation of $n$-rings, where $n$ is the number of Si or O atoms within a ring. The densification process has a large effect on this ordering, as identified by pronounced changes to the first sharp diffraction peak (FSDP) in the measured structure factors. A clear and systematic dependence of the distribution of ring sizes on the position and shape of the FSDP could not be found, i.e., the ring statistics are not directly encoded into the form of this peak. Instead, a significant contribution to the glass densification originates from compaction of the $n$-rings, a metric that is quantified by the radius of gyration and lifetime of the rings. We thereby uncover and quantify a key densification mechanism in amorphous materials.

Synthesis of highly active solid base catalysts of SrO-ZrO2 and SrO-SiO2 by solid–liquid interface reactions of hydrated strontium hydroxide with metal alkoxides

Highly dispersed SrO in amorphous ZrO2 or SiO2, SrO–ZrO2, and SrO–SiO2 mixed oxides were synthesized by applying the solid–liquid interface reaction of Sr(OH)2•8 H2O in the solid phase with an equal number of moles of Zr(OC3H7)4 or with twice the number of Si(OC2H5)4 moles dissolved in 2-propanol. After heat treating at 723 K, the SrO–ZrO2 catalyst exhibited a higher activity than the conventional solid base MgO catalyst for the base-catalyzed retroaldol reaction of diacetone alcohol. The catalytic activity of SrO–ZrO2 was higher by a factor of 1.5 than that of MgO prepared by the thermal decomposition of hydrated magnesium oxalate (MgC2O4•2H2O). By contrast, the highest activity of SrO–SiO2 obtained by thermal activation at 673 K was much lower than that of MgO. The active SrO–ZrO2 catalyst was composed of catalytically inactive species of SrZrO3, and small amounts of Sr(OH)2 and SrCO3. The expected active species of SrO was not detected in powder X-ray diffraction analysis in any sample. The formation of SrO in small crystal size dispersed in amorphous ZrO2 was strongly expected. Similar results were obtained in the SrO–SiO2 sample. An active site formed on SrO–ZrO2 surface is proposed.

Polymeric Structure Evolution Behavior Analysis of Aluminosilicate-Based Smelting Slag

The physical and chemical properties of the CaO–SiO2–Al2O3–MgO slag system depend on structure evolution caused by the synergistic mechanism among the components at high temperature, especially the structural complexity of the anion group. In this study, Si–O, Al–O, and Al–Si–O anion groups were found in the high-temperature slag systems at 1773 K. The [Si2O5]2− (Q3) structural unit of the silicate polymer changed to [Si2O6]4− (Q2), [Si2O7]6− (Q1), and [SiO4]4− (Q0) as the binary basicity (R2) and ω(MgO)/ω(Al2O3) increased, while there was a trend toward a simplified structure. That is, the stability of each structural unit weakened, and the relative content of non-bridging oxygen increased. As a result, the degree of polymerization of slag decreased, and the experimental results of the relative content of non-bridge oxygen can be fitted well with the calculations from the reference documents. At the same time, the number of Si–O–Al structural units gradually decreased. The 27Al-MAS-NMR spectroscopy results showed that the structure of aluminate changed from [AlO4]5− tetrahedral structure to [AlO5]7− pentahedral and [AlO6]9− octahedral structure, and the degree of polymerization of the slag decreased. Comprehensive analysis showed that basicity controlled within 1.2 with the ω(MgO)/ω(Al2O3) ratio; less than 0.55 allows for suitable fluidity and energy-saving ability, which is beneficial for the stable and smooth production of the blast furnace.

DEVELOPMENT OF THE OPTIMAL DESIGN OF A CYCLONE APPARATUS WITH A FLUIDIZED BED FOR THE PROCESS OF METALS PNEUMATIC SEPARATION IN THE COMPOSITION OF INDUSTRIAL WASTE

Recycling of techno genic waste accumulated in recent years in Uzbekistan is currently a pressing problem. In this regard, this paper examines the issue of studying the process of enrichment of man-made waste in a cyclone with a fluidized bed. To conduct the experiment on experimental advanced devices with extended zones five types of samples of techno genic waste with the limits of 0.072÷0.078mm, 0.064÷0.070mm, 0.057÷0.063mm, 0.046÷0.055mm and 0.041÷0.044mm have been prepared. Nomograms have been obtained using mathematical models to determine particle size limits, which ensure good separation. Experiments have been carried out on the separation of techno genic waste in three structures of a cyclone with a fluidized bed: cylindrical, cylindrical with one extended zone and cylindrical with two extended zones. The best results are obtained in a fluidized bed machine with one extended zone. The following results were obtained for a sample with a 0.041÷0.044 mm limit size: the number of Mo increased 40 times, Ag increased 20 times, Mn increased 2.5 times, Cu increased 1 time, Ti increased 6.6 times, Ni decreased 125 times and the number of Si in the selected sample decreased from 20% to 12%.

