Vanadium-catalyzed Hydration of 2-Cyanopyrazine to Pyrazinamide with Unique Substrate Specificity.

Pyrazinamide is an important medicine used for the treatment of tuberculosis(TB). The preparation of pyrazinamide via catalytic hydration of 2-cyanopyrazine is of great economic interest with high atomic economy. Heterogeneous non-precious transition metal-catalyzed hydration of nitriles under neutral reaction conditions would be rather attractive. Herein vanadium-nitrogen-carbon materials were fabricated and employed for selective hydration of nitriles using water as both the solvent and reactant. 2-Cyanopyrazine could be smoothly converted into to pyrazinamide with unique substrate specificity. Additives with different N and O atoms could significantly affect hydration of 2-cyanopyrazine due to competitive adsorption/coordination in the reaction system. This work provides a new approach for non-precious metal catalyzed hydration of nitriles.

The correlation of molecule weight of chitosan oligomers with the corresponding viscosity and antibacterial activity.

In order to explore the correlation between the viscosity of chitosan oligomers-acetic solution and its viscosity average molecular weight (Mv), and determine the Mv range with a strong bactericidal effect. A series of chitosan oligomers were obtained by degraded chitosan (728.5 kDa) with dilute acid and chitosan oligomer (101.5 kDa) was characterized by FT-IR, XRD, H NMR and C NMR. The bactericidal effect of chitosan oligomers with different Mv on E. coli, S. aureus and C. albicans was measured by plate counting method. And the bactericidal rate was taken as the evaluation indicator, the optimum conditions were determined by single-factor experiments. The result showed that the molecular structure of chitosan oligomers and original chitosan (728.5 kDa) were similar. The viscosity of the chitosan oligomers in acetic acid solution was positively correlated with the Mv, and the chitosan oligomers with the Mv of 52.5-145.0 kDa had a strong bactericidal performance. In addition, the bactericidal rate of chitosan oligomers on experimental strains was more than 90% when the concentration of 0.5 g/L (bacteria) and 1.0 g/L (fungi), pH6.0, incubation time of 30 min. Thus, chitosan oligomers had a potential application value when the Mv was in the range of 52.5-145.0 kDa.

PtFeCoNiCu High-Entropy Alloy Catalyst for Aqueous-Phase Hydrogenation of Maleic Anhydride.

High-entropy alloys (HEAs), as new heterogeneous catalytic materials, possess remarkable catalytic performance in numerous reactions. However, rational and controllable synthesis of these complex structures remains a challenge. In this work, bulk and carbon nanotube (CNT)-supported ultrasmall PtFeCoNiCu HEA nanoparticles with an average particle size of 1.58 nm are prepared by lithium naphthalenide-driven reduction under mild conditions. The supported PtFeCoNiCu/CNT catalyst exhibits high catalytic activity in the aqueous-phase hydrogenation of maleic anhydride to succinic acid with a selectivity of 98% at full conversion of maleic acid (the hydrolysis product of maleic anhydride), a low apparent activation energy (Ea = 49 kJ mol-1), and excellent stability. Moreover, a much higher mass-specific activity of Pt in the catalyst is displayed over PtFeCoNiCu/CNT (1515.4 mmolmaleic acid gPt-1 h-1) than that of 5 wt % Pt/CNT (388.0 mmolmaleic acid gPt-1 h-1). This work provides a strong support for HEAs as advanced heterogeneous catalysts and will be of great significance for promoting the research and application of HEAs in the field of selective hydrogenation.

Structural Construction of Au-Pd Nanocomposite for Alkali-Free Oxidation of Benzyl Alcohol.

A bimetallic Au-Pd system is an alternative candidate to catalyze primary alcohol oxidation and is of crucial importance for the sustainable chemical industry. However, understanding the bimetallic system in terms of the nanostructure is still challenging. Herein, we adopt the in situ colloid immobilization to obtain a series of bimetallic AuxPdy/CNT samples supported by carbon nanotubes (CNTs). Elaborate characterizations confirmed the bimetallic structure of AuPd alloy particles with randomly dispersed Pd2+ on the surface, forming the AuPd@PdO structure on CNTs. Unlike the monometallic samples, bimetallic ones, particularly Au1Pd1/CNT, efficiently transformed benzyl alcohol in an alkali-free mild condition. The DFT simulation confirmed the electron-rich gold atoms as a steric and electronic regulator to confine the electron-deficient Pd atoms in alloy particles. The interacted metal sites in the alloy system activated the alcohol with optimized adsorption configuration. Surface Pd2+ transported active oxygen to capture the abstracted H on alcohol. The collaboration between metal sites facilitated the transformation of benzyl alcohol to benzaldehyde with the selectivity of 91.8% by a fast TOF of 1274 h-1 at only 80 °C.

