Methane steam reforming at low steam to carbon ratios over alumina and yttria-stabilized-zirconia supported nickel-spinel catalyst: Experimental study and optimization of microkinetic model

Abstract

An experimental work to acquire reaction kinetic data of methane steam reforming (MSR) to produce syngas was carried out over alumina and yttria-stabilized-zirconia (YSZ) supported nickel-spinel catalyst (Ni-spinel). With the aim of making MSR more energy efficient, the catalyst was tested at 1.25 and 1.50 steam to carbon (SC) ratios, slightly higher than the stoichiometric ratio of 1.0 but far less than normally considered 3.0. The experiments were conducted at isothermal plug-flow conditions and at near atmospheric pressure in a laboratory scale quartz reactor for five different space times (STP) between 55ms and 277ms at three different temperatures of 973K, 1073K, and 1123K. Reaction kinetic data of MSR over Ni-spinel catalyst are presented in terms of methane conversion and products yield or selectivity. To simulate measured kinetic data in a 1D plug-flow reactor model, a surface microkinetic model of MSR over nickel based catalyst was adopted from the literature and validated by optimizing the kinetic parameters of the most influential elementary reaction steps. A stepwise approach based on a partial equilibrium analysis and a local sensitivity analysis was implemented to scrutinize the most influential elementary reaction steps. With the adjustment of only 12 parameters out of 78, the optimized microkinetic model predicted the exit flow rates of chemical species accurately for the entire operating space. Adsorption of H2O, desorption of H2(s), and reaction pairs of surface dehydrogenation of CH4(s) and CH2(s) or formation of CH(s) were found to be the most influential reaction steps for the studied operating conditions. Surface coverages of H(s), CO(s) and H2O(s) were increased in the case of optimized microkinetic model of Ni-spinel catalyst compared to the original microkinetic model. Increased surface coverage of H2O(s) in the case of optimized microkinetic model supports the experimental finding in the literature that the introduction of yttria to zirconia increases the activity of the oxygen pumping component.