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    A. J. Vizcaíno currently works at the Chemical and Energetic Technology, King Juan Carlos University. A. does research in Catalysis, Materials Chemistry and Surface Chemistry. Their most recent publication is 'Production of Renewable Hydrogen from Glycerol Steam Reforming over Bimetallic Ni-(Cu,Co,Cr) Catalysts Supported on SBA-15 Silica.'
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    Glycerol steam reforming (GSR) is a promising alternative to obtain renewable hydrogen and help the economics of the biodiesel industry. Nickel-based catalysts are typically used in reforming reactions. However, the choice of the catalyst greatly influences the process, so the development of bimetallic catalysts is a research topic of relevant interest. In this work, the effect of adding Cu, Co, and Cr to the formulation of Ni/SBA-15 catalysts for hydrogen production by GSR has been studied, looking for an enhancement of its catalytic performance. Bimetallic Ni-M/SBA-15 (M: Co, Cu, Cr) samples were prepared by incipient wetness co-impregnation to reach 15 wt % of Ni and 4 wt % of the second metal. Catalysts were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), N2-physisorption, X-ray powder diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analyses (TGA), and tested in GSR at 600 °C and atmospheric pressure. The addition of Cu, Co, and Cr to the Ni/SBA-15 catalyst helped to form smaller crystallites of the Ni phase, this effect being more pronounced in the case of the Ni-Cr/SBA-15 sample. This catalyst also showed a reduction profile shifted towards higher temperatures, indicating stronger metal-support interaction. As a consequence, the Ni-Cr/SBA-15 catalyst exhibited the best performance in GSR in terms of glycerol conversion and hydrogen production. Additionally, Ni-Cr/SBA-15 achieved a drastic reduction in coke formation compared to the Ni/SBA-15 material.
    The steam reforming of glycerol has been studied at 500 and 600 ºC using Co/SBA-15 and Co/M/SBA-15 (M: Zr, Ce, or La) promoted catalysts. The prepared materials were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray powder diffraction (XRD), hydrogen temperature-programed reduction (H2-TPR), ammonia temperature-programed desorption (NH3-TPD), nitrogen physisorption analysis (N2-BET), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The incorporation of promoters like Zr, Ce and La on SBA-15 support and successive Co impregnation leaded to smaller cobalt crystallites improving metaldispersion. Besides, stronger metal-support interactions between Co species and M/SBA-15 supports were observed. Thanks to the incorporation of Zr, La and mainly Ce, promoted catalysts present higher glycerol conversion than Co/SBA-15 along 5 h of time on stream. Besides, at 600 ºC, Co/M/SBA-15 (M: Zr, Ce, or La) catalysts produce higher hydrogen amounts than Co/SBA-15.
    Cobalt catalysts supported on SBA-15 and modified by Mg and Ca incorporation were tested in the steam reforming of ethanol as a novel application and compared to analogous nickel catalysts. The prepared materials were characterized by N2 physisorption, ICP-AES, XDR, H2-TPR and TGA. Tests on ethanol steam reforming were performed at 600 and 700 °C, using high space velocity. Incorporation of both Mg and Ca promotes the metal dispersion and the interaction between metallic species and the modified SBA-15 support, but this effect is significantly more pronounced in the case of the Co catalysts. As a consequence, Mg- and Ca-promoted Co samples needed higher temperatures to be reduced and were not able to maintain enough active Co0 species under reaction conditions to convert C2 intermediate compounds. Thus, these modified Co catalysts lead to lower ethanol conversion and hydrogen selectivity than a Co/SBA-15 catalyst. Meanwhile, Mg- and Ca-promoted Ni catalysts have intermediate reduction temperatures and achieve higher hydrogen production than a Ni/SBA-15 sample at 700 °C. In this sense, the best catalytic results were obtained with the Ni/Ca/SBA-15 catalyst (complete ethanol conversion and 90.8 mol% of hydrogen selectivity), which was stable for 50 h. Coke formation is also diminished by Ca and Mg addition, but while for Co catalysts this effect is more evident using Mg, in the case of Ni samples, the highest coke formation reduction is achieved by Ca addition. Again, the Ni/Ca/SBA-15 sample obtained the lowest carbon deposition, despite the general tendency of Co samples to form less coke.
