Hydrogen Formation Rate Research Articles

A comparative study of different modification methods on zero-valent iron performance toward nitrate selective reduction to nitrogen

Although nanoscale zero-valent iron (nZVI) has been widely used for nitrate reduction, its application is always limited by the undesired generation of toxic ammonium. In this study, by selecting four commonly used nZVI modification methods (i.e., introducing Fe(II), activated carbon, Cu, and Pd), the roles of direct electron transfer and atomic hydrogen (H*) mediated reaction on nitrate selective reduction were examined. Results revealed that all the modification methods could enhance the reduction rates of nitrate with a promotion factor of 0.94–8.62, while the N2-selectivity could only be increased from ∼4.5 % to less than 25.7 % (in carbon amended system). The enhancing effect of these additives is determined to be highly associated with their ability to promote the direct electron transfer from Fe0 core to nitrate by forming galvanic couples or conductive magnetite layer. Unexpectedly, multiple lines of evidence suggested that H* was not the dominant reducing species responsible for nitrate reduction in Pd-modified nZVI system (and also the other tested systems), despite the presence of Pd could significantly accelerate H* generation. Correlation analysis further showed that there was no reasonable relationship between N2-selectivity and Fe0 corrosion tendency and hydrogen formation rates of different modified nZVI systems. All these finding could improve our understanding of nitrate selective reduction by Fe0.

Hydrogen Evolution Activity of Platinum Nanoparticles Decorated on Silver Nanowire Networks and Graphite Electrodes

The catalytic activity of graphite (C) and conductive silver nanowire (AgNW) networks coated on glass and graphite substrates with low platinum content towards hydrogen evolution reaction (HER) is reported. The results exhibit that the chronoamperometric electrodeposition of platinum on AgNW substrates results in the formation of spherically shaped nanoparticle agglomerates aligned on the nanowires. Also, platinum doped graphite electrodes with a rough surface showed an efficient distribution of platinum nanoparticles (PtNPs). Studies of the electrocatalytic HER activity as a function of platinum loading indicate that the optimum loading is in the range of 60 µg/cm2 and further loading results only in a minor reduction of the overpotential. At low Pt content, a synergistic effect of the AgNW network in terms of enhancement of the HER performance was observed. Tafel analysis showed that in the low overpotential region, the Volmer reaction was the rate determining step for the graphite based electrodes. The graphite substrate in conductive connection with the nanowires was shown to significantly boost the hydrogen formation rate.

Understanding the impact of support materials on CoFe2O4 catalyst performance for hydrogen fuel and nanocarbon production via methane decomposition

This study focuses on assessing the performance and durability of three distinct catalysts, namely CoFe2O4/MgO and CoFe2O4/TiO2 and CoFe2O4/Al2O3 in the methane decomposition process. These catalysts were synthesized using a co-precipitation impregnation route. Their catalytic activity of methane decomposition was examined in a fixed-bed reactor at a temperature of 800 °C under atmospheric pressure. Various appropriate analytical techniques were employed to explore the physicochemical characteristics of both the fresh and spent catalysts. The SEM images, XRD and H2-TPR results of fresh catalysts revealed strong dependence on the support type. The XPS results confirm the presence CoFe2O4 species on the surface of supports. The CoFe2O4/MgO catalyst has a higher inversion degree compared with other catalysts as confirmed from Raman results. The methane conversions at the end of the reaction time (300 min) were found to be 66 %, 34 % and 2.48 %, while the rates of hydrogen formation corresponding to these methane conversions are 134.73 × 10−5, 68.25 × 10−5 and 8.80 × 10−5 mol H2 g−1 min−1 for CoFe2O4/MgO and CoFe2O4/TiO2 and CoFe2O4/Al2O3 catalysts, respectively. SEM images verified the existence of filamentous carbon on the surface of the spent CoFe2O4/MgO catalyst, whereas the spent CoFe2O4/TiO2 catalyst showed a mix of carbon chunks and filaments and fluffy carbon over the CoFe2O4/Al2O3 catalyst. Ultimately, the quantity of deposited carbon was significantly associated with catalytic activity, as they were 56, 46 and 4 wt% for the spent CoFe2O4/MgO, CoFe2O4/TiO2 and CoFe2O4/Al2O3 catalysts, respectively.

