Ru Leaching Research Articles

Ru Nanoparticles Supported on Mesoporous Al‐SBA‐15 Catalysts for Highly Selective Hydrogenation of Furfural to Furfuryl Alcohol

AbstractFurfuryl alcohol, which is the hydrogenated product of furfural, has been identified as a very promising platform chemical with high potential for applications in the manufacture of key chemicals, lubricants, fragrances, and pharmaceuticals. In this work, bare SB, and x % Ru/Al‐SB (x=1.5, 2.5, 3.5, and 4.5 wt. %) samples were fabricated by a hydrothermal method. Bare and most active catalysts were characterized by different techniques, such as BET, FE‐SEM, TEM, FT‐IR, and XRD, to understand their physical and chemical properties. An evaluation of the effects of various reaction parameters, such as catalyst loading, reaction temperature, and reaction time, on the catalytic performance, showed higher catalytic conversion of furfural and selectivity for the desired products. The most active RuS3 catalyst showed 100 % conversion of furfural and 99 % selectivity for furfuryl alcohol. It could be reused for five consecutive reaction cycles without significant loss of performance. In addition, Ru leaching and loss of conversion or selectivity were not noticed during the five‐run recycling test. The EDS elemental mapping analysis of the used catalyst established the preservation of the mesoporous structure, suggesting a strong interaction between the hexagonal porous silicate and the Ru nanoparticles.

Accelerated Stress Test Study on PtRu Anode Catalysts for Reformate PEM Fuel Cells

Proton-exchange membrane fuel cells (PEMFCs) are interesting candidates for heavy duty applications, e.g. in the maritime or bus and truck sector, since they convert renewable fuels into electricity efficiently [1]. Moreover, PEMFCs are flexible with respect to fuels, since they can be operated not only with hydrogen but also with reformate gas, originating from steam reforming of carbohydrates such as renewable methanol [2]. Compared to state-of-the-art carbon-supported Platinum catalysts (Pt), which are severely poisoned by CO, a side product from reforming, carbon-supported Platinum-Ruthenium catalysts (PtRu) prevail in reformate applications due to their promoting effects towards CO oxidation [3]. However, PtRu catalysts are less stable than Pt catalysts due to a higher susceptibility to dissolution [4]. Since the durability of materials in heavy duty applications is crucial to reach long operating times (> 30000 h), major efforts have to be taken to improve the stability of PtRu anode catalysts.To be able to evaluate the stability of catalysts and to investigate, identify, and understand degradation mechanisms with little time and costs, so-called accelerated stress tests (ASTs) are deployed, which induce fast electrode aging and ideally simulate electrode degradation that can be transferred to real operating conditions. For Pt cathode catalysts in PEMFC application, the U.S Department of energy proposed an AST based on square wave potential cycling between 0.6 V and 0.95 V for 30000 cycles [5]. As Ru and possibly PtRu have different dissolution potentials than Pt and are used on the anode side (therefore exposed to different potentials compared to the cathode), an AST designed for PtRu anode catalysts is required.In this work, several AST protocols based on square cycling the anode potential for 30000 cycles were developed and tested on cells with the same material composition. The carbon-supported PtRu anode electrodes were manufactured in-house with a patented technique [6], while for membranes, cathode catalysts, and GDLs commercial available products were applied. The ASTs differ by the upper potential limit, which was chosen at 0.2 VRHE, 0.65 VRHE, 0.8 VRHE, and 1.0 VRHE, respectively. The lower potential limit was set at 0.06 VRHE, (cf. Figure 1b). Before, during, and after the AST, electrochemical characterization was conducted via cyclic voltammetry, CO-stripping, and recording U-I curves (cf. Figure 1a). After the AST, post-mortem analyses were performed by means of transmission electron microscopy, X-ray diffraction, and cross-sectional scanning electron microscopy coupled with energy dispersive X-ray spectroscopy to analyze the prominent degradation mechanisms occurring for the different testing conditions.Strong differences in the degradation of the cells between the different ASTs could be observed. With increasing upper potential limit, the severity of degradation and the observed degradation phenomena increased. For example, Ru leaching occurred at ASTs with upper potentials beyond 0.65 VRHE, and increased with increasing potential, resulting in a reduced CO-tolerance. At the same time, the consequent Ru crossover to the cathode, which lowers the overall cell performance, could be only detected by EDX for ASTs beyond 0.8 VRHE, implying a correlation between Ru crossover and upper potential limit. Moreover, the data indicate that an upper potential limit of 1.0 VRHE may be too high to investigate the stability of Ru in PtRu catalysts, as an additional strong Pt degradation makes the evaluation difficult. Future work will address the correlation of these ASTs to long-term testing at constant potential.

