Catalytic Behavior of K-doped Fe/MgO Catalysts for Ammonia Synthesis Under Mild Reaction Conditions.

An important part of realizing a carbon-neutral society using ammonia will be the development of an inexpensive yet efficient catalyst for ammonia synthesis under mild reaction conditions (<400 °C, <10 MPa). Here, we report Fe/K(3)/MgO, fabricated via an impregnation method, as a highly active catalyst for ammonia synthesis under mild reaction conditions (350 °C, 1.0 MPa). At the mentioned conditions, the activity of Fe/K(3)/MgO (17.5 mmol h-1 gcat -1 ) was greater than that of a commercial fused iron catalyst (8.6 mmol h-1 gcat -1 ) currently used in the Haber-Bosch process. K doping was found to increase the ratio of Fe0 on the surface and turnover frequency of Fe in our Fe/K(3)/MgO catalyst. In addition, increasing the pressure to 3.0 MPa at the same temperature led to a significant improvement of the ammonia synthesis rate to 29.6 mmol h-1 gcat -1 , which was higher than that of two more expensive, benchmark Ru-based catalysts, which are also potential alternative catalysts. A kinetics analysis revealed that the addition of K enhanced the ammonia synthesis activity at ≥300 °C by changing the main adsorbed species from NH to N which can accelerate dissociative adsorption of nitrogen as the rate limiting step in ammonia synthesis.

Co Nanoparticle Catalysts Encapsulated by BaO-La2O3 Nanofractions for Efficient Ammonia Synthesis Under Mild Reaction Conditions.

Ruthenium catalysts may allow for realization of renewable energy-based ammonia synthesis processes using mild reaction conditions (<400 °C, <10 MPa). However, ruthenium is relatively rare and therefore expensive. Here, we report a Co nanoparticle catalyst loaded on a basic Ba/La2O3 support and prereduced at 700 °C (Co/Ba/La2O3_700red) that showed higher ammonia synthesis activity at 350 °C and 1.0-3.0 MPa than two benchmark Ru catalysts, Cs+/Ru/MgO and Ru/CeO2. The synthesis rate of the catalyst at 350 °C and 1.0 MPa (19.3 mmol h-1 g-1) was 8.0 times that of Co/Ba/La2O3_500red and 6.9 times that of Co/La2O3_700red. The catalyst showed ammonia synthesis activity at temperatures down to 200 °C. Reduction at the high temperature induced the formation of BaO-La2O3 nanofractions around the Co nanoparticles by decomposition of BaCO3, which increased turnover frequency, inhibited the sintering of Co nanoparticles, and suppressed ammonia poisoning. These strategies may also be applicable to other non-noble metal catalysts, such as nickel.

Initial MRI findings predict progressive lacunar infarction in the territory of the lenticulostriate artery.

BACKGROUND/AIMS: The mechanisms underlying neurological deterioration in patients with acute lacunar infarction in the lenticulostriate artery (LSA) territory are currently unclear. We aimed to identify predictors for progressive neurological deficits using diffusion-weighted imaging (DWI). METHODS: We studied 40 consecutive patients who were classified into two groups based on their NIHSS scores: progressive infarction (PI) and non-progressive infarction (NPI). We calculated the size of DWI abnormalities and evaluated clinical characteristics on admission for both groups. RESULTS: 19 patients (47.5%) exhibited neurological deterioration. Time from onset to MRI was 8.2 ± 6.7 h for all patients. DWI area was significantly larger in the PI relative to the NPI group (1.1 ± 0.5 cm(2) for PI vs. 0.7 ± 0.3 cm(2) for NPI; p = 0.002), although patients' NIHSS scores at admission were not significantly different between both groups. The optimal cut-off value of infarct area between PI and NPI was 0.98 cm(2). Multivariate analysis revealed that an infarct area on DWI ≥0.98 cm(2) (odds ratio 10.57; 95% confidence interval 2.24-68.32; p = 0.006) was a significant independent predictor of PI. CONCLUSIONS: A large infarct area on initial DWI was an independent predictor of neurological deterioration in patients with acute lacunar infarctions in the LSA territory.

Efficient ammonia synthesis over a Ru/La0.5Ce0.5O1.75 catalyst pre-reduced at high temperature.

Ammonia is an important feedstock for producing fertiliser and is also a potential energy carrier. However, the process currently used for ammonia synthesis, the Haber-Bosch process, consumes a huge amount of energy; therefore the development of new catalysts for synthesising ammonia at a high rate under mild conditions (low temperature and low pressure) is necessary. Here, we show that Ru/La0.5Ce0.5O1.75 pre-reduced at an unusually high temperature (650 °C) catalysed ammonia synthesis at extremely high rates under mild conditions; specifically, at a reaction temperature of 350 °C, the rates were 13.4, 31.3, and 44.4 mmol g-1 h-1 at 0.1, 1.0, and 3.0 MPa, respectively. Kinetic analysis revealed that this catalyst is free of hydrogen poisoning under the conditions tested. Electron energy loss spectroscopy combined with O2 absorption capacity measurements revealed that the reduced catalyst consisted of fine Ru particles (mean diameter < 2.0 nm) that were partially covered with partially reduced La0.5Ce0.5O1.75 and were dispersed on a thermostable support. Furthermore, Fourier transform infrared spectra measured after N2 addition to the catalyst revealed that N2 adsorption on Ru atoms that interacted directly with the reduced La0.5Ce0.5O1.75 weakened the N[triple bond, length as m-dash]N bond and thus promoted its cleavage, which is the rate-determining step for ammonia synthesis. Our results indicate that high-temperature pre-reduction of this catalyst, which consists of Ru supported on a thermostable composite oxide with a cubic fluorite structure and containing reducible cerium, resulted in the formation of many sites that were highly active for N2 reduction by hydrogen.

A low-crystalline ruthenium nano-layer supported on praseodymium oxide as an active catalyst for ammonia synthesis.

Ammonia is a crucial chemical feedstock for fertilizer production and is a potential energy carrier. However, the current method of synthesizing ammonia, the Haber-Bosch process, consumes a great deal of energy. To reduce energy consumption, a process and a substance that can catalyze ammonia synthesis under mild conditions (low temperature and low pressure) are strongly needed. Here we show that Ru/Pr2O3 without any dopant catalyzes ammonia synthesis under mild conditions at 1.8 times the rates reported with other highly active catalysts. Scanning transmission electron micrograph observations and energy dispersive X-ray analyses revealed the formation of low-crystalline nano-layers of ruthenium on the surface of Pr2O3. Furthermore, CO2 temperature-programmed desorption revealed that the catalyst was strongly basic. These unique structural and electronic characteristics are considered to synergistically accelerate the rate-determining step of NH3 synthesis, cleavage of the N[triple bond, length as m-dash]N bond. We expect that the use of this catalyst will be a starting point for achieving efficient ammonia synthesis.