The optimization of Ni–Al2O3 catalyst with the addition of La2O3 for CO2–CH4 reforming to produce syngas

A series of La₂O₃–NiO–Al₂O₃ catalysts promoted by different loading of lanthanum were prepared via the hydrolysis-deposition method to improve the catalytic performance of nickel-based catalyst for CO₂–CH₄ reforming. The catalysts were characterized by N₂ adsorption - desorption, XRD, H₂-TPR, TG-DTG, TEM, Raman and TPH techniques. Results showed that the precursor of active component was mainly in the form of NiAl₂O₄ spinel, which almost disappeared after reduction process from XRD characterization, suggesting well reduction performance. The catalyst with La loading of 0.95 wt% (La–Ni-1) presented a small average Ni grain size of 7.71 nm and exhibited well catalytic performance at 800 °C, with CH₄ conversion of 94.37%, CO₂ conversion of 97.15%, H₂ selectivity of 75.01% and H₂/CO ratio of 0.92. The Ni grain size of La–Ni-1 increased only 5.84% to 8.16 nm after performance test, which was lower than that of others and indicated a well structure stability. Additionally, the strong carbon diffraction peak over La–Ni-0.5 and La–Ni-2 catalysts suggested the presence of crystalline carbon species accumulated on the catalysts, while there was no carbon peak over La–Ni-1 sample. A 150 h stability test for La–Ni-1 demonstrated that the conversion of CH₄ was around 95%, higher than that of La–Ni-0 (without lanthanum addition) and La–Ni-4 (with La content of 3.82 wt%). The carbon deposition rate of La–Ni-1 was only 1.63 mg/(g_cat·h), lower than that of La–Ni-4 (2.20 mg/(g_cat·h)), showing both high activity and well stability. Therefore, the “confinement effect” of La₂O₃ to Ni crystalline grain would inhibit the sintering of active component, prevent the carbon deposition, and improve the catalytic reforming performance.     

Catalytic performance of CH4–CO2 reforming over metal free nitrogen-doped biomass carbon catalysts: Effect of different preparation methods

A series of nitrogen doped biomass carbon catalysts were prepared through two different nitrogen doped methods by using soybean meal as the raw material, melamine as nitrogen source and KOH as the activators. The catalysts were characterized by BET, SEM, CO₂-TPD, EA, FTIR, XPS and Raman. The catalytic performances of CH₄–CO₂ reforming over different samples were also studied. The results show that the preparation method of the catalyst significantly affects the structural characteristics, N content and N species type of the catalyst. The characterization results also show the proportion of pyrrolic-N in the catalyst prepared by in-situ nitrogen doped method (Y-NC) is higher than that in prepared by the post-treatment method (H-NC). Pyrrole-N is more conducive to the adsorption and activation of CO₂. So, the catalyst prepared by in-situ nitrogen doped method has good catalytic activity and stability. The conversion of CH₄ and CO₂ were respectively 40% and 65% at 900 °C after 50 h of CH₄–CO₂ reforming reaction.     

Bioethanol steam reforming over monoliths washcoated with RhPt/CeO2–SiO2: The use of residual biomass to stably produce syngas

Ethanol steam reforming of synthetic bioethanol (i.e., anhydrous ethanol plus water), as well as bioethanol obtained from glucose standards and sugarcane press-mud was evaluated on monoliths washcoated with RhPt/CeO₂–SiO₂. Tests with synthetic bioethanol indicated that the lower pressure drop favors higher ethanol conversion in the monoliths with respect to the powder samples. Also, two monoliths in series with 0.08 g_cat/cm³ improved H₂ yield compared to just one monolith with 0.16 g_cat/cm³. Similarly, a decrease in the amount of carrier gas contributes to diffusion limitations in the monoliths, reducing the H₂/CO ratio. Monoliths stability was also evaluated with “real” bioethanol samples (from glucose standards and sugarcane press-mud-SPM). In all cases, a syngas with >60% of H₂ was produced. For SPM-bioethanol, 3.1 ± 0.2 mol H₂/mol EtOH were obtained without evidence of deactivation for 120 h, at a cost of 6.9 $/kgH₂, becoming a promising way to develop a technology for sustainable energy production.     

