Theoretical Study On The Structure And Stability Of Sustained-release Copper On CuAlO₂ Surface

Methanol has many advantages in hydrogen production,such as low reforming temperature,biodegradable,high hydrogen to carbon ratio and so on.In recent years,the demand for hydrogen and other new energy is increasing rapidly.As one of the ways of methanol hydrogen production,methanol steam reforming technology is considered to be a promising hydrogen production technology for vehicle fuel cells.The conversion of methanol and the yields of hydrogen,carbon monoxide and carbon dioxide in reforming products are largely determined by reforming catalyst.Copper-based catalyst is the most commonly used reforming catalyst,which can effectively convert methanol into hydrogen and carbon dioxide,and has been widely studied and applied in the field of methanol steam reforming to produce hydrogen.Recently,CuAlO2 catalyst has been found to show stable catalytic performance in methanol steam reforming and can be strategically used in reforming reaction through sustained release catalysis technology.The used catalyst can also be completely restored to its original state by simple calcination treatment,demonstrating the super regeneration ability of the catalytic system.In this paper,on the basis of first-principle calculation,density functional theory(DFT)is used to study the structures and properties of sustained released copper components on CuAlO2 surface,in order to understand mechanism of sustained release of CuAlO2 catalyst and provide theoretical guidance for experiments.1.The adsorption and stability of Cun(n=1-4)clusters on CuAlO2(11(?)0)perfect and oxygen defective surface have been systematically researched by DFT-D+U method,which considered dispersion correction and Coulomb correction.According to the calculated adsorption energy,the study results show that the adsorption of Cun(n=1-4)clusters on CuAlO2(11(?)0)oxygen defective surface is much stronger than on CuAlO2(11(?)0)perfect surface,which is consistent with result of Bader charge analysis.This may be because that there exists more charge transfer between the oxygen defective surface and the adsorbed copper clusters.The aggregation and growth energy of copper clusters on CuAlO2(11(?)0)perfect and oxygen defective surfaces are calculated and compared with previous studies about CuAlO4 and Cu/γ-Al2O3 catalysts.The aggregation and growth tendency of Cun clusters on different oxide surfaces and in isolated gas phases are summarized as follows:on CuAl2O4(110)surface<on CuAlO2(11(?)0)oxygen defective surface<on CuAlO2(11(?)0)perfect surface<on γ-Al2O3(110)surface<in gas phase.The work functions of systems before and after Cun adsorption on CuAlO2(11(?)0)perfect and oxygen defective surfaces are also calculated,the results show that the adsorption of Cun(n=1-4)clusters results in decrease of systems’ work function,and the work function of the system with oxygen defect is smaller than that of the system without oxygen defect.The adsorption stability mechanism of Cun(n=1-4)clusters on two CuAlO2(11(?)0)surfaces is also analyzed by using partial density of states(PDOS).2.Hydrogen produced by steam reforming of methanol contains a large amount of CO,which is the main by-products of MSR.CO adsorption on the catalyst surface will affect the MSR reaction process,thus limiting the formation of hydrogen.However,in the MSR process catalyzed by CuAllO2,the interaction mechanism between CO and CuAlO2 surface remains unclear.Therefore,the DFT-D+U calculation method is used to calculate the most stable adsorption structure of CO molecules adsorption on Cun(n=1-4)clusters supported on CuAlO2(11(?)0)perfect and oxygen defective surfaces,and we further analyze the stability of Cun clusters on CuAlO2(11(?)0)perfect and oxygen defective surfaces after CO adsorption.The results show that CO adsorption sometimes leads to the reconstruction of Cun clusters supported on CuAlO2(11(?)0)perfect and oxygen defective surfaces,which is related to the amount of CO adsorption.Phase diagrams drawn by atomic thermodynamics have also been used to analyze the adsorption and desorption of CO molecules on Cun(n=1-4)upon CuAlO2(11(?)0)perfect and oxygen defective surfaces at different temperatures and CO partial pressures.