A PtPdCoCuNi high-entropy alloy nanocatalyst for the hydrogenation of nitrobenzene

High-entropy alloys (HEAs) with multiple elements in near-equiatomic proportions hold great promise in heterogeneous catalysis because of their exceptional physicochemical properties governed by synergy. Herein, we prepared PtPdCoCuNi HEA nanoparticles via a one-step colloid-based route and tested their catalytic performance for nitrobenzene hydrogenation to aniline. The SiO₂ supported PtPdCoCuNi displays 93.9% yield of aniline at 80 °C, which is 2.11 times that of PtPd/SiO₂. Even at room temperature, a 47.4% yield of aniline is attained with the PtPdCoCuNi/SiO₂ catalyst. DRIFTS experiments indicate formation of isolated Pt and Pd sites after alloying the transition metals and evidence a stronger interaction between the HEA catalyst and nitrobenzene. Both XPS data and DFT calculations disclose charge transfer to Pt and Pd species, which eventually enhance the interaction between nitrobenzene and the isolated metal sites and the hydrogenation activity as well. The experimental and theoretical results shed light on mechanistic understanding of the unique catalytic performance of the HEA nanocatalyst and pave a new avenue to realize the high catalytic performance of nitrobenzene hydrogenation over well-isolated noble metal sites with specific geometries.

High-entropy alloys (HEAs) with multiple elements in near-equiatomic proportions hold great promise in heterogeneous catalysis because of their exceptional physicochemical properties governed by synergy.     

Synergistic effect of Pd content and polyelectrolyte multilayer structure on nitrobenzene hydrogenation in a microreactor

In this study, we proposed a Pd–polyelectrolyte multilayer (PEM) hybrid film grafted on the polydopamine coated interior wall of a microreactor for nitrobenzene hydrogenation. Here, Pd nanoparticles were in situ synthesized in the PEMs consisting of poly(diallyldimethylammonium chloride) and poly(styrene sulfonate) via a two-stage ion-exchange and reduction process. The preparation process was monitored by UV-vis spectroscopy, which confirmed the formation of Pd in the PEM film. In addition, SEM and ICP-OES results indicated that the Pd content in the PEM film could be controlled by the number of the ion exchange and reduction cycles. Experimental results also showed that the prepared Pd–PEM hybrid film was active for the hydrogenation of nitrobenzene. The microreactor with the Pd–PEM hybrid film via multiple times had the increased catalyst loading, leading to a high yield of aniline and much better durability. In addition, it was also found that the NaCl concentration in the polyelectrolyte solution could affect the structure of the PEM film and therefore the Pd loading and catalytic performance.

In this study, we developed a Pd–PEMs hybrid film grafted on the polydopamine coated interior wall of a microreactor for nitrobenzene hydrogenation.     

Preparation and catalytic performance of active metal sintered membrane reactor anchored with Pt atoms

In the chemical industry, reactors are typically designed and filled with supported catalyst particles. However, the intrinsic problems associated with the internal/external diffusion effect and catalyst separation/loss in these traditional reactors can be very challenging to mitigate. To address these issues, herein, an active metal sintered membrane reactor anchored with Pt atoms was successfully developed, and applied into continuous, liquid-phase, hydrogenation processes. The catalyzing reactions transpired on the active sites that were fastened onto the surface of the reactor''s microchannels. As a result, the mass transfer at the gas–liquid–solid three-phase was greatly enhanced, and an incredibly high reaction efficiency was obtained. The novel, active reactor demonstrated a superior catalytic performance and stability to nitrobenzene (NB) hydrogenation at 120 °C and 0.5 MPa H₂, which enabled an aniline (ANI) yield of 19.28 mol_ANI h⁻¹ L⁻¹. This work opens a new window for the design of high-performance gas–liquid–solid reactor toward multiphase catalytic reactions.

A novel, active metal sintered membrane reactor anchored with Pt atoms was successfully developed. The membrane reactor exhibited excellent catalytic performance and stability towards continuous liquid-phase hydrogenation of nitroaromatic compounds.     

