An ordered mesoporous carbon (CMK-3)-supported gold catalyst was prepared and used in the aerobic oxidation of glucose to gluconic acid under base-free conditions with molecular oxygen. XRD and TEM results revealed that gold nanoparticles were uniformly dispersed on the surface and in the channels of CMK-3. Catalytic tests showed that conversion remarkably increased with decreased selectivity when oxygen pressure and reaction temperature were increased. Glucose conversion to gluconic acid reached over 92% with 85% selectivity under the conditions of 383 K reaction temperature, 0.3 MPa oxygen pressure, and 2 h reaction time. Hydrogen peroxide was generated during reaction, and the relationship between hydrogen peroxide and the byproduct fructose was discussed. Low glucose/Au molar ratio minimized fructose formation. A 92% gluconic acid yield was obtained after reaction for 15 min when the molar ratio of glucose/Au was set to 100. The spent catalyst treated with an aqueous solution of NaOH at 363 K could produce glucose conversion up to 87%, which was close to the result of as-prepared catalyst and excluded the effect of alkaline residues.Keywords: base-free condition; gluconic acid; glucose oxidation; gold; mesoporous carbon;

Evenly dispersed tungsten carbides with controlled phase compositions that exhibit an impressive capacity to carry out the regioselective hydrogenolysis of inert aryl ether C–O bonds instead of aliphatic C–O bonds to produce aromatic compounds are reported.

Copper nanoparticles exsoluted in situ under a reducing atmosphere at elevated temperatures are socketed into the parent copper phyllosilicate nanotubes and exhibit excellent catalytic performance and superior stability for the selective hydrogenation of various esters to alcohols.

•Ag/AC-N catalysts with different nitrogen contents are synthesized.•Enhanced catalytic performance of Ag/AC-N is obtained.•Electronic interactions of Ag and N account for the performance enhancement.Silver nanoparticles supported on nitrogen-doped activated carbon (Ag/AC-N) are demonstrated as promising catalysts for the chemoselective hydrogenation of dimethyl oxalate to methyl glycolate. Characteristic studies by TPR, XPS, and Raman indicate that AC-N benefits the dispersion of silver nanoparticles due to the strong electronic interactions between nitrogen and silver species. The optimized Ag/AC-N catalyst shows intensified performance in terms of high activity and excellent stability. It is inferred that the co-existence of Ag0 and Ag+ derived from the strong interactions of nitrogen with Ag species renders the superior catalytic performance of Ag/AC-N.Download high-res image (112KB)Download full-size image

The addition of yttrium chloride (YCl3) to an activated carbon-supported Au catalyst (Au/AC) can markedly promote the catalytic performance of acetylene hydrochlorination to the vinyl chloride monomer (VCM). The structure and physicochemical features of the YCl3-modified catalysts (Y–Au/AC) were measured by X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction, C2H2-temperature programmed desorption, and scanning transmission electron microscopy. The presence of YCl3 was found suppressing the reduction of highly oxidized Auδ+ (δ = 1, 3) to metallic Au0 dependently and thus retard the agglomeration of Au nanoparticles during the reaction. In addition, the additive of YCl3 to the Au/AC catalyst greatly inhibits the coke deposition on the catalyst surface. The optimized catalyst with an atomic ratio of Y/Au = 5 (1 wt% Au loading weight) yields an 87.8% acetylene conversion and almost 100% selectivity for VCM under the reaction of GHSV(C2H2) = 800 h−1 at 180 °C. The durability test indicates that the 5Y–1Au/AC catalyst maintains high catalytic activity for more than 2300 h at 30 h−1 GHSV(C2H2) and 180 °C, indicating great promise as a non-mercury catalyst for PVC manufacture.

•Cu−Fe/N-CNT catalysts with different nitrogen contents are synthesized.•Cu−Fe/N-CNT catalysts show good performance in the synthesis of higher alcohols from syngas.•An improved CO conversion and excellent selectivity to higher alcohols were obtained.•The electron donation and surface basicity of N-CNT account for the promotional effects.Heteroatom doping is an attractive approach for improving the properties of carbon materials for various applications. In this study, a series of nitrogen-doped (N-doped) carbon-nanotube-supported Cu–Fe (xCun–Fem/yN-CNT) catalysts were prepared for CO hydrogenation to higher alcohols. The structural and textural properties of N-doped catalysts were characterized by X-ray diffraction, transmission electron microscopy, hydrogen temperature-programmed reduction, and CO2 temperature-programmed desorption. The results revealed that doping N into CNT supports improved the Cu–Fe dispersion, strengthened the interaction of Cu and Fe species with N-CNT, and introduced many surface-basicity sites. Thus, an improved CO conversion and excellent selectivity to higher alcohols [S(C2+–OH)] were obtained. Furthermore, the selectivity to alcohols [S(ROH)] and S(C2+–OH)/S(MeOH) over the optimized 15Cu1–Fe1/1.3N-CNT catalyst reached 27.2% and 2.2, while the corresponding values were 20.2% and 0.4, respectively, over the catalyst without N doping under identical reaction conditions. The present results on N-CNT supported Cu–Fe catalyst will provide further understanding on the catalyst design for the transformation of syngas to higher alcohols.Download high-res image (67KB)Download full-size image

