FUEL CELL

V. GALVITA

Max-Planck-Institute fuer Dynamik Komplexer Tehnischer Systeme, Sandtorstrasse 1, 39106,

Magdeburg, Germany

In the present work the reaction of ethanol steam or autothermal reforming for hydrogen rich gas streams production, over bimetallic catalysts Cu (5wt. %)-Pd(lwt.% )/C and Cu(5wt. %)-Pd(lwt.%)/Ce02-Zr02, and over Pd(lwt.%)/C was investigated. In particular, the dependence of the catalytic activity and selectivity on reaction temperature, H2O/C2H5OH molar ratio and contact time was studied. In order to evaluate the catalytic stability long-term experiments were also performed. It was found that the bimetallic catalyst being essentially more active then the catalyst containing Pd only. Thus, the use of the bifunctional, bimetallic catalyst as the catalyst for the first layer of the two-layer reactor for ethanol decomposition proved to be quite promising for the steam reforming of ethanol to syngas. In the two-layer fixed-bed catalytic reactor ethanol is first converted to a mixture of methane, carbon oxides and hydrogen over a Pd-based catalyst and then this mixture is converted to syngas over a Ni-based catalyst for methane steam or autothermal reforming. It has been shown that the use of the two-layer fixed-bed reactor prevents coke formation and provides the syngas yield closed to equilibrium. For autothermal reforming of methane the Ni (10 wt.%) catalyst supported over Ce02-Zr02- CaO/Al203 was used. This catalyst showed high activity and stability for autothermal reforming of methane.

1. Introduction

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The development of the energy production at the 21 of century must be focuses for highly efficient, environmentally friendly energy devices. Fuel cell technology holds the promise to produce electricity at vehicles and stationary application from a wide range of fuels with high efficiency. On the basic of the electrolyte employed, there are five types of fuel cells, PEMFC, AFC, PAFC, MCFC, and SOFC. Each of them has advantages and disadvantages relative to each other. Hydrogen-rich gas for feeding PEMFC may contain only trace amounts of CO (>10ppm) to avoid poisoning of the electrocatalyst of the FC. Internal reforming and electrochemical conversion of CO (CO is produced after reforming of hydrocarbon fuel) is only possible with high-temperature SOFC and MCFC and this essentially distinguishes them from low-temperature FC.

Currently, the main fuel for all of these types of FC is hydrogen. Chemical storage of hydrogen in liquid fuels is considered to be one of the most advantageous way for supplying hydrogen to fuel cells. A variety of liquid fuels, such as methanol, ethanol, and hydrocarbon are suitable for this purpose.

Among liquid fuels, ethanol is a promising source of hydrogen while it is an easily accessible and non-polluting raw material which can be readily produced from renewable sources by fermenting the sugars founding grains, such as com and wheat, as well as potato wastes, cheese whey, com fiber, rise straw, sawdust, urban wastes, and yard clippings. Hydrogen production from non-fossil, renewable energy sources such as ethanol to became technically, economically an ecologically important for sustainable development in the 21st. century.

Thermodynamic aspects of ethanol steam reforming have attention in the literature [1]. The overall reaction of hydrogen production from ethanol is strongly endotermic and corresponds to the formation of 6 mol of H2 per mol of ethanol:

c2h5oh + 3H20 = 2C02 + 6H2 (1)

However, other undesirable products such as СО, CH4, CH3CHO, and C2H4 are also usually formed during reaction. In addition, the formation of coke on the surface of the catalyst is also not uncommon. Coke formation may occur by Boudouard reaction:

2CO-> C02 + C (2)

Another possible rote for the carbon formation is through ethylene.

At, present, two processes for ethanol SR (step (i)) are available, namely a one – step process on supported metal catalysts [2, 3] and two-step process in a two-layer reactor [4] (Fig. 1). The layer in such reactor are made of different type of catalysts which working at different operating temperature. Within the first layer ethanol is converted into a mixture of CH4, CO, and H2 [4]. Over the second catalyst layer, the products of the ethanol decomposition are converted by autothermal reforming to a gas mixture enrich with hydrogen Fig. 1.

mixture.

and the mixture will be kept 48 h at 100 °С. The sample will be then allowed to cool to room temperature prior to being centrifuged to separate a gel product from the solution. The gel product will be washed with ethanol and dried for 12 h in an oven at 105 °С. Then, the product was calcinated at 400 °С for 4 h. The catalyst consisted of sphere particles of size 1-1.2 mm, pore volume and the BET surface area were 0.44 cm3/g and 120 m2/g, respectively.

Catalysts containing 5wt.% Cu and 1 wt.% Pd will be prepared by incipient wet impregnation of Ce02-Zr02 (or Pd/C for Cu-Pd/C catalyst) with an aqueous solution of Cu nitrate and Pd nitrate. The samples obtained were dried for 12 h in an oven at 105°C and then heated at 400 °С in air for Ce02-Zr02 and in He flow for Pd/C.

The Ce02-Zr02-Ca0/Al203 was prepared by the impregnation method. Commercial alumina granules were immersed in the solution containing metal components. The samples obtained were dried for 12 h in an oven at 105°C and then heated 6h. at 1000°C in air. Ni loading was carrying out by the incipient wet impregnation of Ce02-Zr02-Ca0/Al203 with an aqueous solution of Ni nitrate.

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