Aqueous Catalyst Phase Research Articles

Nature of Glucose Epimerization Catalyzed by Mo-Containing Bulk Catalysts in Aqueous Phase

Nature of Glucose Epimerization Catalyzed by Mo-Containing Bulk Catalysts in Aqueous Phase

Integrated techno-economic and life cycle assessment of hydroformylation in microemulsion systems

This paper presents the first integrated techno-economic and life cycle assessment of microemulsion systems being applied for rhodium-catalyzed hydroformylation of long-chain alkenes at industrial scale. The case study describes a projected 150 kt/a production of tridecanal (US gulf coast, 2019). The industrial success of the hydroformylation of short-chain alkenes lies in the continuous recycling of the rhodium-containing water phase. Microemulsion systems can be applied to transfer this concept to long-chain alkenes by overcoming the miscibility gap between the aqueous catalyst phase and the unipolar alkene phase and, moreover, by generating a temperature-induced multi-phase system enabling the immobilization of the catalyst and its continuous recycling, as demonstrated in miniplant operations with dodecene and rhodium/SulfoXantPhos. Customizable simulation models have been developed for scale-up and assessment of the miniplant data. Surprisingly, a profitability-driven sensitivity study indicates a base case optimum at low residence time with low alkene conversion leading to large throughput streams and high raw material purge rates. The comparison to the industrial cobalt-based benchmark system shows an economic advantage regarding net present value (Rh: 68 M$; Co: 62 M$), while about half of the environmental indicators are in favor or equivalent. In a best-case scenario considering zero leaching of expensive rhodium the net present value increases by almost 40% accompanied by a shift to overall lower environmental impacts than the benchmark. In conclusion, the investigated miniplant data suggest microemulsion systems to be competitive when applied in continuous processes at a large scale.

Synthesis of glycolic acid by selective oxidation of ethylene glycol over Pt/Sn-Beta in a base-free medium

The catalytic oxidation of ethylene glycol with O2 to glycolic acid was carried out using a Pt/Sn-Beta catalyst in aqueous phase under base-free conditions, with a temperature range of 30–70 °C, achieving a glycolic acid yield of up to 73%.

Enabling direct-growth route for highly efficient ethanol upgrading to long-chain alcohols in aqueous phase

Upgrading ethanol to long-chain alcohols (LAS, C6+OH) offers an attractive and sustainable approach to carbon neutrality. Yet it remains a grand challenge to achieve efficient carbon chain propagation, particularly with noble metal-free catalysts in aqueous phase, toward LAS production. Here we report an unconventional but effective strategy for designing highly efficient catalysts for ethanol upgrading to LAS, in which Ni catalytic sites are controllably exposed on surface through sulfur modification. The optimal catalyst exhibits the performance well exceeding previous reports, achieving ultrahigh LAS selectivity (15.2% C6OH and 59.0% C8+OH) at nearly complete ethanol conversion (99.1%). Our in situ characterizations, together with theoretical simulation, reveal that the selectively exposed Ni sites which offer strong adsorption for aldehydes but are inert for side reactions can effectively stabilize and enrich aldehyde intermediates, dramatically improving direct-growth probability toward LAS production. This work opens a new paradigm for designing high-performance non-noble metal catalysts for upgrading aqueous EtOH to LAS.

Breaking the C[sbnd]C bond of glucose on tungsten oxide-based catalysts in aqueous phase

In chemistry, selective activation of CC bonds enables the direct production of valuable chemicals from widely available and inexpensive natural materials but remains a fundamental challenge due to their kinetic inertness. The selective cleavage of CC bond in glucose by tungsten oxide-based catalysts in aqueous phase pioneers a path for converting cellulose biomass into valuable ethylene glycol. However, debates regarding the active phase and how it selectively breaks the C6 into C2 fragments have persisted for over a decade. In this study, we present a comprehensive mechanistic investigation by modeling three potential active phases, i.e. the reduced WO3-x surface, the dissolved tungstic acid, and tungsten bronze, in explicit solvent waters. By constrained molecular dynamics simulations, we have demonstrated that the low-coordinated W center can chelate with glucose, forming a metallacyclic complex with a 5-membered ring after the protonation of carbonyl group. The formation of 5-membered ring serves as the premise for the selectivity to C2 fragments via homolytic cleavage of CC bond. Furthermore, the reduced W5+ center is suggested to be crucial in facilitating the cleavage process by stabilizing the dissociated C4 intermediates via a redox process. In conclusion, we propose that the surface decoration of reduced and low-coordinated W sites can act as active heterogeneous catalysts for the selective conversion of cellulose in aqueous phase. These recent findings have the potential to provide valuable insights and strategies for CC bond activation in both biomass conversion and organic synthesis.