Deciphering the influence of support in the performance of NiFe2O4 catalyst for the production of hydrogen fuel and nanocarbon by methane decomposition

Wet chemical synthesis route was used to synthesis nickel ferrite (NiFe2O4) nanoparticle. Later on the synthesized NiFe2O4 were supported on the surface of three traditional supports such as Al2O3, MgO and TiO2 to get NiFe2O4/Al2O3, NiFe2O4/TiO2 and NiFe2O4/MgO catalysts. The activity profile of each catalyst was evaluated in a fixed-bed reactor for direct methane decomposition at 800 °C. For both fresh and spent catalysts, many characterization techniques have been employed mainly XRD, FESEM, HRTEM, Raman spectroscopy, TGA, and nitrogen adsorption-desorption isotherm. X-ray powder diffraction studies revealed that all synthesized catalysts have a cubic spinel crystal structure. The XRD confirm the presence of NiFe2O4 particles in the component of fresh NiFe2O4/MgO, NiFe2O4/TiO2 and NiFe2O4/Al2O3 catalysts. Temperature Program Reduction (TPR) unveiled the presence of Ni oxides and Fe oxides by displaying reduction peaks in their respective temperature regions. The N2 adsorption-desorption isotherms of the fresh all catalysts reveal that these catalysts have a mesoporous structure. Activity data concluded NiFe2O4/MgO to be the most active catalysts among the tested catalysts methane conversion magnitude of 41.13 % and H2 formation rate of 84.40 × 10−5 mol H2 g−1 min−1. On the other hand, the H2 formation rate drastically declined and very poor activity of both NiFe2O4/TiO2 and NiFe2O4/Al2O3 catalysts was observed in the current work. XRD patterns, FESEM images and TGA analysis of spent NiFe2O4/MgO catalyst shown the filamentous carbon formation which secondarily confirm its higher activity, while its absence in catalysts of NiFe2O4/TiO2 and NiFe2O4/Al2O3. TGA analysis of the carbon deposited on the NiFe2O4/MgO catalyst showed that the amount of carbon was approximately 64 wt%. It was suggested that the formation of nickel-iron carbide revealed by XRD studies of spent catalysts may be the factor related to their poor activity while discussing the structure-activity relationship. Likewise, the higher degree of dispersion related to NiFe2O4/MgO as displayed by XRD, FESEM and TPR investigations, played a vital role in accelerating the rate of hydrogen formation.

Synergetic effects of Al addition on the performance of CoFe2O4 catalyst for hydrogen production and filamentous carbon formation from direct cracking of methane

Improving methane catalytic decomposition process was deemed an effective approach for hydrogen production. Here, a novel catalyst AlxCo1-xFe2O4 with a variable aluminum content was synthesized via a co-precipitation route for the direct cracking of methane. The catalytic activity of AlxCo1-xFe2O4 was performed in a fixed bed reactor at temperature of 800°C and 20 mL/min of fed gas. A sequence of characterizations, including SEM, BET, XRD, XPS, Raman and TGA for fresh and spent catalysts, was exploited to examine the influence of Alx content on the morphology, porosity, structure, chemical composition, and cation distribution of AlxCo1-xFe2O4. As the Alx content increased in AlxCo1-xFe2O4 their morphology became more fractal and decreased in particle size, lattice parameter, lattice size, while their pore surface increased. Further cation re-distributions from octahedral to tetrahedral sites as Fe3+ and Al3+ relocated in the Tetrahedral site and Oxygen lattice decreased as observed from Raman and XPS results. Catalytic activity studies showed that Alx content of 0.6 in AlxCo1-xFe2O4 lead maximum methane conversion up to ∼ 91.10 % and hydrogen formation rate of 1.780 ×10-3 mol H2 g-1 s-1. The catalytic activity behavior was explained in correlation with the characteristics of spent catalysts.

