Aqueous Catalyst Phase Research Articles

Catalytic hydroxylation of phenol to dihydroxybenzene by Fe(II) complex in aqueous phase at ambient temperature

Inspired by natural [Fe]-hydrogenase, mono-iron complex FeII(CO)3I3-[trimethylpyridine-H] (complex 1) was synthesized and characterized by IR, 1H NMR, 13C NMR, EA. The singe crystal structure of the complex 1 was characterized by single crystal X-ray diffraction. The hydroxylation reaction of phenol to dihydroxybenzene was conducted using complex 1 as catalyst in aqueous phase at ambient temperature. Under the optimum conditions, the phenol conversion was 20.5%, dihydroxybenzene selectivity was 83.7%, catechol/hydroquinone (mol/mol) was 2.6. Complex 1 can be a promising catalyst for hydroxylation of phenol to dihydroxybenzene because of mild reaction conditions and good catalytic performance.

Considerations on film reactivity in the aqueous biphasic hydroformylation

In experiments and kinetic models it was shown that the reaction rate of the biphasic aqueous hydroformylation of 1‐octene is linear dependent on the created interfacial area. This phenomenon is directly linked to the question whether the reaction takes place in the bulk phase and is mass transfer limitation or at the surface which would mean an increase of reaction space. To evaluate the place of reaction a mass transfer analysis has been carried out. No mass transfer limitation for the gaseous components carbon monoxide and hydrogen as well as the olefin 1‐octene was determined for the aqueous catalyst phase by calculating the Hatta numbers. With this observation it is possible to exclude the mass transfer as a potential influence and hence the aqueous bulk as the place of reaction. Thus the reaction is most probably surface active. This can be either explained the increase in film volume fraction where non‐polar substrate as well as polar catalyst complex is present or through an increased catalyst concentration at the surface through dipole moment fluctuations. © 2017 American Institute of Chemical Engineers AIChE J, 63: 161–171, 2018

Acceleration of lean aqueous hydroformylation in an innovative jet loop reactor concept

The lean biphasic aqueous hydroformylation without chemical additives of the long chain olefin 1-octene using the simple ligand triphenyl trisulfonate sodium salt was investigated in an innovative jet loop reactor on miniplant scale. This elaborate reactor type offers a unique mixing characteristic and is optimised in terms of mechanical energy transfer into the reaction medium through a jet nozzle and organic phase volume fraction. Both variables are important factors in the emulsification of two immiscible liquids. It is subsequently compared to a standard stirred reactor which was also individually optimised. Both concepts showed individual advantages in terms of productivity and catalytic activity. While the jet loop reactor reached high turnover frequencies of 7640h−1 the stirred tank reactor showed high space time yields of up to 12.6·10−5kmolm−3s−1. At very low amounts of dispersed aqueous catalyst phase even very high catalytic activity (TOF=10,960h−1) was observed in the jet loop reactor. High reactivity could also be preserved in a long time run leading to a total turnover number of 76,500. The jet loop reactor enabled high mass transfer rates for the substrate gases of up to 0.28s−1 for H2 and 0.21s−1 for CO resulting in a mass transfer multiple times faster than the obtained reaction rates. To increase regio-selectivity the bidentate ligand sulfoxanthphos was applied which increased the regio-selectivity up to l:b=53 but reduced catalytic activity.

Kinetic investigation of lean aqueous hydroformylation – An engineer’s view on homogeneous catalysis

The additive-free, biphasic aqueous hydroformylation of the long chain olefin 1-octene was investigated with the goal to derive a mathematical expression for the macro kinetic and to increase selectivity towards aldehydes while maintaining fast reaction rates. The influence of different important chemical parameters such as catalyst precursor, catalyst concentration, ligand excess, pH-value, salt concentration, temperature, gas pressure and gas composition was estimated. At 10MPa and 373K the highest rate of reaction with 41·10–5kmolm−3s−1 was reached. An optimal compromise between high selectivity and activity was found at 8MPa syngas pressure and 353K reaction temperature. Selectivity was thus increased from 20% to 76% with octene isomers as the only by-products. The rate of reaction was linearly dependent on the created interfacial area as shown in previous publications. The optimised conditions were applied to other olefinic compounds with different structural characteristics. Obtained insights were used to establish a rate expression for this reaction, incorporating the interfacial area between organic substrate and aqueous catalyst phase. This novel approach helps to draw attention towards the aspect of procedural rate enhancement in homogeneous catalysis.

