Metal oxides nanoparticles on SBA-15: Efficient catalyst for methane combustion

Catalysts based on crystalline nanoparticles of Mn and Co metal oxides supported on mesoporous silica SBA-15 have been developed. These materials were characterized by XRD, BET and transmission electron microscopy (TEM) techniques. SBA-15 mesoporous silica was synthesized by a conventional sol–gel method using a tri-block copolymer as surfactant. Supported Mn₃O₄ and Co₃O₄ nanoparticles were obtained after calcination of as-impregnated SBA-15 by a metal salt precursor. The catalytic activity was evaluated in the combustion of methane at low concentration.Co₃O₄/SBA-15 (7 wt.%) exhibits the highest performance among the different oxides. Furthermore, this novel generation of catalysts appeared as active as conventional LaCoO₃ perovskite, usually taken as reference for this reaction. Thanks to its organized meso-structures, SBA-15 material creates peculiar diffusion conditions for reactants and/or products.     

Comparison between unsupported mesoporous Co3O4 and supported Co3O4 on mesoporous silica as catalysts for N2O decomposition

Mesoporous Co₃O₄ (meso-Co₃O₄) and Co₃O₄ nanoparticles supported on mesoporous silica SBA-15 (Co/SBA-15) were prepared by hydrothermal synthesis and an impregnation method, respectively. Although the as-prepared meso-Co₃O₄ had mesopores and a higher surface area comparable to that of Co/SBA-15, its catalytic activity for N₂O decomposition was much lower than that of Co₃O₄/SBA-15. The low catalytic activity of meso-Co₃O₄ mainly stems from the drastic decrease of the meso-Co₃O₄ surface area under the reaction condition used. On the other hand, Co/SBA-15 maintained its high surface area and mesopores with the aid of a robust silica support. This finding indicates that Co₃O₄ supported by a support is much more stable and efficient than meso-Co₃O₄ under N₂O decomposition reaction conditions.     

DRIFTS Study on the Decomposition Mechanism of Mn Acetylacetonates Supported on SBA-15

Manganese oxides supported on mesoporous SBA-15 catalysts have been prepared by molecularly designed dispersion method, using Mn(II) and Mn(III) acetylacetonate organic precursors. XRD and in situ Raman studies demonstrate the formation of highly dispersed Mn₂O₃ and Mn₃O₄ nanoparticles on SBA-15 for the calcined samples. The detailed decomposition mechanism was studied by using in situ DRIFTS. Acetylacetonate ligands are stable up to 573 K and can only be completely removed by oxygen treatment.     

Manganese and cobalt-terephthalate metal-organic frameworks as a precursor for synthesis of Mn2O3, Mn3O4 and Co3O4 nanoparticles: Active catalysts for olefin heterogeneous oxidation

The thermal decomposition of manganese and cobalt-terephthalate Metal-Organic Framework precursors was utilized as a synthetic route for fabrication of Co₃O₄, Mn₃O₄ and Mn₂O₃ nanoparticles. The prepared metal oxide nanoparticles of Co₃O₄, Mn₃O₄ and Mn₂O₃ possess average size diameter of 40, 60 and 80 nm respectively. The findings demonstrate that spinel structure nanoparticles of Co₃O₄ and Mn₃O₄ exhibit efficient catalytic activity toward heterogeneous olefin epoxidation in the presence of tert-butyl hydroperoxide. In addition, Co₃O₄ and Mn₃O₄ nanoparticles illustrated excellent catalytic stability and reusability for nine and four cycles, respectively, toward olefin oxidation.     

