Silica Species Research Articles

Silicon isotope variations in hydrothermal systems at Yellowstone National Park, Wyoming, U.S.A.

Silicon (Si) isotopic compositions of authigenic Si-bearing materials can be powerful tracers of geological Si cycling and reconstruction of Earth’s climate. Interpretations of Si isotope data, however, are complicated by an inadequate understanding of natural Si isotopic fractionation pathways. This study investigated Si isotope fractionation between hydrothermal fluids and amorphous silica sinters of Cistern Spring and Deerbone Spring at Yellowstone National Park, USA, with a particular focus on spatial variations along spring flowpaths. Modeling of geochemical data indicate that the fluids at Cistern Spring were supersaturated with respect to amorphous silica whereas the fluids at Deerbone Spring were undersaturated due to lower SiO2 content and a more alkaline pH. The δ30Si values of the spring waters for both sites exhibit small variations, whereas the associated amorphous silica sinters displayed a considerable range and generally decreased downflow (from − 2.25 to −5.04‰ for Cistern and from −0.11 to −0.81‰ for Deerbone). The magnitude of apparent isotopic fractionation between solid and aqueous silica (Δ30Sisolid-fluid) was significantly larger for the samples from Cistern Spring than for Deerbone Spring or similar hot spring systems at Geysir geothermal field in Iceland. The Δ30Sisolid-fluid values for Cistern Spring ranged from −2.40 to −5.49‰ along the flowpath and correlated inversely with the rate of silica precipitation, indicating a process dominated by kinetic isotope fractionation. In contrast, the magnitude of Si isotopic fractionation was significantly smaller at Deerbone Spring (+0.21 to −0.64‰). A portion of the opaline sinters at Deerbone may have formed cryogenically under freezing winter conditions that altered silica saturation and formation pathway. Rapid isotope exchange with silica undersaturated hydrothermal fluids may have erased initial kinetic isotope effects. Re-equilibration between opal-A and fluids was strongly affected by isotopic fractionation between aqueous silica species and fluid ionic strengths. These results document both kinetic and equilibrium Si isotope fractionation from field observations and highlight the pivotal role of fluid-rock interaction on the preservation of Si isotope signatures in the rock record.

Quartz solubility in sodium carbonate solutions at high pressure and temperature

We present new experimental data on the synthetic quartz (Qtz) solubility in the Na2CO3 aqueous solutions ranging in salt concentration from 0.3–3.5 m (mole/kg H2O). The data have been collected in the temperature (T) range 500–700 °C at pressure (P) 4 kbar and 600 °C/5 kbar in an internally heated pressure vessel, with phase assemblage bracketing as a solubility monitor in quench experiments: first disappearance of crystalline Qtz in a succession of runs with constant Na2CO3 concentration but decreasing the Qtz/solution weight ratio was taken for the solubility value. It was possible to “bracket” the solubility within about 1 wt% by carefully observing the presence or absence of crystalline Qtz in the run products. Qtz solubility varies systematically with P, T, and particularly, with the Na2CO3 molality, increasing from 0.7 m for the 0.3 m Na2CO3 to 4 m for the 3.5 m Na2CO3 (at 600 °C/4 kbar). In all cases the SiO2 molality in the solutions exceeds that of Na2CO3, which suggests the presence of polymerized silica species in the solutions. Quantum chemical computations showed the dimer H5Si2O7− as the most stable species, which corresponds to the dehydrated species Si2O4OH− in the framework of the revised Helgeson–Kirkham–Flowers equation of state (HKF). A complete set of thermodynamic quantities for Si2O4OH−, consistent with the revised HKF and the DEW model (Sverjensky et al., 2014) has been retrieved from the experiments. Calculations with the obtained set of thermodynamic parameters reproduce very well the Qtz solubility experiments performed in a simpler H2O-NaOH fluid at 600 °C/4 kbar. Model calculations of silica and Ca solubility in the 15 wt% (3 m) NaCl aqueous solution interacting with a siliceous carbonate rock (Qtz + Calcite saturated) along a 13°/km geotherm, which take into account Si2O4OH−, predict much higher bulk Si and Ca contents in the fluid phase than in equilibrium with the corresponding individual minerals for P above 4–5 kbar.

