The present invention concerns a process and a catalyst for the hydrogenation of the carbon oxides carbon monoxide and carbon dioxide. More specifically, this invention relates to a process for reacting or removing carbon oxides by hydrogenation using a catalyst comprising a support and an active component being of the composition of alloys of Ni, Fe and Co metals in oxide or reduced form.
The presence of carbon monoxide in feed gases is undesired in a number of processes.
In a fuel cell, such as a Polymer Electrolyte Membrane Fuel Cell, the presence of carbon monoxide is very critical since it can poison the noble metal electrodes used in fuel cells and therefore reduce their effectiveness.
Preferably, the CO concentration for fuel cell feed should be less than 100 ppm, more preferably less then 50 ppm. However, the initial concentration of CO, as received from the fuel processor, can exceed 1 wt %. Therefore, further reduction of CO concentration is required. Some of the typical methods for reducing CO concentration are selective catalytic oxidation of CO, pressure swing adsorption, hydrogen separation by membrane and methanation of CO.
Similarly, in ammonia production plants, the presence of CO is also highly undesirable in the ammonia synthesis reactor and the carbon oxide concentrations should usually be reduced to values as low as 5-10 ppmv.
Reacting carbon monoxide and carbon dioxide with hydrogen may also be used in the preparation of methane/synthetic natural gas (SNG). SNG can be produced by gasification of biomass or coal and subsequent methanation.
Methanation is a process where carbon oxides are reacted with hydrogen in the presence of a catalyst to produce methane and possibly smaller amounts of other lower hydrocarbons and water. In the known methanation processes, precious metals supported on a carrier as Al2O3, SiO2 or TiO2 have been used as a catalyst for CO methanation (U.S. Pat. No. 3,615,164 and WO 01/64337). These catalysts are usually able to reduce CO concentrations to values of about 500-800 ppm. Nickel-alumina catalysts, which are presently used in conventional methanation processes, contain large proportions of nickel, generally in excess of about 20 wt %. This requirement places certain limitations on practical methods for manufacturing such catalysts. In ammonia plants, methanation is mainly performed in the temperature range of 250° C. to 350° C. in the presence of Ni/Al2O3 catalysts. Modifications of such catalysts are desirable to achieve reduction and reaction at relatively lower temperatures than in the conventional design.
Alloying an active metal with a second active or inactive metal can change the catalytic performance drastically. For example with a monometallic iron catalyst and bimetallic copper-iron catalysts (E. Boellard, F. Th. van Scheur, A. M. van der Kraan, J. W. Geus, Appl Catal. A 171 (1998) 333. It has further been demonstrated that the reduction profile, carbon monoxide chemisorption properties and the Fischer-Tropsch activity were substantially altered by adding copper to the iron phase.
French patent application FR 863473-A describes a process for the production of hydrocarbons by hydrogenation of carbon monoxide in which the catalyst contains iron and nickel with an atomic ratio of 1:1.
Patent application US 2005/0096211 describes a catalyst for fuel cell applications, which is highly selective in CO methanation, prevents the conversion of CO2 into CO and suppresses CO2 methanation. The catalyst comprises a metal selected from the group consisting of ruthenium, nickel, iron, cobalt, lead, tin, silver, iridium, gold, copper, manganese, zinc, zirconium, molybdenum, other metals that form metal-carbonyl species and combinations thereof on a support.