Chemical heat-pump system working at exhaust temperatures of high-temperature-gas-cooled reactor

A chemical heat-pump system using two hydrogen-absorbing alloys is proposed to utilize heat exhausted from a high-temperature source such as high-temperature-gas-cooled reactor, HTGR, which is designed to produce H₂ more efficiently. The overall system proposed here consists of HTGR, He gas turbines, chemical heat pumps and reaction vessels corresponding to the three-step decomposition reactions comprising the I–S process. A fundamental research is performed experimentally on heat generation in a single bed packed with a hydrogen-absorbing alloy that works at the H₂ production temperature. The hydrogen-absorbing alloy of Zr(V_1−xFe_x)₂ is selected as a material that has a proper plateau pressure for the heat-pump system operated between the input and output temperatures of HTGR. Temperature jump due to heat generated when the alloy absorbs H₂ proves that the alloy–H₂ system can heat up the exhaust gas even at 600 °C without any external mechanical force.     

Integrating chemical kinetics with CFD modeling for autothermal reforming of biogas

Using biogas for hydrogen production via autothermal reforming (ATR) can potentially increase the energy conversion efficiency and correspondingly reduce environmental impact. The present study aimed to investigate the performance and characteristics of biogas ATR. A two-dimensional numerical model was developed based on the integration of computational fluid dynamics (CFD) and chemical kinetics. The mass transport, chemical reactions and heat transfer can be analyzed simultaneously in the porous domain. The results show that the presence of CO₂ in the feedstock will reduce the performance of the biogas ATR. The effects of operating and feeding conditions were examined and the optimal conditions were identified. Operating the reformer with the steam-to-CH₄ ratio (S/CH₄) and air-to-CH₄ ratio (A/CH₄) equal to 0.5 and 2, respectively, can achieve high H₂ concentration, while operation with S/CH₄ and A/CH₄ equal to 4.5 and 2, respectively, can achieve high energy efficiency. The results also show that using either H₂ or O₂ membrane in the reformer can enhance the biogas autothermal reforming performance by producing high concentration of H₂ (40–65%) and solving the harmful hot spot problems.     

Novel quasi-autothermal hydrogen production process in a fixed-bed using a chemical looping approach: A numerical study

This paper presents a novel quasi-autothermal hydrogen production process. The proposed layout couples a Chemical Looping Combustion (CLC) section and a Steam Methane Reforming (SMR) one. In CLC section, four packed-beds are operated using Ni as oxygen carrier and CH₄ as fuel to continuously produce a hot gaseous mixture of H₂O and CO₂. In SMR section, two fixed-beds filled with Ni-based catalyst convert CH₄ and H₂O into a H₂-rich syngas. Four heat exchangers were employed to recover residual heat content of all the exhaust gas currents. By means of a previously developed 1D numerical model, a dynamic simulation study was carried out to evaluate feasibility of the proposed system in terms of methane conversion (100% circa), hydrogen yield (about 0.65 mol_H2/mol_CH4) and selectivity (about 70%), and syngas ratio (about 2.3 mol_H2/mol_CO). Energetic and environmental analyses of the system performed with respect to conventional steam methane reforming, highlights an energy saving of about 98% and avoided CO₂ emission of about 99%.     

Heat transfer model and scale-up of an entrained-flow solar reactor for the thermal decomposition of methane

The solar thermochemical decomposition of CH₄ is carried out in a solar reactor consisting of a cavity-receiver containing an array of tubular absorbers, through which CH₄ flows and thermally decomposes to H₂ and carbon particles. A reactor model is formulated by coupling radiation/convection/conduction heat transfer and chemical kinetics for a two-phase solid-gas reacting flow. Experimental validation is accomplished by comparing measured and simulated absorber temperatures and H₂ concentrations for a 10 kW prototype reactor tested in a solar furnace. The model is applied to optimize the design and simulate the performance of a 10 MW commercial-scale reactor mounted on a solar tower system configuration. Complete conversion is predicted for a maximum CH₄ mass flow rate of 0.70 kg s⁻¹ and a desired outlet temperature of 1870 K, yielding a solar-to-chemical energy conversion efficiency of 42% and a solar-to-thermal energy conversion efficiency of 75%.     

