Carbon nitride–TiO2 hybrid modified with hydrogenase for visible light driven hydrogen production

A system consisting of a [NiFeSe]–hydrogenase (H₂ase) grafted on the surface of a TiO₂ nanoparticle modified with polyheptazine carbon nitride polymer, melon (CN_x) is reported. This semi-biological assembly shows a turnover number (TON) of more than 5.8 × 10⁵ mol H₂ (mol H₂ase)^–1 after 72 h in a sacrificial electron donor solution at pH 6 during solar AM 1.5 G irradiation. An external quantum efficiency up to 4.8% for photon-to-hydrogen conversion was achieved under irradiation with monochromatic light. The CN_x–TiO₂–H₂ase construct was also active under UV-free solar light irradiation (λ > 420 nm), where it showed a substantially higher activity than TiO₂–H₂ase and CN_x–H₂ase due, in part, to the formation of a CN_x–TiO₂ charge transfer complex and highly productive electron transfer to the H₂ase. The CN_x–TiO₂–H₂ase system sets a new benchmark for photocatalytic H₂ production with a H₂ase immobilised on a noble- and toxic-metal free light absorber in terms of visible light utilisation and stability.     

In situ preparation of polymeric cobalt phthalocyanine–decorated TiO2 nanorods for efficient photocatalytic CO2 reduction

The integration of photosensitizers with low-cost and non-toxic metal oxides is a promising strategy to design heterogeneous photocatalysts for CO₂ reduction. Herein, p–n heterojunction photocatalysts (T-CoPPcs) consisting of p-type polymeric cobalt phthalocyanines (CoPPcs) as a photosensitizer coupled with n-type TiO₂ nanorods were fabricated through a facile, eco-friendly, one-pot hydrothermal reaction. In this process, CoPPcs were grown on n-type TiO₂ nanorods, whereas protonated titanate nanorods began converting to the highly crystalline anatase phase with small crystals on the TiO₂ surfaces. The introduction of CoPPcs not only improved the solar light utilization but also accelerated the separation and migration of charge carriers via the p–n heterojunction with the strong interfacial contact Ti–O–Co bond. The increases in crystallinity and surface area of TiO₂ nanorods also contributed to the enhanced photoactivities of T-CoPPcs. The CO₂ photoreduction of the synthesized materials was evaluated in CO₂-saturated MeCN/water using [Co(bpy)₃]²⁺ as a cocatalyst and triethanolamine as a hole scavenger. The optimized nanocomposite exhibited a remarkable CO generation rate of 4.42 mmol/h/g with a high selectivity of 85.3% and outstanding catalytic stability. The influences of cocatalyst concentration, water content, catalyst loading, and hole scavenger concentration were optimized for efficient CO₂ reduction. The photocatalytic CO₂ conversion efficiency of the present system is found to be higher than that of TiO₂-based materials reported in the literature. We believe that this research into a heterostructural design strategy and photocatalytic system may be an inspiration for the development of photocatalytic CO₂-to-CO conversion.     

Unexpected effect of catalyst concentration on photochemical CO2 reduction by trans(Cl)–Ru(bpy)(CO)2Cl2: new mechanistic insight into the CO/HCOO– selectivity

