Preparation and catalytic properties of poly(methyl methacrylate)-supported Pd0 obtained from room-temperature,dark reduction of ionic aggregates of the unstable Pd2+ solution ionomer

A poly(methyl methacrylate)-supported Pd⁰ nanocatalyst was successfully prepared from solution reaction of Pd(CH₃COO)₂ with a copolymer acid, poly(methyl methacrylate-ran-methacrylic acid) (MMA–MAA). The reaction was carried out in a benzene/methanol mixed solvent in the dark at room temperature (∼25 °C) in the absence of a typical chemical reductant. There was coordination between the Pd⁰ nanoclusters and MMA–MAA, resulting in Pd⁰ nanoclusters being stably and uniformly dispersed in the MMA–MAA matrix, with an average particle size of ∼2.5 ± 0.5 nm. Mechanistically, it can tentatively be proposed that PMMA-ionomerization of the Pd²⁺ ions produces intramolecular –2COO⁻–Pd²⁺ aggregate cross-links in the solution. On swelling of the chain-segments that are covalently bound via multiple C–C bonds, the resultant elastic forces cause instantaneous dissociation at the O–Pd coordination bonds to give transient bare (i.e., uncoordinated), highly-oxidative Pd²⁺ ions and H⁺-associative carboxylate groups, both of which rapidly scavenge electrons and protons, respectively, of the active α-H atoms abstracted from the methanol molecules of the solvent to make Pd⁰ nanoclusters supported by the re-formed MMA–MAA. The MMA–MAA acid copolymer, without itself undergoing any permanent chemical change, serves as a mechanical activator or catalyst for the mechanochemical reduction of Pd(CH₃COO)₂ under mild conditions. Compared with traditional Pd/C catalysts, this Pd⁰ nanocatalyst exhibited more excellent catalytic efficiency and reusability in the Heck reaction between iodobenzene and styrene, and it could be easily separated. The supported Pd⁰ nanocatalyst prepared using this novel and simple preparation method may display high-efficiency catalytic properties for other cross coupling reactions.

A polymer-supported Pd⁰ nanocatalyst is prepared by using mechanochemical reduction as the driving force for the reaction.     

Improved hydrogen evolution performance by engineering bimetallic AuPd loaded on amino and nitrogen functionalized mesoporous hollow carbon spheres

A highly efficient heterogeneous catalyst was synthesized by delicate engineering of NH₂-functionalized and N-doped hollow mesoporous carbon spheres (NH₂–N-HMCS), which was used for supporting AuPd alloy nanoparticles with ultrafine size and good dispersion (denoted as AuPd/NH₂–N-HMCS). Without using any additives, the prepared AuPd/NH₂–N-HMCS catalytic formic acid dehydrogenation possesses superior catalytic activity with an initial turnover frequency value of 7747 mol H₂ per mol catalyst per h at 298 K. The excellent performance of AuPd/NH₂–N-HMCS derives from the unique hollow mesoporous structure, the small particle sizes and high dispersion of AuPd nanoparticles and the modified Pd electronic structure in the AuPd/NH₂–N-HMCS composite, as well as the synergistic effect of the modified support.

Anchoring ultrafine AuPd on NH₂-functionalized and N-doped hollow mesoporous carbon spheres for formic acid dehydrogenation.     

Chemoselective hydrogenation of heteroarenes and arenes by Pd–Ru–PVP under mild conditions

Monometallic (Pd, Ru or Rh) and bimetallic (Pd_0.5–Ru_0.5) alloy NPs catalysts were examined for the hydrogenation of quinoline. Pd–Ru alloy catalyst showed superior catalytic activity to the traditional Rh catalyst. The characterization of Pd_0.5–Ru_0.5 catalysts, HAADF-EDX mapping and XPS analysis suggested that the alloy state of PdRu catalysts remained unchanged in the recovered catalyst. Furthermore, the catalyst was highly selective for the hydrogenation of different arenes.

Recyclable Pd_0.5Ru_0.5–PVP catalyst showed higher activity than monometallic Pd or Ru catalyst for the hydrogenation of quinoline. Furthermore, Pd_0.5Ru_0.5–PVP was able to hydrogenate different arenes.

