单分散Co3O4@SiO2核壳催化剂的制备及N2O催化分解性能

N₂O是一种重要的温室气体,且对臭氧层有很大的破坏作用,而直接催化分解法是除去N₂O最经济有效的方法之一。针对目前报道较多的钴氧化物催化剂活性较差的问题,将包覆型Co₃O₄核壳材料引入N₂O直接催化分解反应,利用核壳结构的限域特性与壳层的多孔孔道使Co₃O₄分散性增加,粒径减小,金属载体相互作用与接触反应界面增强,从而提高了催化剂在N₂O直接催化分解反应中的低温活性。此外,还制备了一系列不同金属含量的Co₃O₄@SiO₂球形核壳催化剂来研究包覆结构对催化剂性能的影响,通过X射线荧光光谱（XRF）、透射电镜（TEM）、X射线衍射（XRD）、N₂物理吸附、H₂-程序升温还原（H₂-TPR）等表征,证实在保证稳定单分散核壳结构的前提下,活性Co₃O₄位点越多,催化剂反应活性越好。     

Co3O4-MMT催化剂的制备及其N2O催化分解性能

以MMT为载体,采用原位聚合-配位沉积法制备3种不同Co负载量的Co₃O₄-MMT催化剂。采用N₂物理吸附、XRD和TEM对载体和催化剂进行表征,并在连续流动微反装置上考察其N₂O催化分解性能。结果表明,与Co₃O₄催化剂相比,Co₃O₄-MMT催化剂的比表面积显著增大,且活性组分Co₃O₄具有较高的分散状态。Co₃O₄-MMT催化剂的催化活性随着Co含量的增加先升后降,其中0.015Co-MMT表现出最佳的催化活性,其活性远高于Co₃O₄催化剂,同时,该催化剂还表现出良好的催化稳定性和较好的杂质气体耐受性。     

Co-Cu-Ce-Fe/γ-Al_2O_3催化剂催化分解N_2O的性能

以等体积浸渍法制备γ-Al_2O_3负载的Co、Cu、Ce和Fe氧化物催化剂,利用正交试验设计实验条件,采用XRD、BET和H_2-TPR等对催化剂进行表征,并考察活性组分对催化剂催化分解N_2O活性的影响。结果表明,催化剂具有尖晶石结构,其BET比表面积随着金属氧化物负载量增加而降低。催化剂中铜的氧化物可以降低还原峰温度,进而明显提高催化活性,Co和Fe的加入对活性有一定的提高,Ce对催化活性没有明显影响。     

Fe/beta分子筛催化N2O分解

通过液相离子交换法对H-beta分子筛进行改性得到Fe/beta分子筛,并应用于催化N2O直接分解反应,考察加入HNO3后的体系pH值对Fe/beta催化性能的影响。采用N2物理吸附-脱附、XRD、IR、DR UV-Vis、NH3-TPD和ICP-OES等对Fe/beta分子筛进行分析表征。结果表明,溶液pH值降低过程中催化剂的结晶度、比表面积、孔容及Fe3+含量呈现先增加后减少。溶液pH为2.0时所制备的Fe/beta分子筛催化N2O完全分解温度明显低于pH为2.6和1.0时制备的Fe/beta催化剂,显示了较好的催化活性。     

Cu-Mn氧化物催化N_2O直接分解性能

分别以Cu(NO_3)_2·3H_2O和50%Mn(NO_3)_2水溶液为铜源和锰源,K_2CO_3为沉淀剂,采用沉淀法和共沉淀法制备单一Cu、Mn氧化物催化剂和Cu-Mn-O复合氧化物催化剂,用于催化N_2O直接分解反应,并利用N_2物理吸附-脱附、XRD、FT-IR和TPR等进行表征。结果表明,单一Cu和Mn氧化物分别以体相CuO和Mn2O_3物相形式存在,Cu-Mn-O复合氧化物中除形成CuMn_2O_4尖晶石物相外,还有一定量小晶粒CuO,较单一氧化物具有更加优异的还原性能,表现出较高的催化N_2O直接分解活性。在空速10 000 h~(-1)和N_2O体积分数0.1%条件下,Cu-Mn-O复合氧化物催化剂可在440℃催化N_2O完全分解,分别较单一Cu和Mn氧化物催化剂降低了40℃和60℃。     

