Catalyst Leaching Research Articles

Prins cyclization for the preparation of 2-isobutyl-4-methyl-tetrahydro-2H-pyran-4-ol using supported heteropoly acids

The selective preparation of 2-isobutyl-4-methyl-tetrahydro-2H-pyran-4-ol (also called Florosa or Florol) was performed. Prins cyclization of isoprenol and isovaleraldehyde was used for the preparation of this important fragrant compound. Heteropoly acids (phosphotungstic and phosphomolybdic) were used as a catalyst in homogeneous and also in heterogeneous arrangements (after their immobilization). The only solvent necessary for the reaction was water that enables the increase of the selectivity to the desired product by hydrolysis of catalyst-carbocation intermediates. In a flow, both heteropoly acids were successfully anchored on siliceous MCM-41 and resultant materials were characterized by XRF, XRD, SEM, FTIR, UV–Vis, and nitrogen adsorption. Heterogenization was performed in water as a solvent. Anchored heteropoly acids were used in Prins cyclization under the same conditions (addition of water), and the selectivity was even higher (96 %), comparing the homogeneous arrangement. No leaching of catalyst from solid was observed. Moreover, the catalyst may be reused without loss of activity and selectivity at least four times.

Palladium–S‐propyl‐2‐aminobenzothioate immobilized on Fe3O4 magnetic nanoparticles as catalyst for Suzuki and Heck reactions in water or poly(ethylene glycol)

A moisture‐ and air‐stable heterogenized palladium catalyst was synthesized by coordination of palladium with S‐propyl‐2‐aminothiobenzamide supported on Fe3O4 magnetic nanoparticles. The prepared nanocatalyst was characterized using Fourier transform infrared, energy‐dispersive X‐ray and inductively coupled plasma atomic emission spectroscopies, X‐ray diffraction, vibrating sample magnetometry, transmission and scanning electron microscopies, dynamic laser scattering and thermogravimetric analysis. This catalyst could be dispersed homogeneously in water or poly(ethylene glycol) and further applied as an excellent nano‐organometal catalyst for Suzuki and Heck reactions. The catalyst was easily separated with the assistance of an external magnet from the reaction mixture and reused for several consecutive runs without significant loss of its catalytic efficiency or palladium leaching. The leaching of catalyst was examined using hot filtration and inductively coupled plasma atomic emission spectroscopy. Also, the effects of various reaction parameters on the Suzuki and Heck reactions are discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Pt supported nitrogen doped hollow carbon spheres for the catalysed reduction of cinnamaldehyde

Carbon and nitrogen coated Stöber silica spheres were prepared by a standard procedure using acetonitrile at different CVD temperatures (800–1000°C) and as a function of time (1–4h). HF treatment was used to remove the silica from the carbon coated silica to give monodispersed nitrogen doped hollow carbon spheres (N-HCSs; shell thickness=50nm). The surface areas of the N-CSs increased significantly after removal of the SiO2 core (N-HCS=47m2/g). Platinum nanoparticles, prepared by a [Pt(COD)Cl2] deposition method were dispersed (d=2.8±0.4nm) on the N-HCS supports. Thermal treatment of the Pt/N-HCS900-4 (prepared at 900°C for 4h) in a 5% H2/Ar atmosphere at 120°C (Pt/N-HCS900-4-120) and 300°C (Pt/N-HCS900-4-300) gave metallic Pt (2.48%) which was confirmed by XRD and XPS studies. The XPS N1s spectra of Pt/N-HCS900-4-120 showed the presence of quaternary, pyridinic and pyrollic nitrogen atoms. These nitrogen doped carbon supported Pt nanoparticle catalysts were observed to reduce cinnamaldehyde to the unsaturated alcohol, cinnamyl alcohol (isopropanol/30bar H2/80°C) with >99% conversion and selectivity. The catalyst used in the reduction of cinnamaldehyde to cinnamyl alcohol could be recycled 12 times with minimal loss in conversion and this correlated with the small amount of Pt leaching or physical loss of catalyst (<2%). The corresponding Pt/catalyst made on undoped HCSs showed a much greater loss of activity with recycling. It is seen that N doping of carbon is an effective method to bind Pt to carbon.