Process simulation of high pH reverse osmosis systems to facilitate reuse of coal seam gas associated water

• First simulation of HERO process for CSG associated water treatment. • AqMB software comprehensively evaluated water treatment process options. • Identified major costs as acid consumption and power for air stripper. • Substantially improved economics by softening with sodium exchanged resin. This study has revealed the potential for a high pH reverse osmosis system to desalinate coal seam gas (CSG) (or coal bed methane (CBM)) associated water to facilitate beneficial reuse. To promote technology uptake in the CSG industry greater insight was required to understand the optimal water treatment plant design, the influence of solution composition, and process economics. Therefore, AqMB software was used to simulate the treatment of three CSG water compositions. Unit operations included: Filtration; Softening; Air Stripping; pH raising; and Reverse Osmosis. In all cases, the product water met reuse guidelines. However, process economics were less favourable as solution concentration increased. Hydrochloric acid regenerant for the cation resin was prohibitively expensive (up to A$17,554,687 per annum) and its use required air stripping to remove carbon dioxide formed in acidic conditions (power consumption 70 % of total process demand). Acid solutions also required large amounts of sodium hydroxide (up to A$4,546,682 per annum) to reach pH 10 wherein silica species were soluble. Use of a sodium chloride regenerated resin plus removal of the air stripping stage substantially improved economics to the point that the operational expenditure was predicted to be A$417 per ML of water treated; a value comparable to conventional reverse osmosis desalination units. AqMB software was advantageous in that it; simulated the entire water treatment process, not just reverse osmosis; generated robust predictions; and estimated operational costs. As an outcome, rapid interrogation of water treatment process designs was now possible.

Structural and 3rd order nonlinear optical properties of organic dyes immobilized silica nano-composite

Low-temperature sol-gel route is used to synthesized the silica and three different organic dyes i.e., phenol red (PR), creosol red (CR) and bromophenol blue (BPB) individually encapsulated within silica nano-composite matrix. FTIR analysis shows heterogeneous bonding between silica and dye species. The PR encapsulated silica (PR-Si) nano-composite matrix exhibited average surface roughness (Ra) ~ 1.6 nm than other matrices, which is advantageous for non-linear behaviour. FESEM/EDX analysis confirmed the crack-free, porous structures of successfully dyes encapsulated silica nano-composite matrix. The closed z-scan characterization of PR-Si, CR-Si, and BPB-Si shows self-defocusing phenomena with the negative nonlinear refractive index. From the open z-scan measurement, the strength of nonlinear absorption (NLA) is observed in the order of PR-Si > CR-Si > BPB-Si nano-composite matrix. Smooth surface and low surface roughness of the PR-Si causes strong nonlinear character during the interaction with the excitation beam. The prominent NLO response of the PR-Si nano-composite matrix has provided a new avenue in the development of NLO devices especially all-optical control as well as optical switching.

Complexation between dissolved silica and alginate molecules: Implications for reverse osmosis membrane fouling

Dissolved silica and organic matter are major membrane foulants in desalination of brackish water and wastewater by reverse osmosis. However, the interaction between inorganic silica species and dissolved organic molecules and their combined impact on membrane fouling are poorly understood. In this study, we have used sodium silicate and sodium alginate as model inorganic and organic foulants, respectively. Membrane fouling experiments showed a cooperative effect between the dissolved silica and alginate macromolecules, which aggravated membrane fouling. The molecular interactions between sodium alginate and sodium silicate and the properties of the formed complexes were determined by X-ray diffraction and X-ray photoelectron spectroscopy. Results show that the crystallinity of the formed complexes decreased as we increased the ratio of silica in the silica-alginate mixture, indicating the formation of amorphous complexes. Full reflection Fourier transform infrared spectroscopy also confirms new functional groups following the interaction between silica and alginate. Isothermal titration calorimetry was also employed to quantitatively determine the binding parameters by measuring the heat change during the reaction. When binding occurs between silica and alginate, the measured adsorbed or released heat is used to determine the binding constants as well as the enthalpy and entropy changes. Our results suggest that the interaction between silica and alginate is spontaneously exothermic and dominated by noncovalent bonding. Our findings provide fundamental insights into the complexation between silica and alginate in reverse osmosis membrane fouling and highlight the binding mechanism between silica and alginate molecules.

