CeO₂?modified three?dimensional nitrogen? and phosphorus?doped carbon?based catalysts (CeO₂?NPC) were prepared with cerium chloride hexahydrate as the precursor,sodium chloride as the template,and milk as the carbon source.The results of rotating disc electrode (RDE) and rotating ring?disc electrode (RRDE) tests were used to analyze the influence of catalyst preparation conditions on the oxygen reduction reaction (ORR) process.The influence of the synthesis process on the structure was investigated by X?ray photoelectron spectroscopy (XPS) and Raman spectroscopy.Heteroelements such as N and P spilled out with small molecules during calcination temperature increase.In this process,the degree of defects on the carbon carriers was increasing and the content of CeO₂ was invariably in an increasing trend.

In view of the problems existing in the development of the second⁃class reservoirs in sandstone reservoirs,such as low utilization degree,high water⁃bearing and low oil recovery rate,a set of well pattern, multiple sets of layers,polymer flooding,and the method of reverse⁃exploiting second⁃class reservoirs layer by layer was proposed.The parameters such as pore volume,injection rate, polymer injection volume and slug combination were optimized by numerical simulation in Pu I1-2 layers of Daqing Xing Twelve area.The results showed that when the PV number was 1 PV,the injection rate was 0.16 PV/a,the polymer injection volume was 1 200 mg/L⋅PV,the high⁃concentration polymer slug was injected first, then the low⁃concentration polymer slug was injected,and the recovery rate reached 50.11%.Compared with the predicted water flooding recovery rate,it was improved by 10.1%.