Emulsion Catalyst Research Articles

Pickering Emulsion Catalysis: Interfacial Chemistry, Catalyst Design, Challenges, and Perspectives.

Pickering emulsions are particle-stabilized surfactant-free dispersions composed of two immiscible liquid phases, and emerge as attractive catalysis platform to surpass traditional technique barrier in some cases. In this review, we have comprehensively summarized the development and the catalysis applications of Pickering emulsions since the pioneering work in 2010. The explicit mechanism for Pickering emulsions will be initially discussed and clarified. Then, summarization is given to the design strategy of amphiphilic emulsion catalysts in two categories of intrinsic and extrinsic amphiphilicity. The progress of the unconventional catalytic reactions in Pickering emulsion is further described, especially for the polarity/solubility difference-driven phase segregation, "smart" emulsion reaction system, continuous flow catalysis, and Pickering interfacial biocatalysis. Challenges and future trends for the development of Pickering emulsion catalysis are finally outlined.

Pickering Emulsion Catalysis: Interfacial Chemistry, Catalyst Design, Challenges, and Perspectives

AbstractPickering emulsions are particle‐stabilized surfactant‐free dispersions composed of two immiscible liquid phases, and emerge as attractive catalysis platform to surpass traditional technique barrier in some cases. In this review, we have comprehensively summarized the development and the catalysis applications of Pickering emulsions since the pioneering work in 2010. The explicit mechanism for Pickering emulsions will be initially discussed and clarified. Then, summarization is given to the design strategy of amphiphilic emulsion catalysts in two categories of intrinsic and extrinsic amphiphilicity. The progress of the unconventional catalytic reactions in Pickering emulsion is further described, especially for the polarity/solubility difference‐driven phase segregation, “smart” emulsion reaction system, continuous flow catalysis, and Pickering interfacial biocatalysis. Challenges and future trends for the development of Pickering emulsion catalysis are finally outlined.

Single-Step Fabrication of a Multiscale Porous Catalyst Layer by the Emulsion Template Method for Low Pt-Loaded Proton Exchange Membrane Fuel Cells

Multiscale porosity assures better mass transport for a low Pt-loaded fuel cell; however, achieving a complex pore structure in a simple manner presents a major challenge. In this work, by using the emulsion template method, a multiscale porous catalyst layer with macro- and mesopores was fabricated in a single step. A stable high internal phase emulsion is achieved with catalyst layer components by exploiting a Nafion ionomer as a surfactant. The oil phase of the emulsion catalyst slurry induces the macropores, and the Pt/C and ionomer mixture in the hydrophilic solvent forms a mesoporous framework in the catalyst layer. Scanning electron microscopy and micro X-ray computed tomography confirmed the formation of uniform and well-interconnected macropores. The performance of the low Pt-loaded catalyst layer derived from the emulsion template method considerably improved the mass transport property due to the mitigation of water flooding. The fabrication of an emulsion-based catalyst layer provides an efficient platform to design high-performance low Pt-loaded fuel cells.

Catalytic synthesis of β-sitosterol linolenate by Pickering emulsion-immobilized lipase

In order to promote the application of phytosterol ester, a new kind of catalyst was developed on the basis of traditional enzymatic synthesis method. Pickering emulsion catalyst (CRL@PE) with two-phase structure was constructed using isoctane and Candida rugosa lipase and employing nanotube as emulsifier. Then the CRL@PE was used to catalyze the synthesis of β-sitosterol linolenic acid ester with β-sitosterol and α-linolenic acid as substrates. The effects of temperature, enzyme dosage, linolenic acid concentration and reaction time on the conversion rate of phytosterols were studied by single factor experiment and central composite design of response surface methodology. The optimal process parameters were obtained as follows: temperature of 29.45 oC, lipase dossage of 10.97 U, linolenic acid concentration of 42.35 mmol/L, reaction time of 350.7 min, and phytosterol conversion rate was 96.8±0.7% at these conditions. After reuse of CRL@PE for 10 times, the phytosterol conversion rate was 96.86%, showing that the catalyst had good stability.

