Enhancement of Catalytic Activity via Inevitable Reconstruction of the Ni-Mo Interface for Alkaline Hydrogen Oxidation.

The inevitable oxidation of nickel-metal-based catalysts exposed to the air will lead to instability and poor reproducibility of a catalytic interface, which is usually ignored and greatly hinders their application for the catalysis of alkaline hydrogen oxidation. The details on the formation of a world-class nickel-based HOR catalyst Ni3-MoOx/C-500 are reported via an interfacial reconstruction triggered by passive oxidation upon air exposure. Interfacial reconstruction, initiated with various Ni-Mo metal ratios and annealing temperature, can fine-tune the Ni-Mo interface with an increased work function and a reduced d-band center. The optimized Ni3-MoOx/C exhibits a record high mass activity of 102.8 mA mgNi -1, a top-level exchange current density of 76.5 µA cmNi -2, and exceptional resistance to CO poisoning at 1000 ppm CO for hours. The catalyzed alkaline exchange membrane fuel cell exhibits a maximum power output of 600 mW cm-2 and excellent stability, ranking it as one of the most active non-precious metals HOR catalysts to date.

Oxyanion-Sensitive Catalytic Activity of Ni(II)/Oxyanion Systems for Heterogeneous Organic Degradation: Differential Oxidizing Capacity of Ni(III) and Ni(IV) as High-Valent Intermediates.

This study demonstrated that NiO and Ni(OH)2 as Ni(II) catalysts exhibited significant activity for organic oxidation in the presence of various oxyanions, such as hypochlorous acid (HOCl), peroxymonosulfate (PMS), and peroxydisulfate (PDS), which markedly contrasted with Co-based counterparts exclusively activating PMS to yield sulfate radicals. The oxidizing capacity of the Ni catalyst/oxyanion varied depending on the oxyanion type. Ni catalyst/PMS (or HOCl) degraded a broad spectrum of organics, whereas PDS enabled selective phenol oxidation. This stemmed from the differential reactivity of two high-valent Ni intermediates, Ni(III) and Ni(IV). A high similarity with Ni(III)OOH in a substrate-specific reactivity indicated the role of Ni(III) as the primary oxidant of Ni-activated PDS. With the minor progress of redox reactions with radical probes and multiple spectroscopic evidence on moderate Ni(III) accumulation, the significant elimination of non-phenolic contaminants by NiOOH/PMS (or HOCl) suggested the involvement of Ni(IV) in the substrate-insensitive treatment capability of Ni catalyst/PMS (or HOCl). Since the electron-transfer oxidation of organics by high-valent Ni species involved Ni(II) regeneration, the loss of the treatment efficiency of Ni/oxyanion was marginal over multiple catalytic cycles.

Photocatalytic Hydrogen Production Activity and Mechanism of New Nickel-Based Sulfur Complexes in Aqueous Solution.

The development of industry and the increase in population have caused energy shortages and environmental pollution problems. Developing clean and storable new energy is identified as a key way to solve the problems above. Hydrogen is viewed as the most potential energy carrier due to its high calorific value and pollution-free. To convert solar energy into hydrogen energy, three nickel-based catalysts, Ni(aps)(pys)2 (aps=2-amino-2-phenylacetic salicylaldehyde) (1), Ni(ads)(pys)2 (ads=aniline salicylaldehyde, pys=pyridine-2-thiolate) (2), Ni(acs)(pys)2 (acs=aniline 5-chlorosalicylaldehyde) (3), were synthesized and explored as photocatalysts for hydrogen production. A three-component photocatalytic system for hydrogen production was constructed using target complex as photocatalyst, triethanolamine (TEOA) as electron sacrificial agent and fluorescein (FL) as photosensitizer. Under the optimum conditions, about 1504 µmol of H2 can be obtained with 25 mg catalyst 2 after 3 hours of irradiation. Finally, the hydrogen-production mechanism was discussed by experimental and theoretical methods.

Autothermal Reforming of Volatile Organic Compounds to Hydrogen-Rich Gas.

Industrial emissions of volatile organic compounds are urgently addressed for their toxicity and carcinogenicity to humans. Developing efficient and eco-friendly reforming technology of volatile organic compounds is important but still a great challenge. A promising strategy is to generate hydrogen-rich gas for solid oxide fuel cells by autothermal reforming of VOCs. In this study, we found a more desirable commercial catalyst (NiO/K2O-γ-Al2O3) for the autothermal reforming of VOCs. The performance of autothermal reforming of toluene as a model compound over a NiO/K2O-γ-Al2O3 catalyst fitted well with the simulation results at the optimum operating conditions calculated based on a simulation using Aspen PlusV11.0 software. Furthermore, the axial temperature distribution of the catalyst bed was monitored during the reaction, which demonstrated that the reaction system was self-sustaining. Eventually, actual volatile organic compounds from the chemical factory (C9, C10, toluene, paraxylene, diesel, benzene, kerosene, raffinate oil) were completely reformed over NiO/K2O-γ-Al2O3. Reducing emissions of VOCs and generating hydrogen-rich gas as a fuel from the autothermal reforming of VOCs is a promising strategy.