Effective control of surface composition of bimetallic catalysts is challenging yet important, as synergistic effects between two metals play vital roles in heterogeneous catalysis. This study involves methods of loading control, thermal activation, and selective surface etching to modify the bimetallic surface on the Au–Ag/SBA-15 catalyst and gains insight into the nature of the promotional effect of Ag modification over Au catalysts. The binary Au–Ag/SBA-15 catalyst prepared following a stepwise metal-loading procedure is found for the first time to be active in benzyl alcohol dehydrogenation without oxidant or hydrogen acceptor. A direct correlation is established between the surface compositions of the Au–Ag nanoparticles and their intrinsic catalytic activities. Au–Ag element analytical techniques, including X-ray fluorescence, X-ray photoelectron spectroscopy, and high-sensitivity low-energy ion scattering spectroscopy, are applied to acquire compositional information in bulk and on the surface. As a result, the pronounced improvement of Au catalyst by Ag is from an ensemble with a specific surface composition rather than the bulk composition. The synergy between Au and Ag for benzyl alcohol dehydrogenation is the most pronounced in the case of 4:1 Au–Ag surface compositions, corresponding to the prepared Au1–Ag0.111 catalyst. The electronic promoting effect is suggested as the natural origin of compositional enhancement by differentiating it from the structural effect. This work demonstrates the importance of surface composition control at an atomic level in developing highly efficient multicomponent catalysts.Keywords: alloy; benzyl alcohol; composition; dehydrogenation; gold; silver

Downsizing large Au particles into small particles with controllable size remains challenging. In this study, we redispersed large sintered Au particles on activated carbon (Au/C) to highly dispersed nanoparticles with uniform distribution and controllable size after treatment with iodohydrocarbons. The Au/C catalyst was conducted for a number of deactivation/regeneration cycles with negligible deterioration in catalytic performance for acetylene hydrochlorination. The redispersion behavior reveals a reverse agglomeration process in the presence of iodohydrocarbons under mild conditions. This behavior is significantly related to the C–I bond dissociation energy (BDE) and adsorption of iodic species on Au particles. A novel protocol for controlling the size and predicting the redispersion efficiency of Au particles is established by correlating with the C–I BDEs of iodohydrocarbons. The molecular-level interpretation of redispersion provides a thorough mechanism based on experimental results. This study presents an efficient method for the easy regeneration of sintered Au-based catalysts for practical applications.

A confined Ag nanomaterial in the channels of herringbone multi-walled carbon nanotubes (Ag-in/hCNT) was effectively prepared. The space restriction induces morphological changes of Ag nanoparticles into rough nanowires with an estimated aspect ratio of 60:8 (nm/nm). Dihydrogen activation is enhanced through the vacancy-enriched wire-like Ag nanocatalyst, as well as the confinement effect. The grain boundaries of Ag and rolled-up graphene layers of CNTs are speculated to play vital roles in the diffusion of activated hydrogen species. The Ag-in/hCNT catalyst exhibits an activity that is three times higher than that of Ag nanoparticles located on the CNT exterior walls in DMO hydrogenation. This finding may insinuate that interplanar spaces provide available access to the external surface of CNTs. Designed experiments further confirm the importance of herringbone CNTs with higher reaction rate than parallel CNTs, and confined Ag produces considerably more activated hydrogen species, thereby benefiting the reduction of surface copper nanoparticles or DMO molecules during hydrogenation. This paper presents a study of the effective utilization of hydrogen over herringbone CNT confined Ag and an understanding of the confinement and promotional catalytic effects.

Surfactant-free bimetallic Ni@Ag nanoparticles in mesoporous silica, SBA-15 prepared by simple wet co-impregnation catalyse hydrogenation of dimethyl oxalate to methyl glycolate or ethylene glycol in high yield.

