The co-adsorption of hydrogen and carbon monoxide on Pd₃Ag(111) alloy surfaces has been studied as a model system for Pd-Ag alloys in membrane and catalysis applications using periodic density functional theory calculations (PW91-GGA). We explored the effects of Pd–Ag surface composition, since segregation of silver towards and away from the surface has been suggested to explain the experimentally observed changes in H₂ activation, CO inhibition and reactivity. We found that CO pre-adsorbed on the surface weakens the adsorption of H on Pd₃Ag(111) alloy surfaces irrespective of whether the surface termination corresponds to the bulk Pd₃Ag composition, or is purely Pd-terminated. A higher coverage of H with CO present is obtained for the Pd-terminated surface; this surface also exhibits a larger range of chemical potentials for co-adsorbed hydrogen and CO. The barrier for H₂ activation increases with increasing CO coverage, but the surface composition has the largest impact on H₂ activation at intermediate CO coverage. The results imply that Pd-based membranes with typically ~ 23 wt% Ag are less prone to CO poisoning if the surface becomes Pd-terminated.

氢和一氧化碳在Pd ₃ Ag（111）合金表面上的共吸附已通过周期性密度泛函理论计算（PW91-GGA）作为膜和催化应用中Pd-Ag合金的模型系统进行了研究。我们已经探究了Pd-Ag表面组成的影响，因为已经提出银向表面和远离表面的偏析可以解释实验观察到的H ₂活化，CO抑制和反应性的变化。我们发现，预吸附在表面上的CO减弱了H在Pd ₃ Ag（111）合金表面上的吸附，无论表面终止处是否对应于块体Pd ₃Ag组成，或纯Pd终止。对于Pd封端的表面，H和CO的覆盖率更高。该表面还显示出更大的范围共吸附的氢和CO的化学势的。对于H中的屏障₂与CO覆盖率增加活化的增加，但表面组合物对小时最大冲击₂在中间CO覆盖活化。结果表明，如果表面变为Pd端基，则Ag含量通常约为23 wt％的Pd基膜更不容易发生CO中毒。