COx-free Hydrogen Production Research Articles

Self-combustion Ni and Co-based perovskites as catalyst precursors for ammonia decomposition. Effect of Ce and Mg doping

LaCo1-xNixO3 perovskites have been synthesized by self-combustion, characterized, and examined as catalyst precursors for the COx-free hydrogen production from catalytic ammonia decomposition at low temperatures. The influence of the cobalt content as well as the addition of two dopant in different amount was studied and optimized. Small Ni crystallite size and high total basic sites were found to remarkably enhance the catalytic activity. Moreover, bimetallic perovskites generated cobalt/nickel in higher size, higher impurities and lower active sites than pure nickel perovskite, which decreased the ammonia conversion. On the other hand, the addition of dopant in adequate amount over pure Ni perovskite (La0.1A0.9NiO3; A = Ce or Mg) generated catalyst with low nickel crystallite size and high basicity delivering superior catalytic performance. Catalysts were demonstrated to be stable for at least 40 h. In fact, 96 % and 98 % ammonia conversion were achieved at low temperature (400 °C), when La0.1Ce0.9NiO3 and La0.1Mg0.9NiO3 were employed, resulting from the synergic effect between La-Ce and Ni-Mg-La. Presenting the Mg-doped perovskite the highest catalytic activity at the mild temperature of 350 °C.This study provides new insight in designing diverse catalyst precursors to develop economic and efficient catalysts to achieve high ammonia conversion (high hydrogen production) at low temperature and enhance the ammonia perspective as hydrogen carrier toward the ‘hydrogen economy’.

Performance of microwave reactor system in decomposition of ammonia using nickel based catalysts with different supports

In this study, the ammonia decomposition reaction to produce COx-free hydrogen is investigated in a microwave reactor system using nickel-based catalysts supported by different materials. Unlike the activated carbon supported catalyst (Ni@AC), the alumina supported catalyst (Ni@Alumina) is mixed with carbon in a 1:1 ratio to reach the necessary reaction temperature in the microwave reactor. Ni@Alumina gives an overall hydrogen production rate of 73 mmol/min.g cat with 99% conversion at 400 °C under pure ammonia flow (60 ml/min). Ni@Alumina outperforms Ni@AC under microwave reactor conditions, but underperforms Ni@AC under the conventional testing, which is done for comparison. It is suggested that selective heating of nickel species in Ni@Alumina enables better performance in the microwave reactor in comparison to Ni@AC. On the other hand, high surface area and small nickel particles present in the Ni@AC structure in comparison to the Ni@Alumina structure, causes higher activity in the conventional reactor at temperatures over 550 °C. Between 400 and 550 °C, both Ni@Alumina and Ni@AC have substantially lower activity under conventional heating than microwave heating when compared at the same temperatures. Hot spot formation and microwave selective catalytic effect are considered as possible reasons for the improved performance of microwave reactor system. • COx-free hydrogen for fuel cell application is synthesized from ammonia. • Microwave energy greatly enhances activity of the catalyst for ammonia decomposition. • In microwave reactor system, 99% conversion was achieved with Ni@Alumina at 400 °C. • Mesoporous Carbon was used as a microwave absorber with alumina supported catalysts.

Nanofabrication of Ni-incorporated three-dimensional ordered mesoporous carbon for catalytic methane decomposition

Incorporation of Ni active species with mesoporous carbon and the resulting composite materials have received much attention due to their nature of flexibility derived from a confluence of metallic and carbonic properties and numerous textural advantages inherited from mesoporous carbon substrates, contributing to their versatility in energy transformation. However, the efficient integration of such composite materials with complementary advantages in properties is still highly desired. Herein, confined growth of Ni(OH)2 nanosheets within three dimensionally ordered mesoporous carbon (3DOMC) by steam-assisted crystallization is propose in this paper. High-crystalline Ni(OH)2 species are found in two forms of confined extra-small nanosheets within the mesopores of 3DOMC and staggered nanosheets over the particles of 3DOMC, which can be reduced to the highly segregative Ni nanoparticles by sufficient reduction. By using as a catalyst for methane decomposition to produce COx-free hydrogen, Ni/3DOMC contributes a maximum CH4 conversion of 66.5% and H2 output rate of 7.4 mmol. gcat−1·min−1 at 850 °C, more superior to the conventional Ni-incorporated active carbon (Ni/AC) catalyst. Moreover, the Ni/3DOMC catalyst also exhibits not only a higher initial reaction rate but also an improved catalytic stability attributed to the abundant homodispersed Ni active species by the highly hybrid structure. It is expected that the flexible component, well-defined structure, and superior CMD performance could promote a great application potential of Ni/3DOMC nanocomposites in catalysis.

