Preparation And Modification Of Cerium-based Catalysts And Its Study On Hydroliquefaction Of Rice Straw For Bio-oil Production

With the massive consumption of non-renewable energy and the worsening of environmental problems,the voice of using renewable energy to replace non-renewable energy is increasing day by day.As the renewable carbon resource,biomass has great potential for application in the production of various high-value-added chemicals and fuels.Rice straw is one of the most abundant biomass resources in nature,hydroliquefaction of rice straw to produce liquid bio-oil can not only reduce the environment pollution,but also achieve the purpose of rational use of resources and changing the waste into treasure.Since bio-oil oatined by direct liquefaction has low bio-oil yield and low calorific value,it is of great significance to develop an efficient and cheap method to increase the bio-oil yield and obtain the target compounds.In this paper,a series of Ni/CeO₂ catalysts with different Ni/Ce molar ratios were prepared by hydrothermal method and applied to the catalytic hydroliquefaction of rice straw.The impacts of reaction conditions such as reaction temperature,reaction time,initial H₂pressure and Ni/Ce molar ratios on the rice straw catalytic hydroliqefaction,as well as the effects of catalyst on the chemical composition and calorific value were investigated.Furthermore,the mechanism of Ni/CeO₂ catalyst for hydroliquefaction of rice straw was also studied.The results showed that the optimal reaction conditions of rice straw catalytic hydroliquefaction were as follows:the reaction temperature was 290°C,the reation time was1.0h,the initial H₂ pressure was 2.0MPa and the Ni/Ce molar ratio was 2/10.Under these conditions,the highest conversion of rice straw and bio-oil yield were 89.09%and 66.7%,respectively.The reaction temperature,the reaction time and the initial H₂ pressure greatly affect the composition of bio-oil.Under the optimal reaction conditions,the bio-oil contains high content of phenolic compounds.When adding the Ni/CeO₂ catalysts with different Ni/Ce molar ratios,the contents of acids and ketones decreased,and the content of oxygen in bio oil decreased,resulting in the increase of their calorific value.After five cycles of Ni/CeO₂catalyst,the bio-oil yield decreased only 3.8%,indicating that the catalyst has good cycle stability.In addition,metal?Co,Cu?modified CeO₂ catalysts were also prepared by hydrothermal method,and their catalytic performances were compared with the Ni/CeO₂ catalyst.The results show that the catalytic activities of the three metals?Ni,Co and Cu?modified CeO₂catalysts were Ni/CeO₂>Co/CeO₂>Cu/CeO₂.Transition metals?Ni,Co and Cu?modified CeO₂ catalysts have different selectivity for products produced in bio oil,and Co/CeO₂ and Cu/CeO₂ catalysts are favorable for the formation of phenolic compounds.The highest proportion?86.31%?of C7-C10 compounds and the lowest proportion?5.73%?of C11+compounds were obtained over Ni/CeO₂.The highly dispersed Ni nanoparticles and their stronger interaction between Ni and CeO₂ with more oxygen vacancies enhance the performance of hydrodeoxygenation,which facilitates higher conversion of rice straw and bio-oil yield.