Tunable Multi-Phase System for Highly Chemo-Selective Oxidation of Hydroxymethyl-Furfural.

Three different multiphase systems (MP 1-3) comprised of two immiscible liquids, with or without an ionic liquid (IL: methyltrioctyl ammonium chloride), were investigated for the oxidation of 5-hydroxymethyl-furfural (HMF) over 5 % Ru/C as a catalyst and air (8 bar) as an oxidant. These conditions proved versatile for an excellent control of the reaction selectivity to 4 distinct products derived from full or partial oxidation of the carbonyl and alcohol functions of HMF, and each one achieved in 87-96 % isolated yield at complete conversion. MP1 based on water and isooctane, yielded 2,5-furandicarboxylic acid (FDCA, 91 % yield). In MP2, obtained by adding the IL to MP1, the oxidation proceeded towards the formation of 5-formyl-2-furancarboxylic acid (FFCA, 87-89 % yield). MP2 also proved successful in the design of a one pot-two step oxidation/reduction sequence to prepare 5-hydroxymethyl-2-furancarboxylic acid (HMFCA, 85 % yield). In MP3, the use of an acetonitrile/cyclooctane biphase yielded 2,5-diformylfuran (DFF, 96 % yield). All the multiphase systems MP 1-3 allowed a perfect segregation of the catalyst in a single phase (either the hydrocarbon or the IL) distinct from the one containing HMF and its oxidation products. This was crucial not only for the catalyst/product separation but also for the recycle of Ru/C that was possible under all the tested conditions. Accordingly, MP-reaction were run in a semicontinuous mode without removing the catalyst from the reactor nor resorting to conventional separation and activation techniques. Negligible Ru leaching, less than 0.96 ppb, was measured in all cases.

Uncovering Activity-Stability Relationships in Mixed Ir-Based Catalysts Toward Improved Water Electrolysis