1,2,3,4-Tetrahydroquinolines are important building blocks for the synthesis of fine chemicals, pharmaceuticals and petrochemicals.^1–3 Traditionally, 1,2,3,4-tetrahydroquinolines have been synthesized by catalytic cyclization or the Beckman rearrangement method.^3–6 Direct hydrogenation of readily available quinoline by molecular hydrogen is a simple and atom-economical route for the hydrogenated quinoline compounds. Nevertheless, the hydrogenation of quinolines reaction suffers from catalyst deactivation caused by the strong interaction between the nitrogen atom of quinoline and active sites of the catalyst. Recently, several heterogeneous (Co, Au, Ru, Pt, Pd and Rh) catalysts have been developed to overcome the catalyst deactivation problem (Table S1^†).^7–24 Specifically, Rh catalysts exhibits remarkably excellent activity in comparison with other noble metal catalysts but some of them require high temperature (>80 °C)^13,21 and/or high pressure (>10 bar).^14–21 Later, Rh/AlOOH and Rh nanoparticles (NPs) catalysts have been reported for efficient hydrogenation of quinolines under ambient conditions (1 bar H₂ and 25 °C).^22–24 Although high selectivity and activity of Rh catalysts, the high cost of Rh make it unfavourable for the industrial purposes. From the economical and environmental point of view, the cost-effective catalyst is necessary for the hydrogenation of quinolines under mild condition.Solid-solution alloy method is a promising way for the synthesis of alloy NPs which offers an opportunity to control the electronic state of alloy by changing the composition ratio and/or different combinations of alloy in this method. In search of a cheap alternative for Rh catalyst, Pd and Ru are important metals because both metals are relatively cheaper than Rh metal and their well-known activity for hydrogenation reactions. We believe that Pd_0.5–Ru_0.5 solid solution alloy NPs could be alternative for the traditional Rh catalyst. However, a solid-solution alloy of Pd and Ru is a challenging task due to the immiscibility of Pd and Ru in bulk state.^25,26 Recently, our research group led by H. Kitagawa has reported the first successful example of Pd_0.5–Ru_0.5 NPs via a chemical reduction method using a nano-size effect which showed almost similar catalytic activity than those of Rh for CO oxidation and automobile exhaust purification.^27,28 As part of our continuing interest in the applications of Pd–Ru as pseudo Rh catalyst, we herein report that chemoselective hydrogenation of heteroarenes and arenes under mild condition.In preliminary experiments, we carried out the hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline as model reaction (27,28 We found the similar trend using Pd_0.5Ru_0.5 catalyst and it showed full conversion with 95% yield of 1,2,3,4-tetrahydroquinolines (entry 3). The effect of the solvent showed that the reactivity of Pd_0.5Ru_0.5 was improved using methanol as solvent. Probably, methanol provides the better dispersion of Pd_0.5–Ru_0.5 NPs in the reactions and/or high solubility of hydrogen gas in methanol. Next, we examined the activity of previously reported Rh catalyst. Although, the particle size of Rh and Pd_0.5–Ru_0.5 was similar, the moderate yield of tetrahydroquinoline was obtained in the presence of Rh–PVP (entry 7). Due to the high amount of PVP, the catalytic activity of Rh was slightly declined via less interaction between quinoline and metal sites.²⁹Optimization of reaction conditions for hydrogenation of quinoline^a

Peptide-directed Pd-decorated Au and PdAu nanocatalysts for degradation of nitrite in water

In this work, a palladium binding peptide, Pd4, has been used for the synthesis of catalytically active palladium-decorated gold (Pd-on-Au) nanoparticles (NPs) and palladium–gold (Pd_xAu_100−x) alloy NPs exhibiting high nitrite degradation efficiency. Pd-on-Au NPs with 20% to 300% surface coverage (sc%) of Au showed catalytic activity commensurate with sc%. Additionally, the catalytic activity of Pd_xAu_100−x alloy NPs varied based on palladium composition (x = 6–59). The maximum nitrite removal efficiency of Pd-on-Au and Pd_xAu_100−x alloy NPs was obtained at sc 100% and x = 59, respectively. The synthesized peptide-directed Pd-on-Au catalysts showed an increase in nitrite reduction three and a half times better than monometallic Pd and two and a half times better than Pd_xAu_100−x NPs under comparable conditions. Furthermore, peptide-directed NPs showed high activity after five reuse cycles. Pd-on-Au NPs with more available activated palladium atoms showed high selectivity (98%) toward nitrogen gas production over ammonia.

