Low-temperature selective catalytic reduction of NO on CeO2-CuO/Al2O3 catalysts prepared by different methods.

CeO2-CuO/Al2O3 catalysts were prepared by three different methods and their activities for selective catalytic reduction (SCR) of NO with NH3 were investigated. As can be seen from the experimental results, the catalyst prepared by the single-step sol-gel (SG) method showed the best SCR activity and resistance to SO2 and H2O. In order to investigate the relationship between the preparation method and the performance of SCR catalysts, the catalysts were characterized by using Brunauer-Emmett-Teller, X-ray diffraction, temperature programmed reduction with hydrogen, temperature programmed desorption with ammonia, X-ray photoelectron spectroscopy, Fourier transform infrared and thermo-gravimetric analysis techniques. It was found that the excellent performance of CeO2-CuO/Al2O3 catalyst prepared by the single-step SG method should be resulted from its large surface area, low crystallinity, high oxygen storage capacity, high NH3 adsorption capacity, high concentration of surface chemisorbed oxygen, weak sulphation process and weak water absorption.

Integrated interfacial design of covalent organic framework photocatalysts to promote hydrogen evolution from water.

Attempts to develop photocatalysts for hydrogen production from water usually result in low efficiency. Here we report the finding of photocatalysts by integrated interfacial design of stable covalent organic frameworks. We predesigned and constructed different molecular interfaces by fabricating ordered or amorphous π skeletons, installing ligating or non-ligating walls and engineering hydrophobic or hydrophilic pores. This systematic interfacial control over electron transfer, active site immobilisation and water transport enables to identify their distinct roles in the photocatalytic process. The frameworks, combined ordered π skeletons, ligating walls and hydrophilic channels, work under 300-1000 nm with non-noble metal co-catalyst and achieve a hydrogen evolution rate over 11 mmol g-1 h-1, a quantum yield of 3.6% at 600 nm and a three-order-of-magnitude-increased turnover frequency of 18.8 h-1 compared to those obtained with hydrophobic networks. This integrated interfacial design approach is a step towards designing solar-to-chemical energy conversion systems.

Plasmon Coupling-Induced Hot Electrons for Photocatalytic Hydrogen Generation.

We present the fabrication of core-shell-satellite Au@SiO2 -Pt nanostructures and demonstrate that LSPR excitation of the core Au nanoparticle can induce plasmon coupling effect to initiate photocatalytic hydrogen generation from decomposition of formic acid. Further studies suggest that the plasmon coupling effect induces a strong local electric field between the Au core and Pt nanoparticles on the SiO2 shell, which enables creation of hot electrons on the non-plasmonic-active Pt nanoparticles to participate hydrogen evolution reaction on the Pt surface. In addition, small SiO2 shell thickness is required in order to obtain a strong plamon coupling effect and achieve efficient photocatalytic activities for hydrogen generation.

Grafting Molecular Cobalt-oxo Cubane Catalyst on Polymeric Carbon Nitride for Efficient Photocatalytic Water Oxidation.

In this work, we have successfully constructed a cobalt-oxo (CoIII 4 O4 ) cubane complex on polymeric carbon nitride (PCN) through pyridine linkage. The covalently grafted CoIII 4 O4 cubane units were uniformly distributed on the PCN surface. The product exhibited greatly enhanced photocatalytic activities for water oxidation under visible-light irradiation. Further characterizations and spectroscopic analyses revealed that the grafted CoIII 4 O4 cubane units could effectively capture the photogenerated holes from excited PCN, lower the overpotential of oxygen evolution reaction (OER), and serve as efficient catalysts to promote the multi-electron water oxidation process. This work provides new insight into the future development of efficient photocatalysts by grafting molecular catalysts for artificial photosynthesis.

Building Oxime-Ni2+ Complex on Polymeric Carbon Nitride: Molecular-Level Design of Highly Efficient Hydrogen Generation Photocatalysts.

