Structural Origin: Water Deactivates Metal Oxides to CO Oxidation and Promotes Low-Temperature CO Oxidation with Metals

摘要

Water is perhaps the most common molecule in heterogeneous catalysis, as it is unavoidable in almost any system. Interestingly, it can play completely different roles in the presence of either metals or metal oxides,which are the two most common types of the catalysts. On one hand, a moderate amount of water on the surface of late-transition metals such as Au, Pt, and Pd, Can promote low-temperature CO oxidation, which is one of the hottest topics in catalysis because of the environmental concerns. On the other hand, it can be a devastatingly poisonous species on the surface of metal oxides, the best example being the water-induced deactivation on tricobalt tetraoxide (Co3O4). Specifically, morphology-controlled Co3O4 displays extraordinarily high catalytic activity for CO oxidation at very low temperatures (ca. -77 °C). However, in the presence of trace amounts of water its activity is dramatically reduced. It is worth emphasizing that transition-metal oxides have received an increasing amount of attention for CO oxidation because of their unexpectedly high catalytic activities, low price, and especially the rich surface chemistry which affords the potential to tune the catalytic properties to a considerable degree. Moreover, the poisoning effect of H2O has also been reported for other oxide-based catalysts such as CuO and MnO_x,, and it may well be a common issue in many oxide systems. To comprehend the fundamental role of water in heterogeneous catalysis in general, the following questions need to be answered: What is the mechanism of H2O deactivation on Co3O4 oxide? How can one rationalize such a difference between metal and metal oxide systems regarding H2O effects? Herein we report a thorough investigation uncovering the origin of the deactivation of Co3O4 by H2O and addressing the general effect of H2O on metal and metal oxides by using first principles calculations.