Synthesis of onion-like mesoporous silica from sodium silicate in the presence of α,ω-diamine surfactant

Mesoporous silicas with vesicular and onion-like morphologies were assembled through hydrogen-bonding pathway from sodium silicate as silica source and electrically neutral α,ω-diamine, Jeffamine D2000 surfactant (H₂NCH(CH₃)CH₂[OCH₂CH(CH₃)]₃₃NH₂) as template in aqueous media at different synthesis temperatures (25, 60 and 100 °C). Assembling the material at 100 °C afforded onion-like core shell mesoporous silica, while at relatively lower temperature, e.g. 25 and 60 °C, multilamellar vesicles were obtained. Mesoporous silica with onion-like morphology was also obtained by a two-step synthesis involving an aging period of 20 h at room temperature followed by a hydrothermal stage (1–12 h) at 100 °C. The heavily cross-linked (Q⁴/Q³ ratio of 4.43) onion-like mesophase silica exhibited high hydrothermal stability. The BET surface area, pore volume and KJS (Kruk-Jaroniec-Sayari) pore diameter of the onion-like mesoporous silica were found to be 464 m² g⁻¹, 1.16 m³ g⁻¹ and 7.2 nm, respectively.     

Utilization of aluminum sludge and aluminum slag (dross) for the manufacture of calcium aluminate cement

Four calcium aluminate cement mixes were manufactured from aluminum sludge as a source of calcium oxide and Al₂O₃ and aluminum slag (dross) as a source of aluminum oxide with some additions of pure alumina. The mixes were composed of 35–50% aluminum sludge, 37.50–48.75% aluminum slag (dross) and 12.50–16.25% aluminum oxide. The mixed were processed then sintered at different firing temperatures up to 1500 °C or 1550 °C. The mineralogical compositions of the fired mixes investigated using X-ray diffraction indicated that the fired mixes composed of variable contents of calcium aluminate (CA), calciumdialuminate (CA₂), calciumhexaaluminate (CA₆) in addition to some content of magnesium aluminate spinel (MA). Sintering parameters (bulk density, apparent porosity and linear change) and mechanical properties (cold crushing strength) of the fired briquettes were tested at different firing temperature. Refractoriness of the cement samples manufactured at the optimum firing temperature was detected. Cementing properties (water of consistency, setting time and compressive strength as a function of curing time up to 28 days of hydration) of pasted prepared from the manufactured cement mixes at the selected optimum firing temperatures (1400 °C or 1500 °C) were also tested. Cement mixes manufactured from 45 to 50% aluminum sludge, 37.50–41.25% aluminum slag (dross) with 12.50–13.75% alumina were selected as the optimum mixes for manufacturing calcium aluminate cement since they satisfy the requirements of the international standard specifications regarding cementing and refractory properties as a result of their content of CA (the main hydraulic phase in calcium aluminate cement) and CA₂(the less hydraulic but more refractory phase). Although the recognized high refractoriness of CA₆, its formation affect badly the cementing properties of the other non-optimum mixes.     

A novel sol–gel synthesis of mesoporous ZrO2–MoO3/WO3 mixed oxides

Mesoporous ZrO₂–MoO₃/WO₃ mixed oxides have been synthesized through a novel, convenient one step sol–gel technique. Water soluble molybdate/tungstate and zirconium (IV) carbonate complex have been employed in presence of cationic surfactant, tetradecyltrimethylammonium bromide under basic condition. The synthesized materials have shown high specific surface areas and narrow pore-size distributions which were achieved after optimization of the amount of surfactant. Mesoporous ZrO₂–MoO₃ and ZrO₂–WO₃ mixed oxides have shown specific surface areas of 228 and 275 m² g⁻¹ and pore sizes of 3.65 nm and 4.33 nm, respectively. FTIR and Raman studies prove the formation of hetero bonding in mixed oxides.     

Reactions of cyanamide, dicyandiamide and related cyclic azines in high temperature water

Cyanamide, dicyandiamide, and the related cyclic azines (melamine, ammeline, ammelide, and cyanuric acid) were reacted in water at 100–300 °C in a sealed 316 SS tube (275 bar) for the purpose of characterizing the hydrothermolysis chemistry of cyanamide. The conversion of cyanamide to dicyandiamide dominates at 100–175 °C. At 175–250 °C, when the reaction times are shorter than 15 min, the major pathway is hydrolysis of the cyanamide-dicyandiamide mixture to CO₂ and NH₃. A minor pathway is cyclization to higher azines (melamine, ammeline, ammelide and cyanuric acid). Above about 225 °C, hydrolysis of these cyclic azines to aqueous NH₃ and CO₂ occurs in a relative ratio which depends on the particular cyclic azine, and, to an extent, which increases with temperature. At 300 °C the conversion of all compounds to CO₂ and NH₃ is complete in 10 min. The hydrothermolysis chemistry of cyanamide and urea are compared.     

