Non-oxidative methane transformations into higher hydrocarbons over bimetallic Pt–Co catalysts supported on Al2O3 and NaY

The methane conversion under non-oxidative conditions over Al₂O₃ and NaY supported cobalt, platinum and Pt–Co bimetallic catalysts in a flow system has been investigated. The two-step process was applied in the temperature range between 523 and 673 K and 1 bar pressure and the one-step process was carried out under the conditions of 1073 K and 10 bar pressure. Addition of platinum to NaY and alumina supported cobalt samples results in the formation of metallic Co particles and Pt–Co bimetallic particles. On bimetallic catalysts in the two-step process, the amount of C₂₊ products formed were higher than that on mono-metallic samples. The synergism shown by the bimetallic system can be explained by: (i) enhanced reducibility of cobalt, and (ii) the co-operation of two types of active components (Co facilitates the chain-growth of partially dehydrogenated species produced on Pt in Pt–Co bimetallic particles). The use of higher pressures and high temperature makes it possible to run the process to form primarily ethane (and ethylene) which is predicted from thermodynamic calculations. For NaY as support, significantly enhanced activity and C₂₊ selectivity are obtained compared with Al₂O₃ as support, which can be attributed to the structural differences of metal particles (location, dispersion and reducibility).