Nickel-iron modified natural ore oxygen carriers for chemical looping steam methane reforming to produce hydrogen

Chemical looping steam methane reforming (CL-SMR) is a promising and efficient method to produce hydrogen and syngas. However, oxygen carrier (OC) prepared by synthesis are complex, expensive and poor mechanical performance, while natural ore OCs are low activity and poor selectivity. In order to avoid these problems, Ni/Fe modification of natural ores were proposed to improve the reactivity and stability of OC to CL-SMR. The results indicated that the modified calcite recombined and improved the structural phase during the reaction, enhancing performance and inhibiting agglomeration. Moreover, high ratio of iron to nickel was easy to sinter and decline the OC performance. In addition, with the increase of steam flow, both CH₄ conversion and carbon deposition decreased. Thereinto, the highest H₂ concentration, CH₄ conversion efficiency and H₂ yield were obtained when the ratio of steam to OC was 0.05. Furthermore, CH₄ flow rate had a great impact on CL-SMR performance. When the ratio of CH₄ to OC was 0.04, it achieved the highest CH₄ conversion efficiency of 98.96%, the highest H₂ concentration of 98.83% and the lowest carbon deposition of 3.23%. However, the carbon deposition increased with the increase of CH₄ flow rate. After a long-time chemical looping process, the Ni/Fe modified calcite showed a consistently stable performance with average H₂ concentration of 93.08%, CH₄ conversion efficiency of 88.03%, and carbon deposition of 2.15%.     

Methane steam reforming for producing hydrogen in an atmospheric-pressure microwave plasma reactor

A methane steam reforming process for producing mainly hydrogen in an atmospheric-pressure microwave plasma reactor is demonstrated. Nano carbon powders, CO_x, C₂H₂, C₂H₄, and HCN were also formed. Intermediates such as OH, NH, CH, and active N₂ were identified using optical emission spectroscopy. The selectivity of H₂ was greater than 92.7% at inlet H₂O/CH₄ molar ratio (R) ≧ 0.5, and was higher than that obtained using methane plasmalysis because steam inhibited the formation of C₂H₂. The highest methane conversion was obtained at R = 1, reaching 91.6%, with the lowest specific energy consumption of H₂ formation at [CH₄]_in = 5%, 1.0 kW, and 12 slpm. The plasma-assisted catalysis process, which packed Ni/Al₂O₃ catalysts in the discharge zone and supplied heat using hot effluents, was used to elevate the methane conversion and hydrogen selectivity. However, large amounts of 40–70 nm carbon powder, which is electrically conductive, were produced, resulting in rapid catalyst deactivation due to carbon being deposited on the surface and in the pores of catalysts.     

Effect of methane reforming before combustion on emission and calorimetric characteristics of its combustion process

In this study, combustion and emission characteristics of methane mixed with steam (CH₄/H₂O) and the products of methane reforming with steam (CO/H₂/H₂O) were compared. Four fuel compositions were analysed: CH₄+H₂O, CH₄+2H₂O, and products of complete methane reforming in these mixtures, respectively. A comparison was carried out through the numerical model created via Ansys Fluent 2019 R2. A combustion process was simulated using a non-premixed combustion model, standard k-ϵ turbulence model and P-1 radiation model. The combustor heat capacity for interrelated fuel compositions was kept constant due to air preheating before combustion. The inlet air temperature was varied to gain a better insight into the combustion behaviour at elevated temperatures. The effect of steam addition on the emission characteristics and flame temperatures was also evaluated. NO_x formation was assessed on the outlet of the combustion zone. The obtained results indicate that syngas has a higher combustion temperature than methane (in the same combustor heat capacity) and therefore emitted 27% more NO_x comparing to methane combustion. With the air inlet temperature increment, the pollutant concentration difference between the two cases decreased. Steam addition to fuel inlet resulted in lesser emissions both for methane and syngas by 57% and 28%, respectively. In summary, syngas combustion occurred at higher temperature and produced more NO_x emissions in all cases considered.     