    A series of Ni/Ce x Zr 1−x O 2 /SiO 2 catalysts with different Zr/Ce mass ratios were prepared by incipient wetness impregnation. Ni/SiO 2 , Ni/CeO 2 and Ni/ZrO 2 were also prepared as reference materials to compare. Catalysts' performances were tested in ethanol steam reforming for hydrogen production and characterized by XRD, H 2 -temperature programmed reduction (TPR), NH 3 -temperature programmed desorption (TPD), TEM, ICP-AES and N 2 -sorption measurements. The Ni/SiO 2 catalyst led to a higher hydrogen selectivity than Ni/CeO 2 and Ni/ZrO 2 , but it could not maintain complete ethanol conversion due to deactivation. The incorporation of Ce or Zr prior to Ni on the silica support resulted in catalysts with better performance for steam reforming, keeping complete ethanol conversion over time. When both Zr and Ce were incorporated into the catalyst, Ce x Zr 1−x O 2 solid solution was formed, as confirmed by XRD analyses. TPR results revealed stronger Ni-support interaction in the Ce x Zr 1−x O 2 -modified catalysts than in Ni/SiO 2 one, which can be attributed to an increase of the dispersion of Ni species. All of the Ni/Ce x Zr 1−x O 2 /SiO 2 catalysts exhibited good catalytic activity and stability after 8 h of time on stream at 600 • C . The best catalytic performance in terms of hydrogen selectivity was achieved when the Zr/Ce mass ratio was three.
    Mg- and Ca-modified Ni/SBA-15 catalysts were prepared by incipient wetness impregnation (7 wt% Ni) to be studied for catalytic glycerol steam reforming at 600 °C. High space velocities were selected in order to highlight differences in activity between catalysts and deactivation effects at relatively short time. Characterization of the calcined, reduced and used samples was carried out by XRD, ICP-AES, N2-physisorption, TGA, H2-TPR, TEM and HCNS elemental analysis. XRD and TEM demonstrated dispersing effect of Mg and Ca on the Ni phase, while TPR evidenced strengthening of the Ni-support interaction by Mg and Ca incorporation to the Ni/SBA-15 catalyst. These effects were significantly noticeable in the Ni/Ca/SBA-15 sample. As a consequence, the Ni/Ca/SBA-15 catalyst achieved the highest glycerol conversion (98.4%) and yield to gases formation (69.9 wt%) with a hydrogen content of 53 vol%. Additionally, this catalyst was stable with time on stream under glycerol steam reforming and showed the lowest coke deposition. This was ascribed to the formation of highly defective carbon deposits, easier to be gasified under reaction conditions, mainly in the form of non-encapsulating carbon nanofibres formed on the small and strongly-supported Ni particles.
    Ni catalysts based on ternary mixed oxides, NiMAl (M = Mg, Ca, Zn) and NiMgN (N = La, Ce) were prepared by the coprecipitation method and characterized by N2-sorption measurements, TGA, XRF, XRD, H2-TPR and TEM. NiMAl (M = Mg, Ca, Zn) catalyst precursors exhibited a layered double hydroxide (LDH) structure, not observed in NiMgN (N = La, Ce) samples.NiMgAl mixed oxide exhibited well-stabilized nickel species needing high temperatures to be reduced (around 1100 K). The extent of Ni2+ reduction in the mixed oxides was improved with the replacement of Mg by Ca and Zn or Al by La and Ce. Catalysts were very active and selective in ethanol steam reforming although NiMgN (N = La, Ce) samples deactivate faster than NiMAl (M = Mg, Ca, Zn) having smaller Ni crystallites. In particular, the presence of Ca produced an important dispersing effect over the Ni species, favouring hydrogen production while keeping moderate coke formation. In the case of the reduced NiCaAl mixed oxide H2 selectivity values above 87 mol % were reached.
    The world primary energy demand, currently dominated by fossil fuels in more than 80 %, is projected to expand by 45% from 2006 to 2030, so that global carbon dioxide emissions will increase by 1.8% per year, which would result in critical environmental problems all over the world. The use of hydrogen as a sustainable energy vector is an interesting and promising challenge. Hydrogen can be renewably produced in several ways and its utilization to obtain energy generates just water and no pollutant emission. In this Chapter, the current and future hydrogen production processes are described to focus in one of the most promising ones from the point of view of sustainability: bioethanol steam reforming. Ethanol is a good candidate as a hydrogen feedstock since it can be easily produced from several biomass sources (sugar and starchy crops, agricultural residues, wood and municipal solid wastes). Although bioethanol can be directly used as a fuel, the implementation of fuel cell systems where hydrogen can silently be converted to electricity, without the excessive thermal energy loss and the limit of the thermodynamic yield of the Carnot cycle observed in combustion engines, turns the use of bioethanol to produce hydrogen into a competent alternative. Besides, bioethanol steam reforming is a cost-effective and an efficient process which consists of a complex network of reactions generating hydrogen and several by-products. The use of an appropriate catalyst may favour reaction pathways that minimize the formation of undesirable compounds, enhancing selectivity towards main products. In this Chapter, bioethanol steam reforming is detailed as regards industrial process, including future options such as autothermal reforming and membrane reactors. A review on commonly used and recently investigated catalysts is also provided, including active metals, auspicious supports and promoters which can minimize catalyst deactivation.
