Coke formation and reaction pathways of catalyst-surface-generated radicals during the pyrolysis of ethane using Ni mesh catalyst

Abstract

The use of a conventional porous catalyst in the study of the pyrolysis of ethane (or any hydrocarbon) is complicated because reactions take place both on the catalyst surface and in the gas phase (including pores). A non-porous nickel mesh catalyst was used to study the catalytic pyrolysis of C2H6 in a quartz tubular reactor at 750 °C. Our experimental results strongly indicate that the radicals formed on the catalyst surface could easily desorb from the catalyst surface when the gas film around the mesh wires was thinned by increasing the gas flow rate passing through the mesh. The desorption of radicals from the catalyst surface greatly limited the formation of coke on the catalyst surface, leading to sustained high catalytic activities even in pure C2H6 at 750 °C. The catalyst could have dual roles. It could act as a chain reaction terminator by providing a surface for the chain termination reactions to take place. The mesh catalyst could also act as a chain reaction re-initiator by providing additional radicals into the gas phase in which the desorbed radicals re-initiate and participate in the chain reactions. The dual roles of the mesh catalyst were largely responsible for the changes in net product formation rates and product distribution (e.g. the C2H4/CH4 ratio).