NH3 Conversion Research Articles

Theoretical insights into transition metal clusters supported on graphyne as electrocatalysts for N2–to–NH3 conversion

NH3 is not only an important energy intermediates and carbon-free energy carrier, but also essential for various production and life processes. Under ambient conditions, electrocatalytic nitrogen reduction reaction (NRR) is considered to be a very attractive approach, the process converts clean electrical energy into chemical energy, and realizes the efficient use and conversion of renewable energy, which is of great significance in energy and environmental protection. In this study, density functional theory was applied to transition metal clusters supported on graphyne as electrocatalysts (TM3@GY) to realize the NRR process. The effects of cluster types and doping atoms on catalytic performance were systematically studied. Finally, Fe3@BGY was selected as a potential NRR catalytic system with an initial potential of −0.560 V. The reason of the high catalytic activity was revealed through the calculation of electronic properties, which provides a theoretical basis for designing new high-performance cluster catalysts.

Lattice-Stabilized Chromium Atoms on Ceria for N2O Synthesis.

The development of selective catalysts for direct conversion of ammonia into nitrous oxide, N2O, will circumvent the conventional five-step manufacturing process and enable its wider utilization in oxidation catalysis. Deviating from commonly accepted catalyst design principles for this reaction, reliant on manganese oxide, we herein report an efficient system comprised of isolated chromium atoms (1 wt %) stabilized in the ceria lattice by coprecipitation. The latter, in contrast to a simple impregnation approach, ensures firm metal anchoring and results in stable and selective N2O production over 100 h on stream up to 79% N2O selectivity at full NH3 conversion. Raman, electron paramagnetic resonance, and in situ UV-vis spectroscopies reveal that chromium incorporation enhances the density of oxygen vacancies and the rate of their generation and healing. Accordingly, temporal analysis of products, kinetic studies, and atomistic simulations show lattice oxygen of ceria to directly participate in the reaction, establishing the cocatalytic role of the carrier. Coupled with the dynamic restructuring of chromium sites to stabilize intermediates of N2O formation, these factors enable catalytic performance on par with or exceeding benchmark systems. These findings demonstrate how nanoscale engineering can elevate a previously overlooked metal into a highly competitive catalyst for selective ammonia oxidation to N2O, paving the way toward industrial implementation.

Ethanolammonium chloride-glycerol deep eutectic solvents for efficient and reversible absorption of NH3 through multiple hydrogen-bond interaction

Efficiently separating NH3 from the exit gas of NH3 synthesis tower has significant economic and environmental benefits, such as improving the NH3 conversion rate and reducing pollution emission. In this study, a series of EtOHACl + Gly deep eutectic solvents (DESs) with numerous hydrogen-bond sites were synthesized. The findings suggest that the use of EtOHACl + Gly DESs can result in both exceptional NH3 absorption capacities and superior selectivities. EtOHACl + Gly (1:2) has the NH3 capacities of up to 12.39 mol/kg at 298.2 K and 105.5 kPa, while its N2 and H2 capacities are negligible. Additionally, the absorbed NH3 can be easily released by heating and reducing pressure, and the NH3 capacities remain stable after undergoing six cycles. The study also examined the interaction mechanism of EtOHACl + Gly DESs for the NH3 separation, utilizing spectral characterizations, quantum chemistry calculations and molecular dynamics simulations.

Ammonia cracking for hydrogen production using a microwave argon plasma jet

Ammonia (NH3) is a promising hydrogen carrier that effectively connects producers of blue hydrogen with consumers, giving rapid conversion of ammonia to hydrogen a critical role in utilizing hydrogen at the endpoints of application in an ammonia-hydrogen economy. Because conventional thermal cracking of NH3 is an energy intensive process, requiring a relatively longer cold start duration, plasma technology is being considered as an assisting tool—or an alternative. Here we detail how an NH3 cracking process, using a microwave plasma jet (MWPJ) under atmospheric pressure, was governed by thermal decomposition reactions. We found that a delivered MW energy density (ED) captured the conversion of NH3 well, showing a full conversion for ED > 6 kJ l−1 with 0.5-% v/v NH3 in an argon flow. The hydrogen production rate displayed a linear increase with MW power and the NH3 content, being almost independent of a total flow rate. A simplified one-dimensional numerical model, adopting a thermal NH3 decomposition mechanism, predicted the experimental data well, indicating the importance of thermal decomposition in the plasma chemistry. We believe that such a prompt thermal reaction, caused by MW plasma, will facilitate a mobile and/or non-steady application. A process combined with the conventional catalytic method should also effectively solve a cold start issue.

