Loss Of Specific Surface Area Research Articles

A Three–Dimensional Nanoscale View of Electrocatalyst Degradation in Hydrogen Fuel Cells

AbstractThe loss of platinum (Pt) electrochemically active surface area (ECSA) is a critical degradation mode that often becomes a limiting factor for heavy‐duty proton exchange membrane fuel cell vehicles. High surface area carbon supports have been shown to improve Pt dispersion and limit detrimental ionomer‐electrocatalyst interactions due to their large interior pore volume. In this work, using automated scanning transmission electron tomography, the degradation of nanoparticles located on the interior versus exterior surfaces of the carbon support is compared following a catalyst‐specific accelerated stress test (AST) of 90,000 voltage cycles between 0.6 V to 0.95 V. The results reveal a notable increase in median particle size for both interior and exterior Pt catalyst particles, with a slightly higher increase in particle size distribution and loss of specific surface area for the particles located on the exterior carbon surface. The fraction of Pt nanoparticles that reside within the interior of the carbon support also increased following the AST test, accompanied by evidence of an increase in average carbon mesopore size. The results shed light on the degradation mechanisms affecting electrochemical properties and the enhanced particle accessibility at lower relative humidity.

Improvement of vanadium redox flow battery performance obtained by compression and laser perforation of electrospun electrodes

Flow battery electrodes made of electrospun carbon fibers were synthesized with substantially lower porosity than typical electrospun mats by applying compression during the stabilization stage. The objective was to create flow battery electrodes with higher volumetric surface area to support the electrochemical reaction. The physical, structural, and transport properties of these novel mats were characterized extensively. A porosity reduction of 12% was attained by this method, yielding a 50% increase volumetric surface area, while the in-plane permeability and tortuosity were found to remain relatively consistent. On the other hand, the fibers near the surfaces were somewhat compacted, which hurt the through-plane permeability, so holes were created using a CO2 laser to perforate the structure. The loss of specific surface area caused by laser perforation was quite negligible and still showed improvement compared to the uncompressed control sample. Flow battery performance tests were conducted on all samples. All electrospun samples outperformed commercial carbon mats, with the compressed samples without and without laser perforations showing markedly better performance in the activation region. The non-perforated compressed sample showed mass transfer limitations at higher current density, while the laser perforations largely eliminated this effect, yield the best performance over the entire range of current density.

Revealing M (M = Cu, Co and Zr) oxides doping effects on anti-PbCl2 poisoning over Mn-Ce/AC catalysts in low-temperature NH3-SCR reaction

Lead salts poisoning was a great challenge for the catalysts application in selective catalytic reduction (SCR) reaction of NOx with NH3 in stationary sources. Herein, several typical transition metal (Cu, Co and Zr) oxides modified Mn-Ce/AC catalysts were prepared by impregnation method, and the effects of Cu, Co and Zr doping on resistance PbCl2 poisoning for the catalyst were investigated. The addition of three transition metal oxides improved the PbCl2 resistance of Mn-Ce/AC catalyst and maintained excellent low-temperature denitrification activity of the catalyst. The lead resistance performance of the three metal oxides followed: Cu > Co > Zr oxides. The NO conversion of Cu-doping catalyst after PbCl2 poisoning was only ca. 10% lower than that of fresh Mn-Ce/AC catalyst at 225 °C. Cu, Co and Zr doping could decrease the loss of specific surface area caused by poisoning, while Cu-doped catalyst showed lowest crystallinity of active components. Meanwhile, the contents of Mn4+ and chemisorbed oxygen in Cu-doped catalyst were higher than those in Co- or Zr-doped catalysts. Cu, Co and Zr doping improved the surface acidity and redox performance of the poisoned catalysts, with Cu-doped poisoned catalyst exhibiting nearly the same surface acidity and redox performance as the fresh Mn-Ce/AC catalyst. Furthermore, Cu doping could also improve NO adsorption and was in favor to the SCR process. Besides, in situ DRIFTS results showed that the catalytic reaction pathways of all the poisoned or modified catalysts were in accordance with both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. Finally, a possible anti-PbCl2 poisoning mechanistic model of (Cu, Co and Zr) oxides modified on Mn-Ce/AC catalyst was proposed.

