Preparation of nickel catalysts supported on CaO.2Al2O3 for methane reforming with carbon dioxide

Nanocrystalline calcium aluminate (CaO.2Al₂O₃) was prepared by a simple co-precipitation method using Poly (ethylene glycol)-block-poly(propylene glycol)-block poly(ethylene glycol) (PEG-PPG-PEG, MW:5800) as surfactant and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), Temperature programmed reduction and oxidation (TPR-TPO) and Scanning electron microscopy (SEM) techniques. The results showed that the prepared support has a high potential as support for nickel catalysts in methane reforming with carbon dioxide. The results showed high catalytic activity and stability for the prepared catalysts. Among the prepared catalysts 15% Ni/CaO.2Al₂O₃ was the most active catalyst and showed the highest affinity for carbon formation. In addition, 7% Ni/CaO.2Al₂O₃ possessed high catalytic stability during 50 h time on stream. The TPO analysis revealed that increasing in nickel content increased the amount of deposited carbon over the spent catalysts. SEM results detected only whisker type of carbon for all spent catalysts.     

One-pot sol–gel synthesis of Ni/TiO2 catalysts for methane decomposition into COx free hydrogen and multiwalled carbon nanotubes

A series of mesoporous Ni/TiO₂ catalysts with different loadings of nickel from 10 to 50 wt% was successfully prepared via a facile one-pot sol–gel route; characterized for its structural, textural and redox properties; and tested for the non-oxidative thermocatalytic decomposition of undiluted methane for the first time. The characterization results reveal the presence of both NiO and NiTiO₃ and metallic nickel as active metal phase in the fresh and reduced catalysts, respectively. Spherical catalyst particles were found to be highly inter-aggregated and to provide a porous texture to the catalyst. All of the prepared catalysts exhibited high catalytic activity and stability for methane decomposition. It is due to the fine dispersion of active nickel nanoparticles on the surface of the TiO₂ support with proper metal-support interaction. Moreover, with increasing nickel loading and reaction temperature, the yields of hydrogen and nanocarbon were found to be significantly increased. A maximum hydrogen yield of 56% and a final carbon yield of 1544% were obtained for the 50% Ni/TiO₂ catalyst at 700 °C with an undiluted methane feed of 150 ml/min for 360 min of time on stream. The catalyst showed high catalyst stability, for a period of 960 min of time on stream and ～24% hydrogen yield was observed at the end of long-term run using the 50% Ni/TiO₂ catalyst. Moreover, irrespective of the nickel loading involved, bulk amount of multiwalled carbon nanotubes were deposited on the surface of the catalyst. XRD and Raman analyses of the spent catalysts showed that the crystallinity of nanocarbon increased with increasing nickel loadings, whereas the graphitization degree remained unaffected, with an I_D/I_G value of 0.88.     

Highly stable and active Ni-mesoporous alumina catalysts for dry reforming of methane

Nanostructured Ni-incorporated mesoporous alumina (MAl) materials with different Ni loading (7, 10 and 15 wt %) were prepared by a template assisted hydrothermal synthesis method and tested as catalysts for CO₂ reforming of methane under different conditions (nickel loading, gas hourly space velocity (GHSV), reaction temperature and time-on-stream (TOS)). The most active catalyst tested (Ni(10 wt%)-MAl) showed a very high stability over 200 h compared to a Ni(10 wt%)/γ-Al₂O₃ prepared using a co-precipitation method which had a significant loss in activity after only ∼4 h of testing. The high stability of the Ni-MAl materials prepared by the template assisted method was due to the Ni nanoparticles in these catalysts being highly stable towards migration/sintering under the reaction conditions used (800 °C, 52,000 mL h⁻¹ g⁻¹). The low susceptibility of the Ni nanoparticles in these catalysts to migration/sintering was most likely due to a strong Ni-support interaction and/or active metal particles being confined to the mesoporous channels of the support. The Ni-MAl catalysts also had significantly lower amounts of carbon deposited compared to the catalyst prepared using the co-precipitation method.     