Low-temperature steam reforming of methanol to produce hydrogen over various metal-doped molybdenum carbide catalysts

Various transition metals (M = Pt, Fe, Co, and Ni) were selected to support on molybdenum carbides by in-situ carburization metal-doped molybdenum oxide (M-MoO_x) via temperature-programmed reaction (TPR) with a final temperature of 700 °C in a reaction gas mixture of 20% CH₄/H₂. XRD analysis results indicated that β-Mo₂C phase was formed in the case of Fe, Co, or Ni doping while α-Mo₂C phase was appeared with the β-MoC_1−x phase in the case of Pt doping. With the increase in Pt doping amount, more α-MoC_1−x phase was produced. As-prepared metal doped molybdenum carbides were investigated as alternative catalysts for the steam reforming of methanol. Comparing with the undoped molybdenum carbide such as β-Mo₂C, metal-doped one showed higher methanol conversion and hydrogen yield. It is found that Pt doped molybdenum carbide had the highest catalytic activity and selectivity among the prepared catalysts and methanol conversion reached 100% even at a temperature as low as 200 °C, and remained a long-time stability with a stable methanol conversion.     

Synergistic effects of Ni1−xCox-YSZ and Ni1−xCux-YSZ alloyed cermet SOFC anodes for oxidation of hydrogen and methane fuels containing H2S

Preparation and performance of bimetallic Ni_(1−x)Co_x-YSZ and Ni_(1−x)Cu_x-YSZ anodes were tested to overcome common deficiencies of carbon and sulfur poisoning in SOFCs. Ni_1−xCo_xO-YSZ and Ni_(1−x)Cu_xO-YSZ precursors were synthesized via co-precipitation of their respective chlorides. Single cell solid oxide fuel cells of these bimetallic anodes were tested in H₂, CH₄, and H₂S/CH₄ fuel mixtures. Addition of Cu²⁺ into the NiO lattice resulted in large metal particle sizes and decreased SOFC performance. Addition of Co²⁺ into the NiO lattice to form Ni_0.92Co_0.08O-YSZ anode precursor produced a cermet with a large BET surface area and active metal surface area, thus increasing the rate of hydrogen oxidation for this sample. The performance of both bimetallics was found to quickly degrade in dry CH₄ due to carbon deposition and lifting of the anode from the electrolyte. However, Ni_0.69Co_0.31-YSZ showed superior activity in a 10% (v/v) H₂S/CH₄ fuel mixture, surpassing performance with H₂ fuel, thereby demonstrating the exciting prospect of using sulfidated Ni_(1−x)Co_x-YSZ as SOFC anodes in sulfur containing methane streams. The active anode becomes a sulfidated alloy (Ni-Co-S) under operating conditions. This anode showed enhanced performance, which surpassed those of sulfidated Ni and Co anodes, thereby suggesting a synergistic behaviour in the Ni-Co-S anode.     

Conversion of natural gas jet flame burners to hydrogen

In a study of conversion from CH₄ to H₂, jet flame characteristics of these gases and their blends are compared on a burner diameter scale of mm. Low velocity H₂ and CH₄ jets, burned on pipes of different diameters, indicate higher blow-off limits for H₂, but lower heat release rates, a consequence of its lower specific energy. Compensation for this might be obtained through increased H₂ flow velocity, or a small increase in pipe diameter. Blended CH₄/H₂ flames have lower heat release rates than CH₄ alone, yet small proportions of H_2, with CH₄ might still be burned, on a CH₄ burner. Throughout, fundamental understanding is enhanced through two dimensionless groups: laminar flame thickness normalised by burner diameter, δ_k/D, and the dimensionless flow number, U1. These suggest an optimal role for H₂ combustion, utilizing its high acoustic and blow-off velocities, in high intensity, subsonic, combustors, at low δ_k/D, and high U1.     

Hydrogen absorption in MgNiFe alloys

The hydrogenation properties of the alloys of overall formula Mg₂Ni_1?xFe_x (x ? 0.37) have been studied. In this range of composition multi-phase alloys were obtained containing Mg₂Ni, Mg and more or less finely dispersed Fe in different coordination as proved by the EXAFS technique and Mössbauer spectroscopy. There is no significant substitution of Ni by Fe atoms in the Mg₂Ni lattice. Two or three plateau-pressures are observed on the pressure-composition isotherms of the hydrides with the heats of formation in the range ?18.4 to 20.4 kcal/mol H₂ (?77 to ?85.4 kJ/mol H₂). The hydrides of the Fe containing alloys show higher desorption rates of hydrogen compared to the pure Mg₂Ni hydride.     

