Ammonia decomposition over citric acid chelated γ-Mo2N and Ni2Mo3N catalysts

A novel synthesis route, using citric acid as a chelating agent, for the formation of γ-Mo₂N and pure phase of Ni₂Mo₃N catalysts and their application for NH₃ decomposition reaction for clean hydrogen production, have been performed. Successful formation of a pure bulk phase of Ni₂Mo₃N was confirmed by using XRD, XPS, HRTEM techniques and found that Ni₂Mo₃N is not air sensitive. Ni₂Mo₃N catalyst showed very high catalytic activity for NH₃ decomposition reaction having ～97% conversion of NH₃ at 525 °C at 6000 h^?1 GHSV, better than previously reported results on any non-promoted, non-precious catalysts, which is mainly due to the formation of pure phase and high surface area for this catalyst using a chelating method of preparation.     

Ammonia decomposition over citric acid induced γ-Mo2N and Co3Mo3N catalysts

This work focuses on a novel synthesis route, using citric acid as a chelating agent, for the formation of γ-Mo₂N and Co₃Mo₃N bulk catalyst and their application for NH₃ decomposition reaction for hydrogen production having its application for onboard generation of hydrogen for fuel cell in transportation vehicles. Successful formation of the pure bulk phase of Co₃Mo₃N was confirmed by using XRD, XPS, HRTEM techniques. The prepared Co₃Mo₃N catalyst showed high surface area 15.23 m²/g and high catalytic activity compared to bulk γ-Mo₂N for this decomposition reaction, having 97% conversion of NH₃ at 550 °C at 6000 h^?1.     

Hydrogen production via ammonia decomposition catalyzed by Ni/M–Mo–N (M = Ni,Co) bimetallic nitrides

This study demonstrates the significant improvement in NH₃ decomposition using Ni-decorated M–Mo–N-based catalysts (M = Co and Ni) compared with conventional catalysts. Catalysts are prepared using a mixture of the corresponding metal salts and hexamethylenetetramine, and the impregnation method is used to decorate the Ni-particles on the catalysts. Among all the samples, 10 wt% Ni-decorated Co₃Mo₃N exhibits the highest NH₃ conversion rate (71%) at 500 °C, and the performance remains stable for 30 h of long-term testing. According to the gas chromatography measurements, the H₂/N₂ ratio is approximately 3 in all cases, which is consistent with the theoretical value. X-ray photoelectron spectroscopy results show that Co₃Mo₃N possesses the highest NH₃ conversion efficiency because of the weaker binding energy of Mo–N. Furthermore, Co₃Mo₃N exhibits a stronger Lewis acidity and higher NH₃ decomposition, which is attributed to the easy breaking of the N–H bond on the Co₃Mo₃N surface.     

The effect of barium-promoted for microsphere Ru/CeO2 catalysts in ammonia synthesis

In this essay, the effect of the morphology of the CeO₂ support and the Ba promoter on the ammonia synthesis reaction was studied. CeO₂ support with {110} and {100} crystal planes and more oxygen vacancies enhanced the catalytic activity of ammonia synthesis. The relatively uniform microspheres structure CeO₂ support (CeO₂-MS) with {110} and {100} crystal planes was synthesized. The structural functions of the as-synthesized CeO₂ support for the Ru-based catalyst were investigated in the ammonia synthesis reaction. The results of catalytic performance showed that the catalytic activity of 2.5%Ru/CeO₂-MS catalyst reached 8940 μmol· g^?1· h^?1 at 450 ℃, 3.8 MPa, H₂/N₂ = 3 (60 mL?min^?1), which is higher nearly 2.5 times than the 2.5%Ru/CeO₂-commercial (CeO₂-C). And the catalytic activity of catalysts increased with the increase of reaction temperature. The activity of 6%Ba-2.5%Ru/CeO₂-MS (24000 μmol· g^?1· h^?1) catalyst increased about 268% than that of catalyst without addition of Ba. Their physical and chemical properties were characterized by XRD, BET, HRTEM, H₂-TPR, H₂-TPD, and XPS analyses. Our results indicate that the 2.5%Ru/CeO₂-MS catalyst and catalysts involving promoters (Cs, K, and Ba) exhibit significant support-morphology-dependent catalytic activity for ammonia synthesis.     

