Si Bridges Research Articles

Mechanisms and energetics of calcium aluminosilicate glass dissolution through ab initio molecular dynamics-metadynamics simulations

The dissolution of silicate glasses has implications in diverse fields ranging from the immobilization of radioactive waste to the development of sustainable alternatives to Portland cement. Here, we used ab initio molecular dynamics simulations biased with well-tempered metadynamics to study Si-O-T bridge dissociation in calcium aluminosilicate glasses, crucial for understanding their dissolution. In a departure from the conventional Michalske-Freiman model, our findings reveal a nucleophilic substitution reaction mechanism characterized by a short-lived, 5-fold coordinated Si intermediate or transition state, depending on the Si bridge coordination, with a near-trigonal bipyramidal geometry. We find that the reorganization required for reaching this state causes the activation energy barriers to be dependent on the Si bridge coordination, with Si Q3 species serving as the rate-limiting step in the dissolution reaction. Our findings not only challenge long-standing theoretical models but also pave the way for more accurate and comprehensive frameworks for understanding the dissolution of silicate glasses in various applications.

Advanced Fanout Embedded Bridge Packaging Technology for Chiplets Integration

The increasing amount of data from all sectors driven by digital transformation is raising a problem of operational and storing cost of the data. Meanwhile, the exponential cost leaps of silicon scaling, the unfordable increasing of Si die size over reticle limit and unsustainable computer energy exceeding the world’s energy production have created an inflection point for semiconductor industry. It has driven the development of More-Than-Moore to augment increased device and system performance. Chiplets integration provides more flexible mix-and-match systems to accelerate performance and power efficiency. It is driving the development of advanced packaging technology to enable heterogeneous chiplets integration with separate designs and different manufacturing process nodes within a single package for yield improvement, IP reuse, performance and cost optimization, as well time to market reduction. Several advanced packaging technologies have been developed and used widely to integrate multi-chips with fine line/space interconnections, such as 2.5D Si TSV interposer, Fanout RDL (re-distribution layer) and EMIB (Embedded Multi-die Interconnect Bridge). Different packaging technologies have different sweet spots to fulfill various applications depending on the device design and performance requirements. In ASE, we have developed and introduced FOCoS (FanOut Chip on Substrate) chip first (FOCoS-CF) and FOCoS chip last (FOCoS-CL) technologies by using RDL interconnect for chiplets integration. However, due to the inherent fanout RDL process limitation, it has hit the bottleneck to manufacture RDL with higher layer counts (> 6 layers) and finer Line/Space (L/S < 1um/1um) for the applications that require high density die to die connections, high input/output (I/O) counts and high-speed signal transmitting. In this paper, a new FOCoS technology named as FOCoS embedded Si bridge (FOCoS-B) has been developed for high density die to die interconnect with RDL L/S < 1um/1um chipets integration for HPC application. The FOCoS-B packaging technology enables the USR (Ultra Short Reach) interconnection between die to die by embedded a small Si die in fanout RDL interposer. The small Si die play an interconnection bridge role between chiplets with L/S 0.8um/0.8um. Two FOCoS-B test vehicles (TVs) will be introduced in this study. One TV named as TV-1 is integrated by two chiplets of 1 ASIC die and 1 HBM2e with 1 Si bridge die to form a fanout module, which it is subsequently assembled on a FCBGA package with body size of 40x30mm2. Another TV listed as TV-2 is composed of two identical fanout modules, which are assembled on one FCBGA substrate with body size of 78x70mm2 in MCM (multi-chip-module) arrangement. The fanout module for TV-2 is integrated by 1 ASIC and 4 HBM2e with 4 bridge dies. TV-2 will have total 10 chiplets (2 ASICs and 8 HBM2e with 8 Si bridge dies). The process flow for FOCoS-B will be illuminated. The process DOE and the impact on warpage will be discussed. Furthermore, the reliability validations on two TVs will also be demonstrated. Finally, the comparison on warpage among different FOCoS solutions (FOCoS-B, FOCoS-CL and FOCoS-CL) for chiplets integration have been presented. The results indicated that the material selections and property compatibilities among the multi-layer stacked structures (Si die, RDL, Molding compounds, Underfill) play critical roles in warpage control in FOCoS-B processes. The package warpage of FOCoS-B and FOCoS-CL has showed similar behaviors. FOCoS-CF showed slightly high package warpage than that of FOCoS-B. The results also revealed that FOCoS-B has provided a wide choice and flexibility for multi bridge dies integration successfully for HPC application.

