Medium-chain alkanes have strong ecological impacts on marine ecosystems due to their persistence, toxicity, and ability to travel long distances. Microbial degradation is the dominant and ultimate removal process for n-alkanes in the deep ocean, where high hydrostatic pressure (HHP) regulates microbial activity. To gain insight into the impact of hydrostatic pressure (HP) on n-alkane degradation, we applied the deep-ocean experimental simulation to culture Alcanivorax xenomutans A28, a novel piezotolerant bacterium strain from trench sediment, with n-C 16 as the sole carbon source under different HPs (0.1, 40, and 80 MPa). Activity analysis demonstrated that HHP stimulated the n-C 16 complete mineralization ratio. Transcriptomic and metabolomic analyses showed that HHP induced the intracellular oxidative stress and accelerated the tricarboxylic acid (TCA) cycle. These results indicate a shift of n-alkanes biodegradation pattern regulated by HP, elucidating the fate and ecological risk of n-alkanes in the deep ocean.
Graphical Bifunctional catalysts exhibiting significantly enhanced isomerization yields were synthesized by combining Pt-impregnated γ-Al 2 O 3 with ZSM-23 zeolite. The structures of the di-branched products were meticulously characterized. Furthermore, the influences of thermodynamic stability, zeolite pore structure, and substrate carbon number on product distribution were analyzed concerning the spacing of branched chains. Hydroisomerization of long-chain alkanes is a crucial process in producing high-performance fuel and lubricant base oils. The challenge in this process is enhancing catalytic performance by optimizing the intimacy between metal and Brønsted acid sites in bifunctional catalysts. In this study, a series of bifunctional catalysts with varying metal–acid site intimacy was prepared by depositing platinum (Pt) on the ZSM-23 zeolite or γ-Al 2 O 3 surface. The Pt/A + Z catalyst, exhibiting moderate intimacy, demonstrated superior catalytic performance in the hydroisomerization of n -hexadecane, achieving up to 64 ± 0.8% i-C 16 yield at 89 ± 0.5% conversion. The optimized metal–acid site intimacy facilitated the desorption of reaction intermediates, minimizing cracking at the acid sites and thus improving selectivity. Further analysis revealed that product distributions were closely related to the pore structure of zeolites. Specifically, the formation of di-branched isomers during the isomerization of n -hexadecane, n -dodecane, and n -octane was influenced by the type of zeolite support (ZSM-23, ZSM-48). The present study proposes a direct method to enhance the hydroisomerization performance while reducing the cost of the catalyst. By determining di-branched products more precisely, it introduces a novel approach for evaluating products based on branch chain spacing. Additionally, the combined effects of catalyst structure and thermodynamic stability on product distribution were investigated, along with the influence of reactant stay time.
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