Active sites and effects of co-adsorbed H2O on isolated methanol dehydrogenation over Pt/γ-Al2O3
Active sites and effects of co-adsorbed H2O on isolated methanol dehydrogenation over Pt/γ-Al2O3
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DOI：
10.1016/j.jcat.2021.08.027
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发表时间：
2021-09-02
影响因子：
7.3
通讯作者：
Sievers, Carsten
中科院分区：
文献类型：
--
作者：
Hare, Bryan J.;Carcamo, Ricardo A. Garcia;Sievers, Carsten
脱氢是多元醇水相重整（APR）机理的第一个反应，其速率可能受活性位点环境的影响。本研究的重点是在高真空下用红外光谱探测甲醇在基准Pt/γ-Al 2 O3催化剂上的反应。CO在线性和桥接的协调是占主导地位的表面物种的金属网站。Pt颗粒尺寸和反应温度是不同的，以确定甲醇脱氢的动力学优选的活性位点为低配位（边缘，角落，界面）或高度配位（梯田）的金属原子。高达450摄氏度的温度依赖性红外光谱的解释表明，较大的Pt颗粒在较低的温度下从完全甲醇脱氢产生更多的CO。类似地，在150摄氏度下的时间分辨等温实验表明，较大的Pt颗粒比较小的颗粒发生平衡转化快得多。不断发展的NU（C O）带（形状，振动频率，积分）的功能表明，即使在小的Pt颗粒，CO第一形式上几乎没有可用的梯田，或可能在岛屿的形式。因此，我们已经通过实验确定了高度协调的Pt金属作为更活跃的网站在整体甲醇脱氢。讨论了共吸附水和氢对脱氢活性和CO光谱的电子和化学效应。水的共吸附，水煤气变换反应所需的丰富的APR组分，似乎不会影响甲醇脱氢大Pt颗粒，但阻碍了小Pt颗粒上的反应，这是显而易见的，在各自的nu（CO）带的有限增长。(C)2021爱思唯尔公司All rights reserved.
Dehydrogenation is the first reaction of the aqueous phase reforming (APR) mechanism of polyols, and its rate is likely affected by the environment at the active site. This study focuses on reactions of methanol on benchmark Pt/gamma-Al2O3 catalysts probed by infrared spectroscopy under high vacuum. CO in linear and bridging coordination are the dominant surface species on metal sites. Pt particle sizes and reaction temperatures are varied to identify the kinetically preferred active site for methanol dehydrogenation as either lowly coordinated (edges, corners, interface) or highly coordinated (terraces) metal atoms. Interpretation of temperature-dependent IR spectra up to 450 degrees C show that larger Pt particles produce more CO at lower temperatures from complete methanol dehydrogenation. Similarly, time-resolved isothermal experiments at 150 degrees C showed equilibrium conversion occurred much faster on larger Pt particles than smaller ones. Features of evolving nu(C O) bands (shape, vibrational frequencies, integrals) suggest that, even on small Pt particles, CO first forms on the scarcely available terraces, or possibly in the form of islands. We have thus experimentally identified highly coordinated Pt metal as the more active site in overall methanol dehydrogenation. The electronic and chemical effects of co-adsorbed water and hydrogen on dehydrogenation activity and the CO spectra are discussed. The co-adsorption of water, an abundant APR component needed for the water-gas shift reaction, does not appear to affect methanol dehydrogenation on large Pt particles but hinders the reaction on small Pt particles as evident by limited growth in the respective nu(C O) bands. (C) 2021 Elsevier Inc. All rights reserved.