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氧化物负载的纳米金催化剂对CO氧化反应具有极高的活性,这不仅依赖于金的结构特性,也取决于氧化物载体的结构.近年来,除了氧化硅、氧化铝等惰性载体以及氧化钛、氧化铈、氧化铁等可还原性载体外,人们还致力于探索各类新型氧化物载体.另一方面,锡酸锌是具有反尖晶石结构的化合物,并且在透明导电氧化物、锂离子电池阳极材料、光电转换装置以及传感器等方面应用广泛.然而,迄今为止,锡酸锌仍未被用于负载纳米金催化剂,因此相关的构效关系作用研究也十分有限.基于此,本文采用氮气吸附-脱附实验、电感耦合等离子体原子发射光谱(ICP-AES)、X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)和高分辨电镜(HRTEM)、高角环形暗场像-扫描透射电子显微镜(HAADF-STEM)、X射线吸收精细结构谱(XAFS)和氢气程序升温脱附(H_2-TPD)等手段,系统研究了锡酸锌负载的纳米金催化剂在CO氧化反应中催化性能差异的原因.首先,利用水热法制备了锡酸锌(ZTO)载体,而其织构性质可由碱(N_2H_4·H_2O)与金属离子(Zn~(2+))的比例在4/1(ZTO_1)、8/1(ZTO_2)和16/1(ZTO_3)之间进行调节.结果发现,ZTO_2具有最大的孔体积(0.223 cm~3/g)和最窄的孔径分布.再采用沉积沉淀法将0.7 wt%Au负载于其上,得到金-锡酸锌(Au_ZTO)催化剂.ICP-AES测得样品中Au含量在0.57-0.59 wt%,与投料比接近.CO氧化反应结果显示,Au_ZTO_1和Au_ZTO_2的表观活化能相同,但后者的活性更高;而Au_ZTO_3在220°C以下没有活性,催化性能最差,与纯锡酸锌载体相当.XRD结果显示,反应过程中ZTO晶相、晶胞参数及晶粒尺寸变化不明显;TEM和HRTEM分析表明,载体ZTO在反应前后均为多面体形貌,平均颗粒尺寸在12-16 nm;XPS结果验证了Zn~(2+)和Sn~(4+)离子是新鲜和反应后样品中载体金属的存在形式;HAADF-STEM探测到所有样品中均含有1-2 nm的Au粒子;XAFS结果表明,Au以Au0形式存在,并且在Au_ZTO_3中Au平均粒径大于4 nm,而其它两样品约为2 nm.H_2-TPR结果表明,金的引入对ZTO载体耗氢量影响不大,但还原峰温度向低温移动;金属-载体相互作用强弱与催化活性高低具有正相关性,即Au_ZTO_2>Au_ZTO_1>>Au_ZTO_3.这是由于不同织构性质的锡酸锌载体对于纳米金活性物种的稳定作用不同所致,具有最大孔体积和最窄孔径分布的ZTO_2负载的金纳米颗粒表现出最高活性.
Oxide supported nano-gold catalysts have high activity for CO oxidation reaction, which depends not only on the structural characteristics of gold, but also on the structure of oxide support.In recent years, in addition to silica, alumina and other inert supports and titanium oxide , Ceria, iron oxide and other reducible carriers, people are also devoted to exploring various new oxide carriers.On the other hand, zinc stannate is a compound with a counter-spinel structure, and the transparent conductive oxide, lithium However, so far, zinc stannate has not been used to support the nano-gold catalyst, so the related role of the structure-activity relationship is also very limited.Therefore, this paper uses Nitrogen adsorption-desorption experiments, ICP-AES, XRD, XPS, HRTEM, High-angle annular dark field images such as scanning electron microscopy (HAADF-STEM), X-ray absorptive fine structure (XAFS) and hydrogen temperature programmed desorption (H 2 -TPD) The reason for the difference in the catalytic performance of the supported nano-gold catalysts in the CO oxidation reaction is as follows: Firstly, a hydrotalcite-based ZTO support was prepared and its texture properties were determined by the reaction of alkali (N 2 H 4 · H 2 O) with metal ions (ZT2) and ZTO2 (ZTO3) were adjusted between 4/1 (ZTO_1), 8/1 (ZTO_2) and 16/1 (ZTO_3) .The results showed that ZTO_2 has the largest pore volume (0.223 cm 3 / g) And the narrowest pore size distribution.According to the results of ICP-AES, the content of Au in the sample was 0.57-0.59 wt% by depositing 0.7 wt% The results of CO oxidation show that the apparent activation energies of Au_ZTO_1 and Au_ZTO_2 are the same, but the latter ones are more active. However, Au_ZTO_3 has no activity below 220 ° C and has the worst catalytic performance, which is equivalent to pure zinc stannate carrier . XRD results show that during the reaction, the ZTO crystal phase, unit cell parameters and grain size changes are not obvious; TEM and HRTEM analysis showed that the carrier ZTO polyhedral morphology before and after the reaction, the average particle size in 12-16 nm; XPS The results showed that the Zn 2+ and Sn 4+ ions were present in both fresh and reacted samples. HAADF-STEM detected all samples The results of XAFS show that Au is Au0 and Au is more than 4 nm in Au_ZTO_3 and about 2 nm in the other two samples.The results of H2-TPR show that the introduction of Au The hydrogen consumption of ZTO support has little effect, but the reduction peak temperature moves to low temperature. The metal-support interaction has a positive correlation with the catalytic activity, that is Au_ZTO_2> Au_ZTO_1 >> Au_ZTO_3, which is due to the different texture properties of tin Zinc-supported Zinc-supported gold nanoparticles exhibited the highest activity due to the different stabilizing effects of the zinc-acid supports on the AuNPs.