Enhanced methane decomposition over transition metal-based tri-metallic catalysts for the production of COx free hydrogen

In this study, COx-free hydrogen production via methane decomposition was studied over Cu–Zn-promoted tri-metallic Ni–Co–Al catalysts. The catalysts have been prepared by the constant pH co-precipitation method, and the nominal Ni metal loading was fixed at 50 wt % along with other metals at 10 wt% each. The catalyst activity for methane decomposition reaction was examined in a reactor between 400 °C and 700 °C and at atmospheric pressure. Different techniques such as N2-physisorption, X-ray diffraction, H2-TPR SEM, TEM, ICP-MS, TGA, and Raman spectroscopy were applied to characterize the catalysts. The relation between the catalyst composition and their catalytic activity has been investigated. The controlled synthesis has resulted in a series of catalysts with a high surface area. Ni–Co–Cu–Zn–Al was the most active and productive catalyst. Various characterizations indicate that the promotional effects of Cu–Zn interaction were the critical factor in catalysts' activity and stability. Ni–Co–Cu–Zn catalyst gave the highest methane conversion of 85% at 700 °C. Zn addition improves the stability of the catalyst by retaining the active metal size during the decomposition reaction. The catalyst was active for 80 h of stability study. The rapid deactivation of the Ni–Co catalyst was due to the sintering of the catalyst at 650 °C. Moreover, carbon species accumulated during the methane decomposition reaction depend on the catalysts' composition. Zn promotes the growth of reasonably long and thin carbon nanotubes, whereas the diameter of carbon nanotubes on unpromoted catalysts was large.

Production of COx-Free Hydrogen and Few-Layer Graphene Nanoplatelets by Catalytic Decomposition of Methane over Ni-Lignin-Derived Nanoparticles.

Nickel (Ni)-lignin nanocomposites were synthesized from nickel nitrate and kraft lignin then catalytically graphitized to few-layer graphene-encapsulated nickel nanoparticles (Ni@G). Ni@G nanoparticles were used for catalytic decomposition of methane (CDM) to produce COx-free hydrogen and graphene nanoplatelets. Ni@G showed high catalytic activity for methane decomposition at temperatures of 800 to 900 °C and exhibited long-term stability of 600 min time-on-stream (TOS) without apparent deactivation. The catalytic stability may be attributed to the nickel dispersion in the Ni@G sample. During the CDM reaction process, graphene shells over Ni@G nanoparticles were cracked and peeled off the nickel cores at high temperature. Both the exposed nickel nanoparticles and the cracked graphene shells may participate the CDM reaction, making Ni@G samples highly active for CDM reaction. The vacancy defects and edges in the cracked graphene shells serve as the active sites for methane decomposition. The edges are continuously regenerated by methane molecules through CDM reaction.