A study of the catalytic behavior of phosphotungstic acid-modified Janus particles in a heterogeneous oil/water pickering emulsion system

An emulsion interface materialization method was used to obtain amphiphilic silica Janus nanoparticles. Reducing the photosynthesis of aquatic organisms after water pollution. PW12O403− was introduced onto Janus particles by ion exchange, and an amphiphilic particle emulsion catalyst (PWO-J) was prepared. Hydrogen peroxide was used as the oxygen source, and the amphiphilicty of the catalyst was used to assemble the catalyst at the Pickering emulsion interface. The PWO-J catalyst was found to exhibit very high catalytic activity toward the oxidation of oleic acid in water-in-oil systems. The results showed that PWO-J catalysis of oxidation had similar results as CTAB and phosphotungstic acid (control system) under the same conditions. The azelaic acid recovery rate was 86.7%, and PWO-J could be reused 4 times. A reaction mechanism was proposed, and the constructed model was used to calculate a reaction rate constant of 15.32 × 10−5L•mol−1•s−1 for the PWO-J system. The PWO-J system had a lower activation energy than the control system, showing that the catalytic oxidation of oleic acid into azelaic acid was more likely to occur in the PWO-J system.

Graphene Oxide Emulsions As a Catalyst Support for Metal Catalysts and Catalyst Layer Preparation: Cutting Corners with Hummer’s Method

Hummer’s method is a widely-used method for preparing graphene oxide from graphite powder. After the graphite is oxidized and cleaned with hydrochloric acid and water, an aqueous emulsion is formed that usually undergoes a lengthy drying procedure to form a powder. In this study, such emulsions produced were made to undergo various forms of reduction including solvothermal, microwave-based, and electrochemical instead of being dried and redispersed into a solvent. Graphene oxide was also dried in an oven for comparison. The emulsions were also mixed with various metal salts for a one pot reduction. The graphene oxide emulsions were also applied to Toray carbon electrodes and formed a thin film that didn’t penetrate the electrode like various ink solutions normally synthesized for MEA fuel cell applications. Various characterization techniques including XRD, Raman, SEM, and XPS displayed similar characteristics for the graphene oxide emulsion catalysts, both bare and with the metal salts mixed in. Various half-cell testing also displayed similar performances for the graphene oxide emulsion and dried catalysts.

Oxidative Desulfurization of Diesel Using Vanadium-Substituted Dawson-Type Emulsion Catalysts

In this study, we aimed at investigating the catalytic oxidative desulfurization (CODS) of the model diesel oil and real diesel oil using the vanadium-substituted Dawson-type emulsion catalyst ([cetrimonium]6+xP2W18–xVxO62 (x = 1, 3, 5)). Among all prepared samples, [cetrimonium]11P2W13V5O64 showed the best results in CODS of model diesel oil under determined conditions (10 g/L catalyst and O/S mole ratio = 4). The Taguchi method was then applied to optimize the catalyst dosage, hydrogen peroxide dosage, and the reaction temperature in CODS using the best emulsion catalyst. Then formic acid and acetic acid were used as a co-oxidant to improve the oxidation ability. Under optimum conditions, a mixture of H2O2/formic acid (1:1), in the presence of [cetrimonium]11P2W13V5O62 could remove 98% of dibenzothiophene and 82% of benzothiophene. Finally, under optimum conditions of CODS, 90% of total sulfur was removed from a real diesel sample. It is worth mentioning that we could recycle [cetrimonium]11P2W13V5O64, ...

Desulfurization of Fuel by Extraction and Catalytic Oxidation Using a Vanadium Substituted Dawson-Type Emulsion Catalyst

A vanadium-substituted Dawson-type polyoxometalate [cetronium]11P2W13V5O62 was fabricated to use in the extractive–catalytic oxidative desulfurization (ECODS) of fuels using hydrogen peroxide and ionic liquids (ILs), ethylene glycol, and a deep eutectic solvent. Taguchi robust was utilized to investigate the effects of operation parameters including H2O2 dosage, type of solvent, solvent-to-oil volume ratio, temperature, and contact time. The results demonstrated that the highest level of desulfurization could be achieved using a volume ratio of IL to oil = 1:6, O/(S + N) mole ratio = 4, and temperature = 70 °C after 45 min. The combination of the extraction and catalytic oxidation process showed that the step-by-step system (extraction in series with ECODS) was much better than the one-pot system (ECODS in one pot), which can remove 90% sulfur from 500 ppmw fuel and 87% sulfur from 1500 ppmw fuel under optimized conditions. The best system could also be reused 7 times in a 500 ppmw model fuel desulfurizat...