A Novel 2D/3D X-ray Microscopy Alignment and Inspection Solution for Thermocompression Bonding (TCB) in a Highly Integrated Flip Chip Fan-Out Wafer Level Package (FO-WLP)

As packaging drives to extend the capabilities of Moore’s Law via heterogenous integration, numerous bonding technologies have emerged as potential pathways, allowing for integration of both a variety of devices in the lateral space as well as vertical integration of chips via stacking. As vertical integration on interposer becomes more complex due to shrinking CDs and increasing die layers, alignment and shape control in the bonding process becomes critical. Thermocompression bonding (TCB) is particularly well-suited for larger die, where localized reflow allows a better control of chip gap height and tilt throughout the bonding process. TCB systems require both high accuracy and repeatability in all dimensions to provide a reliable system in package. While a 2D system can provide a plan view assessment of a single bond layer between two chips, it falls short in characterizing the critical z-dimension in a highly integrated chip stacking scenario. Therefore a robust solution is needed for both system alignment validation in the x,y plane as well as a capability to explore gap height and bump quality/buried issues in high aspect ratio TSV. This paper will explore an x-ray application of a stacked 15-layer die-to-interposer structure to qualitatively validate overall health of the TSV (bond, pad, fill) via a nondestructive volumetric method as well as quantitatively evaluate stacked die for via/ball/pad alignment to determine overall alignment shift during the bonding process. In the test vehicle for a flip chip FO-WLP process flow first presented by IMEC, a silicon (Si) bridge is utilized to connect the logic and through-package via dies with a bump pitch of 20µm for the logic die interconnect. This is done by carefully aligning the logic dies on the carrier and then placing the through-package dies aligned to the carrier and logic dies. In the final step, a high accuracy placement and stacking TCB tool attaches the Si bridge. To perform an accurate assessment for bump alignment and bond quality, an initial high-resolution 3D x-ray scan is performed on a 1.5mm3 region of interest with over 2,000 individual projections at a 1.4µm voxel resolution with a 4x objective, taking approximately two hours. The dataset is put through a deep-learning algorithm which generates an AI model. This model is then applied to a faster scan of 15 minutes with a 1.4µm voxel resolution for the same field of view (FOV) on a nearby array and the data is collected and processed. To verify alignment of the entire sample, data is collected on the tightest pitch (in this case 20µm) oriented in both the vertical (x) and horizontal (y) plane in the through-silicon via (TSV) region. The z-plane is analyzed and processed by computer vision algorithms, and individual interconnects are then quantified and sorted for solder height (z), width (x,y) and TSV misalignment (deviation from expected center, x1y1 → x2y2). To validate the model, a high-resolution uncorrected 20h scan and a 15min scan based on deep learning are collected for the same region of interest (ROI). The data is comparable. Furthermore, the global misalignment data between both datasets demonstrates similar misalignment propagating through the 15-layer stack.

Tribological behavior of polycrystalline diamond based on photo-Fenton reaction

Polycrystalline diamonds (PCD) has high thermal conductivity and as heat sinks in semiconductor power devices. However, PCD exhibits high hardness and strong chemical inertness lead to lower processing efficiency and increase processing costs. Hence, achieving efficiently obtain high-quality PCD surfaces is crucial. In this study, we investigated the tribological behavior of PCD in different environments (deionized water, H2O2 + UV, Fenton, and photo-Fenton) and under different photo-Fenton conditions (pH, light intensity, Fe3O4 concentration, and H2O2 concentration) via Si3N4 ball-disk friction and wear experiments. The photo-Fenton reaction improved the material removal rate of PCD, which was the highest (285.4 μm3/min) under optimized conditions of pH = 3, 100 mW/cm2 light intensity, 2 wt% Fe3O4 concentration, and 10 wt% H2O2 concentration. Based on the friction and wear experimental results and X-ray photoelectron spectroscopy, we propose a material removal mechanism for PCD. The hydroxyl radical (·OH) produced by the photo-Fenton reaction oxidize the PCD surface to form CO, CO, and C–OH groups, which are converted into C–O–Si bridge bonds on the PCD surface, resulting in material removal. Our study findings provide theoretical support for the photo-Fenton reaction -assisted CMP of PCD.