分子筛催化剂上N2O催化分解的研究进展

氧化亚氮(N2O)会造成温室效应和臭氧层破坏,N2O的控制日益引起关注。催化分解技术是控制N2O的有效手段,分别对Fe基、Cu基和Co基分子筛催化剂催化分解N2O的研究现状进行总结和评述,并展望未来发展方向。     

CO3O4/MPS催化氧化NO性能

微乳法制备的介孔二氧化硅（MPS）负载Co3O4构成了Co3O4/MPS催化剂,考察了负载量、焙烧温度等制备条件和反应温度、空速、NO进口浓度、O2体积分数等操作条件对Co3O4/MPS催化氧化NO性能的影响,并对载体及催化剂进行了BET和XRD表征。结果表明：MPS比表面积远大于其它载体,Co3O4呈立方晶型,MPS负载25%的Co3O4在300 ℃下焙烧3 h得到催化剂的晶体颗粒最小,分散性好,具有最佳催化氧化活性和良好的稳定性,在NO进口浓度500 μL/L、O2体积分数10%、空速12 000 h－1的条件下,250 ℃时NO氧化率可达50%～60%（此时可获得最高的NOx吸收效率）,300 ℃氧化率达到80%以上,接近热力学平衡值。     

Co3O4-Bi2O2CO3催化剂的制备及其光催化性能

以Bi(NO₃)₃·5H₂O、Co(CH₃COO)₂·4H₂O为原料,采用化学沉淀-水热法制备了Co₃O₄-Bi₂O₂CO₃异质结构复合半导体光催化剂,并通过X射线衍射仪（XRD）、扫描电镜（SEM）、X射线光电子能谱（XPS）、紫外可见漫反射光谱（DRS）、荧光光谱（PL）等手段对所合成的复合型催化剂进行了理化性能表征。研究结果表明：引入Co₃O₄没有改变Bi₂O₂CO₃物相结构,但促进了Bi₂O₂CO₃ 对可见光的吸收能力,提高了Bi₂O₂CO₃表面吸附氧物种的数量,抑制了光生载流子复合。复合光催化剂对罗丹明B（RhB）的光催化脱色实验显示引入Co₃O₄能够明显提高Bi₂O₂CO₃催化剂的光催化脱色能力。尤其是Co₃O₄引入量为0.6%的Co₃O₄-Bi₂O₂CO₃样品对罗丹明B染料的光催化脱色率可达到97%（模拟日光照射30min）。本文为复合型光催化剂制备提供了简单易行的技术路线,制备的新型半导体复合光催化剂Co₃O₄-Bi₂O₂CO₃在环境净化方面表现出了较好的应用前景。     

可见光增强g-C_3N_4/Co_3O_4胶体催化剂的催化产氢性能

通过水热法制备了具有可见光增产氢高性能的g-C_3N_4/Co_3O_4胶体催化剂,采用XRD、TEM、SEM和EDS等分析样品的组成和形貌结构。催化产氢结果表明,光照条件下g-C_3N_4/Co_3O_4胶体催化剂具有极高的催化产氢活性,TOF值高达58.2 min~(-1),通过拟合温度动力学曲线,得到了催化反应的活化能为15.73 kJ·mol~(-1)。对样品进行UV-vis和PL测试发现,g-C_3N_4/Co_3O_4胶体催化剂具有极高的光能利用率和电子-空穴分离率,并进一步阐述了光能促进催化产氢的作用机理。     

沉淀方式对沉淀法制备Co_3O_4催化N_2O直接分解性能的影响

以Co(NO_3)_2·6H_2O为钴源,K_2CO_3为沉淀剂,采用沉淀法制备Co_3O_4催化剂,用于催化N_2O直接分解反应。利用N_2~-物理吸附、XRD、FT-IR、TEM、TPR和ICP等对其进行表征,考察沉淀方式对Co_3O_4催化剂结构及其催化性能的影响。结果表明,沉淀方式对制备的Co_3O_4催化剂织构性质、物相组成和晶粒尺寸等影响不大,但显著影响其K残留量和还原性能,进而决定催化剂直接催化分解N_2O的催化性能。反加法制得的催化剂中K残留量为1.43%,明显高于正加法,同时催化剂中Co~(3+)较正加法更易还原,因而表现出更高的催化性能。在空速10 000 h~(-1)和N_2O体积分数0.1%的条件下,反加法制备的催化剂可在280℃催化N_2O完全分解,较正加法低20℃。     