In this work, a palladium binding peptide, Pd4, has been used for the synthesis of catalytically active palladium-decorated gold (Pd-on-Au) nanoparticles (NPs) and palladium–gold (Pd_xAu_100−x) alloy NPs exhibiting high nitrite degradation efficiency.     

Reusable magnetic PdxCoy nanoalloys confined in mesoporous carbons for green Suzuki–Miyaura reactions

We report herein Pd_xCo_y nanoalloys confined in mesoporous carbons (Pd_x–Co_y@MC) prepared by an eco-friendly one-pot approach consisting in the co-assembly of readily available and non-toxic carbon precursors (phloroglucinol, glyoxal) with a porogen template (pluronic F-127) and metallic salts (H₂PdCl₄ and Co(NO₃)₂·6H₂O) followed by thermal annealing. Three Pd_xCo_y@MC materials with different alloy compositions were prepared (C1: x/y = 90/10; C2: x/y = 75/25; C3 and C4: x/y = 50/50). The nanoalloys were uniformly distributed in the carbon framework and the particle sizes depended on the alloy composition. These composites were then used for Suzuki–Miyaura reactions using either H₂O or a 1 : 1 H₂O/EtOH mixture as solvent. The Pd₅₀Co₅₀@MC catalyst C3 proved to be the most efficient catalyst (in terms of efficiency and magnetic recovery) affording the coupling products in good to excellent yields. After reaction, C3 was recovered quantitatively by simple magnetic separation and reused up to six times without loss of efficiency. The amount of palladium lost in the reaction mixture after magnetic separation was very low (ca. 0.1 % wt of the amount initially used).

(Pd_x–Co_y)@MC were prepared in one-pot via an eco-friendly route and used many times for Suzuki reactions in H₂O or H₂O/EtOH mixture.     

Palladium decorated on a new dendritic complex with nitrogen ligation grafted to graphene oxide: fabrication,characterization, and catalytic application

Immobilized Pd nanoparticles on a new ligand, namely, tris(pentaethylene-pentamine)triazine supported on graphene oxide (Pd_np-TPEPTA_(L)-GO) was introduced as a novel and robust heterogeneous catalyst for use in C–C bond formation reaction. The Pd_np-TPEPTA_(L)-GO catalyst was synthesized by complexation of Pd with TPEPTA as a ligand with high N-ligation sites that were supported on graphene oxide through 3-chloropropyltrimethoxysilane. The prepared catalyst was characterized using some microscopic and spectroscopic techniques. The TPEPTA_(L)-GO substrate is a 2D heterogeneous catalyst with a high specific surface area and a large amount of N-ligation sites. The Pd_np-TPEPTA_(L)-GO catalyst used in the C–C bond formation reaction between aryl or heteroaryl and phenylboronic acid derivatives was applied towards the synthesis of biaryl units in high isolated yields. Notably, a series of competing experiments were performed to establish the selectivity trends of the presented method. Also, this catalyst system was reusable at least six times without a significant decrease in its catalytic activity.

Immobilized Pd nanoparticles on a new ligand, namely, tris(pentaethylene-pentamine)triazine supported on graphene oxide (Pd_np-TPEPTA_(L)-GO) was introduced as a novel and robust heterogeneous catalyst for use in C–C bond formation reaction.     

