Effect of the active metal supported on SiO2 to the selective hydrogen production on the glycerol steam reforming reaction
K.N. Papageridis1,2, G. Siakavelas1, N.D. Charisiou1, M.A. Goula1,2
1
Department of Environmental and Pollution Control Engineering, Technological Educational Institute of Western Macedonia (TEIWM), GR – 50100, Koila, Kozani, Greece 2
Catalysis and Environmental Protection MSc, School of Science and Technology, Hellenic Open University, Parodos Aristotelous 18, GR - 26335, Patras, Greece Keywords: hydrogen, glycerol, steam reforming, SiO2 supported catalysts Presenting author e-mail:
[email protected]
Glycerol is largely generated as the principal co-product in the production of biodiesel through the transesterification process by using alcohols. Due to the increase in the production of biodiesel several alternatives have been proposed for the valorization of crude glycerol [1]. Catalytic steam reforming of glycerol to produce hydrogen is a process that has been extensively investigated in recent years [2]; as it is considered as an interesting reaction for its operational characteristics and its greater efficiency. Generally, for steam reforming reactions, noble metal containing catalysts have been proven to be more active and less susceptible to form carbonaceous deposits than non-noble metal ones. At an industrial scale, the use of Ni-impregnated Al2O3 for steam reforming processes has been adopted as this catalyst has lower cost and higher availability than the noble metal ones. On the other side, Ni/Al2O3 catalysts suffers deactivation during the steam reforming of oxygenated hydrocarbons, due to the formation of carbonaceous deposits and/or the sintering of metallic phase. Only a few studies employed Co/Al2O3 catalysts to produce H2 by steam reforming [3], whereas Co-Ni/Al2O3 bimetallic catalysts were used in processes such as methane dry reforming, glycerol aqueous phase reforming, glycerol steam reforming [4] and acetol steam reforming. Moreover, according to the literature, the most frequently tested catalysts for methanol steam reforming (MSR) and oxidative MSR (i.e. the coupling of methanol selective oxidation and steam reforming) are Cu-based systems, with quite an high copper content (30-50 wt% as CuO). Cu-based catalysts are also active for ethanol steam reforming (ESR), while the reaction mechanisms of MSR and ESR have been also studied over Cu-ZnOAl2O3 showing that water takes the role of oxidant for copper and nickel active phases. In a recent review on glycerol stream reforming reaction Group VIII metals, including Ru, Rh, Ni, Ir, Co, Pt, Pd, Fe, as the active phase on numerous oxides (Y 2O3, ZrO2, CeO2, La2O3, SiO2, MgO, Al2O3) have been reported [5]. It has been shown that acid-base properties of the support influences catalyst’s morphology, as well as, its reactivity and stability in glycerol steam reforming reaction. As a matter of fact, comparatively high acidic supports tend to dehydrate glycerol, which yields undesired coke precursors and can clog the system by subsequent condensation. Although acidic support is not preferred using basic material as MgO does not guarantee for better performances. Furthermore, the reducibility and conductivity of the support may also play a role, so in this work we have selected silica, as an example of insulating, poorly acidic and substantially unreducible material. In this contribution a comparative study of supported on SiO 2 transition metals’, catalytic performance is reported. Catalysts with active phase Ni, Co and Cu, were synthesized applying the wet impregnation method at a series of constant loading (5wt%). The synthesized samples, at their calcined or/and reduced form, were characterized by X-Ray Diffraction (XRD) and N2 adsorption-desorption technique (BET). The chemical composition of the catalysts was determined by inductively coupled plasma (ICP), while the deposited carbon was measured by a CHN analyzer. Catalytic performance of the catalysts concerning the glycerol SRM reaction, was studied in order to investigate the effect of the reaction temperature on (i) glycerol conversion, (ii) hydrogen selectivity, (iii) H2/CO molar ratio, (iv) gaseous and liquid products’ concentration of the mixtures at the outlet of the reactor.
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Figure 1 (a) Glycerol conversion, H2 selectivity (b) Gaseous products concentration versus temperature In Figure 1(a) the glycerol conversion and the hydrogen (H2) selectivity with varying the reaction temperature is presented. It is depicted that conversion values are very high (80-100%) for all catalysts and for the whole temperature range. On the other hand, H2 selectivity values increase with increasing temperature reaching almost 90% for the Ni/SiO2 catalyst, which seems to be more selective to hydrogen (H2) production than the Co/SiO2 and Cu/SiO2 ones. In Figure 1(b) the gaseous products’ concentration at the outlet of the reaction with varying the reaction temperature is presented. As for the H2 concentration the same trend can be observed, while CH 4 remains negligible for all catalysts for the whole temperature range. More importantly, CO concentration reaches a plateau at 600 to 700 oC with a value of 15% for the Co/SiO2, higher enough than the ones for the Ni/SiO2 and Cu/SiO2 catalysts. On the other hand, the CO2 concentration for the same catalyst reaches a minimum value for temperatures between 600-700 oC, lower enough than ones for the other catalysts. Liquid phase’s composition, as determined by GC-MS, revealed chemical substances as acetaldehyde, acetone, allyl alcohol, acetic acid, acetol, phenol, acrolein, propylene glycol for low reaction temperatures (below 600 oC). It can be concluded that the Ni/SiO2 catalyst exhibits improved gaseous products’ concentration, concerning H 2 and CO2, due to the fact that its active phase catalyzes the WGS reaction, so that the CO adsorbed on the surface can be removed and transformed into CO2.
References [1] Bagheri S., Julkapli N. M., Yehye W.A. Catalytic conversion of biodiesel derived raw glycerol to value added products. Renewable and Sustainable Energy Reviews 41 (2015) 113–127 [2] Joel M. Silva, M.A . Soria, Luis M. Madeira. Challenges and strategies for optimization of glycerol steam reforming process. Renewable and Sustainable Energy Reviews 42 (2015) 1187–1213 [3] Cheng CK, Foo SY, Adesina AA. H2-rich synthesis gas production over Co/Al2O3 catalyst via glycerol steam reforming. Catal Commun 2012;12:292-298. [4] Cheng CK, Foo SY, Adesina AA. Glycerol steam reforming over bimetallic Co-Ni/Al 2O3. Ind Eng Chem Res 2010;49:10804-10817. [5] Yu-Chuan Lin. Catalytic valorization of glycerol to hydrogen and syngas Int. J. Hydrogen Energy 38(2013)2678-2700 Acknowledgements Financial support by the program THALIS implemented within the framework of Education and Lifelong Learning Operational Programme, co-financed by the Hellenic Ministry of Education, Lifelong Learning and Religious Affairs and the European Social Fund, Project Title: ‘Production of Energy Carriers from Biomass by Products. Glycerol Reforming for the Production of Hydrogen, Hydrocarbons and Superior Alcohols’ is gratefully acknowledged.
