Reduction of carbonyl compounds by Raney Ni–Al alloy and Al powder in the presence of noble metal catalysts in water

Raney Ni–Al alloy was found to be capable of reducing benzophenones to the corresponding diphenylmethanes (2) in water in good to excellent yields within 3 h at 60 °C in a sealed tube. The complete reduction process of both aromatic rings required 18 h at 80 °C with Raney Ni–Al and Al powder in the presence of Pt/C. The nature of the hydrogenated products was also found to greatly depend on temperature, reaction time, volume of water, and amount of Raney Ni–Al alloy being used.     

Catalytic oxidation of volatile organic compounds (VOCs). Oxidation of o-xylene over Pd and Pt/HFAU catalysts

The transformation of o-xylene in low concentration (1 700 ppmv) into air was investigated over Pd and Pt/HFAU catalysts (framework Si/Al ratio equal to 17 and 100). Whatever the catalyst, o-xylene oxidation into CO₂ and H₂O is accompanied by the retention within the zeolite pores of heavy compounds (‘coke’). The relative significance of these reactions depends on the operating conditions (temperature, time-on-stream) and on the catalyst characteristics (Pd or Pt, Si/Al ratio). Over Pt and Pd/HFAU(17), time-on-stream has a positive effect on the xylene oxidation apparently related to the reducibility of Pd and Pt species during the reaction. The higher activity of Pt/HFAU catalysts can be attributed to its greater number of active species (especially Pt⁰). Those active species can be more rapidly formed than Pd⁰ by auto reduction during the calcination of Pt precursor. Whatever the metal, the higher the Si/Al ratio of the support, the faster the xylene oxidation and the lower the coke formation. This can be related to the higher proportion of reduced species (Pd⁰ and Pt⁰) formed on the more dealuminated catalyst but also to the hydrophobicity of the support. Indeed, the hydrophobicity of the zeolite play a positive role in the oxidation activity in presence of steam; the higher the Si/Al ratio of the zeolite, the faster the o-xylene oxidation. Thus a catalyst with a low platinum content supported on a hydrophobic zeolite (0.10 Pt/HFAU(100)) allows to oxidising totally o-xylene at 210 °C in presence of steam.     

A study of Pt–Pd/γ-Al2O3 catalysts for methane oxidation resistant to deactivation by sulfur poisoning

The catalytic oxidation of methane was studied over calcined and reduced Pt–Pd/γ-Al₂O₃ catalysts, in the presence and the absence of SO₂ in the CH₄–O₂ reaction feed. The effect of sulfation (SO₂ + O₂ for 4 h at 500 °C) was also studied on the catalyst resistance to deactivation by sulfur poisoning. Sulfating the calcined Pt–Pd/γ-Al₂O₃ catalysts resulted in a strong deactivation for the CH₄–O₂ reaction. However, the catalytic activity of the reduced-sulfated Pt–Pd/γ-Al₂O₃ catalyst for CH₄–O₂ reaction remained rather unaffected in the presence and in the absence of SO₂ in the reaction feed. XPS analysis revealed, over reduced-sulfated Pt–Pd/γ-Al₂O₃ catalysts, the presence of Pt(0) metallic surface species on which SO₂ interactions may be faster related to Pd surface species. The presence of Pt(0) may be necessary to prevent the interactions between SO₂ and Pd surface species. Long time catalytic tests showed that the activity of a reduced Pt–Pd/γ-Al₂O₃ catalysts for CH₄–O₂ reactions remained rather unaffected despite the presence of SO₂ in the reaction feed.     

Supportless PdFe nanorods as highly active electrocatalyst for proton exchange membrane fuel cell

The PdFe nanorods (PdFe-NRs) with tunable length were synthesized by an organic phase reaction of [Pd(acac)₂] and thermal decomposition of [Fe(CO)₅] in a mixture of oleyamine and octadecene at 160 °C. They show a better proton exchange membrane fuel cell (PEMFC) performance than commercial Pt/C in working voltage region of 0.80–0.65 V, due to their high intrinsic activity to oxygen reduction reaction (ORR), reduced cell inner resistance, and improved mass transport.     

Oxygen reduction reaction on the low index planes of palladium electrodes modified with a monolayer of platinum film

Oxygen reduction reaction (ORR) has been studied on the low index planes of Pd modified with a monolayer of Pt (Pt/Pd(hkl)) in 0.1 M HClO₄ with the use of hanging meniscus rotating disk electrode. The activity for ORR on bare Pd(hkl) electrode depends on the surface structure strongly, however, voltammograms of ORR on Pt/Pd(hkl) electrodes do not depend on the crystal orientation. The specific activities of Pt/Pd(hkl) electrodes at 0.90 V (RHE) are higher than that on Pt(1 1 0) which has the highest activity for ORR in the low index planes of Pt. The mass activity on Pt/Pd(hkl) electrode is 7 times as high as a commercial Pt/C catalyst.     

