制备方法对La_(2)FeNiO_(6-δ)双钙钛矿氧化物的催化性能的影响

Effect of preparation method on catalytic performance of La_(2)FeNiO_(6-δ)double perovskite oxide

用水热法、共沉淀法和溶胶凝胶法分别制备了La_(2)FeNiO_(6-δ)钙钛矿型氧化物催化剂,并用XRD、XPS、SEM、BET等对样品的晶相结构、离子价态、表面形貌和孔径分布等进行了表征。结果表明,不同方法制备的La_(2)FeNiO_(6)样品均形成了较完整钙钛矿型氧化物结构,孔径分布以介孔结构为主,La离子为+3价,Fe和Ni离子则分别以+3价和+2价出现。镍离子的引入,导致A位离子出现偏析现象,改变了钙钛矿B位离子的化合价态,形成了较多的+2价Fe和Ni离子,产生较多的氧空位。其中溶胶凝胶法制备的样品具有完整的钙钛矿结构、表面积为34.5 m^(2)/g、平均孔径为9.8nm,+2价的Ni和Fe离子数量较多,能形成较多的金属中心和氧空位,在间甲酚催化加氢脱氧反应过程中具有较好的活性和甲苯的选择性,在3MPa、375℃、15mL/min氢气流速条件下间甲酚的转化率达到82.7%,甲苯在产物分布中占54.7%。

La_(2)FeNiO_(6-δ) perovskite oxide catalysts were prepared by hydrothermal method,co-precipitation method and sol-gel method respectively.The crystal structure,ionic valence,exterior morphology and pore size distribution of the samples were characterized by XRD,XPS,SEM and BET.The results show that La_(2)FeNiO_(6-δ) samples prepared by different methods all form a relatively complete perovskite oxide structure.The pore size distribution is mainly mesoporous structure,La ion is shown as+3 valence,and yet Ni and Fe ions are dominated by+3 valence and+2 valence respectively.Due to the introduction of nickel ion,the chemical environment of perovskite B-site ions is changed,that is Ni^(2+) and Fe_(2)+ ions are appear,and the oxygen vacancies is come into being at the same time.This situation promotes the reduction of Ni δ +ions and produces abundant metal centers when the catalyst is activated.The samples prepared by sol-gel method have a complete perovskite structure,a surface area of 34.5 m^(2)/g,an average pore size of 9.8 nm,and also a large number of Ni^(2+ )and Fe^(2+) ions,which beneficial to formation more metal centers and oxygen vacancies that lead to better activity and higher toluene selectivity in the catalytic hydrogenation deoxygenation process of m-cresol.Under the condition of 3MPa working pressure,375 ℃ reaction temperature and 15 mL/min hydrogen flow rate,the conversion of m-cresol reached 82.7% and toluene accounted for 54.7%of the product distribution.