Enhanced hydrogen generation behaviors and hydrolysis thermodynamics of as-cast Mg–Ni–Ce magnesium-rich alloys in simulate seawater

In this study, we developed as-cast (Mg10Ni)_1-xCe_x (x = 0, 5, 10, 15 wt%) ternary alloys by using a flux protection melting method and investigated their hydrolysis hydrogen generation behaviour in simulate seawater. The phase compositions and microstructures of as-cast (Mg10Ni)_1-xCe_x ternary alloys are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with electron energy dispersion spectrum (EDS) and transition electron microscope (TEM). Their kinetics, thermodynamics, rate-limiting steps and apparent activation energies are investigated by fitting the hydrogen generation curves at different temperatures. With increasing Ce content, the (Mg10Ni)_1-xCe_x ternary alloys show increased electrochemical activities and decreased eutectic. When 10 wt% and 15 wt% Ce added, the active intermediate phase of Mg₁₂Ce has been observed. The hydrogen generation capacity of (Mg10Ni)₉₅Ce₅ is as high as 887 mLg⁻¹ with a hydrolysis conversion yield of 92%, which is higher than that of Mg₁₀Ni alloys (678 mLg⁻¹) with a yield only 75% at 291 K. The initial hydrolysis reaction kinetics of Mg–Ni–Ce alloys is mainly controlled by the electrochemical activity and the mass transfer channels formed in the alloys. Such a structure-property relationship will provide a possible strategy to prepare Mg-based alloys with high hydrogen conversion yield and controlled hydrolysis kinetics/thermodynamics.     

Modifying perovskite-type oxide catalyst LaNiO3 with Ce for carbon dioxide reforming of methane

Perovskite-type oxide catalysts LaNiO₃ and La_1−xCe_xNiO₃ (x ≤ 0.5) were prepared by the Pechini method and used as catalysts for carbon dioxide reforming of methane to form synthesis gas (H₂ + CO). The gaseous reactants consisted of CO₂ and CH₄ in a molar ratio of 1:1. At a GHSV of 10,000 hr⁻¹, CH₄ conversion over LaNiO₃ catalyst increased from 66% at 600 °C to 94% at 800 °C, while CO₂ conversion increased from 51% to 92%. The achieved selectivities of CO and H₂ were 33% and 57%, respectively, at 600 °C. To prevent the deposition of carbon and the sintering nickel species, some of the Ni in perovskite-type oxide catalyst was substituted by Ce. Ce provided lattice oxygen vacancies, which activated C–H bonds, and increased the selectivity of H₂ to 61% at 600 °C. XRD analysis indicates that the catalyst exhibited a typical perovskite spinel structure and formed La₂O₂CO₃ phases after CO₂ reforming. The FE-SEM results reveal carbon whisker of the LaNiO₃ catalyst and the BET analysis indicates that the specific surface area increases after the reforming reaction. The H₂-TPR results confirm that Ce metals can store and provide oxygen.     

Cogeneration of H2 and CH4 from water hyacinth by two-step anaerobic fermentation

A novel reaction mechanism of H₂ and CH₄ cogeneration from water hyacinth (Eichhornia crassipes) was originally proposed to increase the energy conversion efficiency. The glucose and xylose hydrolysates derived from cellulose and hemicellulose are fermented to cogenerate H₂ and CH₄ by two-step anaerobic fermentation. The total volatile solid of hyacinth leaves can theoretically cogenerate H₂ and CH₄ yields of 303 ml-H₂/g-TVS and 211 ml-CH₄/g-TVS, which dramatically increases the theoretical energy conversion efficiency from 19.1% in only H₂ production to 63.1%. When hyacinth leaves are pretreated with 3 wt% NaOH and cellulase in experiments, the cogeneration of H₂ (51.7 ml-H₂/g-TVS) and CH₄ (143.4 ml-CH₄/g-TVS) markedly increases the energy conversion efficiency from 3.3% in only H₂ production to 33.2%. Hyacinth leaves, which have the most cellulose and hemicellulose and the least lignin and ash, give the highest H₂ and CH₄ yields, while hyacinth roots, which have the most ash and the least cellulose and hemicellulose, give the lowest H₂ and CH₄ yields.     

