Hyun-Seog Roh

Highly active and stable Ni/Ce–ZrO2 catalyst for H2 production from methane

Steam reforming of methane has been carried out aimed at the development of new and highly active catalysts for H2 production. The catalytic properties of Ni catalysts supported on various supports have been investigated in connection with characterization results obtained from XRD, H2 chemisorption, TPR and CO2-TPD. Among the catalysts examined, Ni/Ce–ZrO2 exhibited the best activity and stability. The remarkable catalytic performance is interpreted as a combined result of high oxygen storage capacity of ceria in Ce–ZrO2, strong interaction between Ni and Ce–ZrO2, basic property of the catalyst and rather high capability of H2 uptake.

Methane reforming over Ni/Ce-ZrO2 catalysts: effect of nickel content

The effect of Ni content on the Ni/Ce-ZrO2 catalyst has been investigated in the methane conversion reactions to syngas, such as oxy-reforming, steam reforming and oxy-steam reforming. Among the catalysts examined, Ni/Ce-ZrO2 catalyst with 15% Ni loading exhibits not only the highest catalytic activity and selectivity but also remarkable stability. The TPR results reveal that strong interaction between support and metal exists and that some part of NiO incorporates into the surface of the Ce-ZrO2 support. Combined with H2 chemisorption results, one may deduce that Ni surface area and the chemical environment of nickel, as well as the properties of the Ce-ZrO2 support, play very important roles in the catalytic activity and stability of Ni/Ce-ZrO2 catalysts. It seems that two kinds of active sites, i.e. one for methane and the other for steam or oxygen, are well-balanced on 15% Ni/Ce-ZrO2 catalyst.

Methane-reforming reactions over Ni/Ce-ZrO2/θ-Al2O3 catalysts

Abstract NiO/Ce-ZrO 2 / θ -Al 2 O 3 catalysts were prepared and investigated after the reduction treatment in methane-reforming reactions such as steam reforming and oxy-steam reforming. Among the catalysts with various Ni loading values, 12% Ni loading exhibited not only the highest catalytic activity and selectivity but also remarkable stability. The TPR results reveal that strong interaction between Ni and support results in forming stable NiO x species. It is speculated that the populations of NiO x compared with NiO and/or NiAl 2 O 4 play very important roles in the catalytic activity and stability. Metallic Ni sites reduced from NiO x species strongly interacting with the support are active sites for methane-reforming reactions and have high coke resistance. The high activity and stability of Ni/Ce-ZrO 2 / θ -Al 2 O 3 is due to a Ce-ZrO 2 layer precoated on θ -Al 2 O 3 , which plays a role in forming stable NiO x species rather than free NiO or inactive NiAl 2 O 4 and in giving mobile oxygen species.

Highly stable Ni catalyst supported on Ce-ZrO2 for oxy-steam reforming of methane

A novel catalyst, Ni/Ce–ZrO2, exhibits very high catalytic activity and stability even in the stoichiometric steam reforming of methane (H2O/CH4 = 1). Furthermore, when it was employed in oxy-steam reforming, it gave enhanced CH4 conversion (99.1%) at 750u2009°C and the activity was maintained for 100 h. The high catalyst stability is mainly ascribed to the synergistic effect of the Ce modifier resulting from high capacity to store oxygen and high ability to produce mobile oxygen.

Comparative Study on Partial Oxidation of Methane over Ni/ZrO2, Ni/CeO2 and Ni/Ce–ZrO2 Catalysts

The partial oxidation of methane has been studied by sequential pulse experiments with CH4 → O2 → CH4 and simultaneous pulse reaction of CH4/O2 (2/1) over Ni/CeO2, Ni/ZrO2 and Ni/Ce–ZrO2 catalysts. Over Ni/CeO2, CH4 dissociates on Ni and the resultant carbon species quickly migrate to the interface of Ni–CeO2, and then react with lattice oxygen of CeO2 to form CO. A synergistic effect between Ni and CeO2 support contributes to CH4 conversion. Over Ni/ZrO2, CH4 and O2 are activated on the surface of metallic Ni, and then adsorbed carbon reacts with adsorbed oxygen to produce CO, which is composed of the main path for the partial oxidation of methane. The addition of ceria to zirconia enhances CH4 dissociation and improves the carbon storage capacity. Moreover, it increases the storage capacity and mobility of oxygen in the catalyst, thus promoting carbon elimination.