Phase evolution and mechanical-hydroscopic properties of alkali-silica reaction gels modified by magnesium nitrate

Alkali-silica reaction (ASR)'s destructiveness is governed by the compositions and properties of ASR products, while methods of converting these hygroscopic-expansive gel-like products into innocuous phases remain unexploited. In this study, the influence of magnesium nitrate on the evolutions of phase, molecular structure, hydroscopic and mechanical properties of ASR gels with varying Mg/Si ratios from 0.1 to 1.1 was investigated. The results indicate that the primary phases of ASR products, tobermorite-type calcium silicate hydrate (C–S–H) and alkali kanemites, can be suppressed into brucite and eventually converted into magnesium-silicate-hydrate (M-S-H) in the presence of increasing Mg/Si ratios and the consequent decreasing pH. The Si–O–Si bridging bonds and Si–O symmetric stretching in the Q3 sites of ASR products can be suppressed. The phase and structure modifications resulted in a 93.5% reduction in hydroscopic swelling, a 94.7% decrease in strength, and a 152.3% drop in modulus of elasticity rendering the ASR products less destructive.

Enhancement and localization of atomistic polarity and polarizability memory in light scattering upon hydrogenation of luminescent spherical 1 nm Si nanoparticles

The classical light interactions of nanosilicon, which is a dielectric material, are exceedingly weak for radius r ≪ λ (wavelength), scaling as r6. It exhibits geometrical anisotropy-based depolarization, which is the basis for the very weak response in isotropic structures (nanosphere). Recently, surface enhanced Raman scattering (SERS) in DNA decorated with ultrasmall Si nanoparticles has been demonstrated, affording an effective alternative to plasmon–metal particles. In this paper, we execute fundamental quantum atomistic computation of 1 nm hydrogenated Si particles, with different surface reconstruction and termination, including Si–H, H–Si–Si–H (dimer molecules), or oxygenated dimer bridges (H–Si–O–Si–H). We obtain the mechanical vibrational modes of the particles. Our results show that by changing the surface configuration one can control the symmetry and normal vibration modes, and enhance the polarizability, polarity, and light interactions (scattering, absorption, and depolarization/memory). The low frequency polarizability (Raman scattering) shifts spatially from the interior to the surface, while the infrared polarity remains on the surface, but its bandwidth narrows spectrally. The results support previous infrared absorption and light scattering and depolarization measurements, as well recent SERS, which enable Si nanoparticles to be an effective alternative to plasmonic metal particles. Molecular surface reconstruction in terms of Si dimers and bridges were suggested as the source of the novel nonlinear and anisotropic luminescence and photonic properties of Si nanoparticles. Such control affords potential for optimizing the design and operation of a wide range of opto-electronic advanced scattering and luminescence devices.

Water disinfection using durable ceramic filter coated with silver nanoparticles synthesized using actinomycetes

Contamination with pathogens degrades water quality and is a major cause of many waterborne diseases. The aim of this research is to reduce the global disease burden by presenting an efficient, durable, and low-cost ceramic filter impregnated with actinomycetes-mediated silver nanoparticles (AgNPs) for water disinfection in rural areas. This marks the first report on the simultaneous biosynthesis of AgNPs utilizing cell-free supernatants obtained from terrestrial actinomycetes. An easy and efficient method was used to impregnate AgNPs onto a ceramic filter using 3-aminopropyltriethoxysilane (APTES). The APTES linker is anchored to the ceramic surface through Si–O–Si bridges, while the terminal amino groups coordinate with AgNPs. Notably, the observed inhibition zone around the filter with AgNPs was ~ 18 mm, suggesting that the silver ions were responsible for the antibacterial activity. After 30 min of sonication, only insignificant traces of AgNPs were released from the filter, making it stable for long-term antibacterial activity when treating water. According to the laboratory simulation experiments, the untreated filter can reject about 99% of spiked bacteria, while the antibacterial efficiency of the filter coated with AgNPs was 100% due to the synergistic effect between filtration and disinfection with AgNPs. In addition, the average concentration of dissolved silver in the outlet water of the ultrafiltration system during three months was 33.7 μg/L, far below the permissible limit (100 μg/L) for drinking water. Overall, this work offers a suitable and affordable water treatment strategy for low-income, isolated, and rural societies in developing countries.