Development of high surface area bulk W2N catalysts for hydrogen production from ammonia decomposition

High surface area tungsten nitride catalysts synthesized from ammonium meta-tungstate and employed as catalysts for ecofriendly H₂ production from NH₃. A series of tungsten nitride catalysts synthesized by using CiA (citric acid) as chelating agent with different molar ratio of W and CiA. The synthesized materials characterized using BET-surface area, X-ray diffraction, X-ray photoelectron spectroscopy and SEM techniques. The BET value of as-synthesized tungsten nitride was raised from 25 to 80 m² g⁻¹. The influence of amount of CiA in preparation on the catalyst's surface area was investigated. The catalyst performance measured within the desired range of temperature 300–600 °C. A pure phase of tungsten nitride was formed by this preparation method. The catalyst with the ratio of CiA/W = 3 exhibited the best catalytic performance. The increased activity of WN-31 catalyst was mainly due to increased surface area, decreased particle size and high surface concentration. The WN-31 catalyst showed stable performance during time on study for 25 h. These bulk tungsten-based materials are easy to synthesize and highly stable material in the reaction atmosphere.     

Towards an efficient CoMo/γ-Al2O3 catalyst using metal amine metallate as an active phase precursor: Enhanced hydrogen production by ammonia decomposition

Two kinds of Co-Mo bimetallic catalysts (i.e., CoMo-I/γ-Al₂O₃ and CoMo-II/γ-Al₂O₃) prepared by using different active phase precursors as well as Co and Mo monometallic catalysts were used to catalyze ammonia decomposition. The Co-Mo bimetallic catalysts show higher activity than the Co and Mo monometallic catalysts, indicating the synergistic effect between Co and Mo. More interestingly, the CoMo-I/γ-Al₂O₃ catalyst using monocomponent metal amine metallate (i.e., Co(en)₃MoO₄) as the active phase precursor exhibits higher activity and stability than the CoMo-II/γ-Al₂O₃ using bicomponent Co(NO₃)₂ and (NH₄)₆Mo₇O₂₄ as the active phase precursor, which could be linked to the higher content of active species Co₃Mo₃N for the CoMo-I/γ-Al₂O₃ catalyst.     

Efficient overall water splitting over a Mo(IV)-doped Co3O4/NC electrocatalyst

To meet the demand of producing hydrogen at low cost, a molybdenum (Mo)-doped cobalt oxide (Co₃O₄) supported on nitrogen (N)-doped carbon (x%Mo–Co₃O₄/NC, where x% represents Mo/Co molar ratio) is developed as an efficient bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This defect engineering strategy is realized by a facile urea oxidation method in nitrogen atmosphere. Through X-ray diffraction (XRD) refinement and other detailed characterizations, molybdenum ion (Mo⁴⁺) is found to be doped into Co₃O₄ by substituting cobalt ion (Co²⁺) at tetrahedron site, while N is doped into carbon matrix simultaneously. 4%Mo–Co₃O₄/NC is the optimized sample to show the lowest overpotentials of 91 and 276 mV to deliver 10 mA cm^?2 for HER and OER in 1 M potassium hydroxide solution (KOH), respectively. The overall water splitting cell 4%Mo–Co₃O₄/NC||4%Mo–Co₃O₄/NC displays a voltage of 1.62 V to deliver 10 mA cm^?2 in 1 M KOH. The Mo⁴⁺ dopant modulates the electronic structure of active cobalt ion (Co³⁺) and boosts the water dissociation process during HER, while the increased amount of lattice oxygen and formation of pyridinic nitrogen due to Mo doping benefits the OER activity. Besides, the smaller grain size owing to Mo doping leads to higher electrochemically active surface area (ECSA) on 4%Mo–Co₃O₄/NC, resulting in its superior bifunctional catalytic activity.     