Ordered Crystalline Mesoporous Oxides as Catalysts for CO Oxidation

Crystalline mesoporous metal oxides have attracted considerable attention recently, but their catalytic applications have rarely been studied. In this work, a series of crystalline three-dimensional mesoporous metal oxides (i.e., CeO₂, Co₃O₄, Cr₂O₃, CuO, Fe₂O₃, β-MnO₂, Mn₂O₃, Mn₃O₄, NiO, and NiCoMnO₄) were prepared using the mesoporous silica KIT-6 as a hard template. These ordered mesoporous metal oxides with highly crystalline walls were characterized by PXRD, TEM, N₂ adsorption and evaluated as CO oxidation catalysts. These mesoporous materials, except for mesoporous Fe₂O₃, exhibit much higher catalytic activities than their bulk counterparts. In particular, mesoporous Co₃O₄, β-MnO₂, and NiO show appreciable CO oxidation activity below 0 °C, and the catalytic activities of mesoporous β-MnO₂, and NiO are even higher than those of their nanoparticulate counterparts with large surface areas. β-MnO₂ is particularly interesting because it combines low cost and low toxicity with high activity (T ₅₀ = 39 °C).     

Calibrated Co3O4 nanoparticles patterned in SBA-15 silicas: Accessibility and activity for CO oxidation

The catalytic performances in CO oxidation of Co₃O₄ nanoparticles patterned in the porosity of SBA-15 silicas are investigated. Accessibility limitations of the reactants to the catalytic sites are clearly revealed, when the Co₃O₄ nanoparticles are embedded in the SBA-15 pores. Despite these limitations, the synthesised Co₃O₄ nanoparticles exhibit promising CO oxidation properties.     

Calibrated Co3O4 nanoparticles patterned in SBA-15 silicas: Accessibility and activity for CO oxidation

The catalytic performances in CO oxidation of Co₃O₄ nanoparticles patterned in the porosity of SBA-15 silicas are investigated. Accessibility limitations of the reactants to the catalytic sites are clearly revealed, when the Co₃O₄ nanoparticles are embedded in the SBA-15 pores. Despite these limitations, the synthesised Co₃O₄ nanoparticles exhibit promising CO oxidation properties.     

Pd (1?wt%)/LaMn0.4Fe0.6O3 Catalysts Supported Over Silica SBA-15: Effect of Perovskite Loading and Support Morphology on Methane Oxidation Activity and SO2 Tolerance

Catalysts of palladium (1?wt%) deposited over silica SBA-15 supported LaMn_0.4Fe_0.6O₃ perovskite (with perovskite loading of 10, 30 and 40?wt%), characterized by several techniques (BET, SAXS, XRD, TPR) are tested in the combustion of methane. Bulk LaMn_0.4Fe_0.6O₃ with the corresponding supported Pd catalyst are also considered for comparison purpose. Dispersing LaMn_0.4Fe_0.6O₃ oxide over silica SBA-15 improves the activity of the supported palladium catalysts to an extent depending on the perovskite loading. After ageing at 600?°C for 14?h, Pd catalysts supported over SBA-15 loaded with 30 and 40?wt% of LaMn_0.4Fe_0.6O₃, deactivate less as compared to Pd over bulk perovskite. Moreover, during catalytic tests carried out in the presence of 10?vol. ppm SO₂ these catalysts exhibit better sulphur tolerance and higher regeneration capability as compared to the Pd/LaMn_0.4Fe_0.6O₃. The superior performance of such catalysts is attributed to the good dispersion of the LaMn_0.4Fe_0.6O₃ over the SBA-15, with consequent increase of the perovskite surface area with respect to bulk perovskite. In addition, the porous structure of the silica contributes to a better stabilization of the active species against sintering and acts as a chemical sink during the catalyst exposure to SO₂.     