Photochemical CO₂ reduction catalysed by trans(Cl)–Ru(bpy)(CO)₂Cl₂ (bpy = 2,2′-bipyridine) efficiently produces carbon monoxide (CO) and formate (HCOO^–) in N,N-dimethylacetamide (DMA)/water containing [Ru(bpy)₃]²⁺ as a photosensitizer and 1-benzyl-1,4-dihydronicotinamide (BNAH) as an electron donor. We have unexpectedly found catalyst concentration dependence of the product ratio (CO/HCOO^–) in the photochemical CO₂ reduction: the ratio of CO/HCOO^– decreases with increasing catalyst concentration. The result has led us to propose a new mechanism in which HCOO^– is selectively produced by the formation of a Ru(i)–Ru(i) dimer as the catalyst intermediate. This reaction mechanism predicts that the Ru–Ru bond dissociates in the reaction of the dimer with CO₂, and that the insufficient electron supply to the catalyst results in the dominant formation of HCOO^–. The proposed mechanism is supported by the result that the time-course profiles of CO and HCOO^– in the photochemical CO₂ reduction catalysed by [Ru(bpy)(CO)₂Cl]₂ (0.05 mM) are very similar to those of the reduction catalysed by trans(Cl)–Ru(bpy)(CO)₂Cl₂ (0.10 mM), and that HCOO^– formation becomes dominant under low-intensity light. The kinetic analyses based on the proposed mechanism could excellently reproduce the unusual catalyst concentration effect on the product ratio. The catalyst concentration effect observed in the photochemical CO₂ reduction using [Ru(4dmbpy)₃]²⁺ (4dmbpy = 4,4′-dimethyl-2,2′-bipyridine) instead of [Ru(bpy)₃]²⁺ as the photosensitizer is also explained with the kinetic analyses, reflecting the smaller quenching rate constant of excited [Ru(4dmbpy)₃]²⁺ by BNAH than that of excited [Ru(bpy)₃]²⁺. We have further synthesized trans(Cl)–Ru(6Mes-bpy)(CO)₂Cl₂ (6Mes-bpy = 6,6′-dimesityl-2,2′-bipyridine), which bears bulky substituents at the 6,6′-positions in the 2,2′-bipyridyl ligand, so that the ruthenium complex cannot form the dimer due to the steric hindrance. We have found that this ruthenium complex selectively produces CO, which strongly supports the catalytic mechanism proposed in this work.     

Highly efficient In–Sn alloy catalysts for electrochemical reduction of CO2 to formate

Gas diffusion electrodes (GDEs), including GDE-In_0.90Sn_0.10, GDE-In_0.47Sn_0.53 and GDE-In_0.22Sn_0.78, were prepared by electrodeposition of In–Sn alloys on carbon fiber paper, and then used to explore the electroreduction of CO₂ to formate in aqueous solution. Compared with commercial indium or Sn foil catalysts, the GDE-In_0.90Sn_0.10 electrode in particular is shown to have excellent catalytic performance towards electroreduction of CO₂ to formate, with a high Faradaic efficiency (~ 92%). More importantly, the catalytic activity of GDE-In_0.90Sn_0.10 remained reasonably stable over a 22-hour period of electrolysis, and a relatively high electrolytic current density (15 mA cm^− 2) was obtained in an aqueous medium, demonstrating its potential for electrochemical reduction of CO₂ to formate.     

Selective reduction of nitroarenes to N-arylhydroxylamines by use of Zn in a CO2–H2O system, promoted by ultrasound

The promoting effect of ultrasound on the selective reduction of nitroarenes to N-arylhydroxylamines by use of Zn in an environmentally benign CO₂–H₂O system has been demonstrated. The yield of N-phenylhydroxylamine reaches 95 % when the reaction is carried out with a Zn-to-nitrobenzene molar ratio of 2.2 under ultrasound (40 kHz) at 25 °C and normal pressure of CO₂ for 60 min. Application of ultrasound to the reaction has the advantages of higher yield of N-arylhydroxylamines, shorter reaction time, and consumption of less Zn.     

Improved catalytic activity and N2 selectivity of Fe–Mn–O x catalyst for selective catalytic reduction of NO by NH3 at low temperature

Research on Chemical Intermediates - FeO x , MnO x and Fe–Mn–O x catalysts were prepared by the co-precipitation method and used for the selective catalytic reduction (SCR) of NO x by...     

Investigation of the effect of cobalt on the Ni–Al2O3 catalyst prepared by the mechanochemical method for CO2 methanation

Research on Chemical Intermediates - Various Ni–Co catalysts supported on alumina were produced by the mechanochemical technique and applied to CO2 Methanation. X-ray diffraction,...     