The role of proton exchange membrane water electrolysers (PEMWE) in providing clean and reliable green hydrogen is undeniable in a fully decarbonized energy system. Indeed, the ambitious “Hydrogen Shot” initiative by the U.S. DoE seeks to decrease in a decade green hydrogen pricing down to 1$/Kg H2.(1) Such endeavour will require a mass-scale implementation of PEMWEs, which is currently bottlenecked by the use of scarce precious metal catalysts, particularly at the anode where loadings of the state-of-the-art iridium (Ir) catalyst typically range between 1-3mgIr cm-2.(2) Thus, recent strategies in the literature have aimed to reduce Ir loading with several approaches such as higher catalyst dispersion and preparation of mixed metal oxides (IrxM1-xOy). The latter is particularly promising if the cation substituent M is an earth-abundant metal highly active to the oxygen evolution reaction (OER), which could lead to drastic catalyst cost reductions retaining high activities. The activity-stability relationships of various Ir phases are well-reported,(3) but hardly studied for IrxM1-xOy where any preferential dissolution of M under OER operation could result in misleading conclusions.The work presented here aims to bridge this knowledge gap by online quantification of catalyst dissolution products with our electrochemical flow cell coupled to inductively-coupled plasma mass spectrometry setup. First, we evaluated these relationships in cationic-substituted IrxM1-xO2 (100) epitaxial thin films, model systems which will allow us to clearly uncover any cation-dependent trends. It was observed that the Ir stability in such model systems directly correlated with the OER enhancement effect of the cation substituent: higher OER activities induced by the cation yielded lower Ir stabilities and vice versa. In addition, the IrO2 matrix does not seem to affect the thermodynamic dissolution trends of the cation M. In conjunction with ex-situ XPS characterization, we successfully identified two promising cation substituents considering the experimental activity-stability trends: Mo and W. Next, we moved to the industrially-promising IrxRu1-xO2 nanoparticle (NP) systems, with different relative compositions and degrees of crystallinity. Although Ru generally presents high dissolution rates under OER potentials, preliminary studies on sputtered thin films revealed a drastic stabilization of the RuO2 matrix upon incorporation of less than 20 at. % Ir.(4) The one-step synthetic approach used here, flame spray pyrolysis, allowed to easily tune the NPs Ir:Ru ratio by the relative content of the metal precursors in the pyrolized solution. Additionally, a post-calcination step enabled to convert the NPs phase from hydrous to rutile-type oxide. Using as start-up/shut-down OER protocol, we observed at 1000-fold lower stability for hydrous vs. rutile-type IrxRu1-xO2 regardless of the composition after selective Ru leaching. For rutile-type IrxRu1-xO2 nanoparticles, the sequential on/off OER operation revealed a ca. 10-fold decrease in Ru dissolution upon Ir incorporation, as well as the key role of surface Ru in OER activity.(5) Minimal Ru losses (<1 at. %) led to the formation of an Ir-rich protective shell, which for Ir0.2Ru0.8O2 resulted in an OER performance shift equivalent to that of pristine Ir0.8Ru0.2O2. These results showcase, contrary to previous reports, that Ru-rich compositions can indeed be implemented in PEMWE devices.

Ru doped graphitic carbon nitride mediated peroxymonosulfate activation for diclofenac degradation via singlet oxygen

Ru sites acted as conductors rather than reductive activators to transfer electrons between pyridine N and PMS, resulting in the PMS activation for O 2 • - generation. Then 1 O 2 species were obtained via hydrolysis of O 2 • - and responsible for DCF degradation. • DCF was completely removed within 10 min in a wide pH range of 3.00–9.00. • 1 O 2 was responsible for DCF removal and showed high tolerance to matrix effects. • The toxicity of almost all intermediates/products was significantly reduced. • CNRu showed high stability and reusability, and few Ru was leached in seven runs. Metals doped carbon nitride (CN) is considered as a class of promising efficient catalysts for peroxymonosulfate (PMS) activation in water purification. Herein, ruthenium doped carbon nitride (CNRu) was synthesized via a facile one-pot method, and CNRu was in form of Ru–N 2 that could efficiently activate PMS for DCF degradation and detoxification via nonradical pathway. DCF was completely removed within 10 min under the optimized condition in a wide working pH range of 3.00–9.00, while other traditional transition metals (e.g. Fe, Co, Ni, Cu) doped CN showed negligible removal of DCF due to adsorption rather than activation of PMS, which was demonstrated by DFT calculations. CNRu showed high stability and reusability after seven cycles and very few Ru leaching was detected in DCF degradation process. Ru was highly dispersed in form of Ru–N bond via coordinating to pyridine nitrogen, and the electron defect transfer between Ru and coordinated N, rather than redox cycle of Ru, mediated superoxide radicals (O 2 •− ) evolution, which was further hydrolyzed into singlet oxygen ( 1 O 2 ) and responsible for DCF removal. Thus, the CNRu/PMS system showed high tolerance to inorganic anions. Much lower toxic intermediates/products than DCF were obtained via the strong electrophilic attack reaction between 1 O 2 and DCF in CNRu/PMS system. This study displayed a new practical application prospect of ruthenium-based materials for high-efficient removal and detoxification of DCF from wastewater.

Synthesis of highly stable dual-site immobilized ruthenium olefin metathesis catalyst without ru leaching

The tri-block copolymer is used as a carrier to simultaneously immobilize the N-heterocyclic and benzylidene ligands precursor of the Ru-based catalyst to form a dual-site immobilized catalyst. The dual-site immobilized catalyst can catalyze ring-opening metathesis polymerization, ring-closing metathesis and self-metathesis. The dual-site immobilized catalyst shows good heterogeneity in dichloromethane, which simplifies the purification of product and recovery of catalyst. The dual-site immobilized catalyst exhibits excellent activity and recycling performance. The excellent recyclability can be attributed to the capture of ruthenium by the excess ligands precursor on carrier. Importantly, ruthenium residues are not detected in product.

