Jae-Soon Choi

Jae-Soon Choi
Oak Ridge National Laboratory | ORNL · Energy and Transportation Science Division

Ph.D.

About

63
Publications
6,022
Reads
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1,344
Citations
Education
August 1996 - October 2000
Sorbonne Université
Field of study

Publications

Publications (63)
Article
Carboxylic acid ketonization has recently gained significant attention to produce biomass-derived hydrocarbon fuels as it not only removes the highly reactive carboxylic functional group but also increases the size of the carbon chain. In this study, Ca-doped CeO2-based catalysts were investigated for acetic acid ketonization using a combined exper...
Article
Hydrothermally stable diesel oxidation catalysts (DOCs) with improved low-temperature activity are desired for the abatement of emissions from diesel vehicles. Herein, novel palladium(Pd)/SiO2(core)@Zr(shell) structured DOCs were developed. SiO2 was completely covered by an 8.4 nm thickness Zr-based shell using a hard template method. The SiO2@Zr s...
Article
Full-text available
An industry-defined evaluation protocol was used to evaluate the hydrocarbon trapping (HCT) and passive NOx adsorption (PNA) potential for BEA, ZSM-5, and SSZ-13 zeolites with ion-exchanged Pd or Ag. All materials underwent 700 °C degreening prior to exposure to an industry-derived protocol gas stream, which included NOx, ethylene, toluene, and dec...
Article
A series of Ce xZr1‐xO2 (x = 1, 0.83, 0.17, 0) supports and 2 wt.% Ni/ CexZr1‐xO2 catalysts were synthesized and evaluated for CH4 oxidation. The CexZr1‐xO2 supports showed moderate activity (T50 = 519‐638 °C) with CO by‐product formation. Nickel incorporation onto CexZr1‐xO2 lowered the T50 to 438‐477 °C and eliminated the formation of CO. The res...
Article
Silver and palladium ion-exchanged BEA zeolites (Si/Al = 12.5) and silver ion-exchanged ZSM-5 zeolites (Si/Al = 15) were studied for their ability to adsorb and desorb propylene and NO under simulated diesel exhaust conditions. The adsorption experiment results demonstrated the excellent ability of bare BEA zeolites to adsorb propylene, but only a...
Article
Full-text available
Catalytic hot gas filtration (CHGF) is used to precondition biomass derived fast pyrolysis (FP) vapors by physically removing reactive char and alkali particulates and chemically converting reactive oxygenates to species that are more easily upgraded during subsequent catalytic fast pyrolysis (CFP). Carboxylic acids, such as acetic acid and propion...
Preprint
Carboxylic acids such as acetic acid and propionic acid have been investigated as representative components for fast pyrolysis (FP) bio-oil upgrading. Selective catalytic conversion of carboxylic acids can enhance bio-refinery processing economics through catalyst preservation and process intensification. Various metal-doped molybdenum carbide bead...
Article
Full-text available
Density functional theory (DFT) calculations were used to investigate the effect of Ni dopants on the removal of chemisorbed oxygen (O*) from the Mo-terminated (TMo) and C-terminated (TC) Mo2C(001) surfaces. The removal of adsorbed oxygen from the catalytic site is essential to maintain the long-term activity and selectivity of the carbide catalyst...
Article
Full-text available
Low-temperature hydrogenation of carbonyl compounds can greatly improve the thermal stability of fast pyrolysis bio-oil, thereby enabling long-term operation of upgrading reactors which generally require high temperatures to achieve deep deoxygenation. The state-of-the-art hydrogenation catalysts, precious metals such as ruthenium, although effecti...
Chapter
By directly resolving spatial and temporal species distributions within operating honeycomb monolith catalysts, spatially resolved capillary inlet mass spectrometry (SpaciMS) provides a uniquely enabling perspective for advancing automotive catalysis. Specifically, the ability to follow the spatiotemporal evolution of reactions throughout the catal...
Article
This paper describes properties of molybdenum carbides as a potential catalyst for fast pyrolysis bio-oil hydroprocessing. Currently, high catalyst cost, short catalyst lifetime, and lack of effective regeneration methods are hampering the development of this otherwise attractive renewable hydrocarbon technology. A series of metal-doped bulk Mo car...
Article
Periodical regeneration of NOx storage catalyst (also known as lean NOx trap) by short rich pulses of CO, H2 and hydrocarbons is necessary for the reduction of nitrogen oxides adsorbed on the catalyst surface. Ideally, the stored NOx is converted into N2, but N2O and NH3 by-products can be formed as well, particularly at low-intermediate temperatur...
Article
Full-text available