Biomass-derived CO2 rich syngas conversion to higher hydrocarbon via Fischer-Tropsch process over Fe–Co bimetallic catalyst

Biomass-derived syngas (CO₂ + CO + H₂) has emerged as a potential non-fossil fuel source to yield transportation fuel via Fischer Tropsch Synthesis (FTS) reaction. Thus, the present study demonstrates the conversion of CO₂ containing syngas into fuel range hydrocarbon via Fischer Tropsch Synthesis over Fe–Co bimetallic catalyst. The experimental tests were carried out in a fixed bed continuous reactor to investigate the effect of CO₂ on CO/CO₂ conversion. Accordingly, obtained data were validated by FTS kinetic model for a plug flow reactor. It was found that the unique combination of Fe and Co bimetallic catalyst facilitates both FTS and water gas shift (WGS) reaction simultaneously that helps to convert CO₂ along with CO. It was also observed that the presence of iron in the catalyst helps in conversion of CO₂ into hydrocarbons, only when a particular concentration of CO₂ in syngas is reached, i.e., critical ratio R_C (CO₂/CO + CO₂) due to the occurrence of reverse water gas reaction (RWGS) which varies with the temperature and the feed gas composition (H₂/CO/CO₂ molar ratio). At 240 °C and hydrogen deficient condition, the critical ratio was measured to be 0.74 whereas for hydrogen balanced condition, it was measured 0.6. The kinetic model developed in the present study predicted trends for % CO conversion, % carbon conversion, and % CO₂ conversion which is applicable for a wide range of critical ratio R_C (CO₂/(CO + CO₂) = 0 to 1). The model also predicted that a positive conversion of CO₂ could be achieved at lower CO₂ concentration by increasing the reaction temperature. At 260 °C and 280 °C, the value of Rc were 0.31 and 0.18 were measured.     

Investigation of combustion and emission characteristics in a TBC diesel engine fuelled with CH4–CO2–H2 mixtures

In this study, an experimental investigation was performed to reveal combustion and emission characteristics of common-rail four-cylinder diesel engine run with CH₄, CO₂ and H₂ mixtures. The engine pistons were thermally coated with zirconia and Ni–Al bond coat by plasma spray method. With a small amount of the pilot diesel, port fuelled methane (100% CH₄), synthetic biogas (80% CH₄ + 20% CO₂), and hydrogen presented (80% CH₄+10% CO₂+10% H₂) mixtures were used as main fuel at different loads (50 Nm, 75 Nm, and 100 Nm) at a constant speed of 1750 min^?1. Comparative analysis of the combustion (cylinder pressure, PRR, HRR, CHR, ringing intensity, CA10, CA50, and CA90), BSFC, and emissions (CO₂, HC, NO_x, smoke, and oxygen) at the various engine loads with and without piston coating was made for all fuel combinations. It was found that coating the engine pistons enhanced the examining combustion characteristics, whereas it slightly changed BSFC and most of the emissions. As compared to the sole diesel fuel, the gaseous fuel operations showed higher in-cylinder pressure, PRR, and ringing intensity values, earlier combustion starting and CAs, and lower diesel injection pressure at the same engine operating conditions. Dramatic increase in the ringing intensity was particularly found by the hydrogen introduced mixture under the tests with coated piston. HC and CO₂ emissions increased in operation with the synthetic biogas; however, hydrogen introduction reduced HC emissions by 4.97–30.92%, and CO₂ emissions by 5.16–10%.     

High quality H2-rich syngas production from pyrolysis-gasification of biomass and plastic wastes by Ni–Fe@Nanofibers/Porous carbon catalyst

