Incorporation of Vanadium in Mesoporous MCM-41 and Microporous AFI Zeolites

Selective C–C Bond Cleavage in Diols and Lignin Models: High-Throughput Screening of Metal Oxide-Anchored Vanadium in Mesoporous Silica

The development of selective and robust heterogeneous oxidation catalysts is an enabling technology for conversion of biomass-derived platform chemicals. Vanadium active sites were incorporated into the structure of mesoporous silica via an ultra-fast, one-pot synthesis method based on microwave-assisted heating. In addition, Al/Ti/Zr/Ce anchoring ions were introduced in order to minimize vanadium leaching and better control its dispersion. The supported V-(Al/Ti/Zr/Ce)-MCM-41 composite materials were assessed as catalysts for aerobic C–C bond cleavage of simple models for lignin (1,2-diphenyl-2-methoxyethanol) and sugar-derived polyalcohols (meso-hydrobenzoin). The TiIV ions proved to be the best anchors to prevent V leaching, while AlIII and ZrIV ions were the best to improve selective conversion of the substrates. The active sites in these catalysts are shown to be 2D VOx layers stabilized on the anchors. In a screen of twelve solvents, weakly polar solvents like toluene were found to be most suitable for this reaction, as was environmentally friendly ethyl acetate. The above properties, together with the high selectivity for C–C bond cleavage, advocate for a heterogeneous catalytic pathway, intrinsically different from that reported previously for molecular oxovanadium (V) catalysts.

Loading of Cisplatin into Mesoporous Silica Nanoparticles: Effect of Surface Functionalization

Cisplatin ( cis-diaminedichloroplatinum(II), CDDP) plays a crucial role in the treatment of various malignant tumors. However, its clinical efficacy and applicability are restricted by issues of toxicity and resistance. Here, for drug delivery purposes, the outer surface of MCM-41 mesoporous silica nanoparticles (MSNs) was functionalized with poly(ethylene glycol) ( M_w = 10 000 g/mol) or low-molecular-weight ( M_w = 1800 g/mol) branched polyethyleneimine (PEI). Given the strong affinity of sulfur for platinum, thiol-functionalized MSNs were synthesized for comparison by co-condensation with (3-mercaptopropyl)triethoxysilane. CDDP loading was performed either by adsorption or impregnation in aqueous media without the use of dimethyl sulfoxide as a solubilizer. CDDP loading capacities obtained by impregnation were higher than those obtained by adsorption and varied from 3.9 to 16.1 wt %, depending on the functional group. Loaded nanomaterials were characterized by scanning electron microscopy, scanning transmission electron microscopy-high-angle annular dark-field, and Raman spectroscopy. Depending on the functional groups, platinum-based species were either dispersed in the nanomaterials as nanocrystals or uniformly distributed as molecular species. The spectral signature of CDDP was strongly modified when platinum species were homogeneously distributed within the nanomaterials. Preliminary drug release studies performed at 37 °C showed that the behavior of CDDP-loaded MSNs strongly depends on the nature of the present functional groups. Among the functionalization routes investigated in this paper, PEI-based functionalization showed the most promising results for further applications in controlled drug release with the absence of burst release and a sustained release over 72 h.

Effect of Cerium Precursor in the Synthesis of Ce-MCM-41 and in the Efficiency for Liquid-Phase Oxidation of Benzyl Alcohol

Understanding the effects of synthetic parameters in the catalytic activity of heterogeneous catalysts is of utmost importance when aiming for optimal reaction conditions. Hence, we disclose in this work the synthesis and characterization of cerium-modified MCM-41 materials. In addition, it was observed for the first time, differences in catalytic activity when using different cerium synthetic precursors: CeCl3·7H2O and Ce(NO3)3·6H2O (Ce-MCM-Cl and Ce-MCM-NO3, respectively). A mechanism for cerium incorporation in MCM-41 was proposed, where [Ce(OH)3] species were hydrogen bonded to silicate anions, forming framework Ce-O-Si bonds during condensation and, consequently, causing distortion of the typical hexagonal mesophase. It was also observed that Ce(OH)3 formed aggregated layers with template assemblies during synthesis, resulting in non-framework CeO2 species on the MCM-41 surface after calcination. These CeO2 species were preferentially formed for Ce-MCM-NO3 and were attributed to the nitrate ions’ strong binding to template molecules. In the solvent free liquid-phase oxidation of benzyl alcohol (BzOH), Ce-MCM-Cl achieved better BzOH conversions and benzaldehyde (BzD) yields, while Ce-MCM-NO3 offered increased BzD selectivity. The catalysts’ reusability was also studied over three catalytic runs, where Ce-MCM-NO3 was more resistant than Ce-MCM-Cl towards deactivation. The observed catalytic behavior shows the importance of metal precursors in the obtainment of materials with desirable final properties.

