Preparation of meso-macroporous α-alumina using carbon nanotube as the template for the mesopore and their application to the preferential oxidation of CO in H2-rich gases

Meso-macroporous α-Al₂O₃ was successfully prepared by using acid-treated carbon nanotube as mesoporous forming agent and polystyrene foam as the template for the macropore. A series of Ru/meso-macroporous α-Al₂O₃ catalysts were prepared by the incipient wetness impregnation method and applied to the preferential oxidation of CO (CO-PROX) in H₂-rich gases. SEM, N₂ adsorption–desorption, H₂-TPR techniques and TEM were employed to characterize the catalysts. The results indicate that the specific surface area was markedly elevated by introducing the mesopores, which led to the higher dispersion of ruthenium nanoparticles on the surface of α-Al₂O₃. The meso-macroporous α-Al₂O₃ supported ruthenium showed very high activity and selectivity for CO-PROX.     

Synthesis of recyclable catalyst-sorbent Fe/CMK-3 for dry oxidation of phenol

The magnetic mesoporous material Fe/CMK-3 acting as a catalyst-sorbent was synthesized by using ordered mesoporous carbon CMK-3 as the supporter, Fe(NO₃)₃ as the iron source, and glycol as the reducing agent. The samples synthesized were characterized by powder X-ray diffraction (XRD), N₂ adsorption-desorption, scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results show that the prepared Fe/CMK-3 preserved the ordered mesoporous structure of CMK-3, and magnetic species was mainly Fe₃O₄, which was dispersed inside channels of CMK-3 as nanoparticles with the diameter of around 10 nm. The adsorption and catalytic dry oxidation efficiency of the prepared Fe/CMK-3 were determined. The results also show that Fe/CMK-3 had good adsorption performance of phenol in aqueous solution and could be easily separated from water and recycled due to its ferromagnetic nature. Iron oxides supported on CMK-3 were excellent catalysts for dry oxidation of phenol. After 15 adsorption-catalytic oxidation cycles, the phenol adsorption capacity of Fe/CMK-3 only decreased a little, suggesting the good practicality. Combined thermogravimetry and mass spectrum (TG-MS) instrument was used to investigate the catalytic oxidation of phenol on Fe/CMK-3 and the ignition characteristics of the catalyst-sorbent. The supported Fe₃O₄ was found to be not only the magnetic component but also the active catalyst for the oxidation of phenol. The adsorbed phenol could be oxidized into CO₂ and H₂O at 220 °C at which no obvious phenol desorption or CMK-3 ignition occurred.     

Enhanced selectivity to benzaldehyde in the liquid phase oxidation of benzyl alcohol using nanocrystalline ZSM-5 zeolite catalyst

In the present paper, nanocrystalline hierarchical ZSM-5 zeolites were successfully synthesized by the hydrothermal method in the presence of tetrapropylammonium hydroxide as a single template with the gel composition of 58SiO₂:Al₂O₃:20TPAOH:1,500H₂O. The prepared zeolite catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Nitrogen adsorption–desorption (BET), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM) techniques. The formation of pure and highly crystalline ZSM-5 zeolite phase is confirmed by XRD. The IR vibration band at 550 cm^?1 is assigned to the double 5-rings of MFI-type zeolites. N₂ adsorption–desorption isotherms showed that the synthesized product had high BET surface area and possessed composite pore structures with both micro and mesopores. The catalytic performance of hierarchical ZSM-5 zeolite was investigated in the selective oxidation of benzyl alcohol (BzOH) with hydrogen peroxide (H₂O₂) under mild conditions. The results showed that the conversion of BzOH and the selectivity to benzaldehyde were about 94 and about 99 % respectively, when using 0.08 g ZSM-5 catalyst with acetonitrile as the solvent and H₂O₂ as the oxidant at 90 °C. This catalyst can be retrieved and reprocessed for five times without a significant loss in its activity and selectivity.     

