Dae-Woon Jeong

A crucial role for the CeO2–ZrO2 support for the low temperature water gas shift reaction over Cu–CeO2–ZrO2 catalysts

A co-precipitation method was employed to prepare Cu dispersed on CeO2, ZrO2 and CeO2–ZrO2 supports to obtain catalysts useful for the low temperature water gas shift (WGS) reaction. To optimize the Cu–CeO2–ZrO2 catalysts, the CeO2/ZrO2 ratio was systematically changed. The cubic phase Cu–Ce0.8Zr0.2O2 catalyst exhibited the highest turnover frequency and the lowest activation energy among the catalysts tested and its CO conversion was maintained without significant loss during the reaction for 100 h. The enhanced catalytic activity and stability of the co-precipitated Cu–Ce0.8Zr0.2O2 was mainly attributed to an enhanced oxygen mobility and a strong resistance against the sintering of Cu, resulting from a large amount of defect oxygen and the strong interaction between CuO and cubic phase Ce0.8Zr0.2O2.

Hydrogen production by the water-gas shift reaction using CuNi/Fe2O3 catalyst

Incorporation of both Cu and Ni together into the crystalline lattice of Fe2O3 results in a significant increase in the catalytic activity and also suppresses the methanation reaction in the high-temperature water-gas shift (HT-WGS) reaction. CuNi/Fe2O3 exhibited the highest CO conversion with negligible CH4 selectivity at the extremely high GHSV of 101 000 h−1 (XCO = 85% at 400 °C). The high activity of CuNi/Fe2O3 catalyst is mainly due to the increase in the lattice strain and the decrease in the binding energy of lattice oxygen. In addition, X-ray photoelectron spectroscopy (XPS) results provide direct evidence for the formation of surface CuNi alloy, which plays a critical role in suppressing the methanation reaction. The detailed characterization by powder X-ray diffraction (XRD), XPS, BET, and H2 temperature-programmed reduction (TPR) techniques was used to understand the role of dopants on host iron oxides in the enhancement of catalytic activity for HT-WGS reaction.

Enhancing the catalytic performance of cobalt oxide by doping on ceria in the high temperature water–gas shift reaction

The high temperature water–gas shift (HT-WGS) reaction was performed using a Co–CeO2 catalyst, prepared through a co-precipitation method. The catalyst showed stable activity performance at 400 °C with 90% CO conversion without any side reactions (methanation) at a very high GHSV of 143 000 h−1, which is the highest value reported for the HT-WGS reaction. This remarkable performance is attributed to the superior reducible nature of ceria and the preferential exposure of (220) and (112) facets of CeO2 and Co3O4, respectively. The time-on-stream study substantiates that ceria stabilizes the surface area of the Co–CeO2 catalyst during the WGS reaction compared to the bulk Co3O4.

Mesoporous NiCu–CeO2 oxide catalysts for high-temperature water–gas shift reaction

Mesoporous NiCu–CeO2 oxide catalysts were synthesized by using the evaporation-induced self-assembly method applied to the high-temperature, water–gas shift reaction (HT-WGS) between 350 to 550 °C. Nickel and copper loadings on mesoporous ceria were tailored to achieve high activity and selectivity by suppressing methane formation in HT-WGS. Among the prepared catalysts, NiCu(1 : 4)–CeO2 exhibited the highest selectivity to CO2 and H2 with 85% CO conversion at a very high GHSV of 83 665 h−1. The higher activity of the catalysts was due to the mesoporous architecture, which provides more accessible active sites for the WGS reaction. Powder X-ray diffraction (XRD), small angle X-ray scattering (SAXS), N2-adsorption/desorption isotherm, high-resolution transmission electron microscopy (HR-TEM), and H2-temperature-programmed reduction (TPR) techniques were used to understand the role of mesoporosity and bimetallic composition of various NiCu–CeO2 oxides in enhancing catalytic activity for HT-WGS.

Effect of Composition and Pretreatment Parameters on Activity and Stability of Cu-Al Catalysts for Water-Gas Shift Reaction

We investigated various Cu species responsible for highly efficient Cu–Al oxide catalyst for the water–gas shift reaction (WGSR). The formation of various Cu species was achieved by systematically varying the Cu–Al composition in the coprecipitated mixed Cu–Al oxides. The Cu–Al composition of 70:30 (Cu–Al‐7) was the best for WGSR using the reformate gas composition. In addition, the Cu–Al‐7 catalyst reduced under 100 % H2, was relatively stable with time on stream of 100 h, at higher gas hourly space velocity of 36 201 h−1.The structural investigation of our coprecipitated catalysts with varying Cu–Al compositions revealed the formation of nonzero oxidation state copper and metallic Cu to be essential for the observed WGSR activity. In addition, the highest activity and stability of Cu–Al‐7 catalysts reduced under 100 % H2 at lower temperature was attributed to particle‐size stabilization and a lower extent of Cu aggregation by Cu2O and boehmite phases, respectively, along with the formation of various Cu species during the activation protocol for 12 h. Complete CO2 selectivity without methanation was observed for all the Cu–Al compositions irrespective of their pretreatment conditions.

