The Influence of the Mg–Al–O Support Composition on the Performance and Stability of Platinum Catalyst in the Reaction of Oxygen-Free Methane Condensation

Mg–Al mixed oxides (MgAlO, Mg:Al = 0.5, 2), γ-Al2O3 and γ-Al2O3, modified with Mg through impregnation (3 or 15 wt %) with supported Pt (1 wt %) showed principally different activity and stability in the reaction of nonoxidative methane coupling at 600 °C. In the most active Pt/Al2O3 and Pt/MgAlO samples under the reaction conditions, most of Pt was included into the reduced clusters (Pt/Al2O3 case) or their mixture with isolated reduced species and octahedral [Pt4+OxCly]s (y → 0) complexes (Pt/MgAlO case). Stabilization by possible bonding with Mg2+ in the MgAlO spinel lattice inhibited the irreversible Pt sintering, resulting in samples deactivation, and allowed a complete restoration of catalytic characteristics after burning out the carbonaceous deposits accumulated during the reaction. The Mg–Al solid solution formed in γ-Al2O3-based samples could stabilize low-reactive Mg2PtOxCly-like compounds. The addition of 1.2 vol % H2 into 50 vol % CH4/N2 mixture substantially prolonged the period of stable formation of C2 reaction products due to the retardation of coke accumulation on the catalyst surface.