The enhanced resistance to Na+-poisoning of MnCoCrOx SCR catalyst by acidity regulation: The mechanism of sulfuric acid pretreatment

Low-temperature NH3-selective catalytic reduction (NH3-SCR) catalysts with enhanced resistance to alkali-metal compounds are urgently needed for glass furnace, biomass boilers, etc. flue gases denitrification. A sulfuric acid pretreatment approach, which would be more widely applicable relative to the metal oxides addition method at present, was carefully explored for the excellent MnCoCrOx (MCC) catalyst in this work. The catalytic performance tests show that the decrease in de-NOx efficiency and N2 selectivity caused by Na+ poisoning could be well alleviated via H2SO4 pretreatment. 0.1 M sulfuric acid-treated 1 wt.% Na+ poisoned MnCoCrOx (0.1S-1Na-MCC) catalyst still exhibits a broad T90 (the temperature when de-NOx efficiency reaches 90%) window between 199 and 400 °C. The characterization results demonstrate that H2SO4 pretreatment well restrains the blockage of pore channels and loss of specific surface area caused by Na2O species deposition. A majority of acidity and redox ability of 0.1S-1Na-MCC catalyst were also retained compared with fresh MCC catalyst, which was essential to the SCR process. Sulfuric acid could introduce excessive Brønsted acid sites and cut the loss of Lewis acid sites effectively by the presence of Na2O. Besides, the as-formed HSO4− species would serve as acid sites for NH3 adsorption and activation. The above findings provide new insights with respect to improving the tolerance of metal oxides SCR catalyst to alkali metals by tuning the surface physicochemical properties by acid pretreatment.

CO2 hydrogenation to C5+ hydrocarbons over K‐promoted Fe/CNT catalyst: Effect of potassium on structure–activity relationship

Developing efficient catalysts for direct CO2 hydrogenation to fuel hydrocarbons is of great significance for the effective utilization of CO2, and C5+ selectivity is one critical indicator for the process economics. In this work, a series of K‐promoted Fe/CNT catalysts were prepared by the co‐impregnation method, and their catalytic performance for CO2 hydrogenation was studied in a slurry‐bed reactor. As a result, CO2 conversion and C5+ selectivity showed positive correlation with the increase of K/Fe ratio from 0 to 0.3, but further increase of K/Fe ratio above 0.3 slightly affected its. The catalyst with a K/Fe molar ratio of 0.3 achieved the best performance with CO2 conversion of 23.7% and C5+ selectivity of 56%. In addition, the structure–activity relationship of the catalyst was discussed based on various characterization results. K‐modified catalysts presented a higher specific surface area and stronger CO2 chemisorption, which helped to improve CO2 conversion and C5+ selectivity. However, excessive potassium loading caused a loss of specific surface area, reduction degree, and graphitization degree of the catalyst, which inhibited the CO2 chemisorption and the formation of C5+ hydrocarbons.

On the multifaceted roles of NiSx in hydrodearomatization reactions catalyzed by unsupported Ni-promoted MoS2

A series of unsupported Ni-Mo sulfide catalysts with varying Ni contents (0.13–0.72 molNi molNi+Mo-1) was post-synthetically treated with concentrated HCl to remove large crystallites of accessible NiSx. These sulfide particles inevitably form and grow at Ni concentrations required for the synthesis, but generally have very low activities. In all cases, Ni concentrations were greatly reduced by the HCl treatment. While this ‘leaching’ strategy successfully improved the reaction rates of high Ni-content (>0.4 molNi molmetal-1) catalysts for the hydrogenation of phenanthrene, modest to drastic decreases in catalytic rates (×0.1–0.8) were registered for catalysts with lower Ni concentrations. For the lowest Ni-loaded catalyst (0.05 molNi molmetal-1), HCl treatment caused a dramatic loss of specific surface area and catalytic activity by more than a factor of 6 and shifted the selectivity pattern to that of pure MoS2. These observations allow us to conclude that Ni atoms incorporated at the slab edges are inherently susceptible to HCl attack. NiSx, however, are the preferential sites at which HCl induces dissolution. Experiments with inter-particle mixtures and segregated beds of NiSx and MoS2 demonstrate that NiSx not only activates H2, but also acts as a reservoir to dynamically incorporate Ni in the MoS2 slabs at reaction conditions. These beneficial effects are reduced, as nickel sulfide particles become excessively abundant as typical for high Ni-content catalysts, for which edge substitution by Ni is near or at its maximum. The areal activity and concentration of chemisorbed nitric oxide (NO) are well correlated for the leached catalysts, with the exception of the lowest Ni-containing catalyst that has a low degree of Ni edge substitution (<20% of total edge atoms) and predominantly unpromoted sites. This linear correlation shows that the Ni-promoted sites are more than five-fold as active as the unpromoted sites.

