Selective formation of methane in reduction of CO2 with water by Raney alloy catalyst

The reduction of carbon dioxide with water has been investigated for the di rect synthesis of methane in the presence of Raney alloy. The reduction of CO2 using Raney Fe in an aqueous alkali solution gave selectively an alkali formate 32.9% based on the alkali employed. The similar reaction using Ran ey Ni gave methane (25.7%) in high selectivity together with a small amount of an alkali formate (4.2%). The mixed catalyst of Raney Fe and a supporte d ruthenium catalyst on activated carbon (Raney Fe-Ru/C) exhibited a high c atalytic activity for the reduction of CO2 and gave exclusively methane in moderate yield (45.3%). The reaction products were also controlled by the r eaction temperatures, i.e., the yield and selectivity of methane increased with an increase in the reaction temperatures by suppressing the formation of an all;ali formate. The apparent activation energy for the formation of methane was estimated to be 17 kcal/mol for the Raney Fe-Ru/C mixed catalys t in aqueous NaOH solution. The mechanism for the unique methanation of CO2 involving formate intermediate is discussed. (C) 1999 Elsevier Science B.V . All rights reserved.