Synthesis,characterization and sulfide oxidation activity of vanadyl Schiff base complexes anchored on MCM-41

Vanadyl Schiff base complexes covalently attached on the surface of MCM-41 have been synthesized by anchoring Schiff base and subsequent reaction with VO(acac)₂. XRD, nitrogen adsorption and desorption, UV-visible spectroscopy and FT-IR show that vanadyl Schiff base complexes were successfully anchored on the surface of MCM-41 and the mesopore ordering decreased after the anchoring. The so-prepared heterogeneous catalysts have showed high activity for sulfide oxidation.     

The Role of Nanosize Particles of Uranium Oxide in the Adsorption/Reaction of Methanol Over U3O8/MCM-48: FTIR Study

The surface species formed over MCM-48, U₃O₈ and U₃O₈/ MCM48 catalysts during the adsorption/reaction of methanol were monitored using FTIR spectroscopy, in order to get an insight into the high catalytic activity exhibited by the nanosize crystallites of uranium oxide dispersed in MCM-48. The results of this in situ study revealed that the title catalysts exhibited a distinct behavior for adsorption and subsequent reaction of methanol. Thus, while the room temperature adsorption over bulk U₃O₈ resulted in the formation of formate complex and oxymethylene species, the interaction over MCM-48 resulted in simultaneous and instant formation of surface methoxy groups and dimethyl ether. On the other hand, the exposure of methanol over U₃O₈/MCM-48 under similar conditions resulted in the appearance of intense IR bands due to surface-adsorbed (–OCH₂)_n species, where n1, in addition to those of formate complexes, oxymethylene and methoxy groups. The role of the above-mentioned intermediate species in the formation of different reaction products is discussed in brief.     

Alkynes Hydrogenation over Pd-Supported Catalysts

The liquid-phase stereoselective hydrogenation of phenyl alkyl acetylenics at 298 K and atmospheric pressure on Pd-supported catalysts has been studied. The catalysts were prepared by impregnation of Pd(acac)₂ precursor (1 wt% of Pd) on different siliceous substrates such as amorphous SiO₂, mesoporous MCM-41 and silylated MCM-41. The poisoning effect of lead incorporation on the supported palladium was also studied. All the catalysts displayed high selectivity to cis-alkene isomer, with Pd/MCM-41 being the most active catalyst. Deliberately adding lead to the base, palladium catalysts underwent changes in the selectivity to cis-alkene isomer and a significant drop in the activity. All the solids were characterized by nitrogen adsorption–desorption isotherms at 77 K, TGA, TPR, H₂ and CO chemisorption, XRD, XPS, and TEM.     

Gas transport behavior of DMDCS modified MCM-48/polysulfone mixed matrix membrane coated by PDMS

Mesoporous MCM-48 silica was synthesized by templating method and the structure of particles was characterized by XRD, TEM and N₂ adsorption techniques. The surface modification of particles in order for introducing into PSF matrix was performed by dimethyldichlorosilane (DMDCS) silylation agent. SEM images of as-synthesized and modified MCM-48/PSF MMMs indicate that in the modified MCM-48 silica particles adhered well to the PSF matrix and that the synthesized MMMs were defect free. The incorporation of MCM-48 particles in to the PSF matrix and also surface coating of these MMMs by polydimethylsiloxane (PDMS) were performed. The quality of surface coating was investigated by SEM images and permeability tests. For all gases tested (N₂, CO₂, CH₄ and O₂), the permeabilities increased in proportion to the weight percent of MCM-48 present in the film and the calculated CO₂/CH₄ and O₂/N₂ selectivities of PDMS coated membranes showed enhancement in ideal and actual selectivities both.     

Synthesis of Ni/H-Zr-MCM-48 and their isomerization activity of <Emphasis Type="Italic">n</Emphasis>-heptane

H-Zr-MCM-48 was synthesized by ion exchange from Zr-MCM-48 which was synthesized by hydrothermal method and Ni/H-Zr-MCM-48 was synthesized by impregnation method. MCM-48, Zr-MCM-48 and Ni/H-Zr-MCM-48 were characterized by various physicochemical methods including X-ray diffraction (XRD), N₂ adsorption–desorption, Fourier transform infrared spectroscopy techniques and NH₃ temperature programmed desorption (NH₃-TPD), etc for comparison. XRD, TEM and N₂ adsorption–desorption results suggest that Zr-MCM-48 samples still maintained typical cubic mesoporous framework of MCM-48, with slight decrease of specific surface areas and mesopore orders. MCM-48, Zr-MCM-48 and Ni/H-Zr-MCM-48 were also investigated by n-heptane isomerization as a probe reaction. Compared with MCM-48, Zr-MCM-48 and H-Zr-MCM-18, Ni/H-Zr-MCM-48 catalyst exhibited significantly higher selectivity for the formation of isoparaffin, with lower coke deposition and excellent catalyst stability.     