Investigation of the photodegradation properties of iron oxide doped mesoporous SBA-15 silica

Mesoporous silica (SBA-15) and iron oxide incorporated silica (Fe₂O₃-SBA-15) were synthesized by co-operative self-assembly technique. Samples were characterized using nitrogen adsorption–desorption isotherm, electron microscopic and spectroscopic techniques. The results confirm the uniform distribution of pores, presence of metal oxides in the pores as well as in the surface of the mesoporous wall and oxidation state of iron in the Fe₂O₃-SBA-15. The photocatalytic degradation of methylene blue (MB), sulphorhodamine B (SR-B) and methyl orange (MO) by Fe₂O₃-SBA-15 was investigated. It was observed that Fe₂O₃-SBA-15 degraded 98 % of MB, 96 % of SR-B and 99 % of MO within 3 h after exposure to sunlight. SBA-15 does not exhibit any photocatalytic effect. These results demonstrate the potential of Fe₂O₃-SBA-15 for environmental pollution control.     

Novel Colloidal Nanothermite Particles (MnO<Subscript>2</Subscript>/Al) for Advanced Highly Energetic Systems

Nanothermites (metal oxide/metal) are tremendously exothermic and run with self sustaining oxygen content. Manganese oxide is one of the most effective oxidizers for nanothermite applications. This paper reports on the sustainable fabrication of different nanoscopic forms of colloidal manganese oxides including: MnO₂ nanoparticles of 20 nm average particle size and Mn₂O₃ nanorods of 50 nm diameter and 1 µm length. TEM micrographs demonstrated mono-dispersed particles and rods. XRD diffractograms revealed highly crystalline materials. MnO₂ nanoparticles (oxygen content 37 wt%) can offer high oxidizing ability compared with Mn₂O₃ nanorods (oxygen content 30 wt%). The integration of colloidal particles into energetic matrix can offer enhanced dispersion characteristics; consequently stoichiometric binary mixture of MnO₂ and Al nanoparticles were re-dispersed in organic solvent. The integration of developed colloidal nanothermite particles into tri-nitro toluene offered enhanced shock wave strength by 35% using ballistic mortar test. Thanks to nanotechnology which offered sustainable manufacture and subsequent integration of one of the most effective nanothermite particles into highly energetic system.     

Assessment of Fe2O3/SiO2 catalysts for the continuous treatment of phenol aqueous solutions in a fixed bed reactor

Different iron-containing catalysts have been tested for the oxidation of phenol aqueous solutions in a catalytic fixed bed reactor in the presence of hydrogen peroxide. All the catalysts consist of iron oxide, mainly crystalline hematite particles, over different silica supports (mesostructured SBA-15 silica and non-ordered mesoporous silica). The immobilization of iron species over different silica supports was addressed by direct incorporation of metal during the synthesis or post-synthesis impregnation. The synthesis conditions were tuned up to yield agglomerated catalysts with iron loadings between 10 and 15 wt.%. The influence of the preparation method and the type of silica support was evaluated in a catalytic fixed bed reactor for the continuous oxidation of phenol in terms of catalysts activity (phenol and total organic carbon degradation) as well as their stability (catalyst deactivation by iron leaching). Those catalysts prepared by direct synthesis, either in presence of a structure-directing agent (Fe₂O₃/SBA-15(DS)) or in absence (Fe₂O₃/SiO₂(DS)), achieved high catalytic performances (TOC reduction of 65% and 52%, respectively) with remarkable low iron leaching in comparison with their silica-based iron counterparts prepared by impregnation. Catalytic results have demonstrated that the synthesis method plays a crucial role in the dispersion and stability of active species and hence resulting in superior catalytic performances.     

An efficient strategy for highly loaded,well dispersed and thermally stable metal oxide catalysts

A family of metal oxides (Co₃O₄, NiO and CeO₂) confined in SBA-15 with high loadings (≥ 20 wt%) was prepared through a solvent-free method. Characterizations of X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that aggregation-free nanoparticles were obtained and N₂ physisorption confirmed they were studded in mesopores. It was proposed that the intermediate molten salt phases ensured successful encapsulation and homogeneous dispersion of metal oxides. Lastly, the importance of the strategy was exemplified by NiO, and the high thermal stability together with superior performance in hydrodechlorination of chlorobenzene suggested great potential of these samples in heterogeneous catalysis.     