Visible light photocatalytic activities of BiOBr-activated carbon (derived from waste polyurethane) composites by hydrothermal process

Hybrid materials such as activated carbon based photocatalysts are very promising advanced materials which are bifunctional with both adsorption and photocatalytic properties. In the present work, activated carbon (AC) was prepared from waste polyurethane foam materials. The photocatalytic hybrid materials were synthesized from bismuth oxide precursor (BiOBr) and activated carbon by hydrothermal process. The prepared AC-BiOBr composite was characterized by XRD, FE-SEM, surface area, porosity, zero point charge and UV-DRS. The prepared AC-BiOBr composite had lesser band gap energy (2.64eV) when compared to pristine BiOBr (2.84eV). The photodegradation efficiency of the prepared composite was evaluated for the degradation of malachite green dye under visible light irradiation. Preliminary photocatalytic studies were carried out by varying initial aqueous phase pH, catalyst dosage and initial malachite green dye concentration. Kinetic studies were also carried out for the degradation of malachite green dye by pristine BiOBr and AC-BiOBr composite. The rate constants of the photodegradation were evaluated by fitting the kinetic data with pseudo first-order model equation and the rate constants of AC-BiOBr composite was slightly higher than that of pristine BiOBr. The effect of adsorption on photocatalytic degradation was evaluated by adsorption experiments using AC, BiOBr and AC-BiOBr composite as dark reactions. The equilibrium adsorption data were modelled using Langmuir and Freundlich isotherms. The plausible mechanism for the photodegradation of malachite green dye was also proposed using MALDI-TOF spectral analysis. The prepared adsorbent-photocatalytic composite had good adsorption and photocatalytic degradation efficiency for the removal of malachite green dye molecules from aqueous solution.

Effect of Ru Particle Size on Hydrogenation/Decarbonylation of Propanoic Acid Over Supported Ru Catalysts in Aqueous Phase

The aqueous-phase hydrogenation of propanoic acid was performed over the Ru/ZrO2 and Ru/Al2O3 catalysts with different Ru loading. Combined with multiple characterization techniques, such as H2-TPR, XRD, CO-FTIR, and DRIFTS of propanoic acid, the effect of Ru loading on the decarbonylation/hydrogenation of propanoic acid was investigated. Although hydrogenation/decarbonylation of carboxylic acids were strongly affected by the nature of supports, the increase of metal loading can cause the larger Ru particles and more bare Ru metal sites, which can facilitate the C–C bond cleavage reaction derived from the decarbonylation of propanoyl species over Ru metal sites.

Electrochemical Atom Transfer Radical Polymerization in Miniemulsion with a Dual Catalytic System.

An electrochemical approach was used to control atom transfer radical polymerization (ATRP) of n-butyl acrylate (BA) in miniemulsion. Electropolymerization required a dual catalytic system, composed of an aqueous phase catalyst and an organic phase catalyst. This allowed shuttling the electrochemical stimulus from the working electrode (WE) to the continuous aqueous phase and to the dispersed monomer droplets. As aqueous phase catalysts, the hydrophilic Cu complexes with the ligands N,N-bis( 2-pyridylmethyl)-2-hydroxyethylamine (BPMEA), 2,2'-bipyridine (bpy), and tris(2-pyridylmethyl)amine (TPMA) were tested. As organic phase catalysts, the hydrophobic complexes with the ligands bis(2-pyridylmethyl)-octadecylamine (BPMODA) and bis[2-(4-methoxy-3,5-dimethyl)-pyridylmethyl]octadecylamine (BPMODA*) were evaluated. Highest rates and best control of BA electropolymerization were obtained with the water-soluble Cu/BPMEA used in combination with the oil-soluble Cu/BPMODA*. The polymerization rate could be further enhanced by changing the potential applied at the WE. Differently from traditional ATRP systems, reactivity of the dual catalytic system did not depend on the redox potential of the catalysts but instead depended on the hydrophobicity and partition coefficient of the aqueous phase catalyst.