Comparison of electrocatalytic activity of Pt1−xPdx/C catalysts for ethanol electro-oxidation in acidic and alkaline media

In this paper, a comparision of Pt_1−xPd_x/C catalysts for ethanol-oxidation in acidic and alkaline media has been investigated. We prepared Pt_1−xPd_x/C catalysts with different ratios of Pt/Pd (x at% = 0, 27, 53, 77 and 100) by the formic acid reduction method. The obtained Pt_1−xPd_x/C catalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), induced coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Structural and morphological investigations of the as-prepared catalysts revealed that the metallic particle size increases with increasing Pd content in the catalyst. The electrocatalytic performances and stabilities of Pt_1−xPd_x/C catalysts were tested by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) measurements for ethanol oxidation in acidic and alkaline media. The electrochemical measurements demonstrate that Pt_1−xPd_x/C catalysts exhibit much higher electrocatalytic activity for alcohol oxidation in alkaline media than that in acidic media. The composition of Pt/Pd has a significant impact on the ethanol-oxidation in both acidic and alkaline media. The Pt₂₃Pd₇₇/C catalyst shows the highest electrocatalytic performance with a mass specific peak current of 2453.7 mA mg_PtPd⁻¹ in alkaline media, which is higher than the Pt₇₇Pd₂₃/C with the maximum of peak current of 339.7 mA mg_PtPd⁻¹ in acidic media. Meanwhile, the effect of electrolyte, CH₃CH₂OH concentrations and scan rates was also studied for ethanol-oxidation in acidic and alkaline media.

The Pt_1−xPd_x/C catalysts exhibit much higher electrocatalytic activity in alkaline media than in acid media.     

Reaction induced robust PdxBiy/SiC catalyst for the gas phase oxidation of monopolistic alcohols

Reaction induced Pd_xBi_y/SiC catalysts exhibit excellent catalytic activity (92% conversion of benzyl alcohol and 98% selectivity of benzyl aldehyde) and stability (time on stream of 200 h) in the gas phase oxidation of alcohols at a low temperature of 240 °C due to the formation of Pd⁰–Bi₂O₃ species. TEM indicates that the agglomeration of the 5.8 nm nanoparticles is inhibited under the reaction conditions. The transformation from inactive PdO–Bi₂O₃ to active Pd⁰–Bi₂O₃ under the reaction conditions is confirmed elaborately by XRD and XPS.

Reaction induced Pd_xBi_y/SiC catalysts exhibit excellent catalytic activity and stability in the gas phase oxidation of monopolistic alcohols at a low temperature of 240 °C due to the formation of Pd⁰–Bi₂O₃ species.     

Enhanced oxygen reduction activity of Pt shells on PdCu truncated octahedra with different compositions

Pd@Pt core–shell nanocrystals with ultrathin Pt layers have received great attention as active and low Pt loading catalysts for oxygen reduction reaction (ORR). However, the reduction of Pd loading without compromising the catalytic performance is also highly desired since Pd is an expensive and scarce noble-metal. Here we report the epitaxial growth of ultrathin Pt shells on Pd_xCu truncated octahedra by a seed-mediated approach. The Pd/Cu atomic ratio (x) of the truncated octahedral seeds was tuned from 2, 1 to 0.5 by varying the feeding molar ratio of Pd to Cu precursors. When used as catalysts for ORR, these three Pd_xCu@Pt core–shell truncated octahedra exhibited substantially enhanced catalytic activities compared to commercial Pt/C. Specifically, Pd₂Cu@Pt catalysts achieved the highest area-specific activity (0.46 mA cm⁻²) and mass activity (0.59 mA μg_Pt⁻¹) at 0.9 V, which were 2.7 and 4.5 times higher than those of the commercial Pt/C. In addition, these Pd_xCu@Pt core–shell catalysts showed a similar durability with the commercial Pt/C after 10 000 cycles due to the dissolution of active Cu and Pd in the cores.

Pd_xCu@Pt core–shell truncated octahedra were synthesized and exhibited substantially enhanced catalytic properties for oxygen reduction reaction relative to Pt/C.     

Enhanced catalytic activity over palladium supported on ZrO2@C with NaOH-assisted reduction for decomposition of formic acid

A ZrO₂@C support based on t-ZrO₂ embedded in amorphous carbon was obtained via the pyrolysis of a UiO-66 precursor. Highly dispersed Pd nanoparticles (NPs) were subsequently deposited onto this support, using NaOH-assisted reduction, to obtain a formic acid (FA) decomposition catalyst. This material showed a turnover frequency (TOF) for the heterogeneously-catalyzed decomposition of FA of 8588 h⁻¹ at 60 °C, with 100% H₂ selectivity. This performance is ascribed to the uniform dispersion of smaller palladium nanoparticles and a synergistic effect between the metal NPs and support. Even at 30 °C, the complete decomposition of FA was achievable in FA/SF (SF, sodium formate) solution, with a TOF as high as 1857 h⁻¹.