Synthesis,characterization and catalytic properties of mesoporous MCM-48 containing zeolite secondary building units

Mesoporous aluminosilicate MCM-48 containing zeolite secondary building units in the pore wall has been synthesized in alkaline media with a two-step procedure. The aluminosilicate precursors comprising zeolite secondary building units were first synthesized by carefully controlling reaction conditions and then were assembled using co-templates of gemini surfactant [C₁₈H₃₇N(CH₃)₂(CH₂)₃-N(CH₃)₂C₁₈H₃₇]²⁺ (18-3-18) and triethanolamine (TEA). X-ray Diffraction (XRD) patterns of the as-made samples indicated that highly ordered mesostructured MCM-48 was formed. Transmission Electron Microscopy (TEM) images further verified the formation of MCM-48 with uniform cubic pore channel system having the pore opening diameter of about 25 ?. Compared with the conventionally synthesized MCM-48, the as-synthesized MCM-48 sample showed an adsorption band at 520–600 cm⁻¹ in its FT-IR spectrum, which was assigned to five-membered ring vibration from zeolite structure. This suggested the presence of zeolite building units in the pore wall. N₂ adsorption data showed that the material had a much higher specific surface area (1 200 m²/g) than the conventional MCM-48(1 100 m²/g). Finally, the catalytic performance of the as-made MCM-48 was evaluated by hydrogenation dealkylation reaction of heavy aromatic hydrocarbons. Catalytic results showed that the as-made MCM-48 catalyst exhibited higher conversion than the conventional MCM-48 catalyst. The as-made mesostructured MCM-48 may have a potential catalytic application in the conversion of bulky molecules. Translated from Journal of Fuel Chemistry and Technology, 2006, 34(1): 105–108 [译自: 燃料化学学报]     

Synthesis and characterization of nanocomposite MCM-48-PEHA-DEA and its application as CO2 adsorbent

Three nanocomposites containing MCM-48-35PEHA-15DEA (35 and 15 as weight percent of amine addition), MCM-48-30PEHA-20DEA and MCM-48-25PEHA-25DEA of mesoporous silica MCM-48 modified by the mixture of pentaethylenehexamine (PEHA) and diethanolamine (DEA) have been synthesized and used to study the adsorption of carbon dioxide (CO₂). They are characterized by low angle x-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Brunauer-Emmet-Teller (BET) analysis. MCM-48-35PEHA-15DEA (as optimized adsorbent) shows CO₂ adsorption capacity of 0.51 (m·mol CO₂/g-adsorbent) at 1 bar and 298 K, much higher than CO₂ adsorption capacity on polyethyleneimine, pyrrolidinepropyl and polymerized aminopropyl loaded MCM-48.     

Adsorptive separation of carbon dioxide by polyethyleneimine modified adsorbents

Utilization of carbon dioxide (CO₂) has become an important global issue due to significant and continuous rise in atmospheric CO₂ concentrations. To find a potential solution, two types of mesoporous materials, MCM-41 and MCM-48, were synthesized and impregnated with 30, 50 and 70 wt% of polyethyleneimine (PEI) in methanol to evaluate the performance of the materials in terms of CO₂ adsorption. The materials were characterized by XRD, TGA, FTIR, TEM, SEM, N₂-physisorption and BET techniques. All the PEI-loaded materials exhibited substantially higher reversible CO₂ adsorption-desorption behaviors with >99% recovery. The above study proved that MCM-48 is a better material as compared to MCM-41 for loading of PEI. The material with 50 wt% loading of PEI on MCM-48, showed maximum adsorption of 248 mg/g-PEI at 80 °C which is about 30 times higher than that of MCM-48 and about 2.3 times that of pure PEI.     