Unveiling the origin of the anti-fogging performance of plasma-coated glass: Role of the structure and the chemistry of siloxane precursors

The application of (super)hydrophilic coatings in sectors of activity concerned by fogging, such as the food industry, the architectural sector, and medicine has attracted enormous attention over the past few years. However, despite this interest, most of the coating deposition techniques used thus far are not suitable for large-scale production because of their multistep nature. In this regard, the use of atmospheric pressure dielectric barrier discharges (AP-DBD) operated under a controlled N2/N2O atmosphere offers a promising alternative to conventional deposition techniques for the fabrication of anti-fogging coatings. Using this one-step coating approach, four siloxane precursors with different structures and different number of Si―H and Si−CH3 groups; namely, 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane (OMCTS), 1,1,3,3-tetramethyldisiloxane (TMDSO), and hexamethyldisiloxane (HMDSO) were deposited on glass samples. Because of their extreme wetting behavior (WCA < 5°), TMCTS-coated glasses featured an excellent anti-fogging performance, in contrast to OMCTS-, TMDSO-, and HMDSO-coated glasses which were not fogging-resistant (WCA ≈ 80°)). Coupled with hydrophilic functionalities, such as CO, O CO, and SiOH groups, the relatively high surface roughness of TMCTS-coated glass, compared with that of OMCTS-, TMDSO-, or HMDSO-coated glass, accounted for its superior visual characteristics when exposed to water vapor at 80 °C. These results allow us to confidently conclude that the cyclic structure of TMCTS in conjunction with the high reactivity of the Si-H bonds is responsible for the observed anti-fogging effect.

Effect of CeO2 Doping on the Structure and Properties of Titanium Barium Silicate Glass

Glasses with the composition 50SiO2 · 20TiO2 · 15BaO · 7.5SrO · 7.5CaO doped with the varied content of CeO2 were prepared by conventional melt quenching technique. The effect of CeO2 on the structure of glasses was investigated by X-ray photoelectron spectroscopy and Raman spectroscopy. The density, thermal stability, dielectric properties and acid resistance of glasses were studied by Archimedes method, differential thermal scanning analysis and X-ray diffraction, dielectric measuring as well as the powder method. The results showed that the coordination of Ti, which existed in glasses as [TiO4], did not change. An increase in the content of non-bridging oxygen atoms and a corresponding decrease in the content of bridging oxygens correlated. The depolymerization of the glass network was attributed to an increase in the number of Si–O–Ti bonds and the change of the Qn distribution. With an increase in the CeO2 content, the thermal stability and acid resistance of glass first increased and then decreased, and the dielectric constant and dielectric loss of glass decreased first and then increased.

Preparation and mechanism of graphene oxide/isobutyltriethoxysilane composite emulsion and its effects on waterproof performance of concrete

Abstract In the present paper, graphene oxide (GO) was used to modify isobutyltriethoxysilane. GO/isobutyltriethoxysilane composite emulsion was then prepared by the sol–gel method. The properties of the obtained composite emulsion were characterized by Fourier Transform Infrared (FT-IR), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS). The waterproof performance of GO/isobutyltriethoxysilane composite emulsion was studied by capillary water absorption and water contact angle experiments. The FT-IR results showed that the number of Si–O bonds in the composite emulsion were superior to that in silane emulsion while carboxyl groups were found to be less. This indicated that GO was successfully grafted to the isobutyltriethoxysilane monomer. The XPS data showed that amounts of C–OH in the composite emulsion were lower than those in silane emulsion, suggesting that part of C–OH in the composite emulsion participated in formation of Si–O–C covalent bond between GO and silane. SEM and EDS revealed that the composite emulsion and silane emulsion could form a dense hydrophobic layer on the concrete surface, thereby achieving waterproof effect. Water contact angle and capillary water absorption tests of concrete indicated composite emulsion with significantly improved waterproof performances when compared to silane emulsion.