Carbon nanofibers decorated SiC foam monoliths as the support of anti-sintering Ni catalyst for methane dry reforming

A silicon carbide (SiC) foam monolith decorated with a carbon nanofibers (CNFs) layer was employed as the catalyst support for Ni-based catalyst preparation, used for the CO₂ dry reforming of methane (DRM) reaction. The loading amount of CNFs on the SiC foam monolith was 6.6 wt.%, which obviously increased the surface area of the pristine SiC foam from 4 m²/g to 24 m²/g. The prepared CNFs layer strongly attached to the pristine SiC surface and was considerably stable even after 100 h time on stream (TOS) DRM reaction. The CNFs decorated SiC composite support provided more anchorage sites for improving the dispersion of the Ni particles and enhanced the metal-support interaction compared to the pristine SiC support. Compared with other catalysts such as Ni/SiC and Ni/CNFs, the Ni/CNFs-SiC catalyst exhibited not only the highest activity but also remarkable stability during DRM reaction. The XPS and SEM-EDS results showed that the carbon deposition over the nickel surface of Ni/CNFs-SiC catalyst was much less than those of Ni/SiC and Ni/CNFs catalysts. In addition, the XRD analysis verified that almost no sintering of nickel particle was detected over the Ni/CNFs-SiC catalyst, which was prepared with CNFs-SiC composite as catalyst support, even after 100 h TOS DRM reaction at 750 °C.     

Carbon dioxide reforming of methane over nickel catalysts supported on TiO2(001) nanosheets

As we all know, the critical problem of nickel catalysts for carbon dioxide reforming of methane is the deactivation of catalysts due to the carbon deposition and sintering of the active components under high temperature. It was reported that anatase TiO₂ nanosheets with high-energy (001) facets had strong interaction with nickel, which was probably beneficial to resist sintering of nickel nanoparticles and to eliminate deposited carbon via oxygen migration. In this study, Ni nanoparticles were supported on TiO2 nanosheets with exposed high-energy (001) facets. The Ni/TiO₂(001) catalysts were characterized by means of X-ray diffraction, transmission electron microscopy, physisorption of N₂, X-ray photoelectron spectroscopy and H₂ temperature-programmed reduction, and the spent catalysts were characterized by Roman and thermogravimetry analysis. The catalytic performance of Ni/TiO₂(001) catalysts were measured for carbon dioxide reforming of methane reaction. It was found that the prepared Ni/TiO₂(001) catalysts showed reasonably higher catalytic activity and stability compared with the nickel catalyst supported on commercial titanium oxide (P25). The high dispersion of nickel nanoparticles of Ni/TiO₂(001) catalysts was helpful to the resistance towards carbon deposition and the strong metal-support interaction was helpful to the resistance towards nickel sintering on account of the unusual surface properties of TiO₂(001).     

New performing hydroxyapatite-based catalysts in dry-reforming of methane

Dry reforming of methane (DRM) is a promising process for the production of synthetic gas from carbon dioxide and methane. However, the design of a performing catalyst for this reaction is still challenging since catalyst deactivation usually takes place, principally by thermal sintering at high temperatures (700–950 °C) and by carbon deposition. In this work, calcium hydroxyapatite (HAP) and HAP-doped magnesium (Mg_HAP) supported nickel catalysts were synthesized by wet precipitation method, characterized by various physico-chemical and thermal techniques, and evaluated in DRM reaction. Outstanding catalytic performance in DRM could be obtained with Ni/ HAP and Ni/Mg_HAP catalysts, thanks to a tunable acidity-basicity of these supports, a strong metal-support interaction, and a good thermal stability of nickel nanoparticles. H₂ and CO were the main products, with stable selectivity up to 85 ∓ 3%, while H₂O and solid carbon were byproducts with 5–10% of selectivity.     

