(491d) Auto Thermal Reforming of Lpg over Bimetallic Pt-Ni Catalyst

Hydrogen feed for fuel cells must either be supplied from a storage tank or be produced on site/on board. The former needs safe and economically feasible storage technologies which can only be developed in the mid- to long-term, comparing the targeted 6.5 wt% hydrogen storage capacity at ambient temperature with the currently obtained ca. 1 wt% storage level. Thus, hydrogen production from hydrocarbons on board the vehicle for mobile fuel cell applications and on site for immobile fuel cell applications via using efficient fuel processors is a very reliable short-term solution. At that point, the hydrocarbons that already have well established distribution networks are the best choices to be used as the fuels in hydrogen production via auto thermal reforming (ATR). The two possible hydrocarbon feed options are natural gas, which is mostly methane, and LPG, which is a mixture of propane and butane; as a result, the design and development of reforming catalysts for these hydrocarbon feeds is of crucial importance. Indirect partial oxidation, or auto thermal reforming (ATR), tests of a bimetallic Pt-Ni catalyst supported on d-alumina were conducted for different propane-n-butane mixtures (LPG) used as feeds. 75%propane-25% butane (LPG1) and 50% propane-50% butane (LPG2) mixtures were used as the hydrocarbon feed in the first and second part of the tests, respectively [1,2]. The tests were conducted for 623-743 K temperature range. The effects of steam to carbon ratio (S/C), carbon to oxygen ratio(C/O2) and residence time (W/F (g.cat-h/mol LPG)) on the hydrogen production activity, selectivity and product distribution were studied in detail. The results of the previously performed propane IPOX tests were used as reference basis whenever necessary [3]. An Increasing Temperature Program (ITP) was applied during all experiments and the results showed that the presence of n-butane in the feed enhances hydrogen production activity and selectivity. It was found that higher steam content in the reactant stream increases both the activity and the H2/CO selectivity of the process. Low residence times created a positive impact on catalyst activity not only for hydrogen production but also for carbon monoxide production due to the increased amount of fresh hydrocarbon in the feed stream. Hence, the highest selectivity level was obtained at intermediate residence times. The response of the system to C/O2 ratio was found to depend on the available steam content due to the complex nature of IPOX. The Pt-Ni catalyst was very prone to catalyst deactivation at low S/C ratios accompanied by high C/O2 ratios, but this problem was not encountered at high S/C ratios. A comparison of catalyst performance for LPG feeds with different compositions indicated that the Pt-Ni catalyst has slightly better activity and selectivity at higher n-butane contents at the expense of becoming more sensitive to coke deposition. The higher n-butane concentration in the feed led to slightly higher activities at low reaction temperatures, most probably due to the higher heat of oxidation of n-butane that resulted in higher temperatures at the active sites of the catalyst through micro-scale heat exchange from TOX sites to SR sites. However, at high reaction temperatures, the catalyst suffered from possible partial coke depositions due to the high n-butane content which eventually resulted in slightly lower activities. Considering the well established distribution network of LPG and the superior performance of the bimetallic Pt-Ni catalyst in the IPOX of LPG, Pt-Ni system seems a very promising catalyst alternative to be used in commercial fuel processors.

ACKNOWLEDGEMENTS This work was supported by DPT (State Planning organization of Turkey) through projects DPT 01 K 120300 and DPT 03 K 120250. A. E. Aksoylu acknowledges TUBA-GEBIP program.

References

1. Çağlayan, B. S., Önsan, Z. I., Aksoylu, A. E., ?Production of Hydrogen over Bimetallic Pt-Ni/dAl2O3: II. Indirect Partial Oxidation of LPG?, Catalysis Letters, 102 (2005) 63-67

2. Gökaliler F, Çağlayan, B.S., Önsan, Z. İ., Aksoylu, A. E., ?Fuel flexibility of the Pt-Ni Bimetallic Catalyst in ATR?, in preparation

3. Çağlayan, B. S., Avcı, A. K., Önsan, Z. I., Aksoylu, A. E., ?Production of Hydrogen over Bimetallic Pt-Ni/dAl2O3: I. Indirect Partial Oxidation of Propane?, Applied Catalysis A: General, 280 (2) (2005) 181-188