Ru supported on micro and mesoporous carbons as catalysts for biomass-derived molecules hydrogenation

Supported ruthenium based materials are active for the catalytic hydrogenation of biomass-derived molecules. However, such catalysts still have problems regarding deactivation coming from Ru leaching and particles aggregation. In this work we demonstrate that spatial restriction on metal nanoparticles limits aggregation and eliminates performance losses upon subsequent testing. We synthesized and compared Ru supported on activated (Ru/AC) or mesoporous carbon (Ru/MC). Electron tomography characterization showed preferential Ru location depending on the material porosity; Ru nanoparticles were located inside mesoporous carbon pores and showed narrower size distribution. In catalytic reactions, Ru/MC reached the complete conversion of levulinic acid with the 96% selectivity to γ-valerolactone while it converted 74% of glycerol compared to the 34% showed by Ru/AC. The Ru/AC materials deactivated after 1 catalytic cycle, however the Ru/MC maintained constant activity for multiple catalytic cycles.

Ammonium tagged Hoveyda-Grubbs catalysts immobilized on magnetically separable core-shell silica supports for ring-closing metathesis reactions

Ammonium tagged Hoveyda-Grubbs (Ru-1) catalyst was immobilized on core-shell structured silica gel bearing a magnetic nano-sized α-Fe2O3 core via non-covalent interactions. Core-shell silica gel materials were synthesized using a two-step coating procedure of α-Fe2O3 in the presence of cationic (dodecyl trimethyl ammonium chloride, DTMAC) and non-ionic (Synperonic F108) surfactants and tetraethoxysilane (TEOS) as the silica source. Double SiO2 coated SiO2(2)@α-Fe2O3 supports with a high surface area of 646 m2/g and pore size/volumes of 2.88 nm/0.393 cm3 were obtained after removal of template surfactants from silica gel by extraction. Supported catalyst, Ru-1@SiO2(2)@α-Fe2O3, was found to be very active in ring-closing metathesis (RCM) reactions of diethyl diallyl malonate (DEDAM) and various dienes. The catalyst can be easily separated from the reaction mixture with the aid of a magnet and was reusable up to eight times with low Ru leaching levels.

Dendritic Core‐Frame and Frame Multimetallic Rhombic Dodecahedra: A Comparison Study of Composition and Structure Effects on Electrocatalysis of Methanol Oxidation

AbstractThe composition and structure of multimetallic nanostructures can be tailored to enhance electrocatalytic properties. This work reports a seed‐mediated synthesis of novel multimetallic dendritic core‐frame and frame nanostructures with a rhombic dodecahedral shape for enhanced methanol oxidation reaction (MOR). The synthesis involves in situ formation of Cu seeds and the subsequent selective deposition of Pt and Ru on the edges and vertices of the Cu seeds to generate CuPt and CuPtRu dendritic core‐frame nanostructures. The core‐frame nanostructures undergo a post acetic acid etching process to form the frame nanostructures. While transmission electron microscopy reveals the morphology and elemental distribution of the nanostructures, X‐ray diffraction patterns confirm the alloy compositions of dendritic frames for both the core‐frame and frame nanostructures. Compared to the bimetallic CuPt nanostructures, the trimetallic CuPtRu nanostructures lower the onset potential and completely suppress the peak current in the reverse scan for MOR. The CuPtRu alloyed frame nanostructures are the best to prevent Ru leaching compared to the CuPtRu core‐frame nanostructures and PtRu catalysts. X‐ray photoelectron spectroscopy reveals that all three elements become more electron rich in the frame nanostructures. Further refining the composition ratio of the CuPtRu alloyed dendritic frame nanostructures can lead to more efficient catalysts at a lower cost for MOR.