Thermal Aging of Perovskite Based Natural Gas Vehicle Catalysts: Dependency of the Mode of Pd Incorporation

Catalytic performance of fresh and aged impregnated Pd/LaFeO3 and sol gel LaFe1−xPdxO3 Natural Gas Vehicle Three-Way Catalysts, in powder form and wash-coated on ceramic monolith, have been investigated. Aging at 980 °C in wet atmosphere has no detrimental effect on the structural properties with the preservation of the orthorhombic structure of the perovskite. On the other hand, a loss of specific surface area is accompanied with surface Pd enrichment on LaFe1−xPdxO3 through ex solution process. It was found that the mode of Pd incorporation and subsequent aging has a limited impact on the catalytic performance at low temperature for the NO/H2 reaction. On the other hand, sharp rate enhancement in NO and methane conversion occurs at high temperature related to change in the reaction pathway from methane combustion to reforming reactions producing more efficient reducing agents to reduce NO. Such behaviour has been explained by the coexistence of palladium stabilized at different oxidation state at the surface and inside the perovskite structure.

Scaling behavior of iron in capacitive deionization (CDI) system

This study investigated the fouling and scaling behaviors in a capacitive deionization (CDI) system in the presence of iron and natural organic matter (NOM). It was found that the salt adsorption capacity (SAC) significantly decreased when treating Fe-containing brackish water, with higher Fe concentrations leading to severer SAC reduction. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis demonstrated that Fe2O3 appeared to be the predominant foulant attached on the electrode surface, which was difficult to be removed via backwashing, indicating the irreversible property of the foulant. Further characterizations (e.g., N2 sorption-desorption isotherms, electrochemical impedance spectroscopy and cyclic voltammetry) revealed that the CDI electrodes suffered from obvious deterioration such as specific surface area loss, resistance increase and capacitance decline with the occurrence of Fe scaling. While the presence of NOM alleviated the Fe scaling through NOM-Fe complexing effects, NOM itself was found to have negative impacts on CDI desalination performance due to their strong interactions with the carbon electrodes.

Room temperature sintering of polar ZnO nanosheets: III-Prevention

Abstract In this study, the coating of high specific surface area stainless steel wire mesh-supported ZnO with a monolayer of silica was investigated with the aim of preventing the room temperature sintering of the polar ZnO sample (75% specific surface area loss in two months in the presence of moisture, oxygen or light). This research study is the logical conclusion of previous works by the authors in which the room temperature sintering of polar ZnO was detected and analyzed for the first time ( https://doi.org/10.1039/c7cp02306e and https://doi.org/10.1039/c7cp02307c ). The ZnO surface was modified by inducing a substitution reaction between 3-aminopropyltriethoxysilane (APTES) and surface hydroxyls, followed by a low-temperature calcination step to produce a monolayer of silica (2 atom%) that would provide stability to the ZnO surface. The textural and structural characteristics of the protected material hardly differ from those of freshly calcined (unprotected) ZnO samples, and remain unchanged for long storage periods. This is due to the action of the silica coating, which causes an increase in the number of oxygen interstitials and a decrease in the amount of oxygen vacancies. The combination of these factors provokes the immobilization of the Zn interstitials, whose mobility is responsible for the room temperature sintering of unprotected ZnO. The efficiency of the polar ZnO as a sacrificial template remains unchanged in the presence of silica. Additionally, the photocatalytic activity of the protected ZnO sample in the continuous photodegradation of methylene blue shows a slight improvement compared to that of the unmodified sample calcined at the same temperature. Moreover, losses of Zn during the reaction diminished.