A nanobiocatalytic system based on the self-assembly of ferrous phosphate with a high regioselectivity nitrile hydratase.

Our previous study identified a novel nitrile hydratase (NHase) with remarkable biotransformation activity toward adipamide during the production of 5-cyanovaleramide (5-CVAM), an important intermediate of herbicide and chemical raw material. Nevertheless, free NHase will face harsh conditions if they are applied directly in industrial processes. In this study, we, therefore, prepared Fe3(PO4)2 hybrid nanoflowers for NHase immobilization based on the protein-inorganic hybrid self-assembly by establishing a novel and facile method. The results showed that the NHase@Fe3(PO4)2 nanoflowers had significantly enhanced tolerance to the temperature ranging from 40°C to 60°C when compared with free NHase. The catalytic activity of NHase@Fe3(PO4)2 nanoflowers remained high in extreme pH environments such as weak acid (pH 5) and strong alkali (pH 10) environments. In addition, the storage stability and reusability of encapsulated NHase were also superior to that of free NHase. NHase@Fe3(PO4)2 nanoflowers had a notable feature of high substrate tolerance. We found NHase@Fe3(PO4)2 nanoflowers still had 65% activity as the adiponitrile concentration increased up to 200 mmol L-1, whereas free NHase almost lost their catalytic activity when the adiponitrile concentration was just 100 mmol L-1. All of these results clearly demonstrated that ferrous phosphate nanocrystals might offer a novel strategy for 5-CVAM production with nanobiocatalytic systems.

Hydrogenolysis-Isomerization of Waste Polyolefin Plastics to Multibranched Liquid Alkanes.

Upcycling of waste polyolefin plastics still meets with economic and technological challenges in practice. In this work, the catalytic hydrogenolysis-isomerization of nondegradable polyolefin plastic waste to high-value gasoline, diesel, and light lubricants with highly branched chain is achieved over a bifunctional Rh/Nb2 O5 catalyst under relatively mild conditions. Owing to the high efficiency of metallic Rh active sites, the dehydrogenation/hydrogenation of long carbon chains of polyolefins is enhanced. With the assistance of strong Brønsted acidity of Nb2 O5 , the cleavage of C-C bonds, skeletal rearrangements, as well as the ß-scission of alkylcarbenium ions occurs, which boosts the one-step solvent-free catalytic hydrogenolysis and isomerization of polyolefins. In addition, the preliminary economic analysis shows that this technology is economical, feasible, and has great potential in accelerating the transition to a circular plastics economy for sustainable development.

Modification of nitrile hydratase from Rhodococcus erythropolis CCM2595 by semirational design to enhance its substrate affinity.

Nitrile hydratase (NHase, EC 4.2.1.84) is an excellent biocatalyst that catalyzes the hydration of nitrile substances to their corresponding amides. Given its catalytic specificity and eco-friendliness, NHase has extensive applications in the chemical, pharmaceutical, and cosmetic industries. To improve the affinity between Rhodococcus erythropolis CCM2595-derived NHase (ReNHase) and adiponitrile, this study used a semirational design to improve the efficiency of ReNHase in catalyzing the generation of 5-cyanopentanamide from adiponitrile. Enzyme kinetics analysis showed that Km of the mutant ReNHaseB:G196Y was 3.265 mmol l-1, which was lower than that of the wild-type NHase. The affinity of the mutant ReNHaseB:G196Y to adiponitrile was increased by 36.35%, and the efficiency of the mutant ReNHaseB:G196Y in catalyzing adiponitrile to 5-cyanopentamide was increased by 10.11%. The analysis of the enzyme-substrate interaction showed that the hydrogen bond length of the mutant ReNHaseB:G196Y to adiponitrile was shortened by 0.59 Å, which enhanced the interaction between the mutant and adiponitrile and, thereby, increased the substrate affinity. Similarly, the structural analysis showed that the amino acid flexibility near the mutation site of ReNHaseB:G196Y was increased, which enhanced the binding force between the enzyme and adiponitrile. Our work may provide a new theoretical basis for the modification of substrate affinity of NHase and increase the possibility of industrial applications of the enzyme.