Heterogeneously Catalyzed Hydrothermal Processing of C5-C6 Sugars.

Biomass has been long exploited as an anthropogenic energy source; however, the 21st century challenges of energy security and climate change are driving resurgence in its utilization both as a renewable alternative to fossil fuels and as a sustainable carbon feedstock for chemicals production. Deconstruction of cellulose and hemicellulose carbohydrate polymers into their constituent C5 and C6 sugars, and subsequent heterogeneously catalyzed transformations, offer the promise of unlocking diverse oxygenates such as furfural, 5-hydroxymethylfurfural, xylitol, sorbitol, mannitol, and gluconic acid as biorefinery platform chemicals. Here, we review recent advances in the design and development of catalysts and processes for C5-C6 sugar reforming into chemical intermediates and products, and highlight the challenges of aqueous phase operation and catalyst evaluation, in addition to process considerations such as solvent and reactor selection.

Rhodium-Catalyzed Hydroformylation of Long-Chain Olefins in Aqueous Multiphase Systems in a Continuously Operated Miniplant

We investigate aqueous multiphase systems for catalytic gas/liquid reactions, namely, the rhodium-catalyzed hydroformylation of the long-chain olefin 1-dodecene. The multiphase system was formulated from 1-dodecene, water, and a nonionic surfactant, which increases the solubility between the two nonmiscible liquid phases. On the basis of these systems, we present in this paper a transfer of lab experiments (semibatch) to a successful operation of a miniplant in continuous mode. Under optimized conditions, the reaction showed turnover frequencies of ∼200 h–1 and high selectivity of 98:2 to the desired linear aldehyde. The miniplant was operated continuously for a total of 130 h. The control of the phase separation and catalyst recycling for product isolation for a long time period appeared to be challenging. Nevertheless, the separation was kept stable for over 24 h. The organic components in the product phase amounted to desired values between 95 and 99 wt %. The desired 99.99% of the catalyst remained in the aqueous catalyst phase.

Hydroaminomethylation of the Renewable Limonene with Ammonia in an Aqueous Biphasic Solvent System

AbstractWith the hydroaminomethylation of the natural compound limonene with ammonia an atom‐economic method for the synthesis of primary amines is described. This tandem reaction allows the direct conversion of the unfunctionalized monoterpene to a valuable amine product. For the first time, ammonia served as substrate to result in a maximum primary amine yield of 25 %. To overcome unwanted side reactions, a biphasic solvent system was used, consisting of an aqueous catalyst phase and an organic product phase. As catalyst the water‐soluble transition metal complex [Rh(cod)Cl]2/triphenylphosphine trisulfonate was chosen. In combination with the surfactant hexadecyltrimethylammonium chloride it provided a good phase interaction and the possibility for easy phase separation after the reaction.

ChemInform Abstract: Multiphase Reaction Media Involving Water and Carbon Dioxide for Selective Hydrogenation

AbstractReview: 43 refs.

Suzuki–Miyaura reactions promoted by a PdCl2/sulfonate‐tagged phenanthroline precatalyst in water

This work reports Suzuki–Miyaura cross‐coupling reactions of arylboronic acid with aryl halide or aryl dibromide mediated by PdCl2 (0.05 mol%) and sodium 4‐(1H‐imidazo[4,5‐f][1,10]phenanthrolin‐1‐yl)butane‐1‐sulfonate (0.05 mol%) at 100 °C in water. The corresponding cross‐coupling products were obtained in good to excellent yields. The catalytic system was recovered from the organic products by extraction with ether and the residual aqueous catalyst phase showed high activity after reuse of at least four cycles. Copyright © 2014 John Wiley & Sons, Ltd.

