Catalysts For Ammonia Decomposition Research Articles

Enhanced activity of Ru-based catalysts for ammonia decomposition through nitrogen doping of hierarchical porous carbon carriers

Activated carbon (AC) materials, renowned for their high specific surface area, excellent conductivity, and customizable functional groups, are widely employed as catalyst carriers. However, enhancing the activity of Ru-based catalysts supported on AC (Ru/AC) for ammonia decomposition remains a challenge. In this study, commercial AC was utilized as a substrate, with glucose and urea employed as modifiers. Specifically, the surface of the AC was modified via a hydrothermal pyrolysis method, resulting in the successful post-treatment in situ co-doping of nitrogen (AC-GN). Experimental results revealed that Ru/AC-GN exhibited a hydrogen production rate 46% higher than that of Ru/AC at 475 °C, indicating improved activity and stability. The characterization of AC-GN demonstrated that nitrogen doping primarily occurred on the external surface and macropores of the AC, increasing the nitrogen content in the carrier, particularly pyrrolic nitrogen content, while preserving the original structural and morphological integrity of the AC. The enhanced dispersion of Ru, combined with the improved electronic transmission capabilities and strengthened interactions between the metal and the modified carrier, were identified as pivotal factors contributing to the enhanced low-temperature efficacy of Ru/AC-GN. This paper presents a novel direction for the large-scale preparation of efficient catalysts for ammonia decomposition.

Supported highly dispersed molybdenum nitride derived from molybdate-intercalated Mg‒Al hydrotalcite-like compounds as a catalyst for ammonia decomposition

Molybdate-intercalated magnesium–aluminum hydrotalcite-like compounds (HTlc) were synthesized by anion-exchange and used as precursor to prepare supported molybdenum nitride catalyst for ammonia decomposition. The as-synthesized precursors and the derived mixed metal oxides and nitride catalysts were characterized by ICP, XRD, Raman spectroscopy, XPS, H2-TPR, and HAADF-STEM-EDX. The characterizations indicated that molybdate was well intercalated into the HTlc interlayer as MoO42– and the Mo content was tunable by altering the intercalation degree of molybdate. Upon calcination, molybdena was dominantly presented as isolated tetrahedrally coordinated MoOx species. Upon nitridation with ammonia at 700 ºC, highly dispersed and composition-uniform molybdenum nitride (Mo2±xN) was formed. The Mo0.5Mg3Al nitride catalyst showed good activity for ammonia decomposition, providing nearly full conversion of ammonia at 625 ºC under a space velocity of 5,000 mL gcat–1 h–1. The optimal catalyst also exhibited high catalytic stability during 100 h operation at 625 ºC, and no obvious aggregation took place, attributable to the strong metal–support interaction between molybdenum nitride and Mg–Al mixed oxide. It is suggested that the hydrotalcite-derived Mg–Al mixed oxide supported highly dispersed Mo2±xN species was active and stable for ammonia decomposition.

Ammonia decomposition over vanadium oxide supported Ni catalyst for hydrogen production

The performance of vanadium oxides as support is investigated to develop a new nickel catalyst for ammonia decomposition to produce hydrogen. The catalytic activity is in the order of Ni/V2O3 > Ni/VO2 > Ni/V2O5, depending on the oxidation states of vanadium oxide. The VOx supports in all of the spent catalysts are V2O3, suggesting that V2O3 is the stable phase of VOx support during the ammonia decomposition. 3 wt%Ni/V2O3 gives an ammonia conversion of 38.3% (SV = 3000 L kg−1h−1) at 530 °C. Excellent active sites with a TOF of 33.6 s−1 at 500 °C form on 3 wt%Ni/V2O3. Ni/VOx works effectively as a catalyst for ammonia decomposition to produce hydrogen.