Chemical kinetics and promoted Co-immobilization for efficient catalytic carbonylation of ethylene oxide into methyl 3-hydroxypropionate.

The carbonylative transformation of ethylene oxide (EO) into methyl 3-hydroxypropionate (3-HPM) is a key process for the production of 1,3-propanediol (1,3-PDO), which is currently viewed as one of the most promising monomers and intermediates in polyester and pharmaceuticals industry. In this work, a homogeneous reaction system using commercial Co2(CO)8 was first studied for the carbonylation of EO to 3-HPM. The catalytic behavior was related to the electronic environment of N on aromatic rings of ligands, where N with rich electron density induced a stronger coordination with Co center and higher EO transformation. A reaction order of 2.1 with respect to EO and 0.3 with respect to CO was unraveled based on the kinetics study. The 3-HPM yield reached 91.2% at only 40°C by Co2(CO)8 coordinated with 3-hydroxypyridine. However, Co-containing colloid was formed during the reaction, causing the tough separation and impossible recycling of samples. Concerning the sustainable utilization, Co particles immobilized on pre-treated carbon nanotubes (Co/CNT-C) were designed via an in situ reduced colloid method. It is remarkable that unlike conventional Co/CNT, Co/CNT-C was highly selective toward the transformation of EO to 3-HPM with a specific rate of 52.2 mmol·g Co - 1 ·h - 1 , displaying a similar atomic efficiency to that of coordinated Co2(CO)8. After reaction, the supported Co/CNT-C catalyst could be easily separated from the liquid reaction mixture, leading to a convenient cyclic utilization.

Boosting the catalytic behavior and stability of a gold catalyst with structure regulated by ceria.

In this work, a series of colloidal gold nanoparticles with controllable sizes were anchored on carbon nanotubes (CNT) for the aerobic oxidation of benzyl alcohol. The intrinsic influence of Au particles on the catalytic behavior was unraveled based on different nanoscale-gold systems. The Au/CNT-A sample with smaller Au sizes deserved a faster reaction rate, mainly resulting from the higher dispersion degree (23.5%) of Au with the available exposed sites contributed by small gold particles. However, monometallic Au/CNT samples lacked long-term stability. CeO2 was herein decorated to regulate the chemical and surface structure of the Au/CNT. An appropriate CeO2 content tuned the sizes and chemical states of Au by electron delivery with better metal dispersion. Small CeO2 crystals that were preferentially neighboring the Au particles facilitated the generation of Au-CeO2 interfaces, and benefited the continuous supplementation of oxygen species. The collaborative functions between the size effect and surface chemistry accounted for the higher benzaldehyde yield and sustainably stepped-up reaction rates by Au-Ce5/CNT with 5 wt% CeO2.

Vanadium-catalyzed Oxidative Conversion of Primary Aromatic Alcohols into Amides and Nitriles with Molecular Oxygen.

Amides or nitriles are important building blocks because of the widespread occurrence in chemistry and biology. The development of green and efficient catalytic approaches to introduce nitrogen functionality is highly desired. Herein, a vanadium-based material V-N-C-700 was prepared via a simple and convenient method and employed for liquid-phase catalytic ammoxidation of alcohols with molecular oxygen. By using V-N-C-700/2-picolinic acid, primary aromatic alcohols was smoothly converted into the amides and nitriles in the presence of urea. The corresponding aldehydes are the key intermediates, and 2-picolinic acid could significantly enhance oxidation of alcohols into aldehydes. The amides were formed simultaneously along with nitriles, rather than only from nitriles via successive hydration. This work further expands non-noble metal catalysts for the preparation of amides and nitriles.

Low-energy Hemiacetal Dehydrogenation Pathway: Co-production of Gluconic Acid and Green Hydrogen via Glucose Dehydrogenation.

