NiCo/SiO2 nanospheres for efficient synergetic decarboxylation of fatty acids and upgrading of municipal sludge HTL bio-crude to biofuels

Municipal sludge (MS) and derived HTL (hydrothermal liquefaction) bio-crude contains a large quantity of organics, including fatty acids, which may be a potential resource for producing biofuels via catalytic treatment. Herein, decarboxylation of fatty acids is chosen as the model reaction to screen a series of nickel-based bimetallic catalysts supported on homemade SiO2 nanospheres to investigate the synergetic effect. NiCo/SiO2 turned out with the best performance compared to NiCu-, NiZn-, NiMo-and NiFe/SiO2. An 83% conversion of stearic acid and an 84% selectivity of heptadecane via hydrothermal decarboxylation were achieved at 280 degrees C under 1 MPa H2. XPS results revealed the electron transfer from Co to Ni, leading to the formation of Ni & delta;-, which is more accessible to bond with C & delta;+ in the carboxyl group of fatty acids, thus facilitating the decarboxylation reaction. Compared to commercial SiO2, our homemade SiO2 showed a stronger carbon accumulation resistance, indicating a medium specific surface area was essential. Both the synergetic effect of NiCo bimetal and the carbon accumulation resistance of homemade SiO2 nanospheres contributed to the efficient hydrothermal decarboxylation. The NiCo/SiO2 catalyst was further applied for upgrading of MS HTL bio-crude to biofuels, and the theoretical higher heating value (HHV) was significantly improved from 34.4 to 37.2 MJ/kg, suggesting the potential application of converting MS bio-crude to biofuels.

Automated summary

In this study, a series of nickel-based bimetallic catalysts supported on homemade SiO2 nanospheres were investigated for the decarboxylation of fatty acids. The NiCo/SiO2 catalyst showed the best performance, achieving high conversion and selectivity. The synergy between Ni and Co and the carbon resistance properties of homemade SiO2 contributed to the efficient decarboxylation reaction. The NiCo/SiO2 catalyst was also successfully applied for the upgrading of MS HTL bio-crude, resulting in a significant improvement in the theoretical higher heating value (HHV), indicating the potential for converting MS bio-crude to biofuels.