Preparation of La-Ce oxide-modified platinum-cobalt nano-bimetallic catalysts with perovskite-type composite oxides as precursors and their performance in CO oxidation
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摘要: 利用钙钛矿型复合氧化物(PTO)可以将多种金属离子限域并均匀混合于钙钛矿晶格中的特点,提出了一种构筑氧化物修饰的纳米双金属催化剂团簇的新构想。以担载于大比表面积SiO2上的钙钛矿型复合氧化物La1-yCeyCo0.87Pt0.13O3/SiO2作为前驱体,将La、Ce、Co和Pt多种金属离子均匀混合并限域于PTO晶粒中,还原后得到Pt-Co/La-Ce-O/SiO2催化剂;通过氮气吸附-脱附、XRD、H2-TPR和TEM等手段对Pt-Co/La-Ce-O/SiO2催化剂进行了表征,考察了其对CO氧化的催化性能,研究了构效关系。结果发现,La-Ce-O-Pt-Co构成了纳米团簇,担载于SiO2表面,形成了Pt-Co纳米双金属颗粒;Co修饰Pt提高了其催化活性,而添加Ce进一步改善了其催化性能。当Ce含量(y)为0.2时,催化剂La0.8Ce0.2Co0.87Pt0.13O3/SiO2的活性最佳,在120℃下即可实现CO完全转化,且在含体积分数15% H2O及12.5% CO2的气氛中仍具有较好的催化性能。稳定性测试表明,所制得的Pt-Co/La-Ce-O/SiO2催化剂具有良好的稳定性和抗烧结性能。Abstract: A new scheme for constructing composite catalyst composed of oxide-modified bimetallic nanoparticles was proposed, where perovskite-type oxide (PTO) is utilized to confine multifold metal ions in the perovskite crystal lattice. With a perovskite-type oxide (PTO) of La1-yCeyCo0.87Pt0.13O3 loaded on large surface area SiO2 as the precursor, where the La, Ce, Co and Pt ions were uniformly mixed and confined in the PTO crystallites, a series of Pt-Co/La-Ce-O/SiO2 catalysts were prepared through reduction. The Pt-Co/La-Ce-O/SiO2 catalysts were characterized by nitrogen physisorption, XRD, H2-TPR and TEM; their catalytic performance in CO oxidation was investigated. The results indicate that La-Ce-O-Pt-Co clusters are constructed on the SiO2 surface, forming platinum-cobalt nano-bimetallic particles after reduction; the modification of Pt with Co can enhance the catalytic activity and the addition of Ce can further improve the catalytic performance in CO oxidation. The La0.8Ce0.2Co0.87Pt0.13O3/SiO2 catalyst with y=0.2 (representing the Ce content) exhibits high activity in CO oxidation; over it, a complete conversion of CO can be achieved at 120℃. The La0.8Ce0.2Co0.87Pt0.13O3/SiO2 catalyst performs well for CO oxidation even in the presence of 15% (volume ratio) H2O and 12.5% (volume ratio) CO2. Moreover, the oxide-modified platinum-cobalt nano-bimetallic catalysts display excellent stability with high resistance against sintering.