Influence of pre-treatment of straw biomass and additives on the release of nitrogen species during combustion and gasification

The aim of this study is to investigate how pre-treatment of herbaceous straw biomass for ash control affects the release of nitrogen species during combustion and gasification. To comprehend the formation of NO and its precursors, NH3 and HCN, the release of these species was investigated and compared under both combustion and gasification-like conditions at 950 °C. The effects of various upgrading methods, such as torrefaction, water-leaching, a combination of leaching and torrefaction, and CaCO3 addition, were studied. The assessment of nitrogen release was divided into two consecutive conversion steps – devolatilization/pyrolysis and ash/char reactions. The release of nitrogen is highly dependent on the reaction conditions. For instance, the emissions of NO from the combustion conditions (3 vol% O2) for all fuel samples were, on average, six times higher than under gasification conditions (14.5 vol% H2O and 5 vol% CO2). The emissions of NO from the combustion and gasification of torrefied biomass were, on average, 20 % higher than those from raw biomass. Water-leaching had a suppressing effect on NO formation during char conversion. Approximately 62 % of the char-N formed NO for raw and torrefied material, whereas only 26 %–35 % was formed for pre- or postwashed samples. The effect of the applied pre-treatment approaches on the release of nitrogen was particularly significant during char conversion. Increasing calcium and decreasing potassium content had catalytic effects, mainly on the conversion of volatile-N to NH3. The Ca-doped biomass feedstock showed approximate 10 % increase in volatile-N to NH3 conversion compared to the source material.

Au Nanocrystals Modified Holey PtTeAu Metallene Heteronanostructures for Plasmon‐Enhanced Nitrate Electroreduction

AbstractAmmonia (NH3) is an essential chemical for agricultural production and a promising next‐generation hydrogen‐rich fuel. The electrocatalytic nitrate (NO3−) reduction reaction (NO3RR) to NH3 provides a sustainable and low‐energy method to replace industrial NH3 synthesis. However, the NO3− to NH3 conversion is limited by the complex eight‐electron and nine‐proton reduction processes, thus it is highly desirable to develop efficient electrocatalytic materials to overcome the kinetic barrier of NO3RR. Herein, Au nanocrystals (Au‐NCs) modified holey PtTeAu metallene (PtTeAu‐ML) heteronanostructures (Au‐NCs/PtTeAu‐MLs) are designed through phase and interface engineering, which achieve the high NH3 yield (3.499 mg h−1 mgcat−1) and Faradaic efficiency of 96.3% for NO3RR at −0.03 V versus RHE. Detailed investigations reveal that the introduction of Te atoms significantly inhibits the high activity of Pt atoms for hydrogen evolution reaction that competes with NO3RR. Density functional theory results demonstrate that Au atoms further modulate the electronic structure of Pt in PtTe‐MLs, resulting in the upward shifted d band center of Pt and in turn the optimized NO3RR process on PtTeAu‐MLs. Furthermore, Au‐NCs allows the sustainable sunlight energy to accelerate the NO3RR kinetics at PtTeAu‐MLs because of the localized surface plasmon resonance of Au, inducing a higher NH3 yield of 4.684 mg h−1 mgcat−1 under light irradiation condition.