In-situ deoxygenation of methyl palmitate to hydrocarbons on highly dispersed Ni–Re/TiO2 catalyst in aqueous phase using methanol as a hydrogen donor

Herein, TiO2 supported Ni–Re alloy catalysts (i.e., NiRe(x:y)/TiO2, x:y denotes the Ni/Re atomic ratio) were prepared and tested for in situ deoxygenation of methyl palmitate to hydrocarbons in aqueous phase using methanol as hydrogen donor. Raman spectra indicates that there is interaction between NiO and ReO4− species via forming Ni–O-Re(=O)3 species in the calcined catalysts, which contributes to the formation of Ni–Re alloy and promotes the Ni dispersion during the reduction with H2. Particularly, the Ni–Re alloy particles with average size of ∼1.4 nm highly disperse on spherical TiO2 particles (∼14 nm in diameter) in NiRe(3:4)/TiO2 (the nominal Ni content of 3 wt%). XPS reveals a charge transfer from metallic Ni to Re in the Ni–Re alloy. In in situ deoxygenation of methyl palmitate, compared with Ni/TiO2, NiRe(x:y)/TiO2 give remarkably higher deoxygenation activity and lower activity for the C–C bond hydrogenolysis, ascribed to the synergistic effect between Ni and Re species and the geometrical effect of Re, respectively, which are further verified by propanoic acid-TPD and TPSR. The yield of C6∼C16 liquid hydrocarbons can achieve as high as 98.0% on NiRe(3:4)/TiO2 at 330 °C. There is no obvious sintering of Ni–Re alloy and support TiO2 particles during the recycling of NiRe(3:4)/TiO2, while the carbon deposition and the leaching of Re species slightly reduce the catalyst activity.

Li-promoted C3N4 catalyst for efficient isomerization of glucose into fructose at 50 °C in water

Efficient and selective glucose-to-fructose isomerization is a crucial step for production of oxygenated chemicals derived from sugars, which is usually catalyzed by base or Lewis acid heterogeneous catalyst. However, high yield and selectivity of fructose cannot be simultaneously obtained under mild conditions which hamper the scale of application compared with enzymatic catalysis. Herein, a Li-promoted C3N4 catalyst was exploited which afforded an excellent fructose yield (40.3 wt%) and selectivity (99.5%) from glucose in water at 50 °C, attributed to the formation of stable Li–N bond to strengthen the basic sites of catalysts. Furthermore, the so-formed N6–Li–H2O active site on Li–C3N4 catalyst in aqueous phase changes the local electronic structure and strengthens the deprotonation process during glucose isomerization into fructose. The superior catalytic performance which is comparable to biological pathway suggests promising applications of lithium containing heterogeneous catalyst in biomass refinery.

Aldehyde Hydrogenation by Pt/TiO2 Catalyst in Aqueous Phase: Synergistic Effect of Oxygen Vacancy and Solvent Water.

The aldehyde hydrogenation for stabilizing and upgrading biomass is typically performed in aqueous phase with supported metal catalysts. By combining density functional theory calculations and ab initio molecular dynamics simulations, the model reaction of formaldehyde hydrogenation with a Pt/TiO2 catalyst is investigated with explicit solvent water molecules. In aqueous phase, both the O vacancy (Ov) on support and solvent molecules could donate charges to a Pt cluster, where the Ov could dominantly reduce the Pt cluster from positive to negative. During the formaldehyde hydrogenation, the water molecules could spontaneously protonate the O in the aldehyde group by acid/base exchange, generating the OH* at the metal-support interface by long-range proton transfer. By comparing the stoichiometric and reduced TiO2 support, it is found that the further hydrogenation of OH* is hard on the positively charged Pt cluster over stoichiometric TiO2. However, with the presence of Ov on reduced support, the OH* hydrogenation could become not only exergonic but also kinetically more facile, which prohibits the catalyst from poisoning. This mechanism suggests that both the proton transfer from solvent water molecules and the easier OH* hydrogenation from Ov could synergistically promote aldehyde hydrogenation. That means, even for such simple hydrogenation in water, the catalytic mechanism could explicitly relate to all of the metal cluster, oxide support, and solvent waters. Considering the ubiquitous Ov defects in reducible oxide supports and the common aqueous environment, this synergistic effect may not be exclusive to Pt/TiO2, which can be crucial for supported metal catalysts in biomass conversion.

