Influencing factors and reaction mechanism for catalytic CO2 gasification of sawdust char using K-modified transition metal composite catalysts: Experimental and DFT studies

Abstract

Gasification of renewable biomass, sawdust char in this study, was carried out with CO2 to observe the effect of the gasification temperature, CO2 adsorption, and K-modified transition metal composite catalysts; this was known as the Boudouard reaction. The catalysts were characterized using inductively coupled plasma-optical emission spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction analysis, BET surface area analysis, and scanning electron microscopy. The reaction mechanism of the catalytic gasification was investigated using thermogravimetry and density functional theory. The results showed that temperature was one of the most important operating variables for char gasification, and carbon conversion increased 2.55 times within 40 min when the temperature increased from 750 °C to 800 °C. Composite catalysts effectively improved the char conversion at low temperatures, and the order of catalytic performance was KCo > KNi > KFe > KCe. The catalytic CO2 gasification activity depended not only on the CO2 quantity adsorbed, but also on the CO2 decomposition activity on the catalyst surfaces. The CO2 reaction mechanism over Co, Ni, and Fe surfaces can be written as follows: M + CO2 → M-Oads + CO, M-Oads + C* → M + CO. Over CeO2 surface, the reaction mechanism was the following: CeO2 + C* → CeO2vacO + CO, CeO2vacO + CO2 → CeO2 + CO. These results can aid in the CO2 catalytic gasification mechanism and provide further theoretical guidance to improve the industrialization of biomass gasification.