Synthesis Of Ir-La Catalyst For Reforming Of Ethanol And The Improvement Of The Micro-reformer Performance For Hydrogen Production

Autothermal Reforming (ATRE) process has attracted much attention as it offers advantages on efficiency for hydrogen production and less dependence on additional power sources. However, effective catalyst and reactor should be required as the ATRE reaction is complex, and requires high temperature (500⁸00℃). The materials for synthesizing the ATRE catalyst were investigated carefully, the result Ir/La₂O₃ was high active and stable for ATRE reaction for hydrogen and Ir-La interaction during the reaction was studied systemically. An in situ dispersion effect of Ir on La₂O₂CO₃ support was observed, and an upgrade Ir/La₂O₃ base on this effect was obtained. Subsequently, an active and selective Ir-La structured catalyst was synthesized. The reactants distribution on the catalyst surface and its influences on the ATRE performances were investigated and optimized.LaMnO₃, LaFeO₃, LaCoO₃ and LaNiO₃ perovskite oxides were prepared using combustion method for the autothermal reforming of ethanol (ATRE). The perovskite-type oxides can catalyze the ATRE reaction with a moderate activity. Well dispersed Ni particles supported on lanthanum oxide species were obtained by reducing the LaNiO₃ sample. It favors the dehydrogenation, decomposition of ethanol/acetaldehyde, methane reforming and water gas shift reactions, thus leads to good activity and H2 selectivity in ATRE reaction. A comparison between LaNiO₃ derived and impregnated Ni/La₂O₃ shows that the LaNiO₃ derived sample favored the dispersion of Ni, which increased the activity and the resistance to coke deposition.Hydrogen was produced over noble metal (Ir, Ru, Rh, Pd) catalysts supported on various oxides, includingγ-Al₂O₃, CeO₂, ZrO₂ and La₂O₃, via the autothermal reforming reaction of ethanol (ATRE) and oxidation reforming reaction of ethanol (OSRE). It was discovered that lanthana alone have considerable activity for the ATRE reaction, which can be used as a functional support for ATRE catalysts. It was demonstrated that Ir/La₂O₃ can prevent the formation of methane. ATRE reaction can be carried out over La₂O₃-supported catalysts (Ir/La₂O₃) with good stability on stream, high conversion, and excellent hydrogen selectivity approaching thermodynamic limitation under autothermal condition. The results presented in this paper indicate that Ir/La₂O₃ can be used as a promising catalyst for hydrogen production via ATRE reaction from renewable ethanol.La₂O₃ supported Ir catalyst was prepared by wetness impregnation method for the oxidative steam reforming of ethanol (OSRE). La₂O₃ would transform into hexagonal La₂O₂CO₃ during OSRE, which suppress coking effectively. Reduced Ir metal can interplay with La₂O₂CO₃ to form Ir doped La₂O₂CO₃. It dynamically forms and decomposes to release active Ir nanoparticles, thereby prevent the catalyst from sintering and afford high dispersion of Ir/La₂O₃ catalysts at elevated temperatures. By introducing ultrasonic during the preparation of catalyst, the surface Ir concentration was significantly improved, while the in situ dispersion effect inhibited Ir from sintering. The Ir/La₂O₃ catalyst by the ultrasonic assistant impregnation method is highly active and stable for the OSRE reaction, on which the Ir crystallite size was maintained at 3.2 nm after 100 h on stream at 650℃and metal loading high up to 9 wt%.An ethanol autothermal reforming micro-reformer was constructed to produce hydrogen for polymer electrolyte membrane fuel cells (PEMFCs), in which an Ir/La₂O₃ catalyst supported on ceramic foams was employed. To optimize the performance of micro-reformer, the effect of ceramic foam materials, including Al₂O₃, SiC and ZrO₂ foams, on the catalytic property was investigated in details from the aspects of activity, selectivity and stability. It was found that the ZrO₂ foam was the most suitable material to support the Ir/La₂O₃ catalyst. The La content in the catalyst layer influences the Ir dispersion greatly. The in situ dispersion effect of Ir on La oxide support worked well. The in situ dispersion effect improved the ethanol reforming activity, selectivity and stability significantly. Based on this, an Ir-La/ZrO₂ structured catalyst was synthesized to catalyze the ATRE reaction for hydrogen production in the micro-reformer. The outlet temperature distribution, product gas composition and reaction stability were investigated systematically. A reagent corresponding time of ⁹0 s was obtained in this micro-reformer. It produced 3.1 mol H2 per mol ethanol, and showed nice stability for reaction start-up and stable reaction. The distribution of reagents on the surface of catalyst and its influences on the ATRE performances were investigated by the Fluent simulation and the experiment. The reagents passed though the center of the catalyst without any obvious diffusion since the distributor was absent in the reactor. According to simulating results, by fixing a distributor in the entrance of the reactor, the uneven distribution of reagents on the surface of the catalyst was depressed. Hemisphere with a diameter of 14mm as distributor showed the most promising distribution performance. The experiment results showed that the conversion of ethanol and selectivity to hydrogen were improved greatly by this hemisphere distributor. The largest difference in temperature obtained on the outlet of the catalyst was only 21oC. At lower space velocity (GHSV=8.4×10⁴ 1/h), the distribution performance of hemisphere (14mm) observed by experiment data fit well with that from fluent simulation. Improving the GHSV further, the agreement between the two was unsatisfactory probably due to the error during the fabrication of the reactor. However, the micro-reformer with hemisphere (14mm) distributor can convert 91% ethanol with a hydrogen selectivity of 74.1% at GHSV=1.6×105 1/h under ATRE reaction condition. It produced 3.3 mol H₂ per mol ethanol, with a hydrogen flow rate of ⁰.58m³/h, which can feed fuel cells to produce power at 1100 W level. These results are helpful for the rational design and fabrication of micro-reformers for PEMFCs.