A series of new ruthenium complexes with rigid ligand o-(diphenylphosphino)aniline, including [(PPh3)(o-PPh2C6H4NH2)RuCl2]2 (1), (o-PPh2C6H4NH2)2RuCl2 (2), [(o-PPh2C6H4NH2)2(o-PPh2C6H4NH)Ru]+Cl− (3), Ph3P(η2-H2)Ru(μ-H)(μ-o-PPh2C6H4NH)2RuH(PPh3) (4), (o-PPh2C6H4NH2)(o-PPh2C6H4NH)RuCl(CO) (5), (o-PPh2C6H4NH2)(o-PPh2C6H4NH)RuH(CO) (6), and [(o-PPh2C6H4NH)2Ru(CO)]2 (7) were synthesized and employed as catalysts for chemoselective hydrogenation of esters. Among them, complexes 1, 2, and 5 exhibited excellent performance in hydrogenation of dimethyl oxalate to methyl glycolate, in comparison with the ruthenium complexes with a flexible aminophosphine ligand, such as (Ph2P(CH2)2NH2)2RuCl2, (Ph2P(CH2)3NH2)2RuCl2, and (o-Ph2PC6H4CH2NH2)2RuCl2, under identical conditions. Complexes 1 and 2 also displayed good activities in the hydrogenation of other aliphatic and cyclic esters. The catalytic mechanism of hydrogenation was discussed according to the results of NMR spectroscopic studies and control experiments.

Selective oxidation of glycerol was carried out over Pt catalysts supported on nitrogen-doped carbon nanotubes (Pt/N-CNTs) with molecular oxygen under atmospheric pressure in base-free aqueous solution. The N-CNTs were readily synthesized through a catalyst-free approach of annealing the mixture of CNTs and melamine. Results of X-ray diffraction, nitrogen absorption, and Raman spectroscopy confirmed that the tubular structure of CNTs was intact during annealing. Analyses of transmission electron microscopy, X-ray photon spectroscopy, and temperature-programmed desorption indicated that the surface of the CNTs was successfully functionalized with nitrogen atoms, which changed the electronic structure and surface basicity of the N-CNTs. Pt/N-CNTs out-performed Pt/CNTs for glycerol oxidation in terms of glycerol conversion and glyceric acid selectivity. Pt/N-CNTs showed highly stable catalytic performance during consecutive recycles when the used catalyst was reduced in a H2 atmosphere.

A series of polyvinylpyrrolidone-stabilized heteropolyacids (PVP-HPAs) are generated by self-assembly of HPAs and PVP in methanol. The PVP-HPAs are then employed as catalysts for the synthesis of poly(oxymethylene) dimethyl ethers (DMMn, n⩾1) by the methanolysis of trioxane. The results suggest that the acidity of PVP-HPAs is tunable by changing the ratio of PVP and HPAs, which is a key factor for the selectivity of the DMMn product. By optimizing the composition and reaction conditions, two types of PVP-HPA, PVP-phosphotungstic acid (PVP-HPW) in a PVP/HPW ratio of 1/4:1 and PVP-silicotungstic acid (PVP-HSiW) in a PVP/HSiW ratio of 1/4:3/4, respectively afford 52.4% and 50.3% yields of DMM2–5. The optimized catalysts are reusable for a minimum of 10 times without a significant drop in performance.

Polyvinylpyrrolidone-stabilized heteropolyacids (PVP–HPAs) are synthesized by self-assembling in alcohol. The structure of PVP–HPAs is determined by various characteristic techniques. HPAs can protonate PVP to form polymeric cations. In turn, the protonated PVP interacts strongly with the heteropolyanion by forming an ionic liquid (IL)-like structure. The self-assembling separation and recyclability characteristics are related to the PVP's IL-like structure. The catalyzing performance of PVP–HPAs varies with the species of HPA and the content of PVP. The optimized PVP–H4SiW12O40·5H2O (HSiW) (1/5:3/4) gives more than 60% conversion of cellulose and complete conversion of highly selective cellobiose into butylglucosides. The optimized PVP–HSiW is separated directly by centrifugation and retains the activity without any post-treatment during recycling. The deactivation of PVP–HPAs is related to the loss of the catalyst during recycling. The functional mechanism of the IL-like structure is explored in this control experiment.

Supported bimetallic Ru–Fe catalysts were prepared using a step-deposition–reduction method. The selective hydrogenolysis of acetic acid to ethanol was investigated as a reaction, which is considered to be related to the transformation of biomass-derived carboxylic acids to fuels and value-added chemicals. An SBA-15-supported Ru–Fe catalyst displayed significant improvements in catalytic performance for the hydrogenolysis of acetic acid to ethanol compared with monometallic catalysts and that with SiO2 as a carrier. When the Ru/Fe atomic ratio was set at 2/1, the prepared catalyst could give a nearly 100% conversion of acetic acid and 88% selectivity to ethanol. The catalyst showed considerable stability in terms of structure and performance for a long-term run on stream. Characterization results indicated that a small portion of Fe species was alloyed with Ru, whereas the other portion of Fe species, likely FeO1+x (0 < x < 0.5), was dispersed on the catalyst surfaces. The Fe species were crucial for the stabilization of Ru–Fe bimetallic nanoparticles and activation of acetic acid molecules in the hydrogenolysis reaction. Moreover, several other carboxylic acids, such as propionic acid, levulinic acid, and lactic acid, could also be efficiently converted to their corresponding alcoholic chemicals or lactone using the optimized Ru–Fe/SBA-15 catalyst under relatively mild conditions.