Elucidation of Aqueous Solvent-Mediated Hydrogen-Transfer Reactions by ab Initio Molecular Dynamics and Nudged Elastic-Band Studies of NaBH4 Hydrolysis

The rational development of aqueous-phase catalysts is limited by a lack of fundamental understanding of the precise role of solvent molecules in the reactions. For deeper insight into these general processes, we carried out a detailed theoretical study of NaBH4 hydrolysis to unravel a plethora of complex reaction pathways. Our study involves no a priori assumptions about individual reactant or product states, which are identified through a combination of ab initio molecular dynamics and nudged elastic-band methods. Snapshots of our computational modeling identify canonical reaction mechanisms whereby the aqueous environment facilitates proton and hydride transfers as well as solvent rearrangements extending across multiple layers of solvation. In addition to providing the most comprehensive computational study of NaBH4 hydrolysis to date, the mechanisms presented herein are relevant for characterizing other reaction processes involving coupled proton-hydride reactions influenced by subtle changes in reaction environments (e.g., those that would be encountered in hydrogen evolution, water oxidation, and CO2 conversion processes). This novel and unbiased quantum chemistry modeling approach shows great promise for computational elucidation of homogeneous phase chemistry.

First-principles study of phenol hydrogenation on Pt and Ni catalysts in aqueous phase.

The effect of an aqueous phase on phenol hydrogenation over Pt and Ni catalysts was investigated using density functional theory-based ab initio molecular dynamics calculations. The adsorption of phenol and the addition of the first and second hydrogen adatoms to three, ring carbon positions (ortho, meta, and para with respect to the phenolic OH group) were explored in both vacuum and liquid water. The major change in the electronic structure of both Pt(111) and Ni(111) surfaces, between a gaseous and liquid phase environment, results from a repulsion between the electrons of the liquid water and the diffuse tail of electron density emanating from the metal surface. The redistribution of the metal's electrons toward the subsurface layer lowers the metal work function by about 1 eV. The lower work function gives the liquid-covered metal a higher chemical reduction strength and, in consequence, a lower oxidation strength, which, in turn lowers the phenol adsorption energy, despite the stabilizing influence of the solvation of the partly positively charged adsorbate. At both the solid/vapor and the solid/water interface, H adatom addition involves neutral H atom transfer hence the reaction barriers for adding H adatoms to phenol are lowered by only 10-20 kJ/mol, due to a small stabilizing at the transition state. More importantly, the liquid environment significantly influences the relative energetics of charged, surface-bound intermediates and of proton-transfer reactions like keto/enol isomerization. For phenol hydrogenation, solvation in water results in an energetic preference to form ketones as a result of tautomerization of surface-bound enol intermediates.

Multiphase reaction media involving water and carbon dioxide for selective hydrogenation

The features of multiphase reaction media using water (bulk water, supported thin aqueous phase) and dense phase carbon dioxide are reviewed for selective hydrogenation of carbonyl, nitro, and cyano compounds. The interface of aqueous and organic phases is important in determining the rate of hydrogenation and the product selectivity. For supported aqueous phase catalysts, the interface between the thin aqueous film and a support material (for example, porous silica gel) has also an influential impact. The pressurization of a liquid reaction mixture (organic and/or aqueous phases) with carbon dioxide shows interesting positive effects on the reaction rate, the product selectivity, and the deactivation of a conventional supported metal catalyst. In some cases the use of both water and dense phase carbon dioxide serves as an effective reaction medium. In other words, these green solvents may act as reaction promoters. Possible roles of their actions are discussed.