Synergistic effects of ZrO2 crystallite islands and high dispersion of active Ni0 nanoparticles on CH4/CO2 reforming reaction

A series of mesoporous 9NixZrO₂/SBA-15 were prepared by coupled self-assembly and evaluated for CO₂/CH₄ reforming, which revealed that high activity and stability of 9Ni9ZrO₂/SBA-15 correlated closely with the synergistic effects of ZrO₂ crystallite islands and high dispersion of active Ni⁰ nanoparticles which promote adsorption of CO₂ and facilitated high efficient conversion of residual CH_x species. The XRD, O₂-TPD, HAADF-Zr mapping and UV–vis DRS analysis verified the existence of stable ZrO₂ crystallites and the formation of surface oxygen vacancies. The XPS and HRTEM images of 9NixZrO₂/SBA-15 before and after CH₄/CO₂ reforming proclaimed the distribution of catalyst surface active species, synergistic action between CO₂ and vacancies as well as formation character of CNTs. A catalytic mechanism of CH₄/CO₂ conversion into CO/H₂ has been put forward. The allotropes of coke and physical properties of catalysts were systematically analyzed by TG/DTG, first derivative XAES, H₂-TPR, N₂-physisorption and FT-IR.     

Laminar flame speed of H2/CH4/air mixtures with CO2 and N2 dilution

The laminar flame speeds of H₂/CH₄/air mixtures with CO₂ and N₂ dilution were systematic investigated experimentally and numerically over a wide range of H₂ blending ratios (0–75 vol%) with CO₂ (0–67 vol%) and N₂ (0–67 vol%) dilution in the fuels. The experimental measurements were conducted via the Bunsen flame method incorporating the Schlieren technique under the condition of equivalence ratios from 0.8 to 2.0. To gain an insightful understanding of the experimental observations, detailed numerical simulation was carried out using Chemkin-Pro with GRI3.0-Mech. The experimental measurements were also used to validate the corresponding performance of a semiempirical correlation derived through asymptotic analysis method coupled with the reduced chemistry mechanism. The results showed that at lower H₂ fraction (x_H2 ≤ 0.5), the laminar flame speeds of H₂/CH₄/air mixtures displayed great linearly increase with the growth of H₂ fractions. The combustion of mixtures with low H₂ contents was dominated by CH₄ conversion which was mainly controlled by the increasing OH radicals produced from the key oxidation reactions of H + O₂ = O + OH. With the further increase of H₂ fractions, the methane-dominated combustion gradually transformed into the methane-inhibited hydrogen combustion, resulting to the growth of laminar flame speeds was dramatical and non-linear. Due to the larger heat capacity and chemical kinetic effect, CO₂ presented a stronger dilution effect on reducing the laminar flame speeds than N₂. With the addition of CO₂, the increasing stronger competition for H radical through CO + OH = CO₂ + H with H + O₂ = O + OH due to the significant reduction of H mole fractions, leading to the larger decrease of laminar flame speeds of mixtures. Besides, although the contribution of thermal effect of CO₂ decreased near the equivalence ratio, the thermal effect of CO₂ still preformed the dominated contribution to the total dilution effect. A comparison between the experimental data and estimated results using the semiempirical correlation showed that, the correlation using new modified coefficients provided the satisfactorily accuracy predictions on the laminar flame speeds of diluted H₂/CH₄/air mixtures at lower x_H2 (x_H2 ≤ 0.5) and lower x_dilution (x_dilution = 0.25). The estimated results were generally located within a deviation range of ±20% errors except for two unsatisfactory eases occurred at conditions of x_H2 = 0.75 and x_CO2 = 0.67. The considerably poor predictions were attributed to the significantly variation of the chemical kinetics under high H₂ content and large CO₂ dilution conditions.     

Equilibrium composition of ethanol steam reforming reaction to produce H2 applied to Ni,Co and Pt/hydrotalcite–WOx catalysts

The purpose of this work was to investigate the difference between the experimental molar fractions of products obtained during the evaluation of Pt, Co and Ni/Hydrotalcites–WOx catalysts and the calculated composition in equilibrium for the ethanol steam reforming reaction. Mole fractions of H₂, CO₂, CH₃CHO, CH₂CH₂, CH₄ and H₂O were calculated using the stoichiometric and the minimization of the Gibbs free energy methods. The difference between calculated and experimental mole fractions was used to determine the intermediate and final compounds in the reaction mechanism and also how close to equilibrium are the reactants and final products. In addition, by comparing H₂ and the conversion, it was possible to distinguish which series of catalysts were more active. From our experimental results, the conversion order of these catalysts was as follows: Pt > Ni > Co and the reaction rate per g-atm of metal was: Pt ? Ni ≈ Co.     

