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Pyrolytic reforming of toluene over Ni-based catalysts loaded on nano-sized and micro-sized γ-Al 2 O 3 is investigated in a fixed bed reactor under the temperature from 500 °C to 800 °C. The physicochemical properties of γ-Al 2 O 3 and Ni/Al 2 O 3 catalysts were characterized by HRTEM, XPS, XRD and H 2 -pulse chemisorption. The metal Ni loaded on micro-sized γ-Al 2 O 3 gave the steady toluene conversion of more than 80% and graphite yield of 87.3% after 1 h of reforming reaction. The rapid decrease of H 2 yield from 5.2 mmol/g-toluene to 0.4 mmol/g-toluene over Ni/nano-Al 2 O 3 was obtained during the 1 h of reforming reaction at 500 °C. The particle size of metal Ni over nano-sized and micro-sized γ-Al 2 O 3 were centered at 7.8 nm and 28.8 nm, respectively. The metastable NiC x crystallites were observed over the spent Ni/nano-Al 2 O 3 catalyst, while only metal Ni were obtained over the spent Ni/micro-Al 2 O 3 catalyst. Ni0+ particle size-dependent crystalline phase was evidenced by MD simulations, where incorporation of more carbon atoms was achieved on small Ni particles. The energy barrier for –CH 2 dehydrogenation over Ni 32 C, Ni 4 C and Ni 3 C were estimated to be 90.2, 105.1 and 116.0 kJ/mol through the DFT simulation, respectively. It can be concluded that the crystalline Ni phase was maintained over Ni/micro-Al 2 O 3 with large Ni particle size, prolonging the catalytic endurance and promoting the CNTs (Carbon Nanotubes) growth without the deposition of unexpected amorphous carbon. • The influence of γ-Al 2 O 3 on Ni/Al 2 O 3 catalytic reforming performance was investigated. • Ni0+ particle size-dependent pyrolytic reforming for co-production of H 2 and CNTs was revealed. • The carbon solubility on Ni particles with different sizes was simulated. [ABSTRACT FROM AUTHOR]

The development of carbon-based catalysts with excellent activity for hydrogen evolution reaction (HER) is highly desirable but still remains a significant challenge. Chemical doping and morphology engineering are paramount to enhance their catalytic performance toward HER. Herein, we present a novel and effective strategy to synthesize heteroatoms-doped three-dimensional (3D) carbon nanotubes/graphene hierarchical architecture (N,S-CNTs/N,S-G) on layered double oxide substrates, in which the N,S-doped CNTs are in-situ grown on both sides of N,S-doped graphene, by two differentiated chemical vapor deposition (CVD) processes. The high concentrations of N and S dopants (up to 6.5 at.%) provide sufficient catalytic active sites for HER, while the CNTs seamlessly grafted on graphene ensure the excellent electric conductivity of N,S-CNTs/N,S-G hybrids. Consequently, the 3D N,S-CNTs/N,S-G composites display superior electrocatalytic activity for HER with an onset potential of 62 mV vs. RHE (achieve current density of 1 mA cm−2) and a small overpotential of 126 mV at 10 mA cm−2, which outperforms most of reported chemical doped carbon-based composites. The synthetic strategy facilitates the fabrication of other heteroatoms-doped 3D electrochemical catalysts. The hierarchical architecture formed by CNTs anchoring on graphene greatly impedes the aggregation of CNTs and stacking of graphene sheets, ensuring the exposure of catalytic active sites in both CNTs and graphene sheets. The synergistic N, S co-doping successfully increases the active sites and enhances the electron transfer, and thus significantly improving the HER catalytic activities of N,S-CNTs/N,S-G hybrids. Image 1 • The CNTs are in-situ welded on both sides of graphene by C–C covalent bonding. • There are high concentrations of N and S dopants in N,S-CNTs/N,S-G. • N,S-CNTs/N,S-G composites display superior electrocatalytic activity for HER. [ABSTRACT FROM AUTHOR]

Nanodiamond has varies of mechanical, chemical and biomedical advantages, but its nano-size and discrete particle properties hinder its wide applications. In this work, we have fabricated a nanodiamond electrode by spark plasma sintering technology and applied it as a heavy metal detection sensor. The detonation nanodiamond was pressed by using spark plasma sintering compaction at 900 K under 0.2 GPa pressure. Then, its structure and composition were analyzed by many characteristic techniques, while the porous electrode having a density of 1.45 g/cm3 with hardness >0.17 GPa. Comparing with traditional carbon-based electrodes, the spark plasma sintering nanodiamond electrode is inexpensive and environment friendly. The analytical performance was characterized and optimized to be 1.52–2.82 μA·μg·L−1 for vary types of heavy metal ions in acetate buffering solution. Ultimately, with stable, accurate and precise electrochemical spectroscopy, this nanodiamond sensor permits rapid detection of Cd2+, Ni2+, Mn2+, Co2+ as well as Pb2+, and could potentially be coupled with point-of-use portable measurement equipment in order to substitute the noble electrodes. Unlabelled Image • A feasible technique to fabricate a hybrid nanodiamond/metal/CNTs electrode • Rapid detection of heavy metal ions through accurate electrochemical spectroscopy • Relative high detecting sensitivity compared with other electrodes • Real-time online detection for civil and industrial pollution monitoring applications [ABSTRACT FROM AUTHOR]