Copper loading effect on active species formation over Cu/SSZ-13 catalysts for selective catalytic oxidation of high-concentration NH3

Cu/SSZ-13 catalysts not only exhibit superior SCR performance but also possess excellent selective catalytic oxidation (SCO) ability to remove NH3 escaped from engine exhaust gas fueled by NH3. To elucidate the effect of Cu loading on Cu/SSZ-13 catalysts, a series of Cu/SSZ-13 catalysts were prepared through wet impregnation method to remove high-concentration NH3 (5000 ppm). The SCO activity test results showed that when Cu loading increased from 1% to 10%, there was an obvious improvement effect on NH3 conversion performance at low temperature. Cu10/SSZ-13 catalyst reached a high NH3 conversion of 96% at 250 °C, and N2 selectivity was higher than 86% in the whole temperature range. However, when further increasing Cu loading from 10% to 20%, there was no distinctive difference in NH3 conversion and N2 selectivity. The characterization results indicated that there were abundant active species, adsorbed oxygen species, and acid sites on the surface of Cu10/SSZ-13 catalyst. The [Cu(OH)]+ and isolated Cu2+ species in zeolite channels of Cu10/SSZ-13 catalyst rather than CuO species on the surface played a key role in NH3-SCO reactions. Since 20% Cu loading would result in a significant decrease in isolated Cu2+ species, it resulted in both [Cu(OH)]+ species in zeolite channels and superfluous Cu species on zeolite surface being main active species in NH3-SCO reactions. In-situ DRIFTS experiments suggested that NH3-SCO reactions over Cu/SSZ-13 catalysts followed the internal selective catalytic reduction (i-SCR) mechanism.

Understanding the Reaction Chemistry of 1,1,3,3-Tetramethyldisilazane as a Precursor Gas in a Catalytic Chemical Vapor Deposition Process.

The reaction chemistry of 1,1,3,3-tetramethyldisilazane (TMDSZ) in catalytic chemical vapor deposition (Cat-CVD), including its primary decomposition on a heated W filament and secondary gas-phase reactions in a Cat-CVD reactor, was studied using 10.5 eV vacuum ultraviolet single-photon ionization and/or laser-induced electron ionization in tandem with time-of-flight mass spectrometry. It has been demonstrated that TMDSZ initially breaks down to form various species, including methyl radical (•CH3), ammonia (NH3), and 1,1-dimethylsilanimine (DMSA). The activation energies (Ea) for the formation of •CH3 and NH3 were determined to be 61.2 ± 1.0 and 42.1 ± 0.9 kJ mol-1, respectively, in the temperature range of 1400-2000 and 900-2400 °C. It was found that the formation of DMSA may have two different contributing routes, i.e., a concerted one (Ea = 33.6 ± 2.3 kJ mol-1) at lower temperatures of 900-1500 °C and a stepwise one (Ea = 155.0 ± 7.8 kJ mol-1) at higher temperatures of 2100-2400 °C. The secondary gas-phase reactions occurring in the Cat-CVD reactor environment were found to stem from two competing processes. The first one, free-radical short-chain reactions initiated by •CH3 formation and propagated by H abstraction reactions, is the dominating chemical process, producing many high-mass stable alkyl-substituted or silyl-substituted disilazane or trisilazane products via radical recombination reactions. Head-to-tail cycloaddition of unstable DMSA is the second contributing chemical process, which forms cyclodisilazane species. In addition, evidence was found for the conversion of NH3 into H2 and N2 in the Cat-CVD reactor.

Achieving equilibrium conversions for low-temperature NH3 decomposition: Synergy between catalyst and electric field effects

