Molecular-level precise hydro-deconstruction over Al-modified dendritic mesoporous silica nanospheres supported CoMo catalysts: Alkyl positioning cracking and polycyclic aromatic preservation

Traditional hydrocracking faces challenges such as excessive alkane cracking, poor dealkylation selectivity and oversaturation of polycyclic aromatics (PAHs). This study developed a hydro-deconstruction catalytic system to precisely dissociate saturated and aromatic carbon structures while preserving product integrity. First, Al-modified dendritic mesoporous silica nanospheres (DMSNs- x , x is SiO 2 /Al 2 O 3 ratio) were synthesized as catalytic materials by hydrothermal method. The objective is to endow the material with suitable acidity and open mesoporous structures, enabling high selectivity for dealkylation and minimizing secondary cracking activity. The effects of aluminum doping on properties and precise dissociation performance of catalytic materials were systematically investigated. Increasing aluminum content enhanced acidity and shifted pore morphology from exterior-expanded mesopores to slit-like micropores. DMSNs-50 (0.28 mmol/g B acid, 15.7 nm pores) demonstrated outstanding alkyl positioning dissociation, achieving 68.4 % dodecylbenzene conversion with 86.5 % dealkylation selectivity, yielding 25.5 m% benzene and 26.8 m% C 9 -C 12 alkanes. Optimizing the active components for hydrogenation is essential to ensure moderate hydrogenation performance and maintain PAH structures. The 3 %CoMo-CM catalyst (3 m% MoO 3 , 0.7 m% CoO 2 ) showed optimal controlled hydrogenation, achieving less than 33 % conversion of phenanthrene, over 60 % selectivity of moderate hydrogenation, and more than 85 % retention of the PAH structure. Microstructural analysis of hydrogenation active phases indicates that the optimal sulfidation was about 38 %. At this point, the size and stacking number of formed MoS 2 slabs were 4.1 nm and 1.9 layers. This catalyst demonstrated excellent hydro-deconstruction for mixed hydrocarbons. It achieved 89 % dealkylation selectivity while retaining over 85 % long-chain alkane and 70 % aromatic ring. During reusability testing, the catalyst primarily deactivated due to the loss of B acid sites and the sintering of the hydrogenation active phase. This innovative catalytic system enables molecular-level transformation of petroleum resources, offering novel approaches for their efficient utilization.