A Robust Ru/ZSM‐5 Hydrogenation Catalyst: Insights into the Resistances to Ruthenium Aggregation and Carbon Deposition

AbstractA long‐life topic in the field of heterogeneous catalysis has been to develop supported catalysts that are stable against the aggregation of active metal and carbon deposition. Herein, we report a highly stable Ru/ZSM‐5 catalyst for the hydrogenation of levulinic acid in water, which can be recycled at least 10 times without apparent loss of activity (conv. &gt;95 %, yield &gt;85 %). The influences of types of Al species, structure of support, Ru sizes, Ru leaching, and carbon deposition, etc. on activity and stability were discussed in detail. It was confirmed that the tetrahedral‐coordinated framework Al in ZSM‐5 contributed to the favorable metal–support interaction, and thus suppressed the aggregation and leaching of ruthenium during recycling. Besides, the suitable pore volume and channel network connectivity successfully prevent from deposition of carbonaceous residues.

Ru-Catalyzed Estragole Isomerization under Homogeneous and Ionic Liquid Biphasic Conditions.

The isomerization of estragole to trans-anethole is an important reaction and is industrially performed using an excess of NaOH or KOH in ethanol at high temperatures with very low selectivity. Simple Ru-based transition-metal complexes, under homogeneous, ionic liquid (IL)-supported (biphasic) and “solventless” conditions, can be used for this reaction. The selectivity of this reaction is more sensitive to the solvent/support used than the ligands associated with the metal catalyst. Thus, under the optimized reaction conditions, 100% conversion can be achieved in the estragole isomerization, using as little as 4 × 10–3 mol % (40 ppm) of [RuHCl(CO)(PPh3)3] in toluene, reflecting a total turnover number (TON) of 25 000 and turnover frequencies (TOFs) of up to 500 min–1 at 80 °C. Using a dimeric Ru precursor, [RuCl(μ-Cl)(η3:η3-C10H16)]2, in ethanol associated with P(OEt)3, a TON of 10 000 and a TOF of 125 min–1 are obtained with 100% conversion and 99% selectivity. These two Ru catalytic systems can be transposed to biphasic IL systems by using ionic-tagged P-ligands such as 1-(3-(diphenylphosphanyl)propyl)-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide immobilized in 1-(3-hydroxypropyl)-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl) imide with up to 99% selectivity and almost complete estragole conversion. However, the reaction is much slower than that performed under solventless or homogeneous conditions. The use of ionic-tagged ligands significantly reduces the Ru leaching to the organic phase, compared to that in reactions performed under homogeneous conditions, where the catalytic system loses catalytic performance after the second recycling. Detailed kinetic investigations of the reaction catalyzed by [RuHCl(CO)(PPh3)3] indicate that a simplified kinetic model (a monomolecular reversible first-order reaction) is adequate for fitting the homogeneous reaction at 80 °C and under biphasic conditions. However, the kinetics of the reaction are better described if all of the elementary steps are taken into consideration, especially at 40 °C.

Controlled Ring-Opening Metathesis Polymerization with Polyisobutylene-Bound Pyridine-Ligated Ru(II) Catalysts.

This study describes the use of polyisobutylene (PIB) to phase-anchor pyridine ligands that form a phase-separable Grubbs third-generation catalyst. We further show that this complex is useful in ring-opening metathesis polymerization (ROMP) reactions. These PIB-bound pyridine-ligated Grubbs catalysts provide the same benefits of control over polymer chain growth and polydispersity of the product as their low-molecular-weight analogs and reduce Ru leaching in ROMP products from approximately 16% (820 ppm residues) as seen with a similar pyridine-ligated catalyst to a value of approximately 3% (160 ppm residues). These labile ligands are shown to be as effective at generating separable metal complexes as less labile PIB-functionalized N-heterocyclic carbene catalyst ligands that are typically used for immobilization but that require a multistep synthesis.

Ru complexes of Hoveyda-Grubbs type immobilized on lamellar zeolites: activity in olefin metathesis reactions.