In the advent of an energy shift towards renewable energy sources, ammonia is considered a promising energy carrier for convenient hydrogen storage and transport. However, ammonia decomposition requires temperatures higher than 500 °C to achieve 100% conversion. Here, we present the facile synthesis and use of nanocluster RuCeO2 catalysts for the low-temperature electric field-assisted ammonia decomposition reaction. The catalysts obtained desirable properties and achieved high conversions for ammonia decomposition under conventional conditions. Interestingly, catalyst activities significantly increased upon exposure to an electric field, achieving 100% conversion at 450 °C and obtaining exceptional conversions of up to 34% at a low temperature of 200 °C and a high GHSV of 30,000 mLNH3/gcath. Optimization of reaction parameters effectively increased NH3 conversions, allowed highly stable long-term activities, and enabled the catalyst to achieve equilibrium conversions at remarkably lower temperatures. Further studies reveal that the electric field essentially reduces apparent activation energies and boosts the ammonia decomposition reaction by promoting the recombinative desorption of N2 and H2, thereby alleviating the rate-determining step and preventing deactivation due to H2 poisoning. The occurrence of surface protonics as a result of N-H bond scission and transport of H+ species to the support, along with increased NH3 activation and oxygen vacancy migration improves charge transfer between the support and the Ru active sites, thereby resulting in increased desorption of N2 and H2 products. Thus, an energy-efficient route toward economical hydrogen production is achieved by combining electric field effects with a highly active RuCeO2 catalyst.

Experimental analysis of ammonia as input fuel for molten carbonate fuel cell

Hydrogen fuel cells can generate clean and efficient energy, and ammonia as a hydrogen carrier contains more hydrogen in its molecule than hydrogen itself. Utilizing green ammonia as fuel for fuel cells can reduce dependency on fossil fuels. However, there has been less study on the electrochemical performance of ammonia molten carbonate fuel cells (MCFCs). Hence, this paper sets up a single MCFC experimental bench to conduct research on direct ammonia molten carbonate fuel cells. The electrochemical performance of a direct ammonia MCFC is investigated in terms of key parameters such as temperature and the volume flow ratio of NH3/H2 entering the anode. Additionally, Scanning Electron Microscopy (SEM) is employed to study the electrodes of the MCFC. Experimental findings demonstrate that the direct ammonia MCFC performs optimally at 680 °C with a current density of 0.059 A/cm2 and an ammonia conversion rate up to 91.6%. When the mixture gas of NH3 and H2 is used as the cell fuel, the current density (0.057 A/cm2) and the conversion rate of NH3 (84.9%) are higher when the volume flow ratio of NH3/H2 is 9, indicating that the increase of H2 proportion in the mixed gas will affect the conversion of NH3. SEM image analysis of the MCFC electrodes post-experiments reveals that ammonia does not destruct the loose and porous structure of MCFC electrodes, affirming that NH3 can be directly used as the MCFC fuel.

Plasma-Promoted Ammonia Decomposition over Supported Ruthenium Catalysts for COx -Free H2 Production.

The efficient decomposition of ammonia to produce COx -free hydrogen at low temperatures has been extensively investigated as a potential method for supplying hydrogen to mobile devices based on fuel cells. In this study, we employed dielectric barrier discharge (DBD) plasma, a non-thermal plasma, to enhance the catalytic ammonia decomposition over supported Ru catalysts (Ru/Y2 O3 , Ru/La2 O3 , Ru/CeO2 and Ru/SiO2 ). The plasma-catalytic reactivity of Ru/La2 O3 was found to be superior to that of the other three catalysts. It was observed that both the physicochemical properties of the catalyst (such as support acidity) and the plasma discharge behaviours exerted significant influence on plasma-catalytic reactivity. Combining plasma with a Ru catalyst significantly enhanced ammonia conversion at low temperatures, achieving near complete NH3 conversion over the 1.5 %-Ru/La2 O3 catalyst at temperatures as low as 380 °C. Under a weight gas hourly space velocity of 2400 mL gcat -1 h-1 and an AC supply power of 20 W, the H2 formation rate and energy efficiency achieved were 10.7 mol gRu -1 h-1 and 535 mol gRu -1 (kWh)-1 , respectively, using a 1.5 %-Ru/La2 O3 catalyst.

Remarkable N2 selectivity enhancement of NH3-SCO reactions over V0.5/Pt0.04/TiO2 catalyst through Cu-Er co-modification.

