Evaluation of reactor and catalyst performance in methane partial oxidation over modified nickel catalysts

The process of catalytic partial oxidation (CPO) of methane was investigated at moderate furnace temperatures (500-973 K) and 1 atm over a series of modified Ni catalysts. By exposing the catalysts to different GHSV (15-600 N 1 CH4/g h), the conditions ranged from approaching equilibrium at bed exit gas temperatures to oxygen break-through with associated effects on methane conversion and product composition. By modifying Ni catalysts we illustrate that the expected availability of reducible oxygen species influence the combustion activity of the catalyst. This is reasoned from observations of stronger temperature gradients and a higher maximum gas temperature with modifiers such as Co, Mo, Pt, Pd, Rh and to some degree Cr, as compared to a pure Ni catalyst. Modifiers which are generally difficult to reduce, such as oxides of W, Fe and Mn did not increase combustion activity at the bed entrance. At conditions where oxygen break-through was observed, the formation of coupled products, in particular ethane was promoted. It is reasoned that hetero-homogeneous coupling may be involved. The pure Pt and Pt-modified Ni catalysts were found to promote ethane formation even at 100% oxygen conversion. Interestingly, we here report results suggesting a direct route to synthesis gas over Rh, most likely working in parallel to a combustion reforming mechanism at high GHSV. This is argued based on an evaluation of water-gas-shift and the H-2/CO ratio at low bed exit gas temperatures. The conclusion appears reasonable even when accounting for a potentially higher surface temperature than gas temperature. (C) 2009 Elsevier B.V. All rights reserved.