Ultrastable and strongly acidic Al-SBA-15 with superior activity in LDPE catalytic cracking reaction

Ordered mesoporous molecular sieve materials, Al-SBA-15 was respectively synthesized from the strong acidic and the acid-free media by using a very small quantity of surfactants because of the economic and environmental considerations. The effects of various Al sources on the structural and acidic properties of the final materials were investigated with powder X-ray diffraction (XRD), nitrogen adsorption–desorption at 77 ​K, transmission electron microscopy (TEM), scanning electron microscopy (SEM), inductively coupled plasma (ICP) analyses, and chemical sorption (Py-IR). When following the acid-free strategy, a highly ordered mesostructure can be facilely constructed even with a very low surfactant concentration, extremely regardless of the kind of Al source that used. The resulting Al-SBA-15 exhibited a much higher aluminum content, a stronger acid strength and especially the predominant Brønsted acidic properties in comparison with those synthesized under the traditional strong acidic conditions, thanks to the high-quality crosslinking and self-assembly of silica and alumina species. In addition, the morphology of the product can also be modulated by simply altering the type of aluminum sources. The Al-SBA-15 synthesized with the aluminum nitrate as Al source exhibited very high catalytic activity in the Low Density Polyethylene (LDPE) cracking reaction, and the temperature corresponding to the maximum cracking rate was even comparable to the zeolitic catalyst.

Design of Dendritic Large-Pore Mesoporous Silica Nanoparticles with Controlled Structure and Formation Mechanism in Dual-Templating Strategy.

Dendritic large-pore mesoporous silica nanoparticles (DLMSN) is an important biodegradable drug carrier due to its high porosity, which can be prepared by coassembly of a major template and an auxiliary template in aqueous solution, followed by hydrolysis of tetraethyl orthosilicate (TEOS). The auxiliary template is key to obtaining dendritic large-pore structures; however, how to choose the auxiliary template to obtain the desired pore structure is largely unknown. This is because the formation mechanism of DLMSN is still not clear. In this study, a series of therapeutic agent molecules were used as the auxiliary templates to study the control of the pore morphology of DLMSN. Transmission electron microscopy observation and theoretical modeling were used to study the micelle formation, and early stage silica formation was also observed. It is proposed that the silica branches and sheets formed by hydrolysis of TEOS on single micelle and micelle bundles, which formed the initial nanoparticles with spherical structures and new silica species growing on the early formed particles to form DLMSN. The fine control of pore morphology was demonstrated by using auxiliary templates with different structural characteristics, which were used for selective drug loading. This work provides a design strategy of how to choose suitable auxiliary templates for preparing DLMSN with desired pore structure for biomedical applications.

Comparative structural investigations of nuclear waste glass alteration layers and sol-gel synthesized aerogels

While various glass alteration layer formation mechanisms have been debated in recent years, the glass alteration community generally agrees that more information on physical properties of the alteration layers is needed to further the understanding of their impacts on overall glass alteration. In this work, pore volumes and solid structures of glass (International Simple Glass, ISG) alteration layers formed in solutions of various pH conditions in initially dilute conditions at 90 °C are evaluated with positron annihilation spectroscopy, small-angle X-ray scattering, and scanning transmission electron microscopy. Pore volumes of alteration layers formed at pH 9 were found to be at their lowest near the surfaces of the alteration layers. Solid structures of alteration layers are compared with those of synthetic aerogels of comparable compositions produced under various pH conditions. Alteration layers formed at pH 11 on ISG were shown to contain large structures (>10 nm) similar to synthetic aerogels created under neutral and basic conditions whereas alteration layers formed at pH 9 did not. Available dissolved silica species defined by silica solubility were proposed to have the greatest impact on alteration layer structure.

High Ethylene Selectivity in Methanol‐to‐Olefin (MTO) Reaction over MOR‐Zeolite Nanosheets

AbstractPrecisely controlled crystal growth endows zeolites with special textural and catalytic properties. A nanosheet mordenite zeolite with a thickness of ca. 11 nm, named as MOR‐NS, has been prepared using a well‐designed gemini‐type amphiphilic surfactant as bifunctional structure‐directing agent (SDA). Its benzyl diquarternary ammonium cations structurally directed the formation of MOR topology, whereas the long and hydrophobic hexadecyl tailing group prevented the extensive crystal growth along b axis. This kind of orientated crystallization took place through the inorganic–organic interaction between silica species and SDA molecules present in the whole process. The thin MOR nanosheets, with highly exposed (010) planes and 8‐membered ring (MR) windows, exhibited a much improved ethylene selectivity (42.1 %) for methanol‐to‐olefin (MTO) reactions when compared with conventional bulk MOR crystals (3.3 %).

High Ethylene Selectivity in Methanol-to-Olefin (MTO) Reaction over MOR-Zeolite Nanosheets.