Natural radioactivity of the crust as an important factor of the chemical evolution of the early Earth

The long-lived (billions of years) 40K, 235U, 238U, and 232Th isotopes have a high energy capacity and represent a potent internal source of energy. Together with the external action of the Sun, the natural radioactivity was apparently an important component of evolution of the early Earth and development of Earth's life. The decay of isotopes initiated radiation chemical reactions involving water, which were accompanied by the formation of hydrogen and oxygen and the transformation of Earth's inorganic matter into organic compounds, including prebiotic molecules. Water radiolysis in the Earth's crust continuously produces H2, which is now considered as the main electron donor (food) for microorganisms several kilometers below the Earth's surface. Here we calculate the initial radioactivity of the early Earth's crust from the relative abundances of elements and dynamics of variation of the radioactivity and energy release upon the decay of particular radioactive isotopes. The energy released upon the decay of heavy 235U, 238U, and 232Th throughout the existence of the Earth (4.6 billion years) was 4.5 × 1030 J, while the energy released upon the decay of 40K was approximately 1.0 × 1030 J. The energy release per year during the first billion years decreased from 3.0 × 1021 J to 1.5 × 1021 J for heavy isotopes and from 0.70 × 1021 J to 0.45 × 1021 J for 40K. Over the last billion years, the energy decreased approximately threefold. Analysis of the data on the radiation chemical formation of hydrogen in the wet components of the Earth's crust (cements, zeolites, geopolymers, and other) and bottom sediments indicates that hydrogen is formed upon direct action of radiation on water in yields characteristic of pure water. According to calculations, over the past 4 billion years, approximately 1.7 × 1022 M of hydrogen was formed. Furthermore, ∼93 % of H2 was due to the decay of uranium and thorium, while the contribution of 40K did not exceed 7 %. The global rate of hydrogen formation in the Earth's crust is ∼ 1.5 × 1012 mol per year. A mechanism involving ionic and radical products of water radiolysis was proposed to describe the formation of prebiotic molecules (amino acids, sugars, etc.) from carbon-, nitrogen-, and sulfur-containing inorganic compounds.

Cleavage of the Disulfide Bonds via Hydrogenolysis for Recovering Iso‐octyl Thioglycolate from Distillation Residue in Iso‐octyl Thioglycolate Production

AbstractAbout 10–15 wt% of distillation residue, which is mainly composed of the oxidation products of iso‐octyl thioglycolate, harmful to the environment and difficult to dispose, is generated during refining through distillation. Herein we report an effective approach to recover iso‐octyl thioglycolate from the distillation residue by hydrogenolysis of the disulphide bonds. The effects of reaction temperature, reaction time, and feeding speed were examined. It is found that the rate of hydrogen formation is a key factor affecting the yield of iso‐octyl thioglycolate. The orthogonal test shows that the influence order is: reaction time > mass ratio of distillation residue/HCl > the molar ratio of HCl/Zn > reaction temperature. About 63.64 % iso‐octyl thioglycolate could be harvested after hydrogenolysis at 30 °C for 3.0 h. The mechanism study shows that iso‐octyl thioglycolate was regenerated by cleavage the disulfide bonds in iso‐octyl thioglycolate disulfides. Therefore, an alternative way for resource utilization of iso‐octyl thioglycolate distillation residue was developed.

Scalable Synthesis of Oxygen Vacancy-Rich Unsupported Iron Oxide for Efficient Thermocatalytic Conversion of Methane to Hydrogen and Carbon Nanomaterials.

Thermocatalytic methane decomposition (TCMD) involving metal oxides is a more environmentally friendly and cost-effective strategy for scalable hydrogen fuel production compared to traditional methane steam reforming (MSR), as it requires less energy and produces fewer CO/CO2 emissions. However, the unsupported metal oxide catalysts (such as α-Fe2O3) that would be suited for this purpose exhibit poor performance in TCMD. To overcome this issue, a novel strategy was developed as a part of this work, whereby oxygen vacancies (OVs) were introduced into unsupported α-Fe2O3 nanoparticles (NPs). Systematic characterization of the obtained materials through analytical techniques demonstrated that mesoporous nanostructured unsupported α-Fe2O3 with abundant oxygen vacancies (OV-rich α-Fe2O3 NPs) could be obtained by direct thermal decomposition of ferric nitrate at different calcination temperatures (500, 700, 900, and 1100 °C) under ambient conditions. The thermocatalytic activity of the resulting OV-rich α-Fe2O3 NPs was assessed by evaluating the methane conversion, hydrogen formation rate, and amount of carbon deposited. The TCMD results revealed that 900 °C was the most optimal calcination temperature, as it led to the highest methane conversion (22.5%) and hydrogen formation rate (47.0 × 10-5 mol H2 g-1 min-1) after 480 min. This outstanding thermocatalytic performance of OV-rich α-Fe2O3 NPs is attributed to the presence of abundant OVs on their surfaces, thus providing effective active sites for methane decomposition. Moreover, the proposed strategy can be cost-effectively scaled up for industrial applications, whereby unsupported metal oxide NPs can be employed for energy-efficient thermocatalytic CH4 decomposition into hydrogen fuel and carbon nanomaterials.