Electrodeposited Cu–ZnO and Mn–Cu–ZnO nanowire/tube catalysts for higher alcohols from syngas

Cu–ZnO and Mn–Cu–ZnO catalysts have been prepared by electrodeposition and tested for the synthesis of higher alcohols via CO hydrogenation. The catalysts were prepared in the form of nanowires and nanotubes using a nanoporous polycarbonate membrane, which served as a template for the electrodeposition of the precursor metals from an aqueous electrolyte solution. Electrodeposition was carried out using variable amounts of Zn(NO₃)₂, Cu(NO₃)₂, Mn(NO₃)₂ and NH₄NO₃ at different galvanostatic conditions. A fixed bed reactor was used to study the reaction of CO and H₂ to produce alcohols at 270 °C, 10–20 bar, H₂/CO = 2/1, and 10,000–33,000 scc/h g_cat. In addition to methane and CO₂, methanol was the main alcohol product. The addition of manganese to the Cu–ZnO catalyst increased the selectivity toward higher alcohols by reducing methane formation; however, CO₂ selectivity remained high. Maximum ethanol selectivity was 5.5%, measured as carbon efficiency.     

Catalytic reduction of NH4NO3 by NO: Effects of solid acids and implications for low temperature DeNOx processes

Ammonium nitrate is thermally stable below 250 °C and could potentially deactivate low temperature NO_x reduction catalysts by blocking active sites. It is shown that NO reduces neat NH₄NO₃ above its 170 °C melting point, while acidic solids catalyze this reaction even at temperatures below 100 °C. NO₂, a product of the reduction, can dimerize and then dissociate in molten NH₄NO₃ to NO⁺ + NO₃⁻, and may be stabilized within the melt as either an adduct or as HNO₂ formed from the hydrolysis of NO⁺ or N₂O₄. The other product of reduction, NH₄NO₂, readily decomposes at ≤100 °C to N₂ and H₂O, the desired end products of DeNO_x catalysis. A mechanism for the acid catalyzed reduction of NH₄NO₃ by NO is proposed, with HNO₃ as an intermediate. These findings indicate that the use of acidic catalysts or promoters in DeNO_x systems could help mitigate catalyst deactivation at low operating temperatures (<150 °C).     

Al2O3 nanoparticles with and without polyoxometalates as reactive sorbents for the removal of sulphur mustard

Nanoparticles of AP–Al₂O₃ (aerogel produced alumina) have been produced by an alkoxide based synthesis involving aluminum powder, methanol, toluene and water. Thus produced alumina nanoparticles were characterized by N₂-BET, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transformed infra-red spectroscopy and thermogravimetry techniques. The data indicated the formation of nanoparticles of alumina in the size range of 2–30 nm with high surface area (375 m²/g) and microporous–mesoporous characteristics. Thereafter, these nanoparticles were impregnated with polyoxometalates and other reactive chemicals, which have already proven to be effective against sulphur mustard (HD). Adsorptive removal kinetics for HD was monitored by GC–FID (gas chromatograph coupled with flame ionization detector) technique and found to be following pseudo first order reaction kinetics. Among polyoxometalates impregnated alumina nanoparticles based novel mesoporous reactive sorbent systems AP–Al₂O₃ impregnated with 9-molybdo-3-vanadophosphoric acid (10%, w/w) was found to be the most reactive with least half life value (214 min). In addition to this, degradation products of sulphur mustard on prepared mesoporous reactive sorbents were identified using GC/MS technique. Hydrolysis, dehydrohalogenation and oxidation reactions were found to be the route of degradation of sulphur mustard.     

