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.     

Bismuth as an additive modifying the selectivity of palladium catalysts

The influence of bismuth addition on the activity and selectivity of palladium catalysts supported on SiO₂ in the reaction of glucose oxidation to gluconic acid was studied. The catalysts modified with Bi show much better selectivity and activity than palladium catalysts. The XRD studies proved the presence of intermetallic compounds BiPd and Bi₂Pd, which probably increase activity and selectivity of PdBi/SiO₂ catalysts in the oxidation of glucose. The TPO studies of catalysts containing 5 wt.% Pd/SiO₂, 3 wt.% Bi/SiO₂ and 5 wt.% Pd–5 wt.% Bi/SiO₂ show that palladium oxidation occurs at much higher temperatures than in the case of bismuth. The maximum rate of Pd oxidation occurs at around 580 K while the maximum rate of Bi oxidation takes place at around 430 K. Considering the above facts, a reaction involving bimetallic catalysts in oxidizing atmosphere at 333 K should not lead to surface oxidation of palladium and thus their deactivation.     

Thermal stability of fatty acids in subcritical water

In this work, hydrolytic reaction conditions of various temperatures (300–370 °C) and times (0–30 min) at a constant pressure of 20 MPa were applied to the thermal decomposition of three kinds of fatty acids (FAs), stearic acid, oleic acid, and linoleic acid, in subcritical water. The degradation characteristics were investigated from the derived data, and the thermal stability of FAs in subcritical water was estimated. The primary reactions we observed were isomerization and pyrolysis of FAs. The main pathway of degradation was deduced by analyzing the contents of pyrolyzed products. We found that more saturated FAs have greater thermal stability in subcritical water. All FAs remained stable at 300 °C or below. Based on these results, we recommend that hydrolysis of vegetable oils and fats using subcritical water should be carried out below 300 °C (at 20 MPa) and for less than 30 min to obtain high-yield FA production.     

Impact of palladium silicide formation on the catalytic properties of Pd/SiO2 catalysts in liquid-phase semihydrogenation of phenylacetylene

In this study, palladium silicide was formed on the sol–gel derived SiO₂ supported Pd catalysts when they were prepared by ion-exchange method using Pd(NH₃)₄Cl₂ as a palladium precursor. No other palladium phases (PdO or Pd⁰) were evident after calcinations at 450 °C for 3 h. The Pd/SiO₂ catalysts with Pd silicide formation were found to exhibit superior performance than commercial SiO₂ supported ones in liquid-phase semihydrogenation of phenylacetylene. From XPS results, the binding energy of Pd 3d of palladium silicide on the Pd/SiO₂ catalyst shifted toward larger binging energy, indicating that Pd is electron deficient. This could probably result in an inhibition of a product styrene on the Pd surface and hence high styrene selectivities were obtained at high phenylacetylene conversions. The formation of Pd silicide, however, did not have much impact on specific activity of the Pd catalysts since the TOFs were quite similar among the various catalysts with or without palladium silicides if their average particle sizes were large enough. The TOFs decreased by an order of magnitude when palladium dispersion was very high and their average particle sizes were smaller than 3–5 nm.     

Pd Nanostructures with High Tolerance to CO Poisoning in the Formic Acid Electrooxidation Reaction

Pd architectures such as nanobars and nanoparticles were synthetized by the polyol method using di-ethylene glycol as reaction media. The morphology, composition and electrocatalytic properties were investigated by transmission electronmicroscopy (TEM), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and electrochemical measurements. The electrocatalytic activity of Pd nanostructures was tested in terms of formic acid electrooxidation reaction (FAOR) in acid media (0.5 M H₂SO₄) and compared with commercial Pd/XC-72 (Pd/C). Results from the electrochemical studies showed that Pdnanobars (PdNB/C) presented higher tolerance to the CO and CO₂ poisoning effect compared with Pd nanoparticles (PdNP/C) and commercial Pd/C. Furthermore, the onset potential toward formic acid electrooxidation at high concentration (1 M) on PdNB/C exhibited a negative shift ca. 100 mV compared with commercial Pd/C. Finally, PdNB/C in the presence of 1 M FA showed a lower poisoning degree compared with commercial Pd/C and PdNP/C.     

Reduction of aromatic compounds with Al powder using noble metal catalysts in water under mild reaction conditions

In water, Al powder becomes a powerful reducing agent, transforming in cyclohexyl either one or both benzene rings of aromatic compounds such as biphenyl, fluorene and 9,10-dihydroanthracene under mild reaction conditions in the presence of noble metal catalysts, such as Pd/C, Rh/C, Pt/C, or Ru/C. The reaction is carried out in a sealed tube, without the use of any organic solvent, at low temperature. Partial aromatic ring reduction was observed when using Pd/C, the reaction conditions being 24 h and 60 °C. The complete reduction process of both aromatic rings required 12 h and 80 °C with Al powder in the presence of Pt/C.     

