High-temperature sulfuric acid decomposition over complex metal oxide catalysts

• Published in: International journal of hydrogen energy Vol. 34; no. 9; pp. 4065 - 4073
• Main Authors: Ginosar, Daniel M., Rollins, Harry W., Petkovic, Lucia M., Burch, Kyle C., Rush, Michael J.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Kidlington Elsevier Ltd 01.05.2009; Elsevier
• Subjects: 08 HYDROGEN; Alternative fuels. Production and utilization; Applied sciences; C (programming language); Catalysis; CATALYSTS; CHROMIUM; COPPER OXIDE; DECOMPOSITION; DESORPTION; DISCOLORATION; Energy; Exact sciences and technology; Fuels; Hydrogen; Hydrogen production; LEACHING; Metal oxides; NITROGEN; OXIDATION; OXIDES; STABILITY; Sulfur-based cycles; SULFURIC ACID; Sulfuric acid decomposition; SURFACE AREA; Thermochemical water splitting; TITANIUM DIOXIDE; WATER; X-RAY DIFFRACTION; Thermochemical water splitting; Sulfuric acid decomposition; Sulfur-based cycles; Hydrogen production; Stability; High temperature; Physisorption; Sulfuric acid; Thermochemical cycle; Platinum; Oxidation; Surface area; X ray diffractometry; Titanium oxide; Sulfur; Catalyst activity; Catalyst
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2008.09.064

Activity and stability of FeTiO 3, MnTiO 3, NiFe 2O 4, CuFe 2O 4, NiCr 2O 4, 2CuO·Cr 2O 3, CuO and Fe 2O 3 for the atmospheric decomposition of concentrated sulfuric acid in sulfur-based thermochemical water splitting cycles are presented. Catalyst activity was determined at temperatures from 725 to 900 °C. Catalytic stability was examined at 850 °C for up to 1 week of continuous operation. The results were compared to a 1.0 wt% Pt/TiO 2 catalyst. Surface area by nitrogen physisorption, X-ray diffraction analyses, and temperature programmed desorption and oxidation were used to characterize fresh and spent catalyst samples. Over the temperature range, the catalyst activity of the complex oxides followed the general trend: 2CuO·Cr 2O 3 > CuFe 2O 4 > NiCr 2O 4 ≈ NiFe 2O 4 > MnTiO 3 ≈ FeTiO 3. At temperatures less than 800 °C, the 1.0 wt% Pt/TiO 2 catalyst had higher activity than the complex oxides, but at temperatures above 850 °C, the 2CuO·Cr 2O 3 and CuFe 2O 4 samples had the highest activity. Surface area was found to decrease for all of the metal oxides after exposure to reaction conditions. In addition, the two complex metal oxides that contained chromium were not stable in the reaction environment; both leached chromium into the acid stream and decomposed into their individual oxides. The FeTiO 3 sample also produced a discoloration of the reactor due to minor leaching and converted to Fe 2TiO 5. Fe 2O 3, MnTiO 3 and NiFe 2O 4 were relatively stable in the reaction environment. In addition, CuFe 2O 4 catalyst appeared relatively promising due to its high activity and lack of any leaching issues; however it deactivated in week-long stability experiments. Complex metal oxides may provide an attractive alternative to platinum-based catalyst for the decomposition of sulfuric acid; however, the materials examined in this study all displayed shortcomings including material sintering, phase changes, low activity at moderated temperatures due to sulfate formation, and decomposition to their individual oxides. More effort is needed in this area to discover metal oxide materials that are less expensive, more active and more stable than platinum catalysts.