To produce the high quality H₂-rich syngas from biomass and plastic wastes, a two-stage pyrolysis-gasification system involving pyrolysis and catalytic gasification is considered as a suitable route. Generally, synthesis of highly active, low cost and coke-resistant catalyst for tar cracking is the key factor. A series of monometallic catalysts of Ni@CNF/PCs and Fe@CNF/PCs and the bimetallic Ni–Fe@CNF/PCs catalyst were prepared by a simple one-step pyrolysis approach for high quality syngas production from pyrolysis-gasification of biomass and plastic wastes. The results indicated that the bimetallic Ni–Fe@CNF/PCs catalyst appeared as the optimal catalyst in affording the best compromise between catalytic activity and stability with the existence of the excellent dispersibility of the Fe0.64Ni0.36 alloy nanoparticles and the carbon nanofibers/porous carbon composite structure. In addition, the optimal operation conditions of biomass/plastic ratio of 1/2 and gasification temperature of 700 °C were observed for the bimetallic Ni–Fe@CNF/PCs catalyst to play best roles in the H₂-rich syngas quality, with up to 33.66 mmol H₂/g biomass, and tar yields as low as 5.66 mg/g.     

On how CO2 partial pressure on corrosion of HNBR rubber O-ring in CO2–H2S–CH4 environment

Effect of CO₂ partial pressure on corrosion of HNBR and FKM rubber O-rings was studied by using a HTHP autoclave and a self-designed O-ring pressure bearing device to simulate the service environment of the packer in the process of associated gas reinjection. Their mechanical properties, EDS and fracture morphology were analyzed. The results showed that as the CO₂ partial pressure increased, the tensile strength, elongation and hardness of the two types of O-rings all decreased. Moreover, the fracture of both O-rings changed from ductile fracture to brittle fracture. In the free-state, the corrosion of the two O-rings in the liquid phase was more serious than in the gas phase. On the contrary, in the compressed state their corrosion in the gas phase was more serious than in the liquid phase. On the whole, the corrosion of the two O-rings in the free-state was more serious than in the compressed state. Their corrosion in CO₂–H₂S environment was influenced by the swelling and chemical reactions of medium molecules. The two O-rings in the compressed state reduced the contact area between O-ring and corrosive medium, resulting in slight corrosion of O-rings under compression. Due to its poor corrosion resistance and the sealing performance, HNBR O-ring had certain risk in the process of associated gas reinjection. FKM O-ring has good corrosion resistance and sealing performance in the CO₂–H₂S environment, so it can be well applied in this environment.     

Various calcium loading and plasma-treatment leading to controlled surface segregation of high coke-resistant Ca-promoted NiCo–NiAl2O4 nanocatalysts employed in CH4/CO2/O2 reforming to H2

High coke-resistant Ca-promoted NiCo–NiAl₂O₄ nanocatalysts with different calcium loading (0, 0.25, 0.5 and 1.5 wt%) were synthesized via hybrid sol-gel-plasma method. Synthesized samples were applied in the CH₄/CO₂/O₂ reforming to H₂ reactions. Analyses revealed that the calcium addition caused the lower surface area, non-uniform distribution and larger particle size. Therefore, higher activity and yield were found for the nanocatalyst without calcium while catalytic activity and yield were descended for the other ones. This trend was according to the covering effect of calcium and undesirable effect of calcium over the surface area and particle size distribution. But owing to the enhanced coke gasification rate of Ca-rich samples, by increasing of Ca amount, coke deposition was descended and stable performance was promoted. Due to the time on stream performance (TOS) during the 48 h and at 750 °C, 1.5 wt% Ca-promoted NiCo–NiAl₂O₄ (NCCa1.5A (SGP)) was stable, but demonstrated the lower yield. Moreover, 0.25 wt% Ca-promoted NiCo–NiAl₂O₄ nanocatalyst (NCCa0.25A (SGP)) was illustrated the higher yield in comparison with NCCa1.5A (SGP). It must be noted that just 2.7% deactivation for H₂ yield was detected for NCCa0.25A (SGP) during the 48 h TOS performance. H₂ yield of the NCCa0.25A (SGP) at 850 °C was 84%. Based on the reverse trends of the yield and TOS performance, NCCa0.25A (SGP) was able to present as a promising nanocatalyst for CH₄/CO₂/O₂ reforming to H₂. Moreover, this offer was ascribed to the excellent coke resistance and superior catalytic performance of NCCa0.25A (SGP).     