Hoveyda–Grubbs type catalysts with cationic tags on NHC ligands were linker-free immobilized on the surface of lamellar zeolitic supports (MCM-22, MCM-56, MCM-36) and on mesoporous molecular sieves SBA-15. The activity of prepared hybrid catalysts was tested in olefin metathesis reactions: the activity in ring-closing metathesis of citronellene and N,N-diallyltrifluoroacetamide decreased in the order of support MCM-22 ≈ MCM-56 > SBA-15 > MCM-36; the hybrid catalyst based on SBA-15 was found the most active in self-metathesis of methyl oleate. All catalysts were reusable and exhibited low Ru leaching (<1% of Ru content). XPS analysis revealed that during immobilization ion exchange between Hoveyda–Grubbs type catalyst and zeolitic support occurred in the case of Cl− counter anion; in contrast, PF6− counter anion underwent partial decomposition.

Total degradation of p-hydroxybenzoic acid by Ru-catalysed wet air oxidation: a model for wastewater treatment

Catalytic wet air oxidation using heterogeneous catalysts is a promising technology for treatment of wastewaters. Wastewaters from olive oil mills are difficult to clean because effluents contain high levels of phenolic compounds that cannot be removed by biological treatment or incineration. Therefore, we tested the catalytic wet air oxidation of p-hydroxybenzoic acid, as model molecule of olive oil mills wastewaters, over Ru-supported CeO2–TiO2 mixed oxides. We focussed on the Ce/Ti molar ratio because this ratio modifies the properties of the Ru catalysts. Supports were prepared by using the sol–gel method. The Ru catalysts were prepared by impregnation. Those products were characterized by N2 adsorption–desorption, X-ray diffraction, H2 chemisorption, transmission electron microscopy and inductively coupled plasma. Catalytic wet air oxidation of p-hydroxybenzoic acid was performed in a batch reactor at 140 °C and 50 bar of air. Our results show that the most efficient catalyst was Ru with a Ce/Ti ratio of 1/5, which converted totally p-hydroxybenzoic after 7 h of reaction without Ru leaching. We explain this finding by an enhanced dispersion of Ru due to better structural properties of the CeO2–TiO2 support.© 2015, Springer International Publishing Switzerland.

Polyethylene as a Cosolvent and Catalyst Support in Ring-Opening Metathesis Polymerization

Polyethylene oligomers (PEOlig) can be used as cosolvents and sometimes soluble catalyst supports in ring-opening metathesis polymerization (ROMP) reactions. As a catalyst support, this polyolefin serves as an N-heterocyclic carbene ligand for a ROMP catalyst, making it soluble at 70 °C and insoluble at room temperature. As a cosolvent, unfunctionalized PE oligomers facilitate quantitative separation of PEOlig-bound Ru-catalyst residues from polymer products. In these cases, the insolubility of the unfunctionalized polyethylene (Polywax) and its entrapment of the PEOlig-supported Ru residue in the product phase at room temperature afford ROMP products with Ru contamination lower than other procedures that use soluble catalysts. These separations require only physical processes to separate the product and catalyst residues—no additional solvents are necessary. Control experiments suggest that most (ca. 90%) of the Ru leaching that is seen results from Ru byproducts formed in the vinyl ether quenching step and not from the polymerization processes involving the PEOlig-supported Ru complex.

Metathesis of cardanol over Ru catalysts supported on mesoporous molecular sieve SBA-15

The Hoveyda–Grubbs type Zhan catalysts (ZC) and Grubbs second generation catalyst (GII) were immobilized on SBA-15 mesoporous molecular sieve by non-covalent interactions and phosphine linkers, respectively. Both hybrid catalysts proved to be highly active and selective in cardanol metathesis and cardanol cross-metathesis with ethene and cis-1,4-diacetoxy-2-butene (DAB). GII/SBA-15 was less active than ZC/SBA-15, however, Ru leaching was significantly lower for GII/SBA-15 (0.5%) than for ZC/SBA-15 (2.5%). In ethenolysis of cardanol, 3-(non-8-enyl)phenol was isolated as a major product. In cross-metathesis with DAB 9-(3-hydroxyphenyl)non-2-enyl acetate and non-2-enyl acetate were formed with high selectivity. Easy catalyst–product separation and low Ru leaching provide the products (applicable as detergent precursors and fragrance and flavor agents) free from the catalyst residue.