Biocrude production by catalytic hydrothermal liquefaction of wood chips using NiMo series catalysts

In this work, hydrothermal liquefaction of wood chips was studied for biocrude production using a mix of Ni–Mo nitrides and carbides. The catalytic materials were synthesized by a temperature-programmed reaction method at 800 °C under a hydrogen atmosphere with nickel loads from 0 to 20 wt%. Lignin contained in the lignocellulosic biomass was successfully release via Kraft process. Hydrothermal liquefaction was carried out in a batch reactor at 320 °C with an initial pressure of 1000 psi of H₂. According to characterization results, nanostructured catalysts with a mix of Ni₂Mo₃N/Mo₂C compo4unds were obtained. NiMo series catalysts composition varies with nickel loads. The catalytic activity shows a reduction in the amount of solid products and an increase in the production of gaseous products as a function of the increase Ni loadings on the catalyst. The most optimal production of biocrude was obtained with the NiMo-10 catalyst, since 81.43% of the total product corresponded to water soluble products (WPS) fraction and the oil fraction, while the solids fraction represented the 6.43% of the total product. Hydrothermal liquefaction catalytic processes were selective towards WSP fraction, improving biocrude quality and favoring biocrude conversion into advanced biofuels.     

Mo remarkably enhances catalytic activity of Cu@MoCo core-shell nanoparticles for hydrolytic dehydrogenation of ammonia borane

Ammonia borane (AB) has been identified as one of the most promising candidates for chemical hydrogen storage. However, the practical application of AB for hydrogen production is hindered by the need of efficient and inexpensive catalysts. For the first time, we report that the incorporation of Mo into Cu@Co core-shell structure can significantly improve the catalytic efficiency of hydrogen generation from the hydrolysis of AB. The Cu_0.81@Mo_0.09Co_0.10 core-shell catalyst displays high catalytic activity towards the hydrolysis dehydrogenation of AB with a turnover frequency (TOF) value of 49.6 molH₂ mol_cat^?1 min^?1, which is higher than most of Cu-based catalysts ever reported, and even comparable to those of noble-metal based catalysts. The excellent catalytic performance is attributed to the multi-elements co-deposition effect and electrons transfer effect of Cu, Mo and Co in the tri-metallic core-shell NPs.     

Hierarchical molybdenum carbide/N-doped carbon as efficient electrocatalyst for hydrogen evolution reaction in alkaline solution

Development of highly-active and noble-metal-free electrocatalysts for hydrogen evolution reaction (HER) is of critical challenge for water splitting, and optimizing the structure and the composition of the relative materials is very necessary to obtain the high-quality catalysts. Herein, a novel molybdenum carbide/N-doped carbon (Mo₂C/NC) hybrid is fabricated by using the hierarchical polyaniline tube network as a carbon source and a reactive template, and the as-fabricated Mo₂C/NC hybrid possesses a uniform hierarchical tube structure. The coupling of the ultrafine Mo₂C nanoparticles and the N-doped carbon substrate provides the abundant active sites and accelerates the charge transfer process. The final Mo₂C/NC catalyst gives the excellent catalytic activity for HER in alkaline condition, which shows a lower overpotential of 142 mV at 10 mA cm^?2 and a small Tafel slope of 61 mV decade^?1 in 1 M KOH.     

Various nickel doping in commercial Ni–Mo/Al2O3 as catalysts for natural gas decomposition to COx-free hydrogen production

Non-oxidative decomposition of natural gas to CO_x-free hydrogen production over commercial nickel-molybdate hydrotreating catalysts with different Ni loading from 5 to 40wt% were studied at 700 °C. The catalysts were characterized by XRD, BET, TEM, Raman spectroscopy and TG-DTA analysis. The catalytic decomposition activities showed that a tremendous hydrogen production (∼90%) was obtained over 20–40wt%Ni/Mo–Al₂O₃ catalysts. Moreover, all catalysts exhibited excellent durability up to 9 h with stable catalytic activity toward H₂ production. Although the increase of Ni content reduces the catalyst surface area, the H₂ productivity and longevity increases with increased Ni content, i.e., the catalytic decomposition activity primarily depends on the active Ni sites which overcompensates the surface deficiencies. TEM, TGA and XRD data of used catalysts indicated that a higher thermal stability and graphitization degree of multi-walled carbon nanotubes were obtained on all Ni containing catalysts. Higher metal loading produced carbon nanofibers beside CNTs due to increment of particle size and long reaction time.     

