Gas phase hydrogenation of maleic anhydride at low pressure over silica-supported cobalt and nickel catalysts

The gas-phase hydrogenation of maleic anhydride over Ni/SiO2 and Co/SiO2 catalysts, prepared by the incipient wetness impregnation method, was studied. The catalytic tests were carried out at 1 bar pressure, between 170 and 220 degrees C and W/F-MA(0) in the range 5-25 g h mol(-1). In this work, the product distribution was different to those obtained at high pressures, previously reported in the open literature. Both Ni/SiO2 and Co/SiO2 catalysts were active for the selective hydrogenation of maleic anhydride (MA) into succinic anhydride (SA). Subsequently, SA was converted to gamma-butyrolactone (GBL) and propionic acid (PA). Neither tetrahydrofurane nor butanediol were detected at the reactor outlet. GBL/PA ratio was strongly depending on the metallic catalyst and temperature. At 170 degrees C, Ni/SiO2 was more selective to GBL than Co/SiO2. Besides. with Ni/SiO2, GBL formation rate diminished during the experiment while PA production showed a small increase. Instead, over Co/SiO2, both the PA and GBL formation rate decayed with time on stream. At 220 degrees C, Co/SiO2 showed a higher initial selectivity to GBL than Ni/SiO2. However, the GBL formation rate diminished more rapidly with Co/SiO2 than with Ni/SiO2. Thus, both catalysts gave similar selectivity to GBL after 3 h reaction at 220 degrees C. The observed catalyst deactivation was attributed to carbonaceous species of different nature deposited on the metallic phase during reaction. The amount and type of these species depends on both metal catalysts and reaction conditions. Selectivity and stability of Ni/SiO2 and Co/SiO2 catalysts is explained on the basis of their hydrogenolytic activity. (C) 2011 Elsevier B.V. All rights reserved.