Thermocatalytic ammonia synthesis beyond conventional Haber-Bosch: Principles, advances, challenges and opportunities

The impact of alkali and alkaline earth metals on green ammonia synthesis

A kidney epithelial cell line, LLC-PK1, which does not synthesize prostaglandins, provides an ideal in vitro model system to investigate the effect of prostaglandins in the regulation of renal ammoniagenesis. Previous studies from our laboratory have demonstrated significant increases in glutamine-dependent ammonia and alanine production by rocked cultures of LLC-PK1 cells subjected to either acute metabolic or respiratory acidosis. In the study presented here, experiments were conducted to investigate the role of prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2) in the response of ammonia metabolism to acute metabolic acidosis by LLC-PK1 cells. A low dose of PGF2 alpha (0.1 ng/mL) dramatically inhibited the stimulatory effect of a low pH (pH 6.8) on ammonia production. In contrast, the inhibition of cytosolically generated alanine was less dramatic and averaged only 20% of the effect on ammonia production. Furthermore, PGF2 alpha increased cellular alpha-ketoglutarate concentration, suggesting an increase in intramitochondrial pH. Thus, the cellular mechanism of PGF2 alpha action appears to involve either interference with the cytosolic pH signal or its translation to the intramitochondrial compartment. The inhibitory response of PGF2 alpha on pH-stimulated ammoniagenesis was progressively lost at higher concentrations. Both low-dose (0.1 ng/mL) and high-dose (10 ng/mL) PGF2 alpha had no significant effect on the basal rates of ammonia and alanine production at pH 7.4. PGE2, on the other hand, did not exhibit any significant response on ammonia or alanine production at either pH 6.8 or 7.4 when given in a wide range of doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis and angiotensin II stimulate ammonia production and transport by the proximal tubule. We examined the modulatory effect of the type 1 angiotensin II receptor blocker losartan on the ability of metabolic acidosis to stimulate ammonia production and secretion by mouse S2 proximal tubule segments. Mice given NH(4)Cl for 7 days developed metabolic acidosis (low serum bicarbonate concentration) and increased urinary excretion of ammonia. S2 tubule segments from acidotic mice displayed higher rates of ammonia production and secretion compared with those from control mice. However, when losartan was coadministered in vivo with NH(4)Cl, both the acidosis-induced increase in urinary ammonia excretion and the adaptive increase in ammonia production and secretion of microperfused S2 segments were largely blocked. In renal cortical tissue, losartan blocked the acid-induced increase in brush-border membrane NHE3 expression but had no effect on the acid-induced upregulation of phosphate-dependent glutaminase or phosphoenolpyruvate carboxykinase 1 in cortical homogenates. Addition of angiotensin II to the microperfusion solution enhanced ammonia secretion and production rates in tubules from NH(4)Cl-treated and control mice in a losartan-inhibitable manner. These results demonstrate that a 7-day acid challenge induces an adaptive increase in ammonia production and secretion by the proximal tubule and suggest that during metabolic acidosis, angiotensin II signaling is necessary for adaptive enhancements of ammonia excretion by the kidney and ammonia production and secretion by S2 proximal tubule segments, as mediated, in part, by angiotensin receptor-dependent enhancement of NHE3 expression.

Relation of glutamate to ammonia production in the rat kidney.

To determine whether angiotensin II (ANG II) affects ammoniagenesis in renal proximal tubule, ammonia production was measured in suspensions of canine renal proximal tubule segments (PCT) incubated with L-glutamine and varying concentrations of ANG II. Ammonia production from PCT was significantly increased by 15.5 +/- 1.1% in the presence of ANG II (10(-6) M) at 2 h. Similarly, glucose production significantly increased by 10.0 +/- 0.9%. Half-maximal stimulation occurred at approximately 10(-9) M ANG II. Stimulation of ammonia production by ANG II was blocked in the presence of the ANG II antagonist, [Sar1-Ile8]ANG II (10(-6) M). Enhancement of ammonia production in PCT by ANG II occurred in acidotic and neutral media but not in alkalotic medium. When extracellular [Na+] = intracellular [Na+] ANG II significantly increased ammonia production in PCT. Absence of extracellular Ca2+ or addition of trifluoperazine or N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W-7) (Ca2(+)-calmodulin-dependent pathway inhibitors) blocked the action of ANG II to enhance ammonia production. We conclude that ANG II stimulates ammonia and glucose production in canine renal PCT via a receptor-mediated signal. The action of ANG II on ammoniagenesis may be mediated by a calcium-calmodulin-dependent pathway. Stimulation of ammoniagenesis in vitro under normal and acidotic conditions may reflect a role in vivo for ANG II in the regulation of renal acid-base metabolism.