Photocatalytic hydrogenation of acetophenone on a titanium dioxide cellulose film

A previously developed sustainable immobilization concept for photocatalysts based on cellulose as a renewable support material was applied for the photocatalytic hydrogenation of acetophenone (ACP) to 1-phenyl ethanol (PE). Four different TiO₂ modifications (P25, P90, PC105, and PC500) were screened for the reaction showing good performance for PC25 and PC500. PC500 was selected for a detailed kinetic study to find the optimal operating conditions, and to obtain a better understanding of the photocatalytic pathway in relation to conventional and transfer hydrogenation. The kinetic data were analyzed using the pseudo-first-order reaction rate law. A complete conversion was obtained for ACP concentrations below 1 mM using a 360 nm filter and argon as the purge gas within 2–3 hours. High oxygen concentrations slow down or prevent the reaction, and wavelengths below 300 nm lead to side-products. By investigating the temperature dependency, an activation energy of 22 kJ mol⁻¹ was determined which is lower than the activation energies for conventional and transfer hydrogenation, because the light activation of the photocatalyst turns the endothermic to an exothermic reaction. PC500 was immobilized onto the cellulose film showing a 37% lower activity that remains almost constant after multiple use.

The photocatalytic hydrogenation of acetophenone to 1-phenylenthanol was investigated with cellulose-immobilized titanium oxide (TiO₂) particles.     

The production of tyramine via the selective hydrogenation of 4-hydroxybenzyl cyanide over a carbon-supported palladium catalyst

The selective production of primary amines is a problem that plagues heterogeneously catalysed nitrile hydrogenation reactions. Whilst the target amine tyramine (HOC₆H₄CH₂CH₂NH₂) is biochemically available through the action of enzymes, synthetic routes to this species are not widely reported. Here, a heterogeneously catalysed method is proposed that utilises a Pd/C catalyst to effect the selective hydrogenation of 4-hydroxybenzyl cyanide within a three-phase reactor. The aforementioned selectivity issues are overcome by adjustment of various experimental parameters (hydrogen supply, agitation rate, temperature, use of an auxiliary agent) that result in improved catalytic performance, such that the desired tyramine salt (tyramine hydrogen sulphate) can be produced in quantitative yield. Accordingly, through consideration of the interconnectivity of hydrogenation and hydrogenolysis processes, a selective synthetic strategy is achieved with the findings suitable for extension to other substrates of this nature.

Tyramine hydrogen sulphate is produced via the heterogeneously catalysed selective hydrogenation of 4-hydroxybenzyl cyanide within a three-phase reactor.     

Template-free hydrothermal synthesis of MgWO4 nanoplates and their application as photocatalysts

As a semiconductor, MgWO₄ has a potential in photocatalytic applications; however, it has been overlooked in previous studies; in this study, it has been demonstrated that MgWO₄ exhibits the ability to drive photocatalytic hydrogen evolution. Compared to nanoparticle structures, MgWO₄ nanoplates show an increased photocatalytic ability due to their higher specific surface area. Moreover, the formation mechanism of MgWO₄ nanoplates has been discussed. An oriented attachment and ripening process is proposed for the formation of the MgWO₄ nanoplates. This study demonstrates that MgWO₄ can be considered a valuable photocatalytic material, and future studies should be focused on how to promote its photocatalytic conversion efficiency.

As a semiconductor, MgWO₄ has a potential in photocatalytic applications; however, it has been overlooked in previous studies; in this study, it has been demonstrated that MgWO₄ exhibits the ability to drive photocatalytic hydrogen evolution.     

Effect of the organic sulfur source on the photocatalytic activity of CdS

By controlling the species of the organic sulfur source, CdS samples were produced with different photocatalytic performances by a low-temperature solvothermal method. Different species of the organic sulfur source were chosen as the coordination agent to control the interactions in the crystal growth process. Among them, thioacetamide was the best coordination agent. The hydrophobic chain could be good for reducing the resistance of charge transfer, and increasing the rate of surface charge transfer and the lifetime of the photoexcited electrons. Benefiting from the hydrophobic chain, CdS shows an excellent photocatalytic hydrogen evolution rate of 943.54 μmol h⁻¹ g⁻¹ and a rhodamine B photocatalytic degradation rate of 99.1% in 60 min, which is superior to the photocatalysis of pure CdS prepared by many other methods.

By controlling the species of the organic sulfur source, CdS samples were produced with different photocatalytic performances by a low-temperature solvothermal method.     

Novel mesoporous Ag@SiO2 nanospheres as a heterogeneous catalyst with superior catalytic performance for hydrogenation of aromatic nitro compounds

Mesoporous core–shell structure Ag@SiO₂ nanospheres are constructed to prevent Ag nanoparticles from aggregation during the hydrogenation reaction. The prepared catalyst shows superior catalytic performance for hydrogenation of nitro compounds with 100% conversion and selectivity without any by-products, which also indicates good recycling performance for several times use.

Mesoporous core–shell structure Ag@SiO₂ nanospheres are constructed to prevent Ag nanoparticles from aggregation during the hydrogenation reaction.     