Exploring low-energy reaction pathway of catalytic biomass conversion can lead to wider application and the achievement of sustainability objectives. Since glucose dehydrogenation to gluconic acid and H2 is a cost-effective alternative to glucose oxidation, this study aims to elucidate its mechanism. The detection of lactone as an intermediate indicates that cyclic glucose reacts directly via its hemiacetal group-ring opening is not involved; that is, cyclic glucose is dehydrogenated to lactone, which is further hydrolyzed to gluconic acid. The source of hydrogen is confirmed to be from glucose and water by Isotope tracing analysis. Density function theory calculations demonstrate that Hemiacetal Dehydrogenation Pathway (this work) is less energy intensive than Ring-opening Oxidation Pathway (previous works). This study provides a new dehydrogenation strategy to produce gluconic acid and H2 from biomass under mild conditions.

Overcoming Limitations in the Strong Interaction between Pt and Irreducible SiO2 Enables Efficient and Selective Hydrogenation of Anthracene.

Interactions between metals and oxide supports are crucial in determining catalytic activity, selectivity, and stability. For reducible oxide supported noble metals, a strong metal-support interaction (SMSI) has been widely recognized. Herein we report the intermediate selectivity and stability over an irreducible SiO2 supported Pt catalyst in the hydrogenation of anthracene that are significantly boosted due to the SMSI-induced formation of intermetallic Pt silicide and Pt-SiO2 interface. The limitation in the strong interaction between Pt nanoparticles and irreducible SiO2 has been breached by combining the strong electrostatic adsorption method and following the high temperature reduction strategy. Due to the isolated Pt active sites by Si atoms, the activated H species produced over the Pt2Si/SiO2 catalyst with an initial catalytic activity of 2.49 µmol/(m2/g)/h as well as TOF of 0.95 s-1 preferentially transfer to the outer ring of anthracene to 87% yield of symmetric octahydroanthracene (sym-OHA) by subsequent hydrogenation. In addition, the Pt2Si/SiO2 catalyst presents an excellent stability after five cycles, which can be attributed to the fact that intermetallic Pt2Si nanoparticles are anchored firmly onto the surface of the SiO2 support. The discovery contributes to broaden the horizons on the SMSI effect in the irreducible oxide supported metal particle catalysts and provides guidance to design the metal-SiO2 interface and tune the surface chemical properties in diverse application conditions.

Nano-Sized NiO Immobilized on Au/CNT for Benzyl Alcohol Oxidation: Influences of Hybrid Structure and Interface.

Tiny gold nanoparticles were successfully anchored on carbon nanotubes (CNT) with NiO decoration by a two-step synthesis. Characterizations suggested that Ni species in an oxidative state preferred to be highly dispersed on CNT. During the synthesis, in situ reduction by NaBH4 and thermal treatment in oxidation atmosphere were consequently carried out, causing the formation of Au-Ni-Ox interfaces and bimetal hybrid structure depending on the Ni/Au atomic ratios. With an appropriate Ni/Au atomic ratio of 8:1, Ni atoms migrated into the sub-layers of Au particles and induced the lattice contraction of Au particles, whilst a higher Ni/Au atomic ratio led to the accumulation of NiO fractions surrounding Au particles. Both contributed to the well-defined Au-Ni-Ox interface and accelerated reaction rates. Nickel species acted as structure promoters with essential Au-Ni-Ox hybrid structure as well as the active oxygen supplier, accounting for the enhanced activity for benzyl alcohol oxidation. However, the over-layer of unsaturated gold sites easily occured under a high Ni/Au ratio, resulting in a lower reaction rate. With an Au/Ni atomic ratio of 8:1, the specific rate of AuNi8/CNT reached 185 µmol/g/s at only 50 °C in O2 at ordinary pressure.

Intermetallic PdZn nanoparticles catalyze the continuous-flow hydrogenation of alkynols to cis-enols.

Designing highly active and stable lead-free palladium-based catalysts without introducing surfactants and stabilizers is vital for large-scale and high-efficiency manufacturing of cis-enols via continuous-flow semi-hydrogenation of alkynols. Herein, we report an intermetallic PdZn/ZnO catalyst, designed by using the coupling strategy of strong electrostatic adsorption and reactive metal-support interaction, which can be used as a credible alternative to the commercial PdAg/Al2O3 and Lindlar catalysts. Intermetallic PdZn nanoparticles with electron-poor active sites on a Pd/ZnO catalyst significantly boost the thermodynamic selectivity with respect to the mechanistic selectivity and therefore enhance the selectivity towards cis-enols. Based on in situ diffuse reflectance infrared Fourier-transform spectra as well as simulations, we identify that the preferential adsorption of alkynol over enol on PdZn nanoparticles suppresses the over-hydrogenation of enols. These results suggest the application of fine surface engineering technology in oxide-supported metal (particles) could tune the ensemble and ligand effects of metallic active sites and achieve directional hydrogenation in fine chemical synthesis.

