Catalytic wet air oxidation of formic acid over Pt/CexZr1-xO2 catalysts at low temperature and atmospheric pressure

CexZr1-xO2-based Pt catalysts were investigated in the catalytic wet air oxidation (CWAO) of formic acid at low temperature (294-326 K) under atmospheric pressure in order to evaluate the impact of the high oxygen mobility over the ceria-zirconia supports on the catalytic performances. The effect of the support composition, the Pt loading and the reaction conditions (reaction temperature, formic acid concentration, oxygen partial pressure) was studied. The bare supports, in the absence of any active metal, appeared to be only slightly active. The 0.080 wt.%Pt/Ce0.9Zr0.1O2 catalyst (0.5 g L-1) exhibited the best performances: 100% formic acid (5 g L-1) conversion was achieved after 360 min at 326 K under atmospheric pressure. The reaction apparent activation energy was ca. 36 +/- 4 kJ mol(-1). In the lowest temperature range (T <= 313 K), the initial reaction rate was proportional to the dissolved oxygen concentration and, accordingly, the reaction order with respect to oxygen was ca. 1 +/- 0.1. The oxygen transfer to the active site was rate limiting and formic acid saturated the catalyst surface. More interestingly, from ca. 326 K, the reaction order with respect to formic acid increased to ca. 0.5 +/- 0.1 and the reaction order with respect to oxygen decreased to 0.8 +/- 0.1, indicating that oxygen might already be efficiently activated on the CexZr1-xO2 mixed oxide supports even under moderate temperature conditions. (C) 2010 Elsevier B.V. All rights reserved.