Enhanced charge storage properties of ultrananocrystalline diamond films by contact electrification-induced hydrogenation

We report the enhanced charge storage characteristics of ultrananocrystalline diamond (UNCD) by contact electrification-induced hydrogenation. The non-catalytic hydrogenation of UNCD films was achieved by using platinum as an electron donor and sulfuric acid as a hydrogen proton donor, confirmed by Raman spectroscopy and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Chemical treatment with only a H₂SO₄ solution is responsible for the surface oxidation. The oxidation of UNCD resulted in an increase in the quantity and duration of the tribocharges. After non-catalytic hydrogenation, the generation of friction-induced tribocharges was enhanced and remained for three hours and more. We show that the hydrogen incorporation on grain boundaries is responsible for the improvement of charge storage capability, because the doped hydrogen acts as a trap site for the tribocharges. This lab-scale and succinct method can be utilized to control charge trap capability in nanoscale memory electronics.

The enhanced charge storage characteristics of ultrananocrystalline diamond caused by contact electrification-induced hydrogenation was demonstrated by using atomic force microscopy.     

Electronic effects on polypyridyl Co complex-based water reduction catalysts

Three new isomeric cobalt complexes of TPA (tris(2-pyridylmethyl)amine) based on methoxy substitution at the ortho, meta and para positions, respectively, were constructed and their photocatalytic proton reduction efficiencies were compared. It was found that there are good linear correlations with the Hammett constants of the substituents for the computed Co–N bond lengths, redox potentials of Co^II/I and Co^I/0 events, and the photocatalytic activities of the complexes. The ortho-substituted Co complex distinguished itself from the others remarkably in all these comparisons, demonstrating the presence of a steric effect besides the electronic effect. For other examined complexes, a stronger electron-donating substituent may lead to a higher hydrogen evolution efficiency, suggesting that the formation of a Co(iii) hydride intermediate is the rate-limiting step.

Three isomeric Co complexes showed a significant substituent electronic effect in photocatalytic hydrogen production.     

Photocatalytic hydrogen production and storage in carbon nanotubes: a first-principles study

As it is a promising clean energy source, the production and storage of hydrogen are crucial techniques. Here, based on first-principles calculations, we proposed an integral strategy for the production and storage of hydrogen in carbon nanotubes via photocatalytic processes. We considered a core–shell structure formed by placing a carbon nitride nanowire inside a carbon nanotube to achieve this goal. Photo-generated holes on the carbon nanotube surface promote water splitting. Driven by intrinsic electrostatic field in the core–shell structures, protons produced by water splitting penetrate the carbon nanotube and react with photo-generated electrons on the carbon nitride nanowire to produce hydrogen molecules in the carbon nanotube. Because carbon nanotubes have high hydrogen storage capacity, this core–shell structure can serve as a candidate system for photocatalytic water splitting and safe hydrogen storage.

The production and storage of hydrogen in CNNW/CNT core–shell structures via photocatalytic processes.     

Atomic-scale synthesis of nanoporous gallium–zinc oxynitride-reduced graphene oxide photocatalyst with tailored carrier transport mechanism

Surface modified gallium–zinc oxynitride solid solution exhibited outstanding stability and visible-light activity for water splitting. However, the considerable rate of photo-induced charge recombination and the low surface area of the bulk photocatalyst limited its performance. Here, an efficient technique is proposed for the synthesis of a nanoporous oxynitride photocatalyst and its graphene-hybridized material. The nanoporous oxynitride photocatalyst was prepared via a nanoscale solid-state route, using microwave irradiation as an intermolecular-state activation method, Ga³⁺/Zn²⁺ layered double hydroxide as an atomic-level uniform mixed-metal precursor, and urea as a non-toxic ammonolysis soft-template. The graphene-hybridized photocatalyst was fabricated using a facile electrostatic self-assembly technique. The photocatalytic activity of the synthesized graphene hybridized nanoporous oxynitride photocatalyst was systematically improved through shortening the majority-carrier diffusion length and enhancing the density of active hydrogen evolution sites within the quasi-three-dimensional nanostructure, reaching 7.5-fold sacrificial photocatalytic hydrogen evolution, compared to the conventional 1 wt% Rh-loaded oxynitride photocatalyst.

Synthesis of nanoporous GaZnON-RGO composite photocatalyst with enhanced capacity for HER active site and improved visible light hydrogen evolution performance is reported.     