Precisely controlled crystal growth endows zeolites with special textural and catalytic properties. A nanosheet mordenite zeolite with a thickness of ca. 11 nm, named as MOR-NS, has been prepared using a well-designed gemini-type amphiphilic surfactant as bifunctional structure-directing agent (SDA). Its benzyl diquarternary ammonium cations structurally directed the formation of MOR topology, whereas the long and hydrophobic hexadecyl tailing group prevented the extensive crystal growth along b axis. This kind of orientated crystallization took place through the inorganic-organic interaction between silica species and SDA molecules present in the whole process. The thin MOR nanosheets, with highly exposed (010) planes and 8-membered ring (MR) windows, exhibited a much improved ethylene selectivity (42.1 %) for methanol-to-olefin (MTO) reactions when compared with conventional bulk MOR crystals (3.3 %).

Enhanced hydrogen-assisted cracking of 1,3,5-triisopropylbenzene over fibrous silica ZSM-5: Influence of co-surfactant during synthesis

In this study, unique fibrous silica ZSM-5 was successfully synthesized by using three type of alcohol possessing different alkyl-chain length as the co-surfactant. The effect of diverse co-surfactant was observed in the changes of physical properties, such as crystallinity, inter-dendrimer distances and pore properties. According to the IR and temperature programmed desorption of ammonia (NH3-TPD) analyses, all catalysts exhibited different acid strengths which could be triggered by the different amount of additional silica species. All catalysts exhibited high catalytic performance in the hydrocracking of 1,3,5-triisopropylbenzene due to the absence of diffusion limitation. However, FZSM5C3 exhibited the highest catalytic activity which corresponded to its high number of Brønsted acid sites. It was observed that different length of co-surfactant alkyl-chain has resulted in different degree of oil penetration into the microemulsion system which subsequently triggered in various inter-dendrimer distances and amount of incorporated silica species. Hence, the altered physicochemical properties led to the difference in catalytic performance due to the presence of different number of Brønsted acid sites.

Postsynthesis of hierarchical core/shell ZSM-5 as an efficient catalyst in ketalation and acetalization reactions

Hierarchical core/shell Zeolite Socony Mobil-five (ZSM-5) zeolite was hydrothermally postsythesized in the solution of NaOH and diammonium surfactant via a dissolution-reassembly strategy. The silica and alumina species were firstly dissolved partially from the bulky ZSM-5 crystals and then were in situ reassembled into the MFI-type nanosheets with the structure-directing effect of diammonium surfactant, attaching to the out-surface of ZSM-5 core crystals. The mesopores thus were generated in both the core and shell part, giving rise to a micropore/mesopore composite material. The micropore volume and the acidity of the resultant hybrid were well-preserved during this in situ recrystallization process. Possessing the multiple mesopores and enlarged external surface area, the core/shell ZSM-5 zeolite exhibited higher activity in the ketalation and acetalization reactions involving bulky molecules in comparison to the pristine ZSM-5.

Silica treatment technologies in reverse osmosis for industrial desalination: A review

Reverse osmosis (RO) is the main process of current industrial desalination, and its performance is affected by the quality of water source. Natural water contains a certain level of silica, which is originated from metal silicate in the earth crust. Due to its complexity, silica fouling is difficult to control, which often causes less efficient design of RO system for safe operation. In the present work, we review the current state of silica treatment technology in RO desalination. Silica chemistry is investigated in standpoint of the scale formation mechanism among multiple forms of silica species and its synergistic interaction with other foulants such as organic matter. Then, pretreatment methods to remove silica in the RO feed water are outlined. They include softening/coagulation, seed precipitation/aggregation, tight ultrafiltration, ion exchange, adsorbents media, and electro coagulation. We finally highlight the mitigation of RO fouling under silica rich conditions, whose concept can be implemented in different ways of antiscalant dosing, high/low pH operation, and intermediate softening of the RO concentrate, respectively. This review will provide comprehensive information and insight about the optimal operation of industrial RO susceptible to silica fouling.

