Selective Hydrogenation of Acetylene to Ethylene in the Presence of a Carbonaceous Surface Layer on a Pd/Cu(111) Single-Atom Alloy
Selective Hydrogenation of Acetylene to Ethylene in the Presence of a Carbonaceous Surface Layer on a Pd/Cu(111) Single-Atom Alloy
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DOI：
10.1021/acscatal.7b02862
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发表时间：
2017-12-01
期刊：
影响因子：
12.9
通讯作者：
Trenary, Michael
中科院分区：
文献类型：
--
作者：
Kruppe, Christopher M.;Krooswyk, Joel D.;Trenary, Michael
采用反射吸收红外光谱（RAIRS）同时监测单原子合金（SAA）在乙炔和氢环境压力下的气相和表面物种。该合金由孤立的Pd原子组成，在Cu（111）表面的表面覆盖率在0.0028-0.085 ML范围内。当存在C_2H_2（g）而不存在H-_2（g）时，在180 ~ 500 K温度范围内，Cu（111）的RAIR谱与Pd的存在和不存在的情况相似，与C_2H_2（g）压力无关。H2（g）的加入导致不同的RAIR光谱，这取决于Pd的存在。在C2 H2：H-2比为1：100和具有小于196 Pd的SAA-Pd/Cu（111）表面的情况下，C2 H2（g）在400 K和高达10 Torr的总压力下转化为C2 H4（g）。从气相IR峰的变化率，初始周转频率的范围进行了估计，这取决于哪些网站被认为是活跃的氢化。反应后的表面分析与俄歇电子能谱（AES）显示了显着的碳覆盖率，这与增加Pd覆盖率下降。结合RAIRS和AES的结果表明，通过增加乙烯形成的反应性，Pd也限制了沉积的碳的量，同时也改变了低聚物形成的程度。
Reflection absorption infrared spectroscopy (RAIRS) was used to simultaneously monitor gas-phase and surface species in the presence of ambient pressures of acetylene and hydrogen over a single-atom alloy (SAA). The alloy consisted of isolated Pd atoms at surface coverages in the range of 0.0028-0.085 ML in a Cu(111) surface. When C2H2(g) is present, but not H-2(g), the RAIR spectra are similar for Cu(111) with and without Pd, independent of C2H2(g) pressure for temperatures between 180 and 500 K. The addition of H2(g) leads to different RAIR spectra depending on the presence of Pd. With a C2H2:H-2 ratio of 1:100 and a SAA-Pd/Cu(111) surface with less than 196 Pd, C2H2(g) is converted to C2H4(g) at 400 K at total pressures up to 10 Torr. From the rate of change in the gas-phase IR peaks, a range of initial turnover frequencies was estimated, which depend on which sites are assumed to be active for hydrogenation. Postreaction surface analysis with Auger electron spectroscopy (AES) showed a significant carbon coverage, which decreased with increasing Pd coverage. The combined RAIRS and AES results suggest that, by increasing reactivity for ethylene formation, Pd also limits the amount of carbon that is deposited, while also changing the extent of oligomer formation.