Study of the water-gas shift reaction on Mo2C/Mo catalytic coatings for application in microstructured fuel processors

The activity and stability of two types of molybdenum carbide coatings deposited on molybdenum substrates (Mo2C/Mo) were compared in the water-gas shift reaction at 513–631 K. The activity of the Mo2C/Mo coatings obtained by carburization of preoxidized molybdenum substrates in a CH4/H2 mixture at 973 K decreased to 20% of the initial value after 23 h on stream at 631 K in a mixture containing 0.5 vol.% CO, 1.5 vol.% H2O and 40 vol.% H2 balanced by helium. The activity of the Mo2C/Mo coatings obtained by molten salt synthesis in a melt containing 5 wt.% Li2CO3 in an equimolar NaCl–KCl mixture at 1123 K for 7 h, was stable for more than 500 h on stream at similar reaction conditions. There was no evidence of methanation activity on both Mo2C/Mo coatings below 621 K. The kinetics of the WGS and reverse WGS reactions was measured on Mo2C/Mo coatings obtained by molten salt synthesis in a microstructured reactor operating in a differential mode. A combined power-law Eley–Rideal kinetic model is proposed to describe the reaction in the 531–631 K range. It was shown that, if molybdenum carbide is present as a thin layer over a molybdenum substrate (Mo2C/Mo), the catalytic activity is enhanced compared to that of the pure Mo2C phase.