Understanding the adsorption behavior of oxygen on the 3C–SiC(1 1 0) surface: A first‐principles study

The adsorption behavior of atomic oxygen and molecular O2 on the 3C–SiC(1 1 0) surface is investigated by first-principles calculations. The atomic O prefers to be adsorbed at the C top site (C–O) with adsorption energy of −1.95 eV after zero-point energy correction, followed by the C–O–Si bridge site, Si–O–Si bridge site, and the Si top site (Si–O) with adsorption energies of −1.46, −1.36, and −1.13 eV, respectively. The molecular O2 separately trapped by the second nearest neighboring C and Si atoms (C–O–O–Si, M4 type) is the most stable configuration with the adsorption energy of −2.46 eV, which is followed by the Si–O–O–Si (M5 type), C–O–O–Si (M3 type), O–Si–O (M2 type), and Si–O=O (M1 type) configurations with the adsorption energies of −2.24, −1.87, −1.07, and −0.75 eV, respectively. All these molecular O2 adsorption configurations exhibit high tendency to dissociate with the dissociation barriers range of 0.09–0.19 eV. The adsorbed atomic O seems to be easily trapped at the C–O site due to the extremely low diffusion barrier. In addition, the infrared spectra of all the atomic O and molecular O2 adsorption configurations are predicted and compared with available experimental observations.

Hybrid Bicyclo[1.1.0]butanes [(R4Si3)CH2] and [(R4Si2Ge)CH2] (R = SiMetBu2): Synthesis and Thermal Isomerization to Alkyl-Substituted Cyclopropenes [R3Si3]CH2R and [R3Si2Ge]CH2R

Hybrid bicyclo[1.1.0]butanes comprised of different group 14 elements, namely, 1,2,3-trisilabicyclo[1.1.0]butane and 1,3-disila-2-germabicyclo[1.1.0]butane, were readily prepared by the reductive dichlorination of 1,3-dichlorocyclobutane precursors. Both compounds feature exceptionally short bridging Si–Si bonds and practically planar geometry around the bridging Si atoms, thus representing a novel structural motif in the chemistry of the heavy analogues of bicyclo[1.1.0]butanes. These peculiar structures were explained by the steric interaction between the substituents at the bridging and bridgehead positions. Thermolysis of the title bicyclo[1.1.0]butanes in toluene at 130 °C resulted in their isomerization to the alkyl-substituted cyclopropene analogues. The mechanism of this isomerization was revealed in detail on the basis of deuterium-labeled experiments, kinetic investigations, trapping experiments, and computational studies to establish the nature of the key intermediate of the whole isomerization process.

Dual-Site Model for Ab Initio Calculations of Gibbs Free Energies and Enthalpies of Adsorption: Methane in Zeolite Mobile Five (H-MFI).

Quantum chemical hybrid MP2:PBE+D2 calculations in combination with molecular statistics are employed to calculate enthalpies and Gibbs free energies of adsorption for CH4 at Brønsted acid sites [bridging Si-O(H)-Al groups] and silica wall sites (Si-O-Si) of the proton form of zeolite MFI (H-ZSM-5) and its purely siliceous analogue Silicalite-1. A Langmuir model is adopted to calculate the amounts of CH4 adsorbed at each type of site from the Gibbs free energies. The combination of these results according to the ratio of silica wall sites and Brønsted acid sites in the sample yields adsorption isotherms for zeolites with different Si/Al ratios. The zero-coverage isosteric heats of adsorption, calculated as thermal averages of the adsorption enthalpies of the individual sites, vary between 20.2 kJ/mol for the pore wall site and 29.2 kJ/mol for the acid site and agree well within ±1 kJ/mol with experimental results.

Manipulating the Spin State of Fe Sites via Fe-O-Si Bridge Bonds for Enhanced Polysulfide Redox Kinetics in the Li-S Battery.