Reforming of a model sulfur-free biogas on Ni catalysts supported on Mg(Al)O derived from hydrotalcite precursors: Effect of La and Rh addition

Ni catalysts supported on calcined Mg–Al hydrotalcite, Mg(Al)O, were prepared and the effect of the addition of La and/or Rh was tested in the performance of the catalysts in the dry reforming of methane with excess of methane in the feed, simulating a model sulfur-free biogas. The effect of adding synthetic air was assessed. The catalysts were characterized by surface area (BET), XRD, TPR and XPD. The results showed the reconstruction of the hydrotalcite structure during the Ni(NO₃) impregnation, with the segregation of the lanthanum. In the catalyst without Rh and La, Ni showed a strong interaction with the support Mg(Al)O, showing high reduction temperatures in TPR test. The addition of Rh and La increased the amount of reducible Ni species and facilitated the reduction of the species interacting strongly with the support which resulted in high rates of carbon deposition. The NiMgAl catalyst presented the strong Ni-support interactions and the best performance with low carbon deposition at both conditions of reaction. The NiMgAl catalyst did not present deactivation during 24 h of stability testing in the oxidative reforming of a model biogas.     

Methane cracking using Ni supported on porous and non-porous alumina catalysts

Porous and non-porous alumina catalysts were used as nickel supports to catalyze methane cracking. Different operating parameters were studied in a thermal gravimetric analyzer, including methane and hydrogen partial pressures, temperature and flow rate. During CH₄ cracking, carbon builds up on the catalyst surface and therefore the catalyst requires periodic regeneration. Cycling tests were performed, using air during the regeneration phase to burn off the carbon. The results showed that the non-porous catalyst performed better than the porous catalyst in terms of cracking during the first cycle. Full regeneration of the catalysts by oxidizing the deposited carbon was achieved at 550 °C, while oxidation was very slow at 500 °C. After full regeneration, the performance of the porous catalyst became considerably better than the non-porous. The porous catalyst kept its activity for 24 cracking/regeneration cycles, while the non-porous catalyst lost half of its activity by the second cracking cycle and almost all of its activity after six cycles. NiAl₂O₄ formation and Ni sintering caused the non-porous catalyst activity loss. TPO results showed that two carbon types were deposited on the catalysts, namely Cβ and Cγ, where Cβ is more active than Cγ.     

Synthesis of Ni@Al2O3 nanocomposite with superior activity and stability for hydrogen production from plastic-derived syngas by CO2-sorption-enhanced reforming

Catalytic dry (CO₂) reforming of plastic-derived syngas is a promising method of producing hydrogen-rich syngas and reducing greenhouse gases. The development of catalysts with high activity and stability is critical for this reaction. In this study, we fabricated core-shell structured Ni@Al₂O₃ catalysts with different shell thicknesses using advanced polyol and sol-gel methods. The effects of different Al/Ni ratios on the activity and stability of the catalysts in the CO₂ reforming reaction were investigated. The main challenge for CO₂ reforming of methane is carbon deposition. In the developed catalysts, the mesoporous Al₂O₃ coating outside the Ni core enhances the stability. However, the interaction between the core and the shell strongly affects the catalyst activity and product selectivity in the reaction. The catalyst with an Al/Ni ratio of 2 exhibited the highest methane conversion of up to 88% and the lowest carbon deposition, compared to the congeners with Al/Ni ratios of 1 and 3.     

Effect of Ca,Ce or K oxide addition on the activity of Ni/SiO2 catalysts for the methane decomposition reaction

To increase the activity and stability of Ni/SiO₂ catalysts, a series of Ni–Ca, Ni–K and Ni–Ce promoted catalysts were prepared by successive impregnations. The textural properties, reducibility and catalytic performance in the methane decomposition reaction were investigated. The catalyst containing 30 wt.% Ni and 30 wt.% cerium oxide greatly increased the conversion of methane (90% of equilibrium value) and improved the stability, whereas the Ni–K and Ni–Ca were less active and stable than the Ni/SiO₂ catalyst. The results suggest that Ce addition prevents the sintering of nickel particles during reduction process maintaining a random distribution between the silica and cerium oxide improving the distribution and migration of deposited carbon.     

