The mechanism of the poisoning of ammonia synthesis catalysts by oxygenates O2, CO and H2O: an in situ method for active surface determination

FeOx-Modified Ultrafine Platinum Particles Supported on MgFe2O4 with High Catalytic Activity and Promising Stability toward Low-Temperature Oxidation of CO

Catalytic oxidation is widely recognized as a highly effective approach for eliminating highly toxic CO. The current challenge lies in designing catalysts that possess exceptional low-temperature activity and stability. In this work, we have prepared ultrafine platinum particles of ~1 nm diameter dispersed on a MgFe2O4 support and found that the addition of 3 wt.% FeOx into the 3Pt/MgFe2O4 significantly improves its activity and stability. At an ultra-low temperature of 30 °C, the CO can be totally converted to CO2 over 3FeOx-3Pt/MgFe2O4. High and stable performances of CO-catalytic oxidation can be obtained at 60 °C on 3FeOx-3Pt/MgFe2O4 over 35 min on-stream at WHSV = 30,000 mL/(g·h). Based on a series of characterizations including BET, XRD, ICP, STEM, H2-TPR, XPS, CO-DRIFT, O2-TPD and CO-TPD, it was disclosed that the relatively high activity and stability of 3FeOx-3Pt/MgFe2O4 is due to the fact that the addition of FeOx could facilitate the antioxidant capacity of Pt and oxygen mobility and increase the proportion of adsorbed oxygen species and the amounts of adsorbed CO. These results are helpful in designing Pt-based catalysts exhibiting higher activity and stability at low temperatures for the catalytic oxidation of CO.

Sulfidation of MoO3/γ-Al2O3 towards a highly efficient catalyst for CH4 reforming with H2S

The structural evolution of MoO₃/γ-Al₂O₃ during sulfidation and a subsequent CH₄/H₂S reforming reaction is revealed, and the structure–performance relationships are established.

New approach to consecutive CO oxidation and CO2 chemisorption using Li2CuO2 ceramics modified with Na- and K-molten salts

The addition of alkali carbonates to Li₂CuO₂ improved the CO oxidation and the subsequent CO₂ with a high ratio of captured/released CO₂. Materials modified with a single carbonate presented the best enhancement for the removal of both CO_X.

Poisoning of Ammonia Synthesis Catalyst Considering Off-Design Feed Compositions

Activity of ammonia synthesis catalyst in the Haber-Bosch process is studied for the case of feeding the process with intermittent and impurity containing hydrogen stream from water electrolysis. Hydrogen deficiency due to low availability of renewable energy is offset by increased flow rate of nitrogen, argon, or ammonia, leading to off-design operation of the Haber-Bosch process. Catalyst poisoning by ppm levels of water and oxygen is considered as the main deactivation mechanism and is evaluated with a microkinetic model. Simulation results show that catalyst activity changes considerably with feed gas composition, even at exceptionally low water contents below 10ppm. A decreased hydrogen content always leads to lower poisoning of the catalyst. It is shown that ammonia offers less flexibility to the operation of Haber-Bosch process under fluctuating hydrogen production compared to nitrogen and argon. Transient and significant changes of catalyst activity are expected in electrolysis coupled Haber-Bosch process.

Biomimetic O2 adsorption in an iron metal-organic framework for air separation

Bio-inspired motifs for gas binding and small molecule activation can be used to design more selective adsorbents for gas separation applications. Here, we report an iron metal–organic framework, Fe-BTTri (Fe₃[(Fe₄Cl)₃(BTTri)₈]₂·18CH₃OH, H₃BTTri = 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene), that binds O₂ in a manner similar to hemoglobin and therefore results in highly selective O₂ binding. As confirmed by gas adsorption studies and Mössbauer and infrared spectroscopy data, the exposed iron sites in the framework reversibly adsorb substantial amounts of O₂ at low temperatures by converting between high-spin, square-pyramidal Fe(ii) centers in the activated material to low-spin, octahedral Fe(iii)–superoxide sites upon gas binding. This change in both oxidation state and spin state observed in Fe-BTTri leads to selective and readily reversible O₂ binding, with the highest reported O₂/N₂ selectivity for any iron-based framework.

Bio-inspired motifs for gas binding and small molecule activation can be used to design more selective adsorbents for gas separation applications.

Synthesis of ammonia directly from air and water at ambient temperature and pressure

The N≡N bond (225 kcal mol⁻¹) in dinitrogen is one of the strongest bonds in chemistry therefore artificial synthesis of ammonia under mild conditions is a significant challenge. Based on current knowledge, only bacteria and some plants can synthesise ammonia from air and water at ambient temperature and pressure. Here, for the first time, we report artificial ammonia synthesis bypassing N₂ separation and H₂ production stages. A maximum ammonia production rate of 1.14 × 10⁻⁵ mol m⁻² s⁻¹ has been achieved when a voltage of 1.6 V was applied. Potentially this can provide an alternative route for the mass production of the basic chemical ammonia under mild conditions. Considering climate change and the depletion of fossil fuels used for synthesis of ammonia by conventional methods, this is a renewable and sustainable chemical synthesis process for future.