Acid washed lignite char supported bimetallic Ni-Co catalyst for low temperature catalytic reforming of corncob derived volatiles

Acid washed Shengli lignite (AWSL) supported Ni, Co and Ni-Co catalysts were prepared, characterized and evaluated in catalytic reforming (CR) of corncob pyrolysis volatiles at a relatively low catalytic temperature of 450 °C. Moreover, the production and selectivity of H2 were also investigated. Amongst the catalysts studied, bimetallic Ni-10%Co/AWSL exhibited the most remarkable activity, yielding 36.3 mmol H2/g corncob and 710 μmol min−1 g−1 formation rate of syngas (H2 + CO + 4CH4) with trace of tar. It also tuned the gas composition and showed the greatest selectivity of H2 due to the promotion of the water gas shift reaction (with H2 accounting for the maximum 50.3% and 63% under Ar and steam atmosphere, respectively). Regardless of the loss of specific surface area, the superior performance of Ni-Co based catalysts under mild circumstance was attributed to the better reducibility and electronic properties along with a high dispersion of active metal. Additionally, the synergy of Ni and Co contributed to the combined and enlarged activity for CR of corncob volatiles and great selectivity for H2-rich syngas under moderate condition.

Study of hydrothermal aging impact on Na- and P-modified diesel oxidation catalyst (DOC)

The effects of hydrothermal aging (HT-aging), of a biodiesel oxidation catalyst in presence of Na and P impurities were studied. The synthesized reference-PtPd/CeZrO2/La-Al2O3 and Na-, P-modified-PtPd/CeZrO2/La-Al2O3 catalysts were HT-aged, characterized by several techniques and catalytically tested. The characterization results showed the loss of specific surface area due to the sintering of the catalyst. H2-TPR results evidenced the decrease of the catalytic redox activity. TEM results indicated that sodium impurities did not modified the catalyst structure while phosphates were formed. In general, lower reaction rates were found for CO, C3H6 and NO involved reactions after HT-aging. The electronic changes induced by sodium species were attenuated after HT-aging due to the sintering of the catalyst. The lower metal-adsorbates charge transfer enhanced CO oxidation while had a negative effect for C3H6 and NO involved reactions. Diffuse Reflectance Infrared Fourier Transform Spectroscopy experiments indicated that phosphates inhibited the intermediates adsorption on the catalyst surface.

Influence of carburization time on the activity of Mo2C/CNF catalysts for the HDO of guaiacol

Carbon nanofiber (CNF) supported β-Mo2C-based catalysts were synthetized by carbothermal hydrogen reduction at 750 °C for different times (1, 2, 4, 6 and 18 h) in order to study both the carbide phase formation and the CNF stability during this key stage. Catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectrometry and scanning transmission electron microscopy. Subsequently, catalysts were evaluated in the hydrodeoxygenation (HDO) of guaiacol using a batch autoclave reactor at mild conditions of temperature and pressure (300 °C and 20 bar of H2). Liquid products were analysed after 2 h of reaction by gas chromatography. In all cases, β-Mo2C phase was formed during the carburization, and crystal sizes increased (from 6 to 18 nm as measured by XRD) as the carburization time did. However, a deep gasification of the support was observed in catalysts carburized above 6 h, resulting in a dramatic loss of specific surface area. In the guaiacol HDO reaction, higher conversions (72–80 %) and HDO ratios (53–63 %) were obtained using catalysts carburized for 2 h and onwards. Considering the carbide content in the catalyst, 1 and 2 h carburized catalysts exhibited the highest values of formation of HDO products: phenol, cyclohexane + benzene and anisole. Besides this, a clear relationship between the Mo2C surface area (SMo2C) and the product formation rate could be inferred for the catalysts carburized at 1, 2 and 4 h, in which the textural properties were not affected by the carburization time. On the other hand, longer carburization times had a worse performance despite the largest values of SMo2C, being this fact related to the dramatic loss of the catalyst textural properties.

