Catalytic upgrading of Hami coal pyrolysis volatiles over NiO-loaded calcined/acid/alkali-modified kaolin

The catalytic upgrading of coal pyrolysis volatiles represents a crucial route for the value-added utilization of low-rank coal. This study addresses the role of kaolin support modification in controlling the performance of NiO-based catalysts for this process. A series of NiO catalysts were synthesized via precipitation-deposition on kaolin supports subjected to different pre-treatments: calcination (MK800, CK1100), acid-modification (AMK800), and alkali-modification (ACK1100). Comprehensive characterization established a clear structure–activity relationship. The strong metal-support interaction in NiO/Kaolin catalysts facilitated high NiO dispersion, enhanced redox activity, and increased accessible sites density. Beyond the redox activity of NiO, modification strategies also critically influenced the textural and acidic properties. While NiO infilled micropores in the pre-etched AMK800 and ACK1100 with high specific surface area to form mesoporous networks, it induced leaching and pore generation in the solely calcined supports. Catalytic tests in upgrading Hami coal pyrolysis volatiles revealed superior performance of the NiO/Kaolin systems over bare supports, arising from a synergy between NiO redox sites and surface acidity. This synergy promoted oxidative cracking and deoxygenation, elevating the light tar fraction to 63.7–71.9 wt% (from 42.9 wt%) and reducing the tar O/C ratio by 16.3%–53.4% compared to non-catalytic pyrolysis. The 10NiO/AMK catalyst delivered optimal tar lightening and BTEX yield (increasing from 4.6 mg/g to 12.8 mg/g), whereas 10NiO/ACK achieved the highest deoxygenation efficiency and aromatic selectivity. This work clarifies how targeted kaolin modification dictates catalyst architecture and function, providing a foundation for designing efficient, clay-based catalysts for industrial tar upgrading.