Kinetic, mechanistic and optimization studies of catalytic methane dry reforming over light rare-earth oxides supported Co catalysts / Ayodele Bamidele Victor

Faculty of Chemical & Natural Resources Engineering

Thesis (Doctor of Philosophy of Engineering in Chemical Engineering) -- Universiti Malaysia Pahang – 2017

Bibliography : p. 76-84

Methane dry reforming has been reported as a promising technological route for mitigating greenhouse effect and has been widely investigated for syngas production using supported nickel (Ni)-catalysts. However, Ni-based catalysts are susceptible to sintering and poisoning which often lead to catalyst deactivation. Nowadays, there is a growing interest in the use of cobalt (Co)-based catalysts for methane dry reforming due to their stability. The use of Co/light rare earth oxides catalysts for methane dry reforming is a new study. This thesis therefore investigates for the first time the kinetics, mechanisms and optimization of methane dry reforming over 20wt%Co/CeO2, 20wt%Co/La2O3, 20wt%Co/Sm2O3, 20wt%Co/Nd2O3, and 20wt%Co/Pr2O3 catalysts. The catalysts synthesized by wet impregnation technique were assessed in a fixed bed reactor over CH4: CO2 ratio range of 0.1 to 1.0, and temperature range of 923 to 1023 K under atmospheric pressure. Interestingly, the catalysts displayed net-basic sites and good reducibility under H2 atmosphere. The activity tests gave the highest CH4 conversions of 79.50%, 47.67%, 71.00%, 62.70, and 41.49% respectively for 20wt%Co/CeO2, 20wt%Co/La2O3, 20wt%Co/Sm2O3, 20wt%Co/Nd2O3, and 20wt%Co/Pr2O3 at temperature of 1023 K and feed ratio of 1.0. At the same conditions, the highest CO2 conversions of 87.60%, 60.14%, 74.00%, 82.00% and 42.36% were obtained for 20wt%Co/CeO2, 20wt%Co/La2O3, 20wt%Co/Sm2O3, 20wt%Co/Nd2O3, and 20wt%Co/Pr2O3 respectively. The stability test showed that all the catalysts were stable until 20 h of time-on-stream (TOS). However, at TOS > 20 h, 20wt%Co/Sm2O3, 20wt%Co/La2O3, and 20wt%Co/Pr2O3 displayed decreased stability. The artificial neural network (ANN) and Box-Behnken design (BBD) models showed good prediction of the syngas yields. The optimum conditions of 1008 K, 47.87 kPa, and 48.92 kPa for the reaction temperature, CH4 partial pressure, and CO2 partial pressure respectively produced H2 and CO yields of 79.37% and 79.00% respectively using the 20wt%Co/Sm2O3 catalyst. The kinetic studies gave activation energies of 40.17, 88.88, 19.85 31.28, and 61.67 kJ mol-1 for the rate of consumption of CH4 over 20wt%Co/CeO2, 20wt%Co/La2O3, 20wt%Co/Sm2O3, 20wt%Co/Nd2O3, and 20wt%Co/Pr2O3 catalysts, respectively. The mechanistic model evaluated on the basis of statistical adequacy revealed that the methane dry reforming over the five catalysts can be described by 2-step dual site rate determining steps namely CH4 activation by Co and carbon (C) gasification by adsorbed CO2 on support site.