Influence of Various Spinel Materials Supported Ni Catalysts on Thermocatalytic Decomposition of Methane for the Production of Cox-Free Hydrogen

Influence of Various Spinel Materials Supported Ni Catalysts on Thermocatalytic Decomposition of Methane for the Production of Cox-Free Hydrogen

Influence of Ce substitution in LaMO3 (M = Co/Ni) perovskites for COx-free hydrogen production from ammonia decomposition

The La based perovskite type LaMO3 (M = Ni, Co) oxides were prepared by combustion synthesis method using citric acid as organic fuel. These catalyst precursors tested for ammonia decomposition. The LaNiO3 and LaCoO3 catalysts showed good activity for NH3 decomposition. The LaNiO3 catalyst displayed greater activity than LaCoO3. This due to high surface area and easily reducibility of Ni species. A 50% of La was substituted by Ce in both LaNiO3 and LaCoO3 catalysts. A remarkable effect on catalytic performance was observed with the partial substitution of La by Ce in perovskite catalyst especially at lower temperatures. The La0.5Ce0.5NiO3 catalyst exhibited highest activity among all prepared samples. The achieved superior activity is due to boost in surface area, reducibility and suitable basicity. The SEM elemental mapping of La0.5Ce0.5NiO3 catalyst concluded that metal oxide constituents dispersed homogeneously. The La0.5Ce0.5NiO3 catalyst showed excellent stable catalytic performance during 50 h time on study at 550 °C.

COx-free hydrogen production from ammonia at low temperature using Co/SiC catalyst: Effect of promoter

Cobalt catalysts (5 wt%) using β-SiC as a support and modified with different alkaline (K and Cs), alkaline-earth (Ca and Mg) and rare-earth (La and Ce) metals were prepared, characterized, and examined in the hydrogen production from ammonia decomposition at low temperatures. Porous SiC has been proved to be a suitable support for promoted cobalt catalysts, which are highly active for the target decomposition reaction. Catalysts modified with small amount (1 wt%) of K and La remarkably enhanced the catalytic activity whereas the addition of Cs, Mg, Ca or Ce to cobalt catalyst decreased the ammonia conversion with respect to the unpromoted catalyst. The total basic sites and electron-donor properties of the K metal modified the electronic structure of cobalt active sites increasing the ammonia conversion at low temperatures. However, an excess of K promoter resulted in a decrease in the hydrogen production due to the blockage of the active sites. Therefore, the catalyst containing 1 wt% K and 5 wt% Co resulted in an excellent H2 production associated with an ammonia conversion close to 100% at 450 °C. Moreover, the selected catalyst provided suitable performance stability after one day of reaction.

SYNGAS PRODUCTION FROM GREENHOUSE GASES VIA DRM OVER Ni/Al2O3 CATALYST: EFFECT OF Ca ADDITION

In view of the escalating global warming phenomenon, utilization of CO2 has become an important event in recent decades. Syngas production via Dry Reforming of Methane (DRM) is one of the promising methods to produce COX-free hydrogen as a renewable and sustainable energy source. DRM requires an active functioning catalyst since it is a highly endothermic process. The catalytic behaviour of 10 wt.% Ni supported on Al2O3 and doped with CaO is investigated for DRM. In the present study, the effect of alkaline earth metal oxide (CaO) loading (varying from 0.5-2.0 wt.%) on the structure, properties, stability, and performances of the Ni-CaO/Al2O3 catalyst for the DRM process is studied. The catalysts were prepared by wet impregnation method and characterized by Scanning Electron Microscopy (SEM) to study the morphology of the fresh and spent catalyst and Thermogravimetric Analyzer (TGA), which changes in physical and chemical properties of the catalysts are measured as a function of increasing temperature and time. DRM is carried out in a fixed-bed reactor at a temperature range from 600°C to 800°C. Further, the effect of CH4 partial pressure on the conversion of CH4, CO2 and syngas ratio were also investigated. The thermal stability of the catalyst increased on loading with CaO, and CAT-4 (1.5 wt.% CaO, 8.5 wt.% Ni on Al2O3) displayed the optimum activity, stability, and least coke formation.Keywords: Global warming, syngas, catalyst, wet impregnation

Fe-based catalyst derived from MgFe-LDH: Very efficient yet simply obtainable for hydrogen production via ammonia decomposition