Extractive-oxidative removals of dibenzothiophene and quinoline using vanadium substituted Dawson emulsion catalyst and ionic liquid based solvents

Extractive-catalytic oxidative desulfurization (ECODS) of model diesel using vanadium substituted Dawson-type emulsion catalyst has been investigated for the first time. At different operational conditions, ECODS was studied using selected solvents and [cetrimonium]11P2W13V5O62 by means of Taguchi methods Under the optimized conditions (ionic liquids/oil volume ratio 1:8, 7.5 g/L catalyst, O/S mole ratio 8, T = 70 °C after 45 min) 94% of sulfur and 100% of quinoline were removed. It is worth mentioning that in the presence of catalyst, solvent/oil volume decreases by 45% while sulfur removal increases by 54% compared to extraction desulfurization.

Design and Preparation of Nanoscale Catalysts for Slurry Bed Hydrocracking Using the Microemulsion Method

Slurry bed hydrocracking, as a pioneering technology in heavy residue upgrading, is becoming commercial and will be the predominant process among the available upgrading technologies. The general trends in reaction performance and operating pressure imply that reduction of catalyst particle size would lead to the lower operational pressure. It this study, the microemulsion method has been used to reduce the catalyst size of the slurry hydrocracking process by a factor of 10. Bright stock as the oil phase, aqueous solution of ammonium heptamolybdate (hydrocracking catalyst), and two types of surfactant packages (A and B) containing fatty acid, ethanolamine, alcohols, and Span 80 have been used to produce clear emulsions. Dynamic light scattering and transmission electron microscopy experiments indicated that the catalyst size has been reduced to 1–2 and 8–15 nm in laboratory and pilot scales, respectively. The best percentage of hydroconversion using the emulsion catalyst (surfactant/catalyst ratio = 2:1) and heavy oil as feed in the pilot test was about 50% at once through operation. At higher surfactant/catalyst ratios, the conversion decreased in comparison to the case where no emulsion catalyst was used.

Preparation of Liquid Fuels from Chark Chemical Tar

In the course of study the optimal conditions of conduction of the process are found. Optimal temperature for preparation of motor oils from chark chemical tar is 400 °С. On the increase of temperature from 350 °С to 400 °С the yield of liquid products on Mo-containing catalyst increases from 47,1 mass. % to 65.2 mass. % compared to the yield of liquid products obtained without the catalyst. The yield of gasoil fraction constitutes 15 mass. %. Optimal quantity of catalyst for preparation of liquid products from the tar is 0,05 mass. %. According to the results of study the catalytic effect of synthesized from emulsion catalyst appears at low concentration of molybdenum (0,05 mass.%). But the double increase of concentration of molybdenum weakly affects the improvement of indicators of the process.

Back Cover: Phase‐Reversal Emulsion Catalysis with CNT–TiO2 Nanohybrids for the Selective Oxidation of Benzyl Alcohol (Chem. Eur. J. 48/2013)

Carbon nanotube–TiO2 nanohybrids have been fabricated with a simple and efficient method that allows for control over the carbon nanotube content. In the Communication on page 16192 ff., J. Qiu et al. report on the use of these nanohybrids as phase-reversal emulsion catalyst supports for ruthenium in the selective oxidation of benzyl alcohol to benzaldehyde.