Several lanthanum oxide-modified Cu/SiO2 (La-Cu/SiO2) catalysts synthesized by urea-assisted gelation and postimpregnation were used for the vapor-phase chemoselective hydrogenation of dimethyl oxalate (DMO) into ethylene glycol (EG). The 1.0La-Cu/SiO2-u catalyst with 1.0 wt % La loading was found to have the highest activity, whereas the catalyst with higher La loading at 3.0 wt % adversely affected the deterioration of catalytic activity. H2-TPR results revealed that strong interactions between La promoters and Cu species substantially changed catalyst reducibility and made some Cu2+ species on catalyst precursors difficult to be reduced. Several positive variations induced by the introduction of La were confirmed by in situ XRD, N2O chemisorption, H2-TPD, X-ray Auger electron spectroscopy, and in situ FT-IR of chemisorbed CO. These variations included increased Cu metallic dispersion, improved ability for H2 activation, elevated surface concentration of Cu+ species, and enhanced stability of catalyst nanostructure. The formation of unique Cu–O–La bonds between LaOx and cupreous species located at interfacial sites was presumably responsible for the improved catalytic performance and stability of La-Cu/SiO2-u catalyst.Keywords: copper; dimethyl oxalate; ethylene glycol; hydrogenation; lanthanum oxide

The conversion of methanol to aromatics such as benzene, toluene, and xylenes (BTX) was performed over HZSM-5-supported bimetallic Zn–Sn catalysts. The results indicated that Sn species preferentially healed the defects in HZ crystals to create new active sites. The catalyst with Zn species markedly enhanced the aromatization performance but easily produced heavy coke. Thus, an optimized catalyst with 1 wt% Zn and 1 wt% Sn exhibited improved catalytic performance in terms of selectivity and BTX yield compared with a catalyst with a single metal. Consequently, the BTX yield was 64.1 % under the reaction conditions of 0.1 MPa and 0.8 h−1 methanol weight hourly space velocity at 450 °C.

The performance of an SBA-15-supported Cu catalyst for hydrogenation of dimethyl oxalate to ethylene glycol is markedly promoted with Au. A key genesis of the high activity of the catalyst is ascribed to the formation of Cu–Au alloy nanoparticles which stabilize the active species and retard their agglomeration during the hydrogenation process.

Na+-intercalated carbon nanotubes (Na-CNTs) were obtained by impregnation of CNTs with sodium acetate followed by annealing at high temperatures under argon. Stable Na-CNTs-supported Pt catalysts (Pt/Na-CNT catalysts) were then prepared for hydrogen purification via preferential CO oxidation in a H2-rich stream (CO-PROX). Characteristic studies show that the content of Na+ species in CNTs is increased with increased annealing temperature and the Pt nanoparticles with an average size of 2–3 nm are uniformly dispersed on the surfaces of Na-CNTs. An optimized Pt/Na-CNT catalyst with 5 wt% Pt loading can completely remove CO from 40 °C to 200 °C. This catalyst also exhibits long-term stability for 1000 h at 100 °C in feed gas containing 1% CO, 1% O2, 50% H2, 15% CO2, and 10% H2O balanced with N2. The electron transfer between the Pt nanoparticles and Na+ species plays an important role in enhancing the CO-PROX performance of the catalyst.Graphical abstractHighlights► Na+-intercalated CNTs (Na-CNTs) are obtained by annealing NaOAc/CNTs under Ar. ► The content of Na+ species in CNTs is increased with increased annealing temperature. ► 5% Pt/Na-CNTs-500 can completely remove CO in a H2-rich stream at 40−200 °C. ► CO-PROX can be accomplished in a H2 stream containing CO2 and H2O vapor for 1000 h. ► The electronic interactions between Pt and Na+ account for the enhanced performance.

We proposed basic principles for biosolvent design on the viewpoint of ionization. Two classes of biosolvents, based on cyclic carbonate moiety and amide moiety, were designed through hydroxyl functionalization of highly dielectric compound. The newly designed compounds, glycerol carbonate (GC) and N-hydroxymethyl formamide (HOF), were synthesized for the development of soluble enzymatic systems and characterized by 13C NMR and 1H NMR. All the characterization data were consistent with the expected structures. Using conductance measurements, the pKa values of trichloroacetic acid in GC and HOF were determined as 0.80 and 0.85 at 25.0 °C, which was very close to that in water (pKa = 0.70), suggesting that the ionizing and dissociating abilities of GC and HOF are similar to those of water. The effects of various reaction parameters on activity and stability of Candida antarctica lipase B and lipase from Pseudomonas cepacia were investigated using the transesterification of ethyl butyrate with n-butanol as a model reaction. The activities of lipases in GC and HOF were comparable to those in water, indicating that the newly designed compounds were biocompactible. Biosolvent design is a promising and versatile method for developing new biosolvents.