Highly ordered crystalline mesoporous metal oxides for hydrogen peroxide decomposition

Highly ordered mesoporous metal oxides (meso-MO _x ) such as CeO₂, Co₃O₄, Cr₂O₃, Mn₂O₃, NiO, RuO₂, SnO₂ and TiO₂ were successfully synthesized using mesoporous silica KIT-6 as a hard template via the nano-replication method. The physicochemical properties of as-prepared meso-MO _x were characterized by scanning electron microscopy, X-ray diffraction, N₂ adsorption–desorption and temperature programmed techniques. Their catalytic behavior toward H₂O₂ decomposition was investigated and compared with the corresponding bulk metal oxides (bulk-MO _x ) synthesized by the conventional precipitation method. These meso-MO _x materials exhibited much higher catalytic activities than their bulk counterparts. In particular, meso-Mn₂O₃ and meso-RuO₂ showed high activities, while meso-SnO₂ resulted in no activity toward H₂O₂ decomposition. The overall conversion of H₂O₂ followed a general order: Mn₂O₃ > RuO₂ > Co₃O₄ > CeO₂ > NiO > Cr₂O₃ > TiO₂ > SnO₂.     

Structure and catalytic properties of Pd encapsulated in mesoporous silica SBA-15 fabricated by two-solvent strategy

The two-solvent method was employed to prepare Pd encapsulated in mesoporous silica (Pd/SBA-15). A 3.01 wt% Pd loading was achieved without the loss of pore ordering. Highly dispersed and uniform palladium nanoparticles could be detected using transmission electron microscopy confirming also the absence of large particles outside the mesopore silica. The catalytic activities of the Pd/SBA-15 nanocomposites were investigated in Heck coupling reactions with activated and non-activated aryl substrates. The Pd/SBA-15 nanocomposite exhibits excellent catalytic activities and reuse ability in air for the Heck carbon–carbon coupling reactions.     

The Nature of Active Sites of Co/Al2O3 for the Selective Catalytic Reduction of NO with C2H4

The effects of Co loading and calcination temperatures on the catalytic activity of Co/Al₂O₃ for selective catalytic reduction (SCR) of NO with ethylene in excess oxygen were investigated. Co/Al₂O₃ showed high and low activities when calcined at high (800 °C) and low (350 °C) temperatures, respectively. The formation and dispersion of cobalt species for catalysts calcined at 350 and 800 °C as well as for Al₂O₃ were studied by XRD, UV–vis and FTIR spectra. Combined with DRIFTS results of ad-species and reaction experiments, it allowed us to correlate the catalytic activity with active sites of Co/Al₂O₃, and the catalytic functions of active cobalt species and support were clarified. Co₃O₄ species contributed to the oxidation of NO to various nitrates and of C₂H₄ to reactive formate species, even in the absence of O₂, whereas the side reaction of ethylene combustion occurred simultaneously when excess oxygen was present. Tetrahedral Co²⁺ ions in CoAl₂O₄, which acted as the active sites, were responsible for the reaction between formate and nitrate species to form organic nitro compound.     

Formation of catalytic active sites in copper and manganese modified SBA-15 mesoporous silica

A series of copper and manganese oxides modified SBA-15 mesoporous silicas with different composition was prepared by incipient wetness impregnation with the corresponding nitrate precursors and compared with the analogous materials supported on conventional SiO₂. Nitrogen physisorption, XDR, FTIR, UV–Vis and temperature programmed reduction with hydrogen were used for samples characterization. Their catalytic activity was tested in ethyl acetate oxidation and methanol decomposition. The ordered porous structure of the support facilitates the interaction between different metal oxide nanoparticles and increases their dispersion due to the formation of mixed oxide phase. The ethyl acetate oxidation on SBA-15 binary materials is suppressed due to the lower accessibility of the metal oxide particles, located deeply into the micro-meso pores of the support. The reaction medium which forms during the methanol decomposition provides the reduction/decomposition transformations with the mixed oxide phase. The final phase composition of finely dispersed Cu/CuO and MnO_x particles stabilizes in a highly dispersed state into the porous matrix of SBA-15 support and increases the catalytic activity in methanol decomposition due to the appearance of synergistic effect between them.     

