Methane OSR over Pt-Ni/δ-Al2O3: Performance and power law type kinetics

Abstract

Methane oxidative steam reforming (OSR) performance of two bimetallic Pt-Ni/δ-Al2O3 catalysts, having Pt:Ni loadings, 0.2:10 and 0.3:10, were tested first. In the tests, residence time (W/F), carbon-to-oxygen (C/O2) feed ratio, and temperature were used as the experimental parameters. Increase in temperature resulted in direct and indirect - through enhanced TOX yielding higher energy - increase in SR rate. As Pt:Ni metal loading ratio did not lead to significant changes in activity, the preliminary kinetic tests to determine merely kinetically controlled region were conducted over 0.2Pt-10Ni catalyst. Considering the outcomes of the preliminary tests, the kinetic experiments were performed for practical reaction conditions extending up to 20% methane conversion with feed ratio intervals of 4.0 < C/O2 < 7.34 and 2.03 < S/C < 3.08 at two different residence time (W/F) values to obtain a power-law type rate equation. Reaction orders were estimated as 0.81, 1.60 and 0.44 for methane, oxygen and steam, respectively, by using multivariable non-linear optimization function of MATLAB™. The apparent activation energy of methane OSR was calculated as 24.61 kJ mol−1 and pre-exponential factor as 0.110 μmol mgcat−1 s−1 kPa−2.85 for the 375–450 °C temperature interval. The same analysis performed for a narrower temperature range, 375–425 °C, gave k0 and EA values as 0.251 μmol mgcat−1 s−1 kPa−2.85 and 29.17 kJ mol−1, respectively, confirming the high sensitivity of OSR pathway to temperature.