Yasushi Ozawa

Low temperature oxidation of methane over Pd catalyst supported on metal oxides

Supported Pd catalysts were investigated for low temperature oxidation of methane for catalytic combustor. Both, Pd/ZrO2 and Pd/SnO2 demonstrated excellent activity in spite of its low surface area. The activity of Pd/ZrO2 was strongly dependent on the crystal phase of the support materials. ZrO2 with a monoclinic phase enhanced the activity than that with a tetragonal phase. The catalytic activity of Pd/SnO2 was affected by the preparation procedure. Impregnation of Pd on SnO2 using Pd(C5H7OO)2 aqueous solution was most effective in enhancing the catalytic activity. It is considered that catalytic activity is strongly influenced by the existence of interaction between palladium and support materials.

Low temperature oxidation of methane over Pd/SnO2 catalyst

Abstract Catalytic activities of supported Pd were investigated for low temperature oxidation of methane. Pd/SnO2 catalysts demonstrated excellent activity for methane oxidation in spite of their low surface area. The catalytic activity of Pd/SnO2 was strongly affected by the preparation procedure. Impregnation of Pd on SnO2 using aqueous solution of Pd(CH3COO)2 was most effective in enhancing the catalytic activity. The catalytic activity was also improved when well-crystallized SnO2 was employed as a support material. TEM observations revealed that catalytic activity is strongly influenced by the dispersion state of Pd. For the active catalysts, strong interaction between Pd and SnO2 support was observed in the adsorption of oxygen.

PdO/Al2O3 in catalytic combustion of methane: stabilization and deactivation

In the recently developed catalytically assisted combustors for gas turbines using natural gas, deactivation of the palladium oxide (PdO) catalyst needs to be prevented. The effects of additives such as lanthanum and neodymium in PdO/Al 2 O 3 on the catalytic durability at 1123 K were studied using a conventional fixed-bed flow reactor at atmospheric pressure. The surface properties of the catalysts were investigated using CO chemisorption, XRD, and TPD after CH 4 adsorption. The catalyst deactivation during CH 4 oxidation followed the equation Φ=r 1 [1/(1+α 1 t)] n1 +r 2 [1/(1+α 2 t)] n2 , where r, α and n are constants, subscripts 1 and 2 are the rapid and slow deactivation species, respectively, and t is time on stream. The PdO/Al 2 O 3 catalyst was rapidly deactivated by the transformation of PdO to metallic Pd and slowly deactivated by the particle growth of PdO. The addition of Nd 2 O 3 and La 2 O 3 to PdO/Al 2 O 3 prevented the particle growth of PdO as well as the transformation of PdO to Pd up to high temperature.

Preparation of a Nickel Molybdenum Carbide Catalyst and Its Activity in the Dry Reforming of Methane

Abstract Nickel molybdenum carbide catalysts were prepared and their activities in the CO 2 reforming of methane at a low CO 2 /CH 4 reactant ratio were investigated using a microreactor at atmospheric pressure and at 973 K. The effect of the catalyst preparation method and the Ni/Mo ratio on the increase in catalyst life and the promotion of catalytic activity were investigated using N 2 adsorption, X-ray diffraction, temperature-programmed carburization, temperature-programmed reaction, and a reforming reaction. The 25Ni75Mo catalyst that was carburized at 813 K exhibited the highest hydrogen formation ability and gave the least carbon deposition. The incomplete carburization of the Mo oxide species in the catalyst that was carburized at a lower temperature gradually gave a more active carburized species. The NiMoO x C y in the catalyst was more active in hydrogen formation during the dry reforming of methane while β-Mo 2 C and η-Mo 3 C 2 were less active.

Effect of addition of Nd2O3 and La2O3 to PdO/Al2O3 in catalytic combustion of methane

Abstract The addition of both La 2 O 3 and Nd 2 O 3 strongly prevents the deactivation of the PdO/Al 2 O 3 catalyst during CH 4 combustion at 1123 K, compared with the addition of either La 2 O 3 or Nd 2 O 3 alone. This is not due to stabilization of the surface area of alumina but the prevention of the decrease in number of active sites as well as prevention of the transformation of PdO to Pd in the reaction.

Development of a low NOx catalytic combustor for a gas turbine

Abstract Catalytic combustion is an advanced combustion technology and is effective as a NO x control for a 1300°C class gas turbine for power generation, but the catalyst reliability at high temperatures is still insufficient. To overcome this difficulty, catalytic combustors combined with premixed combustion were designed. In this concept, it is possible to obtain combustion gas at a temperature of 1300°C while keeping the catalyst bed temperature below 1000°C. Catalyst segments are arranged alternately with premixing nozzles for the mixing of catalytic combustion gas and fresh premixture. An air bypass valve was fitted to this combustor for extending the range of stable combustion. As a result of the atmospheric combustion tests, NO x emission was lower than 5 ppm, combustion efficiency was almost 100%, and high combustion efficiency was obtained in the range of 900–1300°C of the combustor exit gas temperature. A full-pressure combustion test is planned to prove the combustor performance.

High Pressure Test Results of a Catalytic Combustor for Gas Turbine

Recently, use of gas turbine systems such as combined cycle and cogeneration systems has gradually increased in the world. But even when a clean fuel such as LNG (liquefied natural gas) is used, thermal NOx is generated in the high temperature gas turbine combustion process. The NOx emission from gas turbines is controlled through selective catalytic reduction processes (SCR) in the Japanese electric industry.If catalytic combustion could be applied to the combustor of the gas turbine, it is expected to lower NOx emission more economically. Under such high temperature and high pressure conditions as in the gas turbine, however, the durability of the catalyst is still insufficient. So it prevents the realization of a high temperature catalytic combustor.To overcome this difficulty, a catalytic combustor combined with premixed combustion for a 1300°C class gas turbine was developed. In this method, catalyst temperature is kept below 1000°C and a lean premixed gas is injected into the catalytic combustion gas. As a result, the load on the catalyst is reduced and it is possible to prevent the catalyst deactivation.After a preliminary atmospheric test, the design of the combustor was modified and a high pressure combustion test was conducted. As a result, it was confirmed that NOx emission was below 10ppm (at 16% O2) at a combustor outlet gas temperature of 1300°C and that the combustion efficiency was almost 100%.This paper presents the design features and test results of the combustor.Copyright

Methane Combustion by A Full Scale Catalytic Combustor for Gas Turbines.

The methane combustion test at atmospheric pressure was carried out by using a full scale catalytic combustor with an improved Pd catalyst for 100MW gas tur-bine. The objective is to clarify the feasibility on application of high temperature catalytic combustion to gas turbines for the LNG combined cycle power plant system. The results can be summerized as follows:1) The manufactured full scale catalytic combustor consists of a reverse annular pre-burner, an annular mixer and Pd catalyst. The dimensions of combustor is 450mm in dia-meter and 800mm in length.2) Pd catalyst showed high activity in methane catalytic combustion and the combustion reaction proceeded enough at even lower temperatures corresponded to the compressed air temperature in gas turbine systems.3) The catalytic combustor showed excellent performance in methane combustion at atmospheric pressure. The NOx emission was extremely low and the combustion efficiency was approximately 100% in wide range conditions. As a result, catalytic combustion is ex-pected to be applied to gas turbine combustors.