Ni nanoparticles supported on mica for efficient decomposition of ammonia to COx-free hydrogen

A wet impregnation method is used to synthesize Ni nanocatalysts supported on naturally abundant mica nanosheets for decomposition of ammonia to CO_x-free hydrogen. The prepared catalysts are characterized by XRD, SEM, TEM, N₂ sorption, TG, XPS, H₂-TPR and NH₃/H₂-TPD techniques. The catalytic tests exhibit that the Ni/mica catalysts are highly active for ammonia decomposition. The two-dimensional structure of mica favors mass transportation, which can remarkably promote the catalytic process. The NH₃/H₂-TPD curves of Ni/mica show no desorption signals of NH₃ and H₂, indicating the presence of weak desorption energy barrier. The content of Ni in the catalysts is related to the crystallite size of Ni species, affecting their catalytic properties. As demonstrated in this study, the Ni/mica catalyst with 15% Ni loading amount exhibits the highest catalytic activity and long-term stability. At a high space velocity of 30000 cm³ g_cat^?1 h^?1, 97.2% ammonia conversion is achieved over the 15%Ni/mica catalyst at 650 °C, indicating the Ni/mica is a promising catalyst for ammonia decomposition.     

Vapor-assisted engineering heterostructure of 1D Mo3N2 nanorod decorated with nitrogen-doped carbon for rapid pH-Universal hydrogen evolution reaction

Reasonable construction of heterostructure is of significance yet a great challenge towards efficient pH-universal catalysts for hydrogen evolution reaction (HER). Herein, a facial strategy coupling gas-phase nitridation with simultaneous heterogenization has been developed to synthesize heterostructure of one-dimensional (1D) Mo₃N₂ nanorod decorated with ultrathin nitrogen-doped carbon layer (Mo₃N₂@NC NR). Thereinto, the collaborative interface of Mo₃N₂ and NC is conducive to accomplish rapid electron transfer for reaction kinetics and weaken the Mo–H_ads bond for boosting the intrinsic activity of catalysts. As expected, Mo₃N₂@NC NR delivers an excellent catalytic activity for HER with low overpotentials of 85, 129, and 162 mV to achieve a current density of 10 mA cm^?2 in alkaline, acidic, and neutral electrolytes, respectively, and favorable long-term stability over a broad pH range. As for practical application in electrocatalytic water splitting (EWS) under alkaline, Mo₃N₂@NC NR || NiFe-LDH-based EWS also exhibits a low cell voltage of 1.55 V and favorable durability at a current density of 10 mA cm^?2, even surpassing the Pt/C || RuO₂-based EWS (1.60 V). Consequently, the proposed suitable methodology here may accelerate the development of Mo-based electrocatalysts in pH-universal non-noble metal materials for energy conversion.     

Hydrangea like composite catalysts of ultrathin Mo2S3 nanosheets assembled on N,S-dual-doped graphitic biocarbon spheres with highly electrocatalytic activity for HER

Water electrolysis is the most clean and high-efficiency technology for production of hydrogen, an ultimate clean energy in future. Highly efficient non-noble electrocatalysts for hydrogen evolution reaction (HER) are desirable for large scale production of hydrogen by water electrolysis. Especially, exposing as many active sites as possible is a vital way to improve activities of the catalysts. Herein, a series of new hydrangea like composite catalysts of ultrathin Mo₂S₃ nanosheets assembled uprightly and interlacedly on N, S-dual-doped graphitic biocarbon spheres were facilely prepared. The unique structure endowed the catalysts highly exposed edge active sites and prominently high activities for HER. Especially, the optimized catalyst Mo₂S₃/NSCS-50 exhibited as low as 106 mV of overpotential at 10 mA/cm² (denoted as ?₁₀). The catalyst also showed low Tafel slope of 53 mV/dec, low electron transfer resistance of 34 Ω and high stability evidenced by the result that the current density only attenuated 11.7% after 10 h i-t test. The catalyst has shown broad prospect for commercial application in water electrolysis.     

