Yuxue Xiao,Qingwei Meng,Xiaoli Pan,Chao Zhang,Zaihui Fu,Changzhi Li
para-Xylene (PX) is a basic building block of polyethylene terephthalate, which is currently produced from petroleum resources. Developing a renewable route to PX is highly desirable to address both economic and environmental concerns. Several attempts used noble metal catalysts, e.g. Pd/Al2O3, to synthesize PX from biomass-derived 4-methyl-3-cyclohexene-1-carboxaldehyde (4-MCHCA), but suffered from a severe decarbonylation reaction, resulting in toluene as the main product. In this paper, we report an FeOx modification strategy to suppress the decarbonylation reaction on a Pd/Al2O3 catalyst, leading to a drastic shift in selectivity towards PX with a yield up to 81% via a cascade dehydroaromatization–hydrodeoxygenation (DHA–HDO) pathway. Characterization and control experiments revealed that the electron density of Pd sites decreased in an FeOx-modified Pd/Al2O3 catalyst compared to Pd/Al2O3, thus tuning the preferential adsorption mode of the substrate from η2-(C,O), the key transition state of the decarbonylation reaction, to the η1-(O) mode that favors the hydrodeoxygenation process. Notably, this designed catalyst is highly stable and is readily applicable in the selective synthesis of a broad range of desired aromatic chemicals via the same DHA–HDO pathway from cyclohex-3-enecarbaldehyde derivatives. Overall, this work develops a controllable catalyst modification strategy that tailors an efficient catalyst for petroleum-independent bio-PX synthesis.
The decarbonylation of biomass-derived fatty acids offers a green and sustainable route to high-value long-chain alkenes. Nitrogen-doped carbon-supported cobalt (Co-NC) catalysts have emerged as promising candidates for fatty acid decarbonylation, attributed to their exceptional catalytic activity and cost-effectiveness. However, identifying the active sites and elucidating the reaction mechanism remain significant challenges. To address these issues, we developed Co single-atom-rich catalysts (CoPc/MWCNT and pyrolyzed derivatives CoPc/MWCNT-X) via the impregnation of cobalt phthalocyanine onto multiwalled carbon nanotubes (MWCNTs), followed by pyrolysis. These catalysts exhibited a high stearic acid decarbonylation activity, increasing the heptadecene yield from 12.9 to 47.4%, with an alkene-to-alkane ratio of up to 4.3. Comprehensive characterization and control experiments conclusively demonstrated that Co single-atom sites serve as the active sites, while coexisting Co/CoO nanoparticles showed negligible activity and no synergistic effects. In situ DRIFTS revealed carbonyl group adsorption on Co single atoms, with DFT calculations confirming directional alkene production via C–O bond cleavage. This work establishes a facile synthetic strategy for high-performance decarbonylation catalysts and unambiguously identifies the critical single-atom active sites while enabling a profound understanding of fatty acid conversion mechanisms.
Herein, the Ni–Co alloy supported on TiO 2 catalysts were prepared by sol–gel method assisted with Polymethyl Methacrylate (PMMA) template, and they were tested for in situ aqueous phase hydrodeoxygenation (HDO) of methyl palmitate to hydrocarbons using methanol as hydrogen donor. It has been found that the introduction of PMMA decreases the Ni–Co alloy particles size, reduces the metal-support interactions (SMSI), constructs the mesopores and enlarges the mesopore size. Also, the Ni–Co alloy particles can be partially embedded in TiO 2 , beneficial to the catalyst stability since the sintering and leaching of the Ni–Co alloy particles can be suppressed under hydrothermal condition. In the in situ HDO of methyl palmitate, the main deoxygenation pathway is decarboxylation/decarbonylation on the Ni–Co alloy catalysts. The catalysts prepared with PMMA exhibits higher activity than that without PMMA, giving the pentadecane yield of 86.2% at 310 °C. This is ascribed to their more exposed active sites and wider mesopores. Moreover, the catalyst is not obviously deactivated during five reactions.
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