Time resolved alkali silicate decondensation by sodium hydroxide solution

Silica is by far the chemical compound the most widespread and used around the world: as a raw product in the buildings and roads industry, as concrete, or as a processed product in the manufacture of glass, ceramics or zeolites. In alkali silicate solutions—often used to synthesize those materials—a complex interplay of decondensation and condensation processes leads to the restructuring of silicate clusters at the atomic scale on a short time-scale. We were able to deconvolute these effects by combining time resolved small angle x-ray scattering, nuclear magnetic resonance, and parallel tempering simulations. We investigated the impact of a dilution by pure water or by a sodium hydroxide solution on the speciation and size of the dissolved silicates in solution. Herein, we show that the silicate clusters are not affected by dilution, suggesting that sodium cations protect the silicate clusters from hydrolysis. Decondensation is triggered by hydroxide ions that weaken and break Si–O bonds. Alongside the decondensation, the evolution of the computed protonation state of the silica species indicates a change in the interaction potential. Our results pave the way towards the investigation at the atomic scale of more complex systems implying alkali silicate solutions in condensation process by the addition of calcium or aluminum to synthesize aluminosilicate binders, hydrogels or zeolites.

Synthesis of Ce/SiO2 Composited Cross‐Linked Chitosan Flocculation Material and Its Application in Decolorization of Tartrazine Dye

AbstractCe/SiO2 composited cross‐linked chitosan (C‐CTS‐S), SiO2 composited cross‐linked chitosan (CTS‐S) and Ce composited cross‐linked chitosan (C‐CTS) flocculation materials are successfully synthesized. The structure along with the decolorization performance and mechanism of treating tartrazine dye wastewater are studied. The results show that the prepared materials are new composites rather than the mixture of the raw agents. Some silica species embed in the matrix or stay on the surface of chitosan (CTS) during the compositing process, and form hydrogen bonds with –NH2 or –OH of CTS. Besides, Ce participate coordination with –NH2 and –OH of CTS. C‐CTS‐S has disorder, unobvious porous and loose sheet‐like structure with smaller particles and positive charge. It shows high performance of tartrazine dye decolorization over a wide range of pH, and produces little sewage sludge after flocculation, providing a favorable condition for later processing. In addition, the possible decolorization mechanism is mainly electroneutralization adsorption and the synergistic effect of deposition netting and bridge aggregation.

Silica Removal Using Magnetic Iron-Aluminum Hybrid Nanomaterials: Measurements, Adsorption Mechanisms, and Implications for Silica Scaling in Reverse Osmosis.

Composite magnetic aluminum hydroxide at iron oxide nanomaterials, Al(OH)3@Fe3O4, with a well-defined core-shell structure, were used as pretreatment adsorbents for the removal of silica in brackish water. The Al(OH)3 outer shell confers silica adsorption capacity, and the superparamagnetic Fe3O4 core allows material separation and magnetic recovery. The as-prepared nanomaterials (2 g L-1) remove ∼95 and ∼80% silica from Si-rich solutions with 0.5 and 2 mM initial silica concentrations, respectively. Regeneration under basic conditions was evaluated, and post-adsorption treatment with 0.05 M NaOH yielded optimal material reusability. After four regeneration cycles, the Al(OH)3@Fe3O4 nanomaterials retain their magnetic property while still being able to remove ∼40% silica from solutions at an adsorbent concentration of 2 g L-1. The mechanism of silica adsorption onto the surface of the nanomaterials was probed using several spectroscopic techniques. ATR-FTIR (attenuated total reflection-Fourier transform infrared) integrated with two-dimensional correlation analysis shows that silica species vary from Q2 to Q4 with adsorption time corresponding to silica polymerization. 29Si solid-state NMR spectra show an upfield chemical shift displacement of the Q2 signal, which indicates the formation of Q4 units, suggesting silica polymerization onto the Al(OH)3 shell. In addition, a laboratory-scale reverse osmosis setup was used to evaluate Al(OH)3@Fe3O4 as pretreatment materials for silica removal. Results show that silica scaling was significantly alleviated, and water recovery was enhanced when feed waters were pretreated with the magnetic nanomaterials. Taken together, our study highlights the promise of magnetic Al(OH)3@Fe3O4 nanomaterials in treating brackish water and achieving higher water recovery for inland desalination.

Nitrogen‐doping microporous adsorbents prepared from palm kernel with excellent CO2 capture property

In post‐combustion CO2 capture, waste biomass is a favourable precursor to prepare porous carbons due to its low cost, renewability, and unique microstructures. This study presents a facile method for preparing N‐doping porous carbons. Palm kernel shell was selected as carbon precursor, and its inherent silica species acted as a natural template to form hierarchical pores. The obtained samples exhibit predominant characteristics with highly developed micropores and a high N content providing an important contribution to CO2 adsorption capacity, which can reach up to 5.29 and 2.30 mmol/g under 100 kPa at 25 and 60 °C, respectively. Moreover, the resultant porous carbons also exhibit excellent cycling stability after 20 cycles. Furthermore, the activation mechanism was investigated by the quantitative thermogravimetry‐mass spectrometry (TG‐MS) method.