Preparation of highly dispersed TiO2 in hydrophobic mesopores by simultaneous grafting and fluorinating

TiO₂ photocatalysts highly dispersed in the MCM-41 mesoporous silica material were synthesized using two different TiO₂ precursors of TiF₄ and (NH₄)₂TiO(C₂O₄)₂. The catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption, transmission electron microscopy (TEM), UV–vis absorption, X-ray photoelectron spectroscopy (XPS), and Ti K-edge X-ray absorption fine structure (XAFS). The hydrophobic properties and catalytic activities of photocatalysts with different TiO₂ precursors and loading amount were examined by adsorption and degradation of iso-butanol diluted in water. The results showed that the TiO₂ loaded MCM-41 prepared from TiF₄ exhibited higher photocatalytic activity than from (NH₄)₂TiO(C₂O₄)₂. The fluorine-modified hydrophobic pore walls formed in the impregnation process using TiF₄ as well as highly dispersed TiO₂ nanoparticles play a crucial role for the high photocatalytic efficiency.     

Highly effective organometallic‐mediated radical polymerization of vinyl acetate using alumina‐supported Co(acac)2 catalyst: A case study of adsorption and polymerization

An alumina support system for cobalt^(II) acetylacetonate (Co(acac)₂) catalyst was studied for the cobalt‐mediated radical polymerization (CMRP) of vinyl acetate (VAc). We report a simple but efficient technique to produce this supported catalysts through the adsorption of Co(acac)₂ on the surface of alumina particles. Moreover, kinetic and thermodynamic study of Co(acac)₂ adsorption on the alumina support were conducted and the influence of effective parameters were investigated. It was found that using alumina‐supported Co(acac)₂ for radical polymerization of VAc yields polymers with controlled molecular weight, narrow molecular weight distribution, and high purity. For the alumina‐supported CMRP, changing the polymerization mechanism and domination of termination pathway compared to degenerate transfer pathway resulted in a 2.5 times increase in polymerization rate (k_ap) and a drop in induction time while maintaining a good control of the VAc polymerization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46057.     

Molecular Dispersion of Metal Complexes within Zeolitic Solids: An Alternative Way to Prepare Supported MOx Catalysts

Molecular Designed Dispersion (MDD) of metal complexes on a highly porous support is a novel synthesis method to prepare high quality heterogeneous catalysts. The process basically consists of two steps: (1) the anchoring of the complex onto the support in a controlled way and (2) the mild oxidation of the grafted complex towards catalytically active metal-oxide surface structures.This article presents two typical case studies: (1) the incorporation of cationic Cu-complexes in a H-ZSM-5 zeolite from the liquid phase and (2) the gas phase modification of pure silica MCM-48, using the VO(acac)₂ complex. In both cases, superior catalysts are obtained. Detailed chemical, physical and catalytical analyses of these catalysts are discussed in the text. Comparison is made with analogous catalysts, prepared by conventional methods.     

Effect of surface Na+ or K+ ion exchange on hydrodesulfurization performance of MCM-41-supported Ni–W catalysts

Ni–W hydrodesulfurization (HDS) catalysts supported on MCM-41 synthesized from two different silica sources (sodium silicate hydrate and tetraethylorthosilicate) as well as on Na⁺ or K⁺ ion exchanged MCM-41 were prepared. These catalysts were used to investigate the influence of the surface properties of MCM-41 on the performance of HDS catalysts with DBT as the model molecule. The XRD and N₂ adsorption results indicated that the MCM-41 prepared from tetraethylorthosilicate (MCM-41(T)) exhibited the best structural properties. The mesostructure of MCM-41 synthesized from sodium silicate (MCM-41(S)) remained after ion exchange with Na₂C₂O₂ and K₂C₂O₂. Both pyridine FT-IR and Hammett indicators showed that only MCM-41(S) possessed some Brönsted and Lewis acid sites. Ni–W/MCM-41(S) showed the highest HDS and hydrogenation activities. The introduction of Na⁺ and K⁺ strongly inhibited the hydrogenation activity of Ni–W/MCM-41(S) but enhanced its hydrogenolysis activity. UV–vis and TPR studies indicated that the introduction of Na⁺ and K⁺ into MCM-41(S) may lead to the segregation of surface Ni species and may hinder the reducibility of the supported Ni–W oxides. Spillover hydrogen, which is “trapped” by Na⁺ and K⁺, may play an important role in the HDS activity and selectivity of Ni–W catalysts.     

