Platinum on alumina, titania, and magnesia supports for the combustion of methanol in a waste gas with trace amount of ammonia

Pt (0.1 wt.%) on Al2O3, TiO2, and MgO supports were used for the low temper ature combustion of methanol in both the absence and the presence of ammoni a. Without NH3 in the gas the performance for the complete combustion decre ases in the order Pt/MgO greater than or equal to Pt/TiO2 much greater than Pt/Al2O3 comparing a fixed amount of Pt surface area. In the presence of a mmonia strong deactivation of Pt/Al2O3 and Pt/TiO2 is observed, whilst almo st no deactivation of Pt/MgO occurs. The results are explained considering CO chemisorption and XPS measurements as well as the TPD profiles generated by adsorbed ammonia and methanol. A comparison of the TPD profiles of the N-2 which is formed from adsorbed ammonia on supported Pt and the support, respectively, reveals that Pt on Al2O3 and TiO2 interacts with the support surface, possibly through Pt-O-support bonding. The inference is supported by the XPS measurements showing that the Pt on Al2O3 and TiO2, as opposed t o that on MgO, is slightly positively charged, making the interaction betwe en ammonia and Pt stronger. Additional insight into the deactivation cause is obtained from TPD experiments with adsorbed methanol. These experiments reveal that on both Pt/Al2O3 and Pt/TiO2 there is competition between metha nol and ammonia for adsorption sites, which is not the case on Pt/MgO. (C) 2001 Elsevier Science B.V. All rights reserved.