Striking activity enhancement of gold supported on Al-Ti mixed oxide by promotion with ceria in the reduction of NO with CO

Abstract

The promotion of an Al-Ti mixed oxide supported gold catalyst (Au/AlTiOx) with ceria is shown to result in an unprecedented enhancement of its activity in the reduction of NO to N2 with CO. The parent Au/AlTiOx catalyst was prepared by depositing 3wt% gold on the mesoporous Al-Ti mixed oxide made by an evaporation-induced self-assembly (EISA) method using a triblock copolymer as a soft template. This parent Au/AlTiOx was impregnated with different loadings of CeOx resulting in molar ratios of Au:Ce in the catalysts of 4:1, 2:1 and 1:1. The deposited gold particles showed a relatively broad size distribution with maxima at 8–12nm, as evidenced by TEM. XRD and XPS analyses showed that the Al-Ti oxide support was made up of amorphous Al2O3-TiO2 mixed oxide and that the Ce component was present as a mixture of Ce3+ (Ce2O3) and Ce4+ (CeO2) partially covering the Au particles. The as-prepared catalysts were tested in the catalytic reduction of NO with CO in a continuous tubular microreactor at temperatures up to 300°C. The parent Au/AlTiOx catalyst showed very low activity (8.2% NO conversion at 300°C), whereas the ceria promoted catalyst containing a molar ratio of Au:Ce of 2:1 exhibited a dramatic enhancement of activity affording 100% NO conversion at the same conditions. The stability of this catalyst was tested in repetitive runs over 16h time-on-stream, which showed a slight loss of activity, while 100% selectivity to N2 was maintained. The spent catalyst could be easily regenerated reaching its original performance by heat treatment in flowing 5% O2/He.