Catalytic hydroliquefaction of rice straw for bio-oil production using Ni/CeO2 catalysts

A series of Ni/CeO2 catalysts were synthesized via a simple one-pot hydrothermal method and characterized by XRD, SEM, TEM, EDX, EDX mapping, Raman, H-2-TPR, BET, XPS, TGA and ICP-MS. Their catalytic performances were systematically evaluated in hydroliquefaction of rice straw. The impact of reaction temperature, reaction time, H-2 pressure and Ni/Ce molar ratios on product yields and distribution was also investigated. The conversion (89.08%) of rice straw and bio-oil yield (66.7%) obtained over Ni/CeO2 catalyst with a Ni/Ce molar ratio of 2/10 are superior to those over no catalyst (conversion of 73.65%, bio-oil yield of 47.96%) and pure CeO2 catalyst (conversion of 77.79%, bio-oil yield of 56.67%) under the optimum condition (290 degrees C, 1.0 h, and 2.0 MPa H-2 pressure). GC-MS results show that the main components of bio-oil are phenols, which are high value-added, important and useful chemicals in transportation and chemical industries. It is worth noting that the highly dispersed Ni nanoparticles and their stronger interaction between Ni and CeO2 with more oxygen vacancies facilitate high conversion of rice straw and bio-oil yield. In addition, a possible catalytic mechanism of Ni/CeO2 catalyst for hydrogenation of rice straw is accordingly proposed. This work thus offers an effective approach to improve the conversion of rice straw and bio-oil yield over Ni/CeO2 catalysts.