The current study provided the first example to develop the Fe-based catalyst for COx-free hydrogen production via ammonia decomposition through the unique MgFe-layered double hydroxides (MgFe-LDHs) of different stoichiometric Mg/Fe ratio. The so obtained Fe-based catalyst is low-cost, readily obtainable, and environmentally friendly. Structurally, the Fe(FeNx) species are 3D-isolated by the nano-MgO entities, improving anti-sintering potential of Fe(FeNx); and electronically, the Fe (FeNx) species are promoted by the nano-MgO matrix, showing the strongest promoting effect of MgO on Fe(FeNx). At a GHSVNH3 of 150,000 mL gcat−1 h−1, the current N–Mg5.3FeOm catalyst can give an outstanding H2 formation rate of 9.83 mol gcat−1 h−1 at 680 °C and a TOFH2 = 2.19 s−1 at 530 °C. The influence of Mg/Fe constitution on catalyst structure, surface property, and performance was systematically investigated. The in-situ ammonia treatment was superior to the usually adopted hydrogen pre-reduction for the Fe–Mg oxide precursor, leading to easy development of small sized FeNx specimen and activity enhancement.

Hydrogen production via methane decomposition over nickel supported on synthesized ZSM-5/MCM-41 zeolite composite material

Catalytic decomposition of methane (CDM) for COx-free hydrogen production is carried out over 20 wt% Ni supported on H-ZSM-5/MCM-41 composite material, synthesized from alkaline desilication of a conventional H-ZSM-5(Si/Al = 40) and surfactant-recrystallization process. The composite material is used, for the first time, as support of Ni-catalyst in CDM. Tested for 6 h at 620 °C under atmospheric pressure, the 20 wt% Ni/H-ZSM-5/MCM-41 exhibits relatively higher H2 production rate than 20 wt% Ni supported on the parent H-ZSM-5(Si/Al = 40) or on the pure MCM-41 in the order H-ZSM-5/MCM-41 > H-ZSM-5 > MCM-41. All catalysts display a remarkable catalytic stability. The higher catalytic activity of Ni/composite could be related to an improvement in both the access to active Ni metal atoms and the dispersion of the latter as evidenced by H2-chemisorption measurement. The fresh catalysts are characterized by several techniques while the reacted ones are studied by the Raman spectroscopy.

Development of a Ba–CoCe catalyst for the efficient and stable decomposition of ammonia

COx-free hydrogen production; cobalt-based catalysts for ammonia decomposition; cerium–barium promoter in cobalt catalysts.

Graphene aerogel-supported ruthenium nanoparticles for COx-free hydrogen production from ammonia

Ruthenium was highly dispersed on graphene aerogel (GA) at high loadings to achieve high performance in COx-free hydrogen production from ammonia. Catalytic performance measurements on ammonia decomposition showed that the GA-supported catalyst with a Ru loading of 13.6 wt% provides an ammonia conversion of 71.5 % at a space-velocity of 30,000 ml NH3 gcat−1 h−1 and at 450 °C, corresponding to a hydrogen production rate of 21.9 mmol H2 gcat−1 min−1. The addition of K increased the ammonia conversion to a record high value of 97.6 % under identical conditions, reaching a hydrogen generation rate of 30.0 mmol H2 gcat−1 min−1, demonstrated to be stable for at least 80 h. A comparison of the turnover frequencies of catalysts indicated that this increase in performance upon the addition of K originated from an increase in the number of the active Ru sites and the corresponding electron density available for reaction.

One-pot synthesis of supported Ni@Al2O3 catalysts with uniform small-sized Ni for hydrogen generation via ammonia decomposition

