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]...

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The recently demonstrated concept to combine CO2 capture and utilization in one process using isothermal unsteady-state operation, namely CO2 capture and reduction (CCR), was applied for the first time to CO2 methanation using unpromoted and K-or La-promoted Ni/ZrO2 catalysts. Both K and La promoters significantly improve CO2 capture capacity and also CO2 conversion selectivity to methane. The K-promoted catalyst (Ni-K/ZrO2) captures a larger amount of CO2 at high temperature but the capture capacity drops at low temperature due to incomplete catalyst regeneration during the cyclic unsteady-state reaction condition. In contrast, the La-promoted catalyst (Ni-La/ZrO2) shows temperatureindependent CO2 capture capacity and rapid reduction of captured CO2, thus leading to stable CCR performance. The nature of the active sites and mechanistic details were gained by TPR, reductive CO2-TPD and space-and time-resolved operando DRIFTS, holistically elucidating the effects of the promoters and their impacts on CCR activity.

Mn-doped La 0.8 Sr 0.2 CoO 3 perovskite oxides (La 0.8 Sr 0.2 Co 1-x Mn x O 3 ; x = 0, 0.1, 0.3, 0.5) were synthesized by a modified sol-gel method. The phase-pure oxides were obtained. CoO and carbonates were formed on the surface of La 0.8 Sr 0.2 CoO 3 . With increasing doping content, these impurities were reduced while the stability of the perovskite structure was improved. The valence state of B-site ions and the amount of absorbed oxygen were influenced by Mn doping. The catalytic activity of the perovskite catalysts was investigated for CO oxidation and simultaneous removal of CO, C 3 H 8 , and NO. For CO and NO removal, La 0.8 Sr 0.2 Co 0.9 Mn 0.1 O 3 exhibited the best performance. For C 3 H 8 removal, the reactivity was promoted linearly with the doping content. The structure-activity relationship is also discussed.