Pt-V bimetallic catalysts maybe promising substitutes to precious metal catalysts for selective catalytic oxidation (SCO) of NH3. But it remains a major challenge for Pt-V bimetallic catalysts to pursue high NH3 conversion rate and N2 selectivity simultaneously. In this work, both Cu and Er were adopted to modify V0.5/Pt0.04/TiO2 catalyst (denoted as V/PT), and the influences of Cu and Er doping amounts on NH3-SCO performance of V/PT catalysts were investigated systematically. The results indicated that the co-modification of Cu and Er imposed little influence on NH3 conversion efficiency, but significantly boosted N2 selectivity. Compared with other Cu-Er-modified V/PT catalysts, CEV/PT-4 catalyst exhibited outstanding NH3-SCO performance, which attained completely 100% NH3 conversion efficiency and > 90% N2 selectivity in the temperature range of 225-450°C. It was significantly superior to the NH3-SCO performance of most previously reported catalysts. The characterization results indicated that the adequate doping amounts of Cu and Er resulted in an obvious enhancement on redox property and surface acidity of CEV/PT-4 catalyst. It also led to abundant Pt0 and surface chemisorbed oxygen species on catalyst surface, which facilitated the oxidation of NH3 to NOx and enhanced i-SCR reactions. In situ DRIFTS results showed that -NH2 species on the surface of CEV/PT-4 catalyst could actively react with nitrate species to generate N2 and H2O.

Comparison of chemical composition and acidity of size-resolved inorganic aerosols at the top and foot of Mt. Hua, Northwest China: The role of the gas-particle distribution of ammonia

Aerosol pH is not only a diagnostic indicator of secondary aerosol formation, but also a key factor in the specific chemical reaction routes that produce sulfate and nitrate. To understand the characteristics of aerosol acidity in the Mt. Hua, the chemical fractions of water-soluble inorganic ions in the atmospheric PM2.5 and size-resolved particle at the top and foot of Mt. Hua in summer 2020 were studied. The results showed the mass concentrations of PM2.5 and water-soluble ions at the foot were 2.0–2.6 times higher than those at the top. The secondary inorganic ions, i.e., SO42−, NO3−, and NH4+ (SNA) were 56 %–61 % higher by day than by night. SO42− was mainly distributed in the fine particles (Dp < 2.1 μm). NO3− showed a unimodal size distribution (peaking at 0.7–1.1 μm) at the foot and a bimodal (0.7–1.1 μm and 4.7–5.8 μm) size distribution at the top. At the top site, the distribution of NO3− in coarse particles (> 2.1 μm) was mainly attributed to the gaseous HNO3 volatilized from fine particles reacting with cations in coarse particles to form non-volatile salts (such as Ca(NO3)2). The pH values of PM2.5 were 2.7 ± 1.3 and 3.3 ± 0.42 at the top and foot, respectively. NH4+/NH3(g) plays a decisive role in stabilizing aerosol acidity. In addition, the increase of the liquid water content (LWC) at the foot facilitates the gas-particle conversion of NH3, while the H+ concentration was diluted, resulting in a decrease in acidity at the foot. NH4+/NH3 had good linear correlations with SO42−, NO3−, and LWC during the daytime at both sites, indicating that SO42−, NO3−, and LWC together affect the gas-particle distribution of ammonia by day: however, the effect of LWC at night was not evident.

Facile synthesis of platinum-loaded carbon nanosheets with high specific surface area for efficient CWAO of ammonia nitrogen: A low-cost alternative route for treating ammonia containing wastewater

Deep treatment is an important tool to solve the environmental pollution of ammonia-containing wastewater. Considering the stability and economy of industrial application, we propose a simple and economical synthesis strategy. The procedure is based on the carbonization of citrate at elevated temperatures to synthesize high specific surface area and pore-rich carbon nanoflowers, and carbon nanoflower-loaded Pt catalysts were constructed for the catalytic wet air oxidation (CWAO) of ammonia-containing wastewater. The results showed that the synergistic effect of Pt, edge carbon and carboxyl groups led to the increase of CWAO activity. During the reaction, Pt activated NH3 to put it in a high-energy state, and there was a positive synergistic effect between the oxygen-containing functional groups (carboxyl groups) on the surface of the porous carbon nanoflowers and the edge carbon exposed at the adjacent defect sites, which promoted the activation of O2 and the generation of reactive oxygen species. At 200 °C, the Pt1/PC catalysts showed high activity and hydrothermal stability for CWAO of NH3. The conversion of NH3 was 98.24 % within 4 h, and the selectivity of N2 was 100 %. The total nitrogen (TN) was reduced to below 15 mg‧L−1, which meets the Chinese emission standard for TN in petrochemical industry. Therefore, the novel catalyst proposed in this study effectively solved the problems of complicated catalyst synthesis steps and poor hydrothermal stability in ammonia CWAO studies. The catalyst has potential industrial applications for CWAO of ammonia-containing wastewater.