A comparison study between V-SBA-15 and V-KIT-6 catalysts for selective oxidation of diphenylmethane

Vanadium incorporated mesoporous SBA-15 and KIT-6 catalysts were prepared by a direct hydrothermal method under mild acidic reaction conditions.

The black rock series supported SCR catalyst for NO x removal

Black rock series (BRS) is of great potential for their plenty of valued oxides which include vanadium, iron, alumina and silica oxides, etc. BRS was used for directly preparing of selective catalytic reduction (SCR) catalyst by modifying its surface texture with SiO₂-TiO₂ sols and regulating its catalytic active constituents with V₂O₅ and MoO₃. Consequently, 90% NO removal ratio was obtained within 300-400 °C over the BRS-based catalyst. The structure and properties of the BRS-based catalyst were characterized by the techniques of N₂ adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), H₂-temperature programmed reduction (H₂-TPR), and NH₃-temperature programmed desorption (NH₃-TPD). The results revealed that the BRS-based catalyst possesses favorable properties for NO _x removal, including highly dispersed active components, abundant surface-adsorbed oxygen O_α, well redox property, and numerous Brønsted acid sites. Particularly, the BRS-based catalyst exhibited considerable anti-poisoning performance compared with commercial TiO₂-based catalyst. The former catalyst shows a NO conversion surpassing 80% from 300 to 400 °C for potassium poisoning, and a durability of SO₂ and H₂O exceeding 85% at temperatures from 300 to 450 °C.

High-Visible-Light Photoactivity of Plasma-Promoted Vanadium Clusters on Nanozeolites for Partial Photooxidation of Methanol

Cold VCl₃-plasma is employed for the preparation of highly dispersed vanadium oxide clusters on nanosized zeolite. Different types of zeolites, such as EMT, FAU (z.X), and Beta, are used. The activity of the prepared catalysts is studied in the selective photooxidation of methanol under polychromatic visible and UV irradiations. The physicochemical properties and catalytic performance of plasma-treated zeolite Beta (P-V₂O₅@Beta) catalyst is compared with zeolite Beta (V₂O₅@Beta) and amorphous silica (V₂O₅@SiO₂) impregnated vanadium oxide catalysts. Pure V₂O₅ is used as a reference material. The set of catalytic data shows that plasma-prepared zeolite Beta based catalyst displays the highest activity. Complementary characterization techniques including XRD, N₂-sorption, FTIR, ionic exchange, pyridine adsorption, Raman, NMR, TPR, and EDX-TEM are used to study the impact of the preparation approach on the physicochemical properties and catalytic performance of photocatalysts.

Dispersed Vanadium in Three-Dimensional Dendritic Mesoporous Silica Nanospheres: Active and Stable Catalysts for the Oxidative Dehydrogenation of Propane in the Presence of CO2

The uniform monodispersed vanadium-doped three-dimensional dendritic mesoporous silica nanospheres (nV-MSNSs) were successfully synthesized in a heterogeneous oil-water biphase stratification reaction system and characterized by several state-of-the-art methods. The synthesized nV-MSNSs were applied to the oxidative dehydrogenation of the propane (ODHP) reaction with the presence of CO₂ and exhibited excellent catalytic performances. The results show that the vanadium loading (1.3-8.0 wt %) evidently influences the textural properties, oxidation state, and polymerization degree of vanadium species of nV-MSNSs. The specific surface area (S_BET), pore diameter (D_p), and pore volume (V_p) of nV-MSNSs decrease with the loading of vanadium species. The excessively high vanadium loading leads to the slight connection of nanospheres, but does not affect the assembly and growth of the three-dimensional (3D) dendritic channels. The percentage of highly dispersed vanadium V^V species gradually increases and attains the maximum value for 5.2V-MSNSs with the loading of vanadium and then decreases with further vanadium addition. The higher-polymerized VO_x species gradually generates above 5.2 wt % vanadium content for nV-MSNSs. The lower-polymerized VO_x species appear to be more active than the higher-polymerized VO_x species. Markedly, the 5.2V-MSNSs exhibit the highest catalytic activity with the initial propane conversion of 58% for the ODHP. The excellent catalytic performance can be maintained after eight reaction-regeneration cycles. The silica mesoporous frameworks can be well preserved in the reaction-regeneration cycles; meanwhile, the highly dispersed vanadium oxide also can be fully recovered after in situ regeneration. Hence, nV-MSNS catalysts exhibit outstanding activity and stability, and it would have a promising application in the DH of alkanes.