Carbon nanotube-supported RuFe bimetallic catalysts (RuFe/CNT) were prepared through a coimpregnation method for the selective hydrogenolysis of 20 wt % glycerol aqueous solution to produce glycols (1,2-propanediol and ethylene glycol). The Ru/CNT catalyst with smaller Ru nanoparticles (NPs) was significantly active for C–C bond cleavage, giving a considerable amount of CH4 in the hydrogenolysis product. The RuFe/CNT catalyst with bimetallic NPs having an average size similar to Ru/CNT was more efficient for C–O bond cleavage, affording higher selectivity to glycols. Almost 100% glycerol conversion and over 75% selectivity to glycol could be obtained using the optimized RuFe/CNT catalyst under relatively mild conditions. The bimetallic RuFe/CNT catalyst was structurally robust and showed excellent reusability. Transmission electron microscopic images revealed that, when an appropriate amount of Fe entity was added, the RuFe bimetallic NPs were uniformly dispersed on the CNT surfaces and had an average size of ∼3 nm. X-ray photoelectron spectroscopy indicated that a portion of the Fe species were interacted with Ru moieties, forming Ru–Fe alloys on the Ru domain, whereas other Fe species were in the forms of iron oxides, likely FeO and FeO1+x (0 < x < 0.5), mostly presenting on the periphery of RuFe bimetallic NPs. The occurrence of iron oxide species is crucial for the stability of RuFe bimetallic NPs during catalytic runs; but excess iron oxides block the surfaces of RuFe bimetallic NPs, resulting in a decrease in catalytic activity. Higher performance of the RuFe/CNT catalyst is attributed to the synergistic effects of the formation of Ru–Fe alloys and the interactions between the RuFe bimetallic NPs and iron oxides on CNT surfaces.Keywords: Bimetallic catalyst; Carbon nanotube; Glycerol; Glycol; Hydrogenolysis; Ru−Fe alloy;

Several lactam-based Brønsted-acidic ionic liquids with different acidities were synthesized and applied to the esterification of carboxylic acids with alcohols. High conversion and perfect selectivity were obtained under mild conditions. Among the ionic liquids investigated, those having a methyl sulfonate anion (which has weaker acidity than those with a tetrafluoroborate anion) afforded the highest activity for esterification. The results indicated that the acidity and immiscibility of Brønsted-acidic ionic liquids has a synergistic effect on their esterification performance. Furthermore, after removal of water under vacuum, such ionic liquids could be reused several times without substantial loss of activity.

A series of (o-alkylaminophenyl)diphenylphosphine ligands (P–N ligands) containing different alkyl carbon numbers or amino groups have been synthesized and characterized by IR and NMR (1H, 13C, 31P). The rhodium complexes ligated with P–N ligands in the hydroformylation of 1-hexene showed a considerable enhancement with the addition of water. NMR characterization studies suggested that the addition of water would engage in hydrogen bonding to the nitrogen atom of the coordinated P–N ligand, inhibiting the internal Rh–N interaction and generating more of the active unsaturated Rh-species that could react with 1-hexene to start the hydroformylation.

A series of supported Ru catalysts with achiral modifier triphenylphosphine (TPP) and chiral modifier (1R,2R)-1,2-diphenylethylenediamine [(1R,2R)-DPEN] were employed for the asymmetric hydrogenation of aromatic ketones. The textural and structural properties of the catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, N2 physisorption, transmission electron microscopy, CO2 and NH3 temperature-programmed desorptions, inductively coupled plasma atomic emission spectrometry, and ultraviolet−visible spectroscopy. Studies revealed that the enantiomeric excess (ee) followed this order according to the oxide supports used: MgO > γ-Al2O3 > CeO2 ≫ ZnO > SiO2, which was correlated with their surface basicity. Moreover, the highest ee value and intrinsic activity for the asymmetric hydrogenation of acetophenone were attained over the catalyst with a mean Ru nanoparticle diameter of 4.4 nm, while those for the asymmetric hydrogenation of 1-acetonaphthone were obtained over a catalyst with 6.2 nm nanoparticle diameter. The catalyst system consisting of Ru/MgO, TPP, and (1R,2R)-DPEN did not show a significant decrease in ee value after several recycles. The results indicate that there is a size matching effect between the Ru particles and the substrates, besides the acid/base influence of the oxide supports on the reaction.