Supported mesoporous Cu/CeO2-δ catalyst for CO2 reverse water–gas shift reaction to syngas

The design and development of a high performance hydrogenation catalyst is an important challenge in the utilization of CO₂ as resources. The catalytic performances of the supported catalyst can be effectively improved through the interaction between the active components and the support materials. The obtained results demonstrated that the oxygen vacancies and active Cu⁰ species as active sites can be formed in the Cu/CeO_2-δ catalysts by the H₂ reduction at 400 °C. The synergistic effect of the surface oxygen vacancies and active Cu⁰ species, and Cu⁰–CeO_2-δ interface structure enhanced catalytic activity of the supported xCu/CeO_2-δ catalysts. The electronic effect between Cu and Ce species boosted the adsorption and activation performances of the reactant CO₂ and H₂ molecules on the corresponding Cu/CeO_2-δ catalyst. The Cu/CeO_2-δ catalyst with the Cu loading of 8.0 wt% exhibited the highest CO₂ conversion rate in the RWGS reaction, reaching 1.38 mmol·g_cat⁻¹ min⁻¹ at 400 °C. Its excellent catalytic performance in the RWGS reaction was related to the complete synergistic interaction between the active species via Ce³⁺-□-Cu⁰ (□: oxygen vacancy). The Cu/CeO_2-δ composite material is a superior catalyst for the RWGS reaction because of its high CO₂ conversion and 100% CO selectivity.     

Effects of preferential diffusion on downstream interaction in premixed H2/CO syngas–air flames

Effects of strain rate and preferential diffusion of H₂ on flame extinction are numerically explored in interacting premixed syngas–air flames with the fuel compositions of 50% H₂ + 50% CO and 30% H₂ + 70% CO. Flame stability diagrams mapping lower and upper limit fuel concentrations at flame extinction as a function of strain rate are examined. Increasing strain rate reduces the boundaries of both flammable lean and rich fuel concentrations and produces a flammable island and subsequently even a point, implying that there exists a limit strain rate over which interacting flame cannot be sustained anymore. Even if effective Lewis numbers are slightly larger than unity on the lean extinction boundaries, the shape of the lean extinction boundary is slanted even at low strain rate, i.e. a_g = 30 s⁻¹ and is more slanted in further increase of strain rate, implying that flame interaction on lean extinction boundary is strong and thus hydrogen (as a deficient reactant) Lewis number much less than unity plays an important role of flame interaction. It is also shown that effects of preferential diffusion of H₂ cause flame interaction to be stronger on lean extinction boundaries and weaker on rich extinction boundaries. Detailed analyses are made through the comparison between flame structures with and without the restriction of the diffusivities of H₂ and H in symmetric and asymmetric fuel compositions. The reduction of flammable fuel compositions in increase of strain rate suggests that the mechanism of flame extinction is significant conductive heat loss from the stronger flame to ambience.     

Sorption-enhanced steam reforming of CH4/CO2 synthetic mixture representing biogas over porous Ni–CaO–MgO microsphere via a surface modified carbon template

Sorption-enhanced steam reforming of biogas (SESRB) provides an efficient way to obtain high-purity hydrogen from biogas. Highly effective bi-functional adsorbent/catalyst materials play a key role in the long-term operation of SESRB process. Here a general template-based approach using carbon microspheres with alkali modification (MCS) as sacrificial templates to synthesize highly effective bi-functional catalyst is reported. FT-IR, XPS and TGA confirm the enhanced adsorption capacity of MCS to metal ions due to the existence of rich oxygen containing functional groups. The amount of the obtained bi-functional catalyst is increased by 14 times after NaOH treatment. Electron microscopy analysis shows the uniformity of composition and the formation of a favorable morphology, including porous structure and separated nanoparticles, are the crucial for yielding high-performance bi-functional catalyst. Due to the excellent stability of the catalyst structure, 92.3 vol % of hydrogen (dry and inert-free gas basis) with 92% CH₄ conversion is obtained over the 1Ni–CaMg6-M catalyst for 10 consecutive reaction-desorption cycles.     

