Construction Of Highly Dispersed Ru-based Nanocatalysts With Surface-interface Structure And Its Effect On Hydrodeoxygenation Of Lignin-derived Moleculars

With the economic development and social progress,people's demand for natural resources has been increasing rapidly,especially for fossil energy represented by coal,oil,and natural gas.The extensive combustion of fossil energy would result in serious environmental problems such as the pollution of the atmosphere,water,and soil.The energy supply of our country strongly relies on imports,which incurs a serious problem in energy security.Searching for green and renewable resources is of great significance to developing sustainable economies and societies.As a possible alternative,biomass resources are being studied extensively.Biomass comes from the photosynthesis of animals and plants which is easy to be acquired.As a representative,lignin-derived biomass can be obtained from fallen leaves and waste wood.These substances can be transformed into important raw materials such as synthesis gas and biomass crude oil after the treatment of gasification,liquefaction,and pyrolysis.On this basis,the required chemicals and fuels can be obtained by further processing.Pyrolysis of the biomass to produce bio-oils not only has a relatively fast reaction speed but also reduces the energy consumption in the process of biomass,therefore it has attracted special attention.Although some of the high-value chemicals can be separated from the bio-oils,it poses no small challenge because of their complex composition.Therefore,it is more economical to try to convert bio-oil into fuels that can be directly used by instruments and equipment.However,the numerous oxygen-containing compounds in bio-oil make it low in heat value and corrosive.It is necessary to be hydrodeoxygenation to remove the oxygen-containing functional groups from the molecule in the form of small molecules such as water and methanol.Hydrodeoxygenation of the biomass often requires catalysts.Supported metal catalysts are widely used in the research of hydrodeoxygenation.Metals in the supported catalysts usually play a decisive role in the catalytic reactions.The suitably regulated metal would be well dispersed on the supports and brings a superior reactivity of hydrodeoxygenation.It is worth noticing that the supports in the catalysts would also activate the model compounds.Apart from this,some of the supports can strongly interact with the supported metal,making the spatial configuration and charge distribution of the metal sites dramatically changed.Such changed metal sites would turn into an alternated reactivity of hydrodeoxygenation.Therefore,the study of the interactions between the metal and support,the support and reactant,also for the metal and reactant existing in the reaction will be helpful for understanding of the mechanism of biomass hydrodeoxygenation and improving the catalytic performance.In this regard,the thesis will focus on the design and synthesis of Ru-based metal catalysts with different compositions and structures.These catalysts were evaluated by anisole and guaiacol hydrodeoxygenation using water or n-decane as the solvent.The activity and selectivity of the catalysts can be well defined by the structure of the active components in the catalysts.Depending on the advanced instrument analysis,theoretical calculations,etc.,the relationship between the catalyst structure and catalytic performance has been deeply studied.Works in detail are listed below:1.MoO_x-ZrO₂ supported Ru catalysts for selective anisole hydrodeoxygenation:effect of metal-support interfaces with oxygen defectsMassive of MoO₃ was modified on nano-tetragonal ZrO₂.After the modification of the supports,Ru was loaded by the liquid-phase reduction method.In this way,Ru/MoO_x-ZrO₂ catalysts with affluent Ru^?+-O_v-Mo⁵⁺interfacial defects were constructed.According to the experiment results,the formation rate of benzene depended on the number of both Ru^?+species and oxygen defects with unpaired electrons,which verified that Ru^?+-O_v-Mo⁵⁺interfacial defects play an important role in the selectivity of benzene.Ru^?+-O_v-Mo⁵⁺interfacial defect sites can effectively inhibit the strong interaction between anisole and metallic Ru in aqueous solution,weakening the hydrogenation and demethylation process to yield methoxycyclohexane and cyclohexanol.At the same time,the interfacial defect sites can strongly interact with the methoxy group in anisole facilitating the demethoxylation of anisole to benzene.2.Study of the basic sites carried by MgO modification on ZrO₂ supported Ru catalysts in promoted guaiacol hydrodeoxygenation.MgO,as a solid base,was successfully modified on the surface of the nano-tetragonal ZrO₂ by the impregnation method,casting MgO-ZrO₂ supports with abundant basic sites.Subsequently,Ru was loaded on the surface of the support by the liquid-phase reduction method.The number of basic sites in the supported catalysts can be regulated by the MgO content and proved to affect the reactivity of guaiacol hydrodeoxygenation in an aqueous solution.The rate of guaiacol hydrodeoxygenation with MgO-ZrO₂ supported Ru with 16.6 wt%MgO content was 9 times higher than that of the catalyst without MgO modification.In situ FT-IR suggested that guaiacol tends to be adsorbed and activated on the metallic Ru and Ru-support interfaces.As for the MgO-modified catalysts,the basic sites on the support services as new active sites for guaiacol which facilitate the guaiacol conversion on the surface of the catalysts.3.Synthesis of structure-tunable pompon-like RuCo single-atom alloys and study on their catalytic performance in guaiacol hydrodeoxygenationThe one-pot method was exploited to synthesize RuCo single-tom alloy.Additionally,the pompon-like macrostructure of RuCo single-atom alloy can be maintained after a high-temperature reduction,however,the crystal phase and the distribution of the Ru atoms in RuCo single-tom alloy were dramatically changed.The RuCo single-atom alloy prepared after a 300?reduction with hexagonal alloy phase exhibits a better catalytic hydrodeoxygenation performance than that RuCo single-atom alloy with cubic alloy phase prepared in 600?.RuCo single-atom alloy with hexagonal alloy phase achieved full deoxygenation of guaiacol to cyclohexanol.Basing on the experiment results and DFT theoretical calculations,RuCo single-atom alloy with numerous atomically dispersed Ru-Co active sites would facilitate the hydrogen adsorption and activation.At the same time,RuCo single-atom alloy with hexagonal Co(110)facet exposure is more conducive to the adsorption and activation of guaiacol.The two synergetic effects above determined the excellent guaiacol hydrodeoxygenation performance of 300?reduced RuCo single-atom alloy.Through the above three parts of work,we have a new understanding of the metal-support interface sites,basic sites of the supports,active metal sites of the Ru-based catalysts in the biomass hydrodeoxygenation.These new insights will provide valuable references for the design and improvement of catalysts.