Renal cortex slices from acidotic dogs incubated with L-glutamine 1 mM at pH 7.05 produced more ammonia and glucose than slices from nonacidotic animals but no significant difference could be demonstrated at pH 7.48. At a phosphate concentration of 20-30 mM in the medium, a 20-30% increase in ammonia and a 25-40% decrease in glucose production were observed. At L-glutamine concentrations from 0 to 8 mM, a curvilinear increase in both ammonia and glucose production was noted, the effect being greater in slices from acidotic animals. D-Glutamine had little effect on ammoniagenesis. Ammonia production (1 mM L-glutamine) in vitro was 50% lower in acidotic dogs than in vivo. Slices from the remnant left kidney (4-6 wk after right nephrectomy) did not behave differently during acidosis than those from the right kidney with regard to ammonia or glucose production. In vitro ammonia and glucose production was higher in the rat than in the dog in acidotic and nonacidotic conditions when comparable concentrations of L-glutamine substrate were used.

Ruminal fluid from steers fed on pasture was incubated with artificial media at pH 5.5 and 7.0 in two experiments. In the first, the effect of monensin level on resistance of ruminal bacteria to potassium depletion was evaluated; in the second, effects of the ionophores monensin and lasalocid on ammonia and protein production were quantified. In experiment 1, culture media affected potassium level. The monensin concentration needed to cause half maximal potassium depletion was 2.77µM at pH 5.5 but was 0.056µM at pH 7.0, showing that bacteria incubated at pH 5.5 were more tolerant to monensin than those incubated at pH 7.0. Both ionophores as well as increased acidity caused decreased ammonia production. Both ionophores inhibited ammonia production by 56%, independently of pH. In cultures incubated at pH 5.5 compared to pH 7.0, ammonia production was decreased by 50.5%, independently of the ionophores. Therefore, effects of ionophores and acidity were additive, and the maximum inhibition occurred in the presence of an ionophore at low pH (75.2%). Microbial protein production was lowest when lasalocid was present in a low pH culture medium, causing inhibition of microbial growth.

The nitrogen and carbon footprints of ammonia synthesis in China based on life cycle assessment

Design, global energy integration, and sustainability analyses of a process coupling renewable energy water electrolysis for hydrogen production with ammonia synthesis

Energy systems used in the future will need to be cleaner and more sustainable. The use of liquid ammonia as a potential medium for hydrogen storage is an efficient solution from an economic, practical and environmental point of view. In this work, a new approach linked to the production of hydrogen and ammonia using a system combining an alkaline water electrolysis, an air separation unit and a Haber Bosch reactor is proposed. The electricity necessary to carry out this process is provided by a dual loop organic rankine cycle (ORC) supplied by a parabolic trough collector and an auxiliary heater system. The survey was carried out by developing mathematical models on the different components of the combined system. The discrepancies between numerical and experimental results did not exceed 2% for the parabolic trough solar collector. Results demonstrated that hydrogen and ammonia flow rates increased as evaporation temperature of working fluid in the high-thermodynamics cycle increased. Results also showed that the thermal performance of the parabolic trough collector increased as inlet temperature and concentration factor increased. It was pointed out that the overall electrical efficiency of the combined system ranged from 15% to 20.28%. The specific energy consumption of the Back-up heater decreased as mass flow rate of Therminol® VP-1 decreased and its values ranged from 0 to 35 kWh kg−1 of ammonia. Ammonia production efficiency and electricity consumption ratio varied between 59–63% and 8.25–8.67 kWh kg−1 of ammonia, respectively. Overall results showed that Cyclohexane, Octane, Toluene and Benzene can be used effectively as working fluid for the high-temperature loop ORC supplied by parabolic trough collectors for hydrogen and ammonia production purpose. Highlights: A combined system suitable for ammonia production purpose is modelled and validated Overall electrical efficiency of the combined system ranged from 15% to 20.28% Electricity consumption ratio varied between 8.25 and 8.67 kWh/kg NH3; Ammonia production efficiency ranged from 59% to 63% Organic fluids suitable for electricity and ammonia production are proposed.

Ammonia production is implicated in the pathogenesis of hepatic encephalopathy (HE), being intestinal glutaminase activity the main source for ammonia. Management of ammonia formation can be effective in HE treatment by lowering intestinal ammonia production. The use of glutaminase inhibitors represents one way to achieve this goal. In this work, we have performed a search for specific inhibitors that could decrease glutaminase activity by screening two different groups of compounds: i) a group integrated by a diverse, highly pure small molecule compounds derived from thiourea ranging from 200 to 800 Daltons; and ii) a group integrated by commonly use compounds in the treatment of HE. Results shown that THDP-17 (10 µM), a thiourea derivate product, could inhibit the intestinal glutaminase activity (57.4±6.7%). Inhibitory effect was tissue dependent, ranging from 40±5.5% to 80±7.8% in an uncompetitive manner, showing Vmax and Km values of 384.62 µmol min−1, 13.62 mM with THDP-17 10 µM, respectively. This compound also decreased the glutaminase activity in Caco-2 cell cultures, showing a reduction of ammonia and glutamate production, compared to control cultures. Therefore, the THDP-17 compound could be a good candidate for HE management, by lowering ammonia production.