We investigated the impact of ZrO2 on the performance of palladium-based oxidation catalysts with respect to low-temperature activity, hydrothermal stability, and sulfur tolerance. Pd supported on ZrO2 and SiO2 were synthesized for a comparative study. Additionally, in an attempt to maximize the ZrO2 surface area and improve sulfur tolerance, a Pd...
Article
The development and optimization of catalysts and catalytic processes requires knowledge of reaction kinetics and mechanisms. In traditional catalyst kinetic characterization, the gas composition is known at the inlet, and the exit flow is measured to determine changes in concentration. As such, the progression of the chemistry within the catalyst...
Article
Ammonia is an important intermediate of the reduction in a storage and reduction catalyst (aka lean trap). NH3 formed under rich conditions in the reduced front part of the catalyst is transported by convection downstream to the unregenerated (still oxidized) zone of the catalyst, where it further reacts with the stored oxygen and . In this paper,...
Article
The dynamics and selectivity of N-2 and N2O formation during and after the regeneration of a commercial NOx storage catalyst containing Pt, Pd, Rh, Ba on Ce/Zr, Mg/AI and Al oxides was studied with high-speed FTIR and SpaciMS analyzers. The lean/rich cycling experiments (60s/5 s and 60 s/3 s) were performed in the temperature range 200-400 degrees...
Patent
A method for synthesizing catalyst beads of bulk transmission metal carbides, nitrides and phosphides is provided. The method includes providing an aqueous suspension of transition metal oxide particles in a gel forming base, dropping the suspension into an aqueous solution to form a gel bead matrix, heating the bead to remove the binder, and carbu...
Article
Abstract This study examined the local structural properties of Pt nanoparticles on SiO2, TiO2-SiO2, and ZrO2-SiO2 supports to better understand the impact of oxide-support type on the performance of Pt-based catalysts. In situ X-ray absorption fine structure (XAFS) measurements were taken for the Pt L3-edge in a temperature range from 300 to 700 K...
Article
Full-text available
We investigated the structural evolution of molybdenum carbides subjected to hot aqueous environments and their catalytic performance in low-temperature hydroprocessing of acetic acid. While bulk structures of Mo carbides were maintained after aging in hot liquid water, a portion of carbidic Mo sites were converted to oxidic sites. Water aging also...
Article
In this study, a kinetic model is developed for NH3-SCR over a honeycomb-monolith-supported Cu-zeolites using intra-catalyst axial species distribution measurements. An ammonia TPD experiment, together with micro calorimetry data were used for tuning the ammonia adsorption and desorption properties. The spatial distribution for NO oxidation, NH3 ox...
Article
Integrating biofuels with conventional petroleum products requires improvements in processing to increase blendability with existing fuels. This work demonstrates analysis techniques for more hydrophilic bio-oil liquids that give improved quantitative and qualitative description of the total acid content and organic acid profiles. To protect infras...
Article
A global kinetic NOX Storage and Reduction (NSR) Model based on flow reactor experiments was developed to investigate the NOX storage and reduction mechanisms with a focus on the breakthrough of NH3 and N2O during the rich phase. Intra-Catalyst Storage and Reduction Measurements (SpaciMS) were used to further validate the model, particularly with r...
Article
A commercial lean NOX trap (LNT) catalyst containing Pt, Pd, Rh, BaO, and CeO2 was evaluated in this investigation. The effects of lean/rich cycle timing on the NOX, CO and C3H6 conversions and on the NH3 and N2O selectivities were considered. Two distinct lean/rich cycling regimes were identified. At low temperatures, NOX release and reduction wer...
Article
In this paper we apply novel experimental and computational methods that investigate the contribution of cracks and cavities to diffusion in catalytic coating (washcoat). A sample of commercial catalytic monolith for automotive exhaust gas after treatment is scanned by X-ray micro tomography (mu CT) to obtain realistic 3D images of the coated layer...
Article
In this paper we propose an effective global kinetic model that allows prediction of N2O and NH3 formation during the reduction of stored NOx in dependence on the composition of the rich mixture (H2/CO/C3H6), actual operating temperature, and length of regeneration period. A bench flow reactor equipped with a high-speed FTIR was used to measure dyn...
Article
Full-text available