Three-Dimensional CFD Simulation of a Proton Exchange Membrane Electrolysis Cell

The energy shift towards carbon-free solutions is creating an ever-growing engineering interest in electrolytic cells, i.e., devices to produce hydrogen from water-splitting reactions. Among the available technologies, Proton Exchange Membrane (PEM) electrolysis is the most promising candidate for coping with the intermittency of renewable energy sources, thanks to the short transient period granted by the solid thin electrolyte. The well-known principle of PEM electrolysers is still unsupported by advanced engineering practices, such as the use of multidimensional simulations able to elucidate the interacting fluid dynamics, electrochemistry, and heat transport. A methodology for PEM electrolysis simulation is therefore needed. In this study, a model for the multidimensional simulation of PEM electrolysers is presented and validated against a recent literature case. The study analyses the impact of temperature and gas phase distribution on the cell performance, providing valuable insights into the understanding of the physical phenomena occurring inside the cell at the basis of the formation rate of hydrogen and oxygen. The simulations regard two temperature levels (333 K and 353 K) and the complete polarization curve is numerically predicted, allowing the analysis of the overpotentials break-up and the multi-phase flow in the PEM cell. An in-house developed model for macro-homogeneous catalyst layers is applied to PEM electrolysis, allowing independent analysis of overpotentials, investigation into their dependency on temperature and analysis of the cathodic gas–liquid stratification. The study validates a comprehensive multi-dimensional model for PEM electrolysis, relevantly proposing a methodology for the ever-growing urgency for engineering optimization of such devices.

Cobalt ferrite for direct cracking of methane to produce hydrogen and carbon nanostructure: Effect of temperature and methane flow rate

Cobalt ferrite (CoFe2O4) was used as a catalyst for direct methane cracking. The reaction was accomplished in a fixed bed reactor at normal atmospheric pressure, while gas flow rate (20–50 mL/min) and reaction temperature (800–900 °C) were varied. The fresh CoFe2O4 morphology is sponge-like particle with inverse spinel structure as revealed from SEM and XRD results. The methane conversions and hydrogen formation rate were increased with reaction temperature, while catalyst stability and induction period decreased. Increases of gas flow rate > 20 mL/min led to a decrease the overall catalytic activity of CoFe2O4 for methane cracking. The XRD results of spent catalysts revealed that CoFe alloy was the active phase of methane cracking. TGA analysis showed that the largest amount of deposited carbon was 70.46 % at (20 mL/min, 900 °C), where it was 34.40 % at (50 mL/min, 800 °C). The deposited carbon has the shape of spherical carbon nanostructures and/or nano sprouts as observed with SEM. Raman data confirmed the graphitization type of the deposited carbon.

Dark fermentative hydrogen gas production from waste peach pulp by intermittent feeding: Effects of hydraulic residence time and substrate loading rate

Peach has a big share of the world fruit market, with significant annual waste production. This study reports dark fermentative hydrogen gas production from waste peach pulp using intermittent feeding. In this context, the effects of hydraulic residence time (HRT) and substrate loading rate (SLR) on hydrogen production were determined in two sets of experiments. All experiments were performed in 310 mL serum bottles. During the first set of experiments, HRT was varied between 1 and 6 days and hydrogen production was more favorable at short HRTs. In the second set of experiments, SLR was varied between 9 and 90 gTOC/L.d, and more efficient hydrogen formation was observed by increasing the SLR. The most convenient HRT and SLR resulting in maximum hydrogen formation rate (931.8 mLH2/L.d) was obtained at 1 day and 90 gTOC/L.d, respectively.