Convenient conversion of hazardous nitrobenzene derivatives to aniline analogues by Ag nanoparticles,stabilized on a naturally magnetic pumice/chitosan substrate

Herein, silver nanoparticles (Ag NPs), as an effective catalyst for the reduction process of nitrobenzene derivatives to non-hazardous and useful aniline derivatives, are conveniently synthesized on an inherently magnetic substrate. For this purpose, an efficient combination of volcanic pumice (VP), which is an extremely porous igneous rock, and a chitosan (CTS) polymeric network is prepared and suitably used for the stabilization of the Ag NPs. High magnetic properties of the fabricated Ag@VP/CTS composite, which have been confirmed via vibrating-sample magnetometer (VSM) analysis, are the first and foremost advantage of the introduced catalytic system since it gives us the opportunity to easily separate the particles and perform purification processes. Briefly, higher yields were obtained in the reduction reactions of nitrobenzenes (NBs) under very mild conditions in a short reaction time. Also, along with the natural biocompatible ingredients (VP and CTS) in the structure, excellent recyclability has been observed for the fabricated Ag@VP/CTS catalytic system, which convinces us to do scaling-up and suggests the presented system can be used for industrial applications.

Silver nanoparticles (Ag NPs), as an effective catalyst for the reduction process of nitrobenzene derivatives to non-hazardous and useful aniline derivatives, are conveniently synthesized on an inherently magnetic substrate.     

Enhancing the photocatalytic hydrogen production activity of BiVO4 [110] facets using oxygen vacancies

The activity of the hydrogen evolution reaction (HER) during photoelectrochemical (PEC) water-splitting is limited when using BiVO₄ with an exposed [110] facet because the conduction band minimum is below the H⁺/H₂O potential. Here, we enhance the photocatalytic hydrogen production activity through introducing an oxygen vacancy. Our first-principles calculations show that the oxygen vacancy can tune the band edge positions of the [110] facet, originating from an induced internal electric field related to geometry distortion and charge rearrangement. Furthermore, the induced electric field favors photogenerated electron–hole separation and the enhancement of atomic activity. More importantly, oxygen-vacancy-induced electronic states can increase the probability of photogenerated electron transitions, thus improving optical absorption. This study indicates that oxygen-defect engineering is an effective method for improving the photocatalytic activity when using PEC technology.

An oxygen-vacancy-induced internal electric field enhances the photocatalytic hydrogen production activity of a BiVO₄ [110] facet.     

Adsorption of aniline from aqueous solution using graphene oxide-modified attapulgite composites

Adsorption is an efficient treatment method for aniline removal in water treatment. In this work, the composites of graphene oxide-modified attapulgite were prepared and used firstly to remove aniline from wastewater. The composites were characterized by Fourier transformed infrared, Brunauer–Emmett–Teller, scanning electron microscopy and X-ray diffraction analysis. The effects of initial concentration, time, temperature and pH value on adsorption of aniline on graphene oxide-modified attapulgite are investigated. pH and temperature are found to have a significant influence on the adsorption amount. The experimental results showed that graphene oxide-modified attapulgite possesses strong adsorption ability for aniline with hydrogen bond interaction. The saturated adsorption amount could reach up to 90 mg g⁻¹ at pH = 2–4. The Langmuir isotherm is found to describe well the equilibrium adsorption data. Finally, graphene oxide-modified attapulgite is also observed to possess excellent reusability.

Adsorption is an efficient treatment method for aniline removal in water treatment.     

Synthesis of highly substituted tetrahydroquinolines using ethyl cyanoacetate via aza-Michael–Michael addition

A three-component cascade reaction involving 2-alkenyl aniline, aldehydes, and ethyl cyanoacetate in the presence of DBU to synthesize highly substituted 1,2,3,4-tetrahydroquinolines is reported. The reaction proceeded through the Knoevenagel condensation of ethyl cyanoacetate with aldehydes followed by the aza-Michael–Michael addition with 2-alkenyl anilines to prepare the tetrahydroquinoline scaffolds.

A three-component cascade reaction involving 2-alkenyl aniline, aldehydes, and ethyl cyanoacetate in the presence of DBU to synthesize highly substituted 1,2,3,4-tetrahydroquinolines is reported.     