Desulfurization of liquid fuels using air-assisted performic acid oxidation and emulsion catalyst

Abstract Catalytic oxidative desulfurization (ODS) of model oil and commercial oil samples was investigated using an air-assisted performic acid oxidation system with a phase transfer or emulsion catalyst comprising a quaternary ammonium salt-based heteropolyoxometalate. Different emulsion catalysts with a Keggin type heteroployoxometalate anion (containing W, Mo, and V) and cetyltrimethylammonium bromide cation were prepared and characterized by X-ray fluorescence, Fourier transform infrared spectroscopy, and scanning electron microscopy. [C16H33N(CH3)3]3[PW9Mo3O40] was the most effective catalyst in the current oxidation system, which reduced the sulfur content of the model oil from 1275 μg/g to 57 μg/g. The reactivity order of different model sulfur compounds was thiophene

Polyoxometalate–Organic Hybrid Molecules as Amphiphilic Emulsion Catalysts for Deep Desulfurization

So emulsional: Two hexavanadate-organic hybrids were synthesized and their amphiphilic properties were confirmed by forming emulsions in mixtures of water and nonpolar organic solvents, and were utilized as "emulsion catalysts" in deep desulfurization reactions (see figure). Their catalytic activities show a pH-dependent behavior, which can be explained by the size-change of emulsions and the appearance of reverse emulsions.

Oxidative Desulfurization of Fuel Oils

Several attractive approaches toward oxidative desulfurization of fuel oils, such as using H 2 O 2 /organic acids, H 2 O 2 /heteropolyacid, H 2 O 2 /Ti-containing zeolites, and other non-hydrogen peroxide systems (e.g., t -butyl hydroperoxide etc.) are reviewed. A new alternative oxidative desulfurization process using emulsion catalysts was developed mainly by our group, is introduced in detail. Limitations because of interphase mass transfer are greatly reduced in the emulsion reaction medium. The amphiphilic emulsion catalysts can selectively oxidize the sulfur-containing molecules present in diesel to their corresponding sulfones when using H 2 O 2 as the oxidant under mild conditions. The sulfones in the oxidized fuel oils can be removed by a polar extractant. The sulfur level of a prehydrotreated diesel can be lowered from a few hundred μg/g to 0.1 μg/g after oxidation and subsequent extraction whereas the sulfur level of a straight-run diesel can be decreased from 6000 to 30 μg/g after oxidation and extraction. 摘要：综述了燃油的氧化脱硫, 包括一些具有吸引力的氧化脱硫方法, 如 H 2 O 2 /有机酸, H 2 O 2 /杂多酸, H 2 O 2 /含钛分子筛和其它非过氧化氢体系 (如叔丁基过氧化物等). 对本课题组开发的新型乳液催化氧化脱硫体系进行了详细的介绍. 在乳液体系中, 界面间的传质限制被大大降低. 在温和条件下, 双亲性乳液催化剂可以将柴油中的含硫化合物选择氧化成其相应的砜类化合物. 氧化得到的砜可以使用极性萃取剂将其从油品中除去. 经过氧化和萃取之后, 加氢柴油中的硫含量可以从几百 μg/g 降低至 0.1 μg/g, 而直馏柴油中的硫含量则可以从 6000 μg/g 降低至 30 μg/g. The sulfur-containing compounds in diesel can be oxidized to their corresponding sulfones by the amphiphilic emulsion catalysts under mild conditions, and the sulfones can be removed by a polar extractant.

Ultra-deep Oxidative Desulfurization of Fuel Oil Catalyzed by Dawson-type Polyoxotungstate Emulsion Catalysts

The Dawson-type polyoxotungstate emulsion catalysts Q18P2W18, Q18P2W17, and Q18P2W12 were successfully synthesized and characterized by IR and 31P MAS NMR. They were used for the oxidation of sulfur-containing compounds such as 4,6-dimethyldibenzothiophene (4,6-DMDBT), dibenzothiophene (DBT), benzothiophene (BT), and 2,5-dimethythiophene (2,5-DMT) with H2O2 as an oxidant under mild conditions. The activity of the catalysts decreased in the order: Q18P2W12 > Q18P2W17 > Q18P2W18. The oxidative reactivity of the sulfur-containing compounds decreased according to DBT > 4,6-DMDBT > BT > 2,5-DMT. BT was completely oxidized into the corresponding sulfone upon catalysis by Q18P2W12 at 60 °C for 30 min. ：合成了 Dawson 型聚氧钨酸乳液催化剂 Q18P2W18, Q18P2W17, 和 Q18P2W12. 采用红外光谱和固体核磁技术对其进行了表征, 并用于温和条件下 H2O2 氧化 4,6-二甲基二苯并噻吩 (4,6-DMDBT)、二苯并噻吩 (DBT)、苯并噻吩 (BT) 和 2,5-二甲基噻吩 (2,5-DMT) 等含硫化合物的反应中. 结果表明, 各催化剂的活性大小顺序为 Q18P2W12 > Q18P2W17 > Q18P2W18. 含硫化合物的氧化活性顺序为 DBT > 4,6-DMDBT > BT > 2,5-DMT. 在 60 °C 反应 30 min 内, Q18P2W12 催化剂能够催化氧化 BT 完全转化成相应的砜.