Hydrogen production via the glycerol steam reforming reaction over nickel supported on alumina and lanthana-alumina catalysts

In the present work, a comparative study of Ni catalysts supported on commercially available alumina and lanthana-alumina carriers was undertaken for the glycerol steam reforming reaction (GSR). The supports and/or catalysts were characterized by PZC, BET, ICP, XRD, NH₃-TPD, CO₂-TPD, TPR and SEM. Carbon deposited on the catalytic surface was characterized by SEM, TPO and Raman. Concerning the Ni/LaAl sample it can be concluded that the presence of lanthana by: (a) facilitating the active species dispersion, (b) strengthening the interactions between nickel species and support, (c) increasing of the basic sites' population and redistributing the acid ones in terms of strength and density, provides a catalyst with improved performance for the GSR reaction, in terms of activity, H₂ production and long term stability. TPO and Raman indicate that the carbon on the Ni/LaAl catalyst was mostly amorphous and was deposited mainly on the support surface. For the Ni/Al catalyst, graphitic carbon was prevalent and likely covered its active sites.     

Ce promoting effect on the activity and coke formation of Ni catalysts supported on mesoporous nanocrystalline γ-Al2O3 in autothermal reforming of methane

In this study methane autothermal reforming (ATR) was investigated over Ni/Al₂O₃ and Ni/Al₂O₃–CeO₂ catalysts. The catalyst carriers were prepared through a facile one-step method, which produced mesoporous nanocrystalline carriers for Ni catalysts. The samples were characterized by XRD, TPR, BET, TPO and SEM characterization techniques and the catalytic activity and stability were also studied at different conditions (GHSV and feed ratio) in methane ATR. It was found that the nickel catalyst supported on 3 wt.% Ce–Al₂O₃ exhibited higher activity compared to the catalysts supported on the Al₂O₃ and promoted Al₂O₃ with 1 and 6 wt.% Ce. The results also showed that the nickel catalyst supported on 3 wt.% Ce–Al₂O₃ possessed the highest resistance against carbon deposition in ATR reaction.     

Nanocrystalline MgO supported nickel-based bimetallic catalysts for carbon dioxide reforming of methane

Nanocrystalline magnesium oxide with high surface area and plate-like shape was employed as catalyst support for preparation of nickel-based bimetallic catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), Temperature programmed oxidation and desorption (TPO–TPD), Thermal gravimetric and differential thermal gravimetric (TGA–DTG), H₂ chemisorption and Transmission and electron microscopies (TEM and SEM) analyses. CO₂–TPD data showed the high CO₂ adsorption capacity of catalysts which improves the resistance of catalysts against the carbon formation. The H₂ chemisorption results also indicated that the addition of Pt to nickel catalyst improved the nickel dispersion. The obtained results revealed that the prepared catalysts showed a high activity and stability during the reaction with a low amount of deposited carbon. Addition of Pt to nickel catalyst improved both the activity and resistivity against carbon formation.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over nickel catalysts supported on cationic surfactant-templated mesoporous aluminas

Two types of mesoporous γ-aluminas (denoted as A-A and A-S) are prepared by a hydrothermal method under different basic conditions using cationic surfactant (cetyltrimethylammonium bromide, CTAB) as a templating agent. A-A and A-S are synthesized in a medium of ammonia solution and sodium hydroxide solution, respectively. Ni/γ-Al₂O₃ catalysts (Ni/A-A and Ni/A-S) are then prepared by an impregnation method, and are applied to hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of a mesoporous γ-Al₂O₃ support on the catalytic performance of Ni/γ-Al₂O₃ is investigated. The identity of basic solution strongly affects the physical properties of the A-A and A-S supports. The high surface-area of the mesoporous γ-aluminas and the strong metal–support interaction of supported catalysts greatly enhance the dispersion of nickel species on the catalyst surface. The well-developed mesopores of the Ni/A-A and Ni/A-S catalysts prohibit the polymerization of carbon species on the catalyst surface during the reaction. In the steam reforming of LNG, both Ni/A-A and Ni/A-S catalysts give better catalytic performance than the nickel catalyst supported on commercial γ-Al₂O₃ (Ni/A-C). In addition, the Ni/A-A catalyst is superior to the Ni/A-S catalyst. The relatively strong metal–support interaction of Ni/A-A catalyst effectively suppresses the sintering of metallic nickel and the carbon deposition in the steam reforming of LNG. The large pores of the Ni/A-A catalyst also play an important role in enhancing internal mass transfer during the reaction.     

