We report an operando examination of a model nanocrystalline In2O3 catalyst for methanol synthesis via CO2 hydrogenation (300 °C, 20 bar) by combining X-ray absorption spectroscopy (XAS), X-ray powder diffraction (XRD), and in situ transmission electron microscopy (TEM). Three distinct catalytic regimes are identified during CO2 hydrogenation: activation, stable performance, and deactivation. The structural evolution of In2O3 nanoparticles (NPs) with time on stream (TOS) followed by XANES-EXAFS-XRD associates the activation stage with a minor decrease of the In–O coordination number and a partial reduction of In2O3 due to the formation of oxygen vacancy sites (i.e., In2O3–x ). As the reaction proceeds, a reductive amorphization of In2O3 NPs takes place, characterized by decreasing In–O and In–In coordination numbers and intensities of the In2O3 Bragg peaks. A multivariate analysis of the XANES data confirms the formation of In2O3–x and, with TOS, metallic In. Notably, the appearance of molten In0 coincides with the onset of catalyst deactivation. This phase transition is also visualized by in situ TEM, acquired under reactive conditions at 800 mbar pressure. In situ TEM revealed an electron beam assisted transformation of In2O3 nanoparticles into a dynamic structure in which crystalline and amorphous phases coexist and continuously interconvert. The regeneration of the deactivated In0/In2O3–x catalyst by reoxidation was critically assessed revealing that the spent catalyst can be reoxidized only partially in a CO2 atmosphere or air yielding an average crystallite size of the resultant In2O3 that is approximately an order of magnitude larger than the initial one.

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]...

Size,m orphology,a nd surface sites of electrocatalysts have amajor impact on their performance.Understanding how, when, and why these parameters change under operating conditions is of importance for designing stable,a ctive,a nd selective catalysts.Herein, we study the reconstruction of aCubased nanocatalysts during the startup phase of the electrochemical CO 2 reduction reaction by combining results from electrochemical in situ transmission electron microscopyw ith operando X-ray absorption spectroscopy. We reveal that dissolution followed by redeposition, rather than coalescence, is the mechanism responsible for the sizei ncrease and morphology change of the electrocatalyst. Furthermore,w e point out the key role played by the formation of copper oxides in the process.U nderstanding of the underlying processes opens apathway to rational design of Cu electro (re)deposited catalysts and to stability improvement for catalysts fabricated by other methods.

Micron/nanosized particles of liquid metals possess intriguing properties and are gaining popularity for applications in various research fields. Nevertheless, the knowledge of their chemistry is still very limited compared to that of other classes of materials. In this work, we explore the reactivity of Ga nanoparticles (NPs) toward a copper molecular precursor to synthesize bimetallic Cu−Ga NPs. Anisotropic Cu−Ga nanodimers, where the two segregated domains of the constituent metals share an interface, form as the reaction product. Through a series of careful experiments, we demonstrate that a galvanic replacement reaction (GRR) between the Ga seeds and a copper-amine complex takes place. We attribute the final morphology of the bimetallic NPs, which is unusual for a GRR, to the presence of the native oxide shell around the Ga NPs and their liquid nature, via a mechanism that resembles the adhesion of bulk Ga drops to solid conductors. On the basis of this new knowledge, we also demonstrate that sequential GRRs to include more metal domains are possible. This study illustrates a new approach to the synthesis of Ga-based metal nanoparticles and provides the basis for its extension to many more systems with increased levels of complexity.

The structural reconstruction dynamics and the real HER/OER active species of cobalt phosphides/chalcogenides were revealed through operando XAS/Raman spectroscopy.

The unmatched efficiency of the direct dimethyl carbonate (DMC) synthesis from CO2 and methanol over CeO2 catalysts in the presence of an organic dehydrating agent (2cyanopyridine, 2-CP) was recently reported with high DMC yield (>90%) in both batch and continuous operations. However, the CeO2 catalyst gradually deactivates in the timescale of days due to suggested surface poisoning by 2-picolinamide (2-PA) produced by hydration of 2-CP. This work seeks for active and stable CeO2-based catalysts and aims to understand the material factors influencing the catalytic performance. Surface modification of CeO2 by the addition of rare earth metal (REM) was found effective to improve the catalyst stability. Surface basicity and reducibility of the Ce 4+ species play important roles in preventing catalyst deactivation by stabilizing the reactive methoxy species in comparison to the poisoning species (2-PA or species alike). This has been evidenced by in situ ATR-IR spectroscopy. CeO2 materials promoted with 1 wt% rare earth metals (La, Gd, and Pr) greatly enhanced the catalyst stability while retaining the high catalytic activity of CeO2. Among them, 1 wt% Pr promotion to CeO2 was the most effective, affording 35% higher DMC yield in comparison to bare CeO2 after 150 h time on stream under the optimized reaction condition of 30 bar and 120 °C.

Correlating the catalyst activity, selectivity, and stability with its structure and composition is of the utmost importance in advancing the knowledge of heterogeneous electrocatalytic processes for chemical energy conversion. Well-defined colloidal nanocrystals with tunable monodisperse size and uniform shapes are ideal platforms to investigate the effect of these parameters on the catalytic performance. In addition to translating the knowledge from single-crystal studies to more realistic conditions, the morphological and compositional complexity attainable by colloidal chemistry can provide access to active catalysts which cannot be produced by other synthetic approaches. The sample uniformity is also beneficial to investigate catalyst reconstruction processes via both ex situ and operando techniques. Finally, colloidal nanocrystals are obtained as inks, a feature which facilitates their integration on different substrates and cell configurations to study the impact of interactions at the mesoscale and the device-dependent reaction microenvironment on the catalytic outcome. In this Review, we discuss recent studies in selected electrochemical reactions and provide our outlook on future developments on the use of well-defined colloidal nanocrystals as an emerging class of electrocatalysts.

Liquid metals (LMs) have been used in electrochemistry since the 19th century, but it is only recently that they have emerged as electrocatalysts with unique properties, such as inherent resistance to coke poisoning, which derives from the dynamic nature of their surface. The use of LM nanoparticles (NPs) as electrocatalysts is highly desirable to enhance any surface-related phenomena. However, LM NPs are expected to rapidly coalesce, similarly to liquid drops, which makes their implementation in electrocatalysis hard to envision. Herein, we demonstrate that liquid Ga NPs (18 nm, 26 nm, 39 nm) drive the electrochemical CO2 reduction reaction (CO2RR) while remaining well-separated from each other. CO is generated with a maximum faradaic efficiency of around 30% at −0.7 VRHE, which is similar to that of bulk Ga. The combination of electrochemical, microscopic, and spectroscopic techniques, including operando X-ray absorption, indicates that the native oxide skin of the Ga NPs is still present during CO2RR and provides a barrier to coalescence during operation. This discovery provides an avenue for future development of Ga-based LM NPs as a new class of electrocatalysts.