Calculated answer: First‐principles calculations have been applied to calculate the energy barrier for the key step in CO formation on a Pt surface (see picture; Pt blue, Pt atoms on step edge yellow) to understand the low CO2 selectivity in the direct ethanol fuel cell. The presence of surface oxidant species such as O (brown bar) and OH (red bar) led to an increase of the energy barrier and thus an inhibition of the key step.
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, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] 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. [1][2][3][4][5][6] On the other hand, it can be a devastatingly poisonous species on the surface of metal oxides, the best example being the waterinduced deactivation on tricobalt tetraoxide (Co 3 O 4 ). [7][8][9][10][11][12][13][14][15] Specifically, morphology-controlled Co 3 O 4 [7, 16, 17] displays extraordinarily high catalytic activity for CO oxidation at very low temperatures (ca. À77 8C). However, in the presence of trace amounts of water its activity is dramatically reduced. [7][8][9][10][11][12] 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. [18][19][20] Moreover, the poisoning effect of H 2 O 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. [13][14][15] To comprehend the fundamental role of water in heterogeneous catalysis in general, the following questions need to be answered: What is the mechanism of H 2 O deactivation on Co 3 O 4 oxide? How can one rationalize such a difference between metal and metal oxide systems regarding H 2 O effects? Herein we report a thorough investigation uncovering the origin of the deactivation of Co 3 O 4 by H 2 O and addressing the general effect of H 2 O on metal and metal oxides by using first principles calculations.The deactivation resulting from the presence of water is the main obstacle currently limiting the application of Co 3 O 4 to CO oxidation, and the deactivation mechanism is much debated. The following suggestions regarding the water poisoning effect have been proposed: [7][8][9][10][11][12] 1) water molecules strongly adsorb at the active site, thus blocking the CO adsorption; or 2) water dissociation occurs on the catalyst surface to form a surface OH group that inhibits the adsorption of CO or O 2 ; or 3) the formation of graphitetype carbon deposits or surface carbonate (CO 3 2À ) species. However, no consensus has been reached. To the best of our knowledge, there is only one theoretical study reported concerning the deactivation mechanism at the molecular level, and it focused on the competing effect of the molecular adsorption of H 2 O at active Co 3+ sites. [11b] In this work, almost all the possible deactivation pathways of Co 3 O 4 with regard to wa...
Fractions of methylated naphthenic acids (NAs) isolated from oil sands process-affected waterwere collected utilizing Kugelrohr distillation and analyzed by proton nuclear magnetic resonance (1H NMR) spectroscopy. 1H NMR analysis revealed that the ratio of methyl ester hydrogen atoms to remaining aliphatic hydrogen atoms increased from 0.130 to 0.214, from the lowest to the greatest molecular weight (MW) fractions, respectively, indicating that the carboxylic acid content increased with greater MW. Acute toxicity assays with exposure to monocarboxyl NA-like surrogates demonstrated that toxicity increased with increasing MW (D. magna LC50 values of 10 +/- 1.3 mM and 0.59 +/- 0.20 mM for the respective lowest and highest MW NA-like surrogates); however, with the addition of a second carboxylic acid moiety, the toxicity was significantly reduced (D. magna LC50 values of 10 +/- 1.3 mM and 27 +/- 2.2 mM forthe respective monocarboxyl and dicarboxyl NA-like surrogates of similar MW). Increased carboxylic acid content within NA structures of higher MW decreases hydrophobicity and, consequently, offers a plausible explanation as to why lower MW NAs in oil sands process-affected water are more toxic than the greater MW NAs.
The reduction in anxiety in the intervention group indicates that preoperative information videos are an effective method of reducing anxiety in parents. Furthermore, the reduction in need for information score in the intervention group indicates that preoperative videos may be a useful tool for providing parents with information.
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