Cerium oxide-based catalyst for low-temperature and efficient ammonia decomposition for hydrogen production research

This study prepared a series of cerium oxide-based catalysts with different metal ruthenium loadings using an initial wet impregnation method. The results demonstrate that the prepared 1.4Ru/CeO2 catalyst exhibits outstanding catalytic performance and activity stability. Under the condition where the Ru loading is only 1.4 wt%, the catalyst achieves almost complete NH3 conversion at 500 °C, with a hydrogen production rate of 16.59 mmol gcat−1 min−1. Furthermore, after a 48-h long-term test, the activity remains stable. Characterization tests show that the metal ruthenium is uniformly distributed on the surface of cerium dioxide, with particle sizes ranging from 3 to 6 nm. Notably, a structure characterized by lattice stripes overlapping between the metal and support is observed. Increasing the Ru loading can enhance the surface acidity sites of the catalyst and the interaction between the metal and the support, which plays a crucial role in the long-term stability of the catalyst. Additionally, the abundant oxygen vacancies in cerium dioxide and its low cerium oxidation-reduction potential facilitate electron transfer to ruthenium, enhancing the adsorption of NH3 and accelerating the desorption of N2.

Nickel perovskite catalysts for ammonia decomposition: DFT calculations and microreaction kinetics

Combining policy guidance, catalyzing ammonia decomposition to produce hydrogen is a new concept for hydrogen energy supply. Alkaline carriers can effectively improve the ammonia decomposition activity on the catalyst by adjusting the dispersion of nickel (Ni) and controlling the size of Ni. However, the activity of Ni-based perovskite catalysts does not seem to be entirely affected by the above factors. Exploring the mechanism of Ni and perovskite alkaline carrier surfaces through theoretical calculations provides deeper theoretical guidance for ammonia (NH3) decomposition. This study uses periodic density functional theory calculation methods to investigate the reaction paths and energy distribution of monomeric ammonia and dimeric ammonia on a nickel-doped barium zirconate (Ni/BaZrO3) catalyst. Molecular dynamics simulations, Bader charge analysis, and density of states assist in understanding the adsorption states of NH3 and the catalytic decomposition mechanism. The energy barriers for N-H bond breaking and nitrogen generation reactions of Ni clusters loaded on the BaZrO3 surface (Ni4/BaZrO3) were compared and analyzed. The results show that Ni/BaZrO3 is more conducive to ammonia decomposition, with a maximum reaction barrier of 0.90 eV. The catalytic activity of the catalyst under oxygen vacancy conditions was further examined. By comparing the mechanisms of dimeric ammonia decomposition on the clean catalyst surface and the oxygen vacancy catalyst surface, it was found that the presence of oxygen vacancies facilitates ammonia decomposition, but Ni doping provides more effective assistance for N-H bond breaking. The rate constant for ammonia decomposition was calculated using transition state theory. This work not only provides theoretical references for the decomposition mechanism of NH3 in Ni-based perovskite materials but also provides kinetic data for the kinetic modeling of NH3 decomposition.

Highly active and stable Ni@SiO2 catalyst for ammonia decomposition

Ammonia is considered as a potential hydrogen carrier as its high hydrogen content. Hydrogen release still presents challenges due to the lack of efficient catalyst. In this work, we report a Ni@SiO2 catalyst prepared through a sol–gel method, which displays satisfied catalytic activity and remarkable long-term stability. The origination of activity and stability has been investigated carefully by various characterizations. The strong interaction between nickel species and silica species is responsible for the excellent performance via generating small nickel particle and hindering the sintering of nickel during the high temperature reaction condition. This study offers novel insights into the design and preparation of highly efficient catalysts for ammonia decomposition to produce hydrogen.

Promotion of Low-Temperature Catalytic Activity of Ru-Based Catalysts for Ammonia Decomposition via Lanthanum and Cesium Codoping

Promotion of Low-Temperature Catalytic Activity of Ru-Based Catalysts for Ammonia Decomposition via Lanthanum and Cesium Codoping

Industrial waste-based Ni-catalysts for ammonia decomposition to produce clean hydrogen