Partial oxidation of ethylbenzene by H2O2 on VOx/HZSM-22 catalyst

Highly dispersed extra-framework vanadium species mainly led to the oxidation of EB with 17.5% yield and 72.5% selectivity to AP.

Short-range interactions between surfactants, silica species and EDTA⁴- salt during self-assembly of siliceous mesoporous molecular sieve: a UV Raman study

The effects of surfactants, counterions and additive salts on the formation of siliceous mesoporous molecular sieves during self-assembly process were investigated by UV Raman spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The surfactant molecules experience the rearrangement after adding the silica species and adjusting the pH value. The obvious change of the Raman bands related to the surfactants supports a cooperative interaction between surfactant and inorganic species during self-assembly process. The addition of EDTANa(4) to the system induces the interaction between the COO(-) groups of EDTA(4-) and silanol groups of silica and a strong interaction between the EDTA(4-) and the N(+)(CH(3))(3) groups of the surfactant. The above interactions may be the main reason for the salt effect. The new information from the change of the chemical bonds allows for a further analysis to the interactions of different salts between surfactants and silica species at molecular level.

Vanadium-Containing Mesoporous Silica of High Photocatalytic Activity and Stability Even in Water

Vanadium-containing mesoporous silica molecular sieve (V proportional HMS) with tetrahedrally coordinated V-oxide species (VVO4) has been prepared by a modified surfactant-templating method, consisting of an addition of surfactant to a mixture of water, alcohol, and Si and V precursors followed by calcination. The V proportional HMS demonstrates high photocatalytic activity even in the presence of water, while other V proportional HMS's prepared by conventional templating methods and V/HMS prepared by an impregnation method show almost no activity owing to hydrolysis of the VVO4 species. ESR and photoluminescence measurements reveal that the modified templating method creates VVO4 species confined within a silica layer, while other methods create VVO4 species exposed on silica surface. The former VVO4 species are highly stabilized by the confinement within the silica, thus suppressing the hydrolysis. Another notable property of the confined VVO4 species is the higher photocatalytic activity even without water, despite their confined structure. This is explained by higher electrophilicity and longer lifetime of the excited-state VVO4 species (VIVO4*) derived from their distorted structure. The obtained findings suggest potential use of the modified surfactant-templating method for synthesis of stable and recyclable V-containing mesoporous silica with high photocatalytic activity.

Isomorphous Substitution of Transition-Metal Ions in the Nanoporous Nickel Phosphate VSB-5

The transition-metal-incorporated nickel phosphate molecular sieves (TMI-VSB-5) have been hydrothermally synthesized at 453 K in weak basic conditions under microwave irradiation. By means of X-ray diffraction, inductively coupled plasma (ICP), ultraviolet-visible (UV-vis) diffuse reflectance, and Mössbauer spectroscopies, successful isomorphous (at least partial) substitution of transition-metal ions in the VSB-5 framework has been verified. Characterization results show that the framework structure of nanoporous VSB-5 can accommodate a substantial level of isomorphous substitution of transition-metal ions up to about 10, 5, and 3 atom % for Fe, Mn, and V, respectively, in both octahedral nickel sites (Mn and Fe) and tetrahedral phosphorus sites (V). The isomorphous substitution including the replacement mechanism was studied by not only the change of unit cell parameters but also spectroscopic analysis. The unit cell parameters of TMI-VSB-5 including a unit cell volume and a-axis length relied on the ionic radii difference between the incorporated ion and the original framework ions such as Ni or P (RTMI - RNi or RTMI - RP).