Steam reforming of n-dodecane over mesoporous alumina supported nickel catalysts: Effects of metal-support interaction on nickel catalysts

Developing a highly active and stable Ni-based catalyst is still a challenge for the generation of on-site hydrogen through steam reforming of long-chained hydrocarbons, such as kerosene fuels. Ni nanoparticles (ca. 5 nm) on mesoporous alumina prepared by atomic layer deposition (ALD) were employed in steam reforming of n-dodecane, and exhibited a turnover frequency (TOF) of 477.6 h⁻¹, whereas Ni nanoparticles on commercial alumina support prepared by impregnation method exhibited a TOF of 100 h⁻¹. The high activity of ALD Ni catalysts was ascribed to high reduction degree, as confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and H₂-chemisorption. A deactivation was also observed on the ALD prepared catalysts, which was ascribed to the weak metal-support interaction, as confirmed by H₂ temperature-programmed reduction (TPR). The ALD Ni/Al₂O₃ catalysts were further modified with CeO₂ and they showed enhanced stability with 8% deactivation degree in steam reforming of n-dodecane. Further characterizations of spent catalysts showed that the presence of CeO₂ was favorable for stabilizing Ni nanoparticles by enhancing moderate metal-support interaction, and reducing the formation of coke on the interfaces of NiCeO₂.     

Efficient H2 production by photocatalytic water splitting under UV or solar light over variously modified TiO2-based catalysts

This paper focused for the first time on the comparison between three different approach to modify the chemico-physical properties of TiO₂-based photocatalysts and their effect in the H₂ production by photocatalytic water splitting both under UV and solar light irradiation, under the same experimental conditions. The application of pulsed laser irradiation to aqueous TiO₂ suspensions (first approach) induced structural transformations both on the bulk and on the surface of TiO₂, boosting the H₂ production, under UV light irradiation, of almost three times (20.9 mmol/g_cat·h) compared to bare TiO₂ (7.7 mmol/g_cat·h). The second strategy was based on a templating method to obtain TiO₂ with a macroporous structure to favour an efficient light absorption process inside the material pores, thus allowing a high H₂ production (0.64 mmol/g_cat·h) under solar light irradiation. This performance was further enhanced when the macroporous TiO₂ was coupled with CeO₂ or W (third approach). In the latter case the H₂ production increased to 0.72 mmol/g_cat·h for macroporous TiO₂CeO₂ and to 0.82 mmol/g_cat·h for macroporous TiO₂W. This work highlights how it is possible to tune the TiO₂ photocatalytic properties with easy and green procedures to obtain environmental friendly catalyst for hydrogen production.     

Steam reforming of acetic acid for hydrogenproduction: Catalytic performances of Ni and Co supported on Ce0·75Zr0·25O2 catalysts

The catalytic steam reforming of acetic acid over both Ni/ and Co/Ce_0·75Zr_0·25O₂ (CZO) catalysts in the temperature range of 450–650 °C and steam-to-carbon molar ratios of 3–9 was studied. It was found that the complete acetic acid conversion was achieved for all the conditions investigated. Nevertheless, the C–C bond cleavage conversion was attained less than the acetic acid conversion at a given condition due to carbon deposition on the catalyst. However, hydrogen yield was obtained in the same trend as C–C bond cleavage conversion as well. The results revealed that the CZO as an active support prefers to promote the ketonization reaction to the C-C bond cleavage reaction at a lower temperature, and vice versa at a higher temperature. The Ni/CZO catalyst exhibits higher C–C bond cleavage conversion than the Co/CZO catalyst particularly at 650 °C whereas the Co/CZO catalyst is more active for ketonization reaction at low temperatures. However, as an increase in reaction temperature, the Co/CZO catalyst promotes ketonization reaction more pronouncedly toward aldol-condensation reaction thus giving rise to the carbon deposition. The results deduced from the effect of space velocity on the activity and product distribution suggested that the steam reforming of acetic acid over Ni/CZO catalyst is dominated by decomposition of acetic acid, while that of Co/CZO catalyst by ketonization reaction.     