Hydrodechlorination of CCl4 over carbon-supported palladium–gold catalysts prepared by the reverse “water-in-oil” microemulsion method

Two series of carbon-supported Pd–Au catalysts were prepared by the reverse “water-in-oil, W/O” method, characterized by various techniques and investigated in the reaction of tetrachloromethane with hydrogen at 423 K. The synthesized nanoparticles were reasonably monodispersed having an average diameter of 4–6 nm (Pd/C and Pd–Au/C) and 9 nm (Au/C). Monometallic palladium catalysts quickly deactivated during the hydrodehalogenation of CCl₄. Palladium–gold catalysts with molar ratio Pd:Au = 90:10 and 85:15 were stable and much more active than the monometallic palladium and Au-richer Pd–Au catalysts. The selectivity toward chlorine-free hydrocarbons (especially for C₂₊ hydrocarbons) was increased upon introducing small amounts of gold to palladium. Simultaneously, for the most active Pd–Au catalysts, the selectivity for undesired dimers C₂H_xCl_y, which are considered as coke precursors, was much lower than for monometallic Pd catalysts. Reasons for synergistic effects are discussed. During CCl₄ hydrodechlorination the Pd/C and Pd–Au/C catalysts were subjected to bulk carbiding.     

Influence of FCC catalyst steaming on HDPE pyrolysis product distribution

A commercial FCC catalyst based on a zeolite active phase has been used in the catalytic pyrolysis of HDPE. The experimental runs have been carried out in a conical spouted bed reactor provided with a feeding system for continuous operation. Different treatments have been applied to the catalyst to improve its behaviour. This paper deals with the optimization of catalyst steaming and pyrolysis temperature in order to maximize the production of diesel-oil fraction. The performance of the fresh catalyst has been firstly studied at 500 °C. This catalyst gives way to 52 wt% gas yield, 35 wt% light liquid fraction and a low yield of C₁₀⁺ fraction (13 wt%). After mild steaming (5 h at 760 °C) the results show a significant improvement in product distribution. Thus, gas yield decreases to 22 wt%, the yield of light liquid is similar to that of the fresh one (38 wt%), whereas the yield of the desired C₁₀⁺ fraction increases to 38 wt%. Nevertheless, the best results have been obtained when a severe steaming is applied to the catalyst (8 h at 816 °C) and pyrolysis temperature is reduced to 475 °C. There is a significant reduction in the gaseous fraction (8 wt%). The light liquid fraction has also been reduced to 22 wt%, but the yield of diesel fraction increases to 69 wt%. Moreover, the deactivation of the catalyst has also been studied under the optimum conditions.     

Well-dispersed palladium nanoparticles on three-dimensional hollow N-doped graphene frameworks for enhancement of methanol electro-oxidation

In this work, palladium (Pd) nanoparticles/three-dimensional hollow N-doped graphene frameworks (HNGF) hybrid catalysts were fabricated by using amine-functionalized poly (glycidyl methacrylate) microspheres-templated HNGF as supporting materials for Pd nanoparticles (NPs). The results demonstrate that the Pd NPs with average sizes of ~ 5.5 nm can be well dispersed on the surfaces of HNGF with internal circular holes of ~ 400 nm. The Pd/HNGF catalysts exhibit high electrocatalytic activity and durability toward methanol electro-oxidation in alkaline medium, compared to Pd/graphene and Pd/carbon.     

Curie-point pyrolysis–gas chromatography–mass spectroscopic analysis of theabrownins from fermented Zijuan tea

Zijuan tea theabrownins (ZTTBs) was extracted from a type of fermented Zijuan tea and separated into fractions according to molecular weight. The extract was found to contain predominantly two fractions: <3.5 kDa and >100 kDa. These two fractions were analyzed for chemical composition, structural characteristics by Curie-point pyrolysis–gas chromatography–mass spectroscopy (CP-Py–GC/MS). The affects of pyrolysis temperature on pyrolytic products were also investigated. The fraction >100 kDa produced 50 GC/MS peaks during pyrolysis at 280 °C, 70 peaks at 386 °C, and 134 peaks at 485 °C. Fourteen of the products formed at 280 °C, 12 of those formed at 386 °C, and 21 of those formed at 485 °C were identified with match qualities of greater than 80%. The fraction <3.5 kDa gave 51 peaks during pyrolysis at 280 °C, 99 peaks at 386 °C, and 257 peaks at 485 °C. Six products formed at 280 °C, four products formed at 386 °C, and 61 products formed at 485 °C were identified with match qualities of greater than 80%. Pyrolysis temperatures of 485 °C and 386 °C were found suitable for the two fractions respectively. CP-Py–GC/MS revealed that, the fraction >100 kDa mainly consisted of phenolic pigments, esters, proteins, and polysaccharides, while the fraction <3.5 kDa contained no polysaccharide. CP-Py–GC/MS is an effective tool for the composition difference and structural characteristics of ZTTBs as well as other complex macromolecular plant pigments.     

