Kinetic assessment for the carburization mechanisms of tungsten trioxide in the presence of methane applied to hydrogen and syngas production

Abstract

This work presents the first kinetic determination of pre-exponential factor and activation energy for carburization of transition metal oxides’ reactions using methane and the assessment of the mechanisms to evaluate its application for novel systems. The transition metal oxide chosen was high purity tungsten trioxide (>99.9 wt%) due its physical chemistry properties that could potentially contribute to reforming reaction systems. The application of the Hancock and Sharp plots presented enough evidence to divide the total carburization process into two reactional mechanisms, which were studied separately using a Partitioning Method. The Generalized Reduced Gradient model was applied to minimize the error between the experimental conversion and each of the 17 kinetic models analyzed and the best model to describe the first mechanism is a nucleation Avrami Erofe’ev second order and the second mechanism is best described by the nucleation power law fourth order, under the tested conditions. Gas analyzes presented the gas evolution very distinct between both mechanisms, having a much superior production of syngas during the second stage of the overall reaction. XRD presented good evidence that the first mechanism could be the responsible for converting the tungsten trioxide (WO3) into its dioxide form (WO2) and the second mechanism is leading the conversion of tungsten dioxide into the transition metal carbide form (WC).