Pd/ZrO₂@C was prepared employing UiO-66-derived ZrO₂@C as the support and showed high catalytic activity for formic acid decomposition.     

Confinement of a Au–N-heterocyclic carbene in a Pd6L12 metal–organic cage

A Au(i)–N-heterocyclic-carbene (NHC)-edged Pd₆L₁₂ molecular metal–organic cage is assembled from a Au(i)–NHC-based bipyridyl bent ligand and Pd²⁺. The octahedral cage structure is unambiguously established by NMR, electrospray ionization-mass spectrometry and single crystal X-ray crystallography. The electrochemical behaviour was analyzed by cyclic voltammetry. The octahedral cage has a central cavity for guest binding, and is capable of encapsulating PF₆⁻ and BF₄⁻ anions within the cavity.

A Au(i)–NHC-edged Pd₆L₁₂ molecular cage is assembled from a Au(i)–NHC-based bipyridyl bent ligand and Pd²⁺.     

A comparative study on atomically precise Au nanoclusters as catalysts for the aldehyde–alkyne–amine (A3) coupling reaction: ligand effects on the nature of the catalysis and efficiency

Atomically precise Au₁₃ nanoclusters stabilized by stibines catalyze the aldehyde–alkyne–amine coupling reaction more efficiently than those stabilized by thiols or phosphines. The nature of the catalytic activity is also different, and may be attributed to the weaker coordinating ability of the stibine ligands.

A stibine-stabilised gold nanocluster which acts as a homogeneous catalyst in the A³ coupling reaction.

