Design of High-Quality Pt–CeO2 Composite Anodes Supported by Carbon Black for Direct Methanol Fuel Cell Application

A Pt on nano-sized CeO₂ particles that in turn are supported on carbon black (CB) was synthesized using the co-impregnation method. This potential anode material for fuel cell applications was synthesized in a stepwise process. The pure CeO₂ was synthesized using an ammonium carbonate precipitation method, and the Pt particles dispersed on the CeO₂ in such a way that a uniform dispersion with the CB was obtained (Pt–CeO₂/CB). The electrochemical activity of the methanol (CH₃OH) oxidation reaction on the Pt–CeO₂/CB was investigated using cyclic voltammetry and chronoamperometry experimentation. The onset potential of CH₃OH oxidation reaction on the Pt–CeO₂/CB anode was shifted to a lower potential as compared with that on commercially available Pt–Ru/carbon (C) alloy anode. In addition, the activation energy of the Pt–CeO₂/CB anode was much lower than that of the Pt–Ru/C alloy anode. Moreover, the current density of the Pt–CeO₂/CB anode was much higher than that of the Pt–Ru/C alloy anode at temperatures between 28° and 60°C. These results suggest that the anode performance of the Pt–CeO₂/CB anode at the operating temperature of typical fuel cells (80°C) is superior to that of the more usual Pt–Ru/C alloy anode. Importantly, the rare metal, Ru, is not required in the present anode material and the amount of Pt required is also significantly reduced. As a consequence, we report a promising candidate Pt–CeO₂/CB composite anode for application in the development of direct methanol fuel cells.     

Halogen-free acylation of toluene over FeSBA-1 molecular sieves

Three-dimensional cage type iron substituted mesoporous silica with different iron contents (FeSBA-1) was synthesized in a highly acidic media using cetyltriethylammonium bromide and tetraethylorthosilicate as a template and a silica source, respectively. Acylation of toluene with acetic anhydride (AA) was carried out over FeSBA-1 mesoporous catalysts with different n_Si/n_Fe ratios in the temperature range 80–180 °C for a time-on-stream of 1–6 h under liquid phase conditions. The important factors affecting the conversion and the selectivity of the reaction, such as the reaction temperature, feed ratio, catalyst weight and time-on-stream were studied and the results are discussed in detail. The reaction conditions were optimized and the n_AA/n_Toluene ratio of 2 and catalyst weight of 0.1 g (3.3 wt% of total reaction mixture) were maintained for all catalytic runs. It was found that the catalytic activity is strongly influenced by the amount of tetrahedral iron in the catalysts. Among the catalysts used in the present study, FeSBA-1(36) showed a high toluene conversion and selectivity to p-methylacetophenone (p-MAP) under the optimized reaction conditions. It was also found that the selectivity for p-MAP was always higher than m-MAP and o-MAP for all the catalysts and the activity of the catalysts changes in the following order: FeSBA-1(36) > FeSBA-1(90) > FeSBA-1(120).     

Quick high-temperature hydrothermal synthesis of mesoporous materials with 3D cubic structure for the adsorption of lysozyme

Three-dimensional cage-like mesoporous FDU-12 materials with large tuneable pore sizes ranging from 9.9 to 15.6 nm were prepared by varying the synthesis temperature from 100 to 200 °C for the aging time of just 2 h using a tri-block copolymer F-127(EO₁₀₆PO₇₀EO₁₀₆) as the surfactant and 1,3,5-trimethyl benzene as the swelling agent in an acidic condition. The mesoporous structure and textural features of FDU-12-HX (where H denotes the hydrothermal method and X denotes the synthesis temperature) samples were elucidated and probed using x-ray diffraction, N₂ adsorption, ²⁹Si magic angle spinning nuclear magnetic resonance, scanning electron microscopy and transmission electron microscopy. It has been demonstrated that the aging time can be significantly reduced from 72 to 2 h without affecting the structural order of the FDU-12 materials with a simple adjustment of the synthesis temperature from 100 to 200 °C. Among the materials prepared, the samples prepared at 200 °C had the highest pore volume and the largest pore diameter. Lysozyme adsorption experiments were conducted over FDU-12 samples prepared at different temperatures in order to understand their biomolecule adsorption capacity, where the FDU-12-HX samples displayed high adsorption performance of 29 μmol g⁻¹ in spite of shortening the actual synthesis time from 72 to 2 h. Further, the influence of surface area, pore volume and pore diameter on the adsorption capacity of FDU-12-HX samples has been investigated and results are discussed in correlation with the textural parameters of the FDU-12-HX and other mesoporous adsorbents including SBA-15, MCM-41, KIT-5, KIT-6 and CMK-3.     

Influence of Ho-Doping on the Electromagnetic Field-Dependent $E$–$J$ Characteristics of (Bi,Pb)-2212 Superconductor

The magnetic field (B ) dependence of electric field versus transport current density (E-J characteristics) of Bi_1.6Pb_0.5Sr_2-xHo_xCa_1.1Cu_2.1O_8+delta superconductor was studied for x from 0.000 to 0.200. The behavior of supercurrent flow under magnetic fields in Ho-doped (Bi,Pb)-2212 is explained using thermally activated flux-creep. The n -value and characteristic pinning energy ( U_c) estimated from E-J characteristics show that at applied fields, the flux-lines in Ho-doped samples are in the glass-state. A correlation is observed between n -index and J_c of doped samples. The highly enhanced critical current density (J_c) and n-index in both self- and applied-fields due to Ho-doping is of great scientific and technological significance.     

