Nickel catalysts for internal reforming in molten carbonate fuel cells

Abstract

Natural gas may be used instead of hydrogen as fuel for the molten carbonate fuel cell (MCFC) by steam reforming the natural gas inside the MCFC, using a nickel catalyst (internal reforming). The severe conditions inside the MCFC, however, require that the catalyst has a very high stability. In order to find suitable types of nickel catalysts and to obtain more knowledge about the deactivation mechanism(s) occurring during internal reforming, a series of nickel catalysts was prepared and subjected to stability tests at 973 K in an atmosphere containing steam and lithium and potassium hydroxide vapours. All the catalysts prepared showed a significant growth of the nickel crystallites during the test, especially one based on c~-Al203 and a coprecipitated Ni/AI20 3 sample having a very high nickel content. However, this growth of nickel crystallites only partially explained the very strong deactivation observed in most cases. Only a coprecipitated nickel/alumina catalyst with high alumina content and a deposition-precipitation catalyst showed satisfactory residual activities. Addition of magnesium or lanthanum oxide to a coprecipitated nickel/alumina catalyst decreased the stability.Adsorption and retention of the alkali was the most important factor determining the stability of a catalyst in an atmosphere containing alkali hydroxides. This is because the catalyst bed may remain active if a small part of the catalyst bed retains all the alkali.

Preparation of core (Ni base)–shell (Silicalite-1) catalysts and their application for alkali resistance in direct internal reforming molten carbonate fuel cell

“…This is due to the higher transport resistance across the zeolite shells and the calculated methane diffusivity of 10 −5 m kg −1 through the zeolite shell is comparable to that reported for zeolite membranes [49,50]. Ni/Al 2 O 3 was inactive after exposure to the electrolyte vapor and has a low methane conversion of 1.3% [13]. The table indicates that the zeolite shell ameliorates the poisoning of the nickel catalyst with thicker shells being more effective.…”

“…This can be prevented by separating the catalyst and the anode chamber with ceramic barriers [9,10] and metal foils [11]. There are also significant efforts in developing alkali-resistant catalysts including Ru/ZrO 2 [12] and Ni catalysts supported on alkali-resistant ␥-LiAlO 2 [13], MgO-TiO 2 [14] and MgO-Al 2 O 3 [15]. A nonuniform catalyst distribution can also ameliorate the effects of poisons by locating the catalysts in an interior location of the pellet [16][17][18][19].…”

Structural Characteristics of (NiMgAl)Ox Prepared from a Layered Double Hydroxide Precursor and its Application in Direct Internal Reforming Molten Carbonate Fuel Cells

“…Berger et al [3,4] investigated the movement of alkali species toward the catalysts in the DIR-MCFC and proposed that, among the alkali species, lithium carbonate was the most poisonous to the Ni catalyst. Our group′s previous studies [12,13] also support this proposal.…”

“…lap the reforming zone with the heat-producing section of the cell [3]. However, in carrying out the reforming reaction in the anode chamber of a DIR-MCFC unit, two major problems exist.…”

“…One is the deactivation of the catalyst, by the poisoning of the alkali, originating from the molten carbonate electrolyte (mixture of Li 2 CO 3 and K 2 CO 3 ); the other is coke formation on the catalyst surface, mainly due to the very high methane steam reforming (MSR) reaction temperature. Extensive investigations have been carried out in order to overcome these serious problems [2][3][4][5][6]. It has already been concluded that Ni catalyst supported on alumina could effectively increase the resistance to electrolyte poisoning and that Ni on magnesia could suppress carbon deposition.…”