Jia Ding

A self-supported SS-fiber@meso-HZSM-5 core–shell catalyst via caramel-assistant synthesis toward prolonged lifetime for the methanol-to-propylene reaction

A self-supported SS-fiber@meso-HZSM-5 core–shell catalyst was essentially designed and engineered from micro- to macro-scale by caramel-assistant hydrothermal synthesis. The significant role of caramel during the crystallization process was revealed in detail. Caramel not only created the mesoporosity in the ZSM-5 crystals, but also released acid under hydrothermal synthesis conditions which lowered the zeolite crystallinity. By taking advantage of the mesopore development in a hierarchical micro–meso–macropore structure with favourably-tuned acidic properties, such a catalyst provided a dramatically prolonged lifetime of 845 h (>90% conv.) with high propylene selectivity (e.g., 48%) in the MTP reaction. The hierarchical pore structure development mainly increased the accommodation capacity of the zeolite shell for receiving formed coke thereby leading to a dramatically prolonged lifetime in the MTP reaction.

Vapor-phase transport synthesis of microfibrous-structured SS-fiber@ZSM-5 catalyst with improved selectivity and stability for methanol-to-propylene

A microstructured SS-fiber@ZSM-5 core–shell catalyst engineered from micro- to macro-scale in one step is developed through a cost-effective and high-efficiency vapor-phase transport (VPT) synthesis. A sinter-locked three-dimensional microfibrous-structure consisting of 15 vol% stainless steel fibers (SS-fiber, 20 μm dia.) was dip-coated with a synthesis gel containing silicalite-1 and subsequently steamed at 180 °C using ethylenediamine (EDA) solution. The as-synthesized ZSM-5 shell contains fine coffin-shaped crystals and small grains with remarkable intercrystalline mesopores derived from the initial aggregated aluminosilicate particles while the mesopore size is ever-changing with the progression of the crystallization. The catalyst lifetime for the MTP reaction shows a volcano-like evolution against the VPT time length, which correlates well with the crystallization-time-dependent amount of Bronsted acid and mesoporosity. The most promising SS-fiber@HZSM-5 catalyst is the one obtained via VPT synthesis for 120 h, with a high shell diffusion coefficient of 1.6 × 10−14 m2 s−1, delivering a prolonged single-run lifetime of 45 h with a high propylene selectivity of ∼46.9% at 450 °C at a high methanol weight hourly space velocity (WHSV) of 10 h−1.

Microfibrous-structured Al-fiber@ns-Al2O3 core–shell composite functionalized by Fe–Mn–K via surface impregnation combustion: as-burnt catalysts for synthesis of light olefins from syngas

Promising microfibrous-structured Al-fiber@ns-Al2O3@Fe–Mn–K catalysts are developed for the mass/heat-transfer limited Fischer–Tropsch synthesis of light olefins. The Al-fiber@ns-Al2O3 core–shell composites, engineered on the nano- to macro-scale, are first prepared by endogenously growing thin shell (∼0.5 μm) nanosheet γ-Al2O3 (ns-Al2O3) onto the 3-dimentional microfibrous-structured network consisting of 10 vol% 60 μm Al-fiber and 90 vol% voidage. After modification by K through an impregnation method, the Al-fiber@ns-Al2O3 composites are functionalized with nano-structured Fe and Mn active components via a surface impregnation combustion method. The effect of combustion atmospheres (air, N2, and N2 followed by air (N2–air)) on the catalyst performance is investigated. The as-burnt catalyst obtained under air delivers the highest iron time yield of 206.0 μmolCO gFe−1 s−1 at 89.6% CO conversion with 42.1%C selectivity to C2–C4 olefins (350 °C, 4.0 MPa, 10 000 mL (g−1 h−1)), while the other two as-burnt catalysts under N2 and N2–air yield relatively low CO conversions of 58–67%. Combustion under air is helpful to form 6 nm Fe–Mn–K oxide particles with better reducibility and carbonization properties thereby leading to high performance. In contrast, under either N2 or N2–air atmosphere, smaller oxide particles (3–4 nm) are formed but suffer from deteriorated reducibility and carbonization properties due to the strong support–metal interaction. Such as-burnt catalysts obtained under air also demonstrate promising stability.

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

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 H2O (2Al + 4H2O → 2AlOOH + 3H2). 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 CH3ONO/CO/N2 (1/1.4/7.6, vol) and a gas hourly space velocity of 3000 L kg-1 h-1, and particularly, is very stable for at least 150 h without deactivation sign.