Propiconazole and Penconazole as Effective Extractants for Selective recovery and concentration of platinum(IV) and palladium(II) from hydrochloric acid solutions formed in leaching of spent aluminoplatinum and aluminopalladium catalysts

Selective recovery and concentration of platinum(IV) and palladium(II) from hydrochloric acid solutions of varied composition was studied using commercial reagents propiconazole and penconazole as extractants. The ranges of hydrochloric acid concentrations for effective extraction and highly selective separation of platinum metals from Al(III) and Ni(II) with propiconazole (toluene with 15 vol % n-decanol as deluent) and penconazole (chloroform) were determined. The conditions for 10-fold selective concentration of platinum metals with recovery of more than 99.9% of metal ions into the organic phase were found. The conditions for quantitative (>99%) stripping of platinum(IV) with a hydrochloric acid solution of thiourea and palladium(II) with ammonia solution were determined. The results obtained can be used for optimizing the modes of selective recovery of platinum(IV) and palladium(II) from hydrochloric acid solutions formed in leaching of alumina-supported platinum-rhenium, platinum-nickel, and palladium catalysts.

Supercritical CO2 extraction of molybdenum-ligand complexes from sulfuric solutions

The development of environmental-friendly process for strategic metal extraction, limiting organic solvent use and effluent production, appears to be quite a challenging purpose. Production of pure molybdenum using supercritical CO2 extraction process, from sulfuric solution obtained by ore or used catalyst leaching, has been evaluated. Two organic ligands, trioctylamine and 2-ethylhexyl 2-ethylhexylphosphonic acid, were studied to extract Mo as metal complexes solubilized in supercritical CO2. Extraction with trioctylamine revealed to be non-efficient due to a lack of Mo-trioctylamine complex solubility in CO2, even if extraction selectivity of molybdenum versus iron impurity was interesting. On the contrary, extraction with 2-ethylhexyl 2-ethylhexylphosphonic acid leads to high Mo collection efficiency (up to 90% in 7h). However, no selectivity was observed between molybdenum and zirconium. The selectivity of 2-ethylhexyl 2-ethylhexylphosphonic acid towards molybdenum in presence of iron was better but clearly decreased in presence of zirconium.

Metalloporphyrins immobilized in Fe3O4@SiO2 mesoporous submicrospheres: Reusable biomimetic catalysts for hydrocarbon oxidation

We successfully immobilized metalloporphyrins (MeP) in mesoporous silica coating magnetite spheres. In this sense, we prepared two different classes of core@shell supports, which comprise aligned (Fe3O4-AM-MeP, MeP=FeP or MnP) and non-aligned (Fe3O4-NM-MeP, MeP=FeP or MnP) mesoporous magnetic structures. X-ray diffractometry and energy dispersive X-ray spectroscopy confirmed the mesoporous nature of the silica shell of the materials. Magnetization measurements, scanning and transmission electron microscopies (SEM/TEM), electrophoretic mobility (ζ-potential), and infrared spectroscopy (FTIR) also confirm the composition and structure of the materials. The catalysts maintained their catalytic activity during nine reaction cycles toward hydrocarbon oxidation processes without detectable catalyst leaching. The catalysis results revealed a biomimetic pattern of cytochrome P450-type enzymes, thus confirming that the prepared materials are can effectively mimic the activity of such groups.

Investigation of phase behaviour of selected chemical reaction mixtures in microemulsions for technical applications

Abstract The phase behaviour of microemulsion systems, which are used as reaction media for hydroformulation and Heck coupling reactions, is investigated. A detailed analysis of microemulsion systems is the key for a successful implementation in technical processes. In the case of the hydroformulation reaction, the desired three-phase state is shifted depending on the composition of the reaction mixture and a temperature profile is required to maintain this state during the whole reaction. In case of the Heck coupling reaction, the desired state is an oil-in-water (o/w) one-phase microemulsion. We found that the best reaction performance is with K2CO3 as the base, but at higher reactant concentrations with the same base only two-phase systems are obtained. Heck reaction was successfully performed at higher reactant concentrations in the two-phase system consisting of >75 wt% water. The applied heterogeneous sol–gel supported palladium catalyst could be easily recycled with minor catalyst leaching.

Rapid and selective extraction of Pd(ii) ions using the SCS type pincer ligand 1,3-bis(dimethylthiocarbamoyloxy)benzene, and its Pd(ii) extraction mechanism

Extractant1extracts Pd(ii) ionsviapincer type S–C–S tridentate ligands, with the formation of fused six-membered chelate rings. Rapid and selective extraction by1of &gt;99% Pd(ii) ions from an automotive catalyst leach liquor was observed.