In situ generated micro-catalytic system for the epoxidation of allyl chloride with hydrogen peroxide

The epoxidation of allyl chloride and H2O2 catalyzed by heterogeneous catalyst suffers from inadequate mixing between organic phase, aqueous phase and solid catalyst. This work describes a novel micro-catalytic system for the intensification of this multiphase reaction process. Aqueous phase is capsulated with the loaded phosphotungsten heteropoly acid catalyst to produce microdroplets in situ, the oil-water interface consisting of the catalyst particles facilitates the epoxidation reaction. The regulation of microdroplet size can be achieved by changing the hydrophobicity of the catalyst surface, with a suitable hydrophobicity reducing the diameter of microdroplets and exhibiting optimal catalytic activity. The ECH conversion and selectivity in the micro-catalytic system can be reached as high as 98.02 % and 99 %, respectively. The structure and stability of the catalyst are illustrated by SEM, XPS, FT-IR and TGA. Furthermore, inexpensive commercial polystyrene was used as catalyst carriers, and the synthesis process of the catalyst is simple, which enables the large-scale synthesis of the catalyst. This strategy is a promising approach to designing catalysts for oil-water multiphase reactions.

Selective hydrogenation of reducing sugars over SiO2@Ni/NiO hetero-structured nanoreactor in Mg-driven aqueous phase

Selective hydrogenation is of growing interest in biomass upgrading to be performed over non-precious metal-based catalyst in aqueous phase. Herein, a nickel/nickel oxide hetero-structural catalyst to reducing sugars hydrogenation is designed based on the tailored interfacial synergy and structural composition. Such synergistic silica @ nickel/nickel oxide (SiO2@Ni/NiO) with core–shell structure features in i) interconnected tubes on the shell offering spatial restriction to hydrogen attraction and reactant diffusion, ii) hetero-interfaced Ni/NiO shell balancing the H2 and glucose adsorption chemically, iii) the core shell catalyst providing nano-reactor for reactant enrichment, furthering improving the utilization of nickel active sites. Furthermore, the high solubility of in-situ generated H2 driven by Mg in this aqueous phase hydrogenation system greatly assist the interaction among the reactants. The SiO2@Ni/NiO catalyst exhibits high activity in glucose hydrogenation, under which the conversion rate and sorbitol selectivity can achieve 99 % and 90 % under mild condition of 393 K for 3 h, respectively. It also shows remarkable reuse ability and wide application scope to sugars hydrogenation in this in-situ hydrogen generation process. This proposal gains insights to cooperative catalyst design on chemical composition and nanostructure for advancing biomass-based sugars hydrogenation process.

Effects of aqueous phase circulation and catalysts on hydrothermal liquefaction (HTL) of penicillin residue (PR): Characteristics of the aqueous phase, solid residue and bio oil

Hydrothermal liquefaction (HTL) is a promising thermochemical technology for the treatment of hazardous wastes such as penicillin residue (PR). For the treatment of aqueous waste produced by PR in the HTL process, aqueous phase circulation is an attractive solution, both environmentally and economically. The present study shows that aqueous phase circulation can promote the transfer of organic matter from the aqueous phase to bio–oil. The content of organic acids and alcohols in the aqueous phase decreased significantly, and the bio–oil yield and energy recovery efficiency also increased. Under non–catalytic conditions, the bio–oil yield increased from 26.09 wt% to 33.72 wt%. The use of Na2CO3 as a catalyst further improved the bio–oil yield. After a single aqueous phase circulation, the bio–oil yield increased to 34.63 wt%, and the energy recovery efficiency increased to 66.94%. Under catalytic hydrothermal conditions, the content of organic acids in the bio–oil was reduced using aqueous phase circulations, which improved the quality of the bio–oil. At the same time, the Na2CO3 catalyst promoted the hydrolysis of PR to form small molecule organic matter, inhibited the formation of coke, and reduced the content of carbon, hydrogen and oxygen in the solid residue. An increase of cycle times led to excessive accumulation of Na2CO3, which had a negative impact on the yield of bio–oil. Nitrogen–containing compounds in the bio–oil increased to a certain extent, which renders it necessary to consider denitrification treatments in the future. The work provides a useful reference for further research on the preparation of high quality bio–oil by PR hydrothermal liquefaction.