A review of CH4CO2 reforming to synthesis gas over Ni-based catalysts in recent years (2010–2017)

In recent years, global warming issue has been a major environmental concern, so the treatment or utilization of the greenhouse gases CO₂ and CH₄ have become a matter of urgency. Given this realization, dry reforming of methane (DRM) provides a comprehensive utilization of methane and carbon dioxide, which has been investigated systematically. In CH₄CO₂ reforming reaction, Ni-based catalysts are widely used and promisingly industrialized due to their outstanding features and low price compared with precious metals. In this paper, we emphasize the recent accomplishments in catalyst design for DRM reaction, particularly focusing on the influence of supports, promoters, and preparation methods on the DRM reaction with nickel-based catalysts. We also present a review on the catalytic mechanistic and kinetics of the DRM reaction. Furthermore, this review looks ahead the major challenges and opportunities of nickel-based catalysts in DRM reaction research.     

Ni–SiO2 and Ni–Fe–SiO2 catalysts for methane decomposition to prepare hydrogen and carbon filaments

Active and stable Ni–Fe–SiO₂ catalysts prepared by sol–gel method were employed for direct decomposition of undiluted methane to produce hydrogen and carbon filaments at 823 K and 923 K. The results indicated that the lifetime of Ni–Fe–SiO₂ catalysts was much longer than Ni–SiO₂ catalyst at a higher reaction temperature such as 923 K, however, a reverse trend was shown when methane decomposition took place at a lower reaction temperature such as 823 K. XRD studies suggested that iron atoms had entered into the Ni lattice and Ni–Fe alloy was formed in Ni–Fe–SiO₂ catalysts. The structure of the carbon filaments generated over Ni–SiO₂ and Ni–Fe–SiO₂ was quite different. TEM studies showed that “multi-walled” carbon filaments were formed over 75%Ni–25%SiO₂ catalyst, while “bamboo-shaped” carbon filaments generated over 35%Ni–40%Fe–25%SiO₂ catalysts at 923 K. Raman spectra of the generated carbons demonstrated that the graphitic order of the “multi-walled” carbon filaments was lower than that of the “bamboo-shaped” carbon filaments.     

Engineering Ru nanoparticles embedded in 2D N-doped carbon nanosheets decorated with 2D Fe3O4–Fe3C heterostructures for efficient hydrogen evolution in alkaline and acidic media

Tailoring surface composition and structures of catalysts affects their catalytic performance in hydrogen evolution reaction owing to the geometric and electronic effects. Herein, Ru nanoparticles embedded in 2D N-doped carbon nanosheets decorated with 2D Fe₃O₄–Fe₃C heterostructures (Ru/Fe₃O₄–Fe₃C/NC) are fabricated via pyrolysis of the mixture containing 2D-Fe₂O₃ nanosheets, dopamine hydrochloride, RuCl₃·xH₂O, and melamine. Interestingly, the good hydrogen evolution behavior is achieved on Ru/Fe₃O₄–Fe₃C/NC with the high reactivity and stability. Ru/Fe₃O₄–Fe₃C/NC offers an overpotential of 141 mV to realize the current density of 10 mA/cm² in 0.5 mol/L (M) H₂SO₄ electrolyte. As for 1 M KOH, Ru/Fe₃O₄–Fe₃C/NC promotes hydrogen evolution reactivity with 148 mV to achieve 10 mA/cm². The current density slightly degrades after continuous I-t tests, verifying the good stability for Ru/Fe₃O₄–Fe₃C/NC. The high reactivity might stem from high dispersion of Ru nanoparticles, enhanced conductivity due to doping N into carbon nanosheets, and heterointerfaces between Fe–O and Fe–C.     

Effect of ceria content in Ni–Ce–Al catalyst on catalytic performance and carbon/coke formation in dry reforming of CH4

