Engineering topics
Lin, Chao
Publications and source records attributed to Lin, Chao.
The effects of iron oxide overlayers on Pt for CO oxidation
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Decreasing the Overpotential of Aprotic Li-CO 2 Batteries with the In-Plane Alloy Structure in Ultrathin 2D Ru-Based Nanosheets
We report the aprotic Li-CO 2 battery is emerging as a promising energy storage technology with the capability of CO 2 fixation and conversion. However, its practical applications are still impeded by the large overpotential. Herein, the general synthesis of a series of ultrathin 2D Ru-M (M = Co, Ni, and Cu) nanosheets by a facile one-pot solvothermal method is reported. As a proof-of-concept application, the representative RuCo nanosheets are used as the cathode catalysts for Li-CO 2 batteries, which demonstrate a low charge voltage of 3.74 V, a small overpotential of 0.94 V, and hence a high energy efficiency of 75%. Ex/in situ studies and density functional theory calculations reveal that the excellent catalytic performance of RuCo nanosheets originates from the enhanced adsorption toward Li and CO 2 during discharge as well as the elevated electron interaction with Li 2 CO 3 during charge by the in-plane RuCo alloy structure. This work indicates the feasibility of boosting the electrochemical performance of Li-CO 2 batteries by in-plane metal alloy sites of ultrathin 2D alloy nanomaterials.
Flexible atomic layer deposition system for coating porous materials
In this paper, we describe an atomic layer deposition (ALD) system that is optimized for the growth of thin films on high-surface-area, porous materials. The system incorporates a moveable dual-zone furnace allowing for rapid transfer of a powder substrate between heating zones whose temperatures are optimized for precursor adsorption and oxidative removal of the precursor ligands. The reactor can both be evacuated, eliminating the need for a carrier gas during precursor exposure, and rotated, to enhance contact between a powder support and the gas phase, both of which help us to minimize mass transfer limitations in the pores during film growth. The capabilities of the ALD system were demonstrated by growing La 2 O 3 , Fe 2 O 3 , and LaFeO 3 films on a 120 m 2 g -1 MgAl 2 O 4 powder. Analysis of these films using scanning transmission electron microscopy and temperature-programmed desorption of 2-propanol confirmed the conformal nature of the oxide films.
Manganese Oxide Overlayers Promote CO Oxidation on Pt
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Pt Catalysts Modified with Manganese Oxide through Atomic Layer Deposition for CO Oxidation: Establishing a Coating Layer above or below Pt
The effect of atomic layer deposition (ALD) of manganese oxide on CO oxidation over Pt/Al2O3 is investigated. Two types of catalysts with a thin MnOx layer coated on or under the Pt nanoparticles (NPs) are prepared, and a pristine Pt/Al2O3 catalyst is used as a reference sample. The addition of the ALD layers improves the catalyst durability and both catalysts with MnOx exhibit greater stability after thermal aging at 1073-K. Besides, MnOx promotes CO oxidation through active Pt-MnOx interfacial sites, showing a reaction rate up to 35-fold faster than that of unmodified Pt. Interestingly, the CO adsorption ability of the Pt catalysts with MnOx overcoats is greatly suppressed after the high-temperature calcination; however, the reaction rate of CO oxidation is still excellent. This phenomenon is because the uniformly covered MnOx with two atomic layers diminishes the exposed Pt surface, but the reaction near the Pt-MnOx interfacial site still occurs. Our results guide the effective use of ALD, which is actively applied to heterogeneous catalysis, and provide a novel direction to control metal-assisted interactions.
The effects of SMSI on m-Cresol Hydrodeoxygenation over Pt/Nb 2 O 5 and Pt/TiO 2
The hydrodeoxygenation (HDO) of m-cresol was studied on Pt/Nb 2 O 5 /MgAl 2 O 4 and Pt/TiO 2 /MgAl 2 O 4 catalysts to understand the effects of Strong Metal Support Interactions (SMSI). The Nb 2 O 5 and TiO 2 supports were prepared as 0.7-nm films on MgAl 2 O 4 by Atomic Layer Deposition (ALD) to ensure that the structures of the catalyst were the same. When reduced at 773 K to place Pt in the encapsulated state, Pt/Nb 2 O 5 /MgAl 2 O 4 was much less active than Pt/MgAl 2 O 4 at 573 K but much more active at 623 K. While Pt/MgAl 2 O 4 deactivated rapidly due to coking, Pt/Nb 2 O 5 /MgAl 2 O 4 showed significantly better coke tolerance and was almost 100% selective towards toluene production. Pt/Nb 2 O 5 /MgAl 2 O 4 reduced at lower temperatures exhibited intermediate catalytic properties. The effect of reduction temperature on Pt/TiO 2 /MgAl 2 O 4 was much less and this catalyst was more similar to Pt/MgAl 2 O 4 than its Nb 2 O 5 counterpart. Lastly, the implications of these results for understanding the nature of oxide promoters on HDO of m-cresol are discussed.