Preparation of Poly(ionic liquid)s-Supported Recyclable Organocatalysts for the Asymmetric Nitroaldol (Henry) Reaction.

A novel strategy for the embedding of quinine-based organocatalysts in polymerized ionic liquids-based hydrogels is presented. With this technique, the encapsulated organocatalyst was successfully recovered and reused for four cycles without any loss of enantioselectivity (up to 91% ee) for the asymmetric nitroaldol (Henry) reaction. In this study, high catalyst leaching was significantly reduced (<0.01%) by controlling the water content. After catalyst removal, evaporation of the solvent affords the product in 98% purity without any further purification.

Fe3O4@SiO2–imid–PMAn magnetic porous nanosphere as recyclable catalyst for the green synthesis of quinoxaline derivatives at room temperature and study of their antifungal activities

An efficient, simple, and green procedure for the synthesis of quinoxaline derivatives catalyzed by Fe3O4@SiO2–imid–PMAn nanoparticles at room temperature is described. This environmentally benign method provides several advantages such as mild reaction conditions, good to excellent yields, short reaction times, simple work-up and catalyst stability, easy preparation, heterogeneous nature and easy separation of the catalyst. Also, nanocatalyst can be easily recovered by a magnetic field and reused for the next reactions for at least 6 times without distinct deterioration in catalytic activity. SEM, BET, DLS and leaching of catalyst after each reaction cycle were investigated. Furthermore, antifungal activity of various derivatives against three phytopathogenic fungi (Alternaria alternata, Pyricularia oryzae, and Alternaria brassicae) was investigated.

Efficient and selective oxidation of olefins and alcohols using nanoparticles of WO3-supported manganese oxides (W1−x Mn x O3)

Nanoparticles of manganese oxide supported on tungsten oxide (WO3) were synthesized by an impregnation method using Mn(NO3)2 and Na2WO4 as a source of manganese and tungsten. Atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the physicochemical properties of compounds. Due to a highly dispersed state of manganese or insertion of manganese ions into the WO3 lattice, no manganese oxide peak was observed in the XRD patterns of the W1−x Mn x O3 nanoparticles. Investigation of W1−x Mn x O3 by AAS and EDX showed that the relative atomic abundance of Mn present in the bulk and on the surface of WO3 was 3.68% and 4.8% respectively. For the first time, the catalytic oxidation of olefins and alcohols, in the presence of these materials and hydrogen peroxide (H2O2) as a green oxidant at room temperature was studied. The recoverability and catalyst leaching of the W1−x Mn x O3 nanoparticles in epoxidation of styrene as a model reaction were also investigated.

Investigation on the sonocatalytic degradation of nitrobenzene using heterogeneous nanostructured catalysts in absence and presence of surfactant

Because of the extensive use and excessive release of various NB, economical and efficient methods for the treatment of wastewater and cleanup of petrochemical compounds are needed. This study focused on the sonocatalytic degradation of NB in aqueous solution assisted with H2O2 oxidant and nanostructured metal oxide catalysts, prepared in the absence of CTAB (series I), (Fe2O3-I, CuO-I, NiO-I, and Co3O4-I) and nanostructured metal oxide catalysts prepared in the presence of CTAB (series II), (Fe2O3-II, CuO-II, NiO-II, and Co3O4-II). The physicochemical properties of these catalysts were investigated via X-ray powder diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and point of zero charge (PZC).The potential degradation feasibility for NB in US/nano metal oxide (series I and or series II)/H2O2 systems was measured by GC analysis at regular time intervals. Otherwise, some operational parameters such as ultrasonic irradiation time, solution pH value, H2O2 concentration, different weights of the nano-sized catalysts, NB concentration, leaching of the nano-sized catalysts, and reaction kinetics had been examined. It was found that H2O2 oxidant can effectively assist the sonocatalytic degradation of NB in the presence of nano-sized oxides (series I) and with more efficiency in the presence of nano-sized oxides (series II), and the effect of efficiency in degradation was changed in the order of (Fe2O3>CuO>NiO>Co3O4). Therefore, oxides prepared in micellar solution were found to upgrade the economic aspect of NB degradation.

