Methanation Sutdies on Nickel-Aluminum Flame-Sprayed Catalysts

Abstract

Methanation catalysts were prepared by flame-spraying aluminum onto a nickel surface followed by heating to form a Raney-type alloy and then activating with a caustic leach. Different alloying temperatures from 400 to 950 °C were employed. A maximum in methanation activity occurred for a sample alloyed at 725 °C. Little alloying occurred for catalysts preheated at 400 °C whether for 1 h or for 910 h and low activities were obtained. This indicates that active catalysts were not formed by a slow diffusion process at a temperature that might be used for methanation. It was shown that alloying takes place very quickly near or above the melting point of aluminum and that no more than 10 min is required for the heating process. Methanation activity and product selectivity were determined using a pulse microreactor by passing 3:1 synthesis gas over each sample at temperatures ranging from 300 to 400 °C. For all catalysts, the conversion of CO increased with increasing reactor temperature. The selectivity to methane was high (>88%) regardless of reactor temperature, but the selectivity to C02 increased, while that to C2H6 decreased as the temperature was raised from 300 to 400°C. A thermally deactivated sample was completely reactivated by repeating three steps used in the original preparation. X-Ray diffraction and microscopic analyses data show a correlation between the NiAI3 content in the unleached alloy and the methanation activity of the leached catalyst.

Nickel-aluminum flame-sprayed catalysts and their catalytic activities

“…The alloy phases formed at 700 and 800 °C were composed of NiAl3 with a very little Ni2Al3 and Ni2Al3 with a little NiAl3, respectively. This is the same as those reported in the previous papers (Nakabayashi et al, 1969) and is consistent with the detailed investigation by Baird and Steffgen (1977). Analysis of the pattern of nickel aluminide-coated iron plate (method B) indicated that this Raney nickel alloy did not contain NiAl3 or Ni2Al3 but did contain NiAl and Ni3Al.…”

“…The active nickel catalyst is prepared by leaching the aluminum in an aluminum-nickel alloy. Although a similar technique has been used by others (Larson, 1974; Baird and Steffgen, 1977) to prepare hydrogenation catalyst, the hydrogenation activity of the alloy containing only NiAl and Ni3Al has not bee reported.…”

Characterization studies of plasma-sprayed cobalt and iron catalysts

“…The surface areas of plasma-sprayed catalysts using nitrogen were found to be too small to be meaningful. Similar problems were encountered by Baird and Steffgen (1977) while measuring the BET areas for nickel-aluminum flame-sprayed catalysts. Therefore, krypton gas was used for surface area measurements.…”

Fischer—tropsch studies on a plasma‐sprayed iron catalyst in a tube‐wall reactor

“…Similar trend has been reported by Feimer et al, 1981and Zarochak et al, 1982, but according to Dry, 1976, the influence of temperature is not always clearcut and its relative effect on selectivity seems to depend on the type of catalyst, temperature range being considered and on the process conditions. As reported in the literature, carbon dioxide is formed as a result of water-gas shift reaction (Dry et al, 1972;Baird et al, 1977;Feimer et al, 1981;Rofer-DePoorter, 1981;Arcuri, 1982). Thus, higher temperature favours the formation of lower molecular weight compounds.…”

“…Table 3 lists the weight percentages of hydrocarbons, water and COz obtained at different exposure velocities at 260"C, 6.89 X lo5 Pa and Hz/CO feed ratio of 2. As reported in the literature, carbon dioxide is formed as a result of water-gas shift reaction (Dry et al, 1972;Baird et al, 1977;Feimer et al, 1981;Rofer-DePoorter, 1981;Arcuri, 1982). A slight decrease in the extent of water gas shift reaction was observed at higher exposure velocities.…”