CeO2含量对柴油机商用稀土SCR催化剂脱硝性能的影响

考察了不同CeO₂含量对柴油机商用稀土选择性催化还原（SCR）催化剂NH₃-SCR性能的影响。通过X射线衍射、N₂吸附-脱附、X射线光电子能谱、H₂-程序升温还原和NH₃-程序升温脱附等表征手段对催化剂的结构及性能进行了研究。研究发现,CeO₂含量对催化剂的晶体结构没有影响,添加后促进了稀土催化剂表面SiO₂的分散,从而对催化剂的脱硝性能及水热老化性能产生影响;CeO₂含量影响催化剂的织构性质,较大的孔体积和适当的比表面有利于催化剂水热老化后催化剂的脱硝性能的提高;随着CeO₂含量从14%增加到20%,其表面Ce含量呈先降低后升高的趋势,其中Ce⁴⁺含量与催化剂的水热老化后催化剂的脱硝性能成正相关;CeO₂含量的增加会阻碍稀土催化剂中其他组分的还原或增加其热稳定性,从而影响催化剂的还原能力和酸性位数量;通过脱硝性能测试,稀土催化剂中CeO₂的最佳含量为16%。     

Ce在负载Pd催化苯酚氧化羰基化合成碳酸二苯酯反应中的作用

采用微乳液法制备了Ce为助剂的Pd-Ce-O/SiO₂催化剂,用于苯酚氧化羰基化合成碳酸二苯酯（DPC）反应。活性评价结果显示,催化剂性能随着Ce用量的增加而提高,当Ce/Pd摩尔比为10/1时,苯酚转化率为64.4%,碳酸二苯酯选择性为83.4%。利用XRD表征发现,部分Ce⁴⁺进入到PdO晶格中,使得失活Pd原子中的电子更容易向Ce转移,从而易于再生,表现出更好的催化性能。根据上述结果,设计制备了Pd-O/CeO₂催化剂用于本反应,苯酚转化率和碳酸二苯酯选择性分别仅为24.0%和23.3%。表征发现,在Pd-Ce-O/SiO₂催化剂表面,Pd物种主要是PdO,而Pd-O/CeO₂表面的Pd物种则以PdO₂为主。由于苯酚氧化羰基化反应的活性中心为Pd(Ⅱ),所以Pd-O/CeO₂催化性能较差。并且,由于Pd与CeO₂之间存在强相互作用,催化剂表面Pd含量较低,这也是Pd-O/CeO₂催化活性较差的原因之一。     

原位合成有序介孔氧化铝负载Cu-Ce催化剂及其维埃斯吸附消毒性能

以三嵌段共聚物F127(EO₁₀₆PO₇₀EO₁₀₆)为模板剂,Al[OCH(CH₃)₂]₃为铝源,活性组分前体Cu(NO₃)₂·2.5H₂O和Ce(NO₃)₂·6H₂O,采取原位合成法制备有序介孔氧化铝负载的Cu-Ce催化剂,研究合成的有序介孔氧化铝及催化剂对维埃斯(VS)的消毒效果。结果表明,VS在Al-0.05Cu-0.05Ce双金属催化剂表面的消毒降解效果最佳,产物中氧化物相对较多,主要发生S—C键和P—S键的断裂,断裂的碎片进一步氧化,反应4天,VS消毒降解率98.01%。这可能是由于CeO₂中的铈元素能受环境影响在Ce³⁺→Ce⁴⁺间发生可逆转变,催化VS发生氧化消毒反应。     