MAS NMR investigations on a metakaolinite-rich brick after zeolitization by alkaline treatments

Abstract A metakaolinite-containing brick made by craftsmen in Central African Republic was treated with sodium hydroxide at 90 °C. After metakaolinite dissolution, gel state Na - aluminosilicates were initially formed and impregnated the surfaces of no-attacked brick grains (mainly sand). This gel changed progressively with time into crystal seeds at remaining brick surfaces. The generation of ‘low silica’ zeolites (NaA and NaP) with molar Si/Al ratios close to 1 was evidenced by the ESEM/EDS technique and their pore size distribution by using N2 adsorption-desorption isotherm at 77 K. 27Al and 29Si MAS NMR spectra of alkali-brick samples were recorded for studying their evolution with NaOH-reagent level and for characterizing newly-generated zeolitic materials in which Si and Al atoms are identified in the classification of alumino-silicates by the coordination number of the central silicon atom and the number of Si and Al second neighbors used. 27Al MQ (multiple quantum) MAS NMR was employed to study the aluminum coordination in synthesized zeolites. 23Na and 1H MAS NMR measurements were performed on alkali brick for evidencing the abundance of hydrated Na+ ions associated with negatively charged brick sites. After checking in the future the ability of zeolitized brick in the removal of heavy metals from wastewaters, this new composite should be of great interest in water treatments at low cost in Central African Republic.

Resistive switching control for conductive Si-nanocrystals embedded in Si/SiO2 multilayers

In this paper, we report on the enhanced control of resistive switching in multilayer Si/SiO2 structures, which permit the formation of Si nanocrystals with a typical size of 5.88 nm and overall good shape homogeneity. The deposition of a different number of Si and SiO2 bilayers (6, 8 and 10) allowed control of SET/RESET voltages in negative bias ranges 4.5–10 V and 6.3–13 V for six- and ten-bilayer devices, respectively. The corresponding resistance ratio between ON/OFF states varied in the ranges 107–105 for the aforementioned number of bilayers. Based on the result of XPS measurements, we suggest that the resistive switching in the studied system occurs due to the formation and annihilation of Si−Si and Si−O bonds, which serve as conductive pathways and isolating material, respectively.

Experimental evidence of trap level modulation in silicon nitride thin films by hydrogen annealing

The energy level of electron traps in silicon nitride (SiNx) thin films was investigated by discharging current transient spectroscopy (DCTS). Results indicate that the trap level of the SiNx thin films becomes deeper with decreasing composition (N/Si) and shallower after hydrogen annealing. The dependence of the trap level on the SiNx composition and the modulation of the trap level by hydrogen annealing are possibly related to the change in the number of Si–H bonds in the SiNx thin films.

Enhancement of Fire Retardancy Using Surface-Modified Silica Spheres with Aluminum Hydroxide

Large surface area and fire-inert property of sub-micrometer silica spheres were employed to improve the fire retardant performance by attaching large number of Si–O–Al(OH)\(_{2}\) groups. Various amounts of AlCl\(_{3}\) were attached to the surface of silica spheres and the residual –AlCl\(_{2}\) was hydrolyzed by adding excess amount of KOH. Although the FESEM image of pure silica spheres showed smooth surface, the surface-modified silica spheres exhibited nanoparticles on the surface of silica spheres. The characteristic absorption peaks of Al–OH and Si–O–Al were detected by FTIR spectra. Silica spheres attached with Si–O–Al(OH)\(_{2}\) were uniformly distributed on the surface of cellulose acetate films. The performance of the fire retardant was greatly enhanced by increasing the amount of aluminum hydroxide.

Silane and Germane Molecular Electronics.