The Hydroloysis of ammonia borane by using Amberlyst-15 supported catalysts for hydrogen generation

Resin catalysts have the advantage of having various properties and long lifetime due to their ability to be regenerated easily, which makes them attractive supports. In this paper, a comparative study was conducted to optimize the dehydrogenation reaction condition using two different types of support materials: alumina (Al₂O₃), and Amberlyst-15 and to improve the catalytic activity as well as preparing an efficient and low-cost system for practical application, ruthenium metal catalyst was incorporated on Amberlyst-15 resin (a sulfonic acid type based upon a styrene-divinylbenzene copolymer) to release H₂ via hydrolytic dehydrogenation of ammonia borane. Using ruthenium (Ru) catalysts based on Amberlyst-15 support material and comparing the results with Al₂O₃ as the common supporting material is considered to be studied for the first time. The effect of temperature (20–50 °C), the initial ammonia borane concentration (0.05–0.5 %wt), and catalyst amount (0.2–0.5 g) on the produced H₂ yield was also investigated. Ru@Amberlyst-15 nanoparticle was discovered to be an effective catalyst for hydrogen evolution via the hydrolysis of ammonia borane with a turnover frequency value (TOF) of 343.3 min^?1, while Ru@Al₂O₃ yielded a TOF of 87.5 min^?1 at the room temperature. Therefore, it can be concluded that the Amberlyst-15 supporting effect on ruthenium metal leads an increase in the hydrogen production rate.     

Enhanced catalytic activity of NiM (M = Cr,Mo, W) nanoparticles for hydrogen evolution from ammonia borane and hydrazine borane

In this work, a series of Ni_1-xM_x (M = Cr, Mo, W) nanoparticles (NPs) have been successfully synthesized via a simple surfactant-aided co-reduction method and employed as highly efficient and cost effective catalysts for hydrogen generation from aqueous solution of ammonia borane (NH₃BH₃, AB) at room temperature. It is found that the as-synthesized NiM NPs (M = Cr, Mo, W) exhibit much higher catalytic performance for the hydrolysis of AB as compared to that of pure Ni NPs. In addition, among all the Ni_1-xM_x (M = Cr, Mo, W) NPs, the Ni_0.9Cr_0.1, Ni_0.9Mo_0.1, and Ni_0.8W_0.2 NPs show the highest catalytic activities with the turnover frequency (TOF) values of 10.7, 27.3 and 25.0 mol H₂ (mol metal min)^?1, respectively. Remarkably, these optimized NiM catalysts can also perform efficiently in the hydrolysis of hydrazine borane (N₂H₄BH₃, HB). The present low-cost and high-performance of the NiM catalysts system may encourage the practical application of AB and HB as the promising chemical hydrogen storage materials.     

Hydrogen production by catalytic decomposition of methane over Fe based bi-metallic catalysts supported on CeO2–ZrO2

Methane decomposition to produce hydrogen was studied over iron based bimetallic catalysts supported on cerium-zirconium oxide in a continuous flow fixed bed reactor at 700 °C. 15 wt% Fe/CeZrO₂ was prepared by wetness impregnation and the promoted Fe catalysts (15 Fe-5 Co/CeZrO₂ and 15 Fe-5 Mo/CeZrO₂) were prepared by co-impregnation technique. Mo promoted Fe catalyst exhibited the maximum surface area of 24.08 m²/g. X-ray diffraction studies revealed that Fe₂O₃, Co₃O₄ and MoO₃ were the phases present in freshly calcined catalysts, while the reduced catalysts consisted of phases including elemental Fe, Mo and Fe–Co alloys. Both X-ray diffraction and temperature programmed reduction studies confirmed the complete reduction of metal oxide species under H₂ at 700 °C. The catalytic activity of Fe/CeZrO₂ was enhanced upon addition of Co and Mo as promoters. The initial hydrogen yield on 15 Fe-5 Mo/CeZrO₂ was ~90% and it decreased with increase in time on stream (TOS), and finally stabilized around ~50% after 125 min of TOS. The Co promoted catalyst exhibited similar activity while the initial hydrogen yield on 15 Fe/CeZrO₂ was ~83% and dropped to ~33% after 125 min of TOS. Graphitic carbon, Fe₃C and Mo₂C phases were observed in the XRD patterns of spent catalysts along with elemental Fe and Fe–Co alloy. It was evident from temperature programmed oxidation results that coke formation which deactivates the catalyst was dominant in 15 Fe/CeZrO₂ when compared to the promoted (Co and Mo) Fe catalysts where carbon nanostructures were dominant. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the formation of carbon nanostructures on the surface of spent catalysts. The Fe based catalysts supported both tip and base-growth mechanisms for the growth of carbon nanostructures.     