Photoredox Catalyst Free, Visible Light‐Promoted C3−H Acylation of Quinoxalin‐2(1H)‐ones in Water

AbstractA method for the synthesis of 3‐acyl quinoxalin‐2(1H)‐ones through visible‐light promoted decarboxylative acylation of α‐oxo‐carboxylic acids with quinoxalin‐2(1H)‐ones was developed. The reaction was performed in aqueous phase and photoredox catalyst was not required to run the process.magnified image

MoS2 nanosheets supported on carbon hybridized montmorillonite as an efficient heterogeneous catalyst in aqueous phase

Heterogeneous catalysis in aqueous phase plays a pivotal role in energy conversion, environmental remediation and pharmaceutical production. MoS2 has been considered to be a promising catalyst, however its catalytic performance in aqueous phase is greatly restricted by the hydrophobicity and low electrical conductivity. The electrical conductivity and aqueous dispersity of MoS2 nanosheets could be improved by supporting it on the carbon hybridized montmorillonite, which was synthesized through the hydrothermal carbonization and calcination pyrolysis of sucrose with the montmorillonite. Herein, the MoS2 nanosheet supported on carbon hybridized montmorillonite was successfully prepared via in-situ hydrothermal method, which exhibits 2D composite structure with good interface integration. The catalytic performance of nanocomposites was synergistically improved by montmorillonite and carbon material, and the apparent reaction rate constant for the reduction of p-nitrophenol reaches 0.874 cm−1 with nanocomposites as the catalyst. This material design strategy in this study could provide novel idea to develop efficient heterogeneous catalyst in aqueous phase.

Improving Aqueous Biphasic Hydroformylation of Unsaturated Oleochemicals Using a Jet‐Loop‐Reactor

AbstractIn two case studies, the reaction performance of the aqueous biphasic hydroformylation of two industrially relevant oleochemicals, namely methyl 10‐undecenoate (case 1) and methyl oleate (case 2), is significantly improved by the use of a Jet‐Loop Reactor concept. Based on previously reported studies, only the two green and benign co‐solvents, 1‐butanol and isopropanol are applied, respectively, in the absence of any additional auxiliary. Both reactions benefit highly from using this special piece of equipment, specifically designed for improving gas–liquid–liquid mixing to create large interfacial areas with no moving internals. In case 1, the loading of the co‐solvent 1‐butanol is successfully reduced. For the first time significant yields (>40% after 1 h) are obtained in the absence of any co‐solvent, which is very beneficial, since aldehyde products and substrate form a pure product phase enabling straightforward separation. In case 2, the loading of the substrate methyl oleate is successfully increased from 6 to 30 wt% still showing satisfying productivity. At 15 wt%, the yield of the desired internal aldehydes in the jet‐loop reactor is increased by a factor of five compared to a stirred tank reactor after 3 h.Practical Applications: The production of aldehydes from hydroformylation of olefins is highly relevant for the chemical industry, since these can undergo numerous subsequent reactions, to form for instance alcohols, amines, and carboxylic acids. Generally, aldehydes from oleochemicals can serve as platform chemicals for gaining access to bifunctional molecules, which are interesting as polymer precursors. Performing hydroformylation with a water‐based solvent system enables efficient product separation from the aqueous catalyst phase for the realzation of more sustainable processes. By using the Jet‐Loop Reactor, the performance of the reaction system can be greatly improved addressing its practical relevance.

Selective catalytic oxidation of sulfides to sulfoxides or sulfones over amorphous Nb2O5/AC catalysts in aqueous phase at room temperature

Selective oxidation of sulfides into sulfoxides or sulfones is an important transformation in organic synthesis. Activated carbon supported Nb-based catalysts were prepared by the impregnation method and then characterized by the XRD, TEM and XPS. The characterization results indicate Nb species is amorphous Nb2O5. The catalysts were applied for the catalytic oxidation of sulfides in aqueous phase with H2O2 as the oxidant. Sulfides could be converted into the corresponding sulfoxides or sulfones with high conversion and selectivity at room temperature. The recycling experiments showed the Nb2O5/AC catalysts exhibited good reusability. They could be recycled for 10 times without obvious loss of activity and selectivity.

Investigations on Catalyst Stability and Product Isolation in the Extractive Oxidative Desulfurization of Fuels Using Polyoxometalates and Molecular Oxygen

AbstractOur contribution adds important new insight to the recent finding that polyoxometalate catalysts, such as H8PV5Mo7O40 (HPA‐5), are very effective catalysts in the extractive oxidative desulfurization of fuels using molecular oxygen. Our contribution focuses on aspects of catalyst stability and deactivation caused by the accumulation of acidic products and intermediates, i. e. sulfuric acid, formic acid, acetic acid, sulfoacetic acid or 2‐sulfobenzoic acid. These compounds reduce the pH value of the aqueous catalyst phase during the course of the desulfurization reaction. At lower pH values, the higher V‐substituted species rearrange to lower V‐substituted species and VO2+. This rearrangement is responsible for a decreasing activity in extractive oxidative desulfurization. We show that formic acid, acetic acid, sulfoacetic acid and 2‐sulfobenzoic acid block active sites of the catalyst. Oxalic acid, in contrast, has been found to exert a remarkable positive effect on catalyst activity. The feasibility of catalyst recycling and efficient isolation of the decomposition products is demonstrated using four commercially available organic solvent nanofiltration membranes.