Pt/Ni(OH)2–NiOOH/Pd multi-walled hollow nanorod arrays as superior electrocatalysts for formic acid electrooxidation

The catalytic activity and durability are crucial for the development of high-performance electrocatalysts. To design electrocatalysts with excellent electroactivity and durability, the structure and composition are two important guiding principles. In this work, novel Pt/Ni(OH)₂–NiOOH/Pd multi-walled hollow nanorod arrays (MHNRAs) are successfully synthesized. The unique MHNRAs provide fast transport and short diffusion paths for electroactive species and high utilization rate of catalysts. Because of the special surface and synergistic effects, the Pt/Ni(OH)₂–NiOOH/Pd MHNRA electrocatalysts exhibit high catalytic activity, high durability and superior CO poisoning tolerance for the electrooxidation of formic acid in comparison with Pt@Pd MHNRAs, commercial Pt/C, Pd/C and PtRu/C catalysts.     

Cyclodextrin–[RuCl2(Arene)]2 conjugates: another way to enhance the enantioselectivity of aromatic ketones reduction by aromatic ligands' volume

Eight amino alcohol-modified β-CDs CD-1–CD-8 have been synthesized in acceptable yields and were employed to form artificial metalloenzymes with [RuCl₂(Benzene)]₂ and [RuCl₂(Mesitylene)]₂, respectively. All the conformations of CD-1–CD-8, the complexes between CD-1–CD-8 and [RuCl₂(Arene)]₂, and the inclusion complexes between CD-1–CD-8 and acetophenone were characterized by UV, ¹H NMR, ¹H ROESY NMR, and quantum calculation. The catalytic activity of the formed artificial metalloenzymes in the asymmetric hydrogenation of aromatic ketones, especially the effect of the aromatic ligands' volume on the enantioselectivity were investigated in detail, in which it was obvious that the enantioselectivity increased as the increase in the aromatic ligands' volume. For the best artificial metalloenzyme constructed from the complex between CD-8 and [RuCl₂(Mesitylene)]₂, which not only exhibits a good tolerance to a wide range of substrates but also demonstrates some substrate selectivity, 76.39% ee was obtained for acetophenone and 79.67% ee for 2-acetylnaphthalene. A strategy to improve the enantioselectivity in the asymmetric reactions catalyzed by the artificial metalloenzymes based on CDs has been provided.     

Steam pre-reforming of natural gas over nanostructured Ni/12CaO–7Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for hydrogen production: effect of support preparation method

Calcium aluminate (12CaO–7Al₂O₃) powder was synthesized using three methods, viz. Pechini, coprecipitation, and a new novel facile decomposition route starting from activated alumina and calcium nitrate precursors, then used as a support to prepare a series of 31 wt%Ni/12CaO–7Al₂O₃ catalysts by deposition–precipitation method. The resultant catalysts were tested in steam pre-reforming of natural gas at 400–550 °C, low steam-to-carbon (S/C) molar ratio of 1.5, and atmospheric pressure. The obtained samples were characterized by Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), hydrogen chemisorption, and CO₂–temperature-programmed desorption (TPD). Experimental results showed that the basicity and morphology of the supports depended significantly on the synthesis method. Calcium aluminate synthesized using the new decomposition procedure showed surface area of 6.23 m² g^?1, while the surface area of those prepared by the Pechini and coprecipitation method were 1.38 and 3.76 m² g^?1, respectively. The catalytic properties of the 31 wt%Ni/12CaO–7Al₂O₃ catalysts were strongly influenced by the support preparation approach. The highest specific surface area (about 230 m² g^?1), smallest Ni particle size (8.86 nm), and highest nickel dispersion (7.48%) were observed for the catalyst whose support was synthesized by the decomposition method. Even at high gas hourly space velocity (GHSV) of 2 × 10⁵ mL \({\text{g}}^{ - 1}_{\text{catalyst}}\) h^?1, this catalyst exhibited around 100% C₂H₆ and C₃H₈ conversion at temperature above 500 °C. High catalytic stability during 60 h time on-stream was also shown. The TPO profiles of the spent catalyst demonstrated high resistance to carbon formation.