Transition metals with 3d unoccupied orbitals have superior catalytic activity, but inherent high spin suppresses their adsorption capability, leading to sluggish polysulfide conversion kinetics for Li-S batteries. Herein, we provide Fe-O-Si bridge bonds to manipulate eg filling and induce a high-to-medium spin transition of Fe3+ sites, which enhances polysulfide adsorption and facilitates sulfur redox reaction kinetics. The resultant cathodes exhibit outstanding performances under high sulfur loading, which can deliver a high battery specific energy of 1061 mA h·g-1 even after 100 cycles in Li-S pouch batteries. This work provides new insights into the kinetic and multi-step conversion mechanism of the sulfur redox reaction process, helping in the understanding and design of spin-dependent catalysts.

Micro-Analytical Study of a Zeolites/Geo-Polymers/Quartz Composite, Dielectric Behaviour and Contribution to Brønsted Sites Affinity

The chemical and mineralogical surface properties of a brick-derived composite were examined by using an environmental scanning electron microscopy (ESEM) equipped with an energy dispersive X-ray spectrometer (EDS). Investigations revealed that the material could be assimilated to an adsorptive membrane having zeolites deposited onto quartz matrix. In our calculation, the membrane was considered as a diphase composite and its dielectric constant was evaluated from theoretical models developed in the literature. Electro-kinetic analysis showed that composite surfaces were hydroxylated with the formation of hydroxyl groups which behaved amphoterically. A theory-based approach was used for calculating thermodynamic constants relative to surface-protonation equilibriums. In the H-form of the composite, the occurrence of bridging Si–(OH)–Al sites were evidenced by mathematical calculations utilizing equations in direct relation to mineralogical, crystallographic and dielectric surface characteristics. 1H MAS NMR spectroscopy confirmed the existence of bridging Brønsted acid sites at acidified composite surfaces interacting with ammonium (as probe ions). Owing to advancements in brick-based composites research, this should lead more to the development of “ceramic” adsorptive membranes with natural clay materials.

Enhanced luminescence and Judd-Ofelt analysis in SiO2 encapsulated CaWO4@CaWO4:Eu:Bi for visualization of latent fingerprints and anti-counterfeiting

Core nanoparticles (NPs) and core–shell particles have been synthesized using the low temperature reflux method. The structural and photo-physical properties of the developed phosphors have been investigated through various analytical techniques. The transmission electron microscopy (TEM) analysis evidences the formation of the shell on the core NPs. The optical band gap is estimated using the diffuse reflectance spectra. An 8-fold enhancement of emission intensity is observed in the core–shell particles as compared to that of core, due to the reduced surface quenchers after silica coating. In addition, the Judd-Ofelt (J-O) parameters have been calculated to reveal the site symmetry and coordination environment around Eu3+ ions. The tunable red emission on formation of core–shell structures is confirmed from the CIE diagram. These results are ascribed to the formation of the chemical bonds between CaWO4@ CaWO4:3%Eu3+:5%Bi3+ (core) and amorphous SiO2 shell via W – O – Si bridges. Better hydrophilicity developing from active functional groups in solutions and intense luminescence behavior with a quantum efficiency of 91% allow the developed phosphors for various potential applications such as solid state lighting, bio-labelling agent for the visualization of latent fingerprints (LFPs) and anti-counterfeiting, etc.

Fabrication of high-stability W-MFI zeolite membranes for ethanol/water mixture separation

Pure silica MFI (Si-MFI) zeolite membranes with desirable hydrophobicity have the potential to separate ethanol/water mixture. However, its separation performance would significantly decrease in the long-term operation due to the presence of silanol groups formed in alkaline media. In this work, silanol-free MFI zeolite membranes were prepared by the incorporation of tungsten in MFI framework. The occurrence of silanol group can be prevented by formation of W–O–Si bridges. The synthesis parameters affected the W-MFI zeolite membranes’ microstructure and separation performance. For 5 wt% ethanol solution, the W-MFI zeolite membranes prepared at optimum condition showed stable separation performance of permeation flux as 2.81 kg m−2 h−1 with separation factor as 32 over 80 h at 60 °C. The membrane was characterized by XRD, DR UV–vis, XPS and 29Si NMR, and the results confirmed the incorporation of W and the absence of silanol groups. This research showed that W-MFI zeolite membranes are promising candidates for ethanol extraction with high stability.