Pore Structure and Shape Selectivity of Platinum-Promoted Cesium Salts of 12-Tungstophosphoric Acid

Pore-widths and pore-size distributions of 0.5 wt% Pt-Cs_xH_3-xPW₁₂O₄₀ have been studied by means of adsorption of various molecules. For the distributions of micropore and mesopore, isotherms of Ar and N₂ adsorption were analyzed, respectively. Pt-Cs_2.1H_0.9PW₁₂O₄₀ possessed only ultramicropores. On the other hand, the pores of Pt-Cs_xH_3-xPW₁₂O₄₀ (x = 2.3, 2.5, 2.8 and 3.0) showed bimodal distributions in the range from micropore to mesopore, and the widths of both pores tended to increase as the Cs content increased. From the amounts and rates of adsorption for n-butane and isobutane, the pore width of Pt-Cs_2.1H_0.9PW₁₂O₄₀ was determined to be close to the molecular size of n-butane, that is, 0.43 nm. The fraction of external surface area in the total surface area of Pt-Cs_2.1H_0.9PW₁₂O₄₀ was estimated to be only 0.06 from the adsorption of 1,3,5-trimethylbenzene and t-plot of N₂ adsorption. Pt- Cs_2.1H_0.9PW₁₂O₄₀ exhibited a shape selectivity due to the uniform ultramicropores and small external surface area; it catalyzed the oxidation of n-butane but not that of isobutane. SEM and TEM measurements revealed the primary crystallites and their aggregated states.     

Mesoporous TS-1: Nanocasting synthesis with CMK-3 as template and its performance in catalytic oxidation of aromatic thiophene

Mesoporous TS-1, with additional mesopore system formed by packing the TS-1 nanocrystals, was synthesized by nanocasting route using nanoporous carbon (CMK-3) as template and characterized by XRD, BET, TEM, UV–vis and FT-IR. Catalytic performance of mesoporous TS-1 in H₂O₂ oxidation of aromatic thiophene, the model sulfur containing molecule in transportation fuels, was tested and reported. Compared with common TS-1, mesoporous TS-1 shows improved catalytic performance for thiophene oxidation and is able to catalyze oxidation of bulky sulfur containing molecule such as dimethyldibenzothiophene.     

Synthesis,Characterization and Application of Co–MgO Mixed Oxides in Oxidation of Carbon Monoxide

The present work deals with the synthesis of nanostructured Co–MgO mixed oxides with different weight ratios of cobalt by a facile co-precipitation method as a catalyst for low-temperature CO oxidation. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption/desorption (BET), Fourier transform infrared spectroscopy (FTIR), and transmission and scanning electron microscopies (TEM and SEM) techniques. The results revealed that inexpensive cobalt–magnesium mixed metal oxide nanoparticles have a high potential as catalyst in low-temperature CO oxidation. The Co–MgO mixed oxide with 30 wt.% cobalt had the highest activity. The results showed that the catalysts pretreated under O₂-containing atmosphere possessed higher activity compared to the catalyst pretreated under H₂ atmosphere. Co–MgO catalyst showed a good repeatability in reaction condition. The stability test exhibited that the Co–MgO mixed oxides were highly stable for CO oxidation over a 30 h time on stream in the feed gas containing a high amount of moisture and CO₂.     

Synthesis and Toluene Adsorption/Desorption Property of Beta Zeolite Coated on Cordierite Honeycomb by an In Situ Crystallization Method

The beta zeolite on cordierite ceramic monolith was synthesized by an in situ crystallization method and characterized by XRD, N₂ adsorption/desorption, SEM and NH₃‐TPD techniques. Toluene adsorption/desorption was used as probe test for the control of cold‐start emissions and treatment of volatile organic compounds. The presence of beta on the supports was confirmed by XRD, SEM, and N₂ adsorption/desorption measurements. The zeolite crystals grow both into the cordierite macropores and on the surface of the monolith channels, which form an integrated network ensuring a strong adherence. The highly dispersed beta on supports, demonstrated by larger surface area and adsorption capacity of N₂, resulted in a significant increase of the total acidity, and thus a greater adsorption capacity for toluene. Furthermore, it could trap larger amounts of toluene to higher temperature and show considerable activity for toluene cracking and oxidation. These are attributed to the greater acidity and stronger acid sites of in situ synthesized beta.     