Time evolution of the framework structure of SBA-15 during the aging process

In this paper, we discuss time evolution of the framework structure of SBA-15 during the aging process. We synthesize SBA-15 particles with different aging periods and investigate them using x-ray diffraction (XRD), N2 adsorption, and high-resolution scanning electron microscopy (HR-SEM) measurements. A combined study of XRD and N2 adsorption measurements reveals a very interesting relationship, wherein the sum of pore radius and wall thickness of SBA-15 during the aging process is always equal to the radius of the cylindrical P123 micelle, which describes the structural development of SBA-15 during the aging process: densification of the silica wall not only increases the pore radius and decreases the wall thickness, but also enlarges the distance between adjacent micelles by extruding the micelle corona from the wall. HR-SEM measurements show that the top surface of SBA-15 changes greatly during the aging process, and especially within the first 12 h. Most of the external surface parallel to the c-axis of SBA-15 is covered with silica species, and only disordered meso-windows are observed at the beginning of the aging process. As aging proceeds, the disordered mesopores disappear, and finally, periodic trenches remain after aging at 403 K for over 12 h. We also discuss the structural change in the surface perpendicular to the c-axis and demonstrate that these changes in the surface structure of SBA-15 can also be explained by the densification of the silica wall.

Pseudomorphic transformation and post synthetic modification of amorphous silica for CO2 sorption applications

Template directed porous silica has shown significant promise in numerous applications such as gas sorption, catalysis and pharmaceutical drug delivery. Mesoporous silicas such as MCM-41, SBA-15 and KIT-6 have been widely reported; however, thus far these materials require long synthesis processes and expensive starting materials. As an alternative, pseudomorphic transformations can convert low-grade amorphous silica into more useful materials. Herein, we demonstrate the effect of pseudomorphic transformations upon the properties of non-porous silica spheres. Surface area can be increased from < 2 m2 g−1, for non-porous silica spheres, to 724 m2 g−1 for the resulting pseudomorphic species. Silica species were subsequently functionalised with aminopropyltriethoxysilane (APTES) and tetraethylenepentamine (TEPA) via post-synthetic modification. Post-synthetic modification was found to significantly enhance the CO2 sorption performance of the silica species with CO2 sorption capacities of up to ca. 92 mg CO2 g−1 achieved, compared to a maximum uptake of 18 mg CO2 g−1 for the non-porous silica variants.

Hierarchical SAPO-11 molecular sieve-based catalysts for enhancing the double-branched hydroisomerization of alkanes

To convert linear alkanes into double-branched isomers, a novel catalyst was prepared on the basis of hierarchical silicoaluminophosphate-11 (SAPO-11) molecular sieves with the large external surface area (ESA) and the high amount of medium and strong Brønsted (MSB) acid sites. The hierarchical SAPO-11 molecular sieves were synthesized in water with low-temperature crystallization using supercritical carbon dioxide (ScCO2) and the triblock copolymer polyoxyethylene-polyoxypropylene-polyoxyethylene (F127, EO106PO70EO106) as combined mesoporous templates. During the crystallization of hierarchical SAPO-11, the addition of F127 promotes more ScCO2 to be dissolved in water, and the micelles produced by F127 are dilated by ScCO2 to match the SAPO-11 fragments in size. In addition, ScCO2 makes silica species well dispersed in the aluminum phosphate (AlPO4) framework of the as-synthesized SAPO-11, which forms small silica islands (SIs); the small SIs produce a high relative concentration of Si (nAl) (n = 1–3), which increases the number of MSB acid sites. As a result, the as-synthesized SAPO-11 exhibits the ESA of 207 m2/g and the amount of MSB acid sites of 59.5 μmol pyridine/g, which are more than those of the conventional microporous SAPO-11 (87 m2/g and 38.7 μmol pyridine/g) and the counterpart synthesized in ScCO2-water (159 m2/g and 48.6 μmol pyridine/g) or F127-water (117 m2/g and 39.2 μmol pyridine/g). The large ESA and the high amount of MSB acid sites over the as-synthesized SAPO-11 provide accessible active sites for the double-branched hydroisomerization of alkanes. The as-synthesized SAPO-11-based catalyst displays the selectivity of 33.5% to double-branched isomers and the cracking selectivity of 8.0%.