Catalytic mechanism of inherent alkali and alkaline earth metals on energy crop char during the CO₂ gasification process

Abstract

The catalytic mechanism of inherent alkali and alkaline earth metals is crucial for enhancing the gasification efficiency of energy crop char with CO₂. In this study, the gasification reactivity and surface structural characteristics were investigated using a combination of thermogravimetric analysis, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Herein, the char samples were prepared from Arundo donax in a fixed-bed reactor. The results revealed that gasification reactivity of char-samples increased progressively as the temperature rose from 800 to 950 °C. Importantly, despite acid washing inducing a more disordered carbon structure with a higher defect density, the reactivity of the treated char was significantly reduced at the same temperature. Kinetic analysis further quantified that the average activation energy of biochar increased from 164.30 to 210.85 kJ·mol^‒1 after the removal of alkali and alkaline earth metals by acid washing. These results together indicated that the catalysis effects of alkali and alkaline earth metals played the key role on the gasification reactivity. Temperature-programmed desorption demonstrated that alkali and alkaline earth metals acted as catalytic active centers to optimize gasification reaction pathways by promoting carbon-oxygen surface active complex formation.

Graphical abstract

Keywords

char / alkali and alkaline earth metals / gasification / catalytic mechanism

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