Sn掺杂CeO2中Ce3+的形成机制及其对质子交换膜燃料电池耐久性的影响

在质子交换膜燃料电池(PEMFC)运行过程中，产生的自由基会攻击质子交换膜，使其开裂或形成孔洞，导致电池失效。常见的改性方法是在质子交换膜(PEM)中添加自由基清除剂材料。基于此，本文合成了Sn掺杂CeO₂自由基清除剂，通过提高Ce³⁺浓度来增强其在PEMFC中自由基清除性能，避免PEM厚度迅速减薄，从而提高质子PEMFC的耐久性。密度泛函理论计算和试验结果表明，Sn掺杂会引起CeO₂产生晶格畸变，降低氧空位形成能，促进CeO₂中Ce³⁺的形成。同时，Sn²⁺的加入可将CeO₂-Sn样品中的Ce⁴⁺还原为Ce³⁺,提升Ce³⁺的浓度，从而提高PEM的耐久性。单电池测试结果表明，经70 h的开路电压衰减测试，CeO₂-Sn-5%改性后的质子交换膜组装的单电池电压衰减率最低(18%),且功率保留率(56%)比其他样品更高，表明该样品具有更优异的耐久性。     

不同Pt前体制备Pt/CeO2催化剂对其结构及性能的影响

Pt与载体间的相互作用会影响到本征Pt纳米粒子的催化活性,不同Pt前体制备Pt/CeO₂催化剂会使其表现出完全不同的催化性能。分别采用金属胶体粒子原位沉积法、浸渍法以及浸渍还原的方式制备了Pt/CeO₂催化剂,通过X 射线衍射、程序升温还原、X射线光电子能谱以及高分辨透射电镜对催化剂进行表征,在CO氧化以及甲苯燃烧反应中评价催化剂活性。结果表明,胶体粒子原位沉积法制备Pt/CeO₂催化剂,能够将优先合成好的Pt纳米粒子直接以金属态Pt⁰的形式负载到载体表面,且保证其高度均匀分散,丰富的表面Pt⁰很好地充当了CO、甲苯反应时的活化位点,催化剂表现出优异的性能;浸渍还原法中,Pt纳米粒子之间会发生团聚现象,同时部分Pt又以Pt²⁺的形式与CeO₂之间形成了Pt-O-Ce相互作用,载体表面暴露Pt⁰含量的下降是催化剂表现出较弱活性的主要原因;浸渍法中,以Pt离子对Pt进行负载,Pt完全以Pt²⁺的形式参与到Pt-O-Ce键成键中,表面Pt⁰缺失,催化剂表现出明显的失活现象。Pt/CeO₂催化剂中,起主要活性作用的是金属态Pt⁰,胶体粒子原位沉积法能够实现Pt⁰的直接负载,对于提高Pt基催化剂中Pt的利用率,降低Pt资源消耗都具有重要意义。     

CexSnyO2双金属氧化物催化剂用于富氧条件下NO和CO的同时脱除

采用了均相沉淀法,制备了一系列Ce_xSn_yO₂双金属氧化物催化剂,进行催化氨选择性催化还原(NH₃-SCR)反应和CO氧化反应,考察在富氧条件下系列催化剂上NH₃-SCR和CO氧化活性,结合XRD、BET、H₂-TPR,NH₃-TPD和XPS等表征手段对催化剂的物化性质和活性的关联进行了分析。结果表明,相比单组分CeO₂和SnO₂,少量的Sn⁴⁺掺杂进入CeO₂的晶格内,形成铈锡固溶体。增加了催化剂比表面积、孔体积和降低了催化剂的孔尺寸。此外,铈锡双金属氧化物催化剂之间产生协同作用,不仅提高了催化剂氧化还原性能、表面酸性还增加了催化剂Ce³⁺/Ce⁴⁺和表面吸附氧含量,进而有效的提高NH₃-SCR活性和CO活性。     