Catalyst Activation and Influence of the Oil Matrix on Extractive Oxidative Desulfurization Using Aqueous Polyoxometalate Solutions and Molecular Oxygen

Our contribution describes the oxidative desulfurization of dibenzothiophene (DBT) from model oils using an aqueous H8PV5Mo7O40 (HPA-5) catalyst solution and molecular oxygen as the oxidant. In contrast to common oxidative desulfurization (ODS) protocols, the organic sulfur compound DBT is oxidized to water-soluble compounds, such as sulfuric acid (50–55%), sulfoacetic acid (20–25%), and sulfobenzoic acid (25–30%), which are extracted in situ into the aqueous catalyst phase. We describe the activating effect of oxalic acid on the ODS performance of the catalyst and propose a mechanism for the catalyst activation. Moreover, we report on the influence of various organic solvents, i.e., n-alkanes and aromatics, on the oxidative DBT removal. Remarkably, the rate of DBT oxidation and removal enhances with an increasing chain length of the alkane matrix, whereas aromatic compounds in the oil matrix inhibit the desulfurization rate. Moreover, we demonstrate that the aqueous catalyst phase can be reused at least ...

Hexafluoroisopropanol as a Low‐Boiling Extraction Solvent for 5‐Hydroxymethylfurfural Production

AbstractIn this study, we show that the fluorous alcohol hexafluoroisopropanol (HFIP) can act as a superior solvent for the in situ extraction of 5‐hydroxymethylfurfural (HMF) from an aqueous reaction system. HFIP has a far higher partition coefficient for HMF than common extraction solvents such as methyl isobutyl ketone (MIBK) and n‐butanol and has a significantly lower boiling point of 58–59 °C. In a system containing fructose, HCl as the catalyst, and HFIP as the extraction solvent, a high HMF yield of 89 % is achieved, which is far better than the HMF yields in common MIBK/butanol extraction systems. HFIP extracts HMF from the reaction phase without extraction of the fructose educt. In addition, the aqueous catalyst phase can be reused.

Colloidal polymer particles as catalyst carriers and phase transfer agents in multiphasic hydroformylation reactions

HypothesisColloidal particles have been used to covalently bind ligands for the heterogenization of homogeneous catalysts. The replacement of the covalent bonds by electrostatic interactions between particles and the catalyst could preserve the selectivity of a truly homogeneous catalytic process. ExperimentsFunctionalized polymer particles with trimethylammonium moieties, dispersed in water, with a hydrophobic core and a hydrophilic shell have been synthesized by emulsion polymerization and have been thoroughly characterized. The ability of the particles with different monomer compositions to act as catalyst carriers has been studied. Finally, the colloidal dispersions have been applied as phase transfer agents in the multiphasic rhodium-catalyzed hydroformylation of 1-octene. FindingsThe hydrodynamic radius of the particles has been shown to be around 100 nm, and a core-shell structure could be observed by atomic force microscopy. The polymer particles were proven to act as carriers for the water-soluble hydroformylation catalyst, due to electrostatic interaction between the functionalized particles bearing ammonium groups and the sulfonated ligands of the catalyst. The particles were stable under the hydroformylation conditions and the aqueous catalyst phase could be recycled three times.

Water-Assisted Selective Hydrodeoxygenation of Guaiacol to Cyclohexanol over Supported Ni and Co Bimetallic Catalysts

Hydrodeoxygenation (HDO) of guaiacol, a typical lignin-derived phenolic compound, at relatively mild conditions was studied over γ-Al2O3 and ZSM-5 supported catalysts with Ni and/or Co as active metal. Among various catalysts, NiCo/γ-Al2O3 catalysts exhibited better guaiacol conversion up to 96.1% with cyclohexanol as the main product in aqueous, due to the proper acidity and interaction between metal particles and support. The effects of process parameters on guaiacol conversion and product distribution were investigated in detail associated with solvent effect. The cleavage of C–O bonds in guaiacol was investigated over NiCo/γ-Al2O3 catalysts in aqueous phase. Phenol was found as the main intermediate with 1-methyl-1,2-cyclohexanediol as another intermediate instead of 2-methoxy-cyclohexanol. The demethoxylation first happened to form phenol, and then, the aromatic ring was hydrogenated to give cyclohexanol after further hydrogenation of cyclohexanone.