Fabrication and morphological control of three-dimensional cage type mesoporous titanosilicate with extremely high Ti content

TiSBA-1 materials with extremely high Ti content, up to silicon to titanium ratio (n_Si/n_Ti) of 2.4, have been successfully prepared through direct synthesis method by controlling the molar ratio of hydrochloric acid to silicon (n_HCl/n_Si). It has been found that the amount of Ti content and the structure of the TiSBA-1 can easily be controlled by the simple adjustment of n_HCl/n_Si ratio. X-ray diffraction pattern (XRD) of the obtained materials revealed that the materials are highly ordered and possess cubic three-dimensional cage type structure with open windows. N₂ adsorption–desorption measurement confirmed the narrow pore size distribution, high specific surface area (1317–1491 m² g⁻¹), and large specific pore volume (0.68–0.75 cm³ g⁻¹) for all the samples. UV–vis DR spectra of the prepared materials confirmed that Ti atoms are exclusively incorporated within silica framework and occupy the tetrahedral position while the presence of isolated bulk titania could be negligible. Morphologies of the TiSBA-1 materials have been also controlled by simply adjusting the n_Si/n_Ti ratio. With the appropriate Ti content, TiSBA-1 materials can be obtained as regular fine spheres. Moreover, the detailed mechanism on the morphological and phase transition control, and the incorporation of high amount of Ti in the framework of TiSBA-1 materials has been also discussed in detail.     

Highly basic CaO nanoparticles in mesoporous carbon materials and their excellent catalytic activity

Highly basic CaO nanoparticles immobilized mesoporous carbon materials (CaO-CMK-3) with different pore diameters have been successfully prepared by using wet-impregnation method. The prepared materials were subjected to extensive characterization studies using sophisticated techniques such as XRD, nitrogen adsorption, HRSEM-EDX, HRTEM and temperature programmed desorption of CO2 (TPD of CO2). The physico-chemical characterization results revealed that these materials possess highly dispersed CaO nanoparticles, excellent nanopores with well-ordered structure, high specific surface area, large specific pore volume, pore diameter and very high basicity. We have also demonstrated that the basicity of the CaO-CMK-3 samples can be controlled by simply varying the amount of CaO loading and pore diameter of the carbon support. The basic catalytic performance of the samples was investigated in the base-catalyzed transesterification of ethylacetoacetate by aryl, aliphatic and cyclic primary alcohols. CMK-3 catalyst with higher CaO loading and larger pore diameter was found to be highly active with higher conversion within a very short reaction time. The activity of 30% CaO-CMK3-150 catalyst for transesterification of ethylacetoacetate using different alcohols increases in the following order: octanol > butanol > cyclohexanol > benzyl alcohol > furfuryl alcohol.     

Inside Front Cover: Two‐Dimensional Hexagonally‐Ordered Mesoporous Carbon Nitrides with Tunable Pore Diameter,Surface Area and Nitrogen Content (Adv. Funct. Mater. 5/2008)

Two‐dimensional mesoporous carbon nitride (MCN) with tunable pore diameters have been successfully prepared for the first time using SBA‐15 materials with different pore diameters as templates through a simple polymerization reaction between ethylenediamine (EDA) and carbon tetrachloride (CTC) by a nano hard‐templating approach. The obtained materials have been unambiguously characterized using X‐ray diffraction (XRD), N₂ adsorption, high‐resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), high‐resolution scanning electron microscopy (HRSEM), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT‐IR) spectroscopy, and CHN analysis. The results show that the pore diameter of the MCN materials can be easily tuned from 4.2 to 6.4 nm without affecting their structural order. XRD, HRTEM and N₂ adsorption results reveal that the materials are structurally well ordered with a two‐dimensional porous structure, a high surface area and a large pore volume. It is also demonstrated for the first time that the textural parameters such as the specific pore volume, the specific surface area and the pore diameter, and the nitrogen content of the MCN materials can be controlled by the simple adjustment of the EDA to CTC weight ratio. The carbon to nitrogen ratio of the MCN decreases from 4.3 to 3.3 with increasing EDA to CTC weight ratio from 0.3 to 0.9. The optimum EDA to CTC weight ratio required for fabricating the well‐ordered MCN materials with excellent textural parameters and high nitrogen content is around 0.45. The catalytic activity of the materials has been tested in the Friedel‐Crafts acylation of benzene using hexanoyl chloride as the acylating agent. The materials are highly active and show a high conversion and 100 % product selectivity to caprophenone.     

Nanoporous reactor with tunable selectivity on alkylation of ethylbenzene

As nanoporous reactor, mesoporous silicates containing aluminum acidic site with n(Si)/n(Al) ratio up to 7 (AISBA-15) were prepared through a simple one-pot synthesis, which was recently developed by parts of us. The obtained materials were satisfactorily characterized by XRD and nitrogen adsorption/desorption and have regularly arranged hexagonal structures with pore diameters in the 9.6-11.8-nm range. The density and strength of the acid sites were determined using temperature-programmed desorption (TPD) of pyridine and controlled distribution between weak, moderate, and strong acid sites was demonstrated. The alkylation of ethylbenzene in a fixed-bed flow-type reactor using the AISBA-15 nanoporous reactor was carried out under various conditions such as temperature, feed ratio, flow rate, and time on stream. Interestingly, perfect regioselectivity between the m-isomer and the o-/p-isomers of diethylbenzene was achieved, where 100% selectivity of the m-isomer or the o-/p-isomers can be obtained by simply tuning the reaction temperature by using AISBA-15 catalyst with appropriate aluminum content.