Effect of pore characteristics on hydrogen reduction kinetics based on a novel analysis approach combined model-fitting and iso-conversion

Abstract

Carbon reductant used in metallurgy industry is a considerable source of carbon dioxide emissions. Growing concerns over greenhouse effect have urgently prompted research in the application of hydrogen energy as an alternative. However, some basic kinetic problems in the hydrogen reduction process have not been clarified and resolved yet, such as the activation energy fluctuations caused by neglect of pore characteristics, along with the overly subjective division of the whole reaction process to analyze rate limiting mechanisms. In this study, a novel approach for acquiring instantaneous activation energy is proposed that is able to identify the activation energy at every reaction moment and thereby provide a quantitative basis for kinetics segmentation and rate-limiting mechanism determination. Moreover, due to the space requirements, the activation energy for the reaction stage controlled by nucleation and nuclei growth has a strong correlation with specific surface area. Whereas the restriction mechanisms of chemical reaction and diffusion are closely related to the average pore size. These results reveal that the different pore characteristics and changes in value have a direct influence on the corresponding rate limiting mechanisms and restriction degrees.