Nanoscale Solvation Leads to Spontaneous Formation of a Bicarbonate Monolayer on Rutile (110) under Ambient Conditions: Implications for CO2 Photoreduction
Nanoscale Solvation Leads to Spontaneous Formation of a Bicarbonate Monolayer on Rutile (110) under Ambient Conditions: Implications for CO2 Photoreduction
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DOI：
10.1021/acs.jpcc.6b02132
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发表时间：
2016-05-05
影响因子：
3.7
通讯作者：
Hines, Melissa A.
中科院分区：
文献类型：
--
作者：
Song, Anqi;Skibinski, Erik S.;Hines, Melissa A.
在operando中，催化剂的化学状态对于针对少数物种的催化剂尤其重要，例如大气中的CO，其浓度仅为400ppm。反应可以通过反应物的选择性结合来促进，也可以通过阻断活性位点的分子来阻碍。我们发现，在环境条件下，至少在金红石（110）上，吸附的CO2（一种非常弱的结合物）不太可能在CO光还原中发挥关键作用，因为绝大多数不饱和Ti位点被另一种更强结合的碳质物质——吸附的碳酸氢盐（HCO3）终止。利用扫描隧道显微镜（STM）和表面光谱相结合的方法，我们发现大气中的CO可以迅速而稳定地取代金红石（110）上吸附的H2O，形成自组装的HCO3和H单层，即使在真空中也可以在室温下稳定。该反应发生在接近理想的化学计量金红石（110）上，不需要表面缺陷，如0空位、Ti间隙或台阶。这一反应是由HCO3的强双齿键和TiO2在环境条件下自发形成的纳米级水膜共同促进的。密度泛函理论计算表明，吸附在金红石（110）上的纳米水层使产物溶剂化，并显著改变了反应的能量。H2O反应解离产生的半单层吸附H也会影响催化剂在operando中的化学状态。
The chemical state of a catalyst in operando is particularly important for catalysts that target minority species, such as atmospheric CO, which has a concentration of only 400 ppm. A reaction can be promoted by the selective binding of reactants or hindered by molecules that block active sites. We show that adsorbed CO2, a very weakly bonded species on TiO2, is unlikely to play the key role in CO, photoreduction under ambient conditions, at least on rutile (110), as the vast majority of unsaturated Ti sites are terminated by a different, much more strongly bound carbonaceous species: adsorbed bicarbonate (HCO3). Using a combination of scanning tunneling microscopy (STM) and surface spectroscopies, we show that atmospheric CO, readily and stably displaces adsorbed H2O on rutile (110), creating a self-assembled monolayer of HCO3 and H that is stable at room temperature even in vacuum. This reaction occurs on near-ideal, stoichiometric rutile (110) and does not require surface defects, such as 0 vacancies, Ti interstitials, or steps. This reaction is promoted both by the strong bidentate bonding of HCO3 as well as the nanoscale H2O film that spontaneously forms on TiO2 under ambient conditions. Density functional theory calculations show that the nanoscale water layer adsorbed to rutile (110) solvates the products and changes the reaction energetics significantly. The chemical state of the catalyst in operando will also be affected by the half-monolayer of adsorbed H produced by the reactive dissociation of H2O.