Titanium-containing hexagonal mesoporous silicas (Ti-HMS) with wormhole structure and Si/Ti molar ratios ranging from 10 to 40 have been prepared by using long-chain alkyl primary amines as template agents. The Ti-HMS supported Au catalyst (Au/Ti-HMS) was obtained by a deposition−precipitation method for direct gas-phase epoxidation of propylene with use of O2 and H2. The structures of Ti-HMS and Au/Ti-HMS samples were characterized by X-ray diffraction, N2-physisorption, scanning electron microscopy, transmission electron microscopy, UV−vis diffuse reflectance spectroscopy, UV Raman spectroscopy, ammonia-temperature-programmed desorption, and atomic adsorption spectroscopy. The results showed that the Au/Ti-HMS catalyst exhibited superior performance in terms of propylene conversion, propylene oxide (PO) selectivity, and H2 efficiency in comparison with the Au catalysts supported on the conventional Ti-containing mesoporous materials. Besides the Si/Ti molar ratio, the chain length of alkylamine for the Ti-HMS preparation was crucial for the enhancement of catalytic performance. Specifically, 9.0% of propylene conversion, 97.3% of PO selectivity, and 30.4% of H2 efficiency can be obtained at 373 K in the initial 30 min of time-on-stream on the Au/Ti-HMS catalyst, where the Ti-HMS having a Si/Ti molar ratio at 20 was prepared by using tetradecylamine as the template agent. Regeneration of the spent catalyst by calcination in air gave almost no change in the PO selectivity but about 25% loss in the propylene conversion. The enhanced catalytic performance of Au/Ti-HMS catalyst may be essentially attributed to the homogeneous dispersion and uniformity of titanium species in combination with accessible pore structure.

Highly stable dendrimer-encapsulated Pd nanoparticles in ionic liquids were prepared for the first time by using charged PAMAM dendrimers as templates, which could maintain hydrogenation efficiency for up to at least 12 recycles.

A biphasic catalysis system composed of ionic liquid and rhodium complexes with water-soluble or amphiphilic phosphine ligands bearing water-soluble groups of sodium sulfonate have been employed for hydroformylation of 1-hexene. The experimental results show that the activity is almost independent of the hydrotropicity of the phosphine ligands in BMI·BF4. In this system, the extraction of phosphine species by the organics from the IL phase was quite low but larger than that of rhodium species and showed rather good stability of catalytic activity. A slight decrease in the aldehyde n/i ratio during the catalyst reuse could be recovered, in part, by replenishing certain amount of ligand into the used catalyst system.

Asymmetric hydrogenation of dimethyl itaconate by the chiral rhodium complex ligated with water-soluble sulfonated (R)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (labeled as (R)-BINAPS) was performed in ionic liquid-isopropanol biphasic catalytic system. A moderate enantiomeric excess (ee) of 64% and initial turnover frequency (TOFmax) as high as 1234 h−1 could be obtained at 303 K and 2.0 MPa when the molar ration of substrate to rhodium was set at 1000. Application of imidazolium ionic liquid [bmim]BF4 (bmim = 1-butyl-3-methyl imidazolium cation) made it possible to reuse the catalyst several times, showing rather good stability in the catalyst performance. According to the ICP-OES analyses, the total extraction of rhodium species by the reactants from the ionic liquid phase was about 3.24 wt% after the catalyst for four runs, which was about three times lower than that of total loss of phosphorous species. The slight decreases in the ee value and TOFmax during the catalyst reuse could be recovered essentially to the pristine levels by replenishing certain amount of the fresh ligand into the used catalyst.

Ionic liquids with buffering characteristics, synthesized by the reaction of [RMIM]OH base moieties with phthalic and tartaric acid, respectively, are potential reagents for controlling pH in non-aqueous media; remarkable [Base]/[Acid] molar ratio dependence of the catalytic activities has been observed in the hydrogenation of olefins with [RuCl2(PPh3)3] complex in DMF and [BMIM][BF4].

Selective oxidation of methane with hydrogen peroxide was catalyzed by several simple vanadium compounds in CH3CN. The reaction could afford formic acid as the major product. Vanadyl oxysulfate (VOSO4) was found to be an efficient catalyst. Specifically, the selectivity to formic acid of 70% at a methane conversion of 6.5% could be achieved over the VOSO4 catalyst under the reaction conditions of methane pressure 3.0 MPa and temperature 333 K for 4 h. The UV-Vis spectroscopic measurements revealed that the formation of V5+ species during the reaction might be vital for the methane activation. The reaction probably proceeded via radical mechanism.