铈掺杂强化碳纳米管活化过一硫酸盐实验研究

采用浸渍-煅烧法制备了高效稳定的CeO₂/CNT复合材料。利用X射线衍射、X射线光电子能谱和Raman光谱等手段对材料结构进行表征,并研究了复合材料活化过一硫酸盐（PMS）对磺胺异唑的降解性能。结果表明,在材料投加量为75 mg·L^-1、PMS投加量为0.3 mmol·L^-1、初始pH为5.36时,30 min降解率可达90%以上,50 min内可完全去除,反应过程符合伪一级反应动力学模型,活化剂使用5次后仍有77%的去除率。电子顺磁共振实验表明,SO₄?^-、?OH和¹O₂均参与了反应,碳纳米管表面缺陷可能与¹O₂的形成有关。CeO₂的掺杂提高了碳纳米管中缺陷碳的含量,同时Ce³⁺/Ce⁴⁺为反应提供了更多活性位点,从而有效提升了碳纳米管活化PMS的性能,为铈基碳纳米管复合材料应用于过硫酸盐高级氧化技术提供了借鉴。     

aMn-bCu/Y催化剂协同臭氧催化氧化降解甲苯

采用浸渍法合成了一系列不同Mn、Cu负载量的aMn-bCu/Y催化剂,在常温下研究了其协同臭氧催化氧化降解甲苯的性能。BET、XRD、NH₃-TPD、H₂-TPR、XPS结果表明,Mn、Cu负载量对催化剂的比表面积、结晶相、表面酸性、还原性质和表面金属化学价态有着显著影响,其中18Mn-6Cu/Y催化剂(即Mn、Cu质量分数为18%,6%),甲苯降解性能最优,归因于其高度分散的MnO_x物种、适宜的酸性、氧化还原能力强、晶格氧流动性好及丰富的Mn⁴⁺粒子。常温下,协同臭氧催化氧化甲苯反应6 h, 18Mn-6Cu/Y催化剂的甲苯转化率可达98%,CO₂选择性为82.1%,而其它负载量催化剂则呈现不同程度的降低。     

Mn3O4催化协同低温等离子体再生处理工业废活性炭的研究

通过Mn₃O₄催化协同低温等离子体再生废活性炭,考察了放电电压、气体流速、放电时间对甲苯降解率的影响。结果表明,Mn₃O₄催化协同低温等离子体提高甲苯降解率,在电压为12 kV、气体流速为0.5 L/min,放电时间为30 min时,降解率达到最大,为99.78%。通过对吸附复杂污染物的工业废活性炭的研究,Mn₃O₄催化协同低温等离子体提高了VOCs的降解率,表明Mn₃O₄催化协同低温等离子体方法可行。     

CeO2改性WO3/g-C3N4光催化氧化脱硫性能

以钨酸铵、六水硝酸铈、尿素为原料,采用熔融法制备CeO₂-WO₃/g-C₃N₄催化剂,并对样品进行XRD、UV-Vis、TEM、PL和XPS表征。结果表明：CeO₂的引入可以提高WO₃在g-C₃N₄上的分散度,抑制光生电子空穴对的复合,同时Ce⁴⁺/Ce³⁺良好的储氧放氧能力有利于氧空位和活性氧的生成,从而有利于WO₃/g-C₃N₄催化剂的催化性能。在以高压钠灯模拟可见光源的条件下,以过氧化羟基异丙苯为氧化剂,考察了CeO₂的加入量对催化剂氧化二苯并噻吩(DBT)性能的影响,结果表明：最佳的CeO₂引入量为5%(质量分数),在80℃、氧硫摩尔比(O/S)为5.0的反应条件下,反应180 min时DBT在WO₃/g-C₃N₄和CeO₂-WO₃/g-C₃N₄催化剂的作用下转化率分别为72.9%和86.4%,且改性后的催化剂可以循环使用8次而催化活性没有明显降低。     

On the mechanism of model diesel soot-O2 reaction catalysed by Pt-containing La-doped CeO2: A TAP study with isotopic O2

Pt supported on CeO₂ and 10 wt.% La³⁺-doped CeO₂ catalysts have been prepared, characterised and tested for soot oxidation by O₂ in TGA. The reaction mechanism has been studied in a TAP reactor with labelled O₂. Isotopic oxygen exchange between molecular O₂ and ‘O’ on the support/catalyst was observed and soot oxidation is being carried out by lattice oxygen. TAP studies further show that Pt improves O₂ adsorption and, therefore, 5 wt.% Pt-containing catalysts are more active for soot oxidation than the counterpart supports. In addition, CeO₂ doping by La³⁺ leads to an improved support, since La³⁺ stabilises the structure of CeO₂ when calcined at high temperature (1000 °C) and minimises sintering. In addition, La³⁺ improves the Ce⁴⁺/Ce³⁺ reduction as deduced from H₂-TPR experiments and favours oxygen mobility into the lattice. A synergetic effect of Pt and La³⁺ is observed, Pt-containing La³⁺-doped CeO₂ being the most active catalyst for soot oxidation by O₂ among the samples studied.     

