Abstract
This thesis focuses on a catalyst development for Aqueous Phase Reforming (APR). APR operates at high temperatures and at elevated pressures with a target to convert dilute biomass feeds to hydrogen/syngas. Due to the operation conditions and complex feedstocks used, the catalyst stability and selectivity to hydrogen is a challenge.
The objective of this thesis is to understand issues that affect catalyst stability and effect of catalyst properties for maximized hydrogen yields using model feedstock molecules. Furthermore, understanding formation of side products and they role in deactivation/stability of the catalyst is essential. With this in mind, APR studies are carried out with low feed concentrations 2.5-5wt% of reactant (ethylene glycol, EG and hydroxyacetone, HYDA) and at conditions of 225-270 °C/ 35-90 bar.
Starting with catalyst stability, it is well-known that γ-Al2O3 suffers from phase transformation to AlO(OH) under APR. Therefore, we prepared Pt on AlO(OH) and compared its activity to Pt/γ-Al2O3. Pt/AlO(OH) catalyst is stable for APR of EG and interestingly, it has improved H2-selectivity compared to Pt/γ-Al2O3.
As biomass feeds are complex, we continued further to study stability of Pt/AlO(OH), Pt/C (mesoporous) and Pt/ZrO2 for APR of HYDA, a ketone present in biomass feeds in appreciable amounts. The results showed that the oxide supported materials suffered from carbon deposits on the catalysts and deactivated rapidly. Carbon, however, was stable and had a good gasification activity. This showed good promise for further development of this catalyst.
Therefore, we studied Pt/C in more detail by preparing it in different ways to achieve variable Pt size and distribution on the support. The results indicated that catalysts with higher Pt size and more egg-shell type distribution of metal showed higher H2 production rate in APR of EG. This suggested that APR of EG has a structure sensitivity.
Further, possible diffusion limitations of Pt/C catalysts were studied by varying catalysts grain size and reaction conditions under APR of HYDA. The experimental results are discussed in comparison with transport criteria.
Pt/C is stable and active for gasification of the studied model compounds, further development requires improving Water-Gas-Shift activity to increase H2-selectivity.
The objective of this thesis is to understand issues that affect catalyst stability and effect of catalyst properties for maximized hydrogen yields using model feedstock molecules. Furthermore, understanding formation of side products and they role in deactivation/stability of the catalyst is essential. With this in mind, APR studies are carried out with low feed concentrations 2.5-5wt% of reactant (ethylene glycol, EG and hydroxyacetone, HYDA) and at conditions of 225-270 °C/ 35-90 bar.
Starting with catalyst stability, it is well-known that γ-Al2O3 suffers from phase transformation to AlO(OH) under APR. Therefore, we prepared Pt on AlO(OH) and compared its activity to Pt/γ-Al2O3. Pt/AlO(OH) catalyst is stable for APR of EG and interestingly, it has improved H2-selectivity compared to Pt/γ-Al2O3.
As biomass feeds are complex, we continued further to study stability of Pt/AlO(OH), Pt/C (mesoporous) and Pt/ZrO2 for APR of HYDA, a ketone present in biomass feeds in appreciable amounts. The results showed that the oxide supported materials suffered from carbon deposits on the catalysts and deactivated rapidly. Carbon, however, was stable and had a good gasification activity. This showed good promise for further development of this catalyst.
Therefore, we studied Pt/C in more detail by preparing it in different ways to achieve variable Pt size and distribution on the support. The results indicated that catalysts with higher Pt size and more egg-shell type distribution of metal showed higher H2 production rate in APR of EG. This suggested that APR of EG has a structure sensitivity.
Further, possible diffusion limitations of Pt/C catalysts were studied by varying catalysts grain size and reaction conditions under APR of HYDA. The experimental results are discussed in comparison with transport criteria.
Pt/C is stable and active for gasification of the studied model compounds, further development requires improving Water-Gas-Shift activity to increase H2-selectivity.
| Original language | English |
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| Qualification | Doctor of Philosophy |
| Awarding Institution |
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| Supervisors/Advisors |
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| Award date | 11 Jan 2019 |
| Place of Publication | Enschede |
| Publisher | |
| Print ISBNs | 978-90-365-4668-3 |
| DOIs | |
| Publication status | Published - 11 Jan 2019 |