Preparation and characterization of petroleum-based mesophase pitch by thermal condensation with in-process hydrogenation

A petroleum aromatic-rich component was used to prepare mesophase pitch by thermal condensation. In-process hydrogenation method was employed to achieve the hydrogenation reaction of intermediates generated during the thermal reaction using tetrahydronaphthalene (THN) as a hydrogen donor. Impacts of in-process hydrogenation on the properties of intermediates and mesophase pitches were investigated. It was found that the in-process hydrogenation was conducive to the generation of hydrogenated intermediates with concentrated extracted component distribution, uniform molecular structure and abundant naphthenic structures. The characterizations of mesophase pitches showed that the in-process hydrogenation contributed to the preparation of mesophase pitch with concentrated extracted component distribution, low softening point, large domain structure and ordered crystal structure. This was due to the increasing contents of naphthenic structures in intermediates. Moreover, the increase of methylene bridges in the product was the critical reason for improving the product''s properties.

A petroleum aromatic-rich component was used to prepare mesophase pitch by thermal condensation.     

Effective removal of aromatic pollutants via adsorption and photocatalysis of porous organic frameworks

PAF-45 with a wholly aromatic framework, intrinsic microporosity and π–π conjugation system shows excellent performance in aromatic pollutant removal. It exhibits a high adsorption capacity for the benzene series and moderate photocatalytic performance. As an adsorbent, PAF-45 can adsorb 35 wt% benzene and 68 wt% chlorobenzene in static adsorption experiments at room temperature and pressure. In benzene simulation wastewater, PAF-45 also shows excellent adsorption capacity, without significant reduction after 10 cycles of the adsorption–desorption process. Moreover, PAF-45 exhibits an impressive photocatalytic degradability of aromatic compounds, like aniline and phenol, under visible light illumination.

PAF-45 with a wholly aromatic framework, intrinsic microporosity and π–π conjugation system shows excellent performance in aromatic pollutant removal.     

Continuous hydrogen production from glucose/xylose by an anaerobic sequential batch reactor to maximize the energy recovery efficiency

Fermentation of both glucose and xylose is essential to realize efficient bioconversion of renewable and abundant lignocellulosic biomass to hydrogen. In this study, a mixture of glucose and xylose at different ratios was used as a substrate for biological hydrogen production by an anaerobic sequential batch reactor (ASBR). An average glucose and xylose consumption of 80% and 50% with a high hydrogen production rate of 7.1 ± 0.9 mmol L⁻¹ h⁻¹ was obtained, respectively. Hydraulic retention time (HRT) played a critical role in hydrogen production at high glucose to xylose ratios. A maximum hydrogen production rate of 8.9 mmol L⁻¹ h⁻¹ was achieved at an optimized HRT of 12 h with a high glucose and xylose consumption of 92.2% and 82.2%, respectively. Upon further energy conversion analysis, continuous hydrogen production by ASBR provided the maximum energy conversion efficiency of 21.5%. These results indicate that ASBR can effectively accelerate the hydrogen production rate, improve substrate consumption regardless of the glucose to xylose ratio, and thus provides a new direction for efficient hydrogen production from lignocellulosic feedstock.

Fermentation of both glucose and xylose is essential to realize efficient bioconversion of renewable and abundant lignocellulosic biomass to hydrogen.     

CQDs/ZnO composites based on waste rice noodles: preparation and photocatalytic capability

To provide a low-cost photocatalyst and new methodology for the utilization of waste rice noodle (WRN), a carbon quantum dots/zinc oxide (CQDs/ZnO) composite using WRN as the raw material was synthesized and characterized. The CQDs/ZnO composite based on WRN exhibited a highly efficient photocatalytic degradation effect on various organic pollutants and could be a good alternative for commercial ZnO. For methylene blue, the CQDs/ZnO composite showed a good degradation rate of 99.58% within 40 min, a high degradation rate constant of 0.2630 min⁻¹, and could be recycled and reused for ten photocatalytic cycles without an appreciable decrease in the degradation effect, which was much better than that of commercial ZnO. The resulting CQDs/ZnO composite also displayed a nice photocatalytic degradation effect on other common organic pollutants, such as malachite green, methyl violet, basic fuchsin, rhodamine B, aniline and tetracycline. In particular, it could achieve excellent photocatalytic degradation on malachite green with an extremely high degradation rate constant of 1.9260 min⁻¹. Besides, the CQDs/ZnO composite could also be used to control the pollution of tetracycline or aniline. The introduction of CQDs based on WRN to ZnO resulted in efficient electron–hole pair separation and enabled more photogenerated electrons to reduce O₂ and more photogenerated holes to oxidize H₂O, which caused stronger abilities in producing radicals (such as O₂˙⁻ and ˙OH) and a better photocatalytic degradation effect to organic pollutants.

A CQDs/ZnO composite based on waste rice noodles displayed a highly efficient photocatalytic degradation effect on various organic pollutants.