Ultrasound-assisted co-precipitation synthesis of mesoporous Co3O4–CeO2 composite oxides for highly selective catalytic oxidation of cyclohexane

The one-step highly selective oxidation of cyclohexane into cyclohexanone and cyclohexanol as the essential intermediates of nylon-6 and nylon-66 is considerably challenging. Therefore, an efficient and low-cost catalyst must be urgently developed to improve the efficiency of this process. In this study, a Co₃O₄–CeO₂ composite oxide catalyst was successfully prepared through ultrasound-assisted co-precipitation. This catalyst exhibited a higher selectivity to KA-oil, which was benefited from the synergistic effects between Co³⁺/Co²⁺ and Ce⁴⁺/Ce³⁺ redox pairs, than bulk CeO₂ and/or Co₃O₄. Under the optimum reaction conditions, 89.6% selectivity to KA-oil with a cyclohexane conversion of 5.8% was achieved over Co₃O₄–CeO₂. Its catalytic performance remained unchanged after five runs. Using the synergistic effects between the redox pairs of different transition metals, this study provides a feasible strategy to design high-performance catalysts for the selective oxidation of alkanes.     

澄清剂对超白浮法玻璃可见光透过率的影响

探究高温分解型澄清剂Na₂SO₄+C(炭粉)和氧化还原型澄清剂CeO₂+NaNO₃对超白浮法平板玻璃可见光透过率的影响。结果表明,随着Na₂SO₄和C量的增加,超白玻璃的可见光透过率随之增加,从91.30%提升至91.87%。而氧化还原型澄清剂中的CeO₂质量分数小于0.07%时,超白玻璃的可见光透过率并没有实质性增加;CeO₂质量分数超过0.07%时,增长趋势明显。相对于高温分解型澄清剂Na₂SO₄+C,氧化还原型澄清剂CeO₂+NaNO₃具有更显著的氧化性,有助于Fe²⁺/Fe_总减少,但是Ce⁴⁺的自身着色和紫外截止效应影响了可见光透过率,建议使用量的质量分数不超过0.07%。     

Co3O4/CeO2 composite oxides for methane emissions abatement: Relationship between Co3O4–CeO2 interaction and catalytic activity

Co₃O₄/CeO₂ composite oxides with different cobalt loading (5, 15, 30, 50, 70 wt.% as Co₃O₄) were prepared by co-precipitation method and investigated for the oxidation of methane under stoichiometric conditions. Pure oxides, Co₃O₄ and CeO₂ were used as reference. Characterization studies by X-ray diffraction (XRD), BET, temperature programmed reduction/oxidation (TPR/TPO) and X-ray photoelectron spectroscopy (XPS) were carried out.

An improvement of the catalytic activity and thermal stability of the composite oxides was observed with respect to pure Co₃O₄ in correspondence of Co₃O₄–CeO₂ containing 30% by weight of Co₃O₄. The combined effect of cobalt oxide and ceria, at this composition, strongly influences the morphological and redox properties of the composite oxides, by dispersing the Co₃O₄ phase and promoting the efficiency of the Co³⁺–Co²⁺ redox couple. The presence in the sample Co₃O₄(30 wt.%)–CeO₂ of a high relative amount of Ce³⁺/(Ce⁴⁺ + Ce³⁺) as detected by XPS confirms the enhanced oxygen mobility.