•A SiO2-supported CuAg catalyst is prepared by a urea-assisted gelation method.•Ag nanoclusters are involved in Cu nanoparticles on SiO2 surface.•Ag modifies the copper dispersion and surface Cu+ site concentration.•Hydrogenation of dimethyl oxalate to ethylene glycol over CuAg/SiO2 is enhanced.•CuAg/SiO2 can retain the excellent activity for longer than 150 h.We present the application of a one-step urea-assisted gelation method to prepare a SiO2-supported bimetallic catalyst composed of copper (Cu) and silver (Ag). Results show the remarkably enhanced performance of the catalyst for selective hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). Coupled with a series of characterization and kinetic studies, the improved activity is attributed to the formation of Cu nanoparticles containing Ag nanoclusters on the SiO2 surface. The coherent interactions between the Cu and Ag species help create the active Cu+/Cu0 species in a suitable proportion and prevent the transmigration of bimetallic nanoparticles during the hydrogenation process. The optimized CuAg/SiO2 catalyst with an Ag/Cu atomic ratio of 0.05 has a balanced Cu+/Cu0 ratio and highly dispersed bimetal particles, which account for its high turnover frequency, EG selectivity of 97.0%, and excellent catalytic stability during the hydrogenation of DMO to EG for longer than 150 h.A SiO2-supported bimetallic catalyst composed of Cu and a small amount of Ag shows remarkable enhancements in catalytic performance for the selective hydrogenation of dimethyl oxalate to ethylene glycol, which is essentially attributed to the formation of Cu nanoparticles containing Ag nanoclusters on SiO2 surface.Download high-res image (142KB)Download full-size image

Gold (Au)–silver (Ag) bimetallic catalyst supported on ordered mesoporous silica SBA-15 exhibits unprecedentedly high activity and superior stability for the selective hydrogenation of dimethyl oxalate to methyl glycolate at a low temperature of 418 K. By contrast, monometallic Au/SBA-15 and Ag/SBA-15 catalysts are almost inactive under identical conditions. A combined tuning of particle dispersion and its surface electronic structure is shown as a consequence of the changes in the size and valence band structure of Au and Ag, which leads to significantly enhanced synergy. Considerably reduced apparent activation energies indicate that special active sites with the ability to activate substrate molecules more efficiently are generated in Au–Ag alloy nanoparticles. The Au–Ag bimetallic catalyst also displays excellent activity for the selective hydrogenation of some other unsaturated or saturated esters and acetic acid.Graphical abstractAu–Ag bimetallic catalyst supported on ordered mesoporous silica SBA-15 exhibits unprecedentedly high activity and superior stability for the selective hydrogenation of dimethyl oxalate to methyl glycolate at a low temperature of 418 K, which is ascribed to the strong electronic interactions of the resultant Au–Ag alloys.Download high-res image (196KB)Download full-size imageHighlights► Au incorporated with Ag results in the formation of smaller Au–Ag nanoparticle size. ► Au–Ag/SBA-15 displays excellent activity for selective reduction in ester groups. ► The reduction activity depends on the contents of Au and Ag. ► Negligible catalyst deactivation for DMO hydrogenation occurs for 200 h on stream. ► Strong interactions between Au and Ag account for the high catalytic performance.

Ionic-liquid buffer having phosphate anion was synthesized for the development of buffered enzymatic ionic liquid systems. Both the conformation and transesterification activity of Candida antarctica lipase B (CALB) dissolved in the hydroxyl-functionalized ionic liquids were buffer dependent. Intrinsic fluorescence studies indicated that the CALB possessed a more compact conformation in the medium consisted of ionic liquid buffer having phosphate anion and hydroxyl-functionalized ionic liquids like 1-(1-hydroxyethyl)-3-methyl-imidazolium tetrafluoroborate and 1-(1-hydroxyethyl)-3-methyl-imidazolium nitrate. High activity and outstanding stability could be obtained with the CALB enzyme in the buffered ionic liquids for the transesterification.Graphical abstractBoth the conformation and transesterification activity of Candida antarctica lipase B solubilized in ionic liquid are buffer dependent. The resulting catalyst system exhibits high activity and outstanding stability for the transesterification.Download full-size imageResearch highlights▶ Both the conformation and transesterification activity of CALB solubilized in ILs like [C2OHMIM][BF4] and [C2OHMIM][NO3] are buffer dependent. ▶ CALB possesses a more compact conformation in buffered [C2OHMIM][BF4] or [C2OHMIM][NO3], resulting in the enhancement of transesterification activity with highly stability during recycles. ▶ The knowledge gained in this study may be applicable to homogeneous enzymatic catalysis in organic solvents with hydroxyl group.

