Low-Temperature Light-off MnOx -Na2 WO4 -Based Catalysts: A Step Forward to OCM Process Industrialization.

Oxidative coupling of methane (OCM) catalyzed by MnOx -Na2 WO4 -based catalysts has great industrial potential to convert CH4 directly to C2-3 products, but the high light-off temperature is a big challenge to OCM commercialization. The reaction mechanism studies disclosed that O2 /CH4 -activation relevant "Mn2+ ↔Mn3+ " redox cycle is tightly linked with the catalyst light-off. One concept is thus put forward that the OCM light-off temperature could be lowered once a "Mn2+ ↔Mn3+ " redox cycle was established to be triggered at low temperature over MnOx -Na2 WO4 -based catalysts. The relevant studies in recent years are reviewed, showing that the establishment of low-temperature light-off "Mn2+ ↔Mn3+ " redox cycle over the MnOx -Na2 WO4 -based catalysts indeed works effectively toward a low-temperature light-off OCM process. Moreover, three perspectives for the OCM industrialization are discussed based on this concept, including monolithic catalyst, fluidized-bed method and chemical-looping process.

Oxidative Coupling of Methane: Examining the Inactivity of the MnOx -Na2 WO4 /SiO2 Catalyst at Low Temperature.

Oxidative coupling of methane (OCM) catalyzed by MnOx -Na2 WO4 /SiO2 has great industrial promise to convert methane directly to C2-3 products, but its high light-off temperature is the most challenging obstacle to commercialization and its working mechanism is still a mystery. We report the discovery of a low-temperature active and selective MnOx -Na2 WO4 /SiO2 catalyst enriched with Q2 units in the SiO2 carrier, being capable of converting 23 % CH4 with 72 % C2-3 selectivity at 660 °C. From experiments and theoretical calculations, a large number of Q2 units in the MnOx -Na2 WO4 /SiO2 catalyst is a trigger for markedly lowering the light-off temperature of the Mn3+ ↔Mn2+ redox cycle involved in the OCM reaction because of the easy formation of MnSiO3 . Notably, the MnSiO3 formation proceeds merely through the SiO2 -involved reaction in the presence of Na2 WO4 : Mn7 SiO12 +6 SiO2 ↔7 MnSiO3 +1.5 O2 . The Na2 WO4 not only drives the light-off of this cycle but also gets it working with substantial selectivity toward C2-3 products. Our findings shine a light on the rational design of more advanced MnOx -Na2 WO4 based OCM catalysts through establishing new Mn3+ ↔Mn2+ redox cycles with lowered light-off temperature.

Ni-Foam-Structured Ni-Al2O3 Ensemble as an Efficient Catalyst for Gas-Phase Acetone Hydrogenation to Isopropanol.

The free-standing Ni-Al2O3 ensemble derived from NiAl-layered double hydroxides (NiAl-LDHs) grown onto a Ni-foam has been developed for the exothermic gas-phase acetone hydrogenation to isopropanol. This approach works effectively and efficiently to achieve a unique combination of high activity/selectivity and enhanced heat/mass transfer stemmed from the Ni-foam. The outstanding catalyst is obtained by direct reduction of the un-calcined NiAl-LDH/Ni-foam, with a high turnover frequency of 0.90 s-1, being capable of converting 90.8% acetone into isopropanol with almost 100% selectivity under stoichiometric H2/acetone molar ratio, atmospheric pressure at 80 °C, and a WHSVacetone of 10 h-1. The catalyst derivation using the un-calcined NiAl-LDH/Ni-foam enables the Ni nanoparticles to be intertwined with Al2O3 to form a large Ni-Al2O3 interface, without interruption of impurities such as irreducible NiO (in the case of calcined NiAl-LDH/Ni-foam samples), which markedly improves the strong acetone adsorption next to the Ni0 hydrogenation sites, thereby leading to a dramatic improvement of catalyst activity.

Iron Nitride@C Nanocubes Inside Core-Shell Fibers to Realize High Air-Stability, Ultralong Life, and Superior Lithium/Sodium Storages.

Poor air stability and severe structure pulverization are crucial issues for metal nitrides in metal-ion batteries. Herein, core-shell hybrid fibers (CSHN fiber) filled with metal nitride@C hollow nanocubes are introduced to be a new self-supporting anode for sodium-ion and lithium-ion batteries. The hierarchical carbon network provides fast electronic pathways and gives high protection for iron nitrides. Meanwhile, the self-supporting electrode avoids the complicated electrode fabrication process and decreases the opportunity to air exposure. Moreover, its porous nature ensures high buffer to volumetric expansion and improves the cycling stability. Therefore, it is a good platform to realize fast kinetics and high durability. For the first time, Fe2N@N-doped carbon CSHN hybrid fibers are constructed. Their influences on air stability and electrochemical behaviors are studied. Impressively, they achieve high stabilities in both lithium-ion (92.8%, at 5 A g-1, 1000 cycles) and sodium-ion (95.6%, at 2 A g-1, 2000 cycles) batteries. Therefore, this work introduces a new method to construct superior performance nitride anodes. Moreover, it also provides a new insight on the fabrication of highly efficient structures for diverse functional materials.

Nonlinear mechanical behaviors of a nanoparticle monolayer at the air-water interface.

Nanoparticle can adsorb at the air-water interface and gives rise to the special interfacial mechanical properties. With the influence of external stimulus, the adsorption state of the particles may be changed and in turn the mechanical properties of the particle layer. In this work, we study the mechanical properties of a monolayer of silica nanoparticles deposited in the Langmuir trough. The area of the monolayer was varied sinusoidally by two oscillating barriers and the surface pressure was monitored by two orthogonal Wilhelmy plates. It has been found that the surface pressure of the particle layer exhibits a significant anisotropic effect. At the early stage of the oscillation, the surface pressure versus time is sinusoidal. However, with the increase of the oscillation time, the response of the particle layer significantly deviates the sinusoidal function, which implies that the response becomes nonlinear caused by a long-term oscillation. The fast Fourier Transformation (FFT) of the surface pressure data shows that the non-sinusoidal response is composed of several fundamental frequency responses. We eventually obtained the time variation of the compression modulus E and shear modulus G . A possible mechanism was proposed to account for the mechanical properties change and the nonlinear behavior of the particle monolayer.

Novel nano-semiconductor film layer supported nano-Pd Complex Nanostructured Catalyst Pd/Ⓕ-MeOx/AC for High Efficient Selective Hydrogenation of Phenol to Cyclohexanone.

Supported metal as a type of heterogeneous catalysts are the most widely used in industrial processes. High dispersion of the metal particles of supported catalyst is a key factor in determining the performance of such catalysts. Here we report a novel catalyst Pd/Ⓕ-MeOx/AC with complex nanostructured, Pd nanoparticles supported on the platelike nano-semiconductor film/activated carbon, prepared by the photocatalytic reduction method, which exhibited high efficient catalytic performance for selective hydrogenation of phenol to cyclohexanone. Conversion of phenol achieved up to more than 99% with a lower mole ratio (0.5%) of active components Pd and phenol within 2 h at 70 °C. The synergistic effect of metal nanoparticles and nano-semiconductors support layer and the greatly increasing of contact interface of nano-metal-semiconductors may be responsible for the high efficiency. This work provides a clear demonstration that complex nanostructured catalysts with nano-metal and nano-semiconductor film layer supported on high specific surface AC can yield enhanced catalytic activity and can afford promising approach for developing new supported catalyst.