Effect of ethyleneglycol addition on the properties of P-doped NiMo/Al2O3 HDS catalysts: Part I. Materials preparation and characterization

Phosphorous-doped NiMo/Al₂O₃ hydrodesulfurization (HDS) catalysts (nominal Mo, Ni and P loadings of 12, 3, and 1.6 wt%, respectively) were prepared using ethyleneglycol (EG) as additive. The organic agent was diluted in aqueous impregnating solutions obtained by MoO₃ digestion in presence of H₃PO₄, followed by 2NiCO₃·3Ni(OH)₂·4H₂O addition. EG/Ni molar ratio was varied (1, 2.5 and 7) to determine the influence of this parameter on the surface and structural properties of synthesized materials. As determined by temperature-programmed reduction, ethyleneglycol addition during impregnation resulted in decreased interaction between deposited phases (Mo and Ni) and the alumina carrier. Dispersion and sulfidability (as observed by X-ray photoelectron microscopy) of molybdenum and nickel showed opposite trends when incremental amounts of the organic were added during catalysts preparation. Meanwhile Mo sulfidation was progressively decreased by augmenting EG concentration in the impregnating solution, more dispersed sulfidic nickel was evidenced in materials synthesized at higher EG/Ni ratios. Also, enhanced formation of the so-called “NiMoS phase” was registered by increasing the amount of added ethyleneglycol during simultaneous Ni–Mo–P–EG deposition over the alumina carrier. That fact was reflected in enhanced activity in liquid-phase dibenzothiophene HDS (batch reactor, T = 320 °C, P = 70 kg/cm²) and straight-run gas oil desulfurization (steady-state flow reactor), the latter test carried out at conditions similar to those used in industrial hydrotreaters for the production of ultra-low sulfur diesel (T = 350 °C, P = 70 kg/cm², LHSV = 1.5 h⁻¹ and H₂/oil = 2500 ft³/bbl).     

High strength alumina joints via transient liquid phase bonding

Low melting boron oxide, instead of metallic materials in other methods of transient liquid phase bonding, was taken as braze in joining alumina in this paper. Pure boron oxide melts at low temperature and reacts with alumina matrix to form a stable high melting compound. This transient liquid phase bonding has the advantage of producing a ceramic joint for high temperature applications at low processing temperature. In this study, alumina pieces coated with boron oxide layers in various thicknesses were bonded at 800 °C for various times in air under minor loading. The average flexural strength of joints were measured by means of four point bending, while the microstructure of the cross-section and fractured surface was observed by means of scanning electron microscopy. Phases at joints were identified by low angle X-ray diffraction. The maximum flexural strength reaches a value of 155 MPa after joining at 800 °C for 15 h with a 21 μm interlayer. Three compounds, 3Al₂O₃–B₃O₃, 2Al₂O₃–B₃O₃ and 9Al₂O₃–2B₃O₃ have been found at the joint. It is also found that 2Al₂O₃–B₃O₃ whiskers dominate at the joint with the maximum strength.     

Dimethyl ether synthesis via methanol and syngas over rare earth metals modified zeolite Y and dual Cu–Mn–Zn catalysts

A series of zeolite Y modified with La, Ce, Pr, Nd, Sm and Eu were prepared via ion-exchange, and characterized by XRD, FT-IR and NH₃-TPD. It was found that these rare earth metals were encapsulated in the supercage of zeolite Y and resulted in its enhanced acidity. Among them, La-, Ce-, Pr- and Nd-modified zeolite Y exhibited higher activity and stability (than pure HY) for methanol dehydration to dimethyl ether (DME). For DME synthesis directly from CO hydrogenation using the dual Cu–Mn–Zn/modified-Y catalysts, it was found that Cu–Mn–Zn/La–Y and Cu–Mn–Zn/Ce–Y were more active than Cu–Mn–Zn/pure-HY. The conversion of CO on Cu–Mn–Zn/Ce–HY achieved 77.1% in an isothermal fixed bed reactor at 245 °C, 2.0 MPa, H₂/CO = 3/2 and 1500 h⁻¹.     

