WGS kinetics over Pt-based trimetallic catalyst under realistic conditions

Abstract

The aim of this study is to obtain a reliable power law type kinetic expression under realistic conditions for water-gas shift reaction over 1Pt-0.5Re-1V/CeO2 catalyst to be used in designing the WGS unit of a small scale fuel processor. In this content, 1Pt-0.5Re1V/CeO2 catalyst was prepared using incipient-to-wetness impregnation method and the preliminary kinetic tests were conducted to determine kinetically controlled and mass transfer limitations free experimental conditions. The kinetic experiments were performed at 350 °C and atmospheric pressure with S/C feed ratio ranging from 15 to 45. 17 pairs of kinetic experiments were conducted according to an experimental design having partial pressures of carbon monoxide, steam, hydrogen, carbon dioxide and methane, and residence time, W/F, as the parameters. Experimental rate data were used to estimate kinetic parameters of the power-law kinetic model by using the method of initial rates. WGS reaction orders were estimated as 0.82, 0.31, -0.29 and -0.35 for carbon monoxide, steam, hydrogen and carbon dioxide, respectively, by using non-linear regression analysis in MATLABTM within ±6% error margin. Results indicated that the reaction rate increased with an increase in the concentration of CO and H2O in the feed stream, while it decreased slightly with the addition of H2 and CO2. In addition, the effect of methane presence in the feed on WGS kinetics was investigated, and the kinetic reaction rate was found to be practically independent of the concentration of CH4 in the feed stream as there was no change in the predicted reaction orders of CO, steam, H2 and CO2 in the absence and presence of methane term in the rate expression. The apparent activation energy and the frequency factor were calculated as 28.21 kJ mol-1 and 29.09 μmol mgcat-1 s-1 kPa-0.49, respectively in a temperature range of 300-350 ºC.