Reetta Kaila is working as a research scientist aiming for Ph.D. at the Laboratory of Industrial Chemistry, TKK. Her research is focused on reforming reactions of renewable and fossil fuels to produce H₂-rich fuel gas suitable for solid oxide fuel cell (SOFC) applications. In her work she prepares and characterizes heterogeneous noble metal catalysts. These catalysts are tested in a continuous reactor system at high reaction temperatures (500–900 °C). Due to high temperatures, thermal stability of the catalyst materials is essential. Moreover, to control the reaction system and to avoid side reactions, high activity and selectivity of the catalysts for reforming is required.

The Laboratory of Industrial Chemistry employs around 30 people, including teaching personnel, research scientists and administrative staff. In the Laboratory of Industrial Chemistry we study catalytic phenomena and apply this knowledge to the conversion of raw materials into useful products in cost-effective and environmentally friendly ways. Reaction mechanisms and kinetics are studied on the basis of experimental data. Mathematical models describing chemical and physical phenomena are derived, and the models are utilized in process design and scale-up. The laboratory is headed by Professor Outi Krause.

Reforming of renewable and fossil fuels on noble metal catalysts

For energy production, the substitution of fossil fuels by H2 is a suitable option for reducing the greenhouse gas emissions to the atmosphere, in particular CO₂. The major advantages of using H₂ or H₂-rich mixtures as fuel include the diversity of primary fuels (natural gas, biomass, crude oil) that can be used in H2 production, its clean combustion and the possibility of long-term storage of the fuel. Moreover, H₂-rich mixtures can be used as fuel for fuel cells¹.

The growing interest in fuel cell technologies as replacements for internal combustion engines increases the demand for H₂ production. The development of an economy based on H₂ requires major structural changes that could take several decades. Therefore, commercially available fuels such as gasoline and diesel could be used as near- and mid term H₂ carriers to achieve some immediate reduction in green house gas emissions. Moreover, they are easy to store and their volumetric H₂ density is high².
Conventionally H₂ is produced by steam reforming (SR) of methane (CH₄ + H₂O -> 3 H₂ + CO) on Ni-based catalysts. However, the SR reaction becomes very endothermic when the hydrocarbon-chain length is increased. Autothermal reforming (ATR, Figure 1), which combines the endothermic SR with the exothermic partial oxidation (PO) is recommended for H₂ production from liquid fuels³.

Figure 1. Main and side reactions in autothermal reforming of liquid hydrocarbons or alcohols.

In the catalyst studies, series of mono- and bimetallic RhPt/ZrO₂ catalysts are prepared and tested in reforming reactions of ethanol, simulated and commercial fuels (bio diesel (NExBTL), low-sulfur diesel). The Rh/Pt ratio and the total metal loading of the catalysts are varied.

H₂-rich fuel gas is successfully produced in ATR of liquid hydrocarbons and alcohols on these noble metal catalysts. The monometallic Rh catalyst has shown high reforming activity but it deactivates rapidly, whereas the less active monometallic Pt catalyst remains stable⁵. The good properties of these monometallic catalysts are successfully combined in the bimetallic RhPt catalysts and only a small addition of Rh is sufficient to increases the activity of the Pt catalyst remarkably, still retaining the stability. On the bimetallic catalysts, strong synergism between Rh and Pt is observed and the formation of a Rh-Pt alloy appears to take place leading to excellent catalytic performance.

If the activity for reforming reactions is low, thermal cracking of the fuel occurs at the high reaction temperatures producing alkenes that are strong carbon precursors (Figure 1). The reforming of higher hydrocarbons (e.g. aromatic hydrocarbons) increases the risk of undesired side reactions and the carbon formation, especially on the conventional Ni-based catalysts. The carbon deposition on the catalyst might result in breakdown of the catalyst particles. At the worst, the catalyst bed is blocked causing a pressure increase in the reactor. However, by replacing the Ni catalyst with noble metal catalysts, the carbon deposition can be decreased⁴. Moreover, the stability against carbon deposition can be controlled with the Rh/Pt molar ratio of the catalysts. Still, after testing in ATR of commercial, low-sulfur diesel, the carbon formation on the Rh-containing catalysts is visible to the eye (Figure 2). Thus, further investigations are needed, to decrease the carbon deposition rate.

Figure 2. Fresh and used RhPt/ZrO2catalyst particles.

¹ D. Shekhawat et al., Catalysis 19 (2006) 184.
² R. F. Service, Science 305 (2004) 958.
³ R. K. Kaila and A. O. I. Krause, Stud. Surf. Sci. Catal. 147 (2004) 247.
⁴ R. K. Kaila and A. O. I. Krause, Int. J. Hydrogen Energy 31 (2006) 1934.
⁵ R. K. Kaila et al., Catal. Lett. 115 (2007) 70.

Contact information:

Reetta Kaila, Lic. (Tech.)
Laboratory of Industrial Chemistry, TKK
reetta.kaila@tkk.fi
Tel. 09-451 2666
Home page of the laboratory: http://teke.tkk.fi/english/

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