In this study, to enhance the catalytic activity and minimize the carbon/coke formation, cerium incorporated alumina-supported new Ni–Ce–Al catalysts were investigated in dry reforming of biogas. Ni–Ce–Al catalysts were synthesized by the modified one-pot sol-gel method in an inert environment. To determine the effect of the Ce/Al ratio on physicochemical properties of catalysts and their activity, Ni (5 wt %) catalysts with different Ce/Al ratios (0/1, 1/2, 1/1, 2/1 b y wt.) were tested in a fixed-bed flow reactor using an equimolar ratio of CH₄/CO₂/Ar gas mixture. To explain the correlation between catalytic activity and catalyst properties, characterization studies were carried out by using N₂ adsorption-desorption isotherms, XPS, XRD, SEM-EDS, TEM, ICP-OES, DRIFT, O₂-TPO and TGA methods before and after activity tests. XRD analysis showed that both CeO₂ and γ-Al₂O₃ crystalline phases with metallic Ni having different peak intensities were separately formed in all the catalysts. Among the catalysts of different Ce/Al ratios, the Ni–1Ce–1Al catalyst containing equal amounts of Al and Ce has the smallest CeO₂ crystallite size. This catalyst also has the highest pore diameter and volume. XPS analysis showed that Ce incorporation into the Ni-based Al₂O₃ catalyst decreased the NiAl₂O₄ formation. DRIFT analysis indicated that the addition of ceria into the support material decreased the Lewis acidity of alumina. During 25-h long-term activity test, the conversions of CH₄ and CO₂ obtained with the catalyst Ni–1Ce–1Al (Ce/Al ratio is 1/1) were approximately the same and averaged 76% and 85%, respectively. This behavior of the catalyst indicates its high stability. TGA, XRD and SEM analyzes performed with the used Ni–1Ce–1Al and Ni–Al catalysts show very little carbon formation in the catalyst containing equal weights of Ce and Al compared to the catalyst without Ce. This result shows that the addition of cerium to the catalyst structure prevents carbon deposition due to its special oxygen mobility. This study showed that the crystallite size of CeO₂ in the catalyst structure strongly influences preventing carbon accumulation in the dry reforming reaction.     

One-step synthesis of metallic Ni–C/Al2O3 directly applied for CO2 reforming of CH4

In this work, the vacuum co-impregnation of glucose and nickel precursor followed by the carbonization in an inert gas was developed as a new method for the preparation of the directly reduced Ni-based catalysts (Ni–C/Al₂O₃), which can be directly applied for CO₂ reforming of CH₄ (CRM) without any reduction. The materials were characterized by XRD, TEM, and N₂ adsorption-desorption at low temperature. The results showed that H₂ and CH₄ derived from the decomposition of the glucose acted as the reducing agents for synthesizing metallic Ni from Ni precursors, and the reduction content of nickel was strongly dependent on the amount the glucose. The introduction of carbon derived from decomposition of glucose decreased the interaction between Ni and Al₂O₃ and then resulting in bigger Ni particle. Under the same CRM reaction conditions, the as-prepared Ni-0.35C/Al₂O₃ catalyst without further reduction showed highest catalytic activity and stability. The use of the directly reduced Ni-based catalyst without further high-temperature reduction is promising for the development of a more efficient CRM process.     

Enhanced electrochemical performance and durability for direct CH4–CO2 solid oxide fuel cells with an on-cell reforming layer

Coking is a major issue with the traditional Ni-based anodes when directly oxidizing CH₄ in solid oxide fuel cells (SOFCs). Dry reforming to convert CH₄–CO₂ into CO–H₂ syngas before entering Ni-based anode may potentially be an effective and economical method to address the coking problem. Consequently, an on-cell reforming layer outside the Ni-based anode is expected to offer a unique solution for direct CH₄–CO₂ SOFCs without coking. In this study, Ni-GDC anode-supported cells with and without a Sr₂Co_0.4Fe_1.2Mo_0.4O_6-δ (SCFM) layer outside the anode support have been fabricated and evaluated using either H₂ or CH₄–CO₂ as fuel. Both types of cells show excellent electrochemical performance when H₂ is used as fuel, and the SCFM layer has negligible impact on the cell performance. When CH₄–CO₂ is used as fuel, however, the electrochemical performance and durability of the cells with the SCFM layer are much better than those without the SCFM layer outside the Ni-GDC anode, indicating that the SCFM layer can efficiently perform dry reforming. This unique on-cell dry reforming design enables direct CH₄–CO₂ solid oxide fuel cells and offers a very promising route for energy storage and conversion.     