Thermal activation and aging of a V2O5/WO3-TiO2 catalyst for the selective catalytic reduction of NO with NH3

Real-world vanadium-based catalysts for the selective catalytic reduction (SCR) of NO with NH3 are occasionally exposed to high temperatures, which can induce catalyst aging. In this work, a 2.0 wt% V2O5/WO3-TiO2 catalyst based on commercial WO3-TiO2 was lab aged in dry and wet feed at different time lengths and temperatures. Aging carried out in static atmosphere or in flow only marginally influenced its performance, while e.g. temperature and water in the feed heavily affected the SCR activity. The low temperature NOx conversion (≤300 °C) increased after aging up to 600 °C for 16 h and was more pronounced after hydrothermal aging compared to thermal aging, which was associated with the increased surface coverage of the SCR-active vanadyl groups. Measurements of vanadium volatility in the temperature range selected for the aging temperatures revealed the high mobility of V species induced by the (hydro-)thermal treatments. The onset of catalyst deactivation, observed at lower aging temperature for the hydrothermally aged catalyst compared to the thermally treated one, is possibly due to a larger amount of mobile V and W species and the concurrent loss of specific surface area. The set of catalytic and characterization data showed that water is an essential component in aging protocols because it heavily affects the structure and the resulting catalytic activity of the SCR catalyst. Removal of residual sulfate groups, which are present on the commercial support, also contributed to catalyst activation at 550°C aging temperature as a result of structural changes evidenced by surface area measurements and by IR and Raman spectroscopy, including rearrangement of V species and apparent increase of Lewis acidity.

State-of-Health Diagnosis of Lithium-Ion Batteries Using Nonlinear Frequency Response Analysis

Estimation of the State-of-Health (SOH) of Lithium-ion Batteries (LIBs) is commonly conducted using in-situ measurement methods, such as Incremental Capacity Analysis (ICA) and Differential Voltage Analysis (DVA) as well as impedance based techniques. In this study, we present an alternative method for SOH estimation: The nonlinear dynamic measurement method Nonlinear Frequency Response Analysis (NFRA) is shown to be able to estimate capacity fade of LIBs due to loss of active material. Capacity loss correlates with the quotient of the root mean square of the second and the third harmonic response for different excitation amplitudes in the frequency range sensitive to electrochemical reactions at approximately 1 Hz. The results of the experimental cycle-aging study are validated and further analyzed by using a reaction model containing Butler-Volmer kinetics with a dynamic charge balance of the electrode. Simulations show that the NFR quotient and capacity fade due to loss of specific surface area correlate exactly. We identify the NFR quotient as a reliable, easily measurable parameter for the diagnosis of the SOH of LIBs. Therefore, this study reveals a novel approach for SOH estimation of LIBs based on dynamic analysis with NFRA.

Durability of silica aerogels dedicated to superinsulation measured under hygrothermal conditions

Energy efficiency in buildings is a crucial lever for lowering greenhouse gas emissions and a mass market for silica aerogel as retrofitting material. Their durability is therefore a major concern. When applying the precautionary principle, industrial companies have difficulties in estimating the service lifetime of innovative materials such as aerogel. Thus, their costs remain high and market penetration low until the durability of the materials they produce is confirmed. In this paper, commercial silica aerogels were exposed to accelerated ageing over long periods. Microstructural evolutions were tracked by nitrogen and water sorption while thermal conductivities were characterized by heat fluxmeter measurements. 96 and 384 days at 70 °C and 90%RH were sufficient to produce noticeable changes in the physico-chemical properties of certain products but almost none in others. The first change observed was an increase of hydrophilicity, followed by a loss of specific surface area, and a shifted and enlarged pore size distribution. The measurements confirmed that microstructure changes induce higher thermal conductivities. Depending on the specific type of aerogel product, the accelerated ageing tests lead to a significant, but limited increase of thermal conductivity of up to 2,5 mW/(m.K). The main hypotheses for explaining this phenomenon are the growth of neck size between two silica particles and the presence of water in the pores. In addition, it is shown for the first time for a wide range of aerogels that pore size distribution and hydrophobization are the key parameters for tuning aerogel durability in severe conditions. Consequently, the mesoporous community has a framework of tests and mechanisms to design aerogels for their specific efficiency/cost/durability requirements.