Nickel based materials are the most potential catalysts for COx-free hydrogen production from ammonia decomposition. However, the facile synthesis of supported Ni-based catalysts with small size Ni particles, high porosity and good structural stability is still of great demand. In this work, uniform small-sized Ni particles supported into porous alumina matrix (Ni@Al2O3) are synthesized by a simple one-pot method and used for ammonia decomposition. The Ni content is controlled from 5 at.% to 25 at.%. Especailly, the 25Ni@Al2O3 catalyst shows the best catalytic performance. With a GHSV of 24,000 cm3gcat−1h−1, 93.9% NH3 conversion is achieved at 600 °C and nearly full conversion of NH3 is realized at 650 °C. The hydrogen formation rate of 25NiAl catalyst reaches 3.6 mmol gcat−1min−1 at 400 °C and 7.8 mmol gcat−1min−1 at 450 °C. The enhanced activity observed on 25Ni@Al2O3 catalyst can be attributed to the structural characteristic that large amounts of uniform-sized small (7.2 ± 0.9 nm) Ni particles are highly dispersed into porous alumina matrix. The aggregation of active metallic Ni particles during the high temperature reaction can be effectively prevented by the porous alumina matrix due to the strong interaction between them, thus ensuring a good catalytic performance.

Solid Acid Electrochemical Cell for the Production of Hydrogen from Ammonia

Summary Production of high-purity hydrogen by thermal-electrochemical decomposition of ammonia at an intermediate temperature of 250°C is demonstrated. The process is enabled by use of a solid-acid-based electrochemical cell (SAEC) in combination with a bilayered anode, comprising a thermal-cracking catalyst layer and a hydrogen electrooxidation catalyst layer. Cs-promoted Ru on carbon nanotubes (Ru/CNT) serves as the thermal decomposition catalyst, and Pt on carbon black mixed with CsH2PO4 is used to catalyze hydrogen electrooxidation. Cells were operated at 250°C with humidified dilute ammonia supplied to the anode and humidified hydrogen supplied to the counter electrode. A current density of 435 mA/cm2 was achieved at a potential of 0.4 V and ammonia flow rate of 30 sccm. With a demonstrated faradic efficiency for hydrogen production of 100%, the process yields hydrogen at a rate of 1.48 m o l H 2 / g c a t h .

Methane thermocatalytic decomposition to COx-free hydrogen and carbon nanomaterials over Ni–Mn–Ru/Al2O3 catalysts

Thermocatalytic decomposition of methane is proposed to be an economical and green method to produce COx-free hydrogen and carbon nanomaterials. In this work, the catalytic performance of Ni–Mn–Ru/Al2O3 catalyst under different reaction parameters (such as, pre-reduction temperature, reaction temperature, space velocity, etc.) were investigated to obtain optimum reaction conditions. The catalysts were characterized by N2 adsorption/desorption, X-ray diffraction, inductively coupled plasma optical emission spectrometer and hydrogen temperature programmed reduction. For the 60 wt% Ni-5 wt% Mn-10 wt% Ru/Al2O3 catalyst using Ru(NO)(NO3)x(OH)y(x + y = 3) as Ru precursor, the methane conversion rate obtained is high as 93.76% under optimum reaction conditions (reduction at 700 °C for 1 h, reaction at 750 °C, GSHV = 36,000 mL/gcat h). Carbon nanomaterials formed during the process of methane thermocatalytic decomposition were characterized by scanning electron microscopy, thermal gravimetric analyzer and Raman spectroscopy. Carbon nanofibers were formed over all the Ni–Mn–Ru/Al2O3 catalysts.

Ammonia decomposition on a highly-dispersed carbon-embedded iron catalyst derived from Fe-BTC: Stable and high performance at relatively low temperatures

Fe-BTC (iron 1,3,5-benzenetricarboxylic acid), a commercially available metal organic framework (MOF), was used as a sacrificial template to produce a series of carbon-embedded Fe catalysts upon its pyrolysis at different temperatures. The catalyst prepared by pyrolyzing Fe-BTC at 400 °C under flowing N2 provided a high graphitic degree on the carbon support hosting highly dispersed Fe species at a Fe loading of 34 wt%. Performance measurements on ammonia decomposition to produce COx-free hydrogen showed that this catalyst provided an ammonia conversion of 73.8% at a space velocity of 6000 cm3 NH3 h−1 gcat−1 and at 500 °C for at least 120 h. This stable performance, exceeding that of some of the best non-noble metal catalysts, was associated with the presence of highly-dispersed Fe species at a significantly high Fe loading, embedded in a carbonaceous shell. The presence of the carbonaceous shell not only protected the active species against sintering, but also made them electron rich owing to its high level of graphitization.