Effect of Aluminum Alkyls on a Homogeneous and Silica-Supported Phenoxy-Imine Titanium Catalyst for Ethylene Trimerization

A phenoxy-imine titanium catalyst (FI-catalyst) for selective ethylene trimerization was immobilized on methyl aluminoxane (MAO) pretreated silica and its activity and selectivity was compared with that of the corresponding homogeneous catalyst system. The homogeneous and heterogeneous ethylene oligomerization was conducted in the presence of different aluminum alkyls, commonly used as scavengers during olefin polymerization to remove residual oxygen and moisture from the reaction medium. Both the homogeneous and heterogeneous catalysts were strongly affected by the presence of scavenger in the reaction medium. Upon activation with R3Al/MAO (R= Et, nOct, iBu), the homogeneous catalyst switches selectivity from ethylene trimerization to polymerization. NMR spectroscopic investigations indicate that this change of selectivity can be attributed to ligand exchange between the precatalyst and the aluminum alkyl and reduction of the titanium species. The thereby formed ligand-free and/or reduced titanium alkyls act as polymerization catalysts and are responsible for the increasing polymer formation. Using the heterogeneous catalyst, the scavenger employed during ethylene trimerization was found to be of crucial influence regarding the activity of the catalyst and the occurrence of reactor fouling. Employing aluminum alkyls like iBu3Al and nOct3Al resulted in catalyst leaching and homogeneous polymer formation. The latter was prevented using Me3Al or Et3Al as scavengers; however, in general the supported catalyst was poisoned by aluminum alkyls, resulting in a low overall activity. It was found to be beneficial for the heterogeneous trimerization system to employ silica-supported scavengers. By physical separation of the catalyst and the scavenger this poisoning effect was effectively prevented, resulting in a highly active heterogeneous catalyst.

Palladium Loaded on Magnetic Nanoparticles as Efficient and Recyclable Catalyst for the Suzuki- Miyaura Reaction

Palladium is the best metal catalyst for Suzuki cross coupling reaction for synthesize of unsymmetrical biaryl compounds. But its high cost limits its application in wide scale. Using of nanoscale particles as active catalytic cites is a good approach for reducing needed noble metal. By loading precious nanoparticles on magnetic nanocores as a support, recycling and reusing of catalyst will be possible. Magnetic nanoparticles have super paramagnetic feature and applying an external magnetic field can collect the supported catalyst from reaction milieu simply. In this work new palladium catalyst immobilized on modified magnetic nanoparticles containing NNO donor atoms were synthesized. Then the catalyst characterized by FT-IR spectroscopy, thermogravimetric analysis, X-ray diffraction and ICP. Prepared catalyst showed high activity in the Suzuki– Miyaura cross-coupling reaction of phenylboronic acid with aryl halides. Activity, Pd loading, reusability and Pd leaching of catalyst were studied. Results showed that the supported catalyst has the advantage to be completely recoverable with the simple application of an external magnetic field. Article history:

Influence of synthesis method on leaching of the Cr-TiO2 catalyst for visible light liquid phase photocatalysis and their stability

Cr-TiO2 nanoparticles have been synthesized by using flame spray pyrolysis (FSP), co-precipitation, and sol–gel synthesis techniques. Liquid phase photocatalytic activity of the synthesized catalysts by various methods were studied for photocatalytic degradation of 4-chlorophenol under visible light (400–800nm) conditions. It was found that the FSP Cr-TiO2 has superior photocatalytic activity to other synthesis methods. XRD patterns showed that the anatase phase was higher for the sol–gel and co-precipitation made catalyst. Our TPR results indicated higher presence of the Cr+6 of the FSP made catalysts in comparison to the other ones, which had significant influence in the activity of the catalyst. All the three catalysts showed the decline in the activity which was a consequence of the decrease of Cr+6 content of the catalyst along with the forming agglomerates in the spent and reactivated catalyst. The leaching of the Cr into the liquid phase for pH ranging from 3 to 11 was studied of the FSP made catalyst and was found to be minimal with respect to other synthesis methods. For this reason there should be careful consideration for use of Cr containing catalysts for practical water treatment. We developed Si/Ti/Cr catalyst by FSP method which stabilizes the photocatalytic activity of the catalyst. The BET surface area of the FSP Si/Ti/Cr catalyst was stable even with the reactivated catalyst. The developed catalyst also demonstrated an advantage of low levels of metal leaching during the catalytic reaction thus avoiding secondary metal contamination to the treated wastewater. We found higher Cr(VI) concentration in the reactivated materials which is a significant factor for the improvement in the photocatalytic activity of the materials. We have observed the improvement in the activity with the addition of Si by FSP method as a support and it also caused the improvement in the surface area and structural stability.

