(659a) Nitrogen Oxide Mitigation Via a Waste-derived Heterogeneous Mixed Metal Oxide

The solid residual, ash, of municipal solid waste (MSW) combustion is known to contain trace amounts of platinum group metals, rare earth elements, and other critical metals. Some of these metals are known to act as active sites in catalysts designed for the denitrification (deNOx) processes, but to date, no publications detail the use of MSW-derived ashes as a stand-alone deNOx catalyst. This work studies the activity of municipal solid waste (MSW) combustion ash in the reductive decomposition of nitric oxide. Four basic aspects were investigated: the role of oxygen in the treated gas in the catalytic performance, the equilibrium reactions responsible for observed temperature-dependent shifts in selectivity, how reductant choice impacts catalyst stability, and how pretreatment impacts performance.

The presence of oxygen in the treated gas stream was shown to more than double NO conversions despite observing no change in oxygen consumption. An NO oxidation step is proposed as the mechanistic step responsible for the temperature-dependent, non-linear shift in selectivity. The presence of H2O in the treated stream resulted in ash sintering, and thus a loss in surface area, whereas the use of other reductants such as H2 and NH3 did not modify ash surface area during performance testing. Reductive pretreatment of ash improved conversion of NO by as much as double, while oxidative pretreatment depressed conversion to as little as half the conversion of as-received ash.