High Regioselectivity Production of 5-Cyanovaleramide from Adiponitrile by a Novel Nitrile Hydratase Derived from Rhodococcus erythropolis CCM2595.

5-Cyanovaleramide (5-CVAM) is an important intermediate of a herbicide and chemical raw material. Herein, we found a novel nitrile hydratase from the strain Rhodococcus erythropolis CCM2595, exhibiting high regioselectivity with higher substrate specificity toward dinitriles than mononitriles. In the past, the strain was shown to degrade only phenol, hydroxybenzoate, p-chlorophenol, aniline, and other aromatic compounds. In our study, 20 mM adiponitrile was completely consumed within 10 min with 95% selectivity to 5-CVAM and 5% selectivity to adipamide. In addition to its high regioselectivity, our recombinant Escherichia coli showed a higher substrate tolerance of up to 200 mM adiponitrile even after 3 h when compared with two reported strains with their cyano-tolerance concentrations of up to 100 mM, which is considered to be the highest cyano-tolerance. Such a robust biocatalyst is a desirable attribute of a biocatalyst intended for use in commercial applications of 5-CVAM.

Synthesis of Intermetallic Pt-Based Catalysts by Lithium Naphthalenide-Driven Reduction for Selective Hydrogenation of Cinnamaldehyde.

Intermetallic nanoparticles (NPs) with a well-defined atom binding environment and a long-range ordering structure can be used as ideal models to understand their physical and catalytic properties. In this work, several kinds of nanostructured and carbon nanotube (CNT)-supported Pt-based intermetallic compounds (IMCs) have been synthesized by one-step lithium naphthalenide-driven reduction at room temperature without the use of surfactants in light of the reduction potential of metals. In the chemoselective hydrogenation of cinnamaldehyde, the second metal in Pt-M IMCs significantly creates a suitable reaction environment through construction of a good geometric and electronic structure. The Pt3Sn/CNT catalyst presents highly efficient and good chemoselective hydrogenation of cinnamaldehyde to cinnamyl alcohol. This can be attributed to the fact that the incorporated Sn atoms effectively dilute large Pt ensembles and increase the electron density of Pt. The in situ-formed SnOx interfaces as Lewis acid sites facilitate the coordination of C═O bonds, enhancing the selectivity to cinnamyl alcohol. In addition, the SnOx interface as the joint between Pt3Sn IMCs NPs and CNTs significantly improves the stability of the catalyst in the reaction environment.

Selective Hydrogenation of Dimethyl Terephthalate to 1,4-Cyclohexane Dicarboxylate by Highly Dispersed Bimetallic Ru-Re/AC Catalysts.

The fabrication of bimetallic catalysts has been taken great focus in the concept of heterogeneous catalysis due to their high efficiency and economic concerns. In this work, a series of bimetallic Ru-Re catalysts were designed and synthesized for the selective hydrogenation of dimethyl terephthalate (DMT) to 1,4-cyclohexane dicarboxylate (DMCD) under mild condition. Characterization techniques including the XRD, TEM, STEM-HAADF EDX elemental mapping, H2-TPR, and XPS were used to study the surface chemical property, the morphology, as well as the catalytic behavior of different samples. It was revealed that the monometallic Ru catalyst already has the capacity to activate and transform DMT into DMCD. Whilst the promotion effect can be optimized to a maximum with only small amount of Re, with the mass ratio of Ru/Re as 10:1. It was also revealed that the addition of Re could largely enhance the distribution of surface active metal species, facilitate the charge transfer between Ru and Re, as well as strengthen the Ru-Re synergistic interaction, which further led to the modification of the redox ability and the catalytic performances of samples. However, excessive addition of Re caused strong interaction between Ru and Re, and further limited the H2 activation and the seasonable release of the active reducible metal species, which was responsible for the depressed catalytic performances in the presence of higher Re loading. The Ru1.25Re0.13/AC catalyst displayed the DMT conversion of 82% with DMCD selectivity of 96% under mild condition of 70 °C at 3 MPa. The specific rate of Ru1.25Re0.13/AC based on per gram of Ru was 0.44 mol·g-1 Ru·h-1.

