Activation of bimetallic PtFe nanoparticles with zeolite-type cesium salts of vanadium-substituted polyoxometallates toward electroreduction of oxygen at low Pt loadings for fuel cells

The catalytic activity of commercial carbon-supported PtFe (PtFe/C) nanoparticles admixed with mesoporous polyoxometalate Cs3H3PMo9V3O40, (POM3-3–9), has been evaluated towards oxygen reduction reaction (ORR) in acid medium. The polyoxometalate cesium salt co-catalyst/co-support has been prepared by titration using the aqueous solution of phosphovanadomolibdic acid. The synthesized material has been characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results confirm formation of the polyoxometalate salt with the characteristic Keggin-type structure. The composite catalyst has been prepared by mixing the POM3-3–9 sample with the commercial PtFe/C by sonication. The diagnostic rotating ring-disk voltammetric studies are consistent with good performance of the system with low Pt loading during ORR. The fuel cell membrane electrode assembly (MEA) utilizing the PtFe/POM-based cathode has exhibited comparable or better performance (at relative humidity on the level of 100, 62, and 17%), in comparison to the commercial MEA with higher Pt loading at the cathode. Furthermore, based on the cell potential and power density polarization curves, noticeable improvements in the fuel cell behavior have been observed at the low relative humidity (17%). Finally, the accelerated stress test, which uses the potential square wave between 0.4 V and 0.8 V, has been performed to evaluate MEA stability for at least 100 h. It has been demonstrated that, after initial losses, the proposed catalytic system seems to retain stable performance and good morphological rigidity.

Zeolite addition to improve biohydrogen production from dark fermentation of C5/C6-sugars and Sargassum sp. biomass

Thermophilic biohydrogen production by dark fermentation from a mixture (1:1) of C5 (arabinose) and C6 (glucose) sugars, present in lignocellulosic hydrolysates, and from Sargassum sp. biomass, is studied in this work in batch assays and also in a continuous reactor experiment. Pursuing the interest of studying interactions between inorganic materials (adsorbents, conductive and others) and anaerobic bacteria, the biological processes were amended with variable amounts of a zeolite type-13X in the range of zeolite/inoculum (in VS) ratios (Z/I) of 0.065–0.26 g g−1. In the batch assays, the presence of the zeolite was beneficial to increase the hydrogen titer by 15–21% with C5 and C6-sugars as compared to the control, and an increase of 27% was observed in the batch fermentation of Sargassum sp. Hydrogen yields also increased by 10–26% with sugars in the presence of the zeolite. The rate of hydrogen production increased linearly with the Z/I ratios in the experiments with C5 and C6-sugars. In the batch assay with Sargassum sp., there was an optimum value of Z/I of 0.13 g g−1 where the H2 production rate observed was the highest, although all values were in a narrow range between 3.21 and 4.19 mmol L−1 day−1. The positive effect of the zeolite was also observed in a continuous high-rate reactor fed with C5 and C6-sugars. The increase of the organic loading rate (OLR) from 8.8 to 17.6 kg m−3 day−1 of COD led to lower hydrogen production rates but, upon zeolite addition (0.26 g g−1 VS inoculum), the hydrogen production increased significantly from 143 to 413 mL L−1 day−1. Interestingly, the presence of zeolite in the continuous operation had a remarkable impact in the microbial community and in the profile of fermentation products. The effect of zeolite could be related to several properties, including the porous structure and the associated surface area available for bacterial adhesion, potential release of trace elements, ion-exchanger capacity or ability to adsorb different compounds (i.e. protons). The observations opens novel perspectives and will stimulate further research not only in biohydrogen production, but broadly in the field of interactions between bacteria and inorganic materials.

Use of zeolite to reduce the radioactivity of cesium -137 in the liquid waste

Prepared zeolite type A was used for the removal of cesium ions from aqueous solution. The experimental data were analyzed by Langmuir, Freundlich isotherms. Various parameters, such as contact time, zeolite weight, pH, and initial concentration, were studied The results indicated that the highestt removal efficiency was 95.53% at (2h time, 0.04 g weight, and pH=6.8). The results also showed that the Freundlic model fits well with the experimental results and is better than the Langmuir model.

