Search Results (26)

The potential of dry reforming methane (DRM) to convert two greenhouse gases concurrently is drawing interest from around the world. This research focused on developing supported nickel catalysts for the DRM, utilizing stabilized zirconia (SZ31107), which contains 5% SiO₂, as the support material. To promote the catalysts with a 5 wt.% Ni concentration, we used varying gallium loadings, specifically 0.1, 0.25, 0.5, 0.75, and 1 wt.%. After a detailed analysis, characterization was performed using X-ray diffraction, N₂-physorption, temperature-programmed reduction/desorption techniques, thermogravimetry, and Raman spectroscopy. The optimal DRM performance, achieved at 700 °C with a 1:1 CH₄:CO₂ feed, was recorded for the catalyst that has 0.25 wt.% Ga. The catalyst demonstrated remarkable average conversion rates of 56% for CH₄ and 66% for CO₂ after 300 min at 700 °C, with an H₂:CO ratio of 0.84. Activity was further enhanced by raising the temperature to 800 °C, which resulted in an 87% CO₂ conversion and an 80% CH₄ conversion. Studies on the catalyst’s long-term stability revealed a slow deactivation. With computed activation energies of 28,009 J/mol for CH₄ conversion and 21,875 J/mol for CO₂ conversion, temperature-programmed reaction tests conducted over the best catalyst demonstrated the DRM reaction’s endothermic character. Small additions of Ga encouraged the creation of more graphitic carbon structures, according to Raman spectroscopy of spent catalysts; the ideal catalyst had the lowest I_D/I_G ratio. These results suggest that the 5Ni+0.25Ga/SZ31107 catalyst is a promising candidate for large-scale syngas and hydrogen production. Full article

The aim of this work was to investigate the hydrocracking of algae oil derived from Spirulina Platensis species catalyzed with bi-component nickel-zirconia catalysts supported onto different carriers (BEA, ZSM-5 and Al₂O₃) in an autoclave at 320 °C for 2 h with a hydrogen pressure of 75 bar. All catalysts were prepared using the wet co-impregnation method and were characterized by H₂-TPR, XRD, NH₃-TPD, BET and SEM-EDS. Before reactions, catalysts were calcined at 600 °C for 4 h in a muffle furnace, then reduced with 5%H₂-95%Ar reducing mixture at 500 °C, 600 °C or 700 °C for 2 h. The obtained products were analyzed and identified by HPLC and GC-MS techniques. In addition to the investigation of the support effect, the influence of the reduction temperature of catalytic systems on the catalytic activity and selectivity of the products was also examined. The activity results show that Ni-Zr systems supported on zeolites exhibited high conversion of algal oil. A gradual decrease in conversion was observed when increasing the reduction temperature of the catalyst (from 500 °C to 600 °C and 700 °C) for BEA zeolite catalysts. The reaction products contain hydrocarbons from C₇ to C₃₃ (for zeolite-supported catalysts) and C₃₆ (for systems on Al₂O₃). The identified hydrocarbons mainly belong to the gasoil fraction (C₁₄–C₂₂). In the research, the best catalyst for the algal oil hydrocracking reaction was found to be the 5%Ni-5%Zr/BEA system reduced at 600 °C, which exhibited the second highest algal oil conversion (94.0%). The differences in catalytic activity that occur are due to the differences in the specific surface area among the supports and to differences in the acidity of the catalyst surface depending on the reduction temperature. Full article

Biomass valorization is an essential strategy for converting organic resources into valuable energy and chemicals, contributing to the circular economy, and reducing carbon footprints. Glycerol, a byproduct of biodiesel production, can be used as a feedstock for a variety of high-value products and can contribute to reducing the carbon footprint. This study examines the impact of surface-level modifications of Mg, Cu, and Sn on Ni-Ce-Zr catalysts for the hydrogenolysis of glycerol, with in situ generated hydrogen. The aim of this approach is to enhance the efficiency and sustainability of the biomass valorization process. However, the surface modification resulted in a decrease in the global conversion of glycerol due to the reduced availability of metal sites. The study found that valuable products, such as H₂ and CH₄ in the gas phase, and 1,2-PG in the liquid phase, were obtained. The majority of the liquid fraction was observed, particularly for Cu- and Sn-doped catalysts, which was attributed to their increased acidity. The primary selectivity was towards the cleavage of the C–O bond. Post-reaction characterizations revealed that the primary causes of deactivation was leaching, which was reduced by the inclusion of Cu and Sn. These findings demonstrate the potential of Cu- and Sn-modified Ni-Ce-Zr catalysts to provide a sustainable pathway for converting glycerol into value-added chemicals. Full article

