Management of carbon on Earth has become one of the central themes in science, society,a nd politics owing to continuous relocation of carbon from the underground to the atmosphere in the form of carbon dioxide (CO 2 ). This is ac onsequenceo ft he modern life of mankind largely relying on burning or utilising carbon-based fossil fuels, which also causes their depletion. Recently,g lobalw arminga nd consequent climate change have been ascribed to the increasingc oncentration of atmosphericg reen-houseg ases,m ostr epresented by CO 2 ,a nd the world is joining forces to reduce the amount of CO 2 emissiont ot he atmosphere and convertt he "waste" CO 2 into valuable chemicals like polymers and fuels.CO 2 is at hermodynamically stable molecule with the standard formation enthalpy of À393.5 kJ mol À1 . [1] However,C O 2 can be transformed with notable reactivity depending on the chemicale nvironment. Among them catalysis offerss pecific sites to activateC O 2 for its chemical transformation. While CO 2 to polymers is generally enabled by efficient homogeneous catalysts (i.e. reactants and catalyst are in the same liquid phase), large-scale production of useful chemicals like fuels necessitates continuous operation using heterogeneous catalyst to activate CO 2 over its surface. There are several activation methods overc atalyst surfacer eported to date and each methodg enerally leads characteristicr eactivityo fC O 2 and products due to the unique form of activated CO 2 during transformation. Thisa rticle aims at concisely describing the reactivity of CO 2 in general, summarising the state-of-the-art activation methods and also highlighting similarities in different modes of CO 2 activation and correlations to product selectivity to evaluatec oherent views on CO 2 transformation over catalytic surfaces.The general properties of the CO 2 molecule, associatedw ith its reactivity,are summarised in the following four points: 1) Bending of CO 2For the uncharged state, bending of the molecule from its linear equilibrium geometry induces changes in the shape and energy level of the molecular orbitals. Notably,t he more bent the geometry,t he lower the energy level of the in-plane (i.e. to the plane of bending) contribution of 2p u orbital( the lowest unoccupied molecular orbital, LUMO) as shown in Figure 1. Changing the OCO bond angle from 1808 to 1578,t he proportion of the LUMO on the carbon is increased from 61 %t o 78 %, while the distance between carbon ando xygen (< 0.01 )a nd the energy (DE < 0.5 eV) remaina lmostc onstant. [2] Importantly,t his loweringo ft he in-plane 2p u orbital (LUMO) energy upon bending makest he carbon atom electrophilic. 2) Repartition of the ChargesWhen isolated, ap ositive chargec an be found on the carbon atom (the Mulliken's population is + 0.368 e) and negative chargeso nt he two oxygen atoms (with ap opulation of À0.184 e). [3] Ap olarized mediuml ike water can increase the charge on the carbon to + 0.407 e( obtained by DFT using a polarizable continuumm odel with al inear geometry). [3]...

Selective hydrogenation of CO2 into methanol is a key sustainable technology, where Cu/Al2O3 prepared by surface organometallic chemistry displays high activity towards CO2 hydrogenation compared to Cu/SiO2, yielding CH3OH, dimethyl ether (DME), and CO. CH3OH formation rate increases due to the metal–oxide interface and involves formate intermediates according to advanced spectroscopy and DFT calculations. Al2O3 promotes the subsequent conversion of CH3OH to DME, showing bifunctional catalysis, but also increases the rate of CO formation. The latter takes place 1) directly by activation of CO2 at the metal–oxide interface, and 2) indirectly by the conversion of formate surface species and CH3OH to methyl formate, which is further decomposed into CH3OH and CO. This study shows how Al2O3, a Lewis acidic and non‐reducible support, can promote CO2 hydrogenation by enabling multiple competitive reaction pathways on the oxide and metal–oxide interface.

Methyl formate synthesis by hydrogenation of carbon dioxide in the presence of methanol offers a promising path to valorize carbon dioxide. In this work, silica-supported silver nanoparticles are shown to be a significantly more active catalyst for the continuous methyl formate synthesis than the known gold and copper counterparts, and the origin of the unique reactivity of Ag is clarified. Transient in situ and operando vibrational spectroscopy and DFT calculations shed light on the reactive intermediates and reaction mechanisms: a key feature is the rapid formation of surface chemical species in equilibrium with adsorbed carbon dioxide. Such species is assigned to carbonic acid interacting with water/hydroxyls on silica and promoting the esterification of formic acid with adsorbed methanol at the perimeter sites of Ag on SiO2 to yield methyl formate. This study highlights the importance of employing combined methodologies to verify the location and nature of active sites and to uncover fundamental catalytic reaction steps taking place at metal–support interfaces.

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Selective hydrogenation of CO 2 into methanol is ak ey sustainable technology,w here Cu/Al 2 O 3 prepared by surface organometallic chemistry displays high activity to-wardsC O 2 hydrogenation compared to Cu/SiO 2 ,y ielding CH 3 OH, dimethyl ether (DME), and CO.C H 3 OH formation rate increases due to the metal-oxide interface and involves formate intermediates according to advanced spectroscopyand DFT calculations.A l 2 O 3 promotes the subsequent conversion of CH 3 OH to DME, showing bifunctional catalysis,b ut also increases the rate of CO formation. The latter takes place 1) directly by activation of CO 2 at the metal-oxide interface, and 2) indirectly by the conversion of formate surface species and CH 3 OH to methyl formate,w hich is further decomposed into CH 3 OH and CO.T his study shows howA l 2 O 3 ,aLewis acidic and non-reducible support, can promote CO 2 hydrogenation by enabling multiple competitive reaction pathways on the oxide and metal-oxide interface.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.