Effects of CO2 dilution on the interactions of a CH4–air nonpremixed jet flame with a single vortex

We carried out numerical simulations to understand how CO₂ dilution in either fuel or oxidizer stream changes the flame-vortex interactions in terms of hydrodynamic effects in CH₄–air nonpremixed jet flames. The simulation used a time-dependent, axisymmetric computational model and a low Mach number approximation. Reaction rates were calculated from a two-step global reaction mechanism that considered six species. Studies were conducted with fixed initial velocities for three different cases of CO₂ introduction: (1) without dilution, (2) dilution in a fuel stream, and (3) dilution in an oxidizer stream. A single vortex was generated by an axisymmetric jet driven of cold fuel, after a flame development was reached to quasi steady-state condition. The simulation shows that CO₂ dilution in a fuel stream leads to a slightly increased vortex radius and more entrainment of surrounding fluids compared to the other dilution methods tested. Thus, dilution of CO₂ in a fuel stream enhances the mixing inside a single vortex and increases the stretching of the flame surface. The vorticity transport equation budgets were examined to reveal the mechanisms of vortex formation in the presence of CO₂. In the stage of vortex formation, vortex production due to baroclinic torque and vortex destruction due to volumetric expansion were found to be greater in the case of CO₂ dilution in a fuel stream than in the other dilution cases. However, after vortex formation, there terms showed the opposite tendencies.     

Nanoconfined 2LiBH4–MgH2–TiCl3 in carbon aerogel scaffold for reversible hydrogen storage

Nanoconfinement of 2LiBH₄–MgH₂–TiCl₃ in resorcinol–formaldehyde carbon aerogel scaffold (RF–CAS) for reversible hydrogen storage applications is proposed. RF–CAS is encapsulated with approximately 1.6 wt. % TiCl₃ by solution impregnation technique, and it is further nanoconfined with bulk 2LiBH₄–MgH₂ via melt infiltration. Faster dehydrogenation kinetics is obtained after TiCl₃ impregnation, for example, nanoconfined 2LiBH₄–MgH₂–TiCl₃ requires ∼1 and 4.5 h, respectively, to release 95% of the total hydrogen content during the 1st and 2nd cycles, while nanoconfined 2LiBH₄–MgH₂ (∼2.5 and 7 h, respectively) and bulk material (∼23 and 22 h, respectively) take considerably longer. Moreover, 95–98.6% of the theoretical H₂ storage capacity (3.6–3.75 wt. % H₂) is reproduced after four hydrogen release and uptake cycles of the nanoconfined 2LiBH₄–MgH₂–TiCl₃. The reversibility of this hydrogen storage material is confirmed by the formation of LiBH₄ and MgH₂ after rehydrogenation using FTIR and SR-PXD techniques, respectively.     

Improved hydrogen production performance of Ni–Al2O3/CaO–CaZrO3 composite catalyst for CO2 sorption enhanced CH4/H2O reforming

Bifunctional composite catalysts are very intrigued to produce hydrogen via CO₂ sorption enhanced CH₄/H₂O reforming. However, their hydrogen production performance declined over multiple cycles, owing to the structure collapse and the sintering of active component under high-temperature regeneration. This work reported the facile synthesis of long-lasting Ni–Al₂O₃/CaO–CaZrO₃ composite catalysts with less inert components (36 wt%) for stable hydrogen production over the multiple cycles of CO₂ sorption enhanced CH₄/H₂O reforming. The effects of reaction and regeneration temperature on the hydrogen production performance of Ni–Al₂O₃/CaO–CaZrO₃ were explored. Ni–Al₂O₃/CaO–CaZrO₃ demonstrated high activity and stability while fixing reaction temperature as 600 °C and regeneration temperature as 750 °C. Of particular importance, H₂ concentration was 98 vol% even after 10 hydrogen production cycles due to the inert component CaZrO₃ having a cross-linked structure. The distribution of CaZrO₃ in the composite as a coral-like structure inhibited the sintering of CaO through high Taman temperature and physical separation. Moreover, it provided the skeleton support and pore volume for the repeated expansion and contraction process of CaO to CaCO₃ during the cycling process. Finally, the sintering of Ni slowed down in appropriate regeneration temperature to maintain the structure of the composite catalyst, which further improved the catalyst's stability over multiple cycles.