Characteristics and photocatalytic degradation of methyl orange on Ti-RH-MCM-41 and TiO<Subscript>2</Subscript>/RH-MCM-41

Our purpose was to synthesize, characterize and test photodegradation of methyl orange on two catalysts containing 10 wt% titanium supported on mesoporous MCM-41 synthesized with rice husk silica. The first catalyst was Ti-RH-MCM-41 prepared by adding tetrabutyl orthotitanate (TBOT) in a synthetic gel of RH-MCM-41, and the second catalyst was TiO₂/RH-MCM-41 prepared by grafting TBOT on the preformed RH-MCM-41. The mesoporous structures were observed on both catalysts and they had surface area of 1,073 and 1,006 m²/g. The Ti in Ti-RH-MCM-41 was in the form of Ti(IV) with tetrahedral geometry residing in the mesoporous structure. This form was less active for photodegradation of methyl orange than the other one. The Ti in TiO₂/RH-MCM-41 was anatase titania with octahedral geometry located outside the mesoporous framework. This form was more an active phase for the photodegradation and the reaction parameters on this catalyst were further investigated. The optimum catalyst weight to methyl orange volume ratio was 5 g/L and the optimum initial concentration of the dye was 2.0 ppm. The degradation rate obeyed pseudo-first order and the adsorption of methyl orange on TiO₂/RH-MCM-41 obeyed Langmuir isotherm.     

Oxidation state of platinum clusters during the reduction of NOx with propene and propane

The oxidation state of platinum supported on mesoporous SiO₂ and Al₂O₃ with MCM-41 type structure during the reduction of NO_x with propene or propane was investigated using in situ X-ray absorption spectroscopy. Platinum supported on MCM-41 (SiO₂) was reduced at low and oxidized at high reaction temperatures when propene was used as reducing agent, while it was found to be always oxidized in Pt/MCM-41 (Al₂O₃). When propane was used as reducing agent significant NO conversion was not observed over Pt/MCM-41 (SiO₂) and on both supports platinum was in an oxidized state. At the successive adsorption of the reactants, the prereduced catalysts were oxidized after NO adsorption and reduced after addition of the hydrocarbons. Addition of oxygen re-oxidized the catalysts, while the presence of water vapor did not influence the oxidation state.     

MCM-48 supported chromium catalyst for trichloroethylene oxidation

MCM-48 supported chromium (Cr/MCM-48) catalyst was prepared by introduction of chromium chloride during gel-preparation for the hydrothermal synthesis of MCM-48. Based on the N₂ adsorption/desorption isotherm, BET, pore size distribution, XRD, FTIR, TGA, and DTA data, Cr/MCM-48 was found to have high surface area (832 m²/g), uniform pore size distribution (24 Å), mesoporous structures similar to MCM-48 itself, and incorporation of about 3 wt% of Cr component in the mesoporous framework. Cr/MCM-48 was very active for the oxidative destruction of trichloroethylene (TCE), which is a typical chlorinated volatile organic compound (CVOC); 100% conversion of TCE was achieved at 350°C. Based on the TGA of trichloroethylene/water adsorption study, it was found that MCM-48 had high adsorption capacity (>0.25 g TCE/g catalyst). In addition, the hydrophobicity of the adsorptive properties of Cr/MCM-48 materials could be modified. The high adsorption capacity and catalytic activity of Cr/MCM-48 material make it suitable for adsorption/catalysis bifunctional systems for energy-saving treatment of low concentration of VOC or CVOC.     

Chromium catalysts supported on mesoporous silica for ethylene tetramerization: Effect of the porous structure of the supports

Supported chromium catalysts were prepared by loading Cr(acac)₃ and N-isopropyl bis(diphenylphosphino)amine (PNP) onto methylaluminoxane-modified MCM-41 and SBA-15. The structure of supported catalysts was characterized and the influence of the pore structure of supports on the reactivity for ethylene tetramerization was investigated. The results revealed that the chromium was immobilized on the mesoporous silica in different supported patterns, which was affected by the pore size of the supports and affected catalyst performance. The highest selectivity toward 1-octene was provided by the SBA-15-supported Cr(acac)₃/PNP catalyst, and this value was higher than that of the homogeneous analogs.     