Synthesis, sintering and electrical properties of gadolinia- calcia-doped ceria

Crystalline gadolinia and calcia co-doped ceria powders, with Ce_0.85Gd_0.15-xCa_xO_2-δ composition, with x = 0.01, 0.015, 0.02 have been prepared by a co-precipitation procedure from the corresponding nitrates of component cations. Nanopowders were obtained after thermal treatment of the co-precipitated mixtures at 700 °C for 2 h. Isostatically pressed pellets were prepared from the powder. Isothermal sintering was carried out between 1300º and 1400 °C. Apparent densities as high as 98% of the theoretical one, D_th, were attained after sintering at 1300 °C 4h. Microstructure of the ceramics was observed by Scanning Electron Microscopy (SEM). Bulk and grain boundary conductivities, determined by Complex Impedance Spectroscopy, have similar values, and the total conductivity attains good values compatible with the use as electrolyte in SOFC.     

Nickel-catalyzed autothermal reforming of jet fuel surrogates: n-Dodecane,tetralin, and their mixture

The potential of a nickel-ceria-zirconia based catalyst was examined for autothermal reforming of n-dodecane, tetralin and their mixture into a hydrogen-rich product stream suitable for high-temperature fuel cells. n-Dodecane and tetralin were chosen as representative compounds for alkanes and bicyclic compounds in jet fuel. It was possible to reach conversions greater than 90% for both components, as long as sufficiently high oxygen concentrations were maintained in the feed. Tetralin gave larger yields of reforming products than n-dodecane. During the transient start-up phase of the reactor, large temperature excursions were observed, suggesting that the reaction starts with complete combustion of fuel, giving way to autothermal reforming after a few minutes on stream. These high-temperature excursions during reactor start-up are large enough to change the catalyst surface areas. Interestingly, the mixture of tetralin and n-dodecane did not behave as a linear combination of the two pure components, but showed reforming characteristics similar to pure tetralin. The non-linear behavior of the mixture provides a caveat that investigations of single component model compounds may not be able to capture the reforming behavior of more complex fuel mixtures.     

Effect of water of crystallization on synthesis of nanocrystalline ceria by non-hydrolytic method

Nanocrystalline ceria has been synthesized by a non-hydrolytic method using organic solvent and precipitant. The effect of the source compound on final nanocrystalline powder was investigated. The cerium nitrate hexahydrate subjected to different vacuum/thermal treatments to get cerium source compound having different extent of water of crystallization. The nanoceria, synthesized from these compounds was characterized by TGA-MS, XRD, HR-TEM and AFM.     

Fuel-rich catalytic combustion of methane in zero emissions power generation processes

A novel catalytic combustion concept for zero emissions power generation has been investigated. Catalysts consisting of Rh supported on ZrO₂, Ce-ZrO₂ or -Al₂O₃ were prepared and tested under fuel-rich conditions, i.e. for catalytic partial oxidation (CPO) of methane. The experiments were performed in a subscale gas-turbine reactor operating at 5 bar with exhaust gas-diluted feed mixtures.

The catalyst support material was found to influence the light-off temperature significantly, which increased in the following order Rh/Ce-ZrO₂ < Rh/ZrO₂ < Rh/-Al₂O₃. The Rh loading, however, only had a minor influence. The high activity of Rh/Ce-ZrO₂ is probably related to the high dispersion of Rh on Ce-ZrO₂ and the high oxygen mobility of this support compared to pure ZrO₂. The formation of hydrogen was also found to increase over the catalyst containing ceria in the support material.     

Steady-state isotopic transient kinetic analysis of steam reforming of methanol over Cu-based catalysts

Mechanistic aspects of steam reforming of methanol were studied via steady-state isotopic transient kinetic analysis over three copper-based catalysts, namely combustion-synthesized Cu-Ce-O and Cu-Mn-O, and commercial Cu-ZnO-Al₂O₃. The “C-path” and “O-path” for the production of CO₂ via steam reforming of methanol was analysed with the following step changes in the feed: ¹²CH₃OH/H₂O/Ar/He → ¹³CH₃OH/H₂O/He and CH₃OH/H₂¹⁶O/Ar/He → CH₃OH/H₂¹⁶O/H₂¹⁸O/He. The presence of CH₃¹⁸OH in the products after the switch to ¹⁸O-labeled water indicates that a major path of the reaction is the one involving a methyl formate intermediate. This appears to be the main path over the Cu-Mn-O catalyst, while parallel paths via dioxomethylene and methyl formate intermediates appear to be operative over Cu-Ce-O and Cu-ZnO-Al₂O₃ catalysts.