Copper (Cu) is a persistent environmental contaminant that elicits several physiological disturbances in aquatic organisms, including a disruption in ammonia regulation. We hypothesized that exposure to Cu in a model crustacean (blue crab, Callinectes sapidus) acclimated to brackish water (2ppt) would lead to hyperammonemia by stimulating an increase in ammonia production and/or by inhibiting ammonia excretion. We further hypothesized that urea production would represent an ammonia detoxification strategy in response to Cu. In a pilot experiment, exposure to 0, 100, and 200µg/L Cu for 6h caused significant concentration-dependent increases in ammonia excretion (J amm). Based on these results, an acute 24-h 100µg/L Cu exposure was conducted and thissimilarly caused an overall stimulation of J amm during the 24-h period, indicative of an increase in ammonia production. Terminal haemolymph total ammonia content (T amm) was unchanged, suggesting that while ammonia production was increased, there was no inhibition of the excretion mechanism. In support of our second hypothesis, urea excretion (J urea) increased in response to Cu exposure; haemolymph [urea] was unaffected. This suggested that urea production also was increased. To further test the hypothesis that J urea increased to prevent hyperammonemia during Cu exposure, crabs were exposed to high environmental ammonia (HEA; 2.5mmol/L NH4HCO3) for 12h in a separate experiment. This led to a fourfold increase in haemolymph T amm, whereas J urea increased only transiently and haemolymph [urea] was unchanged, indicating that urea production likely does not contribute to the attenuation of hyperammonemia in blue crabs. Overall, Cu exposure in blue crabs led to increased ammonia and urea production, which were both eliminated by excretion. These results may have important implications in aquaculture systems where crabs may be exposed to elevated Cu and/or ammonia.

Ammonia (NH3) synthesis is an essential yet energy-demanding industrial process. Hence, there is a need to develop NH3 synthesis catalysts that are highly active under milder conditions. Metal nitrides are promising candidates, with the η-carbide Co3Mo3N having been found to be more active than the industrial Fe-based catalyst. The isostructural Fe3Mo3N catalyst has also been identified as highly active for NH3 synthesis. In the present work, we investigate the catalytic ammonia synthesis mechanisms in Fe3Mo3N, which we compare and contrast with the previously studied Co3Mo3N. We apply plane-wave density functional theory (DFT) to investigate surface N vacancy formation in Fe3Mo3N, and two distinct ammonia synthesis mechanisms. The calculations reveal that whilst N vacancy formation on Fe3Mo3N is more thermodynamically demanding than for Co3Mo3N, the formation energies are comparable, suggesting that surface lattice N vacancies in Fe3Mo3N could facilitate NH3 synthesis. N2 activation was found to be enhanced on Fe3Mo3N compared to Co3Mo3N, for adsorption both at and adjacent to the vacancy. The calculated activation barriers suggest that, as for Co3Mo3N, the associative Mars van Krevelen mechanism affords a much less energy-demanding pathway for ammonia synthesis, especially for initial hydrogenation processes.

Investigation and optimization of a new hybrid natural gas reforming system for cascaded hydrogen, ammonia and methanol synthesis

Here, the MgAl layered double hydroxide (LDH) supports and relevant metal on LDH catalysts (i.e., Ni, Co, and Ru) were prepared and investigated under non thermal plasma (NTP) conditions to probe the role of surface oxygen vacancy (OV) in NTP-assisted ammonia (NH3) synthesis. The findings show that OV on the LDH carrier is highly beneficial to NH3 formation under NTP conditions, and concentration of OV on the LDH can be regulated by the post-synthesis calcination and hydrogen plasma etching. Additionally, loading of active metal species on the LDH could promote the NH3 synthesis further due to presence of multiple reaction pathways and the synergy between the surface OV and metal sites in such NTP-catalytic systems. As the result, the catalysts developed by this work showed high ammonia synthesis rates of 4.42−4.52 mmol g−1 h−1 and energy efficiencies of 1.67−1.71 gNH3 kWh−1, respectively. The findings of the work pave the way for the rational design and optimization of highly efficient catalysts with dual active sites for intensifying the NTP-catalytic ammonia synthesis.