The catalysts stability under reaction conditions was investigated by XRD and XPS analysis of the used samples, paying particular attention to the Co₃O₄ phase decomposition. Methane oxidation tests were performed over fresh (as prepared) and thermal aged samples (after ageing at 750 °C for 7 h, in furnace). The resistance to water vapour poisoning was evaluated for pure Co₃O₄ and Co₃O₄(30 wt.%)–CeO₂, performing the tests in the presence of 5 vol.% H₂O. A methane oxidation test upon hydrothermal ageing (flowing at 600 °C for 16 h a mixture 5 vol.% H₂O + 5 vol.%O₂ in He) of the Co₃O₄(30 wt.%)–CeO₂ sample was also performed. All the results confirm the superiority of this composite oxide.     

钛酸锶钡微晶玻璃的铈掺杂效应研究

通过X射线光电子能谱、紫外-可见漫反射光谱、傅里叶变换红外光谱和拉曼光谱研究了(Ba,Sr)TiO3微晶玻璃的铈掺杂效应.玻璃体系为BaO-SrO-TiO2-Al2O3-SiO2(Ce摩尔分数为0％、1％、2％、3％).随着Ce摩尔含量增加,Ce在(Ba,Sr)TiO3晶格中的占位从Ce4+取代Ti4+位的形式逐渐变成...     

Potential rare-earth modified CeO2 catalysts for soot oxidation part II: Characterisation and catalytic activity with NO + O2

Ceria (CeO₂) and rare-earth modified ceria (CeReO_x with Re = La³⁺, Pr^3+/4+, Sm³⁺, Y³⁺) supports and Pt impregnated supports are studied for the soot oxidation under a loose contact with the catalyst with the feed gas, containing NO + O₂. The catalysts are characterised by XRD, H₂-TPR, DRIFT and Raman spectroscopy. Among the single component oxides, CeO₂ is significantly more active compared with the other lanthanide oxides used in this study. Doping CeO₂ with Pr^3+/4+ and La³⁺ improved, however, the soot oxidation activity of the resulting solid solutions. This improvement is correlated with the surface area in the case of CeLaO_x and to the surface area and redox properties of CePrO_x catalyst. The NO conversion to NO₂ over these catalysts is responsible for the soot oxidation activity. If the activity per unit surface area is compared CePrO_x is the most active one. This indicates that though La³⁺ can stabilise the surface area of the catalyst in fact it decreases the soot oxidation activity of Ce⁴⁺. The lattice oxygen participates in NO conversion to NO₂ and the rate of this lattice oxygen transfer is much faster on CePrO_x. In general, the improvement of the soot oxidation is observed over the Pt impregnated CeO₂ and CeReO_x catalysts, and can be correlated to the presence of Pt°. The surface reduction of the supports in the presence of Pt occurred below 100 °C. The surface redox properties of the support in the Pt catalysts do not have a significant role in the NO to NO₂ conversion. In spite of the lower surface area, the Pt/CeYO_x and Pt/CeO₂ catalysts are found to be more active due to larger Pt crystal sizes. The presence of Pt also improved the CO conversion to CO₂ over these catalysts. The activation energy for the soot oxidation with NO + O₂ is found to be around 50 kJ/mol.     

稀土复合固体酸催化合成棕榈酸生物柴油的研究

用溶胶凝胶法制备稀土复合固体酸催化剂SO₄^2-/TiO₂/Ce⁴⁺,将其用于棕榈酸与甲醇的加压酯化反应.考察了不同制备条件对催化剂性能的影响,并对其结构进行表征.结果表明,在Ce⁴⁺浓度0.05 mol/L、H₂SO₄浓度1.38 mol/L、煅烧温度450 ℃和煅烧时间3 h的制备条件下,催化剂活性最高.棕榈酸与甲醇的加压酯化反应最佳工艺条件为:醇酸物质的量之比10:1、反应温度110 ℃、反应时间30 min、催化剂用量3%,此时转化率可达到96.33%.催化剂在重复使用4次后,转化率仍在50%以上.