The high mineral containing solid waste materials generated during aluminum production currently lacks any practical application. In this work, the potential of solid waste with/without additional nickel loading (10 to 20 wt%) was investigated as an active catalyst for low temperature ammonia decomposition to produce high purity hydrogen. The X-ray diffraction (XRD) analysis of the samples reveals that iron oxide was the primary component of solid waste with the ability to catalyze the ammonia decomposition reaction. The reducibility, metal support interaction and catalytic activity of the solid waste supported Ni-based catalysts were correlated by the reduction kinetics of the catalysts using temperature-programmed reduction (H2-TPR) data and nucleation/nuclei growth models. Based on the statistical indicators, it was concluded that the random nucleation model describes catalyst reduction adequately. The estimated activation energy for the reduction of the solid waste itself was significantly higher (108.5 kJ/mol) than that of solid waste supported catalyst containing 10 wt% Ni (86.6 kJ/mol). The increase in nickel loading also slightly decreased the activation energy of catalyst reduction, indicating an improvement in the reducibility of the nickel-containing catalysts. These reduction behaviors were also reflected in the ammonia decomposition reaction in a flow reactor. The addition of nickel onto the solid waste resulted in the creation of additional active nickel sites. Consequently, the nickel loaded solid waste supported catalysts exhibited significant improvements in ammonia decomposition activity. Among the three solid waste supported Ni-based catalysts, the catalyst containing 15 wt% Ni displayed the highest activity, that also remained unchanged over extended period, indicating the catalyst stability.

Ru/Attapulgite as an Efficient and Low-Cost Ammonia Decomposition Catalyst

On-site hydrogen generation from ammonia decomposition is a promising technology to address the challenges of direct transportation and storage of hydrogen. The main problems with the existing support materials for ammonia decomposition catalysts are their high cost and time-consuming preparation process. In this work, ammonia decomposition catalysts consisting of in situ-formed nano-Ru particles supported on a naturally abundant mineral fiber, attapulgite (ATP), were proposed and studied. Also, 1 wt.% Ru was uniformly dispersed and anchored onto the surface of ATP fibers via the chemical method. We found that the calcination temperatures of the ATP support before the deposition of Ru resulted in little difference in catalytic performance, while the calcination temperatures of the 1Ru/ATP precursor were found to significantly influence the catalytic performance. The prepared 1 wt.% Ru/ATP catalyst (1Ru/ATP) without calcination achieved an ammonia conversion efficiency of 51% at 500 °C and nearly 100% at 600 °C, with the flow rate of NH3 being 10 sccm (standard cubic centimeter per minute). A 150 h continuous test at 600 °C showed that the 1Ru/ATP catalyst exhibited good stability with a degradation rate of about 0.01% h−1. The 1Ru/ATP catalyst was integrated with proton ceramic fuel cells (PCFCs). We reported that PCFCs at 650 °C offered 433 mW cm−2 under H2 fuel and 398 mW cm−2 under cracked NH3 fuel. The overall results suggest low-level Ru-loaded ATP could be an attractive, low-cost, and efficient ammonia decomposition catalyst for hydrogen production.

Metallic nickel exsolved from a two-dimensional MWW-type zeolitic nickel silicate: An effective catalyst for ammonia decomposition

Exsolution of active species from metal oxide materials is an effective strategy for preparing a highly active and stable catalyst. Here, we prepared two-dimensional nickel (Ni) silicate material with delaminated MWW layers (Ni-DMLs) by hydrothermal treatment of borosilicate MWW precursor (B-MWW(P)) with Ni nitrate solutions and applied on the catalytic decomposition of ammonia (NH3) via exsolution. The layered B-MWW(P) was transformed to a three-dimensional (3D) tectosilicate MWW, a two-dimensional (2D) Ni-DML, and a 2D phyllosilicate structures at temperature regions of 100–120 °C, 140–160 °C, and 170–180 °C, respectively. Meanwhile, the Ni contents on the samples increased from 3.6 to 37.6 wt.% as the hydrothermal temperature increased from 100 to 180 °C, owing to the substitution of framework B by Ni. The chemical state of Ni on each sample was characterized by various analytical tools and correlated with their catalytic properties of NH3 decomposition over the exsolved metallic Ni species. The NH3 decomposition over Ni-DMLs was evaluated in the temperature range of 300–600 °C, and the apparent activation energies were compared. The Ni-DML-160 exhibited the best catalytic activity, achieving an NH3 conversion of 70% at 500 °C and maintained 90% to initial conversion during 100 h on stream at 550 °C. The synergistic effect of the strong interaction between the exsolved metallic Ni and the zeolite support and the 2D nature of Ni-DMLs relieved the catalytic deactivation by sintering and coking, respectively.