This paper is devoted to the study of active and stable nickel catalysts for methane dry reforming based on Pr-doped ceria–zirconia obtained via the solvothermal continuous method. Studies on the physicochemical and catalytic properties of the 5%Ni/Ce_0.75Zr_0.25−xPr_xO₂ series have showed that Pr introduction leads to an increase in the amount of highly reactive oxygen in the oxide lattice. Praseodymium-based catalysts showed significantly higher reactant conversions. In addition to the nature of support, the method of nickel introduction was also studied; Ni was added both using impregnation and the one-pot procedure with mixed oxide preparation. The method of Ni addition was shown to have significant effect on the morphology of its particles and Ni-support interaction, and, respectively, on catalytic activity and coking stability. The 5%Ni/Ce_0.75Zr_0.15Pr_0.1O₂ catalyst prepared by one-pot method showed stable operation in the MDR reaction for 30 h at CO₂ and CH₄ conversions of ~40% and an H₂ yield of ~18% (T = 700 °C, τ = 10 ms). Full article

The utilization of heterogeneous catalysts during the production of biodiesel potentially minimize the cost of processing due to the exclusion of the separation step. The (X wt%)Ni–ZrO₂ (where X = 10, 25 and 50) catalysts prepared through a hydrothermal process were tested for the production of biodiesel by the transesterification of waste cooking oil (WCO) with methanol. The influences of various reaction parameters were systematically optimized. While the physicochemical characteristics of the as-synthesized catalysts were examined using numerous techniques such as FTIR, XRD, TGA BET, EDX, SEM, and HRTEM. Among all the catalysts, (10 wt%)Ni–ZrO₂ exhibited high surface area when compared to the pristine ZrO₂, (25 wt%)Ni–ZrO₂ and (50 wt%)Ni–ZrO₂ nanocatalysts. It may have influenced the catalytic properties of (10 wt%)Ni–ZrO_2, which exhibited maximum catalytic activity with a biodiesel production yield of 90.5% under optimal conditions. Such as 15:1 methanol to oil molar ratio, 10 wt% catalysts to oil ratio, 8 h reaction time and 180 °C reaction temperature. Furthermore, the recovered catalyst was efficiently reused in several repeated experiments, demonstrating marginal loss in its activity after multiple cycles (five times). Full article

Renewed interest in CO₂ methanation is due to its role within the framework of the Power-to-Methane processes. While the use of nickel-based catalysts for CO₂ methanation is well stablished, the support is being subjected to thorough research due to its complex effects. The objective of this work was the study of the influence of the support with a series of catalysts supported on alumina, ceria, ceria–zirconia, and titania. Catalysts’ performance has been kinetically and spectroscopically evaluated over a wide range of temperatures (150–500 °C). The main results have shown remarkable differences among the catalysts as concerns Ni dispersion, metallic precursor reducibility, basic properties, and catalytic activity. Operando infrared spectroscopy measurements have evidenced the presence of almost the same type of adsorbed species during the course of the reaction, but with different relative intensities. The results indicate that using as support of Ni a reducible metal oxide that is capable of developing the basicity associated with medium-strength basic sites and a suitable balance between metallic sites and centers linked to the support leads to high CO₂ methanation activity. In addition, the results obtained by operando FTIR spectroscopy suggest that CO₂ methanation follows the formate pathway over the catalysts under consideration. Full article

The rhodium oxide (Rh₂O₃) doping effect on the activity and stability of nickel catalysts supported over yttria-stabilized zirconia was examined in dry reforming of methane (DRM) by using a tubular reactor, operated at 800 °C. The catalysts were characterized by using several techniques including nitrogen physisorption, X-ray diffraction, transmission electron microscopy, H₂-temperature programmed reduction, CO₂-temperature programmed Desorption, and temperature gravimetric analysis (TGA). The morphology of Ni-YZr was not affected by the addition of Rh₂O₃. However, it facilitated the activation of the catalysts and reduced the catalyst’s surface basicity. The addition of 4.0 wt.% Rh₂O₃ gave the optimum conversions of CH₄ and CO₂ of ~89% and ~92%, respectively. Furthermore, the incorporation of Rh₂O₃, in the range of 0.0–4.0 wt.% loading, enhanced DRM and decreased the impact of reverse water gas shift, as inferred by the thermodynamics analysis. TGA revealed that the addition of Rh₂O₃ diminished the carbon formation on the spent catalysts, and hence, boosted the stability, owing to the potential of rhodium for carbon oxidation through gasification reactions. The 4.0 wt.% Rh₂O₃ loading gave a 12.5% weight loss of carbon. The TEM images displayed filamentous carbon, confirming the TGA results. Full article