Reasonable design of Sm-modified Cu-based catalyst for NH3-SCO: Role of the amide intermediates

The selective catalytic oxidation of ammonia (NH3-SCO) is currently the most effective method used to eliminate NH3. However, one of the major challenges for NH3-SCO is the development of catalyst capable of completely converting NH3 into harmless N2 and water vapor. In this paper, a high N2 selective catalyst prepared by the sol-gel method using TiO2 as the support, Cu as the active species, and Sm as the auxiliary agent is presented. Compared to traditional Cu/TiO2 catalyst, the 4SmCu/TiO2 catalyst has higher catalytic activity and N2 selectivity at low temperatures. The NH3 conversion can reach 100%, and the selectivity of N2 can be maintained at 100% at 275 °C. The excellent catalytic activity is attributed to the highly dispersed active species, abundant Lewis acid sites (LASs), and the generation of large amounts of surface-adsorbed oxygen. In addition, doping Sm species will cause TiO2 lattice distortion, and at the same time load the distorted TiO2 with more active material. Moreover, in-situ DRIFTS analysis suggests that both the 4SmCu/TiO2 and Cu/TiO2 catalysts follow the "internal" selective catalytic reduction (iSCR) mechanism during NH3-SCO reactions. The 4SmCu/TiO2 catalyst generates more amides (-NH2), which reduces the non-selective oxidation of the catalysts and promotes the formation of N2. This provides a new idea and method for the selective catalytic oxidation of NH3 to N2 and water vapor using Cu-based catalysts.

B and Fe co-doped Co2P hollow nanocubes for nitrate electroreduction to ammonia

Nitrate (NO3−) electroreduction reaction (NO3−RR) provides an attractive and sustainable route for NO3− pollution mitigation or energy-saved ammonia (NH3) synthesis. In this work, high-quality B and Fe co-doped Co2P hollow nanocubes (B/Fe-Co2P HNCs) are successfully synthesized though simultaneous boronation-phosphorization treatment, which reveal outstanding selectivity, activity, stability for the NO3− to NH3 conversion in neutral electrolyte because of big surface area, fast mass transport, superhydrophilic surface, and optimized electronic structure. B/Fe-Co2P HNCs can achieve the high NH3 yield rate (22.67 mg h−1 mgcat−1) as well as Faradaic efficiency (97.54%) for NO3−RR, greatly outperforming most of non-precious metal based NO3−RR electrocatalysts.

Discovering a catholyte free design for gas phase electrocatalytic NO gas reduction to NH3 at room temperature

Nitric oxide (NOx) is one of the most contributors to the health risks associated with breathing in flue gases and it is crucial to eliminate this pollutant from the air when solid waste is burned. Electrochemical gas phase reduction of NO to NH3 is the promising method to mitigating the accumulation of NO gas pollutants and producing a valuable NH3 as a product at room temperature. In this investigation, for the first time, we designed a catholyte-free cell for gas phase electrochemical NO to NH3 conversion using K2[Ni(CN)4] coated carbon felt (CF) electrode as a electrocatalyst at room temperature. Herein, K2[Ni(CN)4] heterogeneous mediator transfers the electron between the NO gas molecule and electrode. The NO removal efficiency and NH3 formation were simultaneously monitored by using online gas phase FTIR spectroscopy. In the catholyte-free gas phase NORR process, the K2[Ni(CN)4]/CF electrode exhibits excellent NORR performance, with a high NH3 yield rate of 1128.9 µmol h−1 cm−2, an excellent 89.5 % NH3 faradaic efficiency at − 1 V vs quasi reference Ag and enhanced long term NORR durability. It is noteworthy that, this is the highest yield rate and faradaic efficiency of NH3 during gas phase NORR at room temperature. In addition, K2[Ni(CN)4]/CF electrocatalyst exhibits 99 % of NO removal efficiency with the formation of value-added product (NH3). Moreover, the proposed electrocatalyst shows excellent chemical, and morphological stability after long durability NORR operations. Furthermore, the detailed electrode-electrolyte free cell, NORR reduction mechanism was proposed. Present discovery provides great insights for sustainable NORR operations in real-site applications.

