Auto-thermal combustion of CH4 and CH4–H2 mixtures over bi-functional Pt-LaMnO3 catalytic honeycomb

The range of conditions of stable operation of a catalytic honeycomb-type monolith has been investigated for the combustion of methane. Catalyst is constituted by a Pt-LaMnO3 active phase supported on a γ-Al2O3 washcoat deposited onto the internal channels of 900 cpsi commercial cordierite monolith via a dip-coating technique. The auto-thermal operation of the catalytic reactor is assured provided a certain amount of heat is supplied with an external furnace. The ignition of the CH4/O2 mixture occurs at a defined pre-heating temperature that is a decreasing function of methane concentration and approximately constant with the total flow rate. Once the system is ignited, pre-heating temperature can be lowered also of 150–250 °C, depending on the flow rate, before quenching occurs. System quenching occurs due to extinction at lower investigated flow rates, or to blowout at the highest flow rate investigated. Such ignition/quenching temperatures have been also evaluated when an energetically equivalent CH4–H2 is used as fuel, recognizing that only ignition takes a large and significant advantage by the presence of hydrogen, since quenching occurs at the same pre-heating temperature whatever the fuel composition, being it a phenomenon basically controlled by energy balance with surroundings (heat losses). On the other hand, by partially substituting of fraction of methane with hydrogen the ignition temperature can be lowered of an amount that is higher the higher the flow rate.