Synthesis of aryl alkynyl carboxylic acids and aryl alkynes from propiolic acid and aryl halides by site selective coupling and decarboxylation

The coupling of propiolic acid with aryl iodides afforded the aryl alkynyl carboxylic acids and aryl alkynes in generally good yields. Aryl alkynyl carboxylic acids were obtained when the reaction was performed in the presence of Pd(PPh₃)₂Cl₂ (2.5 mol %), dppb (5.0 mol %) and DBU (5 equiv) at 50 °C. For the synthesis of the terminal aryl alkynes, the reaction was conducted in the presence of Pd(PPh₃)₂Cl₂ (2.5 mol %), dppb (5.0 mol %), DBU (5.0 equiv), and Cu(acac)₂ (10 mol %) at 25 °C for 5 h, and further reacted at 60 °C for 6 h.     

N-heterocyclic carbene–palladium catalysts for the bisdiene cyclization-trapping reaction with sulfonamides under thermal and microwave conditions

Simple palladium-N-heterocyclic carbene catalysts readily effect the palladium-catalyzed cyclization-trapping of bisdienes with sulfonamides. The reaction is quite efficient for a variety of sulfonamides and several bisdienes. For example, using 0.1% of the in situ generated or preformed (IMes)Pd(η³-C₃H₅)Cl complex, the cyclization-trapping of a simple bisdiene with TsN(H)CH₂Ph proceeds in good yield under thermal conditions (74–75%, 75 °C, 9 h). The same reaction run under microwave irradiation proceeds somewhat faster and in even higher yield (86%, 75 °C, 2.5 h).     

Synthesis of Renewable Diesel through Hydrodeoxygenation Using Pd/zeolite Catalysts

Hydrodeoxygenation of oleic acid as model compound of vegetable oils over Pd/zeolite catalysts was investigated under conditions of 375−400 °C and 15 bar in a semi batch stirred autoclave reactor. Pd/zeolite-1 and Pd/zeolite-2 catalysts were prepared using microwave polyol method with different treatment conditions. The liquid hydrocarbon products named Renewable Diesel have suitable density and viscosity, and quite high cetane index in accordance with standard commercial diesel and ASTM D-975. The IR spectrum of Renewable Diesel products have similarities with commercial diesel. The oxygenation removal pathway of oleic acid over Pd/zeolite 1 catalyst was primarily compiled through decarboxylation at 375 °C.     

Hydrogen production by catalytic steam reforming of acetic acid,a model compound of biomass pyrolysis liquids

An environmentally friendly and cost-competitive way of producing hydrogen is the catalytic steam reforming of biomass pyrolysis liquids, known as bio-oil, which can be separated into two fractions: ligninic and aqueous. Acetic acid has been identified as one of the major organic acids present in the latter, and catalytic steam reforming has been studied for this model compound. Three different Ni coprecipitated catalysts have been prepared with varying nickel content (23, 28 and 33% expressed as a Ni/(Ni + Al) relative at.% of nickel). Several parameters have been analysed using a microscale fixed-bed facility: the effect of the catalyst reduction time, the reaction temperature, the catalyst weight/acetic acid flow rate (W/m_HAc) ratio, and the effect of the nickel content. The catalyst with 33% Ni content at 650 °C showed no significant enhancement of the hydrogen yield after 2 h of reduction compared to 1 h under the same experimental conditions. Its performance was poorer when reduced for just 0.5 h. For W/m_HAc ratios greater than 2.29 g catalyst min/g acetic acid (650 °C, 33% Ni content) no improvement was observed, whereas for values lower than 2.18 g catalyst min/g acetic acid a decrease in product gas yields occurred rapidly. The temperatures studied were 550, 650 and 750 °C. No decrease in product gas yields was observed at 750 °C under the established experimental conditions. Below this temperature, the aforementioned decrease became more important with decreasing temperatures. The catalyst with 28% Ni content performed better than the other two.     