This Account provides an overview of our recent efforts to uncover the fundamental charge transport properties of Si-Si and Ge-Ge single bonds and introduce useful functions into group 14 molecular wires. We utilize the tools of chemical synthesis and a scanning tunneling microscopy-based break-junction technique to study the mechanism of charge transport in these molecular systems. We evaluated the fundamental ability of silicon, germanium, and carbon molecular wires to transport charge by comparing conductances within families of well-defined structures, the members of which differ only in the number of Si (or Ge or C) atoms in the wire. For each family, this procedure yielded a length-dependent conductance decay parameter, β. Comparison of the different β values demonstrates that Si-Si and Ge-Ge σ bonds are more conductive than the analogous C-C σ bonds. These molecular trends mirror what is seen in the bulk. The conductance decay of Si and Ge-based wires is similar in magnitude to those from π-based molecular wires such as paraphenylenes However, the chemistry of the linkers that attach the molecular wires to the electrodes has a large influence on the resulting β value. For example, Si- and Ge-based wires of many different lengths connected with a methyl-thiomethyl linker give β values of 0.36-0.39 Å-1, whereas Si- and Ge-based wires connected with aryl-thiomethyl groups give drastically different β values for short and long wires. This observation inspired us to study molecular wires that are composed of both π- and σ-orbitals. The sequence and composition of group 14 atoms in the σ chain modulates the electronic coupling between the π end-groups and dictates the molecular conductance. The conductance behavior originates from the coupling between the subunits, which can be understood by considering periodic trends such as bond length, polarizability, and bond polarity. We found that the same periodic trends determine the electric field-induced breakdown properties of individual Si-Si, Ge-Ge, Si-O, Si-C, and C-C bonds. Building from these studies, we have prepared a system that has two different, alternative conductance pathways. In this wire, we can intentionally break a labile, strained silicon-silicon bond and thereby shunt the current through the secondary conduction pathway. This type of in situ bond-rupture provides a new tool to study single molecule reactions that are induced by electric fields. Moreover, these studies provide guidance for designing dielectric materials as well as molecular devices that require stability under high voltage bias. The fundamental studies on the structure/function relationships of the molecular wires have guided the design of new functional systems based on the Si- and Ge-based wires. For example, we exploited the principle of strain-induced Lewis acidity from reaction chemistry to design a single molecule switch that can be controllably switched between two conductive states by varying the distance between the tip and substrate electrodes. We found that the strain intrinsic to the disilaacenaphthene scaffold also creates two state conductance switching. Finally, we demonstrate the first example of a stereoelectronic conductance switch, and we demonstrate that the switching relies crucially on the electronic delocalization in Si-Si and Ge-Ge wire backbones. These studies illustrate the untapped potential in using Si- and Ge-based wires to design and control charge transport at the nanoscale and to allow quantum mechanics to be used as a tool to design ultraminiaturized switches.

Solid-state MAS NMR investigations for pentavalent cation-replaced pollucite compounds with a negative thermal expansion coefficient

Pollucite compounds with an aluminosilicate structure, V-replaced pollucite, Cs0.7V0.1Al0.8Si2.1O6 (CVAS), P-replaced pollucite, Cs0.7P0.1Al0.8Si2.1O6 (CPAS), and Nb-replaced pollucite, Cs0.7Nb0.1Al0.8Si2.1O6 (CNbAS), were synthesized by a multistep heat treatment of 550–1200 °C. CVAS exhibited the superior thermal expansion with thermal expansion coefficients of 0.9 × 10−6 °C−1 (30–500 °C), −0.9 × 10−6 °C−1 (30–150 °C), and −0.4 × 10−6 °C−1 (30–100 °C). Solid-state 29Si MAS NMR spectroscopy clarified that the number of Si–O–Si bonds of tetrahedra in the framework of CVAS was larger than those of CPAS and CNbAS. The chemical shift for peaks of the 29Si MAS NMR spectrum of CVAS was larger than those of CPAS and CNbAS, suggesting that the bond angle of tetrahedra was enlarged by the V replacement. Solid-state 27Al MAS NMR spectroscopy implied that CVAS had a small amount of sixfold coordinated Al species, which resulted in an increase in the number of Si–O–Si bonds of tetrahedra of CVAS.

An Experimental Study on Effect of T-Joint’s Root Gap on Welding Properties

The aimed of this research is to investigate the effect of T-Joint’s root gap on physical and mechanical properties of weld metal. Low carbon steel were joined in T-joint types using MIG (Metal Inert Gas) with variation of root gap. The root gap used were 0 mm, 3 mm and 6 mm. The physical properties examined with chemical composition, microstructure and corrosion using optical microscope. The mechanical properties were measured with respect to the strength and hardness using Universal testing machine and Vickers Microhardness. The results show that the highest value found in welds with a gap of 3 mm with a value of 163.57 MPa. Hardness value is directly proportional to the tensile strength of the material. The highest value found in welds with root gap of 3 mm, followed by root gap of 6 mm, and 0 mm Hardness values in the welding area is higher than the parent metal and HAZ because the number of Si, Mn and Cu elements in the welding metals are bigger than base metal. Weld with all variation of root gap have a good corrosion resistance because the corrosion rate in welds with various root gap have a value below 0.02 mmpy. Microstructure of weld metals were Accicular ferrite, Widmanstatten ferrite, and grain boundary ferrite, while microstructure of base metal and HAZ were ferrite and perlite.

