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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Ligand Effects at Ionic Liquid-Modified Interfaces: Coadsorption of [C(2)C(1)lm][OTf] and CO on Pd(111)
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Ligand Effects at Ionic Liquid-Modified Interfaces: Coadsorption of [C(2)C(1)lm][OTf] and CO on Pd(111)

机译：离子液体修饰界面上的配体效应：[C（2）C（1）lm] [OTf]和CO在Pd（111）上的共吸附

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Thin films of ionic liquids (ILs) can be used to tune the activity and selectivity of heterogeneous catalysts and electrocatalysts (solid catalysts with IL layer, SCILL). In several cases it has been found that these IL layers have a strong beneficial effect on the selectivity. To explore the molecular origin of this phenomenon, we have performed a model study on ultrahigh-vacuum conditions. We have investigated the coadsorption of CO and the room-temperature IL [C(2)C(1)Im][OTf] (1-ethyl-3-methylimidazolium trifluoromethanesulfonate) on Pd(111) by time-resolved infrared reflection-absorption spectroscopy, temperature-programmed reflection absorption spectroscopy, and temperature-programmed desorption. We find that the [OTf](-) anion adsorbs specifically to the Pd(111) surface via the SO3- group, thereby adopting a well-defined orientation with the molecular axis oriented perpendicular to the surface. At higher IL coverage, unspecific but oriented adsorption occurs, before the orientation is successively lost in the multilayer region. Upon coadsorption of [C(2)C(1)Im][OTf] on a CO-saturated Pd(111) surface at 300 K (theta = 0.5) a well-defined coadsorption layer is formed without any loss of adsorbed CO and with very similar CO site occupation. In the coadsorption layer [OTf](-) is specifically adsorbed between the CO with a molecular orientation perpendicular to the surface. Thus, a dense and homogeneous coadsorption layer is formed in which Pd surface atoms are simultaneously coordinated to both CO and [OTf](-) ions. From this compressed layer, CO desorbs with peak temperature at 410 K (heating rate, 3.3 K/s). Above this temperature, a low-coverage coadsorption phase of CO and surface-adsorbed IL resides, with little influence of the IL on the CO desorption temperature (peak temperature, 470 K). Coadsorption of the IL gives rise to a pronounced red shift of the CO stretching frequency in the order of 50 cm(-1). The effect originates from the electrostatic interfacial field (Stark effect) generated by the coadsorbed IL and, at high coverage, possibly from additional short-range interactions. The results show that ILs form dense and well-defined mixed phases with strongly adsorbing reactants such as CO, in which a specifically adsorbed carpet of IL anions directly modifies the active surface sites by ligand-like effects.
机译：离子液体（ILs）薄膜可用于调节非均相催化剂和电催化剂（带IL层的固体催化剂，SCILL）的活性和选择性。在几种情况下，已经发现这些IL层对选择性具有很强的有益作用。为了探索这种现象的分子起源，我们对超高真空条件进行了模型研究。我们已经研究了CO和室温IL [C（2）C（1）Im] [OTf]（1-乙基-3-甲基咪唑三氟甲磺酸盐）在时间分辨的红外反射吸收上的共吸附光谱，温度程序反射吸收光谱和温度程序解吸。我们发现[OTf]（-）阴离子通过SO3-基团特异性吸附到Pd（111）表面，从而采用明确定义的取向，分子轴垂直于该表面。在较高的IL覆盖率下，在多层区域中连续失去取向之前，发生了非特异性但取向的吸附。在300 K（θ= 0.5）的CO饱和Pd（111）表面上共吸附[C（2）C（1）Im] [OTf]时，形成了明确定义的共吸附层，而不会损失任何吸附的CO和具有非常相似的CO网站职业在共吸附层中，[OTf]（-）以分子取向垂直于表面的方式特别吸附在CO之间。因此，形成致密且均匀的共吸附层，其中Pd表面原子同时与CO和[OTf]（-）离子配位。 CO从该压缩层中以410 K（加热速率，3.3 K / s）的峰值温度解吸。高于该温度，则存在低覆盖率的CO和表面吸附的IL共吸附相，IL对CO解吸温度（峰值温度470 K）的影响很小。 IL的共吸附会导致CO拉伸频率出现明显的红移，约为50 cm（-1）。该效应源自共吸附IL产生的静电界面场（Stark效应），并且在高覆盖范围内可能源自其他短程相互作用。结果表明，IL与强烈吸附的反应物（如CO）形成致密且定义明确的混合相，其中IL阴离子的特异性吸附毯通过类配体效应直接修饰活性表面位点。

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