MnOx/IrOx as Selective Oxygen Evolution Electrocatalyst in Acidic Chloride Solution.

The oxygen evolution reaction (OER) and chlorine evolution reaction (CER) are electrochemical processes with high relevance to water splitting for (solar) energy conversion and industrial production of commodity chemicals, respectively. Carrying out the two reactions separately is challenging, since the catalytic intermediates are linked by scaling relations. Optimizing the efficiency of OER over CER in acidic media has proven especially difficult. In this regard, we have investigated the OER versus CER selectivity of manganese oxide (MnOx), a known OER catalyst. Thin films (∼5-20 nm) of MnOx were electrodeposited on glassy carbon-supported hydrous iridium oxide (IrOx/GC) in aqueous chloride solutions of pH ∼0.9. Using rotating ring-disk electrode voltammetry and online electrochemical mass spectrometry, it was found that deposition of MnOx onto IrO x decreases the CER selectivity of the system in the presence of 30 mM Cl- from 86% to less than 7%, making it a highly OER-selective catalyst. Detailed studies of the CER mechanism and ex-situ structure studies using SEM, TEM, and XPS suggest that the MnOx film is in fact not a catalytically active phase, but functions as a permeable overlayer that disfavors the transport of chloride ions.

Effects of Substrate and Polymer Encapsulation on CO2 Electroreduction by Immobilized Indium(III) Protoporphyrin.

Heterogenization of molecular catalysts for CO2 electroreduction has attracted significant research activity, due to the combined advantages of homogeneous and heterogeneous catalysts. In this work, we demonstrate the strong influence of the nature of the substrate on the selectivity and reactivity of electrocatalytic CO2 reduction, as well as on the stability of the studied immobilized indium(III) protoporphyrin IX, for electrosynthesis of formic acid. Additionally, we investigate strategies to improve the CO2 reduction by tuning the chemical functionality of the substrate surface by means of electrochemical and plasma treatment and by catalyst encapsulation in polymer membranes. We point out several underlying factors that affect the performance of electrocatalytic CO2 reduction. The insights gained here allow one to optimize heterogenized molecular systems for enhanced CO2 electroreduction without modification of the catalyst itself.

Challenges in the Greener Production of Formates/Formic Acid, Methanol, and DME by Heterogeneously Catalyzed CO2 Hydrogenation Processes.

The recent advances in the development of heterogeneous catalysts and processes for the direct hydrogenation of CO2 to formate/formic acid, methanol, and dimethyl ether are thoroughly reviewed, with special emphasis on thermodynamics and catalyst design considerations. After introducing the main motivation for the development of such processes, we first summarize the most important aspects of CO2 capture and green routes to produce H2. Once the scene in terms of feedstocks is introduced, we carefully summarize the state of the art in the development of heterogeneous catalysts for these important hydrogenation reactions. Finally, in an attempt to give an order of magnitude regarding CO2 valorization, we critically assess economical aspects of the production of methanol and DME and outline future research and development directions.

Structural and elemental influence from various MOFs on the performance of Fe@C catalysts for Fischer-Tropsch synthesis.

The structure and elementary composition of various commercial Fe-based MOFs used as precursors for Fischer-Tropsch synthesis (FTS) catalysts have a large influence on the high-temperature FTS activity and selectivity of the resulting Fe on carbon composites. The selected Fe-MOF topologies (MIL-68, MIL-88A, MIL-100, MIL-101, MIL-127, and Fe-BTC) differ from each other in terms of porosity, surface area, Fe and heteroatom content, crystal density and thermal stability. They are re-engineered towards FTS catalysts by means of simple pyrolysis at 500 °C under a N2 atmosphere and afterwards characterized in terms of porosity, crystallite phase, bulk and surface Fe content, Fe nanoparticle size and oxidation state. We discovered that the Fe loading (36-46 wt%) and nanoparticle size (3.6-6.8 nm) of the obtained catalysts are directly related to the elementary composition and porosity of the initial MOFs. Furthermore, the carbonization leads to similar surface areas for the C matrix (SBET between 570 and 670 m2 g-1), whereas the pore width distribution is completely different for the various MOFs. The high catalytic performance (FTY in the range of 1.9-4.6 × 10-4 molCO gFe-1 s-1) of the resulting materials could be correlated to the Fe particle size and corresponding surface area, and only minor deactivation was found for the N-containing catalysts. Elemental analysis of the catalysts containing deliberately added promoters and inherent impurities from the commercial MOFs revealed the subtle interplay between Fe particle size and complex catalyst composition in order to obtain high activity and stability next to a low CH4 selectivity.

Metal organic framework-mediated synthesis of highly active and stable Fischer-Tropsch catalysts.

Depletion of crude oil resources and environmental concerns have driven a worldwide research on alternative processes for the production of commodity chemicals. Fischer-Tropsch synthesis is a process for flexible production of key chemicals from synthesis gas originating from non-petroleum-based sources. Although the use of iron-based catalysts would be preferred over the widely used cobalt, manufacturing methods that prevent their fast deactivation because of sintering, carbon deposition and phase changes have proven challenging. Here we present a strategy to produce highly dispersed iron carbides embedded in a matrix of porous carbon. Very high iron loadings (>40 wt %) are achieved while maintaining an optimal dispersion of the active iron carbide phase when a metal organic framework is used as catalyst precursor. The unique iron spatial confinement and the absence of large iron particles in the obtained solids minimize catalyst deactivation, resulting in high active and stable operation.

A self-assembled delivery platform with post-production tunable release rate.

Self-assembly of three molecular components results in a delivery platform, the release rate of which can be tuned after its production. A fluorophore-conjugated gelator can be hydrolyzed by an enzyme, resulting in the release of a fluorescent small molecule. To allow the release to be tunable, the enzyme is entrapped in liposomes and can be liberated by heating the system for a short period. Crucially, the heating time determines the amount of enzyme liberated; with that, the release rate can be tuned by the time of heating.