科研之友
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摘要
A versatile though straightforward process to functionalize materials is to deposit thin metal films or add coadsorbates in a controlled way. Referring to the direct methanol fuel cell, it is desirable to influence chemical reactivity and selectivity of catalysts to convert methanol to CO(2) instead of CO which acts as a poison affecting continued and stable operation. In this study Fourier transform infrared spectroscopy, temperature-programmed desorption, and X-ray photoelectron spectroscopy were used to study the reactions of methanol (CD(3)OH) on Cu monolayers on Ru(0001). In contrast to the inert pure Cu/Ru(0001) monolayer, the oxygen-covered Cu/Ru(0001) layer exhibits enhanced reactivity toward methanol activation and methoxy (CD(3)O) formation. Interestingly, the ordered (2 x 2)-O phase is unreactive as well, which indicates a reduced affinity of this ordered array of oxygen atoms toward hydrogenation. Activation of methanol therefore occurs primarily in dilute oxygen environments or at defects and domain boundaries of the (2 x 2)-O phase. Under such favorable conditions (upright) methoxy is formed readily, even at low T < 80 K. If oxygen layers are not annealed (T <= 80 K) prior to methanol admission methanol adsorbs dissociatively even at 20 K. In general, methoxy formation is accompanied by the formation of surface hydroxyl (OH) which desorbs as water at 300-350 K Methoxy represents the main intermediate up to 350 K Depending on the oxygen coverage, further annealing transforms methoxy into formaldehyde (D(2)CO), which desorbs instantaneously, or methoxy is oxidized to formate (DCOO), which represents a stable intermediate and eventually produces (desorbing) CO(2) at T > 450 K. As a minority species formyl (DCO) is identified.
- 出版日期2011-8-25
