Tuning Al-modified MCM-41 acidic supports by post-grafting for Pt-based bifunctional hydroconversion of n-hexadecane to jet fuel fractions

The hydroconversion of green diesel over metal–acid bifunctional catalysts is a crucial step for producing bio-jet-fuel-range hydrocarbons, but diffusion limitations in acidic supports often promote secondary cracking and reduce C 9 –C 14 selectivity. Herein, commercial Al-MCM-41 prepared by direct hydrothermal synthesis was used as a commercial benchmark, while commercial siliceous MCM-41 was post-grafted with AlCl 3 , Al(i-PrO) 3 , and Al(NO 3 ) 3 to prepare Al-modified MCM-41 supports. Pt was subsequently loaded to construct bifunctional catalysts for n-hexadecane hydroconversion. Compared with the Pt/Al-MCM-41 benchmark, the post-grafted Pt/MCM-41-Al catalysts showed higher n-C 16 conversion, higher C 16 isomer yields (52.4–61.8%), and improved C 9 –C 14 jet-fuel-range yields (30.3–33.7%). Structural characterization suggested that the post-grafted samples contained Al-derived acid sites in more accessible surface- and pore-wall associated environments of MCM-41. Moreover, the Al precursor strongly affected Al retention and mesoporous structure preservation; Al(i-PrO) 3 and Al(NO 3 ) 3 better maintained open mesoporous channels than AlCl 3 , which is favorable to the transport behavior of bulky hydrocarbon molecules. These results highlight the importance of simultaneously tuning acid-site exposure and lowering effective transport resistance for efficient long-chain alkane hydroconversion to bio-jet-fuel-range hydrocarbons.