Effect of niobia addition on cobalt catalysts supported on alumina for glycerol steam reforming

Cobalt catalysts were prepared by wet impregnation of three distinct supports: alumina, niobia and 10 wt% niobia/alumina, prepared by wet impregnation of niobia precursor on alumina. Niobia addition decreased alumina acidity, improved catalyst reducibility and reduced the formation of spinel phases (CoAl2O4 and Co2AlO4). The catalysts were evaluated on steam reforming of glycerol for 30 h at 500 °C, GHSV of 200,000 h−1 and using a glycerol solution 20% v/v in feed. The best performance was obtained for the catalyst supported on Nb2O5/Al2O3 (CoNbAl), which presented the highest conversion into gas (90%) and hydrogen yield (65%) during the first 8 h of reaction. All the catalysts suffered deactivation after 24 h of reaction due to coke formation, but the nature of coke (amorphous or graphitic) and its formation mechanism is different for each catalyst. A more in-depth study on the effect of temperature on CoNbAl catalyst performance was conducted in the range from 400 °C to 600 °C, keeping glycerol concentration in feed at 40% v/v of glycerol and GHSV of 200,000 h−1. Hydrogen yield increased from 5% at 400 °C to 15% at 600 °C. A kinetic study was also performed for this catalyst, obtaining an apparent activation energy of 16.2 kJmol-1 by Arrhenius equation.