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Density functional studies show that neutral HnPAHs are able to catalyze the formation of water with no activation barrier.

Graphical abstractHighlights  Highest activation barriers for reactions with significant geometric differences between initial and final configurations were found.  The presence of superficial O vacancies promotes surface reactivity in the formation of intermediate species. Our results on surfaces with oxygen vacancies, especially ZnO (0001)vacO, are in line with current interest on these substrates in catalysis applications. Traditional BEP relationship (Eact vs Ereac) did not allow a good correlation to predict activation energy barriers.  BEP relationships referred to the initial and/or final states, allowed to accurately find activation energy barriers. AbstractA systematic theoretical study of the consecutive hydrogenation reactions of the CO molecule for the methanol synthesis catalyzed by different oxides of Zn, Ce and Ga is reported in this work. First, the CO hydrogenation with the formation of formyl species (HCO) was analyzed, followed by the successive hydrogenations that lead to formaldehyde (H2CO), methoxy (H3CO) and, finally, methanol (H3COH). The co-adsorption with H, in almost all the intermediate species, allows the corresponding hydrogenation reaction. Oxygen vacancies promote the reactivity in the generation of both formaldehyde and methoxy species. The formation of these species involves an important geometric difference between the initial and the final states, leading to high activation barriers. Comparing the surfaces studied in this work, we found that ZnO (0001)vacO has shown to be of a greater interest for methanol synthesis. However, the foregoing is not the most relevant of our results, but, instead, that the Brönsted Evans Polanyi (BEP) relationships between the initial or the final states and the transition states (TS) allowed to find a very good correlation between surface structure and reactivity.

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