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Key words:
- nano-bimetal catalyst /
- perovskite-type oxide /
- CO oxidation /
- oxide promoter /
- rare earth metal
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图 2 不同Ce掺杂量(a)负载型催化剂前驱体La1-yCeyCo0.87Pt0.13O3/SiO2和(b)非负载型催化剂La1-yCeyCo0.87Pt0.13O3, 及其(c)局部放大的XRD谱图
Figure 2 XRD patterns of (a) the supported La1-yCeyCo0.87Pt0.13O3/SiO2 catalyst precursors; (b) and (c) unsupported La1-yCeyCo0.87Pt0.13O3 precursorsand
a: La0.8Ce0.2Co0.87Pt0.13O3; b: La0.85Ce0.15Co0.87Pt0.13O3; c: La0.9Ce0.1Co0.87Pt0.13O3; d: La0.95Ce0.05Co0.87Pt0.13O3; e: LaCoO3
图 4 600℃还原后的La0.8Ce0.2Co0.87Pt0.13O3/SiO2的La、Ce、Co、Pt的STEM-EDS照片和线扫描
Figure 4 STEM-EDS mapping images of La, Ce, Co, Pt and line scanning results for the used La0.8Ce0.2Co0.87Pt0.13O3/SiO2 catalyst at 600℃: surface scan area (a); distribution of the La (b), Ce (c), Co (d), and Pt (e) elements; distribution of a combination of four elements (f); sweep path (g); elemental distribution curves along the sweep path (h)
图 5 600℃还原后的((a), (b)) La0.8Ce0.2Co0.87Pt0.13O3/SiO2, ((c), (d)) LaCo0.87Pt0.13O3/SiO2及煅烧后未还原的((e), (f))La0.8Ce0.2Co0.87Pt0.13O3/SiO2的TEM照片
Figure 5 TEM images of the catalysts after reduction at 600℃ ((a) and (b)) La0.8Ce0.2Co0.87Pt0.13O3/SiO2, ((c) and (d)) LaCo0.87Pt0.13O3/SiO2 and fresh ((e) and (f))La0.8Ce0.2Co0.87Pt0.13O3/SiO2
表 1 SiO2和La1-yCeyCo0.87Pt0.13O3/SiO2的物理性质
Table 1 Textural properties of SiO2 and the supported La1-yCeyCo0.87Pt0.13O3/SiO2 catalyst precursors
Sample ABET/
(m2·g-1)dpore
/nmvpore/
(cm3·g-1)SiO2 368.5 9.3 0.87 Co:Pt=7:1 167.5 4.8 0.46 Ce-0.05 182.3 4.9 0.36 Ce-0.10 216.4 4.9 0.41 Ce-0.15 220.0 4.8 0.42 Ce-0.20 229.1 4.9 0.38 表 2 样品理论耗氢与实验耗氢对比
Table 2 Experimental and theoretical H2 consumption values of the supported La1-yCeyCo0.87Pt0.13O3/SiO2 catalyst precursors in H2-TPR
Sample Experimental H2 consumptiona /(μmol·g-1) Theoretical H2 consumption /(μmol·g-1) low temp. high temp. Pt2+→Pt0 Co3+→Co2+ Co2+→Co0 LaCoO3 10.1 23.0 - 11.0 21.9 Ce-0.05 11.9 19.1 2.6 9.0 17.9 Ce-0.1 11.0 18.2 2.6 9.0 17.9 Ce-0.15 10.0 18.9 2.6 9.0 17.9 Ce-0.2 8.2 22.4 2.6 9.0 17.9 a:experimental H2 consumptions calculated using CuO 表 3 近些年制备的具有代表性的催化活性良好的催化剂, 用以与本文所制备的在常压下CO氧化反应中使用的催化剂作对比
Table 3 A comparison of current La0.8Ce0.2Co0.87Pt0.13O3/SiO2 catalyst with the representative catalysts reported in recent years in their performance for CO oxidation
Catalyst Stability performance Ref. WHSV/
(mL·g-1·h-1)t/
℃time
t/h1%Pt-ZrO2 30000 90 40 [31] 5.0%Pt/γ-Al2O3 25000 160 112 [32] 1%Pt/Fe2O3 96000 25 2.2 [33] 3.32%Co/1.44%
Pt/TiO222000 45 2 [34] 1%Pt/Ce0.8Zr0.2O2 16800 60 50a [35] Leached 4%
Pt-0.3%Fe/CB30000 25 11 [36] 1%Pt-Co/La2O3-
CeO2/SiO2b24000 400 250 this
worka: the CO conversion was maintained at 80%; b: the catalyst was obtained by reducing La0.8Ce0.2Co0.87Pt0.13O3/SiO2 at 600℃ -
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