Unveiling the Structure-Property Relationship of MgO-Supported Ni Ammonia Decomposition Catalysts from Bulk to Atomic Structure by In Situ/Operando Studies.

Ammonia is currently being studied intensively as a hydrogen carrier in the context of the energy transition. The endothermic decomposition reaction requires the use of suitable catalysts. In this study, transition metal Ni on MgO as a support is investigated with respect to its catalytic properties. The synthesis method and the type of activation process contribute significantly to the catalytic properties. Both methods, coprecipitation (CP) and wet impregnation (WI), lead to the formation of Mg1-xNixO solid solutions as catalyst precursors. X-ray absorption studies reveal that CP leads to a more homogeneous distribution of Ni2+ cations in the solid solution, which is advantageous for a homogeneous distribution of active Ni catalysts on the MgO support. Activation in hydrogen at 900 °C reduces nickel, which migrates to the support surface and forms metal nanoparticles between 6 nm (CP) and 9 nm (WI), as shown by ex situ STEM. Due to the homogeneously distributed Ni2+ cations in the solid solution structure, CP samples are more difficult to activate and require harsher conditions to reduce the Ni. The combination of in situ X-ray diffraction (XRD) and operando total scattering experiments allows a structure-property investigation of the bulk down to the atomic level during the catalytic reaction. Activation in H2 at 900 °C for 2 h leads to the formation of large Ni particles (20-30 nm) for the samples synthesized by the WI method, whereas Ni stays significantly smaller for the CP samples (10-20 nm). Sintering has a negative influence on the catalytic conversion of the WI samples, which is significantly lower compared to the conversion observed for the CP samples. Interestingly, metallic Ni redisperses during cooling and becomes invisible for conventional XRD but can still be detected by total scattering methods. The conditions of activation in NH3 at 650 °C are not suitable to form enough reduced Ni nanoparticles from the solid solution and are, therefore, not a suitable activation procedure. The activity steadily increases in the samples activated at 650 °C in NH3 (Group 1) compared to the samples activated at 650 °C in H2 and then reaches the best activity in the samples activated at 900 °C in H2. Only the combination of complementary in situ and ex situ characterization methods provides enough information to identify important structure-property relationships among these promising ammonia decomposition catalysts.

Boosting hydrogen production of ammonia decomposition via the construction of metal-oxide interfaces

The ammonia decomposition for the production of carbon-free hydrogen has triggered great attention yet still remains challenging due to its sluggish kinetics, posting the importance of precise design of efficient catalysts for ammonia decomposition under low temperatures. Constructing the metal-support interaction and interface is one of the most important strategies for promoting catalysts. In this work, by coating ceria onto the Ni nanoparticles (NPs), we discover that the Ni–CeO2 interfaces create an exceptional effect to enhance the catalytic decomposition of ammonia by over 10 folds, compared with the pristine Ni. The kinetic analysis demonstrates that the recombinative N2 desorption is the rate-determining step (RDS) and the Ni–CeO2 interface greatly increases the RDS. Based on these understandings, a strategy to fabricate the Ni/CeO2 catalyst with abundant Ni–Ce–O interfaces via one-pot sol-gel method was employed (hereafter denoted to s–Ni/CeO2). The s–Ni/CeO2 catalyst shows a high activity for ammonia decomposition, achieving a H2 formation rate of 10.5 mmol gcat−1 min−1 at 550 °C. Combined with a series of characterizations, the relationship between the catalyst structure and the performance was investigated for further understanding the effect of metal-oxide interfaces.

Reducing temperature difference of a direct ammonia tubular SOFC to 1K

In this study, a three-dimensional direct ammonia solid oxide fuel cell (DA-SOFC) was numerically modeled to investigate the effects of ammonia inlet flow velocity, tube structure, and catalyst filling on the internal temperature distribution of the cell. The results show that shortening the length of the ammonia inlet tube and increasing the inlet flow velocity leads to an increase in the temperature difference inside the cell. By perforating the ammonia inlet tube, the temperature difference can be further reduced, and the low-temperature zone inside the cell gradually decreases with the perforated area percentage increasing. In addition, placing ammonia decomposition catalyst inside the perforated inlet tube can further improve the temperature difference between the electrodes inside the cell, reducing it from 30 K to about 1 K. Furthermore, the temperature distribution pattern inside the fuel cell with metal supports was investigated, and it was found that the metal support can better export the heat generated inside the fuel cell. This study provides a new idea to improve the temperature distribution of DA-SOFC and enhance the stability and reliability of cell operation.

