scholarly journals In situ tuning of electronic structure of catalysts using controllable hydrogen spillover for enhanced selectivity

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Mi Xiong ◽  
Zhe Gao ◽  
Peng Zhao ◽  
Guofu Wang ◽  
Wenjun Yan ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Active Sites ◽  
Pt Nanoparticles ◽  
Atomic Layer ◽  
Hydrogen Spillover ◽  
General Strategy ◽  
Layer Deposition ◽  
Styrene Derivatives ◽  
Enhanced Selectivity

Abstract In situ tuning of the electronic structure of active sites is a long-standing challenge. Herein, we propose a strategy by controlling the hydrogen spillover distance to in situ tune the electronic structure. The strategy is demonstrated to be feasible with the assistance of CoOx/Al2O3/Pt catalysts prepared by atomic layer deposition in which CoOx and Pt nanoparticles are separated by hollow Al2O3 nanotubes. The strength of hydrogen spillover from Pt to CoOx can be precisely tailored by varying the Al2O3 thickness. Using CoOx/Al2O3 catalyzed styrene epoxidation as an example, the CoOx/Al2O3/Pt with 7 nm Al2O3 layer exhibits greatly enhanced selectivity (from 74.3% to 94.8%) when H2 is added. The enhanced selectivity is attributed to the introduction of controllable hydrogen spillover, resulting in the reduction of CoOx during the reaction. Our method is also effective for the epoxidation of styrene derivatives. We anticipate this method is a general strategy for other reactions.

scholarly journals In situ study of the thermal stability of supported Pt nanoparticles and their stabilization via atomic layer deposition overcoating

Nanoscale ◽  
2020 ◽  
Vol 12 (21) ◽  
pp. 11684-11693
Author(s):  
Eduardo Solano ◽  
Jolien Dendooven ◽  
Ji-Yu Feng ◽  
Philipp Brüner ◽  
Matthias M. Minjauw ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Atomic Layer Deposition ◽  
Pt Nanoparticles ◽  
Atomic Layer ◽  
Pt Nanoparticle ◽  
In Situ Study ◽  
Layer Deposition ◽  
Nanoparticle Stabilization ◽  
Thermal Stability Of

Supported Pt nanoparticle stabilization via Atomic Layer Deposition overcoating with Al2O3 has been proved to prevent particle coarsening during thermal annealing for widely spaced nanoparticles while ensuring surface accessibility for applications.

scholarly journals Surface Modification and Enhancement of Ferromagnetism in BiFeO3 Nanofilms Deposited on HOPG

Nanomaterials ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1990 ◽  
Author(s):  
Shikhgasan Ramazanov ◽  
Dinara Sobola ◽  
Farid Orudzhev ◽  
Alexandr Knápek ◽  
Josef Polčák ◽  
...  
Keyword(s):  
Active Sites ◽  
Room Temperature ◽  
Magnetic Measurements ◽  
Pyrolytic Graphite ◽  
Atomic Layer ◽  
Active Centers ◽  
Layer Deposition ◽  
Strong Hybridization ◽  
Two Phases

BiFeO3 (BFO) films on highly oriented pyrolytic graphite (HOPG) substrate were obtained by the atomic layer deposition (ALD) method. The oxidation of HOPG leads to the formation of bubble regions creating defective regions with active centers. Chemisorption occurs at these active sites in ALD. Additionally, carbon interacts with ozone and releases carbon oxides (CO, CO2). Further annealing during the in situ XPS process up to a temperature of 923 K showed a redox reaction and the formation of oxygen vacancies (Vo) in the BFO crystal lattice. Bubble delamination creates flakes of BiFeO3-x/rGO heterostructures. Magnetic measurements (M–H) showed ferromagnetism (FM) at room temperature Ms ~ 120 emu/cm3. The contribution to magnetization is influenced by the factor of charge redistribution on Vo causing the distortion of the lattice as well as by the superstructure formed at the boundary of two phases, which causes strong hybridization due to the superexchange interaction of the BFO film with the FM sublattice of the interface region. The development of a method for obtaining multiferroic structures with high FM values (at room temperature) is promising for magnetically controlled applications.

scholarly journals Enhanced hydrogen generation by reverse spillover effects over bicomponent catalysts

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Zhe Gao ◽  
Guofu Wang ◽  
Tingyu Lei ◽  
Zhengxing Lv ◽  
Mi Xiong ◽  
...  
Keyword(s):  
Hydrogen Generation ◽  
Spillover Effect ◽  
Pt Nanoparticles ◽  
Atomic Layer ◽  
Spillover Effects ◽  
Ammonia Borane ◽  
Pt Catalyst ◽  
Edge Structure ◽  
Layer Deposition

AbstractThe contribution of the reverse spillover effect to hydrogen generation reactions is still controversial. Herein, the promotion functions for reverse spillover in the ammonia borane hydrolysis reaction are proven by constructing a spatially separated NiO/Al2O3/Pt bicomponent catalyst via atomic layer deposition and performing in situ quick X-ray absorption near-edge structure (XANES) characterization. For the NiO/Al2O3/Pt catalyst, NiO and Pt nanoparticles are attached to the outer and inner surfaces of Al2O3 nanotubes, respectively. In situ XANES results reveal that for ammonia borane hydrolysis, the H species generated at NiO sites spill across the support to the Pt sites reversely. The reverse spillover effects account for enhanced H2 generation rates for NiO/Al2O3/Pt. For the CoOx/Al2O3/Pt and NiO/TiO2/Pt catalysts, reverse spillover effects are also confirmed. We believe that an in-depth understanding of the reverse effects will be helpful to clarify the catalytic mechanisms and provide a guide for designing highly efficient catalysts for hydrogen generation reactions.