The role of silver species on Ag/Al2O3 catalysts for the selective catalytic oxidation of ammonia to nitrogen

The role of Ag species on Ag/Al₂O₃ catalyst for the selective catalytic oxidation (SCO) of NH₃ to N₂ was studied using 10 wt% Ag/Al₂O₃ catalysts prepared with impregnation, incipient wetness impregnation and sol–gel methods. The catalyst characterization was preformed using N₂ adsorption–desorption, UV/Vis, TEM and XRD. O₂-chemisorption and H₂–O₂ titration were measured to confirm the metal dispersion on the catalyst. The Ag species state and Ag particle size have significant influence on the Ag/Al₂O₃ activity and N₂ selectivity of the SCO of NH₃ at low temperature. Ag⁰ is proposed to be an active species on the H₂ pretreated catalyst at low temperature (<140 °C). It is evident that well-dispersed and small particle Ag⁰ enhances catalytic activity at low temperature, whereas large particle Ag⁰ is relate to a high N₂ selectivity. In contrast, Ag⁺ could also be the active species at temperatures above 140 °C.     

Effect of Hydrogen Treatment on the Catalytic Activity of Iron Oxide Based Materials Dispersed Over Activated Carbon: Investigations Toward Hydrogen Peroxide Decomposition

The effect of hydrogen treatment (400 °C/1 h) on the catalytic properties toward H₂O₂ decomposition of iron oxide based materials dispersed over activated carbon were investigated. Two different supports were evaluated: a commercial activated carbon (ACM) and an activated carbon produced from spent coffee grounds (ACR). The catalysts were characterized using XRD, SEM, N₂-sorption, XPS and TPR analysis. The main results suggest the formation of composites with high surface area (>800 m² g^?1) and the hydrogen treatment resulted in a great increase in the catalytic activity, probably as a function of the reduced iron species (Fe²⁺ and Fe⁰) formed with the treatment. Moreover, the catalyst prepared with ACR showed to be more active than that prepared from ACM.     

Lithium selective adsorption on low-dimensional titania nanoribbons

Mesoporous titania nanoribbons were synthesized via an optimized soft hydrothermal process and the derived titania ion-sieves with lithium selective adsorption property were accordingly prepared via a simple solid-phase reaction between Li₂CO₃ and TiO₂ nanomaterials followed by the acid treatment process to extract lithium from the Li₂TiO₃ ternary oxide precursors. First, mesoporous titania nanoribbons were prepared and the formation mechanism was discussed; second, the physical chemistry structure and texture were characterized by powder X-ray diffraction (XRD), (high-resolution) transmission electron microscopy (TEM/HRTEM), selected-area electron diffraction (SAED) and N₂ adsorption–desorption analysis (BET); third, the lithium selective adsorption properties were tested by the adsorption isotherm, adsorption kinetics measurement and demonstrated with the distribution coefficient of a series of alkaline and alkaline–earth metal ions.     

Catalytic Activity of Ruthenium Nanoparticles Supported on Carbon Nanotubes for Hydrogenation of Soybean Oil

Ruthenium catalysts supported on multiwalled carbon nanotubes (MCNTs) with different loadings (1% wt, 3% wt, 5% wt) were prepared by reduction with H₂ or NaBH₄ for selective hydrogenation of soybean oil at 338 K and initial pressure of 1.066 MPa. These catalysts were characterized using transmission electron microscopy (TEM), X-ray powder diffraction (XRD), N₂ adsorption–desorption, and H₂-temperature programmed desorption (TPD) techniques. Ru particles were dispersed more homogeneously on the surface of the nanotubes after being reduced with H₂ than with NaBH₄. The catalysts with 3% and 5% Ru loadings had higher hydrogenation activity. The NaBH₄-reduced catalyst had higher cis-isomer selectivity.     