Loaded Catalysts for the Thermal Decomposition of Ammonia

As new energy sources receive more and more attention, the demand for the commercialization of hydrogen energy is also increasing. Hydrogen storage is one of the most important aspects. Currently, the more mature the physical storage technology, but in the future, with the requirements for hydrogen storage, safety, economic cost, hydrogen storage quality density and other indicators, chemical hydrogen storage technology will become a more important and promising research direction. Among them, liquid ammonia hydrogen storage technology has the advantages of product environmental protection, mild storage conditions, and no COx generation when releasing hydrogen. In this paper, several mainstream loaded catalysts used for the pyrolysis process of NH3 are discussed on the basis of literature review, and their respective mechanisms, carriers, and promoters are discussed according to the classification, and the factors affecting the catalysts as well as the suitable action conditions are elaborated, so as to provide some references for the future development of ammonia decomposition catalysts.

Enhanced stability and electrochemical investigations of Ni/ZSM-5 catalyst layer on nickel-based anodes for ammonia-fed solid oxide fuel cells

Ammonia-fed solid oxide fuel cell (SOFC) is a promising clean energy technique with distinctive advantages of zero-carbon emission, easy storage, and high efficiency. However, the typical nickel anode for SOFC is susceptible to structural change and performance degradation under an ammonia environment, particularly at reduced operating temperatures. In addition, obtaining a deep understanding of the individual electrode processes is demanded for the rational design and optimization of NH3–SOFCs. This work enhances the cell performance and durability of ammonia-fed SOFCs by utilizing a cost-effective ammonia decomposition catalyst (Ni/Na-ZSM). The electrode processes are investigated quantitively using distributed relaxation time (DRT) and equivalent circuit model (ECM) analysis. Accelerated degradation tests are conducted for the NH3-based SOFC cells by thermal cycling at operational temperatures of 700 °C-650 °C. Compared to the conventional cell, the cell with the Ni/Na-ZSM catalyst exhibits improved cell performance and five times less decay. In situ measurements and impedance analysis combined with microstructural characterization reveal that the durability enhancement is probably ascribed to protecting the structure of the three-phase boundaries (TPBs), which maintains a stable resistance of the TPB charge transfer processes during the temperature cycling.

Ammonia decomposition for carbon-free hydrogen production over Ni/Al-Ce catalysts: Synergistic effect between Al and Ce

To deeply understand the synergistic effect between Al and Ce in the composite support of Ni-based catalysts for ammonia decomposition, a series of Ni/Al-Ce catalysts with 10 wt% Ni loading were prepared combining coprecipitation and impregnation methods. The activity test results showed that the Ni/Al0.1Ce0.9Ox catalyst exhibited significantly improved activity for ammonia decomposition in the temperature range of 450–600 ℃ compared with Ni/Al2O3, Ni/CeO2, and other Ni/Al-Ce catalysts. Systematic characterization results showed that appropriate ratio of Al and Ce formed an Al-Ce-O solid solution and increased the number of oxygen vacancies on the surface, which induced synergistic effect and played a vital role in the improved activity. Such synergistic effect not only promoted the dispersion of Ni species, facilitated the activation of NH3, but also enhanced the interaction between metal and support. This work provided a new strategy for designing efficient Ni-based catalysts for ammonia decomposition and deepened the understanding of the synergistic effect between Al and Ce in the composite support.

The effect of acidic–basic structural modification of nickel-based catalyst for ammonia decomposition for hydrogen generation