We report an effective strategy to in situ construct the oxime-Ni2+ complex unit on polymeric carbon nitride (PCN) as a molecular catalyst for the highly efficient hydrogen evolution reaction (HER). The PCN was functionalized with oxime groups that allowed for immobilizing Ni2+ to form oxime-Ni2+ complex units on the PCN surface with uniform distribution. The electrochemical characterizations reveal that these oxime-Ni2+ units can effectively capture photogenerated electrons from PCN and serve as active catalytic sites for proton reduction. Notably, the oxime-Ni2+ enriched PCN showed even higher activities for photocatalytic hydrogen evolution than the Pt-loaded PCN. This work provides a new way to synthesize low-cost photocatalysts with surface grafting of noble-metal-free molecular HER catalysts for efficient light-driven hydrogen generation.

Assembly of Ultra-Thin NiO Layer Over Zn1-x Cdx S for Stable Visible-Light Photocatalytic Overall Water Splitting.

Photocatalytic splitting of water into hydrogen and oxygen by using visible light is considered to be a clean, green, and renewable route for solar energy conversion and storage. Although the Zn1-x Cdx S catalysts show comparatively higher activity for photocatalytic hydrogen generation under visible-light irradiation, they suffer from serious photocorrosion during the photocatalytic reaction. The deposition of a protective layer over the Zn1-x Cdx S catalysts is believed to be an effective way to inhibit photocorrosion. However, only a few materials exhibit satisfactory catalytic properties for hydrogen evolution as well as a good protection ability. In this work, a new Zn1-x Cdx S photocatalyst was developed for water splitting under visible-light illumination by assembling an ultrathin NiO layer over Zn0.8 Cd0.2 S through an in situ photodeposition method. The as-prepared NiO/Zn0.8 Cd0.2 S showed significantly higher activity for overall water splitting compared with Pt/Zn0.8 Cd0.2 S under the same conditions without photocorrosion. An apparent quantum efficiency of 0.66 % was achieved for hydrogen evolution at 430 nm with an accomplished multicycle stability for up to 12 h without any significant decay. The strong electronic coupling between the NiO layer and Zn1-x Cdx S also promoted efficient charge separation and migration.

Fabrication of Low Adsorption Energy Ni-Mo Cluster Cocatalyst in Metal-Organic Frameworks for Visible Photocatalytic Hydrogen Evolution.

An effective cocatalyst is crucial for enhancing the visible photocatalytic performance of the hydrogen generation reaction. By using density-functional theory (DFT) and frontier molecular orbital (FMO) theory calculation analysis, the hydrogen adsorption free energy (ΔGH) of Ni-Mo alloy (458 kJ·mol(-1)) is found to be lower than that of Ni itself (537 kJ·mol(-1)). Inspired by these results, the novel, highly efficient cocatalyst NiMo@MIL-101 for photocatalysis of the hydrogen evolution reaction (HER) was fabricated using the double solvents method (DSM). In contrast with Ni@MIL-101 and Mo@MIL-101, NiMo@MIL-101 exhibited an excellent photocatalytic performance (740.2 µmol·h(-1) for HER), stability, and high apparent quantum efficiency (75.7%) under 520 nm illumination at pH 7. The NiMo@MIL-101 catalyst also showed a higher transient photocurrent, lower overpotential (-0.51 V), and longer fluorescence lifetime (1.57 ns). The results uncover the dependence of the photocatalytic activity of HER on the ΔGH of Ni-Mo (MoNi4) alloy nanoclusters, i.e., lower ΔGH corresponding to higher HER activity for the first time. The NiMo@MIL-101 catalyst could be a promising candidate to replace precious-metal catalysts of the HER.

Enhancing catalytic activity and stability for CO2 methanation on Ni@MOF-5 via control of active species dispersion.

A novel, highly active catalyst Ni@MOF-5 showed unexpected activity at low temperature for CO2 methanation. The characterization results indicated that Ni was uniformly and highly dispersed over MOF-5. This catalyst showed high stability and almost no deactivation in long term stability tests up to 100 h.