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.     

Syngas production via CO2 reforming of methane using Co-Sr-Al catalyst

The effect of addition of strontium in Co based catalysts during CO₂ reforming of methane was investigated in the temperature range 500–700 °C. The Co/γ-Al₂O₃ supported catalysts with strontium as a promoter (0–2.25 wt%) were prepared by incipient wet impregnation method. Numerous techniques such as N₂ adsorption–desorption isotherm, H₂ temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Transmission Electron Microscopy (TEM), pulse chemisorption and temperature-programmed oxidation (TPO) were applied for characterization of fresh and spent catalysts. The results of characterizations and catalyst activity test revealed that introduction of Sr in Co/γ-Al₂O₃ catalyst had significant effect on stability and coke suppression. The Sr addition improves the metal–support interaction as well as enhances the Lewis basicity of the catalyst. The improvement in basicity helps the chemisorption and dissociation of CO₂ over the catalyst which in turn reduces carbon deposition.     

Important properties associated with catalytic performance over three-dimensionally ordered macroporous CeO2–CuO catalysts

Three-dimensionally ordered macroporous CeO₂–CuO catalysts were prepared by the template and sol–gel method. The catalysts were characterized via SEM, TEM, XRD, H₂-TPR, XPS, CO₂-TPD and N₂ adsorption–desorption techniques. It is found that the CeO₂–CuO catalysts present the well-defined interconnected macroporous structure in three dimensions, and the skeleton of macroporous structure is composed of the CuO and CeO₂ particles. Catalytic performance for preferential CO oxidation is determined by various properties including composition, structural and textural properties as well as reduction and desorption behavior. The 3DOM CeO₂–CuO structure improves the interaction between CuO and CeO₂, the structural and textural properties, the reduction of oxides and desorption of the adsorbed molecules on the active sites.     

Photocatalyic activity of double pore structure TiO2/SiO2 monoliths

The TiO₂/SiO₂ monoliths with macro- and mesopore structure have been synthsized by sol-gel method. The double pore structure was developed by adding polyethylene glycol and urea in the precurser solution. The morphology, crystallinity, surface area and porosity of the TiO₂/SiO₂ monoliths were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), N₂ adsorption/desorption and mercury intrusion techniques. The photocatalytic activity and applicablity of the monoliths were investigated by degradation of methylene blue and purificaiton of actual dyeing and finishing wastewater. The result showed the prepared TiO₂/SiO₂ monolith to have enhanced photocatalytic activity, reusability and easy recovery, so it may be considered a promising material for practical application in wastewater treatment.     

An organic/inorganic hybrid mesoporous silica membrane: preparation and characterization

An organic/inorganic hybrid mesoporous silica membrane composed of mesoporous silica materials inside the channels of polycarbonate filtration membrane (PC) was synthesized by using aspiration-induced infiltration method, and the surfactant in as-prepared membrane was removed by employing template-extraction method. The obtained materials were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD),transmission electron microscopy (TEM) and N₂ adsorption–desorption measurement. The SEM images and EDS elemental analyses show that as-synthesized materials in PC are one-dimensional silica rods estimated as 200 nm in diameter and 9 μm in length. Moreover, the results of XRD, TEM and N₂ adsorption–desorption analysis clearly demonstrate that such silica rods are mesoporous materials with two-dimensional hexagonal mesostructure and the average mesopore diameter is about 3.0 nm. In addition, the porosity of organic/inorganic hybrid mesoporous silica membrane was further examined by molecule permeation. It is found that small molecule, such as rhodamine B, can transport across the membrane, but relatively large molecule, such as horse radish peroxidase, can not transport across the membrane, indicating that it is size-selectivity of such a membrane for molecule permeation, which has the potential application in the molecule filters to separate bio-macromolecule from small molecule.     