Nanostructured Carbon–Metal Oxide Hybrids as Amphiphilic Emulsion Catalysts

Nanohybrids composed of "onion-like" carbon, single-walled (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) fused to silica or alumina particles have been compared as stabilizers of water/oil emulsions and interfacial catalysts. The amphiphilic character of these nanohybrids makes them effective in stabilizing emulsions (up to 85 % of total volume) comprising of small droplets (less than 40 μm). Furthermore, these nanohybrids have been used as supports for transition metal particles (palladium and copper) to catalyze reactions at the water/oil interface. Three different reaction systems have been conducted in the emulsions to demonstrate the principle: 1) hydrogenation of phenanthrene; 2) hydrogenation of glutaraldehyde and benzaldehyde; 3) oxidation of tetralin. Comparison of the maximum conversions achieved in emulsions as opposed to the single phase, together with much better control of selectivity in the two-phase system shows the benefits of using these nanohybrid catalysts.

The oxidation of benzothiophene using the Keggin-type lacunary polytungstophosphate as catalysts in emulsion

A series of emulsion catalysts were successfully synthesized with quarternary ammonium cations and heteropolyanions, and they were characterized by TG/DTA, FTIR, 31P MAS NMR and EPR. The emulsion catalyst with intact Keggin-structure, [C 18H 37N(CH 3) 3]H 2[PW 12O 40] (PW 12), is inactive for benzothiophene (BT) oxidation with H 2O 2 as oxidant under atmospheric pressure at 30 °C. Moreover, the metal-substituted catalysts PW 11M (M = Ti, Mn, Fe, Co, Ni and Cu) show rather low activity with the conversion less than 15% for BT oxidation. Whereas, the catalyst with mono-lacunary Keggin-structures, [C 18H 37N(CH 3) 3] 5Na 2[PW 11O 39] (PW 11), could completely catalytic oxidize BT into the corresponding sulfone under the same conditions. After careful characterizations of the catalysts, it is found that only PW 11 catalyst could effectively transform into the active polyperoxometalates species in the presence of hydrogen peroxide in non-polar solvent.

Deep desulfurization from fuel oil via selective oxidation using an amphiphilic peroxotungsten catalyst assembled in emulsion droplets

A recyclable amphiphilic catalyst, which composed of peroxotungsten anion and quaternary ammonium cation assembled in the interface of the emulsion droplets, shows high selectivity and activity in the oxidation of sulfur-containing molecules to sulfones with hydrogen peroxide in diesel under mild reaction conditions. All the sulfur-containing molecules present in diesel can be completely oxidized into sulfones with ∼100% selectivity of sulfones in W/O (H 2O 2-in-diesel) emulsion system. The sulfones can be readily separated from the diesel, and the sulfur level of the desulfurized diesel can be lowered from about 500 ppm to below 1 ppm with about 98% yield of oil. In addition, the S-containing molecules in straight-run gas oil are also readily oxidized to their corresponding products in the O/W emulsion reaction medium. The S-level of oil layer of the oxidized oil was reduced to below 1 ppm from 312 ppm in the original straight-run gas oil with above 99% yield of oil. The amphiphilic catalysts serve as not only a catalyst but also an emulsifying agent to stabilize the emulsion droplets. The emulsion droplets are not only in the highly dispersed form but also behave like homogenous catalyst with high activity. The limitations due to interphase mass transport are greatly reduced in emulsion reaction medium. Moreover, the emulsion catalysts can be easily separated and recycled by demulsifying.