Potassium-doped Co3O4 catalyst for direct decomposition of N2O

Direct decomposition of nitrous oxide (N₂O) on K-doped Co₃O₄ catalysts was examined. The K-doped Co₃O₄ catalyst showed a high activity even in the presence of water. In the durability test of the K-doped Co₃O₄ catalyst, the activity was maintained at least for 12 h. It was found that the activity of the K-doped Co₃O₄ catalyst strongly depended on the amount of K in the catalyst. In order to reveal the role of the K component on the catalytic activity, the catalyst was characterized by XRD, XPS, TPR and TPD. The results suggested that regeneration of the Co²⁺ species from the Co³⁺ species formed by oxidation of Co²⁺ with the oxygen atoms formed by N₂O decomposition was promoted by the addition of K to the Co₃O₄ catalyst.     

Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst

A series of CeO₂ promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N₂O). Addition of CeO₂ to Co₃O₄ led to an improvement in the catalytic activity for N₂O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N₂O conversion could be attained over the CoCe0.05 catalyst below 400 °C even in the presence of O₂, H₂O or NO. Methods of XRD, FE-SEM, BET, XPS, H₂-TPR and O₂-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO₂ could increase the surface area of Co₃O₄, and then improve the reduction of Co³⁺ to Co²⁺ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N₂O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO₂, are responsible for the enhancement of catalytic activity of Co₃O₄.     

负载型钴锰复合金属氧化物催化剂催化分解N_2O

以ZrO_2为载体,采用浸渍法制备负载型钴锰复合金属氧化物催化剂,研究催化剂活性组分负载量、Co与Mn物质的量比、焙烧条件及含H_2O气氛对N_2O转化率的影响。结果表明,催化剂最佳制备条件为:活性组分Co负载质量分数3%,Co与Mn物质的量比为1∶1,焙烧升温速率2℃·min-1,焙烧温度900℃。该条件制备的负载型钴锰复合金属氧化物催化剂在反应温度850℃时,N_2O转化率达98.7%。当反应气氛中H_2O体积分数小于20%条件下,850℃时N_2O转化率高于90%,表明催化剂具有较强的抗水性能。     

N2O catalytic decomposition over various spinel-type oxides

Various spinel-type catalysts AB₂O₄ (where A = Mg, Ca, Mn, Co, Ni, Cu, Cr, Fe, Zn and B = Cr, Fe, Co) were prepared and characterized by XRD, BET, TEM and FESEM-EDS. The performance of these catalysts towards the decomposition of N₂O to N₂ and O₂ was evaluated in a temperature programmed reaction (TPR) apparatus in the absence and the presence of oxygen. Spinel-type oxides containing Co at the B site were found to provide the best activity. The half conversion temperature of nitrous oxide over the MgCo₂O₄ catalyst was 440 °C and 470 °C in the absence and presence of oxygen, respectively (GHSV = 80,000 h⁻¹).

On the grounds of temperature programmed oxygen desorption (TPD) analyses as well as of reactive runs, the prevalent activity of the MgCo₂O₄ catalyst could be explained by its higher concentration of suprafacial, weakly chemisorbed oxygen species, whose related vacancies contribute actively to nitrous oxide catalytic decomposition. This indicates the way for the development of new, more active catalysts, possibly capable of delivering at low temperatures amounts of these oxygen species even higher than those characteristic of MgCo₂O₄.     

负载型RuO_2/Me_xO_y(Me=La,Mg,Al)催化剂催化分解N_2O

采用共沉淀法制备LaMgAlO(简称Me_xO_y)复合金属氧化物,以Me-xO_y为载体,采用浸渍法制备系列负载型RuO_2/Me_xO_y催化剂,应用BET、TEM、XRF和SEM对代表性样品进行表征。结果表明,实验条件下,RuO_2负载质量分数2.0%时比较合适,在气体混合物中含有氧和少量水蒸汽条件下,催化剂具有较好的催化分解N_2O稳定性。