The influence of molecular weight of siloxane macromere on phase separation morphology, oxygen permeability, and mechanical properties in multicomponent silicone hydrogels

To clarify the influence of molecular weight of siloxane macromonomer on phase separation morphology, oxygen permeability, and mechanical properties, silicone hydrogels were prepared by copolymerizing mixtures of methacrylate-terminated siloxane macromonomer (MTSM), silicon-containing monomers tris(trimethylsiloxy)-3-methacryloxpropylsilane, and three hydrophilic monomers N,N-dimethylacrylamide, N-vinylpyrrolidone, and hydroxypropyl methacrylate. The number of Si–O–Si repeating units was equal in every silicone hydrogel while the molecular weight of MTSM ranged from 1000 to 10000 g/mol. The oxygen permeability coefficient (Dk), equilibrium water content (EWC), light transmittance, mechanical properties, and internal morphologies of obtained silicone hydrogels were characterized, and their relationships were discussed in detail. The results showed that the Dk value increased first and then decreased with the chain length of MTSM increasing. The EWC presented an increasing trend and the light transmittance decreased with the increase of MTSM chain length. The elongation increased while the modulus and the tensile strengths of the silicone hydrogels decreased along with the MTSM molecular weight increasing. The internal morphologies of the silicone hydrogels were observed by transmission electron microscope. The results indicated that the silicone hydrogels presented different phase separation structures depending on the molecular chain length of MTSM. The continuous silicone phase formed and made significant contributions to high Dk value as the molecular chain length of MTSM was moderate. Besides, a model was proposed to explain the effect mechanism of the MTSM chain length on the oxygen permeability and the EWC. This work provided a facile method to preparing the silicone hydrogel materials with desirable water absorption and high oxygen permeability by adjusting the molecular weight of macromonomers.

Acid modified mesoporous Cu/SBA-15 for simultaneous adsorption/oxidation of hydrogen sulfide and phosphine

In this study, acid modified Cu/SBA-15 adsorbents were used to simultaneously remove H2S and PH3. The adsorbent was prepared by the wet impregnation method in which acid type and concentration are the main factors investigated. The test results showed that adsorbent modified by hydrogen nitrate had the highest adsorption potential of all materials tested, and the breakthrough adsorption capacity of this adsorbent was determined to be 35.25mgS/g and 104.84mgP/g with 8wt% hydrogen nitrate. Characterization results showed that hydrogen nitrate does not do great damage to the original groups on or the surface structures of Cu/SBA-15 adsorbent. FT-IR and XRD analysis showed that the removal capacity of H2S and PH3 is dependent on the number of Si–OH groups and active components available to transform the target gases to corresponding sulfur and phosphorus species (CuS, S, P2O5). Pore structure tests indicated that modification did not change the mesoporous structure of the Cu/SBA-15 adsorbent and that the performance of the Cu/SBA-15-[N] adsorbent was optimized for simultaneous adsorption/oxidation of H2S and PH3. Alternatively, pores in the range of 7–9nm favored the simultaneous adsorption/oxidation of H2S and PH3. In addition, in situ IR analysis revealed that the exhaustion of sample adsorption sites was accompanied by the disappearance of active components and the generation of sulfur and/or phosphorus species. The NH2− and NH2− groups on Cu/SBA-15-[N] may function as a trap for target gases, and the copper salts serve mainly to purify them further in the presence of O2. Because the reaction processes for H2S, PH3 adsorption and oxidation are different from one another, it was hypothesized that different gases may also participate in competitive adsorption on the surface of the Cu/SBA-15-[N] adsorbent.

Generation and Properties of Brønsted Acid Sites in Bifunctional Rh-, Ir-, Pd-, and Pt-Containing Zeolites Y Investigated by Solid-State NMR Spectroscopy

In the present work, the generation and properties of Bronsted acidic bridging OH groups (Si(OH)Al) in Rh-, Ir-, Pd-, and Pt-containing zeolites Y were quantitatively investigated by multinuclear solid-state NMR spectroscopy. The number of Si(OH)Al groups formed per noble metal atom upon their reduction was found to be 0.3 to 1.3 instead of the theoretically expected values of 2 (Pd2+, Pt2+) or 3 (Rh3+, Ir3+). For zeolites Y with low noble metal loadings, a significantly lower acid strength of Si(OH)Al groups in comparison with those of H,Na–Y zeolites occurred. Interestingly, noble metal-containing zeolites Y with lower acid strength have a significant content of not completely reduced noble metal atoms with partially cationic character. The spatial distribution of Si(OH)Al groups in noble metal-containing zeolites Y was found to differ significantly from that in H,Na–Y zeolites. This effect is explained by the migration of a significant content of noble metal atoms into the sodalite cages of zeolites Y ...