Yanchun Shi

Catalytic hydrodeoxygenation of palmitic acid over a bifunctional Co-doped MoO2/CNTs catalyst: an insight into the promoting effect of cobalt

Novel Co-doped MoO2/CNTs catalysts were prepared by a wet-impregnation method and employed in catalytic hydrodeoxygenation (HDO) of palmitic acid. The obtained catalysts were systematically characterized using various techniques, namely, XRD, BET surface area, XPS, FT-IR spectroscopy of adsorbed pyridine, Raman, H2-TPD, and H2-TPR. Characterization studies revealed the doping of Co ions into the lattice of MoO2, the interaction between metal species modified the electrical properties of the catalytic active sites, and the formation of new active sites and defects. The catalytic results showed that Co ions could significantly improve catalytic performance, and the best selectivity to hexadecane reached 89.3% at an extremely low temperature of 180 °C. The increased presence of Mo2C particles, Lewis acidic sites and oxygen vacancies were all responsible for the noticeable catalytic performance of the Co doped catalyst. The mechanistic insights from this work confirmed the bifunctional role of Co-doped MoO2/CNTs catalysts for HDO of palmitic acid, which was catalyzed either solely by Mo2C or synergistically by Mo2C and MoO2. Insights into the nature of the active site would provide a useful knowledge for rational design of effective Mo-based HDO catalysts and assist future studies on more efficient catalytic conversion systems.

Upgrading of palmitic acid to iso-alkanes over bi-functional Mo/ZSM-22 catalysts

Bi-functional Mo/ZSM-22 catalysts were designed to upgrade palmitic acid and further to isomerize n-alkanes. Besides the effects on acidity, H+ cations might be beneficial for the distribution of MoOx particles, the higher surface Mo/Si ratio and the greater surface Mo4+ content of bi-functional Mo/ZSM-22 catalysts. In the upgrading of palmitic acid, strong acid sites of catalysts were proven to favor hydrodecarbonylation (HDC), isomerization and cracking. Mo6+ (or MoO3) preferred to support the HDC reaction, whereas Mo4+ (or MoO2) suitably improved the hydrodeoxygenation (HDO) reaction without carbon atom loss. That is, the Mo4+/Mo6+ ratio of Mo/ZSM-22 catalysts significantly influenced HDO/HDC selectivity. More importantly the improvement in HDO rather than HDC with the complete conversion of palmitic acid, could significantly decrease the negative effects of strong acid sites (such as HDC and cracking) to facilitate isomerization of n-alkanes to afford more branched alkanes with a higher iso-alkanes/n-alkanes ratio.

Recent progress on upgrading of bio-oil to hydrocarbons over metal/zeolite bifunctional catalysts

Upgrading of bio-oil is of high necessity and popularity in converting biomass to high-quality hydrocarbons (transportation fuels and petrochemicals) to reduce the overall CO2 emissions of fossil based materials. There are hundreds of different oxygenated compounds identified in bio-oil, resulting in a high oxygen content (30% to 50%). This review focuses on recent progress in the upgrading of bio-oil over metal/zeolite bifunctional catalysts, with model compounds and real bio-oil included. Firstly, typical model compounds and corresponding reaction routes are summarized, based upon the composition of the bio-oil and a basic knowledge of chemical reactions. Secondly, careful analyses are conducted on the deoxygenation mechanisms over different metal active centers and acid-catalyzed reactions, such as isomerization and cracking, over zeolitic acid sites, respectively. Moreover, detailed analyses have focused on the effect of metal loadings on zeolites, the effects of zeolitic porosity and acidity on the metal, and their overall effects on reaction activity, selectivity and stability. Thirdly, the fundamental understanding of the interaction between the metal centers and zeolite acid sites in bifunctional catalysts and their influences on complex reaction networks, including deoxygenation and acid-catalyzed reactions, is analyzed. The metal/acid balance may be the key in improving the catalytic activity and product selectivity in the upgrading of bio-oil, which needs further careful design. Finally, the potential challenges and opportunities for the upgrading of bio-oil over metal/zeolite bifunctional catalysts are outlined.

Upgrading of palmitic acid over MOF catalysts in supercritical fluid of n-hexane

The addition of phosphotungstic acid (PTA) to the synthesis mixture of PdCu@FeIII–MOF-5 yields the direct encapsulation of PTA inside the MOF structure (i.e. PTA@PdCu@FeIII–MOF-5) through a facile solvothermal approach. The deoxygenation reaction of palmitic acid has been investigated over PdCu@FeIII–MOF-5 and PTA@PdCu@FeIII–MOF-5 under a hydrogen atmosphere in the supercritical fluid (SCF) of n-hexane. The results showed that palmitic acid can be converted completely at 240 °C on PTA@PdCu@FeIII–MOF-5 with a high selectivity of hexadecane. Owning to the improvement of acidity of the MOF catalyst by the encapsulation of PTA inside the hollow octahedral nanostructures of PdCu@FeIII–MOF-5, the selectivity for hexadecane over the PTA@PdCu@FeIII–MOF-5 catalyst is higher than that over PdCu@FeIII–MOF-5. The excellent performance in the catalytic hydrodeoxygenation (HDO) of palmitic acid is associated with the synergistic effect between yolk–shell PTA@PdCu@FeIII–MOF-5 nanostructures and SCF medium.