A study on kinetics of methane oxidative steam reforming (OSR) over PPt-Ni/δ-Al2O3 bimetallic catalysts

Abstract

The aim of the current study is to obtain a reliable power law type rate expression for methane OSR over Pt-Ni/δ-Al2O3 catalyst valid for practical experimental condition ranges. In this context, 0.2wt.%Pt-10wt.%Ni/δ-Al2O3 and 0.3wt.%Pt-10wt.%Ni/δ-Al2O3 catalysts were prepared by sequential impregnation method. Methane OSR performance of these catalysts were tested for constant S/C feed ratio at 450 °C. The performance test results showed that increasing residence time and C/O2 feed ratio decreased OSR activity, whereas increase in temperature led to higher methane conversions. As the effect of Pt:Ni metal loading did not lead to significant changes in activity, the following preliminary kinetic tests were conducted over 0.2Pt-10Ni catalyst to determine kinetically controlled, mass transfer limitations free, experimental conditions. Based on the outcomes of the preliminary test results, the kinetic study was performed at 375 °C with feed ratio regions of 4.0 < C/O2 < 7.34 and 2.03 < S/C < 3.08. 17 pairs of kinetic experiments were conducted by changing partial pressures of reactants, methane, oxygen, and steam, and residence time, W/F. Reaction orders were estimated as 0.81, 1.60 and 0.44 in methane, oxygen and steam, respectively, by using multivariable non-linear optimization function of MATLABTM. The apparent activation energy of methane OSR was calculated as 31.99 kJ mol-1 and pre-exponential factor as 0.366 μmol mgcat-1 s-1 kPa-2.85 for the 350-425 °C temperature interval. The same analysis performed for a narrower temperature range, 350-400 °C, i.e. 375+ 25 °C, gave k0 and EA values as 0.956 μmol mgcat-1 s-1 kPa-2.85 and 39.05 kJ mol-1, respectively, confirming the high sensitivity of OSR pathway to temperature.