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Ni(OH)2shows great promise as an electrocatalyst for the urea oxidation reaction (UOR), which can be employed in energy conversion devices such as direct urea fuel cells. The stacking of nickel hydroxide layers with different chemistries results in diverse crystal structures of nickel hydroxide. Compared to the β phase, α-Ni(OH)2allows more than one electron transfer during redox transition, which is beneficial to energy conversion applications. This study reveals that the synthesized α-Ni(OH)2electrocatalyst exhibits higher current responses (increased by 138% at 1.5 V vs.RHE), a lower slope in the Tafel plot (89 vs.121 mV dec−1), and an improved reaction rate constant (increased by 290%) for the UOR in comparison with its nickel hydroxide counterpart (i.e., β-Ni(OH)2). Moreover, quantitative analyses based on the normalized current responses with respect to the double-layer electrochemical surface area of the nickel hydroxide electrodes indicate the higher intrinsic UOR catalytic activity of the α-Ni(OH)2catalyst. More importantly, the α-Ni(OH)2catalyst exhibits superior stability toward urea electrolysis in a 20 000 s test without noticeable degradation of the catalyst.

The effect of coke distribution (external versusinternal coke) on the deactivation behavior was investigated in methane dehydroaromatization (MDA) using benchmark metal-modified HZSM-5 catalysts. A hollow HZSM-5 capsule zeolite (HC) was facilely prepared by a one-step hydrothermal strategy with the assistance of Na2EDTA and n-butylamine, and a commercial HZSM-5 (CZ) with a similar Si/Al molar ratio was used as a reference support. Four catalysts (Mo/HC, W/HC, Mo/CZ, and W/CZ) were synthesized viaan incipient wetness impregnation method, and tested in the MDA reaction. The properties of coke species were characterized by means of the TG, TPO, HRTEM, and UV-Raman techniques, and different locations of coking over the spent catalysts were obtained. The results showed that external coke can give rise to a more severe deactivation than internal coke owing to the blockage of the pore mouths with external coke that decreased the diffusion length of feed gas in the zeolite channels. This phenomenon could be explained by the excellent catalytic stability over the hollow Mo/HZSM-5 capsule catalyst during the MDA reaction, which is associated with the lower external coke formation rate. Finally, the evolution of Mo species and coke species over the coked Mo/HC catalyst was determined by in situUV-Raman spectroscopy during the TPO process, and the regeneration by O2was conducted for the hollow Mo/HZSM-5 capsule catalyst.

The adsorption configurations, growth modes and morphology of a Ru promoter under the approximate conditions of cobalt catalyzed Fischer–Tropsch synthesis (FTS) were investigated by density functional theory (DFT) calculations. On both Co(111) and Co(311) surfaces, the Runaggregation growth mode is energetically more favored than the dispersion mode, and two-dimensional adsorption configurations are more stable than three-dimensional isomers that possess more edge and vertex atoms with higher surface energies. On both surfaces, the diffusion barriers for Ru atoms are very small, which allows them to occupy the most favorable adsorption site readily and thus facilitates the Runaggregation. Ab initiomolecular dynamics (AIMD) simulations reveal that three-dimensional adsorption structures will collapse to planar monolayer structures under FTS reaction conditions, consistent with thermodynamic studies showing that the planar structure is lower in energy. Electronic structure analyses suggested that accompanied by electron transfer from surfaces to clusters, the interaction of Runclusters with Co surfaces derives from the hybrid d orbitals between the Co and Ru.

The intrinsic effect of the support microstructure on the catalytic function of VOx/Al2O3in the oxidative dehydrogenation of propane (ODHP) was studied. The results of characterization indicate that similar vanadia species are supported on Al2O3with different microstructures, but that the interactions between VOxand alumina are slightly modified. In this case, the microstructure-dependent catalytic function in the ODHP reaction is rigorously revealed. The flower-like morphology with non-compact and non-monolithic particles assembled as nanoribbons exhibits inter-particle stacking pores, which contribute to a severe extra-granular diffusion limitation (EGDL). The sphere-like morphology with compact and monolithic particles assembled as nanosheets possesses both inter-particle and intra-particle pores, which lead to a moderate EGDL. However, neither catalyst exhibits an intra-granular diffusion limitation (IGDL). Conversely, the bulk-like morphology with monolithic particles and without the assembly of secondary granules only exhibits intra-particle pores, which results in a slight EGDL and IGDL. Moreover, these two disturbances of diffusion can be excluded by means of controlling the reaction parameters. A comparison of the apparent and intrinsic kinetics, together with the structure–function relationship, determines that the EGDL might play an important role in influencing the ODHP efficiency. An in situFT-IR study shows that the adsorption-activation of propane and that of propylene proceed viadifferent initial intermediates and transformation processes. The former initially involves surface propoxide species that will be transformed into aldehydic and ketonic intermediates at the reaction temperature. The latter directly involves π-allyl alkoxidic and σ-allyl aldehydic species, as well as vanadia-carboxylate species with a quasi-anhydride structure at ambient temperatures, at which these intermediates are prone to catalytic combustion.

A core–shell ZSM-22 (Z@S) was synthesized viaepitaxial growth. The characterization results of Z@S validated that the acid sites located on the external surface of core ZSM-22 were passivated by the epitaxial shell of highly siliceous ZSM-22 and the acid strength of ZSM-22 remained unchanged. For comparison, highly siliceous and boron-containing ZSM-22 were also synthesized and characterized. In n-dodecane hydroisomerization, highly siliceous ZSM-22 almost without acid sites at the external surface achieved a much higher iso-dodecane selectivity than boron-containing ZSM-22 with weak acid sites. Z@S with strong acid sites and passivated surface acidity showed high activity and favored pore mouth catalysis but exhibited a lowered iso-dodecane selectivity. The reduced external surface acid sites enhanced the diffusion of n-alkane into the micropores, leading to severe cracking reaction caused by acid sites on the internal surface. Further modifying Z@S viamicropore blockage could greatly inhibit cracking reaction inside the micropores and confine isomerization at the pore mouth of ZSM-22. This new ZSM-22 catalyst achieved higher activity and a higher iso-dodecane yield than catalysts with weak acidity.