Ru Nanoparticles Entrapped in Ordered Mesoporous Carbons: An Efficient and Reusable Catalyst for Liquid-Phase Hydrogenation

Ru nanoparticles entrapped in ordered mesoporous carbons (CMK-3) served as an efficient and reusable catalyst for liquid-phase hydrogenation of benzaldehyde and its derivatives under our tested conditions (medium hydrogen pressure, room temperature, water as solvent). The Ru nanoparticles can be well stabilized by CMK-3 ordered mesoporous carbons so that the Ru leaching was below the detection limit of ICP-AES. Therefore, the Ru/CMK-3 catalyst can be used for at least five times without distinct loss in activity or selectivity for the hydrogenation of benzaldehyde. It is worthy of note that the Ru/CMK-3 catalyst was more efficient than the commercial Ru/C and homemade Ru/AC catalyst for the liquid-phase hydrogenation of benzaldehyde. The Ru/CMK-3 catalyst can also catalyze the liquid-phase hydrogenation of nitrobenzene and its derivatives with high conversions and excellent selectivities under optimal conditions.

Recoverable Reusable Polyisobutylene (PIB)-Bound Ruthenium Bipyridine (Ru(PIB-bpy)3Cl2) Photoredox Polymerization Catalysts.

Polyisobutylene (PIB)-bound ruthenium bipyridine [Ru(PIB-bpy)3]2+ metal complexes were prepared from PIB ligands formed by alkylation of 4,4'-dimethylbipyridine with polyisobutylene bromide. The product Ru(PIB-bpy)3Cl2 complexes with at least one PIB ligand per bipyridine unit function as soluble recyclable photoredox catalysts in free radical polymerization of acrylate monomers under visible light irradiation at 25 °C with ethyl 2-bromoisobutyrate as the initiator in the presence of diisopropylethylamine. The polyacrylate products contained only about 1 ppm Ru contamination. This PIB-bound catalyst was recyclable and showed about 50-fold less Ru leaching as compared to Ru leaching in a polymerization catalyzed by the low molecular weight Ru catalyst, Ru(bpy)3(PF6)2.

Synthesis of BINAP ligands with imidazole tags for highly enantioselective Ru-catalyzed asymmetric hydrogenation of β-keto esters in ionic liquid systems

The imidazole-tagged BINAP ligands were synthesized and used for Ru-catalyzed asymmetric hydrogenation of β-keto esters in ionic liquid (IL) systems. The Ru-BINAP catalysts with the imidazolium tags show high catalytic activity and enantioselectivity, which closely parallel the performance of unmodified BINAP. The catalyst recycling experiments using [bmim]Tf2N/MeOH system demonstrated that introducing imidazolium moieties to the BINAP backbone can effectively enhance the affinity of the Ru-catalysts to the IL, reduce Ru leaching and improve catalysts stability, and after several cycles no significant loss of activity and enantioselectivity was observed.

Grubbs Catalysts Immobilized on Mesoporous Molecular Sieves via Phosphine and Pyridine Linkers

Hybrid catalysts for olefin metathesis were prepared by the immobilization of Ru alkylidenes (Grubbs catalysts) on mesoporous molecular sieves SBA-15 and MCM-41 having the surface modified with molecules bearing dicyclohexylphosphine (PCy2) and pyridine end groups. Hybrid catalysts with Ru attached to the surface via PCy2 ligands exhibited higher activity and stability than those with Ru attached via pyridine ligands. The former catalysts exhibited a high activity in a series of metathesis reactions (RCM, ROMP, and cross-metathesis) reaching turnover numbers (TONs) from 200 to 2000 and being reusable several times. The filtration tests for all catalysts suggested that the solid catalysts were responsible for catalytic activity during the reactions. Only low Ru leaching was observed. A positive effect of the pore size of the support on catalyst activity was observed for the metathesis of methyl oleate.