8 research outputs found

    The delay diversity for different pre-fetch windows.

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    <p>(a) delay diversity for <i>Zipf</i>(0.8). (b) delay diversity for <i>Zipf</i>(1.2).</p

    Microfibrous-Structured Pd/AlOOH/Al-Fiber for CO Coupling to Dimethyl Oxalate: Effect of Morphology of AlOOH Nanosheet Endogenously Grown on Al-Fiber

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    We report a green, template-free, and general one-pot method of endogenous growth of free-standing boehmite (AlOOH) nanosheets on a 3D-network 60 μm-Al-fiber felt through water-only hydrothermal oxidation reaction between Al metal and H<sub>2</sub>O (2Al + 4H<sub>2</sub>O → 2AlOOH + 3H<sub>2</sub>). Content and morphology of AlOOH nanosheets can be finely tuned by adjusting the hydrothermal oxidation time length and temperature. Palladium is highly dispersed on such AlOOH endogenously formed on Al-fiber felt via incipient wetness impregnation method and as-obtained Pd/AlOOH/Al-fiber catalysts are checked in the CO coupling to dimethyl oxalate (DMO) reaction. Interestingly, Pd dispersion is very sensitive to the thickness (26–68 nm) of AlOOH nanosheet, and therefore the conversion shows strong AlOOH-nanosheet-thickness dependence whereas the intrinsic activity (TOF) is AlOOH-nanosheet-thickness independence. The most promising structured catalyst is the one using a microfibrous-structured composite with the thinnest AlOOH nanosheet (26 nm) to support a small amount of Pd of only 0.26 wt %. This catalyst, with high thermal-conductivity and satisfying structural robustness, delivers 67% CO conversion and 96% DMO selectivity at 150 °C using a feed of CH<sub>3</sub>ONO/CO/N<sub>2</sub> (1/1.4/7.6, vol) and a gas hourly space velocity of 3000 L kg<sup>–1</sup> h<sup>–1</sup>, and particularly, is very stable for at least 150 h without deactivation sign

    Free-Standing NiO-MgO-Al<sub>2</sub>O<sub>3</sub> Nanosheets Derived from Layered Double Hydroxides Grown onto FeCrAl-Fiber as Structured Catalysts for Dry Reforming of Methane

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    An FeCrAl-fiber-structured NiO-MgO-Al<sub>2</sub>O<sub>3</sub> nanocomposite catalyst engineered from nano- to macro-scale in one-step is developed via thermally decomposing NiMgAl layered double hydroxides (LDHs) that can be grown onto the FeCrAl-fiber only through a γ-Al<sub>2</sub>O<sub>3</sub>/water interface-assisted method. By taking advantages of homogeneous component-distribution in the LDHs-derived NiO-MgO-Al<sub>2</sub>O<sub>3</sub> nanocomposites and enhanced heat transfer, this promising catalyst delivers satisfying performance with enhanced coking/sintering resistance in the title reaction. At 800 °C and a gas hourly space velocity of 5000 mL g<sup>–1</sup> h<sup>–1</sup>, CH<sub>4</sub>/CO<sub>2</sub> conversion maintains almost constant at 91%/89% within the initial 90 h and then slides in a smooth downturn (to 80/85%) within another 180 h of reaction

    Microfibrous-Structured SS-fiber@meso-HZSM‑5 Catalyst for Methanol-to-Propylene: Steam-Assisted Crystallization Synthesis and Insight into the Stability Enhancement

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    Free-standing stainless-steel (SS)-fiber@meso-HZSM-5 core–shell catalysts engineered from micro- to macro-scale were highly efficiently synthesized via cost-effective steam-assisted crystallization (SAC) method. Impact of synthesis conditions on their morphology and textural/acidic properties was investigated by means of XRD, SEM, TEM, solid-state NMR, NH<sub>3</sub>-TPD, Py-IR and N<sub>2</sub> physisorption. Single-run lifetime of such structured catalysts for MTP process was strongly dependent on their preparation conditions but slightly the product distribution. A volcano-like relationship for lifetime was observed against the SAC time, which was correlated well with the crystallization-time-dependent crystallinity, mesoporosity and crystal size. The promising SS-fiber@meso-HZSM-5 was the one obtained after the SAC for 12 h, which delivered a prolonged single-run lifetime of 620 h with a high propylene selectivity of ∼42% at 450 °C using a methanol weight hourly space velocity (WHSV) of 1 h<sup>–1</sup>, as the result of high crystallinity, well-developed mesoporosity and small crystal size. Note that well-developed mesoporosity was paramount for the catalyst stability improvement, because of enhanced accommodation capacity of zeolite shell for receiving formed coke

    High-Performance PdNi Nanoalloy Catalyst in Situ Structured on Ni Foam for Catalytic Deoxygenation of Coalbed Methane: Experimental and DFT Studies

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    A Ni-foam-structured PdNi nanoalloy catalyst engineered from nano- to macro-scales has been successfully fabricated for the catalytic deoxygenation of coalbed methane (CBM). The catalyst was obtainable by embedment of Pd nanoparticles onto Ni-foam substrate via a galvanic exchange reaction method and subsequent in situ activation in the reaction, which was active at low temperature, selective (no CO formation), and oscillation free in this CH<sub>4</sub>-rich catalytic combustion process. Special Pd@NiO (Pd nanoparticles partially wrapped by tiny NiO fragments) ensembles were formed in the galvanic deposition stage and could merely be transformed into PdNi nanoalloys in the real reaction stream at elevated temperatures (e.g., 450 °C or higher). Density functional theory (DFT) calculations were carried out to reveal the role of Ni decoration at Pd in PdNi nanoalloy catalyst for the CBM deoxygenation. By nature, the Pd–Ni alloying modified the electronic structure of surface Pd and led to a decrease in the O adsorption energy, which can be taken as the activity descriptor for the CBM deoxygenation. A reaction kinetic study indicated that the Ni decoration at Pd by Pd–Ni alloying lowered the apparent activation energy in comparison to the pristine Pd catalyst, while leading to an increase of the reaction order of O<sub>2</sub> from −0.6 at Pd catalyst to −0.3. The foam-structured PdNi nanoalloy catalyst thus offered enhanced low-temperature activity and the elimination of oscillating phenomena as the result of a transient balance obtained between the cycles of O<sub>2</sub> adsorption/activation and CH<sub>4</sub> oxidation