Atomically precise Au nanoclusters have recently emerged as a new class of catalysts for a range of reactions, including the A³ coupling reaction, which involves a highly efficient assembly, in a single step, of an aldehyde, an amine and an acetylene to form a propargylamine. Propargylamines are valuable precursors to a number of organic heterocyclic substrates, natural products and therapeutic drugs, and have thus found broad applications in synthetic and pharmaceutical chemistry.¹ The A³ coupling reaction is generally catalyzed by transition metal species, for example, those of Cu, Zn, Rh, Ru, Ir, Ni, Fe, Ag and Au.² Among them, noble-metal salts, complexes or nanoparticles, especially those of Au, are found to be more efficient as they can more readily activate the acetylene as the corresponding acetylide.³ Recently, recyclable Au(0) nanoparticles have been shown to be more efficient than the widely used Au(i) and Au(iii) complexes as catalysts for this reaction.⁴A challenge with the Au nanoparticle catalysts is the establishment of correlations between the particle structure and its catalytic performance, due to the fluidity of the surface structure (coordination pattern between surface metal and ligands).⁵ Compared to larger gold nanoparticles, therefore, atomically precise Au nanoclusters with their well-defined molecular structures, make it possible to correlate their surface structures with catalytic performance. The higher surface area to volume associated with their smaller metal core size (<2 nm) also translates to a reduced amount of the catalyst needed. For example, Jin, et al., have reported that the thiolate-protected nanocluster [Au₃₈(SC₂H₄Ph)₂₄] (Au₃₈) could catalyze the A³ coupling reaction, and the high catalytic efficiency was ascribed to the synergistic effect between the electron-rich Au core and the electron-deficient surface of the nanoclusters.⁶ The group of Obora reported the use of the thiolate-protected nanocluster [Au₂₅(SC₂H₄Ph)₁₈][TOA] (Au₂₅, TOA = tetraoctylammonium) as an efficient catalyst for the reaction and they believed that the surface Au atoms, sterically unblocked by the thiolate ligands, served as active sites in the catalytic process,⁷ and Li, et al., reported that the reaction could also be catalyzed by supported Au nanoparticles derived from [Au₂₅(PPh₃)₁₀(C CPh)₅]X₂ (Au′₂₅, X = Cl or Br), which has phosphine and alkyne as protecting ligands. It was demonstrated in the latter that removal of one phosphine ligand from the supported Au′₂₅ cluster was necessary to enable catalysis.⁸ Finally, Wu, et al., reported an Au–Cd nanocluster, [Au₁₃Cd₂(PPh₃)₆(SC₂H₄Ph)₆(NO₃)₂]₂Cd(NO₃)₄ (Au₂₆Cd₄), with high catalytic activity which was ascribed to the cooperative effect between the peripheral Cd and adjacent Au atoms on the surface of the Au₁₃ icosahedral core.⁹It is clear from the foregoing that the surface structure of the Au nanocluster, including the ligand binding strength, may have a significant influence on the catalytic performance. In this regard, Au nanoclusters protected by more labile ligands may be expected to be more efficient catalysts. We have recently reported the preparation of an Au₁₃ nanocluster stabilized by stibine ligands, viz., [Au₁₃{Sb(p-tolyl)₃}₈Cl₄][Cl] (Au₁₃).¹⁰ We anticipated that it may catalyze the A³ coupling reaction more readily than the previously reported phosphine- and thiolate-protected clusters [Au₁₁(PPh₃)₈Cl₂][Cl] (Au₁₁),¹¹ and Au₂₅;¹² the weaker bond between the Au₁₃ core and stibine ligands should lead to more ready ligand dissociation to expose catalytically active Au sites.The thermogravimetric analysis (TGA) curves for crystalline Au₂₅, Au₁₁ and Au₁₃ show that weight loss at 300 °C is ca. 37, 50 and 56%, respectively (Fig. 1), matching the theoretical values (37, 50 and 57%, respectively) corresponding to loss of all coordinating ligands. While the loss for Au₁₃ begins at ca. 145 °C, that for Au₁₁ and Au₂₅ begin at ca. 165 °C and 195 °C, respectively, clearly demonstrating that the stibine-protected nanocluster is thermally less stable than the phosphine- and thiolate-protected ones.Open in a separate windowFig. 1TGA curves for Au₂₅, Au₁₃ and Au₁₁.A comparative study was carried out for the A³-coupling reaction of phenylacetylene, piperidine and benzaldehyde with Au₃₈, Au₂₅, Au′₂₅ and Au₂₆Cd₄ as catalysts (i) salts as catalysts.13 (2) It has been suggested that elevated reaction temperatures were required as it favoured formation of the cationic imine intermediate, and facilitated catalyst activation via removal of the protecting ligands (entry 4). (3) An inert atmosphere was needed in order to avoid rapid oxidation of the substrates exacerbated by the elevated temperature. From the economic and environmental perspectives, therefore, an efficient catalyst which can catalyze the A³ coupling reaction under ambient conditions, without an organic solvent (neat), and in air, would be desirable.A³ coupling reaction of benzaldehyde, piperidine, and phenylacetylene with Au nanoclusters as catalysts^a

One pot synthesis of aryl nitriles from aromatic aldehydes in a water environment

In this study, we found a green method to obtain aryl nitriles from aromatic aldehyde in water. This simple process was modified from a conventional method. Compared with those approaches, we used water as the solvent instead of harmful chemical reagents. In this one-pot conversion, we got twenty-five aryl nitriles conveniently with pollution to the environment being minimized. Furthermore, we confirmed the reaction mechanism by capturing the intermediates, aldoximes.

In a formic acid–H₂O solution (60% : 40%), most aromatic aldehydes react efficiently with hydroxylamine hydrochloride and sodium acetate to form nitriles, where formic acid acts as both catalyst and solvent.     

Microwave-assisted pyrolysis of Pachira aquatica leaves as a catalyst for the oxygen reduction reaction

In this study, biomimetic Mg–N_x–C_y from Pachira aquatica leaves were mixed with carbon black (L/C catalyst), in which the mixture was treated by a conventional microwave oven at 700 W and 2 min, exhibiting high catalytic activity for the oxygen reduction reaction (ORR). By using a microwave-assisted process, it not only offers a cheaper and faster way to synthesize the catalyst compared to the conventional furnace process but also avoids the decomposition of the N₄-structure. Using the optimized conditions, the L/C catalyst exhibits an electron transfer number of 3.90 and an HO₂⁻ yield of only 5% at 0.25 V vs. RHE, which is close to the perfect four electron-transfer pathway. Besides, the L/C catalyst offers superior performance and long-term stability up to 20 000 s. The L/C catalyst contains a high proportion of quaternary-type nitrogen, Mg–N_x–C_y, and –C–S–C– which can be the active sites for the ORR.