COx-free hydrogen production from ammonia – mimicking the activity of Ru catalysts with unsupported Co-Re alloys

On-demand production of hydrogen from ammonia is a challenge limiting the implementation of ammonia as a long term hydrogen vector to overcome the difficulties associated with hydrogen storage. Herein, we present the development of catalysts for the on-demand production of hydrogen from ammonia by combining metals with high and low N-adatom adsorption energies. In this way, cobalt-rhenium (Co-Re) catalysts show high activity mimicking that of ruthenium. EXAFS/XANES analyses demonstrate that the bimetallic Co-Re contribution is responsible for the activity and the stability of the catalysts in consecutive runs with no observable formation of nitrides (Co-N and Re-N) occurring under the ammonia atmosphere. While cobalt is partially re-oxidised under ammonia, re-reduction in the presence of rhenium is observed at higher temperatures, coinciding with the on-set of catalytic activity which is accompanied by minor structural changes. These results provide insight for the development of highly active alloy based ammonia decomposition catalysts.

Spray-dried Fe/Al2O3 as a carbon carrier for COx-free hydrogen production via methane cracking in a fluidized bed process

Herein, we report the production of COx-free hydrogen from catalytic methane cracking. Spherical, porous and fluidizable catalyst has been produced by spray-drying of 10 wt-% Fe2O3 and 90 wt-% Al2O3. This material can accommodate the deposited solid carbon from the methane cracking reaction in its pores. In fluidized bed experiments, the kinetics of reduction of the catalyst with methane were determined. A high activation energy of 313 kJ mol−1 for the reduction of the intermediate spinel phase (FeAl2O4) to metallic iron indicates the need for high temperatures for the reduction step. The subsequent cracking of methane could be well described by applying a simple backmixed flow model. The reaction order with respect to methane concentration in the gas was nc = 0.63 and the apparent activation energy at T > 800 °C wasEa,c,T>800°C = 21.5 kJ mol−1 andEa,c,T<800°C = 128.1 kJ mol−1 at T < 800 °C. This is indicative of mass transfer limitations at temperatures greater than 800 °C. The activity of the bed material for methane cracking was found to decrease linearly with an increasing amount of carbon deposited on its surface. When the carbon deposited on the bed material was limited to below 10 wt-%, mechanical and structural stability of the spherical particles was maintained. Likewise, bed expansion and particle break-up were observed when more than 10 wt-% carbon was deposited. These results confirm the principal suitability of the developed material as a carbon carrier, and the obtained kinetic data can be useful for design and scale-up considerations of this fluidized bed methane cracking process.

Multiwall carbon nanotube-supported molybdenum catalysts for ammonia decomposition reaction under microwave effect.

In this study, microwave-assisted ammonia decomposition reaction was investigated over molybdenum incorporated catalysts. Due to the selective, volumetric, and noncontact heating properties of the microwave system, higher conversion values could be achieved at relatively lower reaction temperatures, which is important for on-site COx-free hydrogen production. Multiwall carbon nanotube-supported molybdenum catalysts were prepared following the impregnation procedure with different metal loading (3.5%–12.5% wt%), and inductively coupled plasma, nitrogen physisorption, X-ray diffraction, and transmission electron microscopic techniques were employed to characterize the fresh and used samples. Reaction experiments were performed under the flow of pure ammonia with a gas hourly space velocity of 36,000 mL/gcat.h for both the microwave and conventionally heated reaction systems. It was found that ammonia conversion was obtained even at 400 °C, reaching 40%, and total conversion was observed even at 450 °C, while the activities of these catalysts were negligible at a reaction temperature lower than 550 °C, in the conventional heated system, which included an electrically heated furnace. Crystals of α-Mo2C as well as MoO2 were observed in the structures of the synthesized catalysts and the formation of nitride species was more easily observable under microwave heating, possibly due to the nitridation of molybdenum carbide species during the reaction.