In the present work, the catalytic behavior of nickel-based catalysts supported on ceria/zirconia, undoped and doped with lanthanum and neodymium (3.5Ni/Ce_0.8La_0.5Nd_0.2Zr_0.13O_2−x), was investigated under different reactions: steam reforming, partial oxidation and autothermal reforming of different fuels (methane, biogas, and propane). The catalytic properties of these catalysts were evaluated at a temperature of 800 °C, under atmospheric pressure, at GSHV = 120,000 h⁻¹, using steam/carbon and oxygen/carbon ratio, respectively, of S/C = 2.5 and O/C = 0.5 and, in the case of autothermal conditions, with the addition of H₂S (100 ppm) as a contaminant. Depending on the tested fuel, ATR, SR, and POX reactions over doped and undoped catalysts showed different results. In particular, the doped catalyst, due to neodymium and lanthanum doping, better distributed nickel species on the catalyst surface, promoting a higher concentration of defect groups and oxygen vacancies. This resulted in improved catalytic performance and resistance to deactivation. Endurance catalytic test also confirmed the beneficial effect of the doped catalysts. Full article

Graphene-encapsulated nickel nanoclusters are a feasible strategy to inhibit the nickel deactivation of nickel-based catalysts. In this work, graphene-encapsulated catalysts (Ni@C/HZSM-5) were prepared by a compression forming process, using pseudo-boehmite, Al₂O₃, and ZrO₂ as binders. The pseudo-boehmite was gradually transformed from amorphous to crystalline alumina at high temperatures, which destroyed the nucleation of Ni@C. In contrast, the crystal-stabilized zirconia was more favorable for the nucleation of Ni@C. The extensive dispersion of alumina on the surface of HZSM-5 covers the acid sites of HZSM-5. In contrast, when zirconia was used as the binder, the binder existed in the form of the direct aggregation of ~100 nm zirconia spheres; this distribution form reduced better the damage of the binder to the acid site of the catalyst. Furthermore, the particle size of Ni crystals in the graphene-encapsulated catalysts decreased significantly (mostly <11 nm), and no evident agglomeration of nickel particles appeared. It was found that the stabilization of the metal interface delayed, to an extent, the accumulation rate of carbon deposits and, thus, postponed the deactivation of the acid sites. After 8 h of continuous reaction, the conversion of the traditional catalyst Ni/Z5+Zr dropped significantly to 60%. In contrast, the conversion of Ni@C catalysts prepared with ZrO₂ remained above 90%. The regeneration test shows that air roasting could effectively remove carbon deposits and restore the catalyst activity. Full article

Dry reforming of methane was studied over high-ratio zirconia in ceria-zirconia-mixed oxide-supported Ni catalysts. The catalyst was synthesized using co-precipitation and impregnation methods. The effects of the catalyst support and Ni composition on the physicochemical characteristics and performance of the catalysts were investigated. Characterization of the physicochemical properties was conducted using X-ray diffraction (XRD), N₂-physisorption, H₂-TPR, and CO₂-TPD. The results of the activity and stability evaluations of the synthesized catalysts over a period of 240 min at a temperature of 700 °C, atmospheric pressure, and WHSV of 60,000 mL g⁻¹ h⁻¹ showed that the 10%Ni/CeZrO₂ catalyst exhibited the highest catalytic performance, with conversions of CH₄ and CO₂ up to 74% and 55%, respectively, being reached. The H₂/CO ratio in the product was 1.4, which is higher than the stoichiometric ratio of 1, indicating a higher formation of H₂. The spent catalysts showed minimal carbon deposition based on the thermo-gravimetry analysis, which was <0.01 gC/gcat, so carbon deposition could be neglected. Full article

The formation of tars during coal or biomass gasification is a serious issue resulting in decreasing efficiency of the process and increased maintenance costs. The decomposition of tars can be conducted via catalytic steam reforming that enriches the produced gas in hydrogen. Nevertheless, the catalyst should be characterized by high activity, stability, and resistance towards carbon deposition. Ceria-zirconia supported nickel (Ni/CeZrO₂) is a very good candidate to catalyze tar removal—Ni is an active phase for reforming reactions, while CeZrO₂ provides the active sites that play important roles in protecting the catalyst from carbon deposition. Ni/CeZrO₂ shows high activity in the steam reforming of model tar compounds. In this paper, its performance in the steam reforming of toluene and carbon deposition is discussed considering the changing parameters of the reaction: the temperature, steam to carbon ratio, and the contact time. Full article