Synergistic effects of Mo2C/CeO2 nanoparticles anchored on nitrogen-doped carbon as an efficiently electrocatalyst for hydrogen evolution reaction

As a catalyst, Mo₂C has excellent hydrogen evolution reaction (HER) performance due to its platinum-like structure. However, insufficient exposure of active sites and excessive Mo–H binding energy of single Mo₂C catalyst limits the improvement of HER performance. In this work, a nitrogen-doped porous carbon anchored Mo₂C and CeO₂ nanoparticles (Mo₂C/CeO₂/NC) for HER was manufactured by utilizing electronic fuel injection (EFI) technology. At the current density of 10 mA cm⁻², it revealed a lower overpotential of 220 mV and a smaller Tafel slope value of 123 mV dec⁻¹, and after 20 h of continuous tests and 2000 CV cycles, and exhibited excellent electrochemical stability. Owing to the synergetic effects between Mo₂C, CeO₂ and nitrogen-doped porous carbon, the intrinsic catalytic activity of the catalyst was greatly improved, and the electron/proton transport was accelerated, therefore the Mo₂C/CeO₂/NC catalyst exhibited excellent HER catalytic performance and superior durability. And this work was expected to promote the development of nonmetal-doped carbon-supported nanoparticle-based catalysts in the field of electrochemistry.     

Effect of preparation methods on the catalyst performance of Co/MgLa mixed oxide catalyst for COx-free hydrogen production by ammonia decomposition

This work deals with the effect of catalyst preparation method of the mixed Co, Mg and La oxide catalysts on their structure and catalytic properties for ammonia decomposition. Two methods are used for catalysts preparations impregnation and co-precipitation (in air and in pure O₂ atmosphere), The Mg/La = 2 molar ratio and 5 wt% of cobalt content was maintained same in all catalysts. The catalyst performance was evaluated in the temperature range 300–550 °C at atmospheric pressure. The prepared catalysts were characterized by BET, XRD, TPR, XPS, CO₂-TPD and SEM techniques. No pronounced differences were observed in BET among the catalysts. It was found that the 5CML-OXY (5 wt%Co over MgLa catalyst prepared by co-precipitation method in oxygen atmosphere) has superior activity among the other catalysts. This could be attributed to availability of easily reducible cobalt species determined by TPR studies and enhanced interaction between Mg and La determined by SEM and XPS. The moderate basic site density determined by CO₂-TPD results was also increased in 5CML–OXY catalysts compared with other catalysts. These consequences are might be one of the reasons for enhanced activity of 5CML–OXY catalyst compared to other catalysts. Hence catalyst preparation by co-precipitation in oxygen atmosphere is the best method which might be one of the parameters that influenced on catalytic properties of the cobalt on MgOLa₂O₃ system, for ammonia decomposition.     

Effect of ceria addition on NiRu/CeO2Al2O3 catalysts in steam reforming of acetic acid

NiRu bimetallic catalysts with different amount of CeO₂ loaded on the γ-Al₂O₃ support were prepared. The properties of catalysts were characterized by means of N₂ adsorption-desorption, XRD, H₂-TPR and XPS techniques. Catalytic activities for the steam reforming of acetic acid over these catalysts were investigated at the temperature range from 650 °C to 750 °C. The addition of CeO₂ dramatically improved the activity and stability of the catalyst. Among these catalysts, the NiRu/10CeAl catalyst showed the highest catalytic activity as well as a good stability owing to the abundant Ce³⁺ on the surface of catalyst. The existence of Ce³⁺ promoted the formation of CO₂ from CO because of the mobilizable oxygen, which was favorable for the formation of hydrogen. The coke amount and species deposited on the catalysts after the activity tests were analyzed by DTG. As expected, the NiRu/10CeAl catalyst showed the best resistance to carbon formation. The temperature stepwise steam decoking experiment of the spent catalysts was conducted to elucidate the relationship between the existence of Ce³⁺ and the decoking abilities of various catalysts. It was verified that the existence of Ce³⁺ significantly promoted the decoking abilities of the catalysts.