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  • ΔΗΜΟΣΙΕΥΣΗ - APPLIED SURFACE SCIENCES

    Title: Investigating the correlation between deactivation and the carbon deposited on the surface of Ni/Al2O3 and Ni/La2O3-Al2O3 catalysts during the biogas reforming reaction [view paper]

     

    Journal: Applied Surface Sciences 474 (2019) 862-874.

     

    Authors: N.D. Charisiou1, L. Tzounis2, V. Sebastian3,4, S.J. Hinder5, M.A. Baker5, K. Polychronopoulou6, M.A. Goula1,*

     

    1Laboratory of Alternative Fuels and Environmental Catalysis (LAFEC), Department of Environmental and Pollution Control Engineering, Western Macedonia University of Applied Sciences, GR-50100, Greece

    2Composite and Smart Materials Laboratory (CSML), Department of Materials Science & Engineering, University of Ioannina, GR-45110, Ioannina, Greece

    3Chemical and Environmental Engineering Department & Nanoscience Institute of Aragon (INA), University of Zaragoza, Zaragoza, SP-50018, Spain
    4Networking Research Center on Bioengineering, Biomaterials and Nanomedicine, CIBERBBN, 28029 Madrid, Spain

    5The Surface Analysis Laboratory, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford, GU2 4DL, UK

    6Department of Mechanical Engineering, Khalifa University of Science and Technology, Abu Dhabi, P.O. Box 127788, UAE

                

     

    ABSTRACT

    Ni/Al2O3 and Ni/La2O-Al2O3 catalysts were investigated for the biogas reforming reaction using CH4/CO2 mixtures with minimal dilution. Stability tests at various reaction temperatures were conducted and TGA/DTG, Raman, STEM-HAADF, HR-TEM, XPS techniques were used to characterize the spent samples. Graphitized carbon allotrope structures, carbon nanotubes (CNTs) and amorphous carbon were formed on all samples. Metallic Ni0 was recorded for all (XPS), whereas a strong peak corresponding to Ni2O3/NiAl2O4, was observed for the Ni/Al sample (650–750°C). Stability tests confirm that the Ni/LaAl catalyst deactivates at a more gradual rate and is more active and selective in comparison to the Ni/Al for all temperatures. The Ni/LaAl exhibits good durability in terms of conversion and selectivity, whereas the Ni/Al gradually loses its activity in CH4 and CO2 conversion, with a concomitant decrease of the H2 and CO yield. It can be concluded that doping Al2O3 with La2O3 stabilizes the catalyst by (a) maintaining the Ni0 phase during the reaction, due to higher dispersion and stronger active phase-support interactions, (b) leading to a less graphitic and more defective type of deposited carbon and (c) facilitating the deposited carbon gasification due to the enhanced CO2 adsorption on its increased surface basic sites.

     

     

Research focus

 

Reforming of Glycerol

Biodiesel production has grown, between 2005 and 2015, at almost 25% per annum (reaching approximately 32 billion liters), leading to a seven-fold expansion of the sector. Although biodiesel is thought of as a renewable, biodegradable, environmentally-friendly fuel, there are concerns over the production of glycerol, the main by product of the transesterification reaction (it accounts for 10% of the volume of oil undergoing the reaction).

An innovative option is the energetic utilization of glycerol via steam reforming (SR), as every mole of glycerol fed to the reactor can theoretically produce seven moles of hydrogen. At LAFEC we have devoted our efforts towards the design of appropriate catalysts based on transition metals that can be used in the GSR. In some of our previous works, we reported on the performance of different transition metals (Ni, Co, Cu) on silica [BioResources 11 (2016) 10173-89] and alumina [Fuel Process Technol 152 (2016) 156-75], of Ni catalysts based on alumina, zirconia, silica [Top Catal 60 (2017) 1226-50] and apatite-type lanthanum silicates supports [RSC Adv 6 (2016) 78954-8], the influence of the synthesis method on Ni/Al catalysts [Chinese J Catal 37 (2016) 1949-65], the effect of the addition of lanthana on Ni/Al catalysts [Int J Hydrogen Energ 42 (2017) 13039-60], the effect of the addition of CaO-MgO on Ni/Al catalysts [Int J Hydrogen Energ 44 (2019) 256-273], the use of AlCeO3 as supporting material for a Ni catalyst [Catalysts 9 (2019) 411], the effect of the addition of silica [Top Catal 60 (2017) 1226-1250] or yttria [Int J Hydrogen Enrg, In press] on Ni/ZrO2 catalysts. We have also tested Ce-Sm-xCu [Sust Energ Fuels 3 (2019) 673-691] and Ni/Ce-Sm-xCu [Nanomaterials 8 (2018) 931] catalysts. A comprehensive literature review with particular focus on the main catalysts and support systems under development has also been carried out [Surf Coat Technol 352 (2018) 92-111].

