Storage and reduction of lean-NOx by using H3PW12O40·6H2O supported on TixZr1−xO4

NOx storage and reduction with H3PW12O40·6H2O (HPW) supported on TixZr1−xO4 (0 ≤ x ≤ 1) were measured under representative lean-gas mixture conditions. Storage capacity is high (28 mg of NOxgHPW−1 at 170 °C) and depends on support Zr/Ti molar ratio. NOx reduction highly depends on reducing mixture (CO, H2 or H2 + CO), on the presence of noble metal (platinum) and support, and on the operating conditions (long or short cycles). H2 + CO mixture proved to be effective for NOx reduction into N2 even if low activity was detected for each gas separately. With short cycles of lean/rich (2/1 min) at 250 °C, (HPW-Pt)/TixZr1−xO4 (with Zr/Ti molar ratio equal to 0.5) is significantly more active than unsupported HPW-Pt, delivering upto 40% NOx reduction into N2 with 75% of NOx storage efficiency. Experimental results evidence the kinetic coupling between NO2 reduction and CO oxidation during NOx reduction. The combination of NOx storage and reduction concept with a multifuctional catalyst is very promising.