(628f) Cobalt As an Efficient Promoter in Low-Loading Pd/BEA Catalysts for CH4 Oxidation

Palladium (Pd)-based zeolite catalysts have been quite successful at reducing CH₄ emissions from natural gas vehicles (NGVs). Decreasing the Pd loading to lower than 1-2 wt.% is of current interest due to its prohibitive cost but it can lead to an undesirable increase in the ionic Pd/PdO ratio [1], since ionic Pd is less active than PdO nanoclusters for the CH₄ oxidation reaction. Thus, there is a critical need to design catalysts for NGVs containing a decreased amount of Pd while compressing the formation of ionic Pd.

Herein, we report a facile method that decreases Pd usage in 1 wt.% Pd/BEA while maintaining the CH₄ oxidation performance. These results are achieved by introducing 0 – 1.5 wt.% cobalt (Co) in 0.5 wt.% Pd/BEA (Pd(0.5)/BEA) zeolites (Si/Al = 12.5). CH₄ conversion of Pd(0.5)/BEA at 500℃ was as low as 12% (Fig. 1a), attributed to the majority of Pd being present in its ionic form. Co-impregnation of Co with Pd in BEA zeolites led to an enhanced CH₄ oxidation performance. Specifically, an increase in Co loading from 0.1 to 1 wt.% led to a decrease in the CH₄ oxidation T₅₀ from 456 to 352℃. Pd(0.5)Co(1.0)/BEA showed the best performance with T₅₀ and T₉₀ equal to 352 and 419℃, respectively. Stability tests at 450℃ (Fig. 1b) showed that Pd(0.5)Co(1.0)/BEA had a similar CH₄ conversion (~94%) and was more water resistant than Pd(1.0)/BEA. This work illustrates that Co incorporation in Pd/BEA zeolites can achieve the same CH₄ oxidation performance results with 50% reduction of precious metal usage.

Reference

[1] K. Khivantsev, N.R. Jaegers, L. Kovarik, J.C. Hanson, F. Tao, Y. Tang, X. Zhang, I.Z. Koleva, H.A. Aleksandrov, G.N. Vayssilov, Angew. Chem., 57 (2018) 16672-16677.