Ca promoted Ni–Co bimetallic catalyzed coal pyrolysis and char steam gasification

Coal catalytic pyrolysis has been applied in the clean and efficient utilization of low-rank coal to obtain combustible gases and high value-added chemicals. Herein, Ni–Co–Ca catalysts were added into coal through impregnation for catalytic pyrolysis of Yunnan lignite and the char steam gasification. The H2 production reached 3.24 mmol/g of coal and the gas conversion was 27.84% of the coal pyrolysis under 5Ni–5Co–1Ca. The char conversion reached 98.21% and the H2 production was 90.68 mmol/g of char steam gasification. Ni and Co could promote coal catalytic pyrolysis by cracking the C–H and C–C bonds. The formation of Ni–Co alloy could prevent catalysts inactivation due to the metal oxidation, lattice distortion and carbon deposition. Density functional theory (DFT) calculations indicated that the electron transfer from Co to Ni has been improved due to the Ca promoting effect, enhancing Ni catalytic activity and promoting coal pyrolysis for more small gaseous molecules. Ca could endow char with abundant pore structure, improving the irregular degree of char crystallite structure, which was attributed to the char gasification at high temperature to obtain H2. This study provided guidance to modulate pyrolysis products distribution by regulating catalysts properties.