scholarly journals Surface mobility and impact of precursor dosing during atomic layer deposition of platinum: in situ monitoring of nucleation and island growth

2020 ◽  
Vol 22 (43) ◽  
pp. 24917-24933 ◽  
Author(s):  
Jolien Dendooven ◽  
Michiel Van Daele ◽  
Eduardo Solano ◽  
Ranjith K. Ramachandran ◽  
Matthias M. Minjauw ◽  
...  
Keyword(s):  
Pt Nanoparticles ◽  
Particle Morphology ◽  
Atomic Layer ◽  
In Situ Monitoring ◽  
Island Growth ◽  
X Ray ◽  
Surface Mobility ◽  
Layer Deposition ◽  
And Diffusion

The nucleation rate and diffusion-driven growth of Pt nanoparticles are revealed with in situ X-ray fluorescence and scattering measurements during ALD: the particle morphology at a certain Pt loading is similar for high and low precursor exposures.

Atomic Layer Deposition of LiF and Lithium Ion Conducting (AlF3)(LiF)x Alloys Using Trimethylaluminum, Lithium Hexamethyldisilazide and Hydrogen Fluoride

2017 ◽  
Author(s):  
Younghee Lee ◽  
Daniela M. Piper ◽  
Andrew S. Cavanagh ◽  
Matthias J. Young ◽  
Se-Hee Lee ◽  
...  
Keyword(s):  
Lithium Ion ◽  
Atomic Layer ◽  
Mass Gain ◽  
Alloy Film ◽  
Ex Situ ◽  
X Ray ◽  
Layer Deposition ◽  
Ion Conducting ◽  
Good Agreement

<div>Atomic layer deposition (ALD) of LiF and lithium ion conducting (AlF<sub>3</sub>)(LiF)<sub>x</sub> alloys was developed using trimethylaluminum, lithium hexamethyldisilazide (LiHMDS) and hydrogen fluoride derived from HF-pyridine solution. ALD of LiF was studied using in situ quartz crystal microbalance (QCM) and in situ quadrupole mass spectrometer (QMS) at reaction temperatures between 125°C and 250°C. A mass gain per cycle of 12 ng/(cm<sup>2</sup> cycle) was obtained from QCM measurements at 150°C and decreased at higher temperatures. QMS detected FSi(CH<sub>3</sub>)<sub>3</sub> as a reaction byproduct instead of HMDS at 150°C. LiF ALD showed self-limiting behavior. Ex situ measurements using X-ray reflectivity (XRR) and spectroscopic ellipsometry (SE) showed a growth rate of 0.5-0.6 Å/cycle, in good agreement with the in situ QCM measurements.</div><div>ALD of lithium ion conducting (AlF3)(LiF)x alloys was also demonstrated using in situ QCM and in situ QMS at reaction temperatures at 150°C A mass gain per sequence of 22 ng/(cm<sup>2</sup> cycle) was obtained from QCM measurements at 150°C. Ex situ measurements using XRR and SE showed a linear growth rate of 0.9 Å/sequence, in good agreement with the in situ QCM measurements. Stoichiometry between AlF<sub>3</sub> and LiF by QCM experiment was calculated to 1:2.8. XPS showed LiF film consist of lithium and fluorine. XPS also showed (AlF<sub>3</sub>)(LiF)x alloy consists of aluminum, lithium and fluorine. Carbon, oxygen, and nitrogen impurities were both below the detection limit of XPS. Grazing incidence X-ray diffraction (GIXRD) observed that LiF and (AlF<sub>3</sub>)(LiF)<sub>x</sub> alloy film have crystalline structures. Inductively coupled plasma mass spectrometry (ICP-MS) and ionic chromatography revealed atomic ratio of Li:F=1:1.1 and Al:Li:F=1:2.7: 5.4 for (AlF<sub>3</sub>)(LiF)<sub>x</sub> alloy film. These atomic ratios were consistent with the calculation from QCM experiments. Finally, lithium ion conductivity (AlF<sub>3</sub>)(LiF)<sub>x</sub> alloy film was measured as σ = 7.5 × 10<sup>-6</sup> S/cm.</div>

scholarly journals Scalable nanoporous carbon films allow line-of-sight 3D atomic layer deposition of Pt: towards a new generation catalyst layer for PEM fuel cells

2021 ◽  
Author(s):  
Marwa Atwa ◽  
Xiaoan Li ◽  
Zhaoxuan Wang ◽  
Samuel Dull ◽  
Shicheng Xu ◽  
...  
Keyword(s):  
Atomic Layer Deposition ◽  
Pt Nanoparticles ◽  
Catalyst Layer ◽  
Atomic Layer ◽  
Pem Fuel Cells ◽  
Nanoporous Carbon ◽  
Carbon Films ◽  
Layer Deposition ◽  
Binder Free ◽  
New Generation

A self-supported, binder-free and scalable nanoporous carbon scaffold serves as an excellent host for the efficient and uniform atomic layer deposition of Pt nanoparticles, showing exemplary performance as a cathode catalyst layer in a PEM fuel cell.

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