Hydrogen generation ability of B-site substituted two-dimensional Can-1Tin-3Nb3O3n+1− perovskite nanosheets in photoelectrochemical cell

Many semiconductor materials have been researched for hydrogen evolution application, in which 2D nanosheet materials are given a bunch of investigation due to their suitable energy band edges and proper band gap. The studying of a novel B-site substituted 2D perovskite nanosheets, Can-1Tin-3Nb3O3n+1− (CTNO−), with a layer number n = 4, 5, and 6 shows that these n-type semiconductors have unique properties with large band gaps (3.71 – 3.78 eV). These Dion-Jacobson family members, titaniobate nanosheets, are fabricated by substituting partially transition metal Ti elements into the Nb element positions (B sites) of the niobate (NbO6) perovskite structure. A well crystalline structure and the ability in hydrogen generation are exhibited. The energy band diagrams of CTNO− (n = 4, 5, and 6) nanosheets are determined and established. The photoelectrochemical devices made of B-site substituted CTNO−nanosheets are carried out for investigating of the ability in hydrogen generation reaction. The CTNO− (n = 5) nanosheets performs the water splitting capability with the highest hydrogen generation efficiency. The hydrogen generation efficiency is improved by a p-n composite combining CTNO− (n = 4, 5, and 6) nanosheets with a conductive polymer of PEDOT:PSS. The highest efficiency of hydrogen generation is belonging to CTNO− (n = 4)/PEDOT:PSS with a hydrogen formation rate of 5.576 × 102 µmol h−1 g−1. Concerning all these performances, these Dion Jacobson phase CTNO− (n = 4, 5, and 6) nanosheets are considered for ultrathin scale photoelectrochemical cell or phototransistor applications.

Obtaining molecular hydrogen from water radiolysis in the nano-SiO 2 (d = 20 nm)/H 2 O system under the influence of γ-quanta

Abstract Under the influence of γ-quanta (60Co, P = 9.276 rad/s, T = 300 K), the amount, formation rate, and radiation-chemical yield of molecular hydrogen obtained from the radiolysis process that changes the mass of water (m = 0.0001 ÷ 0.8 g) have been defined in the created nano-SiO2/H2O system with m = 0.2 g mass and d = 20 nm particle size. It was determined that the radiation-chemical yield of molecular hydrogen obtained from the water radiolysis process in the nano-SiO2/H2O system created by the adsorption of water on the nanoparticle surface had a low value. In systems created with the addition of water, the radiation-chemical yield of molecular hydrogen obtained from its radiolysis increased in direct proportion to the water mass. This proves that due to ionizing rays, the yield of electrons emitted from the nanoparticle surface into the water and solvated there increases. Therefore, the radiation-chemical yield of molecular hydrogen is higher than that of the adsorbed system.

Nickel-iron catalyst for decomposition of methane to hydrogen and filamentous carbon: Effect of calcination and reaction temperatures

Nickel-ferrite Ni-Fe (molar ratio 1:2) were synthesised and calcined at different temperatures. The catalytic performances of Ni-Fe for methane decomposition and production of hydrogen and carbon nanostructures were evaluated at various calcination (350–800 °C) and reaction temperatures (700–800 °C). Fresh and spent catalysts were characterized using scanning electron microscopy (SEM), BET surface area, X-ray diffraction (XRD), TGA and Raman spectroscopy. XRD results revealed the formation of highly crystalline NiFe2O4 in calcined samples, while Ni-Fe alloys were observed in the spent catalysts. The NiFe2O4 catalyst has a mesoporous structure with monomodal pore distribution. The surface area decreased from 107.0 to 3.8 m2/g with increasing calcination temperature from 350 to 800 °C. Methane conversion, 48.50%, and hydrogen formation rate, 97.70 × 10-5 mol H2 g−1 min−1 was obtained at reaction temperature of 800 °C. The catalyst activity slightly improved by increasing calcination temperature. The SEM images of spent catalysts revealed the formation of some filamentous carbon over all spent catalysts except for that operated at reaction temperature of 700 °C. TGA studies revealed that the deposited carbon increased with increase in reaction and calcination temperatures and achieved 42.50 and 59.32 wt%, respectively. The graphitization and crystalline of the deposited carbon slightly decreases as calcination temperature increased.

