Interactions Of Ni-based Bimetals With Supports And Their Effects On CO₂Adsorption And Dissociation

Catalytic reforming of CH4with CO2to produce synthesis gas has received extensive attention for the significance in reducing greenhouse gas emission and the application of synthesis gas to industry. Usually, metal Ni is selected as the catalyst in the reforming reaction. However, serious carbon of coke formation made Ni catalysts deactivate and restricted the industrialization process.One of the effective methods of removing carbon is that the O species from CO2dissociation may interact with the formed carbon. Further, the adsorption of CO2is an initial step for dissociation process. Compared to pure metal catalysts, bimetal catalysts have superior performance to reduce carbon. Formed carbon also can be reduced when strong metal support interaction exists in the catalysts.In the present work, we carry out the density functional theory (DFT) calculations combined with XPS characterization method on the interactions between Ni-based bimetals (NiMn, NiFe, NiCo and NiCu) and supports (MgO and γ-Al2O3) as well as their effects on CO2adsorption and dissociation,and several conclusions have been got.The interaction between bimetal and support is electronic.Analyzing the binding energies of NiM on supports as well as the the transferred charges between NiM and supports, we can get that the interaction between NiM and γ-Al2O3is stronger than that of NiM with MgO support, and the interaction between NiM and defective MgO is stronger than that of NiM with perfect MgO; On the MgO support, NiCo shows the strongest interaction with the support, and NiCu shows the weakest, while on the γ-Al2O3support, NiFe shows the strongest interaction with the support, and NiCu shows the weakest.The interactions of bimetals and supports can affect the adsorption ability of catalysts to CO2directly. In the perfect MgO, defective MgO and γ-Al2O3systems, the stronger the interaction of bimetal and support is, the weaker the CO2adsorption is; in different NiMn, NiFe, NiCo and NiCu system for each support, the stronger the interaction of bimetal and support is, the stronger the CO2adsorption is. Besides, the elongation of C-0bond lengths increases with the increases of the net charges of the adsorbed CO2within a linear relationship.Comparing the CO2dissociation on four NiM/γ-Al2O3bimetals catalysts, we find NiCo/γ-Al2O3and NiCu/γ-Al2O3are favor of dissociating CO2to O atom, and further to react with formed C to remove carbon. Comparing the CO2dissociation on Ni2Co2/γ-Al2O3, defective Ni2Co2/MgO and perfect Ni2Co2/MgO catalysts to analyze the effects of the interactions between different supports and bimetal on CO2dissociation, we find that the stronger the interactions of support and bimetal is, the stronger the CO2dissociation ability is.