Mechanistic insights into copper slag as a thermal carrier and catalyst in lignite steam gasification: Experimental and DFT study

In order to explore the catalytic mechanism and optimize the operating parameters of copper slag as a thermal carrier in the coal gasification process, this study integrates experimental investigations with DFT calculations. TGA and characteristic reaction experiments, the effects of copper slag addition on the steam gasification of lignite were systematically examined. The presence of copper slag significantly inhibits volatile release while promoting char gasification by providing heat and participating in catalytic redox reactions. Conversely, copper slag enhances the adsorption and dissociation of H2O, significantly promoting the PWG (coal primary water gasification) reaction. DFT calculations were performed using the Dmol3 module to provide atomic-level insights into the catalytic mechanism of copper slag. Zigzag and armchair coal char edge models were constructed to simulate the interactions between carbon edges and Fe2SiO4, the primary catalytic component of copper slag. Analysis of electronic structure, differential charge density, and frontier molecular orbitals (HOMO and LUMO) indicates that copper slag alters the electronic environment of coal char, reducing its adsorption affinity for CO2 while enhancing its interaction with H2O. Adsorption energy and reaction energy barrier calculations further confirm that CO2 adsorption is the rate-limiting step for the CGR(coal CO2 gasification) reaction, while H2O dissociation is the rate-limiting step for the PWG reaction. These results not only demonstrate the dual role of copper slag as a thermal carrier and catalytic promoter but also provide theoretical guidance for improving gasification efficiency, increasing hydrogen selectivity, and advancing the clean utilization of coal resources.