Towards a combined use of Mn(Salen) and quaternary ammonium salts as catalysts for the direct conversion of styrene to styrene carbonate in the presence of dioxygen and carbon dioxide

The use of oxygen in combination with carbon dioxide to afford the direct conversion of alkenes into cyclic carbonates could help to promote the greenhouse gas while minimizing the impact of the oxidation reaction on the environment. In this work, we focused, for the first time, on the association of two catalytic systems individually efficient for the epoxidation of styrene (Mn(salen)/O₂ bubbling/isobutyraldehyde at 80 °C) and the cyclocarbonatation of styrene oxide (choline chloride/CO₂ at 15 bar and 120 °C). First, the feasibility of the cyclocarbonatation reaction, starting from the non-isolated epoxide, has been proven as styrene carbonate was formed with a 24% yield. The objective was, then, to determine the best conditions allowing the overall transformation in a common solvent. Taking into account the differences in optimal temperatures and kinetics of the two individual steps, it was decided to vary the temperature during the reaction [first 80 °C (3 h) and 120 °C (23 h)]. Under these conditions, styrene was converted into the epoxide but, unfortunately, styrene carbonate formation could not be demonstrated. Blank experiments have clearly shown that isobutyraldehyde, which is essential to the first step, must be completely consumed before the temperature rise. Otherwise, autoxidation of the aldehyde in the presence of styrene oxide at 120 °C leads to other products than styrene carbonate.     

Preparation of (2,2-difluoroethenylidene)bis(tributylstannane) and arylation reaction: efficient approach to 1,1-diaryl-2,2-difluoroethenes

Reaction of 2,2-difluoro-1-tributylstannylethenyl p-toluenesulfonate (1) with bis(tributyltin) in the presence of 5 mol % Pd(PPh₃)₄ and 30 equiv LiBr in THF at reflux temperature for 7 h afforded (2,2-difluoroethenylidene)bis(tributylstannane) (2) in a 70% yield. Coupling reaction of 2 with aryl iodides in the presence of 5 mol % Pd(PPh₃)₄ and 5 mol % CuI in DMF at 80 °C for 3–4 h provided the coupled products 3 in 59–85% yields.     

A novel approach for synthesis of nanocrystalline γ-LiAlO2 from spent lithium-ion batteries

Synthesis of nanocrystallite γ-LiAlO₂ from spent lithium-ion batteries has been investigated. XRD results show that γ-LiAlO₂ phase can be synthesized by thermal treatment of the cathode material over its aluminum sheet at 800–900 °C for 2 h. This is accompanied with the formation of Co₃O₄ and CoO phases as colored powders. SEM investigation revealed the formation of dense grains as coconut-like shape structure of γ-LiAlO₂ phase. Comparatively, reaction of chemical grade Al powder with LiOH in stoichiometric ratio at 800 °C gives γ-LiAlO₂ phase of cotton-like morphology.     

Unveiling the crucial role of temperature on the stability of oxygen reduction reaction electrocatalysts

The stability of Pt-based/C electrocatalysts used in proton exchange membrane fuel cell (PEMFC) systems is commonly evaluated via accelerated stress testing in half-cell configuration at temperature close to ambient (20 ≤ T ≤ 25 °C), and 100% relative humidity (liquid electrolyte). Those conditions are by far different from those encountered in PEMFC systems (solid electrolyte, 60 ≤ T ≤ 80 °C, 0 ≤ relative humidity ≤ 100%), and fail in reproducing the morphological changes and the performance losses encountered during real life. Here, using a high surface area Pt/C electrocatalyst, we show that the gap between half-cell and real PEMFC configurations can be bridged by considering the pronounced effect of the temperature. The accelerated stress tests (ASTs) conducted in liquid electrolyte at T = 80 °C more accurately reflect the changes in morphology and surface reactivity occurring in real PEMFC environment, and provide gain in time. Due to massive release of Pt^z + ions in the electrolyte during ASTs performed at T = 80 °C, using fresh electrolyte is strongly recommended for correct determination of the oxygen reduction reaction (ORR) kinetics.     

Ni–Al hydrotalcite-like material as the catalyst precursors for the dry reforming of methane at low temperature

Nickel–aluminium and magnesium–aluminium hydrotalcites were prepared by co-precipitation and subsequently submitted to calcination. The mixed oxides obtained from the thermal decomposition of the synthesized materials were characterized by XRD, H₂-TPR, N₂ sorption and elemental analysis and subsequently tested in the reaction of methane dry reforming (DRM) in the presence of excess of methane (CH₄/CO₂/Ar = 2/1/7). DMR in the presence of the nickel-containing hydrotalcite-derived material showed CH₄ and CO₂ conversions of ca. 50% at 550 °C. The high values of the H₂/CO molar ratio indicate that at 550 °C methane decomposition was strongly influencing the DRM process. The sample reduced at 900 °C showed better catalytic performance than the sample activated at 550 °C. The catalytic performance in isothermal conditions from 550 °C to 750 °C was also determined.     

Al-doped ZnO powdered materials: Al solubility limit and IR absorption properties

Al-doped ZnO powder was synthesized via the Pechini route with a doping rate varying from 1 to 4 mol.%. A solubility limit has been estimated under 0.3 mol.% of Al using X-ray diffraction refinements. The incorporation of aluminium into the ZnO lattice was investigated by ²⁷Al NMR, which suggests an extremely low amount of Al in a distribution of sites in ZnO. In order to assess the impact of such a low dopant amount, diffuse reflection experiments were performed for a wavelength range from 200 to 2500 nm. If the effect of doping was negligible for samples prepared at 850 °C, annealing at 1200 °C clearly reveals enhanced IR absorption properties for the doped samples, which are similar whatever be the nominal Al content.     