Promotional Effect of Pd Addition on the Catalytic Activity of Composite Pt-Pd/AlSBA-15–β Catalyst for Enhanced n-Heptane Hydroisomerization

Hierarchical AlSBA-15–zeolite materials were utilized as a supports for preparing hydroisomerization catalysts. Detailed consideration was given to: (i) the effect of the zeolite type introduced into AlSBA-15–zeolite composites (where zeolite is β, mordenite or ZSM-5) as well as (ii) the promotion effect of Pd addition. The composites showed higher activity in isomerization as compared to Pt/AlSBA-15. The enhanced isomerization efficiency were explained by the appropriate metallic and acidic function as well as suitable transport properties. The modification of the hydrogenating function by Pd incorporation increases the hydroisomerization efficiency of Pt-Pd/AlSBA-15–β catalyst. Over bimetallic Pt-Pd/AlSBA-15–β, the high yields of isomers (68 wt%) with respect to 50 wt% for a control catalyst. The most promising Pt-Pd/AlSBA-15–β catalyst allows to improve research octane number from 0 to the 74 value.

Activation and conversion of alkanes in the confined space of zeolite-type materials

Microporous zeolite-type materials are able to activate and efficiently convert stable C1+ alkanes. This review analyzes, at the molecular level, the role of active sites and the contribution of diffusion, shape-selectivity and confinement effects.

Construction of Zeolite A Type Multivariate Metal-Organic Framework for Selective Sensing of Fe3+ and Cr2O72-

Construction of zeolite type framework is of broad interest and mainly achieved by using imidazolate linkers. Incorporation of multiple linkers/functionalities into this unique type of framework would potentially expand its...

Synthesis of Zeolite A from Iraqi Natural Kaolin Using a Conventional Hydrothermal Synthesis Technique

The synthesis of zeolite materials by hydrothermal transformation of kaolin using a conventional hydrothermal method was investigated. Different analytical techniques were used to characterize the starting kaolin and produced zeolite A samples, including scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), x-ray diffraction (XRD), x-ray fluorescence (XRF), thermogravimetric analysis (TGA), and Fourier transform infrared (FT-IR) spectroscopy. The synthetic zeolite type A was obtained after activation of kaolin and metakaolin followed by different thermal and chemical treatments. The metakaolinization phase was achieved by calcining the kaolin in air at 600°C for 3 hours, a much lower temperature than previously reported in the literature. Metakaolin was treated with 3 M sodium hydroxide solution at a ratio of 1:5 and, using stainless steel autoclaves with teflon liners, heated the mixture to 200°C in a microwave for 24 hours. The results from this synthesis route showed that zeolite A with a cubic crystal habit has been successfully synthesized.

Limousinite, BaCa[Be4P4O16]·6H2O, a New Beryllophosphate Mineral with a Phillipsite-Type Framework

Limousinite, ideally BaCa[Be4P4O16]·6H2O, is a new beryllophosphate mineral discovered in the Vilatte-Haute pegmatite, Chanteloube near Razès, Limousin, Haute-Vienne, France. The new mineral is intimately associated with microcrystalline pale brown greifensteinite, black amorphous vitreous Mn-oxyhydroxide, triplite, and quartz. It forms isolated, partly corroded, colorless to snow-white crystals up to 0.9 mm long, showing rhombic cross sections. Limousinite is transparent with a vitreous luster, non-fluorescent, without cleavage planes; its calculated density is 2.58 g/cm3. Optically, the mineral is biaxial negative, α = 1.532(2), β = 1.553(3), γ = 1.558(2) (measured under 589 nm wavelength light), 2Vcalc. = 18°, non-dispersive, with Z parallel to the elongation of the prismatic crystals. Electron-microprobe analyses indicate an empirical formula of (Ba0.91K0.07)Σ0.98(Ca0.87Na0.05)Σ0.92[(Be3.87Al0.13)Σ4P4O16]·5.56H2O, calculated on the basis of 4 P atoms per formula unit, assuming 4 (Be + Al) pfu and a water content calculated from refined site-occupancy factors. A single-crystal structure refinement was performed to R1 = 4.90%, in the P21/c space group, with a = 9.4958(4), b = 13.6758(4), c = 13.4696(4) Å, β = 90.398(3)°, V = 1749.15(10) Å3, Z = 4. The crystal structure is characterized by a beryllophosphate framework similar to that of phillipsite-group zeolites, based on corner-sharing BeO4 and PO4 tetrahedra forming interconnected four- and eight-membered rings. Large cages within this zeolite framework contain Ba, Ca, and water molecules. Limousinite is the third known natural zeolite-type beryllophosphate, together with pahasapaite and wilancookite; it is also the first phosphate with a framework identical to that of a natural zeolite silicate.