Partial Oxidation of n-Tetradecane over 1 wt % Pt/γ-Al2O3 and Co0.4Mo0.6Cx Carbide Catalysts: A Comparative Study

Catalytic partial oxidation (CPOX) of liquid fuels is being widely studied as an option for producing a hydrogen-rich gas stream for fuel cells. However, deactivation of catalysts by carbon deposition and sulfur poisoning in this process is a key technical challenge. Here, the deactivation of Co0.4Mo0.6Cx has been compared to that of 1 wt % Pt/γ-Al2O3 in a fixed-bed catalytic reactor, using mixtures of n-tetradecane and either 1-methylnaphthalene (1-MN) or dibenzothiophene (DBT) to simulate diesel fuel. The results show that Co0.4Mo0.6Cx is stable and active for the CPOX of n-tetradecane at 850 °C, 50000 scc/(gcat h), and an O/C ratio of 1.2. This catalyst produces slightly lower H2 and CO yields than Pt/γ-Al2O3, but still close to equilibrium values for 5 h. A low concentration of sulfur (50 ppmw as DBT) has little effect on either activity or selectivity for the carbide or Pt/γ-Al2O3 catalyst. However, the presence of 1-MN or a high sulfur concentration (1000 ppmw as DBT) deactivates both catalysts, resulting in reaction products that are typical of gas-phase reactions in a blank reactor. The addition of 1-MN or 1000 ppmw DBT to n-tetradecane produces qualitatively similar results on both catalysts: H2 production decreases continuously in the presence of either 1-MN or DBT, and CO drops to a stationary level. This drop in synthesis gas yields corresponds to an increase in steam, CO2, and olefin yields, suggesting that the contaminants deactivate sites that are active for steam and dry reforming reactions downstream of the reactor inlet, where rapid oxidation takes place. Once the contaminants are removed, initial activity returns more quickly for the carbide than for Pt/γ-Al2O3.