Abstract:
The aim of this study was to investigate the effects of various second promoters on Pt- Co/Al2O3 and Pt-Ce/Al2O3 catalysts for water gas shift reaction. For this purpose, seven metal oxides were used as the second promoters. Ni, K and Co were employed as the second promoter for Pt-Ce/Al2O3 and Ce, Mg, Mn, Fe and Zr were employed for Pt-Co/Al2O3. Pt- Co/Al2O3, Pt-Ce/Al2O3 were also studied for comparison. The catalysts were prepared by wetness impregnation method with 1.25 weight per cent promoter and 1.4 weight per cent platinum. The catalytic activity tests were conducted in a microreactor flow system. Total 100 ml/min gas reacted over 0.25 gr catalyst. Four different gas streams were used in experiments; one containing no CO2 and H2, one containing CO2 only, one containing H2 only and the last one containing both CO2 and H2. In addition, the effect of temperature and H2O/CO ratio was also investigated. It was found that Ni, K and Co addition to Pt-Ce/Al2O3 catalyst decreased the CO conversion while Ce, Mn, Fe and Zr addition to Pt-Co/Al2O3 improved the activity. Mg addition, however, did not have any significant impact in the absence of CO2 and H2. The conversion dropped in all the cases in the presence of CO2. The smallest decrease was observed in K containing catalyst. The activity of catalysts decreased more in the presence of H2 than CO2. With the addition of H2, the biggest and the smallest decreases were seen on Pt- Ce/Al2O3 and Pt-Co-Mg/Al2O3 catalysts, respectively. The presence of both CO2 and H2 had negative effects on all the catalysts studied. The effect of temperature at 275 and 250°C were also tested over Pt-Ce/Al2O3, Pt-Co-Ce/Al2O3, Pt-K-Ce/Al2O3 and Pt-Co-Fe/Al2O3 catalysts and the activity decreased with decreasing temperature for all the catalysts. Finally the effect of H2O/CO ratio was tested on Pt-Ce/ -Al2O3 and Pt-Co-Fe/ -Al2O3 at 275oC and it was found that CO conversion increased significantly as the H2O/CO ratio increased from 2 to 3 over Pt- Ce/ -Al2O3. On the other hand, no change was observed on Pt-Co-Fe/ -Al2O3 catalyst.
