A Study On CO₂ Methanation Performance On TiO₂-supported Ru And Ni Catalysts

Designing and fabricating highly active low-temperature catalysts for CO₂methanation holds significant implications for power-to-gas technology,circular carbon economy,and CO₂ energy-saving and emissions reduction.Metal oxide-supported Ni and Ru catalysts are commonly used for CO₂ methanation,where complex metal-support interactions exist between the metal components and the support,directly affecting the catalytic performance.Revealing the impact of metal-support interactions is crucial for the rational design of efficient and stable CO₂methanation catalysts.In this study,we focused on Ni and Ru catalysts supported on Ti O₂,regulating their metal-support interactions via Mn ion doping and varying the preparation methods for use in CO₂ methanation reactions.In conjunction with in situ characterization techniques,we investigated the effects of different modification approaches on catalyst metal-support interactions,methanation activity,and reaction mechanisms.The primary research findings are as follows:1.Through hydrothermal synthesis,we prepared Ru catalysts supported on anatase Ti O₂ doped with varying concentrations of Mn for use in CO₂ methanation reactions.The results demonstrated that Mn doping significantly enhanced the CO₂methanation activity of Ru/a-Ti O₂.Among the catalysts,Ru/Ti_0.8Mn_0.2O₂ with a Mn/Ti molar ratio of 2:8 exhibited optimal low-temperature performance,delivering a turnover frequency（TOF）for CO₂ conversion 6.5 times that of Ru/a-Ti O₂ at 200°C.Various test results revealed that Mn doping in the Ti O₂ support lattice increased the specific surface area,reduced the grain size,and effectively strengthened metal-support interactions,leading to enhanced dispersion of Ru species.XPS findings indicated that,compared to unmodified Ru/a-Ti O₂ catalysts,Mn doping intensified metal-support interactions,causing more electrons to transfer from Ru to the support on Ru/Ti_0.8Mn_0.2O₂,thereby enhancing the positive charge of Ru components.In-situ FTIR results revealed that the CO₂ methanation process on both Ru/a-Ti O₂ and Ru/Ti_0.8Mn_0.2O₂ catalysts followed the CO pathway,with the linear-CO*infrared vibration frequency on Ru/Ti_0.8Mn_0.2O₂ undergoing a blue shift.This was attributed to the weakening of theπbackbonding between Ru and CO due to the increased positive charge of Ru,rendering the C-terminus of linear-CO*more favorable for hydrogenation to form CH₄.Concurrently,Mn doping also promoted the cyclic transformation of surface carbonates and increased the mobility of surface CO₂.Collectively,these findings suggest that Mn doping,by enhancing metal-support interactions between the support and Ru,improved the CO₂ methanation performance of the catalyst.2.Various synthesis methods were employed to prepare Ni/Ti O₂ catalysts with differing metal-support interaction strengths for use in CO₂ methanation reactions.The results indicated that,compared to Ni catalysts supported on Ti O₂ calcined at 600°C（Ni/Ti O₂-C）,the activity of Ni catalysts supported on hydrothermally synthesized but uncalcined Ti O₂（Ni/Ti O₂-UC）was significantly enhanced,while the activity of Ni/Ti O₂-PM catalysts,created by simply mixing Ni O with Ti O₂ calcined at 600°C,markedly decreased.The findings revealed that Ni/Ti O₂-UC catalysts exhibited the strongest metal-support interactions,enabling Ni to enter the Ti O₂ lattice and form nickel titanate species.The formation of nickel titanate species was beneficial in suppressing the sintering and phase transformation of the Ti O₂ support.Furthermore,the reduced Ni species that precipitated on the support had stronger metal-support interactions,which led to an increase in CO₂ methanation activity.The order of metal-support interaction strength for the three catalysts was Ni/Ti O₂-UC>Ni/Ti O₂-C>Ni/Ti O₂-PM.The Ni/Ti O₂-UC catalyst,possessing the strongest interactions,featured Ni species that were more difficult to reduce and had a greater abundance of Ni²⁺species and Ni-O-Ti interfaces.H₂-TPD,CO₂-TPD,and in-situ FTIR analyses further elucidated that the enhanced metal-support interactions resulted in an increased number of Ni-O-Ti interfaces,promoting the spillover effect of hydrogen and providing adsorption-activation sites for CO₂,ultimately enhancing the catalyst’s CO₂methanation activity..3.Mn ion doping and synthesis method modulation independently bolstered the metal-support interactions in both Ru/a-Ti O₂ and Ni/Ti O₂ catalyst systems.The enhancement of these interactions in both systems promoted surface metal dispersion,elevating CO₂ methanation activity and selectivity.In particular,the increased activity of the Ru/Ti_0.8Mn_0.2O₂ catalyst was primarily attributed to the strengthened metal-support interactions,which facilitated charge transfer from Ru to the support and encouraged the formation of highly active linear-CO*species.Meanwhile,the enhanced activity of Ni/Ti O₂-UC was mainly due to the robust metal-support interactions leading to the generation of nickel titanate species and the proliferation of Ni-O-Ti interfaces,further stimulating hydrogen spillover effects and CO₂ adsorption-activation.The findings reveal that the augmentation of metal-support interactions can modulate the physicochemical properties of metal components through electronic characteristics and spatial structure,thereby improving CO₂ methanation activity.This offers a novel approach to the rational design of CO₂ methanation catalysts based on metal-support interactions.