Phase transformation in CeO2–Co3O4 binary oxide under reduction and calcination pretreatments

The CeO₂–Co₃O₄ binary oxide was prepared by impregnation of the high surface area Co₃O₄ support (S.A. = 100m² g⁻¹) with cerium nitrate (20 wt% cerium loading on Co₃O₄). Pretreatment of CeO₂–Co₃O₄ binary oxide was divided both methods: reduction (under 200 and 400 °C, assigned as CeO₂–Co₃O₄–R200 and CeO₂–Co₃O₄–R400 and calcination (under 350 and 550 °C, assigned as CeO₂–Co₃O₄–C350 and CeO₂–Co₃O₄–C550). The binary oxides were investigated by means of X-ray diffraction (XRD), nitrogen adsorption at −196 °C, infrared (IR), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and temperature programmed reduction (TPR). The results showed that the binary oxides pretreatment under low-temperatures possessed larger surface area. The cobalt phase of binary oxides also was transferred upon the treating temperature, i.e., the CeO₂–Co₃O₄–R200 binary oxide exhibited higher surface area (S.A. = 109m² g⁻¹) and the main phase was CeO₂,Co₃O₄ and CoO. While, the CeO₂–Co₃O₄–R400 binary oxide exhibited lower surface area (S.A. = 40m² g⁻¹) and the main phase was CeO₂, CoO and Co. Apparently, the optimized pretreatment of CeO₂–Co₃O₄ binary oxide can control both the phases and surface area.     

介孔分子筛SBA-15的改性研究进展

从金属改性、酸改性和氧化物改性三方面综述了介孔分子筛SBA-15的改性研究进展,重点介绍了SBA-15表面功能化后引入金属改性的方法。评述了金属纳米粒子的制备对改性的SBA-15催化剂催化性能的影响。     

Catalytic Behavior of Alumina-Promoted Sulfated Zirconia Supported on Mesoporous Silica in Butane Isomerization

Alumina-promoted sulfated zirconia was supported on mesoporous molecular sieves of pure-silica MCM-41 and SBA-15. The catalysts were prepared by direct impregnation of metal sulfate onto the as-synthesized MCM-41 and SBA-15 materials, followed by solid state dispersion and thermal decomposition. Measurements of XRD and nitrogen adsorption isotherms showed that the structures of resultant materials retain well-ordered pores, even with ZrO₂ loading as high as 50 wt%. The characterization results indicated that most of the promoted sulfated zirconia were well dispersed on the internal surface of the ordered mesopores. The catalytic behavior of the alumina-promoted sulfated zirconia supported on mesoporous silica was studied in n-butane isomerization. The supports of mesoporous structures led to high dispersion of sulfated zirconia in the meta-stable tetragonal phase, which was the catalytic active phase. The high performance of alumina-promoted catalysts was ascribed to the sulfur retention by alumina.     

Catalytic Removal of Toluene over Co3O4–CeO2 Mixed Oxide Catalysts: Comparison with Pt/Al2O3

The catalytic oxidation of toluene, chosen as VOC probe molecule, was investigated over Co₃O₄, CeO₂ and over Co₃O₄–CeO₂ mixed oxides and compared with the catalytic behavior of a conventional Pt(1 wt%)/Al₂O₃ catalyst. Complete toluene oxidation to carbon dioxide and water was achieved over all the investigated systems at temperatures below 500 °C. The most efficient catalyst, Co₃O₄(30 wt%)–CeO₂(70 wt%), showed full toluene conversion at 275 °C, comparing favorably with Pt/Al₂O₃ (100% toluene conversion at 225 °C).