Holey Graphene Aerogel to Support Pt Nanoparticles for Direct Methanol Fuel Cell

Direct methanol fuel cell (DMFC) has been the focus of researchers in the past decades, due to its simple structure, high energy density and easy integration [1-2]. As a device that converts chemical energy stored in methanol to electricity, the activity and stability of the catalyst applied in DMFC directly determines the output performance of the fuel cell. Until now, the low activity and high cost of catalyst are still the biggest problems that impede DMFC’s further commercialization. Pt nanoparticles, revealing the highest activity among all catalysts, are usually dispersed on carbon materials to enhance the utilization and decrease the cost [3-4]. The structure and properties of carbon support have a significant influence on the size and distribution of Pt nanoparticles, which plays a key role in the activity and stability of the catalysts. Here in this work, holey graphene aerogel was utilized to support Pt nanoparticles as the catalyst for DMFC. The three-dimensional porous structure of holey graphene aerogel can effectively prevent the stacking due to van der Waals forces between graphene sheets. More importantly, the large number of defects on the graphene sheet induced by hydrogen peroxide etching will anchor Pt nanoparticles, leading to smaller sizes and more uniform distribution. Graphene oxide (GO) was obtained via a modified Hummers’ method [5]. 50 ml GO aqueous solution was heated to 100 °C, after which 30% H2O2 solution was added [6]. The mixture was kept stirring for certain time and then cooled down. After the removal of excess H2O2, the etched graphene oxide was mixed with L-ascorbic acid in a glass vial and kept at 40°C for 6h. The obtained hydrogel was then dialyzed and freeze-dried to form the aerogel, on which Pt nanoparticles were later dispersed via a typical microwave-assisted process [7]. The catalysts with 0.5h and 1h etching time were recorded as 0.5h Pt / HGA and 1h Pt / HGA, while the non-etched sample was denoted as 0h Pt / GA for comparison. Transmission electron microscopy (TEM) and high-resolution transmission electron microscope (HRTEM) were performed for surface morphology using FEI Tecnai G2F30. Cyclic voltammetry (CV) was conducted at 0.05Vs-1 by using a three-electrode cell with a Hg/Hg2SO4 reference electrode in the solution of 0.5M H2SO4 mixed with or without 0.5M methanol, in order to estimate the electrochemical surface area (ESA) and electrocatalytic activity of the catalysts. Fig.1 shows the TEM (a) and HRTEM (b) images of 0.5h Pt / HGA. It can be seen that Pt nanoparticles with average size smaller than 2nm were dispersed uniformly on graphene sheets. Fig.2 demonstrates CV curves of three samples in 0.5M H2SO4. The ESA is calculated with columbic charges accumulated during hydrogen adsorption and desorption. The values of ESAs for three samples are 55.12 m2 g-1, 88.35 m2 g-1, 69.57 m2 g-1respectively. Among them, 0.5h Pt / HGA exhibits the largest ESA, followed by 1h Pt / HGA and 0h Pt / GA. For 0.5h Pt / HGA, the etching process increases the defects on graphene sheets, which contributes to the anchoring of Pt nanoparticles. The better dispersion and smaller sizes of Pt nanoparticles lead to the increased electrochemical active sites, thus a larger ESA. For 1 h Pt /HGA, due to the longer etching time, the scale of graphene oxide layer becomes smaller, resulting in a loss of specific surface area during the gel formation and the decline of ESA. All three catalysts show much larger ESAs than the commercial Pt/C catalyst with the value of 43 m2g-1. Fig.3 shows CV curves of three catalysts for methanol oxidation. All curves have two oxidation peaks. One located at 0.2V in the positive scanning direction is for methanol oxidation and the other located at 0V in the negative direction is for the oxidation of intermediate products. It is obvious that 0.5h Pt / HGA reveals the highest catalytic activity for methanol oxidation, followed by the 1h sample. This result is consistent with the ESA results. In addition, the onset potentials of three catalysts shifted negatively as the etching time extended, indicating that methanol oxidation is more likely to occur. In conclusion, holey graphene aerogel supported Pt nanoparticles reveals higher electrocatalytic activity for direct methanol fuel cell. References Applied Energy, 2011, 88 (5): 1681-1689.Journal of Power Sources, 2016,306 :49-61.Applied Catalysis B: Environmental 2017; 204: 173-184.Carbon, 2016, 87 (C): 424-433.Journal of the American Chemical Society, 1958, 80:1339.Science, 2017, 356 :599-604.Journal of Power Sources, 2010, 195: 1799-1804. Figure 1

A Comparative Study of Mn/Co Binary Metal Catalysts Supported on Two Commercial Diatomaceous Earths for Oxidation of Benzene

