Sulfur dioxide-tolerant strontium chromate for the catalytic oxidation of diesel particulate matter

• Published in: Catalysis science & technology Vol. 8; no. 6; pp. 1712 - 1721
• Main Authors: Khobragade, Rohini, Einaga, Hisahiro, Jain, Suman, Saravanan, Govindachetty, Labhsetwar, Nitin
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2018
• Subjects: Aluminum oxide; Catalysts; Catalytic activity; Catalytic converters; Catalytic oxidation; Chromates; Citric acid; Diesel fuels; Fuel consumption; High temperature; Oxidation; Particulate emissions; Physiochemistry; Platinum; Strontium; Sulfur; Sulfur dioxide; Thermal stability
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/C7CY02553J

A sulfur dioxide (SO 2 )-tolerant, stable mixed oxide as an alternative to platinum (Pt) group metal (PGM) catalysts has been explored for the catalytic oxidation of particulate matter (PM) due to its low-cost, desirable physiochemical properties, thermal stability, tailoring options, etc. Herein, a mixed oxide of Sr and Cr was prepared via a solution combustion method by mixing stoichiometric amounts of Sr- and Cr-precursors with citric acid and urea as fuels followed by calcination at 800 °C in air. A pure mixed oxide phase of Sr and Cr (SrCrO 4 ) ( P 2 1 / n [14]) ( a = 0.7090 nm, b = 0.7394 nm, and c = 0.6755 nm) has been successfully prepared, and the SrCrO 4 particles are larger in size with semi-oval shapes due to their agglomeration at elevated temperatures. The SrCrO 4 catalyst shows significantly improved intrinsic catalytic performance for PM oxidation in the tested temperature range as compared to the reference catalysts, Pt/Al 2 O 3 and Pt-dispersed SrCrO 4 (Pt/SrCrO 4 ) (loading weight: 5 wt%) are used as internal reference catalysts. The onset temperature ( i.e. , intrinsic catalytic activity at 10% conversion, T 10 ) is observed at 426 °C, which is significantly lower than that of the reference Pt/Al 2 O 3 ( T 10 = 537 °C) and comparable with that of the Pt/SrCrO 4 catalyst ( T 10 = 414 °C). The SrCrO 4 catalyst shows a stable, multi-cycle PM oxidation performance for the tested five cycles, and both its crystalline structure and morphology remain unchanged even after its multiple cycles of use. The structure of the SrCrO 4 catalyst is stable even after moisture and SO 2 treatments, and the catalytic PM oxidation activity of SrCrO 4 is not compromised even after these harsh treatments. Importantly, the SrCrO 4 catalyst is also stable after PM oxidation conducted using real world PM from a heavy-duty vehicle. These results demonstrate that the mixed oxide phase of SrCrO 4 shows promise for PM oxidation.