Effect of Tungsten Addition on Nickel-Based Catalyst for Combined Steam and CO2 Reforming of Methane.

In this study, we investigated the effect of tungsten addition on Ni-based catalyst in methane steam-CO2 reforming. All the catalysts were prepared by the co-impregnation method with varied tungsten loading. The as-prepared catalysts were characterized by inductively coupled plasma atomic emission spectrometer, X-ray diffraction, temperature-programmed reduction and thermogravimetric analysis. The tungsten-loaded catalyst showed improved coke resistance and CO2 reactivity by the conducting activity test under fixed conditions.

Preparation of 3D Nd2O3-NiSe-Modified Nitrogen-Doped Carbon and Its Electrocatalytic Oxidation of Methanol and Urea.

Developing renewable energy sources and controlling water pollution are critical but challenging problems. Urea oxidation (UOR) and methanol oxidation (MOR), both of which have high research value, have the potential to effectively address wastewater pollution and energy crisis problems. A three-dimensional neodymium-dioxide/nickel-selenide-modified nitrogen-doped carbon nanosheet (Nd2O3-NiSe-NC) catalyst is prepared in this study by using mixed freeze-drying, salt-template-assisted technology, and high-temperature pyrolysis. The Nd2O3-NiSe-NC electrode showed good catalytic activity for MOR (peak current density ~145.04 mA cm-2 and low oxidation potential ~1.33 V) and UOR (peak current density ~100.68 mA cm-2 and low oxidation potential ~1.32 V); the catalyst has excellent MOR and UOR characteristics. The electrochemical reaction activity and the electron transfer rate increased because of selenide and carbon doping. Moreover, the synergistic action of neodymium oxide doping, nickel selenide, and the oxygen vacancy generated at the interface can adjust the electronic structure. The doping of rare-earth-metal oxides can also effectively adjust the electronic density of nickel selenide, allowing it to act as a cocatalyst, thus improving the catalytic activity in the UOR and MOR processes. The optimal UOR and MOR properties are achieved by adjusting the catalyst ratio and carbonization temperature. This experiment presents a straightforward synthetic method for creating a new rare-earth-based composite catalyst.

Stability and Activity of Rhodium Promoted Nickel-Based Catalysts in Dry Reforming of Methane.

The rhodium oxide (Rh2O3) doping effect on the activity and stability of nickel catalysts supported over yttria-stabilized zirconia was examined in dry reforming of methane (DRM) by using a tubular reactor, operated at 800 °C. The catalysts were characterized by using several techniques including nitrogen physisorption, X-ray diffraction, transmission electron microscopy, H2-temperature programmed reduction, CO2-temperature programmed Desorption, and temperature gravimetric analysis (TGA). The morphology of Ni-YZr was not affected by the addition of Rh2O3. However, it facilitated the activation of the catalysts and reduced the catalyst's surface basicity. The addition of 4.0 wt.% Rh2O3 gave the optimum conversions of CH4 and CO2 of ~89% and ~92%, respectively. Furthermore, the incorporation of Rh2O3, in the range of 0.0-4.0 wt.% loading, enhanced DRM and decreased the impact of reverse water gas shift, as inferred by the thermodynamics analysis. TGA revealed that the addition of Rh2O3 diminished the carbon formation on the spent catalysts, and hence, boosted the stability, owing to the potential of rhodium for carbon oxidation through gasification reactions. The 4.0 wt.% Rh2O3 loading gave a 12.5% weight loss of carbon. The TEM images displayed filamentous carbon, confirming the TGA results.

Fast microwave-assisted catalytic gasification of biomass for syngas production and tar removal.

In the present study, a microwave-assisted biomass gasification system was developed for syngas production. Three catalysts including Fe, Co and Ni with Al2O3 support were examined and compared for their effects on syngas production and tar removal. Experimental results showed that microwave is an effective heating method for biomass gasification. Ni/Al2O3 was found to be the most effective catalyst for syngas production and tar removal. The gas yield reached above 80% and the composition of tar was the simplest when Ni/Al2O3 catalyst was used. The optimal ratio of catalyst to biomass was determined to be 1:5-1:3. The addition of steam was found to be able to improve the gas production and syngas quality. Results of XRD analyses demonstrated that Ni/Al2O3 catalyst has good stability during gasification process. Finally, a new concept of microwave-assisted dual fluidized bed gasifier was put forward for the first time in this study.