    The production of hydrogen from ethanol steam reforming with Cu–Ni catalysts supported on MgO- and CaO-modified silica has been studied. Two promoting effects have been found: reduction of the metallic Cu–Ni particles size and strengthening of the metal–support interaction. Moreover, Mg- and Ca-promoted catalysts favour the formation of defective carbon, which is more reactive and thermodynamically easier to be removed during the ethanol steam reforming process. Consequently, higher hydrogen production and lower coke formation are achieved when Cu–Ni catalysts are supported on Mg- or Ca-modified silica in comparison to unmodified Cu–Ni/SiO2 catalyst. The highest hydrogen selectivity (84.8mol%) is reached with a Cu–Ni/Mg–SiO2 catalyst containing 10wt% Mg, while the incorporation of 10wt% Ca into Cu–Ni/SiO2 catalyst reduces considerably the amount of coke deposited from 58.4 to 26.3wt%, after 3h of time on stream.
    A series of Ni catalysts supported on Al-SBA-15 mesoporous materials (Si/Al = 20, 60, 140, 240, ∞) was prepared and tested in ethanol steam reforming. The catalysts were characterized by XRD, H2-TPR, NH3-TPD, TEM, ICP-AES, 27Al-MAS-NMR and N2-sorption measurements. It was found that the incorporation of Al atoms into SBA-15 structure is responsible for the formation of catalyst acid sites, an increase of the size of nickel species and stronger metal-support interaction between Ni and Al-SBA-15 carrier. Regarding ethanol steam reforming, catalysts with higher Al content keep ethanol conversion along time. However, Ni/Al-SBA-15 catalysts produce larger amounts of ethylene and coke, with slightly lower hydrogen selectivity than Ni/SBA-15. This is the consequence of ethanol dehydration in Ni/Al-SBA-15 acid sites, while ethanol dehydrogenation mechanism predominates in Ni/SBA-15 catalyst.
    The effect of Mg and Ca incorporation (0–20wt%) into CuNi/SBA-15 catalysts for hydrogen production by ethanol steam reforming has been studied. Promoting elements, Ca and Mg, were added to SBA-15 support prior to the active phase, Cu (2wt%) and Ni (7wt%). In both cases, the metals were incorporated to SBA-15 by incipient wetness impregnation followed by calcination to obtain the corresponding oxides. XRD analyses and TEM images demonstrated that CaO and MgO improved the dispersion of the Cu–Ni phase. Moreover, TPR profiles showed that Ca or Mg strengthened the interaction between the SBA-15 support and the Cu–Ni phase. Both promoting effects of Ca and Mg, together with their basic character enhanced the catalytic performance of CuNi/SBA-15 catalysts on ethanol steam reforming, giving higher hydrogen selectivity and lower coke deposition.
    The design of new anode materials to promote the reforming of methanol is important for the development of intermediate temperature direct methanol solid oxide fuel cells. A previous study showed Pd/CeO2−Sm2O3 to be a good candidate. Here, the influence of the calcination pretreatment of the support and the reduction temperature of the catalyst on the steam reforming of methanol are investigated, as they can become key factors in the performance of the catalyst. Conversion, H2 yield, and TOF were considerably higher when the support was calcined at 800 °C (Pd/CS-800) instead of 1000 °C (Pd/CS-1000). Characterization results suggest a stronger interaction of Pd particles with the support in Pd/CS-1000, which hinders its accessibility to the gas atmosphere, and a less homogeneous distribution of Pd particles. In both cases, the activity increases on increasing the reduction temperature from 400 to 500 °C. In addition, these catalysts were highly resistant to deactivation.
    A series of Cu–Ni catalysts supported on Ce- or La-modified SBA-15 was prepared and tested on ethanol steam reforming for hydrogen production. Samples were characterized by TGA, XRD, ICP-AES, N2-physisorption, TPR and TEM. XRD analyses revealed different tendencies in the dispersion of Ce and La on the SBA-15 mesoporous support. Bulk CeO2 particles together with large NiO crystallites found on CuNi/CeO2/SBA-15 catalysts were responsible for their lower metallic dispersion and hydrogen production in comparison to CuNi/SBA-15 sample. At high La loadings (10–20%), the development of a La2O3 layer over the SBA-15 support strengthened metal-support interaction and enhanced metallic dispersion, achieving an improvement in the CuNi/La2O3/SBA-15 catalytic performance. Particularly, the incorporation of 20wt% of La led to a significant enhancement of hydrogen selectivity (from 77.2 to 85.4mol%) and, mainly, an important reduction in coke deposition (from 42.3 to 26.3w/w% after 3h of time on stream).