Identifying Crystallographically Different Si-OH-Al Brønsted Acid Sites in LTA Zeolites.

A clear understanding of the acidic properties of bridging Si-OH-Al groups containing crystallographically different oxygen atoms in zeolites is a prerequisite for optimizing their performance as industrial solid catalysts and developing new acid-catalyzed reactions, but presents many challenges. Here, we report the direct observation of yet unrecognized bridging Si-OH-Al groups in the LTA zeolite whose oxygen atoms are crystallographically different from those of already known Brønsted acid sites. We also report that the creation of a crystallographically particular type of bridging OH groups in zeolites and its concentration and acid strength can vary strongly with the content and spatial distribution of framework Al atoms, thus being synthetic in nature, which has been rationalized in terms of the secondary building unit concept.

Identifying Crystallographically Different Si−OH−Al Brønsted Acid Sites in LTA Zeolites

AbstractA clear understanding of the acidic properties of bridging Si−OH−Al groups containing crystallographically different oxygen atoms in zeolites is a prerequisite for optimizing their performance as industrial solid catalysts and developing new acid‐catalyzed reactions, but presents many challenges. Here, we report the direct observation of yet unrecognized bridging Si−OH−Al groups in the LTA zeolite whose oxygen atoms are crystallographically different from those of already known Brønsted acid sites. We also report that the creation of a crystallographically particular type of bridging OH groups in zeolites and its concentration and acid strength can vary strongly with the content and spatial distribution of framework Al atoms, thus being synthetic in nature, which has been rationalized in terms of the secondary building unit concept.

Syntheses of Silylene-Bridged Thiophene-Fused Cyclopentadienyl ansa-Metallocene Complexes for Preparing High-Performance Supported Catalyst

We synthesized a series of Me2Si-bridged ansa-zirconocene complexes coordinated by thiophene-fused cyclopentadienyl and fluorenyl ligands (Me2Si(2-R1-3-R2-4,5-Me2C7S)(2,7-R32C13H6))ZrMe2 (R1 = Me or H, R2 = H or Me, R3 = H, tBu, or Cl) for the subsequent preparation of supported catalysts. We determined that the fluorenyl ligand adopts an η3-binding mode in 9 (R1 = Me, R2 = H, R3 = H) by X-ray crystallography. Further, we synthesized a derivative 15 by substituting the fluorenyl ligand in 9 with a 2-methyl-4-(4-tert-butylphenyl)indenyl ligand, derivatives 20 and 23 by substituting the Me2Si bridge in 12 (R1 = Me, R2 = H, R3 = tBu) and 15 with a tBuO(CH2)6(Me)Si bridge, and the dinuclear congener 26 by connecting two complexes with a –(Me)Si(CH2)6Si(Me)– spacer. The silica-supported catalysts prepared using 12, 20, and 26 demonstrated up to two times higher productivity in ethylene/1-hexene copolymerization than that prepared with conventional (THI)ZrCl2 (21–26 vs. 12 kg-PE/g-(supported catalyst)), producing polymers with comparable molecular weight (Mw, 330–370 vs. 300 kDa), at a higher 1-hexene content (1.3 vs. 1.0 mol%) but a lower bulk density of polymer particles (0.35 vs. 0.42 g/mL).

Selective transformation of typical sugars to lactic acid catalyzed by dealuminated ZSM-5 supported erbium

The tremendous demand of lactic acid (LaA) in widespread applications has impelled the development of chemical strategies for LaA production. We developed dealuminzated ZSM-5 loaded erbium catalyst, which exhibited outstanding activity. As high as >96% of LaA yield was obtained using triose as raw material over 15-Er/deAl-ZSM-5 (2) catalyst. When xylose-glucose mixture (C-molar ratio, 1:1) was employed, the simultaneous conversion of xylose and glucose selectively to LaA with ∼69.1 C-mol% yield could be achieved. The characterization of catalyst revealed that the pretreatment by HNO3 successfully removed partial Al in the extra-framework of ZSM-5, leading to enlarged surface areas and promoted dispersion of Er species, as well as strengthened weak interaction between Er species and support. Er loading might replace the H of OH group in bridging (Si–O(H)–Al) and Si–OH/Al–OH, which significantly strengthened the Lewis acidity of catalyst but decreased the Brønsted acidity. Consequently, LaA formation was remarkably promoted, while levulinic acid generation was inhibited. The catalyst also showed good catalytic activity for the conversion of other water-soluble polysaccharides. This work might provide a potential approach for the simultaneous conversion of cellulose and hemicellulose in actual biomass to produce LaA in an effective, low-cost and environment-friendly chemical way.

