Development of bimetallic nickel-based catalysts supported on activated carbon for green fuel production

Abstract

In this work, the catalytic deoxygenation of waste cooking oil (WCO) over acid-base bifunctional catalysts (NiLa, NiCe, NiFe, NiMn, NiZn, and NiW) supported on activated carbon (AC) was investigated. A high hydrocarbon yield above 60% with lower oxygenated species was found in the liquid product, with the product being selective toward n-(C₁₅ + C₁₇)-diesel fractions. The predominance of n-(C₁₅ + C₁₇) hydrocarbons with the concurrent production of CO and CO₂, indicated that the deoxygenation pathway proceeded via decarbonylation and decarboxylation mechanisms. High deoxygenation activity with better n-(C₁₅ + C₁₇) selectivity over NiLa/AC exposed the great synergistic interaction between La and Ni, and the compatibility of the acid-base sites increased the removal of oxygenated species. The effect of La on the deoxygenation reaction performance was investigated and it was found that a high percentage of La species would be beneficial for the removal of C-O bonded species. The optimum deoxygenation activity of 88% hydrocarbon yield with 75% n-(C₁₅ + C₁₇) selectivity was obtained over 20% of La, which strongly evinced that La leads to a greater enhancement of the deoxygenation activity. The NiLa/AC reusability study showed consistent deoxygenation reactions with 80% hydrocarbon yield and 60% n-(C₁₅ + C₁₇) hydrocarbon selectivity within 6 runs.

Fig. 1. X-ray diffractograms of the binary metal oxide-supported AC: (a) activated carbon (AC), (b) NiLa/AC, (c) NiCe/AC, (d) NiW/AC, (e) NiFe/AC, (f) NiZn/AC and (g) NiMn/AC.

Fig. 2. FESEM images of (a) AC, (b) NiLa/AC, (c) NiCe/AC, (d) NiW/AC, (e) NiFe/AC, (f) NiZn/AC and (g) NiMn/AC. (Magnifications ×50 000).

Fig. 3. Temperature-programmed desorption patterns of (a) TPD-NH₃ and (b) TPD-CO₂ of binary metal oxide-supported AC catalysts.

Fig. 4. Thermal gravimetric analysis profiles of the prepared AC and binary metal oxide-supported AC catalysts.

Fig. 5. Data collected from the deoxygenation process: (a) hydrocarbon yield and (b) n-(C₁₅ + C₁₇) selectivity for blank and catalysed deoxygenation (operating parameters: 3 wt% of catalyst loading, 350 °C reaction temperature, 2 h reaction time under inert conditions).

Fig. 6. Data collected from liquid deoxygenized liquid products: (a) product distribution, (b) FTIR spectra of the WCO and deoxygenized liquid product catalysed by AC and binary mixed oxide-supported AC (c) the compositions of CO₂ and CO gases over catalytic deoxygenation (operating parameters: 3 wt% of catalyst loading, 350 °C reaction temperature, 2 h reaction time under inert conditions).

Fig. 7. The proposed reaction mechanism for a Ni-based catalyst in the catalytic deoxygenation of WCO for (a) oleic acid and (b) palmitic acid.

Fig. 8. (a) Hydrocarbon yield, (b) hydrocarbon selectivity, (c) TPD-NH₃, (d) TPD-CO₂ for the catalytic deoxygenation of WCO over different concentrations of La (5–30 wt%).

Fig. 9. Optimization studies of WCO: (a and b) the effects of catalyst loading, parameters: 350 °C and 2 h reaction time. (c and d) The effects of reaction time, parameters: 350 °C and 3 wt% catalyst loading. (e and f) The effects of reaction temperature, parameters: 3 wt% catalyst loading and 2 h reaction time with a stirring rate of 300 rpm and under an inert atmosphere.

Fig. 10. Reusability studies of the Ni₂₀La₂₀AC catalyst for the 6^th run: (a) the hydrocarbon yield profile, (b) hydrocarbon selectivity.

Fig. 11. Stability studies of the Ni₂₀La₂₀AC catalyst for the 6^th run: (a) the XRD profile, (b) TGA, (ci) FESEM image for the fresh catalyst, (cii) FESEM image for the spent catalyst.