Ammonia Decomposition over Alkali Metal (Li, K, Cs)-Promoted Bulk Mo2N Catalyst

Ammonia (NH3), which has a 17.7 wt% gravimetric hydrogen density, has been considered as a potential hydrogen storage material. This study looked at the thermocatalytic decomposition of NH3 using a bulk Mo2N catalyst that was boosted by alkali metals (AM: 5 wt% Li, K, Cs). The K-Mo2N catalyst outperformed all other catalysts in this experiment in terms of catalytic performance. At 6000 h−1 GHSV, 100% conversion of NH3 was accomplished using the K-Mo2N, Cs-Mo2N, and Mo2N catalysts. However, when compared to other catalysts, K-Mo2N had the highest activity, or 80% NH3 conversion, at a lower temperature, or 550 °C. The catalytic activity exhibited the following trend for the rate of hydrogen production per unit surface area: K-Mo2N &gt; Cs-Mo2N &gt; Li-Mo2N &gt; Mo2N. Up to 20 h of testing the K-Mo2N catalyst at 600 °C revealed no considerable deactivation.

Hydrogen production by the catalytic decomposition of ammonia over a Ru/SiCeOx catalyst: The synergistic effect of Si addition

Controlling active metal–support interaction is critical in the catalytic decomposition of ammonia (NH3). In this study, we investigated the generation of oxygen vacancies in the SiCeOx support by Si addition and the increase in catalytic performance for the decomposition of NH3 by their interaction with Ru. The Si content in the Ru/SiCeOx catalysts was controlled by glassware elution during the precipitation of Ce(NO3)3 at a high pH level (10.5) by applying different aging temperatures and times. The formation of oxygen vacancies by the insertion of Si4+ into the CeO2 lattice was characterized by O2-pulse experiments as well as Raman and X-ray photoelectron spectroscopy analyses. The effect of oxygen vacancies on the adsorption strengths of hydrogen and nitrogen on Ru was characterized by H2-temperature-programmed reduction and NH3-temperature-programmed desorption. The correlation between NH3 conversion, oxygen vacancy content, and nitrogen desorption temperature was experimentally proven.

Phyllosilicate-derived Ni catalysts with small nanoparticle size and strong metal-support interaction for efficient and robust decomposition of ammonia

Ammonia decomposition is a structure-sensitive reaction, so the difference in structure of similar catalysts may have a great impact on the catalytic performance of ammonia decomposition reaction. However, it is not clear which structural properties can play a role in ammonia decomposition reaction and the degree of influence on catalytic performance. To explore this question, ammonia evaporation-hydrothermal (AEH), impregnation (IM), and evaporation-induced self-assembly (EISA) methods were used to synthesize Ni/SiO2 catalysts to obtain carbon-free hydrogen from catalyzing NH3 decomposition reaction. Among the three, the Ni/SiO2 catalyst synthesized via ammonia evaporation-hydrothermal method is the smallest in terms of Ni nanoparticles (∼3.0 nm) and the strongest Ni-SiO2 interaction. For ammonia decomposition, it is the highest in activity and thermal stability. The NH3 conversion at 650 °C and 30 000 mL gcat−1h−1 (GHSV) over Ni/SiO2-AEH was close to 90 % and remained stable in an evaluation period of 60 h.