Selective oxidation of ethane: Developing an orthorhombic phase in Mo–V–X (X = Nb, Sb, Te) mixed oxides

Mo–V–X (X = Nb, Sb and/or Te) mixed oxides have been prepared by hydrothermal synthesis and heat-treated in N₂ at 450 °C or 600 °C for 2 h. The calcination temperature and the presence or absence of Nb determines the nature of crystalline phases in the catalyst. Nb-containing catalysts heat-treated at 450 °C are mostly amorphous solids, while Nb-free catalysts heat-treated at 450 °C and samples treated at 600 °C clearly contain crystalline phases. TPR-H₂ experiments show higher H₂-consumption on catalysts with amorphous phases. Catalytic results in the oxidative dehydrogenation of ethane indicate that the selective production of the olefin is strongly related to the development of the orthorhombic Te₂M₂₀O₅₇ or (SbO)₂M₂₀O₅₆ (M = Mo, V, Nb) phase (the so-called M1 phase), which is mainly formed at 600 °C. This active and selective crystalline phase is characterized to show moderate reducibility and active centers enough for the selective oxidative activation of ethane with the minimum quantity possible of active centers for ethylene activation. In this sense, the best yield to ethylene has been achieved on a Mo–V–Te–Nb mixed oxide.     

Synthesis and properties of a zeolite LEV analogue from the system—Na2O–Al2O3–SiO2–N,N-dimethylpiperidine chloride–H2O

A new structure-directing agent (SDA) was firstly reported for the synthesis of a zeolite LEV analogue. N,N-dimethyl piperidine performed the SDA function, and induced the synthesis of products from a zeolite MOR with 12-ring channels to a zeolite LEV analogue with only 8-ring channels. The zeolite LEV analogue was synthesized from gels with initial compositions (5.0–6.0)Na₂O–Al₂O₃–(10–200)SiO₂–(4.0–8.0)N,N-dimethyl piperidine–400H₂O at 150 °C. The ²⁹Si NMR spectra showed that the relative intensities of the first line at −115 ppm for low Si/Al ratios were lower than that at high Si/Al ratios. Varying ion exchanges led to different acidities in the zeolite LEV analogue, with the acidity of H-LEV-HCl higher than that of H-LEV-NH₃·H₂O. Zeolite H-LEV in hydration of propene showed a higher selectivity of 1-propanol.     

Alumina supported Pt(1%)/Ce0.6Zr0.4O2 monolith: Remarkable stabilization of ceria–zirconia solution towards CeAlO3 formation operated by Pt under redox conditions

A structured Pt(1 wt%)/ceria–zirconia/alumina catalyst and the metal-free ceria–zirconia/alumina were prepared, by dip-coating, over a cordierite monolithic support. XRD analyses and Rietveld refinements of the structural data demonstrate that in the Pt supported catalysts ceria–zirconia is present as a Ce_0.6Zr_0.4O₂ homogeneous solid solution and that the deposition over the cordierite doesn’t produce any structural modification. Moreover no Pt sintering occurs.By comparing the XRD patterns recorded on Pt/ceria–zirconia/alumina and ceria–zirconia/alumina after three redox cycles, it results that Pt, favouring the structural reorganization of the ceria–zirconia into one cubic solid solution, prevents any CeAlO₃ formation. On the contrary, such phase due to the interaction between Ce³⁺ and the alumina present in the washcoat is detected when redox cycles are carried out on the ceria–zirconia metal free.Transmission electron microscopy (TEM) investigations of the redox cycled Pt/ceria–zirconia/alumina catalyst detected ceria–zirconia grains with diameter between 10 and 35 nm along with highly dispersed Pt particles (2–3 nm) strongly interacting with ceria.Scanning electron microscopy (SEM) and EDX analyses, recorded on the redox cycled Pt/ceria–zirconia/alumina washcoated monolith evidence a homogeneous distribution of the active components through the channels even after redox aging.Reduction behaviour and CO oxidation activity are in good agreement with the structural modification of the solid solution induced by the redox cycles and reflect the positive effect of Pt/ceria interaction on the catalytic performances.The effect of redox aging on the NO reduction by C₃H₆, in lean conditions, was investigated over the Pt/ceria–zirconia/alumina monolith. The catalyst shows at low temperature (290 °C) good NO removal activity and appreciable selectivity to N₂.     

3D Ln–Ag (Ln = Nd; Eu) coordination polymers based on isonicotinate and oxalate ligands: Synthesis, crystal structures and luminescence

The self-assembly of isonicotinic acid with metal salts under hydrothermal conditions obtained two new 4d–4f coordination polymers, LnAg(OX)(IN)₂·H₂O (Ln = Nd (1); Eu (2), OX = oxalic acid, IN = isonicotinic acid). The 3D isostructural complexes 1 and 2 are constructed by the assembly of 2D layers, which are built by carboxylate groups of isonicotinic acid and oxalate ligands coordinating to metal centers, with 1D linear linkers completed by silver ions. Furthermore, the luminescent property of complex 2 was investigated.     