Thermal and catalytic degradation of pyrolytic oil from pyrolysis of municipal plastic wastes

Thermal and catalytic degradation of pyrolytic oil obtained from the commercial rotary kiln pyrolysis plant for municipal plastic waste was studied by using fluid catalytic cracking (FCC) catalyst in a bench scale reactor. The characteristics of raw pyrolytic oil and also thermal and catalytic degradation of pyrolytic oil using FCC catalyst (fresh and spent FCC catalyst) under rising temperature programming was examined. The experiments were conducted by temperature programming with 10 °C/min of heating rate up to 420 °C and then holding time of 5 h. During this programming, the sampling of product oil was conducted at a different degradation temperature and also different holding time. The raw pyrolytic oil showed a wide retention time distribution in GC analysis, from 5 of carbon number to about 25, and also different product characteristics with a comparison of those of commercial oils (gasoline, kerosene and diesel). In thermal degradation, the characteristics of product oils obtained were influenced by reaction temperature under temperature programming and holding time in the reactor at 420 °C. The addition of FCC catalyst in degradation process showed the improvement of liquid and gas yield, and also high fraction of heavy hydrocarbons in oil product due to more cracking of residue. Moreover, the characteristic of oil product in catalytic degradation using both spent and fresh FCC catalysts were similar, but a relatively good effect of spent FCC catalyst was observed.     

A facile preparation of carbon-supported Pd nanoparticles for electrocatalytic oxidation of formic acid

A low temperature approach via the complexing of PdCl₂ with EDTA followed by NaBH₄ reduction has been used to prepare Vulcan XC-72 carbon-supported Pd nanoparticles (Pd/C). The mean particle size of the Pd/C catalysts is found to increase from 3.3 to 9.2 nm with heat-treated temperature. TEM images demonstrated that the Pd nanoparticles are well dispersed on the support with a relatively narrow particle size distribution. A correlation between the electrocatalytic activity of formic acid oxidation and particle size of the Pd/C catalysts indicates that the highest activity of formic acid oxidation is found with a Pd mean particle size of ca. 4.7 nm. The preparation method used here is cost-effective and should be easily scaled for industrial production.     

Effects of H3PO4 and KOH in carbonization of lignocellulosic material

Samples of lignocellulosic material, stem of date palm (Phoenix dactylifera), were carbonized at different temperatures (400–600 °C) to investigate the effects of their impregnation with aqueous solution of either phosphoric acid (85 wt%) or potassium hydroxide (3 wt%). The products were characterized using BET nitrogen adsorption, helium pycnometry, Scanning Electron Microscopy (SEM) and oil adsorption from oil–water emulsion (oil viscosity, 60 mPa s at 25 °C). True densities of the products generally increased with increase in carbonization temperature. Impregnated samples (acid/base) showed wider differences in densities at 400 (1.978/1.375 g/cm³) than at 600 °C (1.955/2.010 g/cm³). Without impregnation, the sample carbonized at 600 °C showed higher density of 2.190 g/cm³. This sample has impervious surface with BET surface area of 124 m²/g. Acid-impregnated sample carbonized at 500 °C has the highest surface area of 1100 m²/g and most regular pores as evidenced by SEM micrographs. The amounts of oil adsorbed decreased with increase in carbonization temperature. Without impregnation, sample carbonized at 400 °C exhibited equilibrium adsorption of 4 g/g which decreases to about a half for sample carbonized at 600 °C. Impregnation led to different adsorptive capacities. There are respective increase (48 wt%) and decrease (5 wt%) by the acid- or base-impregnated samples carbonized at 600 °C. This suggests higher occurrence of oil adsorption-enhancing surface functional groups such as carbonyl, carboxyl and phenolic in the former sample.     

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).     

Investigation on catalyzed combustion of wheat straw by thermal analysis

Combustion of wheat straw incorporating TiO₂, CuO and MnO₂ was investigated by means of thermal analysis carried out at 20 °C/min in the temperature range from 50 °C to 900 °C. Combustion characteristic indexes had been put forward to describe wheat straw combustion characteristics. All the results showed that the catalysis of the catalysts to the wheat straw combustion had been embodied in facilitation of the volatile matters release from wheat straw, which reduced the temperature of the maximum combustion rate, and the relative active sequence of catalysts to the ignition characteristic could be improved remarkably. The catalysis of different catalysts to the Devolatilization Index could be described as follows: MnO₂ > TiO₂ > CuO, and the relative active sequence of catalysts to the Combustion Characteristic Index could be described as follows: CuO > TiO₂ > MnO₂.     