Synthesis gas production in the combined CO2 reforming with partial oxidation of methane over Ce-promoted Ni/SiO2 catalysts

A series of nickel-based catalyst supported on silica (Ni/SiO₂) with different loading of Ce/Ni (molar ratio ranging from 0.17 to 0.84) were prepared using conventional co-impregnation method and were applied to synthesis gas production in the combination of CO₂ reforming with partial oxidation of methane. Among the cerium-containing catalysts, the cerium-rich ones exhibited the higher activity and stability than the cerium-low ones. The temperature-programmed reduction (TPR) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) analysis revealed that the addition of CeO₂ reduced the chemical interaction between Ni and support, resulting in an increase in reducibility and dispersion of Ni. Over NiCe-x/SiO₂ (x = 0.17, 0.50, 0.67, 0.84) catalysts, the reduction peak in TPR profiles shifted to the higher temperature with increasing Ce/Ni molar ratio, which was attributed to the smaller metallic nickel size of the reduced catalysts. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) for the post-reaction catalysts confirmed that the promoter retained the metallic nickel species and prevented the metal particle growth at high reaction temperature. The NiCe-0.84/SiO₂ catalyst with small Ni particle size exhibited the stable activity with the constant H₂/CO molar ratio of 1.2 during 6-h reaction in the combination of CO₂ reforming with partial oxidation of methane at 850 °C and atmospheric pressure.     

Highly coke resistant Ni–Co/KCC-1 catalysts for dry reforming of methane

Nanofibrous KCC-1 supported Ni–Co bimetallic catalysts were investigated for dry reforming of methane for syngas generation. Monometallic catalysts such as Ni/KCC-1 and Co/KCC-1, and a series of bimetallic Ni–Co/KCC-1 catalysts were prepared by impregnation and co-impregnation method, respectively. All the catalysts were characterized by XRD, FT-IR, HR-SEM, FE-SEM, XPS, FT-Raman, BET, UV–Visible DRS and AAS techniques. Monometallic nickel supported catalyst contains NiO as an active phase, whereas bimetallic nickel catalysts contain Ni₂O₃, and NiCo₂O₄ on the surface. In the case of cobalt loaded catalysts, spinel Co₃O₄ is the dominant active species, apart from NiCo₂O₄. The addition of cobalt in Ni/KCC-1 has a pronounced effect on the crystallite size, surface area and active species. The hydrogen pretreatment of the catalyst produces bimetallic Ni–Co alloy on the surface. The catalytic activities of the bimetallic catalysts towards dry reforming of methane are better than monometallic catalysts. Mesoporous silica-based KCC-1 offers easy accessibility to the entire surface moieties due to its fibrous nature and the presence of channels, instead of pores. The 2.5%Ni-7.5%Co/KCC-1 showed the maximum CH₄ and CO₂ conversion along with a remarkably low H₂/CO ratio. The life-time test confirms the high thermal stability of the catalysts at 700 °C for 8 h, with less deactivation due to coke formation. The spent catalysts were characterized by XRD, TGA, FT-Raman, and FE-SEM to understand the structural and chemical changes during the reaction. The insignificant D band and G band of graphitic carbon in FT-Raman spectra for the highly active 2.5%Ni-7.5%Co/KCC-1 and 5%Ni–5%Co/KCC-1 catalysts along with TGA results containing 12% weight loss confirms the minimum coke deposition, formation of amorphous carbon and highest coke resistance. The fibrous support restricts the sintering and aggregation of nickel particles as well the deposition of coke. The addition of amphoteric cobalt increases the activity and stability of the catalysts. Ni–Co/KCC-1 with high coke resistance seems to be a promising catalyst for dry reforming of methane.     

