Methane coupling to acetylene over Pt-coated monoliths at millisecond contact times

We have studied the adiabatic and autothermal oxidative coupling of methane over Pt on α-Al2O3 monoliths at space velocities above 105 h-1. The selectivity to C2 hydrocarbons (primarily acetylene) reaches a maximum of around 20% at low fuel to oxygen ratios, low dilution, and high space velocities. These conditions promote a large temperature gradient in the monolith, with an exit temperature of nearly 1500°C and an entrance temperature of less than 200°C. This temperature gradient appears to be the driving force for C2 hydrocarbon formation under these conditions. Both homogeneous and heterogeneous reactions may be involved in producing coupling products, and a combustion model predicts C2 selectivities similar to those observed.