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.     

Transformation of South African coal fly ash into ZSM-5 zeolite and its application as an MTO catalyst

This study presents a way of using South African coal fly ash by extracting metals such as Al and Fe with concentrated sulphuric acid, and then using the solid residue as a feedstock for the synthesis of ZSM-5 zeolite. The percentage of aluminium and iron oxides decreased from 28.0 ± 0.2% and 5.0 ± 0.1% in coal fly ash to 24.6 ± 0.1% and 1.6 ± 0.01% in the acid treated coal fly ash respectively. The fly ash-based zeolite ZSM-5 sample synthesised from the solid residue after extraction of Al and Fe, contained 62% of ZSM-5 zeolite pure phase with a number of Brønsted acid site density of 0.61 mmol per g_zeolite.By properly treating the as-prepared coal fly ash-based ZSM-5 zeolite, an active and selective methanol-to-olefins acid catalyst could be designed, leading to full methanol conversion during 15 h on stream. The optimised catalyst exhibited a cumulative methanol conversion capacity of 71 g(MeOH_converted)/g(catalyst) and a light olefin productivity of 21 g(C₂₌–C₄₌)/g(catalyst).     

Hydrogénation du CO2 en hydrocarbures sur des catalyseurs bifonctionnels CFA-HZSM-5

The increase of the concentration of greenhouse gases in the atmosphere, especially CO₂, produced mainly by the burning of fossil fuels is one of the principal causes of global warming. The transformation of CO₂ into tangible products such as fuels and/or raw materials for the petrochemical industry (methanol, hydrocarbons) is one of the possible routes. The synthesis of hydrocarbons by hydrogenation of CO₂ can be done in a single step using oxide/zeolite catalysts. The objective of our study was to evaluate the effect of the addition of zeolite and the proximity between the two oxide–zeolite sites where the oxide layer is iron-based and wherein the zeolite is represented by the HZSM-5. For this, a series of hybrid catalysts was prepared by CuO–Fe₂O₃–Al₂O₃/HZSM-5 mechanical mixing. The catalytic conversion of CO₂ has been carried out in a fixed-bed reactor under the following operating conditions: T = 350 °C, P = 30 bar, H₂/CO₂ = 3. The results show that the addition of the zeolite by intimately mixing it does not improve the catalytic properties and that the yield of hydrocarbons is best obtained with the CuO–Fe₂O₃–Al₂O₃ oxide catalyst according to the Fisher–Tropsch process (FT). However, the increase in near-zeolite oxide inhibits the formation of hydrocarbons and promotes the formation of carbon monoxide.     

Synthesis of L10 Fe–Pd films by electrodeposition and thermal annealing

Fe–Pd alloy films have been prepared by electrochemical deposition from an alkaline electrolyte containing Fe sulfate, Pd chloride and 5-sulfosalicylic acid onto polycrystalline titanium substrates. The as-deposited films were nanocrystalline and magnetically soft (coercivity ∼ 25 Oe). L1₀ Fe–Pd films with a (1 1 1) preferred orientation were obtained by post-deposition thermal annealing of films with composition about 37 at% Fe in an (Ar + 5% H₂) gas flow at 500 °C. Such films exhibit hard magnetic properties, with a coercivity up to 1880 Oe, and a slightly anisotropic magnetic response, with a larger in-plane remanence. Preliminary magnetic investigations support magnetization switching through pinning of domain walls.     

Effects of calcination and activation temperature on dry reforming catalysts

The effect of calcination temperatures on dry reforming catalysts supported on high surface area alumina Ni/γ-Al₂O₃ (SA-6175) was studied experimentally. In this study, the prepared catalyst was tested in a micro tubular reactor using temperature ranges of 500, 600, 700 and 800 °C at atmospheric pressure, using a total flow rate of 33 ml/min consisting of 3 ml/min of N₂, 15 ml/min of CO₂ and 15 ml/min of CH₄. The calcination was carried out in the range of 500–900 °C. The catalyst is activated inside the reactor at 500–800 °C using hydrogen gas. It was observed that calcination enhances catalyst activity which increases as calcination and reaction temperatures were increased. The highest conversion was obtained at 800 °C reaction temperature by using catalyst calcined at 900 °C and activation at 700 °C. The catalyst characterization conducted supported the observed experimental results.