Stabilization of Catalytic Surfaces through Core–Shell Structures: Ag–Ir/Al 2 O 3 Case Study
Stabilization of Catalytic Surfaces through Core–Shell Structures: Ag–Ir/Al 2 O 3 Case Study
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通过核-壳结构稳定催化表面：Ag-Ir/Al 2 O 3 案例研究
DOI：
10.1021/acscatal.0c03297
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发表时间：
2020
期刊：
影响因子：
12.9
通讯作者：
Monnier, J. R.
中科院分区：
文献类型：
--
作者：
Parizad, M.;Wong, A. P.;Reber, A. C.;Tengco, J. M.;Karakalos, S. G.;Khanna, S. N.;Regalbuto, J. R.;Monnier, J. R.
为了解决催化剂在高温下的稳定性和活性的挑战，催化剂组合物和制备方法是至关重要的。在此背景下，我们采用强静电吸附和化学沉积（艾德）的方法在不同的氧化铝载体（δ，θ-Al_2O_3和γ-Al_2O_3）上合成了高分散的Ag/Ir。Ag的表面自由能（SFE）（1302 erg/cm 2）远低于Ir的表面自由能（3231 erg/cm 2）;表面热力学指示Ir-Ag系统应布置成提供位于Ir表面上的Ag层的最低自由能，以最小化Ir的高SFE。催化剂在高温退火处理（400、600和800 °C）下保持分散。对于所有的Ag-Ir/δ，θ-Al 2 O3样品，在400和600 °C退火后的H2化学吸附值高于在200 °C退火后的H2化学吸附值，并且显著高于用作基础催化剂的相应的1.0 wt % Ir/δ，θ-Al 2 O3。X-射线衍射数据和扫描透射电子显微镜图像表明，这两个monocrystalline催化剂烧结，但沉积的银壳由艾德防止烧结的Ag和Ir。程序升温脱附H2测量证实了高H2吸收化学吸附实验，并表明额外的H2容量是因为更弱的结合H。计算和X射线光电子能谱的结果表明，过量的H2化学吸附可以通过将多达四个H原子结合到在温度>400 °C下预处理的Pd催化剂的壳中被Ag包围的单表面Ir原子来解释。因此，H2容量从H/Ir = 1：1的正常吸附化学计量增加到高达4：1。
To solve the challenges of catalyst stability and activity at high temperatures, catalyst composition and method of preparation are critical. In this context, the well-established methods of strong electrostatic adsorption and electroless deposition (ED) have been used to synthesize highly dispersed Ag/Ir on different alumina supports (δ,θ-Al2O3and γ-Al2O3). The surface free energy (SFE) of Ag (1302 erg/cm2) is much lower than that of Ir (3231 erg/cm2); surface thermodynamics dictate the Ir–Ag system should arrange to give the lowest free energy of an Ag layer localized on the Ir surface to minimize the high SFE of Ir. The catalysts remained dispersed at high-temperature annealing treatments (400, 600, and 800 °C). For all Ag–Ir/δ,θ-Al2O3samples, H2chemisorption values were higher after annealing at 400 and 600 °C than at 200 °C and were considerably higher than for the corresponding 1.0 wt % Ir/δ,θ-Al2O3used as the base catalyst. X-ray diffraction data and scanning transmission electron microscopy images indicate that both monometallic catalysts sintered, but deposition of an Ag shell by ED prevented the sintering of both Ag and Ir. Temperature-programmed desorption of H2measurements corroborates the high H2uptake chemisorption experiments and indicated the additional H2capacity was because of more weakly bound H. Computational and X-ray photoelectron spectroscopy results suggest the excess H2chemisorption can be accounted for by binding up to four H atoms to single-surface Ir atoms surrounded by Ag in the shell of the bimetallic catalysts that have been pretreated at temperatures >400 °C. As a result, H2capacity increases from the normal adsorption stoichiometry of H/Ir = 1:1 up to as high as 4:1.