Fundamental understanding of the Di-Air system (an alternative NO_x abatement technology). I: The difference in reductant pre-treatment of ceria

Toyota's Di-Air DeNO_x system is a promising DeNO_x system to meet NO_x emission requirement during the real driving, yet, a fundamental understanding largely lacks, e.g. the benefit of fast frequency fuel injection. Ceria is the main ingredient in Di-Air catalyst composition. Hence, we investigated the reduction of ceria by reductants, e.g. CO, H₂, and hydrocarbons (C₃H₆ and C₃H₈), with Temporal Analysis of Product (TAP) technique. The results show that the reduction by CO yielded a faster catalyst reduction rate than that of H₂. However, they reached the same final degree of ceria reduction. Hydrocarbons generated almost three times deeper degree of ceria reduction than that with CO and H₂. In addition, hydrocarbons resulted in carbonaceous deposits on the ceria surface. The total amount of converted NO over the C₃H₆ reduced sample is around ten times more than that of CO. The deeper degree of reduction and the deposition of carbon by hydrocarbon explain why hydrocarbons are the most powerful reductants in Toyota's Di-Air NO_x abatement system.