5 wt.% Ru nanoparticles confined in the channels or dispersed on the outside surfaces of carbon nanotubes (CNTs) were prepared using ultrasonication-added capillarity action or deposition, affording two kinds of catalysts labeled as 5 wt.% Ru/CNTs-in and 5 wt.% Ru/CNTs-out. Characteristic studies by high-resolution transmission electron microscopy, X-ray powder diffraction and H2-temperature programmed reduction revealed that the Ru nanoparticles existed in highly dispersion with a mean Ru particle size of 1.8 nm in the samples of 5 wt.% Ru/CNTs-in and 5 wt.% Ru/CNTs-out. The catalysts were evaluated for preferential oxidation of CO in hydrogen (CO-PROX). For a hydrogen-rich feed gas containing 1.0% CO and 1.0% O2, the 5 wt.% Ru/CNTs-in catalyst showed the best activity with complete CO oxidation at the temperature window of 333–393 K. The CO-PROX performance at 373 K was stable for more than 100 h. However, lower CO conversion and narrower temperature window were obtained over the 5 wt.% Ru/CNTs-out catalyst and 5 wt.% Ru nanoparticles supported on other carriers under identical conditions. It is concluded that the nano-channels of CNTs can selectively increase the density of reactants and the encapsulation of Ru nanoparticles in the channels of CNTs can provide a micro-environment to reinforce the reactivity of catalytic sites.

Stable and efficient B–Cu–SiO2 catalysts for the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol were prepared through urea-assisted gelation followed by postimpregnation with boric acid. Auger electron spectroscopy and CO adsorption by in situ Fourier transform infrared spectroscopy revealed that the Cu+ species on the catalyst surface increased together with an increase in the amount of boric oxide dopant. X-ray diffraction and N2O chemisorption indicated that a suitable amount of boric oxide doping tended to improve copper dispersion and retard the growth of copper particles during DMO hydrogenation. Catalytic stability was greatly enhanced in the B–Cu–SiO2 catalyst with an optimized Cu/B atomic ratio of 6.6, because of the formation and preservation of appropriate distributions of Cu+ and Cu0 species on the catalyst surfaces. The effect of boric oxide was attributed to its relatively high affinity for electrons, which tended to lower the reducibility of the Cu+ species.Doping a proper quantity of boric oxide onto a Cu–SiO2 catalyst significantly improves its stability as well as its activity for the vapor-phase hydrogenation of dimethyl oxalate to ethylene glycol.Download high-res image (148KB)Download full-size image

Glycerol carbonate was synthesized as biosolvent for the development of soluble enzymatic system. The effects of various reaction parameters on activity and stability of lipases were investigated using the transesterification of ethyl butyrate with n-butanol as a model reaction. Enzymatic activity in glycerol carbonate was compared with that in water and in conventional organic solvents with different ionizing and dissociating abilities. The pKa value of trichloroacetic acid and transesterification activities of Candida antarctica lipase B and Candida rugosa lipase in glycerol carbonate are similar to those in water, indicating that ionizing and dissociating powers are capable of satisfactorily predicting the biocompatibility of organic solvents for soluble enzymatic systems.

Copper nanoparticles exsoluted in situ under a reducing atmosphere at elevated temperatures are socketed into the parent copper phyllosilicate nanotubes and exhibit excellent catalytic performance and superior stability for the selective hydrogenation of various esters to alcohols.

Downsizing large Au particles into small particles with controllable size remains challenging. In this study, we redispersed large sintered Au particles on activated carbon (Au/C) to highly dispersed nanoparticles with uniform distribution and controllable size after treatment with iodohydrocarbons. The Au/C catalyst was conducted for a number of deactivation/regeneration cycles with negligible deterioration in catalytic performance for acetylene hydrochlorination. The redispersion behavior reveals a reverse agglomeration process in the presence of iodohydrocarbons under mild conditions. This behavior is significantly related to the C–I bond dissociation energy (BDE) and adsorption of iodic species on Au particles. A novel protocol for controlling the size and predicting the redispersion efficiency of Au particles is established by correlating with the C–I BDEs of iodohydrocarbons. The molecular-level interpretation of redispersion provides a thorough mechanism based on experimental results. This study presents an efficient method for the easy regeneration of sintered Au-based catalysts for practical applications.

Highly stable dendrimer-encapsulated Pd nanoparticles in ionic liquids were prepared for the first time by using charged PAMAM dendrimers as templates, which could maintain hydrogenation efficiency for up to at least 12 recycles.

The performance of an SBA-15-supported Cu catalyst for hydrogenation of dimethyl oxalate to ethylene glycol is markedly promoted with Au. A key genesis of the high activity of the catalyst is ascribed to the formation of Cu–Au alloy nanoparticles which stabilize the active species and retard their agglomeration during the hydrogenation process.

Surfactant-free bimetallic Ni@Ag nanoparticles in mesoporous silica, SBA-15 prepared by simple wet co-impregnation catalyse hydrogenation of dimethyl oxalate to methyl glycolate or ethylene glycol in high yield.