Zirconia has advantageous thermal stability and acid–base properties. The acidity character of ZrO₂ can be enhanced through the sulfation process forming sulfated zirconia (ZrO₂-SO₄). An acidity test of the catalyst produced proved that the sulfate loading succeeded in increasing the acidity of ZrO₂ as confirmed by the presence of characteristic absorptions of the sulfate group from the FTIR spectra of the catalyst. The ZrO₂-SO₄ catalyst can be further modified with transition metals, such as Platinum (Pt), Chromium (Cr), and Nickel (Ni) to increase catalytic activity and catalyst stability. It was observed that variations in the concentrations of Pt, Cr, and Ni produced a strong influence on the catalytic activity as the acidity and porosity of the catalyst increased with their addition. The activity, selectivity, and catalytic stability tests of Pt/ZrO₂-SO₄, Cr/ZrO₂-SO₄ and Ni/ZrO₂-SO₄ were carried out with their application in the hydrocracking reaction to produce liquid fuel. The percentage of liquid fractions produced using these catalysts were higher than the fraction produced using pure ZrO₂ and ZrO₂-SO₄ catalyst. Full article

Catalytic conversion of CO₂ to CO using reverse water gas shift (RWGS) reaction is a key intermediate step for many CO₂ utilization processes. RWGS followed by well-known synthesis gas conversion may emerge as a potential approach to convert CO₂ to valuable chemicals and fuels. Nickel (Ni) based catalysts with ceria-zirconia (Ce-Zr) support can be used to tune the metal-support interactions, resulting in a potentially enhanced CO₂ hydrogenation rate and elongation of the catalyst lifespan. The thermodynamics of RWGS reaction is favored at high temperature for CO₂ conversion. In this paper the effect of Palladium (Pd) and Iridium (Ir) as promoters in the activity of 10 wt%Ni 2 wt%Pd 0.1wt%Ir/CeZrO₂ catalyst for the reverse water gas shift reaction was investigated. RWGS was studied for different feed (CO₂:H₂) ratios. The new active interface between Ni, Pd and Ir particles is proposed to be an important factor in enhancing catalytic activity. 10 wt%Ni 2 wt%Pd 0.1 wt%Ir/CeZrO₂ catalyst showed a better activity with CO₂ conversion of 52.4% and a CO selectivity of 98% for H₂:CO₂ (1:1) compared to the activity of 10%Ni/CeZrO₂ with CO₂ conversion of 49.9% and a CO selectivity of 93%. The catalytic activity for different feed ratios using 10 wt%Ni 2 wt%Pd 0.1 wt%Ir/CeZrO₂ were also studied. The use of palladium and iridium boosts the stability and life span of the Ni-based catalysts. This indicates that the catalyst could be used potentially to design RWGS reactors for CO₂ utilization units. Full article

Development of a transition metal based catalyst aiming at concomitant high activity and stability attributed to distinguished catalytic characteristics is considered as the bottleneck for dry reforming of methane (DRM). This work highlights the role of modifying zirconia (ZrO₂) and alumina (Al₂O₃) supported nickel based catalysts using lanthanum oxide (La₂O₃) varying from 0 to 20 wt% during dry reforming of methane. The mesoporous catalysts with improved BET surface areas, improved dispersion, relatively lower reduction temperatures and enhanced surface basicity are identified after La₂O₃ doping. These factors have influenced the catalytic activity and higher hydrogen yields are found for La₂O₃ modified catalysts as compared to base catalysts (5 wt% Ni-ZrO₂ and 5 wt% Ni-Al₂O₃). Post-reaction characterizations such as TGA have showed less coke formation over La₂O₃ modified samples. Raman spectra indicates decreased graphitization for La₂O₃ catalysts. The 5Ni-10La₂O₃-ZrO₂ catalyst produced 80% hydrogen yields, 25% more than that of 5Ni-ZrO₂. 5Ni-15La₂O₃-Al₂O₃ gave 84% hydrogen yields, 8% higher than that of 5Ni-Al₂O₃. Higher CO₂ activity improved the surface carbon oxidation rate. From the study, the extent of La₂O₃ loading is dependent on the type of oxide support. Full article

To achieve a high activity and coking stability of nickel catalysts in dry reforming of methane, materials comprised of ceria–zirconia doped by Ti were investigated as supports. Ceria–zirconia supports doped with titanium were prepared either via the Pechini method or by synthesis in supercritical alcohol media. Ni-containing catalysts were prepared by two techniques: standard incipient wetness impregnation and one-pot synthesis. The catalytic reaction of DRM to synthesis gas was carried out in the 600–750 °C range over 5% wt. Ni/Ce(Ti)ZrO₂. Dried and calcined supports and catalysts were characterized by physicochemical methods including N₂ adsorption, XRD, Raman, H₂-TPR, and HRTEM. Both preparation methods led to formation of solid solution with cubic fluorite-like structure, as well as after addition of Ti. Introduction of Ti should provide improved oxygen storage capacity and mobility of support oxygen. The highest activity was observed with the catalyst of 5% wt. Ni/Ce_0.75Ti_0.2Zr_0.05O_2−δ composition due to optimized oxide support structure and support oxygen mobility. Full article