    Ethanol steam reforming is an interesting alternative for hydrogen production since ethanol can be renewably obtained. Use of lamellar double hydroxides (LDHs) as precursors of nickel catalysts leads to highly dispersed metal particles in an aluminium structure. In this sense, a Ni(II)Al(III) catalyst was synthesized from a LDH precursor and tested in ethanol steam reforming. Although this catalyst presents high stability, acidity of alumina promotes carbon deposition from ethylene through ethanol dehydration. For this reason, in order to neutralize acid sites, a series of catalysts was prepared by Mg addition to LDH precursors varying Mg/Ni ratio. The effect of Mg/Ni ratio in the catalyst on coke formation during ethanol steam reforming was studied, resulting in significant reduction of the amount of deposited carbon for Mg/Ni ratio higher than 0.1. Moreover, Mg addition increases the catalytic activity due to lower ethylene formation, which competes with ethanol for the same Ni active sites.
    Cu-Ni/SBA-15 supported catalysts prepared by the incipient wetness impregnation method were tested in the ethanol steam reforming reaction for hydrogen production. The effect of reaction temperature and metal loading was studied in order to maximize the hydrogen selectivity and the CO2/(CO+CO2) molar ratio. The best catalytic performance was achieved at 600°C. Products distribution was the result of the combined effects of metal particles size, metal content and Ni/Cu ratio on the catalyst. In addition, two catalysts were prepared by the method of direct insertion of Ni and Cu in the initial stage of the SBA-15 synthesis. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N2- adsorption and inductively coupled plasma atomic emission spectroscopy (ICP-AES) results evidenced that SBA-15 materials with long range hexagonal ordering were successfully synthesized in the presence of copper and nickel salts with the (Cu+Ni) contents around 4–6wt.%. However, lower hydrogen selectivity as well as ethanol and water conversions were obtained with catalysts prepared by direct synthesis in comparison with those prepared by incipient wetness impregnation method. Particularly, the best catalytic results were achieved with a sample impregnated with 2 and 7wt.% of copper and nickel, respectively.
    In the present work, Cu–Ni supported catalysts were tested in ethanol steam reforming reaction. Two commercial amorphous solids (SiO2 and γ-Al2O3) and three synthesized materials (MCM-41, SBA-15 and ZSM-5 nanocrystalline) were used as support. A series of Cu–Ni/SiO2 catalysts with different Cu and Ni content were also prepared. It was found that aluminium containing supports favour ethanol dehydration to ethylene in the acid sites, which in turn, promotes the coke deactivation process. The highest hydrogen selectivity is achieved with the Cu–Ni/SBA-15 catalyst, due to a smaller metallic crystallite size. Nevertheless, the Cu–Ni/SiO2 catalyst showed the best catalytic performance, since a better equilibrium between high hydrogen selectivity and CO2/COx ratio is obtained. It was seen that nickel is the phase responsible for hydrogen production in a greater grade, although both CO production and coke deposition are decreased when copper is added to the catalyst.
    Cu-Ni/SBA-15 supported catalysts prepared by the incipient wetness impregnation method were tested in the ethanol steam reforming reaction for hydrogen production. The effect of reaction temperature and metal loading was studied in order to maximize the hydrogen selectivity and the CO2/COx molar ratio. The best catalytic performance was achieved at 600 ºC with a catalyst containing 2 and 7 wt% of copper and nickel, respectively. In addition, two catalysts were prepared by the method of direct insertion of Ni and Cu ions as precursors in the initial stage of the synthesis. XRD, TEM, N 2 adsorption and ICP-AES results evidenced that SBA-15 materials with long range hexagonal ordering could be successfully synthesized in the presence of copper and nickel salts with the (Cu+Ni) contents around 4–6 wt%. However, lower hydrogen selectivity and together with ethanol and water conversions were observed with catalysts prepared by direct synthesis in comparison with those prepared by incipient wetness impregnation method. KEYWORDS: Ethanol steam reforming, SBA-15, Cu-Ni catalysts, hydrogen production.
    Tesis Doctoral leída en la Universidad Rey Juan Carlos en 2007. Directores de la Tesis: Antonio Calles Martín y Alicia Carrero Fernández
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