Tuning Surface-interface Structures Of Copper-based Catalysts And Its Catalytic Performance On Hydrogenation Of Carbon Dioxide To Methanol And Ethanol

Nowadays,the excess consumption of fossil fuels has caused massive release of greenhouse gas due to the rapid development of society and economy,thereby leading to more and more serious environmental issues（e.g.,global climate change and ocean acidification）.Among the greenhouse gases emitted,CO₂ has been recognized as the most dominant climate pollutant in the recent decades.Therefore,CO₂emissions ought to be controlled to reduce the adverse effects on the atmospheric environment.In addition,various technologies for Carbon Capture Utilization and Storage（CCUS）have been widely developed because it can not only alleviate caused global warming issue but also mitigate the dependence on non-renewable fossil fuels.The development of Carbon Capture Utilization and Storage also enables negative emission technologies,which are essential to solving serious environmental problems.Among the various approaches explored for controlling CO₂ emission,the catalytic hydrogenation of CO₂ to produce value-added fuels（e.g.,light olefins,alcohols,and oxygenates）is a very attractive approach because green water electrolysis can allow hydrogen to be produced at a large scale.Especially,methanol can be utilized to manufacture olefins,aromatics,while ethanol shows broader industrial applications as a renewable fuel additive and indispensable higher-energy-density engine fuel.Therefore,the catalytic CO₂hydrogenation into methanol and ethnaol has become a potentially strategic important process.For the methanol synthesis from CO₂ hydrogenation,although Cu/Zn O-Al₂O₃ catalyst was widely employed in the practical industrial process,some problems such as harsh reaction conditions（high reaction pressure and H₂/CO₂ratio）and poor catalyst performance still exist.Although supported Pd catalysts always exhibit good activity for CO₂hydrogenation to produce methanol,the utilization of noble metal catalysts is still not as common as copper-based catalysts,due to their high cost.For the ethanol synthesis from CO₂hydrogenation,the direct synthesis of ethanol via CO₂ hydrogenation is thermodynamically limited owing to the preferential production of CO or CH₄,which leads to extremely low selectivity to ethanol.The formation of ethanol from CO₂ is also much more difficult than methanol production due to the C-C coupling process involved.For the complex reaction system of CO₂hydrogenation to ethanol,researches have focused on the design of multifunctional catalysts with two or more active sites.Therefore,it is meaningful to develop high-performance catalyst materials for CO₂hydrogenation to methanol and ethnaol under mild reaction conditions.Furthermore,the special surface structure and interfacial sites of supported catalysts can provide key functionalities in complex catalytic reactions.Recently,many researchers devoted themselves to the design of favorable metal-support interfaces to promote CO₂ activation.The existence of special metal-support interface improves the adsorption and activation of CO₂ and hydrogenation of CO intermediate formed at Cu⁰ sites,as well as the stabilization of Cu particles.In addition,it was reported that special surface defective structures also often provided pivotal functionalities in complex multi-step catalytic processes.Previous DFT results indicated that the CO₂hydrogenation on the defective oxygen vacancy of catalyst surface was both thermodynamically and kinetically favorable.Therefore,modulating surface structure and interfacial sites of Cu-based catalysts is of great significance to govern their catalytic performance in the CO₂ hydrogenation to methanol and ethanol.Based on the above discussion,a series of Cu-based catalysts with various structures were constructed in this paper.Combined with structural characterizations,DFT calculation and catalytic results,the effects of electronic structures of the active metal and the interfacial structures of the catalyst on the performance of CO₂ hydrogenation to methanol and ethanol have been deeply explored.Detailed works are as follows:1.Tuning surface-interface structures of ZrO₂ supported