The utilization of non-precious nickel-based catalyst in increasing ammonia dissociation for COx-free hydrogen production was investigated. Typically, Co, La and basic metal oxides (Na, K, Ba) promoters were synthesized with nickel over acidic gamma alumina support. The main objective of the study was to modify the acid-base surface of catalyst structure thereby increasing ammonia dissociation activity. The catalytic activity for ammonia decomposition was strongly influenced by the addition of Na and K oxide promoters over 15 %Ni/Al2O3 resulting in moderate-stronger basic sites suitable for ammonia conversion. The addition of Na and K oxides showed a clear trend in tuning the trimetallic catalyst and significantly reducing the amount of strongly adsorbed hydrogen on the catalyst surface. This results in higher ammonia conversion which increased as a function of temperature to 32.4 %, 67.5 % and 95.3 % at 430 ᵒC, 485 ᵒC, and 533 ᵒC, respectively. Ammonia conversion using promoters was stable with no degradation of performance and the conversion increased with the decrease in WHSV. The catalytic reactivity over trimetallic catalysts was systematically influenced by their basic-acidic property that promoted ammonia dehydrogenation on the surface of nickel oxide-based catalyst.

Systematic in situ Investigation of the Formation of NH3 Cracking Catalysts from Precursor Perovskites ABO3 (A=La,Ca,Sr and B=Fe,Co,Ni) and their Catalytic Performance

AbstractThis work addresses the formation of ammonia (NH3) decomposition catalysts derived from perovskites ABO3 (A=La, Ca, Sr, and B=Fe, Co, Ni) precursors via operando synchrotron X‐ray diffraction experiments. During the reaction in NH3, the perovskite precursors are decomposed and the transition metals are reduced. Depending on their reduction properties, active metallic catalysts are formed in situ on La2O3 as support. The reduction behavior of the perovskites, formation of intermediate phases during activation, and catalytic performance was studied in detail. In addition, microstructure properties such as crystallite sizes and particle morphology were analyzed. Co‐/Ni‐based perovskites decomposed completely during activation to Co0/Ni0 supported on La2O3 while Fe‐based perovskites were fully stable but inactive in catalysis. This difference is due to varying electronic properties of the transition metals, e. g., decreasing electronegativity from Ni to Fe. With decreasing reducibility, the intermediate phases during activation formed more distinct. La3+ was partially substituted by Ca2+/Sr2+ in LaCoO3 to test for advantageous effects in NH3 decomposition. The best performance was observed using the precatalyst La0.8Sr0.2CoO3 with a conversion of 86 % (100 % NH3, 15000 mL g−1 h−1) at 550 °C.

Elucidating the effect of Ce with abundant surface oxygen vacancies on MgAl2O4-supported Ru-based catalysts for ammonia decomposition

Ammonia is a promising COx-free hydrogen (H2) carrier because of its high volumetric H2 density. However, developing highly active/stable ammonia decomposition catalysts for H2 production remains challenging. In this study, the role of ceria (CeO2) as a promoter for Ru-based catalysts was investigated. Ru/Cex/MgAl(y00) catalysts were prepared by the incipient wetness impregnation (IWP) and deposition–precipitation (DP) methods. The surface oxygen vacancy (OV) concentration was controlled by the Ce loading and calcination temperature. By evaluating the surface reaction behavior of the ammonia decomposition catalysts, this study proposes that CeO2 effectively improves the recombination/desorption of N and H atoms. The optimal catalyst Ru/Ce5/MgAl(600) achieved a high H2 formation rate (27.4 mmolH2·gcat−1∙min−1 at 30,000 mL·gcat−1·h−1, 450 °C) and stable performance after exposure at 650 °C for 20 h. This study provides insight into the effect of abundant surface OVs in CeO2 on the physicochemical properties and ammonia decomposition performance of the catalysts.

Development of Direct-Ammonia Solid Oxide Fuel Cells (DA-SOFCs) and the Effect of Incorporating Internal Ammonia Decomposition Catalysts

Direct-ammonia solid oxide fuel cells (DA-SOFCs) are among the most efficient power sources that use ammonia. The high operating temperature of SOFCs enables ammonia decomposition reaction to proceed inside the anode compartment of SOFCs. Coupling exothermal SOFC operation and endothermal ammonia decomposition reaction increases the efficiency of the device. DA-SOFCs function as well as hydrogen-fueled ones over 750 °C. Recently we have reported that DA-SOFCs suffer significant performance loss under 650 °C, especially the high-performance cells. We discuss a range of phenomena taking place inside the anode compartment of DA-SOFCs: interconnect, current collector, and anode support. Interconnect and current collector have the capability of decomposing significant amounts of ammonia. Nevertheless, incorporating a catalyst is important at low operating temperatures.