Ni、Mg掺杂钴尖晶石催化分解N_(2)O的实验

Catalytic Decomposition of N2O Using Cobalt Spinel Catalyst Doped with Ni and Mg

为了解决氨燃料发动机的氧化亚氮(N_(2)O)排放问题,研究一种Ni、Mg掺杂的钴尖晶石催化剂用于N_(2)O高效分解。采用共沉淀法合成一系列过渡金属M(Cu、Ni、Mg)掺杂钴尖晶石(Co3O_(4))形成M_(x)Co_(3-x)O_(4)复合金属氧化物,并探究其在不同气氛下的催化活性。Ni_(0.4)Mg_(0.2)Co_(2.4)O_(4)催化剂可在350℃时达到90%的N_(2)O分解效率,在通有10%水蒸气反应的情况下480℃完全转化。通过一系列表征手段发现:Ni、Mg同时掺杂进入晶格结构较好,形成较为完整的整体尖晶石结构;Ni、Mg协同Co作为活性位点,使钴尖晶石分散度更好,并未像Cu等掺杂时形成对应金属氧化物的杂相而减少活性中心是其改性效果进一步提升的重要原因;同时因Ni、Mg同时掺杂进入晶格,使掺杂后钴尖晶石晶格膨胀,晶格尺寸变大,比表面积有明显提升,高于Ni、Mg单独掺杂,增加了接触活性位点,使其拥有更低的反应温度;通过XPS发现Ni_(0.4)Mg_(0.2)Co_(2.4)O_(4)中Co^(2+)、Ni^(2+)的结合能均最高,电子云密度相对最低,有助于N、O中的电子向其转移,且作为主要分解活性中心的Co^(2+)占比最高,从能量和价态角度解释了其同温度下分解效率最高的现象;此外,在H_(2)-TPR下,随着Ni、Mg掺杂量的增加,H_(2)的还原温度更高,说明其在高低温下的还原性更强,有助于对N_(2)O中的高价N进行吸附还原,而Ni_(0.4)Mg_(0.2)Co_(2.4)O_(4)在60 h时的60000 h-1空速气流下也显示出较好的稳定性(350℃下转化率维持在90%左右)。

Research was conducted on a cobalt spinel catalyst doped with Ni and Mg for the efficient decomposition of nitrous oxide(N_(2)O),to address the issue of N_(2)O emissions from ammonia-fueled engines.Series of transition metal M(Cu,Ni,Mg)doped cobalt spinels(Co3O_(4))were synthesized by the co-precipitation method to form composite metal oxides M_(x)Co_(3-x)O_(4),and their catalytic activities under different atmospheres were investigated.The Ni_(0.4)Mg_(0.2)Co_(2.4)O_(4) catalyst could achieve a 90%decomposition efficiency of N_(2)O at 350℃,and complete conversion is achieved at 480℃under the reaction with 10%steam.A series of characterization methods revealed that:The simultaneous doping of Ni and Mg into the lattice structure was well integrated,forming a more complete overall spinel structure;The synergistic effect of Ni and Mg,along with Co as active sites,resulted in better dispersion of the cobalt spinel,and unlike doping with Cu and other elements that formed corresponding metal oxide impurities,reduced the number of active centers,which was an important reason for the further improvement of its modification effect;Due to the simultaneous doping of Ni and Mg into the lattice,the doped cobalt spinel experienced lattice expansion and increasing of lattice dimensions,resulting in a significant enhancement of the specific surface area,which was higher than that of individual doping with Ni or Mg,thus increased the number of active sites for contact,enabling it to have a lower reaction temperature;XPS analysis revealed that in Ni_(0.4)Mg_(0.2)Co_(2.4)O_(4),Co^(2+)and Ni^(2+)had the highest binding energy,and the density of electron cloud is the lowest,which facilitated the transfer of electrons from N and O to them;The proportion of Co^(2+),as the main decomposition active center,was the highest,which explained the phenomenon of its highest decomposition efficiency at the same temperature from the perspectives of energy and valence state;Under H_(2)-TPR conditions,as the doping amounts of Ni and Mg increase,the reduction temperature of H_(2) was higher,indicating stronger reducibility at both high and low temperatures,which was beneficial for the adsorption and reduction of the high-valent N in N_(2)O;Ni_(0.4)Mg_(0.2)Co_(2.4)O_(4) also showed good stability under a 60000 h-1 air flow at 60 h(maintaining a conversion rate of around 90%at 350℃).