Kinetics of hematite chlorination with Cl2 and Cl2 + O2: Part I. Chlorination with Cl2

Preliminary tests of the chlorination of two iron oxides (wüstite and hematite) in various chlorinating gas mixtures were performed by thermogravimetric analysis (TGA) under non-isothermal conditions. Wüstite started to react with chlorine from about 200 °C generating ferric chloride and hematite as the final reaction products. The presence of a reducing and oxidizing agent in the chlorinating gas mixtures influenced the chlorination reactions of both iron oxides, during non-isothermal treatment, only at temperatures higher than 500 °C.The chlorination kinetics of hematite with Cl₂ have been studied in details between 600 and 1025 °C under isothermal chlorination. The values of the apparent activation energy (E_a) were about 180 and 75 kJ/mol in the temperature ranges of 600–875 and 875–1025 °C, respectively. The apparent reaction order with respect to Cl₂ was found to be 0.67 at 750 °C. Mathematical model fitting of the kinetics data was carried out to determine the most probable reaction mechanisms.     

Oxygen reduction reaction on carbon supported Palladium–Nickel alloys in alkaline media

Carbon supported Palladium–Nickel alloys with various compositions (Pd–Ni/C) were synthesized by chemical reduction of the co-precipitated Pd and Ni hydroxides on carbon. The structure of these alloys was characterized using X-ray diffraction (XRD) analysis. The catalytic activity of Pd–Ni/C for oxygen reduction reaction (ORR) in alkaline media was studied using a glassy carbon rotating disk electrode (RDE). Pd/C showed ORR activity close to that of Pt/C. The activities of Pd–Ni (3:1)/C and Pd–Ni (1:1)/C were found unchanged compared with that of Pd/C. Ni/C showed about 175 mV lower onset potential than Pt/C, and the activity of Pd–Ni (1:3)/C was observed to be between that of Pd/C and Ni/C.     

Evaluation of Pt40Pd60/MWCNT electrocatalyst as ethylene glycol-tolerant oxygen reduction cathodes

Pt–Pd/MWCNT with Pt:Pd atomic ratio 40:60 and Pt/MWCNT electrocatalyst were synthesized and evaluated as oxygen reduction reaction (ORR) cathodes for Direct Ethylene Glycol Fuel Cells (DEGFC) applications. As reference, a commercial Pt/C material was also tested. We found that Pt–Pd/MWCNT has high tolerance capability to EG and higher selectivity for the ORR compared to the Pt-alone materials. As a result, the shift in onset potential for the ORR, E_onset, at Pt–Pd/MWCNT was considerably smaller than the shift at Pt/MWCNT or Pt/C. The average particle size (from XRD) was 3.5 and 4 nm for Pt/MWCNT and Pt–Pd/MWCNT, respectively. A moderate degree of alloying was determined for the Pt–Pd material. An advantageous application of Pt–Pd electrocatalysts should be in DEGFCs.     

Hydrogen sensing properties of a Pd/SiO2/AlGaN-based MOS diode

Hydrogen sensing properties of a Pd/AlGaN-based Schottky diode are improved by the deposition of SiO₂ at the metal/semiconductor (MS) interface. The wide Schottky barrier height variation of the MOS diode could be attributed to the large electric field across the SiO₂ layer. This leads to the presence of more hydrogen dipoles caused by the polarization effect. The sensing response of the MOS diode at room temperature (1.3 × 10⁵) is comparable to that of the MS one at 150 °C (2.04 × 10⁵). Thus, the MOS-type sensing device shows the benefit of low-temperature operation. Kinetic analyses confirm that the short response times of the MOS diode are attributed to high reaction rate at the Pd/SiO₂ interface.     

Surface modified Pt/C as a methanol tolerant oxygen reduction catalyst for direct methanol fuel cells

A new procedure has been successfully developed by which PtN_x/C is synthesized to enhance methanol tolerance while maintaining a high catalytic activity for the oxygen-reduction reaction (ORR). The nitrogen-modified Pt surface, which is prepared using a chelating agent followed by heat treatment, exhibits considerable selectivity toward the ORR in the presence of methanol. The high methanol tolerance could be attributed to the suppression of methanol adsorption resulting from the modification of the Pt surface with nitrogen. A direct methanol fuel-cell (DMFC) test showed that a power density of up to 120 m W cm⁻² was generated when PtN_x/C was used as the cathode catalyst (1 mg cm⁻²) in 6 M methanol and oxygen at 70 °C.