Carbon Dioxide Reforming of Methane Over Co-precipitated Ni-Ce-ZrO2 Catalysts

An active and relatively stable Ni-Ce-ZrO2 catalyst has been designed and prepared conveniently by a novel one-step co-precipitation/digestion method. This catalyst exhibited higher stability compared with a catalyst having the same composition but prepared using the conventional impregnation method. It was found that 15% Ni (w/w) co-precipitated with Ce-ZrO2 making the cubic phase of Ce0.8Zr0.2O2 gave synthesis gas with CH4 conversion more than 97% at 800 °C and that the activity was maintained for 100 h during the reaction. The higher activity, conversion and stability of these catalysts are mainly related to the nano-crystalline nature of cubic Ce1-xZrxO2 producing strong interaction with finely dispersed nano-sized NiOx crystallites.

Hydrogen production for fuel cells through methane reforming at low temperatures

Abstract Hydrogen production for fuel cells through methane (CH4) reforming at low temperatures has been investigated both thermodynamically and experimentally. From the thermodynamic equilibrium analysis, it is concluded that steam reforming of CH4 (SRM) at low pressure and a high steam-to-CH4 ratio can be achieved without significant loss of hydrogen yield at a low temperature such as 550xa0°C. A scheme for the production of hydrogen for fuel cells at low temperatures by burning the unconverted CH4 to supply the heat for SRM is proposed and the calculated value of the heat-balanced temperature is 548xa0°C. SRM with and/or without the presence of oxygen at low temperatures is experimentally investigated over a Ni/Ce–ZrO2/θ-Al2O3 catalyst. The catalyst shows high activity and stability towards SRM at temperatures from 400 to 650xa0°C. The effects of O2:CH4 and H2O:CH4 ratios on the conversion of CH4, the hydrogen yield, the selectivity for carbon monoxide, and the H2:CO ratio are investigated at 650xa0°C with a constant CH4 space velocity. Results indicate that CH4 conversion increases significantly with increasing O2:CH4 or H2O:CH4 ratio, and the hydrogen content in dry tail gas increases with the H2O:CH4 ratio.

A highly active and stable catalyst for carbon dioxide reforming of methane: Ni/Ce-ZrO2/θ-Al2O3

A novel catalyst, Ni/Ce-ZrO2/θ-Al2O3 has been designed and examined in carbon dioxide reforming of methane. It gives synthesis gas with CH4 conversion more than 97% at 800 °C and the activity was maintained during the reaction for longer than 40 h. The high stability of the catalyst is mainly ascribed to the beneficial precoating effect of Ce-ZrO2 resulting in the existence of stable NiOx species, a strong interaction between Ni and the support, and an abundance of mobile oxygen species in itself. From TPR results, it has been confirmed that NiOx formation is more favorable than NiO or NiAl2O4 formation, resulting in strong interaction between Ni and the support.

Partial Oxidation of Methane over Nickel Catalysts Supported on Various Aluminas

Partial oxidation of methane (POM) was systematically investigated in a fixed bed reactor over 12 wt% Ni catalysts supported on α-A12O3, γ-A12O3 and θ-A12O3 which were prepared at different conditions. Results indicate that the catalytic activity toward POM strongly depends on the BET surface area of the support. All the Ni/ θ-Al2O3 catalysts showed high activity toward POM due to the less formation of inactive NiAl2O4 species, the existence of NiO, species and stable θ-Al2O3 phase. Although Ni/γ-Al2O3 showed the highest activity toward POM, long-time stability cannot be expected as a result of the deterioration of the support at higher temperature, which is revealed from BET results. From the reaction and characterization results, it is inferred that the optimal conditions for the preparation of θ-Al2O3 are 1,173 K and 12 h.

Pulse study on the partial oxidation of methane over Ni/θ-Al2O3 catalyst

Abstract Pulse reactions of CH 4 , O 2 and mixed gas (CH 4 /O 2 =2) over fresh, partially reduced and well reduced Ni/ θ -Al 2 O 3 catalysts have been carried out at 923 and 1023xa0K to study the mechanism of CH 4 activation and the catalytic partial oxidation of CH 4 . The fresh catalyst showed high activity for the dissociation of CH 4 , and CO rather than CO 2 was the main carbon-containing gaseous product while H 2 being detected for the first CH 4 pulse, suggesting that CH 4 can be partially oxidized to CO and H 2 by the lattice oxygen of NiO. The bond strength of Ni–O seems to be favorable to the partial oxidation of CH 4 , which is due to the strong interaction between NiO and θ -Al 2 O 3 . The results of CH 4 /O 2 pulses indicate that both metallic nickel and NiO x ( x 4 . It has been demonstrated that both the reaction temperature and the C/O ratio are critical to the selectivities to CO and CO 2 . The mechanisms of the oxidation of CH 4 over fresh and reduced catalysts have been proposed.