Influence of Zn and Ni dopants on the physicochemical and activity patterns of CoFe2O4 derived catalysts for hydrogen production by catalytic cracking of methane

Zinc and nickel incorporated CoFe2O4 materials have been synthesized via a wet chemical method. Characterization of these cobalt ferrite based catalysts was undertaken using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and thermal gravimetric analysis (TGA). The catalytic activity of these materials was evaluated by monitoring the direct cracking of methane for the production of hydrogen and carbon. The XRD and SEM results indicated that Ni incorporation preserves the inverse spinel structure of CoFe2O4, whilst Zn incorporation changes its microstructure. The Co 2p, Fe 2p and O 1 s XP spectra confirm the expected oxidation states of the elements in the near surface region of the catalysts. Raman spectra indicate cation redistribution between tetrahedral and octahedral sites upon Ni and Zn incorporation into CoFe2O4. BET surface area analysis revealed Ni incorporation is more effective in increasing the surface area of CoFe2O4 compared to Zn incorporation. Indeed, catalytic activity evaluation showed that Ni incorporation into CoFe2O4 improved methane conversion and correspondingly the hydrogen formation rate. In contrast, Zn incorporation led to very low catalytic activity. The spent catalysts were further characterized and the results are strongly correlated with catalytic activity.

Bimetallic NixCo10-x/CeO2 as highly active catalysts to enhance mid-temperature ammonia decomposition: Kinetics and synergies

Catalytic ammonia decomposition is an attractive method to generate hydrogen at mid-temperatures (<700 °C) but must incorporate precious metals (Pd, Ru, etc.) to ensure high reactivity. Developing Ni-based catalysts to decompose ammonia can enhance its prospect for hydrogen generation. However, the catalytic activity of Ni is hardly satisfactory at mid-temperatures. In this work, we show the bimetallic NixCo10-x/CeO2 towards mid-temperature NH3 decomposition, with the metal loading of Ni and Co tuned. Kinetics study demonstrates that the NH3 decomposition reaction follows the Temkin Pyzhev mechanism and the synergy between Ni and Co can decrease the reaction orders regarding NH3 and increase the reaction orders regarding H2. Mechanistic results indicate that the recombinative N desorption limits the reaction rate. The synergy between Ni and Co can simultaneously decrease the energy barriers of the recombinative N desorption and mitigate the H2 poisoning effect. Therefore, Ni7.5Co2.5/CeO2 displays both high ammonia conversion (96.96%) and hydrogen formation rate (1947.9 mmol/(gcat.h)) at 650 °C. We hope the mechanism in this work can be used to guide the design of inexpensive catalysts to decompose ammonia at mid-temperatures.

A highly active and cost-effective tungsten modified Ni-based catalyst for the production of hydrogen via methane dry reforming

Catalyst community requires a low-cost, high-performance catalyst immediately for cost-effective H2 production through dry reforming of methane. Herein, cost-effective 1–9 wt% tungsten oxide-alumina supported Ni catalysts were prepared, examined and characterized by x-ray diffraction, 27Al solid-state nuclear magnetic resonance, X-ray photoelectron spectroscopy, high resolution-transmission electron microscopy and temperature programmed experiments. On 5.0 wt% W incorporation; minimum crystallinity, additional CO2-surface interacting species, maximum oxygen replenishment capacity by CO2, thermally retainable coordinated Al sites and minimum % weight loss pivot optimum hydrogen production 77% H2 yield, minimum deactivation factor −0.9, and maximum rate of hydrogen formation of 1.1301 molH2gcat−1h−1 at 440-min time-on-stream.

Continuous synthesis of atomically dispersed Rh supported on MgAl2O4 using two‐stage microreactor

AbstractSingle‐atom catalysts with optimal atom utilization and outstanding activity have penetrated the frontier of heterogeneous catalysis. However, the large‐scale synthesis of this class of catalysts is still a bottleneck for their industrialization. Herein, we suggest a two‐stage micro‐dispersion approach to synthesize mesoporous MgAl2O4‐supported atomically dispersed Rh, which is more competitive than the batch method for boosting the uniform dispersion of Rh. By increasing the Rh loading, single‐atom catalysts (SACs, &lt;0.05 wt%), single‐atom catalysts + nanoparticle catalysts (0.05–0.17 wt%), and nanoparticle catalyst (NPCs, 0.17–1.10 wt%) were obtained. For n‐octane steam reforming, the turnover frequency of the 0.01‐Rh‐MgAl2O4 was approximately 30 times that of the 1.10‐Rh‐MgAl2O4, while the Rh amount of the 0.01‐Rh‐MgAl2O4 was only 3% that of the 1.10‐Rh‐MgAl2O4 for the same fuel conversion. Under a high‐temperature (750°C) steam atmosphere for 15 h, the hydrogen formation rate only declined from 25.1 to 23.8 mol/mol‐C8H18.