Preparation of nanostructured porous carbon composite fibers from ferrum alginate fibers

Nano‐microstructured porous carbon composite fibers (Fe₂O₃@C/FeO@C/Fe@C) were synthesized by the thermal decomposition of ferrum alginate fibers. The ferrum alginate fiber precursors were prepared by wet spinning, and calcined at 300–1000°C in high purity nitrogen. The resulting composite fibers consist of carbon coated Fe₂O₃/FeO/Fe nanoparticles and porous carbon fibers. All the prepared nanostructures were investigated using thermal gravimetry, X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscope (TEM), and nitrogen adsorption–desorption isotherm. The results show that there are five stages in the decomposition process of the ferrum alginate fibers. Transitions between the five stages are affected by the decomposition temperature. XRD results show that maghemite (Fe₂O₃), wüstite (FeO), martensite (Fe) nanoparticles were formed at 300–500°C, 600–700°C, 800–1000°C, respectively. Scanning electron microscopy and TEM results indicate that the composite fibers consist of nanoparticles and porous carbon. The diameter of the nanosized particles increased from 100 to 500 nm with increasing reaction temperature. The nitrogen adsorption–desorption results also show that the composite fibers have a micro‐ and mesoporous structure. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Direct oxidation esterification of methacrolein with methanol: Oxygen vacancy promotion of Zr-doped Au/CeO2 nanorods

A series of Zr-doped CeO₂ nanorods supported by Au nanoparticle catalysts with different morphologies were prepared for methyl methacrylate (MMA) synthesis via direct oxidation esterification of methacrolein (MAL) with methanol. Catalytic activities under mild conditions (0.3 MPa; 80°C) were evaluated in the kettle reactor. Different characterization methods, such as XRD, Raman, N₂ adsorption, ICP, TEM, SEM, XPS, and H₂-TPR techniques, were applied to study the relationship between catalytic activity and structural characteristics, especially the form of Zr doped into the lattice of CeO₂ and the promotion mechanism of selective oxidation. The influence of Au supported on Ce_0.6Zr_0.4O₂ nanorods (Au/CZ-R) was also discussed. The results exhibited that the highest catalytic activity for the oxidative esterification with a MAL conversion of 99% and a MMA selectivity of 74% was achieved. The MMA synthesis performance correlated well with the surface oxygen vacancies, in particular for the active oxygen species around the Au particles.     

LiMn2O4 spinel direct synthesis and lithium ion selective adsorption

The cubic phase LiMn₂O₄ spinel is synthesized via a directly soft chemistry method via hydrothermal reaction of Mn(NO₃)₂, LiOH and H₂O₂ at 383 K for 5–10 h, more favorable to control the nanocrystalline structure with well-defined pore-size distribution and high surface area than traditional solid-phase reaction at high temperature. Further, the 1D MnO₂ nanorod ion-sieves with lithium ion selective adsorption property is prepared by the acid treatment process to completely extract lithium ions from the LiMn₂O₄ lattice. The effects of hydrothermal conditions on the nanostructure, chemical stability and ion-exchange property of the LiMn₂O₄ spinel and MnO₂ ion-sieve are examined via powder X-ray diffraction (XRD), N₂ adsorption–desorption at 77 K, high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED) and lithium ion selective adsorption measurements. The results show that the 1D MnO₂ nanorods might be utilized in lithium extraction from aqueous environment including brine, seawater and waste water.     

Synthesis and characterization of porous TiO<Subscript>2</Subscript> with wormhole-like framework structure

A fast and reliable synthetic route for preparing contaminant-free porous TiO₂ with a wormhole-like framework and close packed macropores is demonstrated based on a sol-gel process involving acid hydrolysis of an alkoxide in the presence of a cationic surfactant. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements have been used to characterize the porous structure and the crystallinity. The XRD patterns, TEM and scanning electron microscopy (SEM) images confirm that these materials have disordered wormhole-like topology with close-packed nearly hexagonal macropores. The mesopore diameters and surface area of titanium dioxide, evaluated from the N₂-sorption isotherms, indicate average pore diameters of about 7 and 6 nm and surface areas of about 100 and 335 m²/g, for as-prepared and calcined samples at 400°C.