Catalytic hydrothermal liquefaction of D. tertiolecta over multifunctional mesoporous silica-based catalysts with high stability

In this work, multifunctional mesoporous silica-based catalysts containing metal, acid, or base were successfully synthesized by doping metal cobalt through the impregnation-precipitation method and grafting amino and sulfonic groups by the silicon alkylation method. The catalytic hydrothermal liquefaction (HTL) of Dunaliella tertiolecta was performed at 533 K for 30 min. X-ray diffraction (XRD), small angle X-ray diffraction (SXRD), N2 absorption/desorption isotherm analysis, elemental analysis, inductively coupled plasma optical emission spectrometer (ICP-OES), and transmission electron microscopy (TEM) were employed to characterize SBA-15 and multifunctional mesoporous SBA-15. The hydrothermal testing on the obtained multifunctional mesoporous silica-based material were conducted in a stainless steel autoclave at 533 K for 30 min. SXRD, TEM, and N2 absorption/desorption isotherm analysis results showed that Co doping and sulfonic group grafting, but not amino group grafting, could improve the hydrothermal stability of SBA-15. The results of TEM, XRD, and ICP-OES confirmed that Co existed in the form of Co3O4 and entered into the SBA-15 skeleton. Meanwhile, the results of elemental analysis and ICP-OES showed that amino and sulfonic groups were successfully grafted on SBA-15. Gas chromatography-mass spectrometry and elemental analysis were adopted to identify the composition of the obtained bio-oil. The bio-oil produced by the catalytic HTL of D. tertiolecta at 533 K for 30 min gained high contents of furfural and its derivatives, as well as low contents of acids, N-containing compounds, and esters, when NH2-SO3H-Co-SBA-15 and SO3H-Co-SBA-15 were used as catalysts. However, fewer conversions and lower bio-oil yields were obtained under the use of such catalysts than under catalyst absence.187