A novel development of mixed catalyst–sorbent pellets for steam gasification of coal chars with in situ CO2 capture

• A novel mixed catalyst–sorbent pellets for coal steam gasification was developed.
• A maximum hydrogen yield of 80% was obtained from coal steam gasification at 700 °C.
• The pellets with a catalyst content of 50% demonstrated the best performance.
• Lignite coal produced twice more hydrogen than sub-bituminous coal did.
• CO2 capture favored water gas shift and methane reforming reactions.

The main purpose of this research was the development of a mixed catalyst–sorbent for gasification and in situ CO2 capture; therefore, novel mixed catalyst–sorbent (composite) pellets were prepared with different contents of potassium carbonate and calcium oxide as the catalyst and sorbent, respectively. The pellets were used in steam gasification experiments of two different types of coal. The maximum hydrogen yield of 80% was obtained with 50% of the catalyst in the composite pellets and lignite Boundary Dam (BD) coal at 700 °C. Use of the catalyst enhanced the gasification and water–gas shift (WGS) reaction rates, while the capture of carbon dioxide (CO2) shifted the WGS equilibrium forward, favoring hydrogen production. Trace amounts of CO2 and carbon monoxide were detected. In terms of maximum achievable hydrogen yield, the pellets containing 50% catalyst demonstrated the best performance. As expected, BD coal (a low-rank coal) showed a higher reactivity than the Genesee sub-bituminous (a medium-rank coal) samples. Ultimate analyses and burn-off tests were performed on the residues to determine the amounts of unconverted carbon, and the results of these tests also confirmed the best performance of the pellets with a catalyst content of 50%. Despite the decreasing trend of pore surface area with increasing catalyst percentage, increasing the catalyst content of composite pellets to a certain level had a positive effect on hydrogen production. This indicates that the performance of pellets is almost independent of the pore surface area. Indeed, the optimal ratio is the result of the trade-off among pore surface area, dispersion, formation of a bimetallic solid phase, and the concentration of active catalyst sites on the pellets.

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