Storage and reduction of lean–NO x by using H 3PW 12O 40·6H 2O supported on Ti xZr 1− xO 4

Abstract

NO x storage and reduction with H 3PW 12O 40·6H 2O (HPW) supported on Ti x Zr 1− x O 4 (0 ≤ x ≤ 1) were measured under representative lean–gas mixture conditions. Storage capacity is high (28 mg of N O x g HPW − 1 at 170 °C) and depends on support Zr/Ti molar ratio. NO x reduction highly depends on reducing mixture (CO, H 2 or H 2 + CO), on the presence of noble metal (platinum) and support, and on the operating conditions (long or short cycles). H 2 + CO mixture proved to be effective for NO x reduction into N 2 even if low activity was detected for each gas separately. With short cycles of lean/rich (2/1 min) at 250 °C, (HPW-Pt)/Ti x Zr 1− x O 4 (with Zr/Ti molar ratio equal to 0.5) is significantly more active than unsupported HPW-Pt, delivering upto 40% NO x reduction into N 2 with 75% of NO x storage efficiency. Experimental results evidence the kinetic coupling between NO 2 reduction and CO oxidation during NO x reduction. The combination of NO x storage and reduction concept with a multifuctional catalyst is very promising.