Two commercial diatomaceous earths were used as supports for the preparation of Mn/Co binary metal catalysts at different metal loads (5 to 10 wt % Mn and 5 to 15 wt % Co) by incipient wetness deposition. The activity of the prepared catalysts towards the complete oxidation of benzene to CO2 and water was investigated between 100 and 400 °C. Raw supports and synthesized catalysts were characterized by XRD, N2 physisorption, SEM-EDS, H2-TPR, and TPD. The purification treatment of food-grade diatomite significantly affected the crystallinity of this support while reducing its specific surface area (SSA). A loss of SSA, associated with the increase in the metal load, was observed on samples prepared on natural diatomite, while the opposite trend occurred with food-grade diatomite-supported catalysts. Metal nanoparticles of around 50 nm diameter were observed on the catalysts’ surface by SEM analysis. EDS analysis confirmed the uniform deposition of the active phases on the support’s surface. A larger H2 consumption was found by TPR analysis of natural diatomite-based samples in comparison to those prepared at the same metal load on food-grade diatomite. During the catalytic oxidation experiment, over 90% conversion of benzene were achieved at a reaction temperature of 225 °C by all of the prepared samples. In addition, the formation of coke during the oxidation tests was demonstrated by TGA analysis and the soluble fraction of the produced coke was characterized by GC-MS.

Structure, morphology and reducibility of ceria-doped zirconia

Zr1-xCexOx has been prepared by hydrolysis, in neutral medium, starting from rough ZrO2 and CeO2 materials as simple and cheaper synthesis method compared to sol-gel routes. The oxy-hydroxide precursors thus obtained were calcined under air at 450 °C, 900 °C and 1200 °C. The impact of those thermal treatments on the structure, texture and related redox properties has been investigated. Higher specific surface area than those observed on ceria were observed after calcination at low temperature, i.e., 450 °C. Above that temperature thermal sintering occurs having a detrimental effect on the specific surface area related to crystal growth more accentuated on CeO2. The formation of several ZrCe mixed oxide phases formed by incorporation and substitution of Zr in the structure of ceria was characterized. A complete loss of specific surface area is noticeable after calcination at 1200 °C. XRD and SEM analysis revealed the formation of two mixed oxides structure, i.e. Ce2Zr2O7.04 and Ce2Zr2O7 corresponding to different redox behavior evidenced from H2-TPR experiments.

Encapsulated phosphomolybdic acid in TMU-16 metal organic framework: Study the catalytic activity and structural stability dependent on synthetic solvent

Encapsulated phosphomolybdic acid in the TMU-16, HPMA@TMU-16, at three different solvents was synthesized and characterized. For characterization studies XRD, ICP, TGA, CHNS, BET, SEM-EDS and TEM methods were used. Evidences such as loss of specific surface area, EDS elemental mapping and similar XRD patterns confirmed that HPMA to be import in the TMU-16 pores. A catalytic activity of samples was performed in the oxidation of sulfides and optimum conditions were studied in the dibenzyle sulfide oxidation reactions. Obtained results including short reaction times, selectivity to sulfoxide and reusability exhibited high performance of HPMA@TMU-16 as heterogeneous catalyst. Increasing number of recovered cycles with shorter reaction times revealed effect of polarity of synthetic solvent on the catalytic activity and structural stability.

Oil shale powders and their interactions with ciprofloxacin, ofloxacin, and oxytetracycline antibiotics.

The interaction of oil shale, as a widespread sedimentary rock, with common antibiotics ofloxacine, oxytetracycline, and ciprofloxacine was studied. The selected Moroccan deposit and its thermally treated forms were fully characterized from a chemical and structural point of view, indicating the prevalence of quartz as a mineral component together with aluminum- and iron-rich phase that are converted into Al-doped iron oxide phases upon heating. The presence of 4wt% organics was also detected, which was removed at 550°C without significant loss of specific surface area. The pseudo-second-order kinetic model and Langmuir equation were found the most adequate to reproduce the kinetics and isothermal sorption experiments. These analyses enlighten the contribution of the organic matter on antibiotic retention as well as the key role of hydrophobic interactions on the molecule-mineral surface interactions. Our results emphasize the possible contribution of raw oil shale in the accumulation of antibiotics in soils and suggest that thermally treated oil shell powders can constitute cheap mineral sorbents for environmental cleaning.