Data Driven Conceptual Process Design for the Hydroformylation of 1-Dodecene in a Thermomorphic Solvent System

The purpose of this work is to investigate the effect that a solvent mixture has on the process-wide performance of the hydroformylation of 1-dodecene. A thermomorphic solvent mixture consisting of dimethylformamide and decane is used as a tunable solvent that ensures monophasic conditions during the reaction and that is also used to separate the homogeneous catalyst from the product through temperature controlled phase splitting in a decantation unit. So far reactor and process design for this reaction has been primarily based on a specific composition of the solvent mixture and without considering the economic impact of catalyst leaching. In order to reduce the complexity of the conceptual process design problem, linear regression models were used to accurately estimate the partition coefficients of the multicomponent mixture in the decanter. Using limited available experimental data from the literature, correlations were derived for catalyst loss based on the composition of the thermomorphic solvent sy...

Pd loaded amphiphilic COF as catalyst for multi-fold Heck reactions, C-C couplings and CO oxidation.

COFs represent a class of polymers with designable crystalline structures capable of interacting with active metal nanoparticles to form excellent heterogeneous catalysts. Many valuable ligands/monomers employed in making coordination/organic polymers are prepared via Heck and C-C couplings. Here, we report an amphiphilic triazine COF and the facile single-step loading of Pd0 nanoparticles into it. An 18–20% nano-Pd loading gives highly active composite working in open air at low concentrations (Conc. Pd(0) <0.05 mol%, average TON 1500) catalyzing simultaneous multiple site Heck couplings and C-C couplings using ‘non-boronic acid’ substrates, and exhibits good recyclability with no sign of catalyst leaching. As an oxidation catalyst, it shows 100% conversion of CO to CO2 at 150 °C with no loss of activity with time and between cycles. Both vapor sorptions and contact angle measurements confirm the amphiphilic character of the COF. DFT-TB studies showed the presence of Pd-triazine and Pd-Schiff bond interactions as being favorable.

High catalytic efficiency of palladium nanoparticles immobilized in a polymer membrane containing poly(ionic liquid) in Suzuki–Miyaura cross-coupling reaction

The elaboration of a polymeric catalytic membrane containing palladium nanoparticles is presented. The membrane was prepared using a photo-grafting process with imidazolium-based ionic liquid monomers as modifying agent and microPES® as support membrane. Ionic liquid serves as a stabilizer and immobilizer for the catalytic species, i.e. palladium nanoparticles. The Suzuki–Miyaura cross-coupling reaction was carried out on the catalytic membrane in flow-through configuration. Complete conversion was achieved in 10s through one single filtration, without formation of byproducts. The apparent reaction rate constant was three orders of magnitude greater than in a batch reactor. No catalyst leaching was detected. This membrane offers the possibility of continuous production with no need for a separation step of the catalyst from the reaction medium.

Role of surface intermediates in the deactivation of Mg[sbnd]Zr mixed oxides in acetone self-condensation: A combined DRIFT and ex situ characterization approach

The role of the adsorbed reactants and intermediates on the performance and deactivation behavior of MgZr mixed oxides as acetone self-condensation catalysts is studied in this work. DRIFT spectroscopy was used for identifying the adsorbed species and following their evolution during both acetone self-condensation reaction and thermo-desorption of pre-adsorbed reactants and products. The evolution of these species and the results of the characterization (nitrogen physisorption, temperature-programmed oxidation, and catalyst leaching) of catalysts samples taken in a continuous reactor at different temperatures (523, 623, and 723K) and times on stream allow to determine that two concomitant deactivation causes are present in this reaction: the strong adsorption of dimers and trimers on the catalyst surface (especially important at the lowest temperature) and the formation of heavy condensation products physically deposited on the catalyst surface (more relevant at the highest temperature).

Cyanide leaching of gold catalysts

Gold catalysts remain of great interest, but a high gold price presents a concern. Gold can be leached from gold–titania catalysts using alkaline cyanide solutions. The specific activity of gold for CO oxidation can thereby be increased substantially, though the precise nature of the gold before and after treatment remains unclear. It seems unlikely that leaching proceeds in a simple manner by selective dissolution of metallic gold particles. Rather it is likely that cyanide ions interact with gold centers in several ways and, in addition, alkali metal ions may also modify activity.