Shaping of Porous CeO2 Powders into Highly Active Catalyst Carriers.

CeO2 is attracting more and more attention because of its outstanding performance in heterogeneous catalysis, as an active support and a reaction promoter in reactions of industrial interest. We herein describe a novel and scalable manufacturing process of mm-sized CeO2 spheres by a combination of extrusion and spheronization of CeO2 porous powders. In this study, wet paste formulation and fabrication procedures were optimized, and as a result methylcellulose was identified as the best plasticizer for paste extrusion to provide well-defined spherical shapes and smooth surfaces, as well as reproducible batches. After nickel impregnation (10 wt %), the catalytic performance of CeO2 supports was evaluated in the CO2 methanation reaction (T = 250-350 °C, P = 5 bar·g) and compared with that of commercial Al2O3 spheres doped or not with CeO2. These novel CeO2-based catalysts are easily reduced at a moderate temperature and more active than the Al2O3 analogues, particularly at low reaction temperatures and small reactor volumes, properties that make their implementation in emerging reactor configurations very promising.

Cu2O-Cu@Titanium Surface with Synergistic Performance for Nitrate-to-Ammonia Electrochemical Reduction.

Transition metals, such as titanium (Ti) and copper (Cu) along with their respective metal oxides (TiO2, Cu2O, and CuO), have been widely studied as electrocatalysts for nitrate electrochemical reduction with important outcomes in the fields of denitrification and ammonia generation. Based on this, this work conducted an evaluation of a composite electrode that integrates materials with different intrinsic activities (i.e., Cu and Cu2O for higher activity for nitrate conversion; Ti for higher faradaic efficiency to ammonia) looking for potential synergistic effects in the direction of ammonia generation. The specific performance of single-metal and composite electrodes has shown a strong dependence on pH and nitrate concentration conditions. Faradaic efficiency to ammonia of 92% and productivities of 0.28 mmolNH3 ·cm-2·h-1 at 0.5 V vs reversible hydrogen electrode (RHE) values are achieved, demonstrating the implicit potential of this approach in comparison to direct N2RR with values in the order of µmolNH3 ·h-1·cm-2. Finally, the electrochemical rate constants (k) for Ti, Cu, and Cu2O-Cu/Ti disk electrodes were determined by the Koutecky-Levich analysis with a rotating disk electrode (RDE) in 3.02 × 10-6, 3.88 × 10-4, and 4.77 × 10-4 cm·s-1 demonstrating an apparent synergistic effect for selective NiRR to ammonia with a Cu2O-Cu/Ti electrode.

Improvement of carbon dioxide electroreduction by crystal surface modification of ZIF-8.

Metal-organic frameworks (MOFs) possess high CO2 adsorption properties and are considered to be a promising candidate for the electrochemical carbon dioxide reduction reaction (eCO2RR). However, their insufficient selectivity and current density constrain their further exploration in the eCO2RR. In this work, by introducing a very small proportion of 2,5-dihydroxyterephthalic acid (DOBDC) into ZIF-8, a surface modified ZIF-8-5% catalyst was synthesized by a post-modification method, exhibiting enhanced selectivity (from 56% to 79%) and current density (from -4 mA cm-2 to -10 mA m-2) compared to ZIF-8. Density functional theory (DFT) calculations further demonstrate that the boosted eCO2RR performance on ZIF-8-5% could be attributed to the improved formation of the *COOH intermediate stemming from successful DOBDC surface modification. This work opens a new path for improving the catalytic properties of MOFs via their surface modification.

Engineering the Interfacial Microenvironment via Surface Hydroxylation to Realize the Global Optimization of Electrochemical CO2 Reduction.

The adsorption and activation of CO2 on the electrode interface is a prerequisite and key step for electrocatalytic CO2 reduction reaction (eCO2 RR). Regulating the interfacial microenvironment to promote the adsorption and activation of CO2 is thus of great significance to optimize overall conversion efficiency. Herein, a CO2-philic hydroxyl coordinated ZnO (ZnO-OH) catalyst is fabricated, for the first time, via a facile MOF-assisted method. In comparison to the commercial ZnO, the as-prepared ZnO-OH exhibits much higher selectivity toward CO at lower applied potential, reaching a Faradaic efficiency of 85% at -0.95 V versus RHE. To the best of our knowledge, such selectivity is one of the best records in ZnO-based catalysts reported till date. Density functional theory calculations reveal that the coordinated surficial -OH groups are not only favorable to interact with CO2 molecules but also function in synergy to decrease the energy barrier of the rate-determining step and maintain a higher charge density of potential active sites as well as inhibit undesired hydrogen evolution reaction. Our results indicate that engineering the interfacial microenvironment through the introduction of CO2-philic groups is a promising way to achieve the global optimization of eCO2 RR via promoting adsorption and activation of CO2.