Ni-supported catalysts for ethanol steam reforming: effect of the solvent and metallic precursor in catalyst preparation

International Journal of Industrial Chemistry (2018) 9:61–73 https://doi.org/10.1007/s40090-018-0135-6 RESEARCH Ni‑supported catalysts for ethanol steam reforming: effect of the solvent and metallic precursor in catalyst preparation Alejandra C. Villagrán Olivares1 · Manuel F. Gomez1 · Mariana N. Barroso1 · María C. Abello1 Received: 17 May 2017 / Accepted: 30 December 2017 / Published online: 19 January 2018 © The Author(s) 2018. This article is an open access publication Abstract Ethanol steam reforming was studied over Ni/MgAl2O4–CeO2 catalysts. The catalysts were prepared using different impregnation media (ethanol or water) and Ni precursors (nitrate or acetate). The use of an alcoholic solution did not affect the specific surface area, but promoted the NiO formation reducible at lower temperature affecting the Ni-support interactions and the Ce3+/Ce4+ initial ratios. All catalysts were highly active in the reforming reaction of ethanol with a high initial conversion of ethanol under more severe conditions than those commonly used in literature. The best catalytic behavior was found over the catalyst prepared from an ethanolic solution of Ni(NO3)2. This sample showed a high C e3+/Ce4+ ratio, an adequate interaction Ni-support and an average Ni diameter around 28 nm. This catalyst was stable under the reforming conditions used in this work: initial ethanol concentration: 9.4%, reaction temperature: 650 °C, W/F = 49 g min mol−1 C H OH 2 5 and reaction time: 40 h. The ethanol conversion was almost complete with H2 selectivity around 78%. Keywords Hydrogen · Ethanol reforming · Ni/MgAl2O4–CeO2 catalysts · Deactivation Introduction The climate change observed in the last few decades and its consequences have led the global society to minimize the emissions (mainly CO2) into the environment and to decrease the dependence on fossil fuels. The use of sustainable energy sources is imperative and it is widely accepted that a carbon-free society will not be possible without a hydrogen economy [1]. The hydrogen production from ethanol steam reforming is an interesting option, because ethanol has several advantages compared with other raw materials. The most important one is its renewable origin, because it can be obtained from biomass fermentation (e.g., sugar cane, corn, lignocelluloses, etc.) [2, 3]. The ethanol has relatively high hydrogen content and its reaction with water under steam reforming conditions is able to produce 6 mol of H2 per mole of reacted ethanol: CH3 CH2 OH + 3 H2 O → 6 H2 + 2 CO2 . * María C. Abello 1 Instituto de Investigaciones en Tecnología Química, INTEQUI-CONICET-UNSL, Almirante Brown 1455, 5700 San Luis, Argentina (1) The other important advantage is that CO2 production slightly contributes to greenhouse effect since it is recycled through photosynthesis during the plant growth. The noble metals [4–7], nickel [8–13], cobalt [9, 14–21], etc., supported over several supports have been studied as catalysts for this reaction. Ni catalysts have been used in commercial scale in several reforming processes for more than 40 years [22], especially for its high activity to break C–C bond and its low cost compared to noble metals. The main disadvantage of Ni catalysts is related to deactivation by coke formation, sintering and inactive phase transformation. There are many studies about the carbon formation on Ni systems [13, 23–25] and a considerable effort has been focused on developing new Ni stable catalysts with an improved resistance to coke formation. The type of metal present (base metal or noble metal) and the reaction conditions (initial ethanol concentration, water: ethanol molar ratio, temperature, etc.) affect the mechanism of carbon deposition [3]. The addition of alkaline metals, alkaline earth metals or rare earth metals has been frequently used on Ni catalysts to increase the carbon tolerance [23, 26, 27]. It has been reported that the addition of Na or K changes the surface acidity of catalyst and minimizes the ethylene formation known as coke precursor. The inhibition of carbon deposition has been also related to Ni particle sizes. Ni 13 Vol.:(0123456789) 62 International Journal of Industrial Chemistry (2018) 9:61–73 particles lower than a critical size (around 10 nm [3]) and high dispersion levels could minimize the carbon deposition responsible for the irreversible deactivation or for the pressure increase in the catalytic bed [28]. Other important factor is the Ni-support interaction. Strong interactions of NiO with the support and/or Ni compound formation can hinder the formation of metallic Ni. The anchorage of Ni particles on the support could be also affected by the impregnation medium [29] and/or the Ni precursor nature [30]. The effect of the solvent used in the impregnation step has been investigated in Co-based catalysts. Song and Ozkan [29] have studied the influence of ethanol and water as impregnation media in Co/SiO2 catalysts. The catalysts prepared in ethanol showed a significant improvement in the ethanol steam reforming reaction, ESR: higher H 2 yield, better stability and lower amount of by-products. The authors have assigned this positive effect to the presence of oxygenated carbon species which prevent sintering and exert a site blocking that suppresses the side reactions. Besides, they have suggested an “imprinting” effect that favors the surface acetate formation and provides an optimum surface geometry for the selective reactions. The impregnation with an ethanolic solution of cobalt nitrate instead of an aqueous one has also shown an improvement in the metallic dispersion in Fischer–Tropsch Co catalysts [31]. Ho and Su have reported that the presence of ethoxy groups hinder the aggregation of Co2O3 during its formation from the thermal decomposition of cobalt nitrate [31]. The influence of other solvents in metallic dispersion has been also reported in literature [32, 33]. Lucredio et al. [32] have investigated the effect of methanol in the preparation of Co catalysts. They observed an improvement in the ESR when Co was supported on SiO2. However, the performance of Co/Al2O3 resulted to be independent of the solvent used in preparation. The influence of methanol seems to depend on support nature. In a previous work, Ni catalysts supported on M gAl 2O 4–CeO 2 showed a good performance in ESR, although they suffered deactivation mainly by carbonaceous Table 1  Characteristics of fresh Ni/MgAl2O4–CeO2 catalysts species deposition [30]. As it was mentioned, high dispersion levels of Ni could depress coke formation. Then, it is interesting to examine the interaction of ethanol as impregnation medium in preparation of Ni/MgAl2O4–CeO2 catalysts. In this work, the solids were synthesized by wet impregnation using ethanol with different Ni precursors: Ni(NO3)2 or Ni(CH3COO)2. The catalysts were characterized by different techniques and their catalytic results in ESR were compared with those obtained u (...truncated)