In this study, biomimetic Mg–N_x–C_y from Pachira aquatica leaves were mixed with carbon black, in which the mixture was treated by a conventional microwave oven at 700 W and 2 min, exhibiting high catalytic activity for the oxygen reduction reaction.     

Preparation and investigation of highly selective solid acid catalysts with sodium lignosulfonate for hydrolysis of hemicellulose in corncob

Saccharification of lignocellulose is a necessary procedure for deconstructing the complex structure for building a sugar platform that can be used for producing biofuel and high-value chemicals. In this study, a carbon-based solid acid catalyst derived from sodium lignosulfonate, a waste by-product from the paper industry, was successfully prepared and used for the hydrolysis of hemicellulose in corncob. The optimum preparation conditions for the catalyst were determined to be carbonization at 250 °C for 6 h, followed by sulfonation with concentrated H₂SO₄ (98%) and oxidation with 10% H₂O₂ (solid–liquid ratio of 1 : 75 g mL⁻¹) at 50 °C for 90 min. SEM, XRD, FT-IR, elemental analysis and acid–base titration were used for the characterization of the catalysts. It was found that 0.68 mmol g⁻¹ SO₃H and 4.78 mmol g⁻¹ total acid were loaded onto the catalyst. When corncob was hydrolyzed by this catalyst at 130 °C for 12 h, the catalyst exhibited high selectivity and produced a relatively high xylose yield of up to 84.2% (w/w) with a few by-products. Under these conditions, the retention rate of cellulose was 82.5%, and the selectivity reached 86.75%. After 5 cycles of reuse, the catalyst still showed high catalytic activity, with slightly decreased yields of xylose from 84.2% to 70.7%.

A novel carbon-based catalyst with high catalytic ability and xylose selectivity was prepared from sodium lignosulfonate.     

The influence of the polymerization approach on the catalytic performance of novel porous poly (ionic liquid)s for green synthesis of pharmaceutical spiro-4-thiazolidinones

Although poly (ionic liquids) (PILs) have attracted great research interest owing to their various applications, the performance of nanoporous PILs has been rarely developed in the catalysis field. To this end, a micro–mesoporous PIL with acid–base bifunctional active sites was designed and fabricated by two different polymerization protocols including hydrothermal and classical precipitation polymerization in this paper. Based on our observations, hydrothermal conditions (high temperature and pressure) enabled the proposed sonocatalyst to possess a great porous structure with a high specific surface area (S_BET: 315 m² g⁻¹) and thermal stability (around 450 °C for 45% weight loss) through strengthening cross-linking. In a comparative study, the preferred nanoporous PIL was selected and utilized as the sonocatalyst in a multicomponent reaction of isatins, primary amines, and thioglycolic acid. In the following, a variety of new and known pharmaceutical spiro-4-thiazolidinone derivatives were synthesized at room temperature and obtained excellent yields (>90%) within short reaction times (4–12 min) owing to the substantial synergistic effect between ultrasound irradiation and magnetically separable catalyst.

Sustainable synthesize of a new mesoporous poly (ionic liquid) as acid–base bifunctional catalyst for environmental being preparation of monospiro derivatives has been developed.     

Copper-catalyzed aerobic decarboxylative coupling between cyclic α-amino acids and diverse C–H nucleophiles with low catalyst loading

An aerobic decarboxylative cross-coupling of α-amino acids with diverse C–H nucleophiles has been realized using Cu₂(OH)₂CO₃ (1 mol%) as the catalyst under air. This protocol enables highly efficient formation of various C(sp³)–C(sp³), C(sp³)–C(sp²) and C(sp³)–C(sp) bonds under simple conditions without the use of any ligand or extra oxidant, providing a practical approach to numerous nitrogen-containing compounds in good to excellent yields. The efficiency and practicability were also demonstrated by the gram-scale experiment and three-step synthesis of a Rad51 inhibitor.

An aerobic decarboxylative cross-coupling of α-amino acids was realized using 1 mol% Cu₂(OH)₂CO₃ catalyst under ligand free conditions.     

