Catalytic methane combustion on Pd-Pt-La catalysts and their surface models

Catalytic combustion of methane has been studied over a library of Pd, Pt, and La in mono-, bi-, and tri-element system supported on gamma-Al2O3 washcoated. ceramic monolith using an eight-tubular flow reactor. Simulated operating conditions of a small-size gas turbine were employed to investigate the combustion activity. Lead formulations from an initial high throughput screening were classified into two categories: Pd-Pt bi-element catalysts, and Pd-Pt-La tri-element catalysts with relatively constant 20% Pd (equivalent to 1% Pd of 5% total elemental loading). The substitution of Pd by Pt, while maintaining 5% total loading, was observed to improve the combustion activity as expected due to the co-existence of PdO and Pd-Pt alloy on the catalytic surface. However, its combustion activity was only slightly decreased when Pt was further substituted by La with relatively fixed 20% Pd loading due to the metal dilution by La. Nevertheless, the catalyst with Pd and Pt in equivalent amount with three times of La dilution (Pd:Pt:La = 1: 1:3) was suggested to be the best formula not only due to its high combustion activity at even low temperatures, but also the reduction of noble metal usage. (c) 2004 Elsevier B.V. All rights reserved.