Ordered Mesoporous Silica (OMS) Supported Vanadium Nitride and Carbide Catalysts

Nanostructured vanadium nitride and carbide catalysts were prepared by the nitridation and carburization of vanadium oxide supported on M41S materials (MCM-41 and SBA-15) and activated carbon. The oxide precursors, V₂O₅/M41S, were obtained in three different synthesis strategies using “in situ” and “ex situ” incorporation of vanadia precursors (V(acac)₃) into the mesoporous host. For the oxide precursors specific surface areas exceeding 1,200 m² g⁻¹ were achieved. After nitridation a slight decrease of surface area was observed. All VN catalysts show a high activity in propane dehydrogenation with a selectivity exceeding 80% towards propene. Impregnation and nitridation conditions have profound influence upon the catalytic activity. The highest activity was observed for VN supported on NORIT A.     

Preparation of dendrimer polyol/mesoporous silica nanocomposite for reversible CO2 adsorption: Effect of pore size and polyol content

This paper focuses on the synthesis of polyol/MCM-48 nanocomposite materials with different percentages of polyalcohol dendrimer H20. The obtained materials were used for CO₂ adsorption. CO₂-TPD analysis showed that the samples containing 1 and 3 wt% of H20 dendrimer have low CO₂ adsorption capacity due to the occupation of active sites, The sample prepared with 0.5 wt% of H20 dendrimer exhibited higher adsorption capacity and thermal stability. The affinity toward CO₂ was found to be mainly due to the presence of organic moiety within the MCM-48 pores.     

Zr (IV)-ninhydrin supported MCM-41 and MCM-48 as novel nanoreactor catalysts for the oxidation of sulfides to sulfoxides and thiols to disulfides

Modification of MCM-41 and MCM-48 mesoporous materials with bonded aminosilane species, Schiff base preparation by ninhydrin and finally complexation with zirconium, has attracted much attention in order to design catalyst with advanced applications in the oxidation of sulfides to sulfoxides and thiols to disulfides in the presence of hydrogen peroxide. In all oxidation of sulfides to sulfoxids 0.4 mL H₂O₂ used as oxidant in the presence of Zr(IV)-ninhydrin supported MCM-41 (0.01 g) or Zr(IV)-ninhydrin supported MCM-48 (0.005 g) at room temperature and solvent-free condition. Also the best conditions for oxidation of thiols to disulfides with 0.4 mL H₂O₂ were 0.005 g Zr(IV)-ninhydrin supported MCM-41 or Zr(IV)-ninhydrin supported MCM-48 at room temperature and in ethanol. These catalysts are characterized by SEM, XRD, TGA, FT-IR, EDS, ICP and BET analysis. Also the Turn over frequency (TOF) and Turn over number (TON) of catalysts are calculated. Obtained results by these heterogeneous catalysts revealed several advantages including short reaction times, simple workup, easy isolation and reusability.     

MCM-41 supported CuO/Bi2O3 nanoparticles as potential catalyst for 1,4-butynediol synthesis

CuO/Bi₂O₃ (CuO/Bi₂O₃/MCM-41) nanoparticles supported on MCM-41 were synthesized by a facile impregnation method. The products were characterized by nitrogen adsorption/desorption, X-ray diffraction (XRD), H₂ temperature programmed reduction (H₂-TPR) and scanning electron microscopy (SEM). XRD patterns indicated the presence of crystalline CuO and Bi₂O₃ phase for CuO/Bi₂O₃/MCM-41 catalyst. TPR results revealed CuO nanoparticles were dispersed well on MCM-41. SEM results showed that the nanoparticles were located on the MCM-41. The activity of the catalysts towards ethynylation of formaldehyde for 1,4-butynediol synthesis was evaluated at atmospheric pressure. Compared with unsupported CuO/Bi₂O₃ and commercial Cu/Bi-based catalyst, CuO/Bi₂O₃/MCM-41 catalyst showed maximum conversion (51%) and selectivity (94%) towards 1,4-butynediol. The results show that CuO/Bi₂O₃ catalysts supported on MCM-41 have potential for 1,4-butynediol synthesis in industrial application.