Exploration of the Mechanism of the Dimerization of Hydroxymethylsilanetriol Using Electronic Structure Methods.

Hydroxymethylsilanetriol undergoes condensation reactions to form new structures with an organic part in the formed bridges. As a first step to explore the formation of these bridges, we studied the corresponding mechanisms using simple models and theoretical methods. Three mechanisms were studied for the formation of dimers of hydroxymethylsilanetriol with bridges: Si–O–C–Si, Si–O–Si, and Si–C–O–C–Si. Energies are calculated using M06/6–311+G(d,p) single-point calculations on B3LYP-optimized geometries in solution and including B3LYP thermodynamic corrections. The first mechanism for the formation of the Si–O–C–Si bridge consists of one step. The second mechanism for the formation of the Si–O–Si bridge consists of two steps. The barrier for the last mechanism for the formation of the Si–C–O–C–Si bridge is too high and cannot occur at room temperature. The energy barriers are 31.8, 27.6, and 65.9 kcal mol–1 for the first, second, and third mechanisms, respectively. When adding one explicit water molecule, these energies are 25.9, 22.9, and 80.3 kcal mol–1, respectively. The first and second mechanisms can occur at room temperature, which is in agreement with the experimental results.

Acidic property of YNU-5 zeolite influenced by its unique micropore system

YNU-5 zeolite has the YFI -type framework with a 12-12-8-ring system (2-dimensional 12-oxygen membered ring pores 3-dimensionally connected by twin 8-ring channels), and isolated 8-ring channels separated from the system by a thin (mono-atomic silicate) wall. In this study, the acidic property of YNU-5 zeolite was analyzed mainly by means of the ammonia IRMS-TPD (infrared/mass spectroscopy temperature-programmed desorption) method. In addition, the accessibility of acid sites was evaluated through adsorption of pyridine. The number of Brønsted acid sites approximately agreed with the number of Al atoms, and the amount of Lewis acid sites was negligible, indicating that most acid sites have the nature of bridging Si(OH)Al group in the YFI framework. Most of the Brønsted acidic OH groups on the YNU-5 zeolites (including the dealuminated samples) reacted with pyridine vapor at 343 K to form pyridinium cations, indicating that the Brønsted acid sites are highly accessible through the 12-12-8-ring system. Enthalpy of ammonia desorption from the Brønsted acid site, which can be an index of acid strength or reactivity of the acid site with a basic reactant, was in the following order: FAU < MOR (12-ring) ≈ *BEA < MFI < MWW ≈ YFI < MOR (8-ring), indicating the markedly large ammonia desorption enthalpy on the YNU-5 zeolite compared to the other 12-ring zeolites. The DFT calculations suggest that the Brønsted acidic protons with especially high ammonia desorption enthalpy are located in the isolated 8-ring but accessible from the 12-12-8-ring system side. In addition, dealumination at a high temperature under the reflux conditions with nitric acid resulted in the preferential removal of Brønsted acid sites with low ammonia desorption enthalpy, probably in the 12-12-8-ring system. The presence of reactive Brønsted acid sites in the isolated 8-ring, accessibility to them from the 12-12-8-ring system, and preferential removal of the Brønsted acid sites from the 12-12-8-ring system are reasonably consistent with the previously reported catalytic properties for dimethyl ether-to-olefin reaction. • Enthalpy of ammonia desorption (Δ H ) from the Brønsted acid site on the YNU-5 zeolite was high. • The Brønsted acidic protons with high Δ H were located in the isolated 8-ring but accessible from the 12-12-8-ring system. • Dealumination in the reflux conditions of nitric acid preferential proceeded in the 12-12-8-ring system.