copper catalysts by in situ introduction of indium to promote CO₂ hydrogenation to methanolA series of indium-doped ZrO₂ supported copper-based catalysts for CO₂hydrogenation were constructed via one-pot hydrogen bubble-assisted approach.It was manifested that the in situ introduction of indium facilitated the generation of interfacial defects in the form of Zr-O_v-In³⁺structure（O_v:oxygen vacancy）and interfacial Cu⁺sites,as well as surface basic sites originating from In-O pairs,and the catalytic performance of as-constructed In-doped Cu/ZrO₂catalysts could be efficiently promoted by tuning the indium content.Specifically,the Cu-based catalyst bearing the indium content of 4.0 wt%afforded the quite high space-time yield of methanol(0.398 g _{Me OH}·g^-1_cat·h^-1)at270 ^oC,while the one with the indium content of 8.0 wt%yielded an increased methanol selectivity by 1.8 times at 250 ^oC,compared with undoped one.Combining the structural characterizations with catalytic results,it was found that surface medium-strength and strong basic sites together with the contribution from interfacial defective oxygen vacancies and Cu⁺sites played key promotional roles on the synthesis of methanol.This finding enables us to design new high-performance Cu-based catalysts for CO₂ hydrogenation by finely turning their surface-interface structures.2.Efficient role of nanosheet-like Pr₂O₃ induced surface-interface synergistic structures over Cu-based catalysts for enhanced methanol production from CO₂ hydrogenationZnO-modified Cu-based catalyst over defect-rich Pr₂O₃ nanosheets for high-efficiency CO₂ hydrogenation to produce methanol was successfully constructed.It was demonstrated that as-fabricated nanosheet-like Cu-based catalyst presented several structural advantages including the formation of highly dispersive Cu⁰ sites and the coexistence of abundant defective Pr³⁺-O_v-Pr³⁺structures（O_v:oxygen vacancy）and interfacial Cu-O-Pr sites.Combining structural characterization and catalytic reaction results with density functional theory calculations,it was clearly unveiled that the synergy between surface defective structures and Cu-Pr₂O₃interfaces over the catalyst remarkably promoted the adsorption of CO₂ and CO intermediate,thus boosting the CO₂hydrogenation simultaneously via both the formate intermediate pathway and the intense reverse water-gas shift reaction-derived CO hydrogenation pathway,along with a high space-time yield of methanol of 0.395 g _{Me OH}·g^-1_cat·h^-1under mild reaction conditions（260℃and 3.0 MPa）.The study provides a new strategy to construct high-performance Cu-based catalysts for high-efficiency CO₂ hydrogenation to produce methanol and a deep understanding of the promotional roles of synergy between surface-interface active sites in the CO₂ hydrogenation.3.Ga-promoted bimetallic CuCo catalysts for efficient CO₂ hydrogenation to produce ethanol:the key synergistic role of Cu-Co Ga O_x interfacial sitesWe reported the gallium-promoted bimetallic CuCo catalysts derived from Cu-Co-Ga-Al layered double hydroxide precursors for efficient CO₂hydrogenation to ethanol.It was manifested that the introduction of Ga species could strengthen strong interactions between Cu and Co oxide species,thereby modifying their electronic structures and thus generating abundant metal-oxides interfaces（i.e.,Cu⁰/Cu⁺-Co Ga O_x interfaces）.The results showed that as-constructed CuCo-based catalyst with a Ga:Co molar ratio of 0.4 exhibited a high ethanol selectivity of 23.8%at a 17.8%conversion,along with an unprecedented high space-time yield of 62.6 mg _{Et OH}·g^-1_cat·h^-1 for ethanol under mild reaction conditions（e.g.,220°C,3 MPa pressure）.According to the structural characterizations,it was revealed that CH_xcould be formed at oxygen vacancies of defective Co Ga O_x species,while CO could be stabilized by Cu⁺species.The catalytic synergy of Cu⁰/Cu⁺-Co Ga O_x interfacial sites facilitated the generation of CH_x and CO intermediates to participate in the CH_x-CO coupling reaction and simultaneously inhibited alkylation reaction.The present findings provide a promising strategy for rationally designing highly efficient bimetallic CuCo-based catalysts for efficient CO₂ hydrogenation to produce ethanol.