Moreover, we have also examined glycerol reforming via chemical looping using Ni/ZrO2 nano-composite oxygen carriers [Int J Hydrogen Energ 43 (2018) 13200-11].

 

CO2 Utilization - Biogas Dry Reforming

It is well understood that human activities, emanating from current practices relating to the production and consumption of fossil based energy have an unequivocal impact upon the global climate. A promising technology is the Dry Reforming of Biogas, as the process makes use of the main greenhouse gases (CH4 and CO2), and can provide a renewable resource with a potential zero carbon footprint. The product of this process is syngas, a key chemical feedstock for the synthesis of oxygenated chemicals and hydrocarbons from Fisher – Tropsch synthesis.

At LAFEC we have examined the performance of nickel catalysts based on alumina modified with ceria, lanthana [J Nat Gas Sci Eng 31 (2016) 164-83 & Catal Today 195 (2012) 93-100], magnesia or calcium [Waste Biomass Valori 7 (2016) 725-36]. A theoretical investigation of Ni-Al2O3 and Ni/CeO2-Al2O3 has also been performed [Int J Hydrogen Energ 35 (2010) 9818-27].

We have also devoted effort in investigating the performance of Nickel catalysts based on zirconia modified with ceria, lanthana [Int J Hydrogen Energ 42 (2017) 13724-40] and tugsten [Front Environ Sci 5 (2017) 66]. Moreover, we have examined different synthesis techniques in an effort to maximize the dispersion of active phase and optimize the active species [Catal Today 46, 175-83; Int J Hydrogen Energ 40 (2015) 9183-00].

Finally, we have committed ourselves at investigating the carbonaceous species formed during the reaction [J Catal 161, 626-40; Adv Mater Proc 2 (2017) 807-12; Mater Today: Proc. 5 (2018) 27607-27616; Int J Hydrogen Energ 43 (2018) 18955-18976; Appl Surf Sci 474 (2019) 42-56], as it is one of the main reasons for catalyst deactivation.

 

NOx and SO2 abatement

Nitrogen and sulphur oxide abatement is a subject of major environmental importance, as Nitric (NOx) and Sulphur (SOx) oxides are recognized as important precursors of acid rain, contributors to the formation of photochemical smog and to the destruction of the ozone layer. Recently, a lot of academic and policy attention has focused on N2O emissions control. Nitrous oxide (N2O) is listed as one of the most harmful greenhouse gases with a strong global warming potential (310 times higher than that of CO2), that severely contributes to the stratospheric ozone layer depletion.

At LAFEC, we were the first to investigate the lean NOx reduction by propene, H2 as well as by propene + H2 over supported (on γ-Al2O3), low loading (0.5 wt%), Pt, Pd and Ir catalysts [J Environ Chem Eng 4 (2016) 1629-41]. In addition, we have examined the impact of alkali promoters (K) on the physicochemical properties and catalytic performance of Ir/Al2O3 catalysts towards the N2O decomposition [Top Catal 59 (2016) 1020-7]. Finally, we have examined the deactivation and regeneration procedures of copper oxide catalysts/sorbents that are supported on Al2O3, SiO2, CeO2-Al2O3, in the presence of SO2 and identified the appropriate conditions for the simultaneous removal of NO and SO2 [Global Nest J 14 (2012) 166-74].

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Selective deoxygenation (SDO) of natural triglycerides

There are two main drawbacks associated with the production of biodiesel through the transesterification reaction: (a) The unsuitability of plant oils with relatively high acidity for transesterification catalyzed by basic solutions, and (b) the increasing accumulation of glycerol, the main sub-product of the process.

However, natural triglycerides can be upgraded using selective deoxygenation (SDO), which is realized by hydrotreatment via decarboxylation (deCO2), decarbonylation (deCO) and hydrodeoxygenation (HDO), to hydrocarbons in the range of petro-diesel (green or renewable diesel).

At LAFEC we have set up appropriate experimental procedures and are investigating the: (i) effect of supports, metal loading and promoters on catalytic performance, (ii) SDO pathways over transition metallic catalysts, and (iii) effect of preparation method on catalytic performance.

We have recently published a comprehensive literature review on the topic [Energies 12 (2019) 809].