The nanoscale description of the reaction pathways and of the role of the intermediate species involved in a chemical process is a crucial milestone for tailoring more active, stable, and cheaper catalysts, thus providing “reaction engineering” capabilities. This level of insight has not been achieved yet for the catalytic hydrogenation of CO2 on Ni catalysts, a reaction of enormous environmental relevance. We present a thorough atomic-scale description of the mechanisms of this reaction, studied under controlled conditions on a model Ni catalyst, thus clarifying the long-standing debate on the actual reaction path followed by the reactants. Remarkably, formate, which is always observed under standard conditions, is found to be just a “dead-end” spectator molecule, formed via a Langmuir−Hinshelwood process, whereas the reaction proceeds through parallel Eley−Rideal channels, where hydrogen-assisted C−O bond cleavage in CO2 yields CO already at liquid nitrogen temperature.

We present a computational screening study of ternary metal borohydrides for reversible hydrogen storage based on density functional theory. We investigate the stability and decomposition of alloys containing 1 alkali metal atom, Li, Na, or K ͑M 1 ͒; and 1 alkali, alkaline earth or 3d / 4d transition metal atom ͑M 2 ͒ plus two to five ͑BH 4 ͒ − groups, i.e., M 1 M 2 ͑BH 4 ͒ 2-5 , using a number of model structures with trigonal, tetrahedral, octahedral, and free coordination of the metal borohydride complexes. Of the over 700 investigated structures, about 20 were predicted to form potentially stable alloys with promising decomposition energies. The M 1 ͑Al/ Mn/ Fe͒͑BH 4 ͒ 4 , ͑Li/ Na͒Zn͑BH 4 ͒ 3 , and ͑Na/ K͒͑Ni/ Co͒͑BH 4 ͒ 3 alloys are found to be the most promising, followed by selected M 1 ͑Nb/ Rh͒͑BH 4 ͒ 4 alloys.

In the perspective of a sustainable energy economy, CO2\ud reduction is attracting increasing attention as a key step toward the synthesis of fuels and valuable chemicals. A possible strategy to develop novel conversion catalysts consists in mimicking reaction centers available in nature, such as those in enzymes in which Fe, Ni, and Cu play a major role as active metals. In this respect, NiCu shows peculiar activity for both water-gas shift and methanol\ud synthesis reactions. The identification of useful descriptors to engineer and tune the reactivity of a surface in the desired way is one of the main objectives of the science of catalysis, with evident applicative interest, as in this case. To this purpose, a crucial issue is the determination of the relevant active sites and rate-limiting steps. We show here that this approach can be exploited to design and tailor the catalytic activity and selectivity of a NiCu surface