Support Effect On Ni/MgO And PdO/MO₂?M=Sn,Ti,Si?Supported Catalysts

The interaction between active component and support has important effects on supported catalyst structure and its performance.Studying the nature of the interaction is an important basic subject in the heterogeneous catalysis.In this paper,density functional theory calculation and experiment were used,with Ni and PdO as active component,MgO,MO₂?M=Ti,Sn,Si?as the support,the interaction between metal and support,metal oxide and different supports and their effects on adsorption performance?such as CO₂,H₂,CO and H₂O adsorption?and reaction performance?such as catalytic hydrogenation of CO₂ and CO catalytic oxidation reaction?were studied.The main results are as follows:During the CO₂ methanation reaction,Ni is the active center to the catalytic H₂dissociation and CO₂ hydrogenation.Compared with the pure Ni surface,CO₂ has a larger adsorption energy on Ni/MgO sopported catalyst surface,and it gains more electronic from the surface.Due to the existence of MgO support promoting the CO₂activation.The interaction between metal Ni and MgO support,results in the enhancement of electronic ability of C terminal of CO₂,thus reducing the energy barrier of CO₂ reduction process.In addition,the affinity of MgO surface and the OH of intermediate species lead to the dehydroxylation energy barrier of the Ni/MgO surface is far lower than pure Ni surface.The presence of MgO support increases the reaction heat of CH₃OH formation,thus increasing the selectivity of CH₄ on the surface.For PdO as an active component,the activity of supported catalysts are following the sequence of PdO/TiO₂>PdO/SnO₂>PdO/SiO₂.The best activity of PdO/TiO₂ is proved to the best Pd dispersity on TiO₂ surface,which leads to the maximum CO adsorption amount and surface oxygen content on the catalyst surface.In addition,the DFT calculation results indicate that the support effect changes the adsorption energy and adsorption site of CO in the process of CO oxidation,thus affecting the reaction path way and the energy barrier.When there is in the presence of water in the system,the PdO/SnO₂ catalyst,SnO₂as the support,has higher catalytic activity,and shows the water resistance stability for a long time test.In contrast,the PdO/TiO₂ catalyst,TiO₂ as the support,which activity is reduced,and then the catalyst is gradually deactivated in anti-water stability test.The PdO/SiO₂ catalyst,SiO₂ as the support,which activity remains the same and has good anti-water stability.H₂O-TPD results show that the larger amount of water containing strongly adsorbed OH species was adsorbed on the PdO/SnO₂ and PdO/TiO₂ catalyst.However,the H₂O adsorption amount of PdO/SiO₂ catalysts is small,so that the H₂O molecules have little impact on the activity of PdO/SiO₂ catalyst.DFT calculation results show that the presence of H₂O and OH can lead to the increase the energy barrier of CO oxidation on PdO/TiO₂ catalyst surface,while the improved catalytic activity on the PdO/SnO₂ catalyst surface is resulted from the OH existence on the surface.