Efficient in-situ transfer hydrogenation of palmitic acid into alkanes over Ni/CexZr1-xO2 solid solution catalysts in aqueous medium with methanol as the hydrogen donor

Abstract

Compared to adding high-purity H₂, converting microalgae-oil into high-quality fuel through in-situ transfer hydrogenation is more economical and safer. Multiple Ni/Ce_xZr_1-xO₂ catalysts were prepared using the co-precipitation method and evaluated for in-situ transfer hydrogenation for palmitic acid (PA) with methanol as the hydrogen donor. The results indicated that, compared to Ni/ZrO₂ and Ni/CeO₂, the catalytic activity of all Ni/Ce_xZr_1-xO₂ has been significantly improved by the formation of solid solutions. Wherein, Ni/Ce_0.8Zr_0.2O₂ possessed the best catalytic effect, surpassing commercial Pt/C. And under optimized conditions (330 °C, 4 h, and 9.6 mmol methanol), Ni/Ce_0.8Zr_0.2O₂ (15 wt% Ni-loading) achieved the highest palmitic acid conversion of 93.6 % and alkane yield of 90.4 %. The excellent performance of Ni/Ce_0.8Zr_0.2O₂ was attributed to the combined effect of larger BET surface area, smaller particle size, stronger H-adsorption capacity and spillover hydrogen effect, more surface defects and oxygen vacancy concentrations. The stability testing showed that after four cycles, the main products over Ni/Ce_0.8Zr_0.2O₂ changed from alkanes to methyl palmitate. And the catalyst deactivation was caused by multiple factors such as the decomposition of Ce_0.8Zr_0.2O₂, aggregation and leaching of Ni, and carbon deposition.