Template-Preparation of Hollow PtNi Nanostrings as a Bifunctional Electrocatalyst for the Hydrogen Evolution and Oxygen Reduction Reactions.

Designing a highly active, stable and cost-effective electrocatalyst with multiple functionalities toward hydrogen evolution and oxygen reduction applications is crucial for the development of renewable energy sources. Here, the synthesis of hollow PtNi nanostrings via a facile two-step template method is reported. The PtNi nanostrings own Pt-rich rough surfaces, and hollow string-like structure with the structural disorder morphology. Impressively, the unique hollow PtNi nanostrings exhibit excellent electrocatalytic activity toward the hydrogen evolution and oxygen reduction reactions. The obtained overpotential is only 44.60 mV at current density of 10 mA cm-2 for hydrogen evolution reaction. Furthermore, the hollow PtNi nanostrings exhibit a high mass activity of 2.5 A mg-1Pt and a superior specific activity of 3.89 mA cm-2 at 0.90 V versus reversible hydrogen electrode in oxygen reduction reaction, respectively, which are 10 and 9 times higher than those of the commercial Pt/C. This work provides a promising approach for the synthesis of highly bifunctional electrocatalysts with a hollow sting-like structure to promote their application in the hydrogen evolution and oxygen reduction reactions.

Three-Dimensional Heterostructured NiCoP@NiMn-Layered Double Hydroxide Arrays Supported on Ni Foam as a Bifunctional Electrocatalyst for Overall Water Splitting.

Herein, the rational design and preparation of three-dimensional heterostructured NiCoP@NiMn-layered double hydroxide arrays supported on Ni foam (NiCoP@NiMn LDH/NF) is reported as a new bifunctional water-splitting electrocatalyst with high performance. Prepared with facile hydrothermal reactions and phosphorization, the NiCoP@NiMn LDH/NF is simultaneously highly active toward oxygen evolution reaction (OER) (100, 300, and 600 mA cm-2 at overpotentials of 293, 315, and 327 mV, respectively) and hydrogen evolution reaction (HER) (100, 200, and 300 mA cm-2 at overpotentials of 116, 130, and 136 mV, respectively). Interestingly, with cell voltages of 1.519, 1.642, 1.671, and 1.687 V at 10, 100, 200, and 300 mA cm-2, respectively, for overall water splitting, this electrocatalyst achieves 95.2% faradaic efficiency for OER, suggesting a relatively high contribution of water splitting in the apparent current in spite of the existence of partial catalyst oxidation. The heterostructure arrays supported on Ni foam have some advantages, acting as a bifunctional water-splitting electrocatalyst: (1) heterostructured NCoP@NiMn LDH combines the intrinsic properties of individual NiCoP (excellent activity for HER) and NiMn LDH (high activity for OER) via the effective interface engineering between the two phases; (2) the NiCoP core material serves as a fast electron transfer channel to enhance the electrode's electrical conductivity; and (3) Ni foam with a three-dimensional-network structure as a support is beneficial to exposing more active sites and ensures efficient gas bubble release and electron/mass transfer.

A review on high catalytic efficiency of solid acid catalysts for lignin valorization.

It is imminent to develop renewable resources to replace fossil-derived energies as fossil resources are on the brink of exhaustion. Lignin is one of the major components of lignocellulosic biomass, which is a natural amorphous three-dimensional polymer with abundant C-O bonds and aromatic structure. Hence, valorization of lignin into high value-added liquid fuels and chemicals is regarded as a promising strategy to mitigate fossil resource shortages. Solid acid catalysts are extensively studied due to environmentally friendly in terms of the ease of separation, recovery and reduced amount of wastes. Hence, this review focuses on summarizing the recent progress of catalytic valorization of lignin over different kinds of solid acid catalysts including zeolites, heteropolyacids, metal oxides, amorphous SiO2-Al2O3, metal phosphates, and Lewis acid. Based on reviewing of current progress of lignin conversion, the challenges and future prospects are emphasized.