In this work, we studied how TiO2 and ZrO2 coatings enhance the CO oxidation performance of SiO2-supported Pt catalysts under conditions relevant to automotive emissions control. SiO2 was coated with metal oxides TiO2 or ZrO2 by sol-gel method and the subsequent Pt loading was done by incipient wetness method. The prepared catalysts Pt/TiO2-SiO2 an...
Article
Pathways for N2O formation during lean/rich cycling of a commercial LNT catalyst (containing Pt, Pd, Rh as well as Ba, CeZr, MgAl and Al oxides) were investigated based on bench-reactor experiments with spatiotemporally resolved gas measurements (SpaciMS) and in situ surface analysis (DRIFTS). The inlet gas temperature, composition of the rich gas...
Article
Full-text available
We present results from a computational study of the potential for using low-cost sorbent materials to trap the emissions of hydrocarbons and nitrogen oxides temporally during cold-start periods in hybrid electric vehicles and plug-in hybrid electric vehicles operating over transient driving cycles. The hydrocarbon adsorption behavior of a candidat...
Article
Selective catalytic reduction of NO with NHâ was studied on a Cu-beta zeolite catalyst, with specific focus on the distributed NHâ capacity utilization and inhibition. In addition, several other relevant catalyst parameter distributions were quantified including the SCR zone, or catalyst region where SCR occurs, and NO and NHâ oxidation. We show th...
Article
Components found in a commercial lean NOx trap have been studied in order to determine their impact on sulfate storage and release. A micro-reactor and a diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) were used to compare components MgAl2O4, Pt/MgAl2O4, Pt/Al2O3, Pt/Ba/Al2O3, Pt/CeO2–ZrO2, and Pt/Ba/CeO2–ZrO2, as well as physi...
Article
We summarize results from an investigation of the spatiotemporal distribution of NOâ storage and intermediate gas species in determining the performance of a fully formulated, Ba-based, lean NOâ trap catalyst under lean/rich cycling conditions. By experimentally resolving spatiotemporal profiles of gas composition, we found that stored NOâ was sign...
Article
The selectivity of NOx reduction products during the catalyst regeneration was studied. When reductants reacted with NOx over an incompletely reduced Pt surface, N2O was more likely to form, but this likelihood decreased with progressive reduction of the surface. When the surface became more fully reduced, the reduction products were mainly N2 and...
Article
In order to elucidate the effect of washcoat composition on lean NOx trap (LNT) aging characteristics, fully formulated monolithic LNT catalysts containing varying amounts of Pt, Rh and BaO were subjected to accelerated aging on a bench reactor. Subsequent catalyst evaluation revealed that in all cases aging resulted in deterioration of the NOx con...
Article
Lean NOx Trap (LNT) catalysts can effectively reduce NOx from lean engine exhaust. Significant research for LNTs in diesel engine applications has been performed and has led to commercialization of the technology. For lean gasoline engine applications, advanced direct injection engines have led to a renewed interest in the potential for lean gasoli...
Article
In order to study the effect of washcoat composition on lean NOx trap (LNT) aging characteristics, fully formulated monolithic LNT catalysts containing varying amounts of La-stabilized CeO2 (5 wt% La2O3) or CeO2-ZrO2 (Ce:Zr = 70:30) were subjected to accelerated aging on a bench reactor. Subsequent catalyst evaluation revealed that aging resulted i...
Article
We report observations of the nature and spatial distribution of sulfur species on a sulfated Ba-based commercial lean NOx trap (LNT) catalyst. The monolithic catalyst was sulfated in a bench flow reactor during 60/5-s NOx-storage/reduction cycling to achieve a total sulfur loading of 3.4gL−1 of catalyst. Washcoat composition, structure and sulfur...
Conference Paper
Introduction The Lean NOx Trap (LNT) catalyst is an aftertreatment technology for abatement of nitrogen-oxide emissions from lean-burn vehicle engines. The water-gas-shift (WGS) reaction occurs during LNT regeneration; WGS can contribute to regeneration reactions and be used in catalyst-system control strategies. Exhaust sulfur can limit the over...
Conference Paper
Fundamental understanding of mechanisms associated with sulfation/desulfation of lean NOx trap (LNT) catalysts can enable more durable and energy-efficient aftertreatment systems. Knowledge on the types and spatial distribution of surface sulfur species and how their formation and removal affects the NOx storage/reduction performance is of particul...
Article
The effect of axial length on the NOx reduction performance of two different commercial Lean NOx Trap (LNT) monolithic catalysts was experimentally investigated in a bench flow reactor. The washcoat composition of one of the catalysts consisted of Pt and K on γ-Al2O3; whereas the other catalyst contained a complex mixture of Pt, Pd, Rh, Ba, Ce, Zr,...