Effect of hydroxyl and Mo doping on activity and carbon deposition resistance of hydroxyapatite supported NixMoy catalyst for syngas production via DRM reaction

The doping of the second metal Mo is expected to further enhance the carbon deposition resistance of Ni-based catalysts for syngas production via dry reforming of methane (DRM). In this study, the hydroxyapatite (HAP) was used as the support and a small Mo dosage was doped in the Ni-based catalysts to investigate the effect of intrinsic hydroxyl and Mo doping on the catalytic activity and carbon deposition resistance in DRM reaction. The catalyst characterization results show that both Ni and Mo are doped into the HAP structure with relatively uniform dispersion. The basic site strength of Ni4Mo0.2-HAP catalyst containing Mo is significantly higher than that of without Mo. The Mo dopant significantly improves the initial catalytic activity, but has minimal effect on the stability enhancement. Whether the catalyst is pre-reduced or not is crucial to the initial activity of the DRM reaction, the non-pre-reduced catalysts will go through a “self-activation” stage at the beginning of the reaction, where the “hydroxyl group” are proved to play as an “oxygen supply” for the partial oxidation of CH₄ or the oxidation of the carbon deposition in the initial stage. Only trace amount of carbon deposition is found after 100 h of DRM reaction on Ni3Mo0.2-HAP catalyst. The NiMo-HAP catalysts exhibit excellent initial activity and resistance to carbon deposition due to the synergistic effect of Ni–Mo alloy and hydroxyl groups in the hydroxyapatite support.     

Tri-reforming: A new biogas process for synthesis gas and hydrogen production

In this work biogas valorization – a renewable resource – for synthesis gas and hydrogen generation through dry reforming or tri-reforming (TR) is studied. Several Ni-based catalysts and a bimetallic Rh–Ni catalyst supported on magnesia or alumina modified with oxides like CeO₂ and ZrO₂ were used. For all the experiments, a synthetic biogas (molar composition: 60% CH₄ and 40% CO₂) was fed and the catalytic activities were measured in two different experimental facilities: a bench-scale fixed bed reactor system and a microreactor reaction system, at 1073 K and atmospheric pressure. Those catalysts which achieved high activity and stability in the fixed-bed reactor were impregnated in a microreactor to explore possible process intensification. For TR processes, different steam to carbon ratios, S/C, from 1.0 to 3.0, and O₂/CH₄ ratios of 0.25 and 0.50 were used. The high methane and carbon dioxide conversions reached in the fixed bed reactor were also achieved in the microreactor operating at much higher WHSV. In addition, process intensification improved catalysts stability. Physicochemical characterization of catalyst samples by ICP-OES, N₂ physisorption, H₂ chemisorption, TPR, SEM and XPS showed differences in chemical state, metal–support interactions, average crystallite sizes and redox properties of nickel and rhodium metal particles, indicating the importance of the morphological and surface properties of metal phases in driving the reforming activity.     

CO2 reforming of methane over Pt-Ni/Al2O3 catalysts: Effects of catalyst composition, and water and oxygen addition to the feed

A series of Pt-Ni bimetallic catalysts supported on δ-Al₂O₃ to be used in carbon dioxide reforming of methane was prepared and tested with the objective of optimizing the Ni/Pt metal composition to obtain high activity and stability. Selected catalyst samples, before and after reaction, were characterized by XRD, XPS, TGA/DTA and SEM-EDS. The activity results showed that the catalytic performance of bimetallic Pt-Ni samples strongly depended on the metal loadings and Ni/Pt loading ratio. Among all the catalysts, 0.3%Pt-10%Ni/Al₂O₃, which has the lowest Ni/Pt ratio, exhibited the highest catalytic activity and stability. The combined characterization and catalyst performance tests results reveal that low Ni/Pt molar loading ratio of 0.3%Pt-10%Ni/Al₂O₃ sample led to a relatively easy reduction of nickel oxide species and smaller nano-sized nickel particles having better dispersion caused by the intimate interaction between Pt and Ni sites in the closed vicinity. The changes in the catalysts’ activity and stability under the presence of an additional oxygen source were determined through addition of small amounts of either oxygen or water vapor to the feed stream. The results of the combined dry reforming and partial oxidation tests strongly indicated a change in surface reaction mechanism depending on the Pt load and Ni/Pt ratio of the catalysts. 0.3Pt-10Ni was capable of operating under a variety of feed conditions without significant deactivation suggesting that the catalyst is very promising for synthesis gas production for gas-to-liquid technology.