Electronic metal-support interaction enhanced ammonia decomposition efficiency of perovskite oxide supported ruthenium

The performance of Ru/La 1-x Sr x AlO 3 catalyst in ammonia decomposition was enhanced by modulating its electronic properties via the strategy of cation substitution. • We present an effective strategy of cation substitution to modulate electronic properties of Ru/La 1-x Sr x AlO 3 catalysts. • Electron-rich Ru facilitates associative desorption of N atoms and accelerates the ammonia decomposition reaction. • Ru/La 0.8 Sr 0.2 AlO 3 catalyst shows high catalytic efficiency and excellent stability during a test perid of 70 h. Ammonia has been considered as a promising hydrogen carrier with high energy storage density and easy transport. Here, we report the ruthenium (Ru) nanoparticles supported on LaAlO 3 , a typical ABO 3 perovskite oxide, as an efficient catalyst for ammonia decomposition. By tailoring the cation substitution of La 3+ by Sr 2+ , the electronic properties of support materials were modulated, which exerts an impact on the electronic state of Ru active sites. It is found that the Ru/La 0.8 Sr 0.2 AlO 3 catalyst has a high hydrogen formation rate and low activation energy. In situ spectroscopic investigation and NH 3 temperature programmed desorption (NH 3 -TPD) analyses indicate the electron-rich state of metallic Ru on the La 0.8 Sr 0.2 AlO 3 support, which promotes associative desorption of N atoms and accelerates NH 3 decomposition reactions. This study provides a universal strategy of aliovalent cation substitution to engineer the electronic properties of metal/oxide catalysts as well as their catalytic activities.

Facile modification of cobalt ferrite by SiO 2 and H‐ZSM‐5 support for hydrogen and filamentous carbon production from methane decomposition

In this work, new catalyst composed of cobalt ferrite CoFe2O4 supported on amorphous silica (SiO2) and zeolite (H-ZSM-5) were prepared using impregnation method with loading ratio 1:1. The catalytic activity of the new 50 wt% CoFe2O4/SiO2 and 50 wt% CoFe2O4/H-ZSM-5 catalysts were evaluated for direct methane decomposition to hydrogen production at fixed operating temperature of 800°C. The physiochemical properties of the fresh and spent catalysts were characterized by several techniques such as scanning electron microscope (SEM), X-ray diffractometer (XRD), Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy (XPS), thermogravimetric (TGA), and Raman spectroscopy. The CoFe2O4/H-ZSM-5 catalyst exhibited higher activity and stability than CoFe2O4/SiO2 catalyst. Maximum methane conversion reached 37.35% and hydrogen formation rate of 76.48 × 10−5 mol H2 g−1 min−1 at time on stream (TOS) of 300 min for CoFe2O4/H-ZSM-5, while its 5.80% with 15.82 × 10−5 mol H2 g−1 min−1 at TOS of 30 min. The XRD, Raman, and XPS results confirm the presence of CoFe2O4 particles on the CoFe2O4/H-ZSM-5 catalyst surface, while the CoFe2O4 particles partially shield with SiO2 in CoFe2O4/SiO2 catalyst. SEM images of spent catalysts elucidated the formation of filamentous carbon which indirectly confirm the higher distribution of CoFe2O4 in CoFe2O4/H-ZSM-5 than that of CoFe2O4/SiO2. The deposited carbon on spent CoFe2O4/H-ZSM-5 catalyst was evaluated using TGA, which was found to be ca. 50 wt%. Highlights CoFe2O4/SiO2 and CoFe2O4/H-ZSM-5 catalysts synthesized and characterized by various techniques. H-ZSM-5 and SiO2 support material were found strongly affects the physiochemical properties and the methane decomposition activity of CoFe2O4 catalyst. CoFe2O4/H-ZSM-5 catalyst performance reached 37.4% and the hydrogen formation rate was 76.5 × 10−5 mol H2 g−1 min−1. CoFe2O4/SiO2 catalyst demonstrated a negligible activity toward methane cracking and producing hydrogen. The estimated deposited carbon on the spent catalysts were 1 wt% and 50 wt% for CoFe2O4/SiO2 and CoFe2O4/H-ZSM-5, respectively.