Article
The nature of H2 regeneration of a model Pt/Ba/Al2O3 LNT catalyst was investigated with specific focus on intra-catalyst formation and utilization of NH3 and its role in catalyst regeneration. In-situ measurements of the transient intra-catalyst species (H2, NH3, N2, NOx) distributions at different temperatures were used to detail the reaction evol...
Article
The effect of monolith length on the NOx performance of Lean NOx Traps (LNTs) has been investigated using a bench flow reactor (BFR). The composition of the catalyst samples consists of Pt/K supported on y-Al2O3 washcoat. Samples of 2.22-cm in diameter and three different lengths of 2.54, 5.08 and 7.62 cm were evaluated at a fixed gas hourly space...
Article
The effect of La2O3-stabilized ceria incorporation on the functioning of fully formulated lean NOx trap catalysts was investigated. Monolithic catalysts were prepared, corresponding to loadings of 0, 50 and 100g CeO2/L, together with a catalyst containing 100g/L of ceria–zirconia (Ce0.7Zr0.3O2). Loadings of the other main components (Pt, Rh and BaO...
Article
We experimentally studied the influence of temperature and sulfur loading on the axial distribution of reactions inside a commercial lean NOx trap (LNT) catalyst to better understand the global performance trends. Our measurements were made on a monolith core, bench-flow reactor under cycling conditions (60-s lean/5-s rich) at 200, 325, and 400°C w...
Article
The objective of the present study was to develop an improved understanding of how sulfur affects the spatiotemporal distribution of reactions and temperature inside a monolithic lean NOx trap (LNT). These spatiotemporal distributions are believed to be major factors in LNT function, and thus, we expect that a better understanding of these phenomen...
Article
Understanding how a reductant evolves and is utilized during regeneration of NOx storage-reduction catalyst can lead to predictive kinetic models, improved catalysts and energy-efficient engine-catalyst systems. We performed practically relevant NOx storage/regeneration cycling (56 s/4 s) experiments over a monolithic Pt/K/Al2O3 catalyst in a bench...
Article
We employed a new experimental technique known as spatially resolved capillary-inlet mass spectrometry (SpaciMS) to observe the evolution of multiple species inside the channels of a monolithic NOx storage-reduction (NSR) catalyst. The NSR material consisted of a Pt/K/Al2O3 washcoat deposited inside cordierite monolith channels. Spatially and tempo...
Article
Full-text available
Lean NOx Trap (LNT) catalysts are capable of reducing NOx in lean exhaust from diesel engines. NOx is stored on the catalyst during lean operation; then, under rich exhaust conditions, the NOx is released from and reduced by the catalyst. The process of NOx release and reduction is called regeneration. One method of obtaining the rich conditions fo...
Article
Surface organometallic chemistry has been used to deposit tin atoms on an alumina-supported cobalt–molybdenum sulfide. The EXAFS spectra at the Mo and Co K-edges were not changed significantly by tin doping, which means that the initial morphology of sulfide phases was preserved during the synthesis. Mössbauer spectroscopy indicated that the main n...
Article
In situ diffuse reflectance infrared Fourier transform spectroscopy was applied to monitor the temperature-programmed carburization of molybdenum trioxide. This technique indicated the existence of surface residual oxygen species on Mo2C synthesized even up to 973 K, indicating incomplete carburization. The presence of residual oxygen species on th...
Article
Formation of a 0.25 oxygen monolayer was sufficient to completely deprive bulk Mo2C of its noble metal-like behavior in CO chemisorption and benzene hydrogenation. Recarburization of a passivated Mo2C by flowing a 10 vol % CH4/H2 mixture at 973 K for 1 h could recover the noble metal-like behavior found on a non-passivated sample. On the contrary a...
Article
Surface organometallic chemistry (SOMC) was applied to the selective incorporation of cobalt or tin atoms to the active phase of molybdenum-based sulfides supported on alumina. The nature of involved reactions was investigated by analyzing the gaseous species evolved during the synthesis. The resulting materials were characterized by various techni...
Article
Temperature-programmed carburization of molybdic acid with CH4/H2 mixtures led to hexagonal Mo2C with specific surface areas ranging from 40 to 91 m2 g−1. The carburization was found to go through Mo4O11, MoO2, and Mo metal. Whatever was the parameter of carburization, no significant change of the lattice parameters of Mo2C was detected by XRD. The...

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