Uptake of heavy metal ions from aqueous solution using Mg–Al layered double hydroxides intercalated with citrate, malate, and tartrate

Mg–Al layered double hydroxide (Mg–Al LDH) was modified with organic acid anions using a coprecipitation technique, and the uptake of heavy metal ions from aqueous solution by the Mg–Al LDH was studied. Citrate·Mg–Al LDH, malate·Mg–Al LDH, or tartrate·Mg–Al LDH, which had citrate³⁻ (C₆H₅O₇³⁻), malate²⁻ (C₄H₄O₅²⁻), or tartrate²⁻ (C₄H₄O₆²⁻) anions intercalated in the interlayer, was prepared by dropwise addition of a mixed aqueous solution of Mg(NO₃)₂ and Al(NO₃)₃ to a citrate, malate, or tartrate solution at a constant pH of 10.5. These Mg–Al LDHs were found to take up Cu²⁺ and Cd²⁺ rapidly from an aqueous solution at a constant pH of 5.0. This capacity was mainly attributable to the formation of the citrate–metal, malate–metal, and tartrate–metal complexes in the interlayers of the Mg–Al LDHs. The uptake of Cu²⁺ increased in the order malate·Mg–Al LDH < tartrate·Mg–Al LDH < citrate·Mg–Al LDH. The uptake of Cd²⁺ increased in the order malate·Mg–Al LDH < tartrate·Mg–Al LDH = citrate·Mg–Al LDH. These differences in Cu²⁺ and Cd²⁺ uptake were attributable to differences in the stabilities of the citrate–metal, malate–metal, and tartrate–metal complexes. These results indicate that citrate³⁻, malate²⁻, and tartrate²⁻ were adequately active as chelating agents in the interlayers of Mg–Al LDHs.     

The effect of cationic surfactant and some organic/inorganic additives on the morphology of mesostructured silica templated by pluronics

Tri-block copolymers (poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide), represented as EO_xPO_yEO_x), pluronics (F127 = EO₁₀₆PO₇₀EO₁₀₆, P65 = EO₂₀PO₃₀EO₂₀, P85 = EO₂₇PO₃₉EO₂₇, P103 = EO₁₇PO₅₅EO₁₇, and P123 = EO₂₀PO₇₀EO₂₀) and cationic surfactants (cethyltrimethylammonium bromide (CTAB)), two surfactant systems, form complex micelles that self-assemble into mesostructured particles with distinct morphology depending on the pluronic type, the concentration of the cationic surfactant and the organic–inorganic ingredients in a siliceous reaction media under acidic conditions. The CTAB–P65 and CTAB–P85 systems form spheres, CTAB–P103 and CTAB–P123 systems form wormlike particles, and CTAB–F127 system form single crystals of mesostructured silica particles under very similar conditions. However addition of various salts (such as KCl and NaNO₃) into a CTAB–P103 or CTAB–P123 solution system and cyclohexane and KCl into a CTAB–P85 solution system produces the mesostructured silica spheres and wormlike particles, respectively. By controlling the hydrophilic–hydrophobic character of the pluronics, core–corona interface, by means of additives, such as small organic molecules or salts, one could obtain the desired morphology that is dictated by the shape of the micelles of the pluronic–cationic surfactant complex. The effects of the additives and the formation mechanism of those morphologies have been discussed using spectroscopy (FT-IR and Raman), diffraction (XRD) and microscopy (POM and SEM) data.     

Promotional effect of gold added to palladium supported on a new mesoporous TiO2 for total oxidation of volatile organic compounds