Dehydration of fructose into furans over zeolite catalyst using carbon black as adsorbent

Formation of 5-hydroxymethylfurfural (HMF) from the dehydration of fructose over zeolite catalysts in aqueous phase was studied in a reactive adsorption system using carbon black (BP2000) as an adsorbent. The dehydration of fructose over zeolite beta catalyst in water revealed that selectivity to HMF is largely influenced by the formation of levulinic acid and formic acid from the rehydration of produced HMF as well as subsequent condensation reactions. In order to increase selectivity to HMF, reactive adsorption with carbon adsorbents was used to prevent the further reactions of the produced HMF. It was found that BP2000 carbon black exhibited high selectivity and capacity for the adsorption of HMF and furfural from the aqueous phase. The unique adsorption performance of BP2000 is likely due to the large surface area, hydrophobic nature and micropore structure. With using the carbon adsorbent, furan selectivity (selectivity of HMF and furfural) over zeolite beta was improved from 27% to 44% with a furan yield of 41%. The furan selectivity and yield obtained in the presence of the carbon adsorbent were similar to those obtained from the aqueous/organic reaction system using methyl isobutyl ketone (MIBK) as an extraction phase.

A supported aqueous phase catalyst coating in micro flow Mizoroki–Heck reaction

The application of a supported aqueous phase catalyst (SAPC) coating was investigated for the Mizoroki–Heck reaction in micro flow and favorably compared to the use of an SAPC in a batch system. In batch, an 83% yield was observed after 4h at 180°C with a catalyst loading of 0.4mol%, while in flow a residence time of 2.9min provided a 21% yield with only 0.01mol% catalyst loading. In batch the SAPC could be re-used twice without any significant loss in yield, but further re-use was prevented due to problematic accumulation of an ammonium salt. In the micro flow system, this problem could be overcome by adding water to the product flow prior to cooling, allowing even more effective use of the catalyst.

The structure of AuPd nanoalloys anchored on spherical polyelectrolyte brushes determined by X-ray absorption spectroscopy

Well-defined and facetted bimetallic gold-palladium nanoalloys have been synthesized and anchored in spherical polyelectrolyte brushes (SPB) as composite particles (AuPd@SPB). These particles are better catalysts in aqueous phase than the pure metals. The atomistic arrangement of these nanoalloys has been analysed by extended X-ray absorption fine structure (EXAFS) spectroscopy at the Au-L3 and the Pd-K absorption edge. The samples with high amounts of gold appear as almost statistically mixed random alloys. Alloy compositions with less gold show slight enrichment of Pd at the surface of the particle. In addition, signals of non-metallic palladium appear at the Pd-K edge which indicate the presence of the Pd2+ species in addition to metallic palladium. The relation of these structural features to the catalytic activity is discussed.

Aqueous and biphasic nitrile hydration catalyzed by a recyclable Ru(ii) complex under atmospheric conditions

[RuCl2(PTA)4] (PTA = 1,3,5-triaza-7-phosphaadamantane) was found to be a highly active catalyst for aqueous phase nitrile hydration at 100 °C in air. Near quantitative conversion of aromatic, alkyl, and vinyl nitriles to their corresponding amides was observed. The reaction tolerated ether, hydroxyl, nitro, bromo, formyl, pyridyl, benzyl, alkyl, and olefinic functional groups. Some amides were isolated by simple decantation from the aqueous phase catalyst. Catalyst loading down to 0.001 mol% was examined with turnover numbers as high as 22000 observed. The catalyst was stable for weeks in solution and could be reused more than five times without significant loss of activity.

Silica-supported HgSO 4/H 2SO 4: a convenient reagent for the hydration of alkynes under mild conditions

The silica-supported aqueous-phase catalyst (SAPC) approach has proven convenient for efficiently performing the hydration of alkynes with HgSO 4/H 2SO 4 to give the corresponding carbonyl compounds in dichloromethane under mild conditions. The use of this solid reagent significantly improves the reaction work-up as it merely involves filtering and evaporating the solvent.