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 γ-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.