Gold and palladium were supported on a mesoporous TiO₂ for total oxidation of volatile organic compounds (VOCs). Mesoporous high surface area titania support was synthesised using of Ti(OC₂H₅)₂ in the presence of CTMABr surfactant. After removing the surfactant molecules, 0.5 or 1.5 wt% of palladium and 1 wt% of gold were precipitated on the support by, respectively, wet impregnation and deposition–precipitation methods. The activity for toluene and propene total oxidation of the prereduced samples follows the same order: 0.5%Pd-1%Au/TiO₂ > 1.5%Pd/TiO₂ > 0.5%Pd/TiO₂ > 1%Au-0.5%Pd/TiO₂ > 1%Au/TiO₂ > TiO₂. Moreover, a catalytic comparison with samples based on a conventional TiO₂, shows the catalytic advantage of the mesoporous TiO₂ support. The promotional effect of gold added to palladium could be partly explained by small metallic particles (TEM), but meanly by metallic particles made up of Au-rich core with a Pd-rich shell. Moreover, the hydrogen TPR profile of 0.5%Pd-1%Au/TiO₂ shows only the signal attributed to small PdO particles. Gold also implies a protecting effect of the support under reduction atmosphere. Operando diffuse reflectance infrared fourier transform (DRIFT) spectroscopy was carried on and allowed to follow the VOCs oxidation and the formation of coke molecules, but also a metallic electrodonor effect to the adsorbed molecule which increases in the same order as the activity for oxidation reaction. The presence of coke after test was also shown by DTA–TGA by exothermic signals between 300 and 500 °C and by EPR (g = 2.003).     

Mesoporous H3PW12O40-silica composite: Efficient and reusable solid acid catalyst for the synthesis of diphenolic acid from levulinic acid

Mesoporous H₃PW₁₂O₄₀-silica composite catalysts with controllable H₃PW₁₂O₄₀ loadings (4.0–65.1%) were prepared by a direct sol–gel–hydrothermal technique in the presence of triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer. Powder X-ray diffraction (XRD) patterns and nitrogen sorption analysis indicate the formation of well-defined mesoporous materials. With H₃PW₁₂O₄₀ loading lower than 20%, the materials exhibit larger BET surface area (604.5–753.0 m² g⁻¹), larger and well-distributed pore size (6.1–8.6 nm), larger pore volume (0.75–1.2 cm³ g⁻¹), and highly dispersed Keggin unit throughout the materials. Raman scattering spectroscopy studies confirm that the primary Keggin structure remained intact after formation of the composites. As a novel kind of reusable solid acid catalyst, as-prepared H₃PW₁₂O₄₀-silica composite was applied for the synthesis of diphenolic acid (DPA) from biomass platform molecule, levulinic acid (LA), under solvent-free condition, and remarkably high catalytic activity and stability were observed.     

Nanostructured macro-mesoporous zirconia impregnated by noble metal for catalytic total oxidation of toluene

Hierarchical bimodal macro-mesoporous zirconia oxide has been synthesized by a simple method in the presence of CTMABr surfactant. The synthesized zirconia having uniform macropores of 300–600 nm in diameter with wormhole-like mesoporous walls and high surface area was calcined at 400 and 600 °C and impregnated with 0.5 wt.% of palladium and compared with classical 0.5 wt.% Pd/ZrO₂ catalyst for toluene oxidation. The highest activity of 0.5 wt.%/macro-mesoporous zirconia calcined at 600 °C was mainly explained by a rather high Pd dispersion and by H₂-TPR measurements showing a higher quantity of PdO species easily reducible at 0 °C.     

Incorporation of tin in different types of pores in SBA-15: Synthesis, characterization and catalytic activity

Mesoporous Sn-SBA-15 has been synthesized by three different methods such as conventional hydrothermal route, using cocatalyst NH₄F and in the presence of organosilane precursor. All the materials are thoroughly characterized by powder X-ray diffraction (XRD), SEM, TEM, N₂ sorption and surface area measurements, diffuse-reflectance UV–visible and FTIR spectroscopy, TG–DTA and elemental analysis through ICP. Nitrogen adsorption data, XRD patterns, and TEM observations suggests that the textural properties are retained during the isomorphous substitution of silicon by tin. ICP chemical analysis indicates that tin can be substituted in the range of Si/Sn = 69–162. UV–visible spectra of samples synthesized by the cocatalytic approach exhibit unique absorption band at 213 nm characteristics of tin atom substituted in the smaller pores (2–3 nm) located inside the walls of mesopores. Further, an additional band at 224 nm can be assigned to Sn atoms located in the distorted tetrahedral position along the primary mesopores. In contrary, only one absorption band centered at 224 nm is observed for all the samples synthesized by conventional hydrothermal as well as in the presence of organosilane precursor. ¹⁹F NMR spectra confirmed (no signal) the absence of occluded F⁻ ions in the samples made with NH₄F. Observed high catalytic activity in Baeyer–Villiger oxidation and Meerwin–Pondorf–Verly reduction under the liquid-phase conditions suggest the incorporation of a portion of tin in the smaller pores for the Sn-SBA-15 materials synthesized through cocatalyst method.