Ammonia chemistry in a flameless jet

In this paper, the nitrogen chemistry in an ammonia (NH₃) doped flameless jet is investigated using a kinetic reactor network model. The reactor network model is used to explain the main differences in ammonia chemistry for methane (CH₄) containing fuels and methane-free fuels. The chemical pathways of nitrogen oxides (NO_x) formation and destruction are identified using rate-of-production analysis. The results show that in the case of natural gas, ammonia reacts relatively late at fuel lean condition leading to high NO_x emissions. In the pre-ignition zone, the ammonia chemistry is blocked due to the absence of free radicals which are consumed by methane-methyl radical (CH₃) conversion. In the case of methane-free gas, the ammonia reacted very rapidly and complete decomposition was reached in the fuel rich region of the jet. In this case the necessary radicals for the ammonia conversion are generated from hydrogen (H₂) oxidation.     

A comparison of the emission and impingement heat transfer of LPG–H2 and CH4–H2 premixed flames

Experiments were performed to add hydrogen to liquefied petroleum gas (LPG) and methane (CH₄) to compare the emission and impingement heat transfer behaviors of the resultant LPG–H₂–air and CH₄–H₂–air flames. Results show that as the mole fraction of hydrogen in the fuel mixture was increased from 0% to 50% at equivalence ratio of 1 and Reynolds number of 1500 for both flames, there is an increase in the laminar burning speed, flame temperature and NO_x emission as well as a decrease in the CO emission. Also, as a result of the hydrogen addition and increased flame temperature, impingement heat transfer is enhanced. Comparison shows a more significant change in the laminar burning speed, temperature and CO/NO_x emissions in the CH₄ flames, indicating a stronger effect of hydrogen addition on a lighter hydrocarbon fuel. Comparison also shows that the CH₄ flame at α = 0% has even better heat transfer than the LPG flame at α = 50%, because the longer CH₄ flame configures a wider wall jet layer, which significantly increases the integrated heat transfer rate.     

Plasma-assisted CO2 reforming of methane over Ni-based catalysts: Promoting role of Ag and Sn secondary metals

Carbon dioxide (CO₂) and methane (CH₄) are the primary greenhouse gases (GHGs) that drive global climate change. CO₂ reforming of CH₄ or dry reforming of CH₄ (DRM) is used for the simultaneous conversion of CO₂ and CH₄ into syngas and higher hydrocarbons. In this study, DRM was investigated using Ag–Ni/Al₂O₃ packing and Sn–Ni/Al₂O₃ packing in a parallel plate dielectric barrier discharge (DBD) reactor. The performance of the DBD reactor was significantly enhanced when applying Ag–Ni/Al₂O₃ and Sn–Ni/Al₂O₃ due to the relatively high electrical conductivity of Ag and Sn as well as their anti-coke performances. Using Ag–Ni/Al₂O₃ consisting of 1.5 wt% Ag and 5 wt% Ni/Al₂O₃ as the catalyst in the DBD reactor, 19% CH₄ conversion, 21% CO₂ conversion, 60% H₂ selectivity, 81% CO selectivity, energy efficiency of 7.9% and 0.74% (by mole) coke formation were achieved. In addition, using Sn–Ni/Al₂O₃, consisting of 0.5 wt% Sn and 5 wt% Ni/Al₂O₃, 15% CH₄ conversion, 19% CO₂ conversion, 64% H₂ selectivity, 70% CO selectivity, energy efficiency of 6.0%, and 2.1% (by mole) coke formation were achieved. Sn enhanced the reactant conversions and energy efficiency, and resulted in a reduction in coke formation; these results are comparable to that achieved when using the noble metal Ag. The decrease in the formation of coke could be correlated to the increase in the CO selectivity of the catalyst. Good dispersion of the secondary metals on Ni was found to be an important factor for the observed increases in the catalyst surface area and catalytic activities. Furthermore, the stability of the catalytic reactions was investigated for 1800 min over the 0.5 wt% Ag-5 wt% Ni/Al₂O₃ and 0.5 wt% Sn-5 wt% Ni/Al₂O₃ catalysts. The results showed an increase in the reactant conversions with an increase in the reaction time.