Structural exploration of AuxM− (M = Si,Ge, Sn; x = 9–12) clusters with a revised genetic algorithm

We used a revised genetic algorithm (GA) to explore the potential energy surface (PES) of Au_xM⁻ (x = 9–12; M = Si, Ge, Sn) clusters. The most interesting finding in the structural study of Au_xSi⁻ (x = 9–12) is the 3D (Au₉Si⁻ and Au₁₀Si⁻) → quasi-planar 2D (Au₁₁Si⁻ and Au₁₂Si⁻) structural evolution of the Si-doped clusters, which reflects the competition of Au–Au interactions (forming a 2D structure) and Au–Si interactions (forming a 3D structure). The Au_xM⁻ (x = 9–12; M = Ge, Sn) clusters have quasi-planar structures, which suggests a lower tendency of sp³ hybridization and a similarity of electronic structure for the Ge or Sn atom. Au₉Si⁻ and Au₁₀Si⁻ have a 3D structure, which can be viewed as being built from Au₈Si⁻ and Au₉Si⁻ with an extra Au atom bonded to a terminal gold atom, respectively. In contrast, the quasi-planar structures of Au_xM⁻ (x = 9–12; M = Ge, Sn) reflect the domination of the Au–Au interactions. Including the spin–orbit (SO) effects is very important to calculate the simulated spectrum (structural fingerprint information) in order to obtain quantitative agreement between theoretical and future experimental PES spectra.

We used a revised genetic algorithm (GA) to explore the potential energy surface (PES) of Au_xM⁻ (x = 9–12; M = Si, Ge, Sn) clusters.     

Acid–base sites synergistic catalysis over Mg–Zr–Al mixed metal oxide toward synthesis of diethyl carbonate

In heterogeneous catalysis processes, development of high-performance acid–base sites synergistic catalysis has drawn increasing attention. In this work, we prepared Mg/Zr/Al mixed metal oxides (denoted as Mg₂Zr_xAl_1−x–MMO) derived from Mg–Zr–Al layered double hydroxides (LDHs) precursors. Their catalytic performance toward the synthesis of diethyl carbonate (DEC) from urea and ethanol was studied in detail, and the highest catalytic activity was obtained over the Mg₂Zr_0.53Al_0.47MMO catalyst (DEC yield: 37.6%). By establishing correlation between the catalytic performance and Lewis acid–base sites measured by NH₃-TPD and CO₂-TPD, it is found that both weak acid site and medium strength base site contribute to the overall yield of DEC, which demonstrates an acid–base synergistic catalysis in this reaction. In addition, in situ Fourier transform infrared spectroscopy (in situ FTIR) measurements reveal that the Lewis base site activates ethanol to give ethoxide species; while Lewis acid site facilitates the activated adsorption of urea and the intermediate ethyl carbamate (EC). Therefore, this work provides an effective method for the preparation of tunable acid–base catalysts based on LDHs precursor approach, which can be potentially used in cooperative acid–base catalysis reaction.

Mg/Zr/Al mixed metal oxides were prepared via a facile phase transformation process of hydrotalcite precursors, which showed acid–base sites synergistic catalytic performance toward the synthesis of diethyl carbonate from ethanol and urea.     

Au-based bimetallic catalysts: how the synergy between two metals affects their catalytic activity

Supported bimetallic nanoparticles are particularly attractive catalysts due to increased activity and stability compared to their monometallic counterparts. In this work, gold-based catalysts have been studied as catalysts for the selective base-free oxidation of glucose. TiO₂-supported Au–Pd and Au–Cu series prepared by the sol-immobilization and precipitation-reduction methods, respectively, showed a significant synergistic effect, particularly when the theoretical weight ratio of the two metals was close to 1 : 1 (with an actual experimental bulk Au/Pd molar ratio of ca. 0.8 and ca. 0.4 for Au/Cu) in both cases. XPS analysis showed that the presence of Au^δ+, Pd²⁺ and CuOH species played an important role in the base-free glucose oxidation.

Supported bimetallic nanoparticles are particularly attractive catalysts due to increased activity and stability compared to their monometallic counterparts.