A Study on Pt-Na/CeO 2 Catalysts for Single Stage Water Gas Shift Reaction

Na promoted Pt/ catalysts with various Na amounts (1, 2, and 3wt%) have been applied to water gas shift reaction (WGS) at a gas hourly space velocity (GHSV) of 45515 . 1wt%Pt-2wt%Na/ catalyst exhibited the highest WGS activity at among the catalysts prepared in this study. In addition, 1wt%Pt-2wt%Na/ catalyst showed relatively stable activity with time on stream. The high activity/stability of 1wt%Pt-2wt%Na/ catalyst was correlated to its easier reducibility and higher oxygen storage capacity (OSC). As a result, 2wt% Na promoted Pt/ can be a promising candidate catalyst for the single stage WGS, which requires high intrinsic activity at very high GHSV.

Rapid synthesis of magnetite catalysts incorporated with M (Cu, Ni, Zn, and Co) promoters for high temperature water gas shift reaction

A rapid one step direct synthesis of high temperature water gas shift (HT-WGS) catalysts, magnetite incorporated with various promoters like Cu, Ni, Zn, and Co, has been shown. The key achievements in this work, in terms of catalyst preparation, are as follows: (1) direct synthesis of magnetite, a catalytically active phase in HT-WGS reaction, (2) easy incorporation of various transition metal promoters like Cu, Ni, Zn, and Co, (3) rapid preparation without any washing step by using an ample amount of solvent, and (4) a simplified procedure by avoiding longer digestion time and any specific pH value. To achieve this, an amino acid, glycine, was used as a complexing agent as well as a fuel for the auto-combustion process. The zwitterionic nature of glycine favors the easy incorporation of the promoter metal ions. In addition, the reducing atmosphere created by glycine during its burning makes it possible to prepare magnetite directly. During the HT-WGS reaction, the activity follows the order Cu-FAG > Ni-FAG > Zn-FAG > Co-FAG. The optimization of the Cu promoter is also carried out. At 12.5 mol% of Cu loading the catalytic activity reached a CO conversion value of 87% at 400 °C.

Preferential CO oxidation over supported Pt catalysts

Preferential CO oxidation reaction has been carried out at a gas hourly space velocity of 46,129 h−1 over supported Pt catalysts prepared by an incipient wetness impregnation method. Al2O3, MgO-Al2O3 (MgO=30 wt% and 70 wt%) and MgO were employed as supports for the target reaction. 1 wt% Pt/Al2O3 catalyst exhibited very high performance (XCO>90% at 175 °C for 100 h) in the reformate gases containing CO2 under severe conditions. This result is mainly due to the highest Pt dispersion, easier reducibility of PtOx, and easier electron transfer of metallic Pt. In addition, 1 wt% Pt/Al2O3 catalyst was also tested in the reformate gases with both CO2 and H2O to evaluate under realistic condition.

A Study on Preferential CO Oxidation over Supported Pt Catalysts to Produce High Purity Hydrogen

To develop preferential CO oxidation reaction (PROX) catalyst for small scale hydrogen generation system, supported Pt catalysts have been applied for the target reaction. The supports were systematically changed to optimize supported Pt catalysts. Pt/Al2O3 catalyst showed the highest CO conversion among the catalysts tested in this study. This is due to easier reducibility, the highest dispersion, and smallest particle diameter of Pt/Al2O3. It has been found that the catalytic performance of supported Pt catalysts for PROX depends strongly on the reduction property and depends partly on the Pt dispersion of supported Pt catalysts. Thus, Pt/Al2O3 can be a promising catalyst for PROX for small scale hydrogen generation system.

The investigation of non-noble metal doped mesoporous cobalt oxide catalysts for the water–gas shift reaction

In this study, we report an investigation of the low temperature water–gas shift (LT-WGS) reaction over a series of non-noble metal doped (Me = Mn, Fe, Co, and Ni) mesoporous Co3O4 catalysts. The effect of metal dopants on the structure and reducibility of the mesoporous Co3O4 oxide was examined using X-ray diffraction (XRD), N2-adsorption/desorption isotherm measurements, and H2-temperature programmed reduction (TPR) measurements. Experimental results revealed that among the Me-doped Co3O4 catalysts, Ni/Co3O4 demonstrated the highest catalytic performance (XCO = 93% with 47% H2 yield at 280 °C). The higher activity of the Ni-doped Co3O4 catalyst was mainly due to its smaller crystallite size (8.6 nm) and strong interaction between Co and Ni, which lead to the higher reducibility of Co3O4 compared to the other metal-doped Co3O4. To further optimize the loading of Ni- over the mesoporous Co3O4, a series of Ni(x%)/Co3O4 catalysts were prepared by varying the Ni-loading in the range of 3 to 15 wt%. Among these catalysts, 5 wt% Ni- was found to be the optimum loading, whereas higher Ni-loaded samples (10 and 15 wt%) showed a decrease in catalytic performance and hydrogen yield during the WGS reaction.