Charging a Negatively Curved Nanographene and Its Covalent Network
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A Thermodynamic Investigation of Ni on Thin-Film Titanates (ATiO3)
Thin, ~1-nm films of CaTiO3, SrTiO3, and BaTiO3 were deposited onto MgAl2O4 by Atomic Layer Deposition (ALD) and then studied as catalyst supports for ~5 wt % of Ni that was added to the perovskite thin films by Atomic Layer Deposition. Scanning Transmission Electron Microscopy demonstrated that both the Ni and the perovskites uniformly covered the surface of the support following oxidation at 1073 K, even after redox cycling, but large Ni particles formed following a reduction at 1073 K. When compared to Ni/MgAl2O4, the perovskite-containing catalysts required significantly higher temperatures for Ni reduction. Equilibrium constants for Ni oxidation, as determined from Coulometric Titration, indicated that the oxidation of Ni shifted to lower PO2 on the perovskite-containing materials. Based on Ni equilibrium constants, Ni interactions are strongest with CaTiO3, followed by SrTiO3 and BaTiO3. The shift in the equilibrium constant was shown to cause reversible deactivation of the Ni/CaTiO3/MgAl2O4 catalyst for CO2 reforming of CH4 at high CO2 pressures, due to the oxidation of the Ni.
Investigation of Rh–titanate (ATiO 3 ) interactions on high-surface-area perovskite thin films prepared by atomic layer deposition
Thin, ~1 nm films of CaTiO 3 , SrTiO 3 , and BaTiO 3 were deposited onto MgAl 2 O 4 by Atomic Layer Deposition (ALD) and studied as catalyst supports for Rh. Scanning Transmission Electron Microcopy (STEM) and X-Ray Diffraction (XRD) demonstrated that the films had the perovskite structure and formed uniform coatings stable up to 1073 K. Rh, added by ALD, interacted strongly with CaTiO 3 and somewhat less strongly with SrTiO 3 , while Rh on BaTiO 3 was similar to Rh on unmodified MgAl 2 O 4 . STEM measurements of Rh on CaTiO 3 films showed Rh remained well dispersed after repeated oxidations and reductions at 1073 K; however, the Rh was inactive for CO-oxidation. Rh formed small particles on SrTiO 3 films and was active for CO oxidation after reduction at 1073 K. The reducibility and catalytic activity of Rh/BaTiO 3 /MgAl 2 O 4 were similar to that of Rh/MgAl 2 O 4 . Evidence from CO-TPR, FTIR, and XPS all indicated that the degree of interaction between Rh and the three perovskite films can be ranked in the following order: Rh/CaTiO 3 /MgAl 2 O 4 > Rh/SrTiO 3 /MgAl 2 O 4 > Rh/BaTiO 3 /MgAl 2 O 4 . Here, bulk ex-solution catalysts, synthesized by reduction of ATi 0.98 Rh 0.02 O 3 (A = Ca, Sr, and Ba), were also examined for comparison.
A Perspective on Thin-Film Perovskites as Supports for Metal Catalysts
Perovskite-supported metals have sometimes been referred to as “intelligent catalysts” because of the potential to regenerate sintered particles by driving the metal into the oxide lattice by high-temperature oxidation and releasing the metal by reduction. However, low surface areas and incomplete release of metal from the lattice have prevented the widespread application of these materials. Furthermore, we describe the preparation of thin perovskite films on stable supports by Atomic Layer Deposition (ALD) as a means for avoiding the limitations associated with bulk perovskites. Examples will be given that demonstrate many of the favorable properties of perovskite supports can be retained, while avoiding some of the shortcomings. Potential opportunities for using these materials are discussed.
Controlled One‐pot Synthesis of Nickel Single Atoms Embedded in Carbon Nanotube and Graphene Supports with High Loading
Abstract Single‐atom catalysts (SACs) have attracted much attentions due to the advantages of high catalysis efficiency and selectivity. However, the controllable and efficient synthesis of SACs remains a significant challenge. Herein, we report a controlled one‐pot synthesis of nickel single atoms embedded on nitrogen‐doped carbon nanotubes (NiSA−N−CNT) and nitrogen‐doped graphene (NiSA−N−G). The formation of NiSA−N−CNT is due to the solid‐to‐solid rolling up mechanism during the high temperature pyrolysis at 800 °C from the stacked and layered Ni‐doped g‐C 3 N 4 , g‐C 3 N 4 −Ni structure to a tubular CNT structure. Addition of citric acid introduces an amorphous carbon source on the layered g‐C 3 N 4 −Ni and after annealing at the same temperature of 800 °C, instead of formation of NiSA−N−CNT, Ni single atoms embedded in planar graphene type supports, NiSA−N−G were obtained. The density functional theory (DFT) calculation indicates the introduction of amorphous carbon source substantially reduces the structure fluctuation or curvature of layered g‐C 3 N 4 ‐Ni intermediate products, thus interrupting the solid‐to‐solid rolling process and leading to the formation of planar graphene type supports for Ni single atoms. The as‐synthesized NiSA−N−G with Ni atomic loading of ∼6 wt% catalysts shows a better activity and stability for the CO 2 reduction reaction (CO 2 RR) than NiSA−N−CNT with Ni atomic loading of ∼15 wt% due to the open and exposed Ni single atom active sites in NiSA−N−G. This study demonstrates for the first time the feasibility in the control of the microstructure of carbon supports in the synthesis of SACs.